Spm Publications

Eukaryotic pathogens deploy diverse strategies to manipulate host immunity, yet RNA-based virulence mechanisms remain poorly understood. We describe a mechanism by which the malaria parasite Plasmodium falciparum governs host immune responses through direct interference with host nuclear RNA processing. Malaria-encoded mRNAs of the early transcribed membrane protein family, exported from infected red blood cells, evade cytoplasmic degradation within host immune cells and are imported into their highly secured nuclei. Inside the nucleus, parasite transcripts bind the host RNA-binding proteins ACIN1 and PNN, key components of the splicing machinery that associate with the exon junction complex. This interaction disrupts host splicing regulation, leading to widespread misprocessing of transcripts and altered expression of proteins involved in immune function. Our findings uncover an RNA-based strategy by which pathogen-derived transcripts exploit the host splicing machinery, reshaping transcript isoform landscapes and immune signaling.

Accurate and rapid identification of aggressive cancer cells remains a major clinical challenge. Here, we present a simple, label-free mechanophenotyping platform that integrates controlled colloidal topographies with particle-uptake measurements to reveal biophysical traits associated with metastatic progression. Non-close-packed polystyrene bead arrays were formed on cell culture plates by controlled deposition and stabilized with a thin silicon oxide coating. These arrays display micro- and nano-features with a size range of 0.232.3 μm at diverse densities and were used to assess adhesion across cancer cells exhibiting different levels of malignancy. Particle uptake differences were most pronounced for particle diameters above 0.5 μm, whereas adhesion differences emerged predominantly on particles ≥0.7 μm and increased progressively with larger particle sizes. Colloidal topographies were fabricated at particle deposition concentrations of 500 μg/mL and 1000 μg/mL, and adhesion differences were observed under both conditions, with more potent effects at the higher concentration. At the metastatic site, cells exhibited increased particle uptake, stronger adhesion, and a larger morphological engagement on colloid-coated substrates, characterized by extensive actin-rich protrusions wrapping individual particles. AFM force mapping confirmed higher adhesion forces to a colloidal probe, while transcriptomic profiling revealed enrichment of adhesion and ECM-remodeling pathways in the adhesive metastatic state. We also find that lymphatically selected cells exhibit reduced adhesion on colloid-coated surfaces but higher particle uptake compared to the primary tumor cells. These results indicate that after leaving the primary tumor, metastatic cells have reduced adhesive potential, which is only regained upon reaching secondary sites. By exposing adhesion differences that are undetectable on flat substrates and linking them to particle uptake assays, this platform produces functional signatures of metastatic potential. This method is technically accessible, compatible with imaging and molecular workflows, and adaptable for high-throughput or clinical analysis, offering a potential route for label-free detection and classification of cancer cells by their aggressiveness.

Precise control over crystal morphology is a longstanding challenge in materials science, as crystal shape governs optical, mechanical, and electronic properties. In contrast, living organisms achieve remarkable control over crystal morphology, though the underlying mechanisms are not fully understood. Among the most common organic materials are guanine crystals, notable for their plate-like morphology and high anisotropic refractive index, arising from the stacking of hydrogen-bonded molecular layers along the (100) plane. Here we show that simple synthetic polymers not only reproduce this biogenic plate-like form in vitro but also expand the accessible morphology space to prisms and needles by systematically varying i) multivalent interactions, ii) functional-group identity, and iii) polarity and hydrogen-bonding capacity. Using microscopy, spectroscopy, and molecular dynamics simulations, we find that carbonyl-bearing polymers selectively adsorb to the (100) stacking face, cap layer addition along the a-axis, and yield large plates indistinguishable from biogenic crystals. In contrast, reducing carbonyl polarity, increasing steric-bulk, or introducing highly-polar groups redirect adsorption and produces bulkier prisms or slender needles. Simulations corroborate facet selectivity, identify contact motifs involving carbonyl oxygens and adjacent methylenes. Together, these findings provide design principles for sculpting organic crystals and suggest analogous interactions exploited by biological scaffolds to orchestrate guanine assembly.

Structurally heterogeneous materials present major challenges for characterization due to their complex nanoscale order. Sodium poly(heptazine imide) (NaPHI), a layered carbon nitride photocatalyst, exemplifies this complexity, with its precise structure remaining unresolved. Here, we uncover new structural insights into NaPHI using energy-filtered four-dimensional scanning transmission electron microscopy combined with machine-learning-based diffraction image segmentation, supported by transmission electron microscopy, atomic force microscopy, X-ray diffraction, and Raman spectroscopy. At the mesoscale, NaPHI flakes display bent morphologies, while nanodiffraction patterns reveal features characteristic of stacking disorder. Based on these insights, we modeled a NaPHI-layered structure incorporating out-of-plane undulations (waves) with amplitudes of ∼0.5 Å and wavelengths of 23 nm. This model reproduces the observed line features in nanodiffraction patterns and agrees with powder X-ray diffraction data, thereby bridging local and bulk structural information. The introduced approach uses data-driven machine learning to identify statistically significant features, offering a robust framework for structural analysis of semi-crystalline materials.

In this study, we employed traditional methods and deep learning models to improve resolution and quality of low-resolution AFM images made under standard ambient scanning. Both traditional methods and deep learning models were benchmarked and quanti-fied regarding fidelity, quality, and a survey taken by AFM experts. The deep learning models outperform the traditional methods and yield better results. Additionally, some common AFM artifacts, such as streaking, are present in the ground truth high-resolu-tion images. These artifacts are partially attenuated by the traditional methods but are completely eliminated by the deep learning models. This work shows deep learning models to be superior for super-resolution tasks and enables significant reduction in AFM measurement time, whereby low-pixel-resolution AFM images are enhanced in both resolution and fidelity through deep learning.

How molecular-level understanding of the crystal growth mechanisms and their relation to lattice bonds informs the rational design of crystals with desired shapes and properties has remained elusive. Here we employ theophylline crystals and drive them into classical growth mode, in which the crystals grow molecule-by-molecule and new layers are generated by two-dimensional nucleation. We demonstrate that classical growth allows for controlling the crystal's shape and dimensions. We correlate the anisotropic responses to the supersaturation of the growth rates of crystal layers and crystal faces to the hydrogen and π−π stacking bond chains in the crystal lattice. The obtained insights suggest strategies to direct the crystal shape to either one-dimensional needles or flat sheets. Moreover, we show that crystals that grow by the classical mode of direct monomer incorporation have the potential to regrow and heal once a defect is introduced by mechanical cut or local thermal subliming of crystalline sections.

Cells across biological kingdoms release extracellular vesicles (EVs) as a means of communication with other cells, be their friends or foes. This is indeed true for the intracellular malaria parasite Plasmodium falciparum (Pf), which utilizes EVs to transport bioactive molecules to various human host systems. Yet, the study of this mode of communication in malaria research is currently constrained due to limitations in high-resolution tools and the absence of commercial antibodies. Here, we demonstrate the power of an advanced spectral flow cytometry approach to robustly detect secreted EVs, isolated from Pf-infected red blood cells. By labeling both EV membrane lipids and the DNA cargo within (non-antibody staining approach), we were able to detect a subpopulation of parasitic-derived EVs enriched in DNA. Furthermore, we could quantitatively measure the DNA-carrying EVs isolated from two distinct blood stages of the parasite: rings and trophozoites. Our findings showcase the potential of spectral flow cytometry to monitor dynamic changes in nucleic acid cargo within pathogenic EVs.

The malaria parasite, Plasmodium falciparum, secretes extracellular vesicles (EVs) to facilitate its growth and to communicate with the external microenvironment, primarily targeting the hosts immune cells. How parasitic EVs enter specific immune cell types within the highly heterogeneous pool of immune cells remains largely unknown. Using a combination of imaging flow cytometry and advanced fluorescence analysis, we demonstrated that the route of uptake of parasite-derived EVs differs markedly between host T cells and monocytes. T cells, which are components of the adaptive immune system, internalize parasite-derived EVs mainly through an interaction with the plasma membrane, whereas monocytes, which function in the innate immune system, take up these EVs via endocytosis. The membranal/endocytic balance of EV internalization is driven mostly by the amount of endocytic incorporation. Integrating atomic force microscopy with fluorescence data analysis revealed that internalization depends on the biophysical properties of the cell membrane rather than solely on molecular interactions. In support of this, altering the cholesterol content in the cell membrane tilted the balance in favor of one uptake route over another. Our results provide mechanistic insights into how P. falciparum-derived EVs enter into diverse host cells. This study highlights the sophisticated cell-communication tactics used by the malaria parasite.

Hundreds of thousands die annually from malaria caused by Plasmodium falciparum (Pf), with the emergence of drug-resistant parasites hindering eradication efforts. Antimicrobial peptides (AMPs) are known for their ability to disrupt pathogen membranes without targeting specific receptors, thereby reducing the chance of drug resistance. However, their effectiveness and the biophysical mechanisms by which they target the intracellular parasite remain unexplored. Here, by using native and synthetic AMPs, we discovered a selective mechanism that underlies the antimalarial activity. Remarkably, the AMPs exclusively interact with Pf-infected red blood cells, disrupting the cytoskeletal network and reaching the enclosed parasites with correlation to their activity. Moreover, we showed that the unique feature of reduced cholesterol content in the membrane of the infected host makes Pf-infected red blood cells susceptible to AMPs. Overall, this work highlights the Achilles heel of malaria parasite and demonstrates the power of AMPs as potential antimalarial drugs with reduced risk of resistance.

The extremely low sliding friction of articular cartilage in synovial joints has been attributed to phospholipid boundary layers, lubricating via the hydration lubrication mechanism at their exposed, highly hydrated polar-head-groups, in a medium the synovial fluid where osmolytes, which may modify the hydration layer, are ubiquitous. Here, using a surface force balance (SFB), we carried out a systematic study to elucidate the effect of sucrose, a known osmotic regulator solute, with concentrations c_sucrose, ranging from 5 to 20 wt%, on the normal and shear forces between interacting phosphatidylcholine (PC) bilayers, both in the gel (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC) and liquid (1,2-dimyristoyl-sn-glycero-3-phosphocholine, DMPC) phases, supported on atomically-smooth mica substrates. Several additional approaches including cryo-transmission electron microscope, atomic force microscopy, small- and wide-angle X-ray scattering, differential scanning calorimetry, dynamic light scattering and zeta potential measurements are exploited to get additional insight into the nature of the sucrose-dependent interactions. As c_sucrose is varied, a remarkable variation in the friction is observed: a marked reduction in friction is seen at low c_sucrose, but at higher sucrose levels the friction increases, for both gel and liquid phase lipids. This challenges the expectation that hydration lubrication is degraded by osmotic solutes, due to their competing for water of hydration, and reveals for the first time a non-monotonic effect of a sugar on the interactions, particularly frictional forces, between lipid bilayers. This non-monotonic effect correlates with the bilayer potential, and is attributed to a concentration-dependent affinity of the sugar to the PC headgroups.

Superparamagnetic iron oxide nanoparticles (SPIONs) have attracted wide attention due to their promising applications in biomedicine, chemical catalysis, and magnetic memory devices. In this work, the force is measured between a single SPION coated with chiral molecules and a ferromagnetic substrate by atomic force microscopy (AFM), with the substrate magnetized either toward or away from the approaching AFM tip. The force between the coated SPION and the magnetic substrate depends on the handedness of the molecules adsorbed on the SPION and on the direction of the magnetization of the substrate. By inserting nm-scale spacing layers between the coated SPION and the magnetic substrate it is shown that the SPION has a short-range magnetic monopole-like magnetic field. A theoretical framework for the nature of this field is provided.Magnetic monopole-like phenomenon is observed for a superparamagnetic iron oxide nanoparticle (SPION) coated with chiral molecules. Combining force spectroscopy and calculations, this study reveals that the magnetic moment of the SPION behaves like a monopole at close proximity to the particle, at distance of less than 10 nm, the nanoparticle diameter. image

Protein solutions can undergo liquid-liquid phase separation (LLPS), where a dispersed phase with a low protein concentration coexists with coacervates with a high protein concentration. We focus on the low complexity N-terminal domain of cytoplasmic polyadenylation element binding-4 protein, CPEB4_NTD, and its isoform depleted of the Exon4, CPEB4Δ4_NTD. They both exhibit LLPS, but in contrast to most systems undergoing LLPS, the single-phase regime preceding LLPS consists mainly of soluble protein clusters. We combine experimental and theoretical approaches to resolve the internal structure of the clusters and the basis for their formation. Dynamic light scattering and atomic force microscopy show that both isoforms exhibit clusters with diameters ranging from 35 to 80 nm. Electron paramagnetic resonance spectroscopy of spin-labeled CPEB4_NTD and CPEB4Δ4_NTD revealed that these proteins have two distinct dynamical properties in both the clusters and coacervates. Based on the experimental results, we propose a core-shell structure for the clusters, which is supported by the agreement of the dynamic light scattering data on cluster size distribution with a statistical model developed to describe the structure of clusters. This model treats clusters as swollen micelles (microemulsions) where the core and the shell regions comprise different protein conformations, in agreement with the electron paramagnetic resonance detection of two protein populations. The effects of ionic strength and the addition of 1,6-hexanediol were used to probe the interactions responsible for cluster formation. While both CPEB4_NTD and CPEB4Δ4_NTD showed phase separation with increasing temperature and formed clusters, differences were found in the properties of the clusters and the coacervates. The data also suggested that the coacervates may consist of aggregates of clusters.

Self-healing (SH) of (opto)electronic material damage can have a huge impact on resource sustainability. The rising interest in halide perovskite (HaP) compounds over the past decade is due to their excellent semiconducting properties for crystals and films, even if made by low-temperature solution-based processing. Direct proof of self-healing in Pb-based HaPs is demonstrated through photoluminescence recovery from photodamage, fracture healing and their use as high-energy radiation and particle detectors. Here, the question of how to find additional semiconducting materials exhibiting SH, in particular lead-free ones is addressed. Applying a data-mining approach to identify semiconductors with favorable mechanical and thermal properties, for which Pb HaPs are clear outliers, it is found that the Cs₂Au^IAu^IIIX₆, (X = I, Br, Cl) family, which is synthesized and tested for SH. This is the first demonstration of self-healing of Pb-free inorganic HaP thin films, by photoluminescence recovery.

Mechanical energy, specifically in the form of ultrasound, can induce pressure variations and temperature fluctuations when applied to an aqueous media. These conditions can both positively and negatively affect protein complexes, consequently altering their stability, folding patterns, and self-assembling behavior. Despite much scientific progress, our current understanding of the effects of ultrasound on the self-assembly of amyloidogenic proteins remains limited. In the present study, we demonstrate that when the amplitude of the delivered ultrasonic energy is sufficiently low, it can induce refolding of specific motifs in protein monomers, which is sufficient for primary nucleation; this has been revealed by MD. These ultrasound-induced structural changes are initiated by pressure perturbations and are accelerated by a temperature factor. Furthermore, the prolonged action of low-amplitude ultrasound enables the elongation of amyloid protein nanofibrils directly from natively folded monomeric lysozyme protein, in a controlled manner, until it reaches a critical length. Using solution X-ray scattering, we determined that nanofibrillar assemblies, formed either under the action of sound or from natively fibrillated lysozyme, share identical structural characteristics. Thus, these results provide insights into the effects of ultrasound on fibrillar protein self-assembly and lay the foundation for the potential use of sound energy in protein chemistry.

Unicellular organisms are known to exert tight control over their cell size. In the case of diatoms, abundant eukaryotic microalgae, two opposing notions are widely accepted. On the one hand, the rigid silica cell wall that forms inside the parental cell is thought to enforce geometrical reduction of the cell size. On the other hand, numerous exceptions cast doubt on the generality of this model. Here, we monitored clonal cultures of the diatom Stephanopyxis turris for up to 2 yr, recording the sizes of thousands of cells, in order to follow the distribution of cell sizes in the population. Our results show that S. turris cultures above a certain size threshold undergo a gradual size reduction, in accordance with the postulated geometrical driving force. However, once the cell size reaches a lower threshold, it fluctuates around a constant size using the inherent elasticity of cell wall elements. These results reconcile the disparate observations on cell size regulation in diatoms by showing two distinct behaviors, reduction and homeostasis. The geometrical size reduction is the dominant driving force for large cells, but smaller cells have the flexibility to re-adjust the size of their new cell walls.

Proteolysis of the extracellular matrix (ECM) by matrix metalloproteinases (MMPs) plays a crucial role in the immune response to bacterial infections. Here we report the secretion of MMPs associated with proteolytic extracellular vesicles (EVs) released by macrophages in response to Salmonella enterica serovar Typhimurium infection. Specifically, we used global proteomics, in vitro, and in vivo approaches to investigate the composition and function of these proteolytic EVs. Using a model of S. Typhimurium infection in murine macrophages, we isolated and characterized a population of small EVs. Bulk proteomics analysis revealed significant changes in protein cargo of naïve and S. Typhimurium-infected macrophage-derived EVs, including the upregulation of MMP-9. The increased levels of MMP-9 observed in immune cells exposed to S. Typhimurium were found to be regulated by the toll-like receptor 4 (TLR-4)-mediated response to bacterial lipopolysaccharide. Macrophage-derived EV-associated MMP-9 enhanced the macrophage invasion through Matrigel as selective inhibition of MMP-9 reduced macrophage invasion. Systemic administration of fluorescently labeled EVs into immunocompromised mice demonstrated that EV-associated MMP activity facilitated increased accumulation of EVs in spleen and liver tissues. This study suggests that macrophages secrete proteolytic EVs to enhance invasion and ECM remodeling during bacterial infections, shedding light on an essential aspect of the immune response.

Atomic force microscopy is highly suited for characterizing morphology and physical properties of nanoscale objects. The application of this technique to nanomechanical studies is, therefore, exploited in a wide range of fields from life sciences to materials science and from miniature devices to sensors. Although performing a mechanical measurement can be straightforward and accessible to novice users, obtaining meaningful results requires knowledge and experience not always evident in standard instrumental software modules. In this paper, we provide a basic guide to proper protocols for the measurement and analysis of force curves and related atomic force microscopic techniques. Looking forward, we also survey the budding application of machine learning in this discipline.

The class of materials termed halide perovskites has experienced a meteoric rise in popularity due to their potential for photovoltaic and related applications, rivaling the well-established silicon devices within a few short years of development. These materials are characterized by several intriguing properties, among them their mechanical behavior. The study of their response to stress is essential for proper device development, while being of fundamental scientific interest in its own right. In this perspective, we highlight the key concerns surrounding this topic, critically analyzing the measurement techniques and considering the challenges in the current level of understanding.

Lissencephaly-1 (LIS1) is associated with neurodevelopmental diseases and is known to regulate the molecular motor cytoplasmic dynein activity. Here we show that LIS1 is essential for the viability of mouse embryonic stem cells (mESCs), and it governs the physical properties of these cells. LIS1 dosage substantially affects gene expression, and we uncovered an unexpected interaction of LIS1 with RNA and RNA-binding proteins, most prominently the Argonaute complex. We demonstrate that LIS1 overexpression partially rescued the extracellular matrix (ECM) expression and mechanosensitive genes conferring stiffness to Argonaute null mESCs. Collectively, our data transforms the current perspective on the roles of LIS1 in post-transcriptional regulation underlying development and mechanosensitive processes.

Ice-binding proteins (IBPs) allow organisms to survive below the freezing point by modulating ice crystal growth. These proteins act by binding to ice surfaces, thus inhibiting ice growth. Until now, high-resolution imaging of ice growing in the presence of IBPs has not been possible. We developed a unique in-situ technique that enables atomic force microscopy (AFM) imaging of ice formation and growth in the ice-IBP system. The new technique enables controlling the growth of ice crystals under a strong and focused thermal gradient. We present images of ice crystals with sub-ten nanometer resolution. Ice was grown in the presence of two different IBPs that exhibit specific and unique structures. This development opens the path for fine elucidation of the interaction of IBPs with growing ice surfaces as well as with other frozen systems at unprecedented high resolution. Furthermore, with the exception of crystals growing in thin films, this is the first demonstration for imaging a growing crystal immersed in its own melt with AFM.

Parasites are responsible for the most neglected tropical diseases, affecting over a billion people worldwide (WHO, 2015) and accounting for billions of cases a year and responsible for several millions of deaths. Research on extracellular vesicles (EVs) has increased in recent years and demonstrated that EVs shed by pathogenic parasites interact with host cells playing an important role in the parasite's survival, such as facilitation of infection, immunomodulation, parasite adaptation to the host environment and the transfer of drug resistance factors. Thus, EVs released by parasites mediate parasite-parasite and parasite-host intercellular communication. In addition, they are being explored as biomarkers of asymptomatic infections and disease prognosis after drug treatment. However, most current protocols used for the isolation, size determination, quantification and characterization of molecular cargo of EVs lack greater rigor, standardization, and adequate quality controls to certify the enrichment or purity of the ensuing bioproducts. We are now initiating major guidelines based on the evolution of collective knowledge in recent years. The main points covered in this position paper are methods for the isolation and molecular characterization of EVs obtained from parasite-infected cell cultures, experimental animals, and patients. The guideline also includes a discussion of suggested protocols and functional assays in host cells.

Vesicular transport is a means of communication. While cells can communicate with each other via secretion of extracellular vesicles, less is known regarding organelle-to organelle communication, particularly in the case of mitochondria. Mitochondria are responsible for the production of energy and for essential metabolic pathways in the cell, as well as fundamental processes such as apoptosis and aging. Here, we show that functional mitochondria isolated from Saccharomyces cerevisiae release vesicles, independent of the fission machinery. We isolate these mitochondrial-derived vesicles (MDVs) and find that they are relatively uniform in size, of about 100 nm, and carry selective protein cargo enriched for ATP synthase subunits. Remarkably, we further find that these MDVs harbor a functional ATP synthase complex. We demonstrate that these vesicles have a membrane potential, produce ATP, and seem to fuse with naive mitochondria. Our findings reveal a possible delivery mechanism of ATP-producing vesicles, which can potentially regenerate ATP-deficient mitochondria and may participate in organelle-to-organelle communication.

Protein folding is crucial for biological activity. Proteins failure to fold correctly underlies various pathological processes, including amyloidosis, the aggregation of insoluble proteins (e.g., lysozymes) in organs. The exact conditions that trigger the structural transition of amyloids into β-sheet-rich aggregates are poorly understood, as is the case for the amyloidogenic self-assembly pathway. Ultrasound is routinely used to destabilize a proteins structure and enhance amyloid growth. Here, we report on an unexpected ultrasound effect on lysozyme amyloid species at different stages of aggregation: ultrasound-induced structural perturbation gives rise to nonamyloidogenic folds. Our infrared and X-ray analyses of the chemical, mechanical, and thermal effects of sound on lysozymes structure found, in addition to the expected ultrasound-induced damage, evidence of irreversible disruption of the β-sheet fold of fibrillar lysozyme resulting in their structural transformation into monomers with no β-sheets. This structural transition is reflected in changes in the kinetics of protein self-assembly, namely, either prolonged nucleation or accelerated fibril growth. Using solution X-ray scattering, we determined the structure, the mass fraction of lysozyme monomer, and the morphology of its filamentous assemblies formed under different sound parameters. A nanomechanical analysis of ultrasound-modified protein assemblies revealed a correlation between the β-sheet content and elastic modulus of the protein material. Suppressing one of the ultrasound-derived effects allowed us to control the structural transformations of lysozyme. Overall, our comprehensive investigation establishes the boundary conditions under which ultrasound damages protein structure and fold. This knowledge can be utilized to impose medically desirable structural modifications on amyloid β-sheet-rich proteins.

The spontaneous gelation of poly(4-vinyl pyridine)/pyridine solution produces materials with conductive properties that are suitable for various energy conversion technologies. The gel is a thermoelectric material with a conductivity of 2.25.0 × 106 S m1 and dielectric constant ε = 11.3. On the molecular scale, the gel contains various types of hydrogen bonding, which are formed via self-protonation of the pyridine side chains. Our measurements and calculations revealed that the gelation process produces bias-dependent polymer complexes: quasi-symmetric, strongly hydrogen-bonded species, and weakly bound protonated structures. Under an applied DC bias, the gelled complexes differ in their capacitance/conductive characteristics. In this work, we exploited the bias-responsive characteristics of poly(4-vinyl pyridine) gelled complexes to develop a prototype of a thermal energy harvesting device. The measured device efficiency is S = ΔV/ΔT = 0.18 mV/K within the temperature range of 296360 K. Investigation of the mechanism underlying the conversion of thermal energy into electric charge showed that the heat-controlled proton diffusion (the Soret effect) produces thermogalvanic redox reactions of hydrogen ions on the anode. The charge can be stored in an external capacitor for heat energy harvesting. These results advance our understanding of the molecular mechanisms underlying thermal energy conversion in the poly(4-vinyl pyridine)/pyridine gel. A device prototype, enabling thermal energy harvesting, successfully demonstrates a simple path toward the development of inexpensive, low-energy thermoelectric generators.

Peptide amphiphiles exhibit excellent self-assembly properties and have potential applications ranging from materials science to nanobiotechnology. Yet, a detailed understanding of supramolecular assembly from an atomistic perspective is still lacking. Here, we demonstrate the spontaneous self-association of an aromatic amphiphilic alpha,beta-hybrid into a hierarchically-oriented crystalline supramolecular polymer under aqueous conditions. Single-crystal analysis after fiber recrystallization revealed that the peptide formed a beta-sheet structure stabilized by intermolecular hydrogen bonds and aromatic-aromatic interactions. The head-to-head salt bridge interaction between the opposite charges and hydrogen bonding between the strands account for the elongated shape of the crystal and for the high mechanical strength of the fibers. A new composite biocompatible hydrogel was further fabricated by co-assembly of the hybrid peptide with a well-established hydrogelator. These findings shed light on molecular-level understanding of the supramolecular assembly of hybrid peptide amphiphiles, facilitating development of new composite hydrogels for various applications.

Formation of 8-oxo-7,8-dihydro-2-deoxyguanosine (OG) is one of the most common forms of DNA oxidative damage found in human cells. Although this damage is prevalent in many disease states, it only marginally influences the structure and stability of double-stranded DNA (dsDNA). Therefore, it is a challenge to establish the mechanism by which this damage is detected by repair enzymes. We investigated the position-dependent effect of the damage on the interactions between dsDNA and oligopeptides using atomic force microscopy. The results were confirmed by monitoring the spin and location-dependent polarizability of the damaged DNA, applying a Hall device. The observations suggest that the interaction of peptide with DNA depends on oxidative damage in the DNA and on its location relative to the point of contact between the peptide and the DNA. Hence, a remote search mechanism for damage in DNA is possible.

Silk is a unique, remarkably strong biomaterial made of simple protein building blocks. To date, no synthetic method has come close to reproducing the properties of natural silk, due to the complexity and insufficient understanding of the mechanism of the silk fiber formation. Here, we use a combination of bulk analytical techniques and nanoscale analytical methods, including nano-infrared spectroscopy coupled with atomic force microscopy, to probe the structural characteristics directly, transitions, and evolution of the associated mechanical properties of silk protein species corresponding to the supramolecular phase states inside the silkworm's silk gland. We found that the key step in silk-fiber production is the formation of nanoscale compartments that guide the structural transition of proteins from their native fold into crystalline β-sheets. Remarkably, this process is reversible. Such reversibility enables the remodeling of the final mechanical characteristics of silk materials. These results open a new route for tailoring silk processing for a wide range of new material formats by controlling the structural transitions and self-assembly of the silk protein's supramolecular phases.

Humidity is often reported to compromise the stability of lead halide perovskites or of devices based on them. Here we measure the humidity dependence of the elastic modulus and hardness for two series of lead halide perovskite single crystals, varying either by cation or by anion type. The results reveal a dependence on bond length between, hydrogen bonding with, and polarizability/polarization of these ions. The results show an intriguing inverse relation between modulus and hardness, in contrast to their positive correlation for most other materials. This anomaly persists and is strengthened by the effect of humidity. This, and our overall findings are ascribed to the materials unique atomic-scale structure and properties, viz nano-polar domains and strong dynamic disorder, yet high-quality average order. Our conclusions are based on comparing results obtained from several different nano-indentation techniques, which separate surface from bulk elastic modulus, and probe different manifestations of the hardness.

A protocol for successfully depositing [001] textured, 23 µm thick films of Al_0.75Sc_0.25N, is proposed. The procedure relies on the fact that sputtered Ti is [001]-textured (Formula presented.) -phase (hcp). Diffusion of nitrogen ions into the α-Ti film during reactive sputtering of Al_0.75,Sc_0.25N likely forms a [111]-oriented TiN intermediate layer. The lattice mismatch of this very thin film with Al_0.75Sc_0.25N is ~3.7%, providing excellent conditions for epitaxial growth. In contrast to earlier reports, the Al_0.75Sc_0.25N films prepared in the current study are Al-terminated. Low growth stress (

A micro-electrochemical cell is sealed with a polymer-free single-layer graphene (SLG) membrane to monitor the stability of Cu nanoparticles (NPs) attached to SLG, as well as the interfacial electronic interactions between Cu NPs and SLG both in air and in a mildly alkaline aqueous solution under electrochemical control. A combination of techniques, including in-situ Kelvin probe force microscopy (KPFM) and ex-situ electron microscopy, are applied. When Cu NPs are metallic at cathodic potentials, there is a relatively bias-independent offset in the SLG work function due to charge transfer at the Cu-SLG contact. When Cu NPs are oxidized at anodic potentials, on the other hand, the work function of SLG also depends on the applied bias in a quasi-linear fashion due to electrochemical gating, in addition to charge transfer at the CuO_x-SLG contact. Furthermore, Cu NPs were found to oxidize and detach from SLG when kept under anodic potentials for a few hours, whereas they remain adhered to SLG at cathodic potentials. This is attributed to water intercalation at the CuO-SLG interface associated with the enhanced hydrophilicity of positively polarized graphene, as supported by the absence of Cu detachment following oxidation by galvanic corrosion in air.

Malaria is the most serious mosquito-borne parasitic disease, caused mainly by the intracellular parasite Plasmodium falciparum. The parasite invades human red blood cells and releases extracellular vesicles (EVs) to alter its host responses. It becomes clear that EVs are generally composed of sub-populations. Seeking to identify EV subpopulations, we subject malaria-derived EVs to size-separation analysis, using asymmetric flow field-flow fractionation. Multi-technique analysis reveals surprising characteristics: we identify two distinct EV subpopulations differing in size and protein content. Small EVs are enriched in complement-system proteins and large EVs in proteasome subunits. We then measure the membrane fusion abilities of each subpopulation with three types of host cellular membranes: plasma, late and early endosome. Remarkably, small EVs fuse to early endosome liposomes at significantly greater levels than large EVs. Atomic force microscope imaging combined with machine-learning methods further emphasizes the difference in biophysical properties between the two subpopulations. These results shed light on the sophisticated mechanism by which malaria parasites utilize EV subpopulations as a communication tool to target different cellular destinations or host systems.

Glycoconjugates on extracellular vesicles (EVs) play a vital role in internalization and mediate interaction as well as regulation of the host immune system by viruses, bacteria, and parasites. During their intraerythrocytic life-cycle stages, malaria parasites, Plasmodium falciparum (Pf) mediate the secretion of EVs by infected red blood cells (RBCs) that carry a diverse range of parasitic and host-derived molecules. These molecules facilitate parasite-parasite and parasite-host interactions to ensure parasite survival. To date, the number of identified Pf genes associated with glycan synthesis and the repertoire of expressed glycoconjugates is relatively low. Moreover, the role of Pf glycans in pathogenesis is mostly unclear and poorly understood. As a result, the expression of glycoconjugates on Pf-derived EVs or their involvement in the parasite life-cycle has yet to be reported. Herein, we show that EVs secreted by Pf-infected RBCs carry significantly higher sialylated complex N-glycans than EVs derived from healthy RBCs. Furthermore, we reveal that EV uptake by host monocytes depends on N-glycoproteins and demonstrate that terminal sialic acid on the N-glycans is essential for uptake by human monocytes. Our results provide the first evidence that Pf exploits host sialylated N-glycans to mediate EV uptake by the human immune system cells.

Malaria is one the most devastating infectious diseases in the world: of the five malaria-associated parasites, Plasmodium falciparum and P. vivax are the most pathogenic and widespread, respectively. P. falciparum invades human red blood cells (RBCs), releasing extracellular vesicles (Pf-EV) carrying DNA, RNA and protein cargo components involved in host-pathogen communications in the course of the disease. Different strategies have been used to analyze Pf-EV biophysically and chemically. Atomic force microscopy (AFM) stands out as a powerful tool for rendering high quality images of extracellular vesicles. In this technique, a sharp tip attached to a cantilever reconstructs the topographic surface of the extracellular vesicles and probes their nano-mechanical properties based on forcedistance curves. Here, we describe a method to separate Pf-EV using differential ultracentrifugation, followed by nanoparticle tracking analysis (NTA) to quantify and estimate the size distribution. Finally, the AFM imaging procedure on Pf-EV adsorbed on a Mg2+-modified mica surface is detailed.

Progress in computing capabilities has enhanced science in many ways. In recent years, various branches of machine learning have been the key facilitators in forging new paths, ranging from categorizing big data to instrumental control, from materials design through image analysis. Deep learning has the ability to identify abstract characteristics embedded within a data set, subsequently using that association to categorize, identify, and isolate subsets of the data. Scanning probe microscopy measures multimodal surface properties, combining morphology with electronic, mechanical, and other characteristics. In this review, we focus on a subset of deep learning algorithms, that is, convolutional neural networks, and how it is transforming the acquisition and analysis of scanning probe data.

Poly(L-lactic acid) (PLLA) is a biocompatible, biodegradable, and semi-crystalline polymer with numerous applications including food packaging, medical implants, stents, tissue engineering scaffolds, etc. Hydroxyapatite (HA) is the major component of natural bone. Conceptually, combining PLLA and HA could produce a bioceramic suitable for implants and bone repair. However, this nanocomposite suffers from poor mechanical behavior under tensile strain. In this study, films of PLLA and HA were prepared with small amounts of nontoxic WS₂ nanotubes (INT-WS₂ ). The structural aspects of the films were investigated via electron microscopy, X-ray diffraction, Raman microscopy, and infrared absorption spectroscopy. The mechanical properties were evaluated via tensile measurements, micro-hardness tests, and nanoindentation. The thermal properties were investigated via differential scanning calorimetry. The composite films exhibited improved mechanical and thermal properties compared to the films prepared from the PLLA and HA alone, which is advantageous for medical applications.

An electrochemical micro-reactor sealed with a single-layer graphene (SLG) membrane is demonstrated that allows straightforward measurement with established scanning probe microscopies. SLG serves as a working electrode which separates the liquid electrochemical environment from the ambient to enable direct energy-level determination. Kelvin probe force microscopy (KPFM) thereby reveals the shifts in Fermi-level of suspended SLG under electrochemical reaction conditions in aqueous alkaline media. Polymer-free transfer to create suspended SLG minimizes contributions to doping related to any support or contaminants, such that changes in work function (WF) relate predominantly to the electrochemical system under study. These WF changes are rationalized in the context of a simple model of electrochemical gating, providing insight into the interplay between electronic and electrochemical doping (through redox of water) of suspended graphene. Further changes in WF are attributable to the reversible functionalization of graphene during the oxygen evolution reaction. Mechanical changes in the suspended graphene in the form of bulging also occur, which are attributed to electro-wetting of graphene induced by charge-carrier doping.

We demonstrate the solvent-free amorphous-to-cocrystalline transformations of nanoscale molecular films. Exposing amorphous films to vapors of a haloarene results in the formation of a cocrystalline coating. This transformation proceeds by gradual strengthening of halogen-bonding interactions as a result of the crystallization process. The gassolid diffusion mechanism involves formation of an amorphous metastable phase prior to crystallization of the films. In situ optical microscopy shows mass transport during this process, which is confirmed by cross-section analysis of the final structures using focused ion beam milling combined with scanning electron microscopy. Nanomechanical measurements show that the rigidity of the amorphous films influences the crystallization process. This surface transformation results in molecular arrangements that are not readily obtained through other means. Cocrystals grown in solution crystallize in a monoclinic centrosymmetric space group, whereas the on-surface halogen-bonded assembly crystallizes into a noncentrosymmetric material with a bulk second-order nonlinear optical response.

We demonstrate here a unique metalloorganic material where the appearance and the internal crystal structure are in contradiction. The eggshaped (ovoid) crystals have a brainlike texture. Although these microsized crystals are monodispersed; like fingerprints their grainy surfaces are never exactly alike. Remarkably, our Xray and electron diffraction studies unexpectedly revealed that these structures are singlecrystals comprising a continuous coordination network of two differently shaped homochiral channels. By using the same building blocks under different reaction conditions, a rare series of crystals have been obtained that are uniquely rounded in their shape. In stark contrast to the brainlike crystals, these isostructural and monodispersed crystals have a comparatively smooth appearance. The sizes of these crystals vary by several orders of magnitude.The eggshaped homochiral crystals: A brainlike texture combined with single crystallinity. A series of isomorphous crystals found in a rare space group have been formed with varied morphologies. These crystals contain chiral channels and are made from achiral components.

The process of amyloid nanofibril formation has broad implications including the generation of the strongest natural materials, namely silk fibers, and their major contribution to the progression of many degenerative diseases. The key question that remains unanswered is whether the amyloidogenic nature, which includes the characteristic H-bonded β-sheet structure and physical characteristics of protein assemblies, can be modified via controlled intervention of the molecular interactions. Here we show that tailored changes in molecular interactions, specifically in the H-bonded network, do not affect the nature of amyloidogenic fibrillation, and even have minimal effect on the initial nucleation events of self-assembly. However, they do trigger changes in networks at a higher hierarchical level, namely enhanced 2D packaging which is rationalized by the 3D hierarchy of β-sheet assembly, leading to variations in fibril morphology, structural composition and, remarkably, nanomechanical properties. These results pave the way to a better understanding of the role of molecular interactions in sculpting the structural and physical properties of protein supramolecular constructs.

It is established that electron transmission through chiral molecules depends on the electron's spin. This phenomenon, termed the chiral-induced spin selectivity (CISS), effect has been observed in chiral molecules, supramolecular structures, polymers, and metal-organic films. Which spin is preferred in the transmission depends on the handedness of the system and the tunneling direction of the electrons. Molecular motors based on overcrowded alkenes show multiple inversions of helical chirality under light irradiation and thermal relaxation. The authors found here multistate switching of spin selectivity in electron transfer through first generation molecular motors based on the four accessible distinct helical configurations, measured by magnetic-conductive atomic force microscopy. It is shown that the helical state dictates the molecular organization on the surface. The efficient spin polarization observed in the photostationary state of the right-handed motor coupled with the modulation of spin selectivity through the controlled sequence of helical states, opens opportunities to tune spin selectivity on-demand with high spatio-temporal precision. An energetic analysis correlates the spin injection barrier with the extent of spin polarization.

Eocene flint 4856.0 million years old (mya) from the Negev desert (Israel) was characterized using a suite of analytical techniques. High-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) of the inorganic component showed the texture, morphology, size, and distribution of two silica polymorphs: αquartz and moganite. While euhedral forms were attributed to α-quartz, moganite crystals were comprised of spherulitic grains. An electron less-dense amorphous material (no scattering under SAED) was found between the siliceous crystallites. Energy dispersive X-rays (EDS) and electron energy loss spectroscopy (EELS) demonstrated that this electron less-dense amorphous material is composed solely of carbon. Low vacuum, low energy backscattered environmental scanning electron microscopy (BSE-eSEM) imaging of flint surfaces showed the presence of micrometer-sized organic inclusions randomly distributed throughout the siliceous matrix. Energy-dispersive X-ray studies (EDS) demonstrated that these organic micro-inclusions were composed of carbon, sulfur, and nitrogen with a C/N ratio attributed to marine sources. These micro-inclusions were not directly associated with hard-shell fossils. BSE-eSEM imaging conditions allowed the identification of entrapped carbon-rich organic material, which is not possible when applying commonly used electron microscopy conditions that require carbon coating and high acceleration voltages, rendering carbon-rich features electron-transparent. Phase contrast-enhanced micro-computed tomography (PC-μCT) showed that these organic micro-inclusions were randomly distributed throughout the siliceous matrix.Time-of-flight secondary ion mass spectrometry (ToF-SIMS), nano-Fourier transform infrared spectroscopy (nano-FTIR), and scanning probe microscopy (SPM) were used to further characterize these organic micro-inclusions. These three in situ analytical techniques with nanometer resolution provided complementary information on the chemical composition and structure of the organic material. Specifically, ToF-SIMS analysis revealed amino acid and hydrocarbon mass spectra fingerprints inside the organic micro-inclusions. While the former were exclusively found in the organic micro-inclusions, the mass spectral fingerprints for hydrocarbons were also found in the siliceous matrix in agreement with the HR-TEM/EDS/EELS results, where pure carbon was found between the siliceous nanocrystals. While ToF-SIMS provides chemical information, it does not provide structural information. Nano-FTIR analysis showed the presence of amide I and II infrared vibrations exclusively on the organic micro-inclusions. The scanning probe microscopy (SPM) techniques Peak Force Quantitative Nanomechanics (PF-QNM) and Contact Resonance Atomic Force Microscopy (CR-AFM) were used to assess the mechanical properties. PF-QNM measurements on the organic micro-inclusions, under dry and liquid conditions, demonstrated that the organic micro-inclusions swell upon hydration and soften, pointing toward the presence of hydrophilic molecules in agreement with nano-FTIR and ToF-SIMS results. CR-AFM allows in situ determination of the mechanical properties of materials with high stiffness at nanometer resolution. This technique, rarely used in a geological context, revealed that the organic micro-inclusions had an unusually high stiffness atypical for modern organic material, which was attributed to molecular cross-linking promoted by diagenesis.This work provided a comprehensive view of the inorganic and organic components of Eocene flint from the Negev desert with implications for paleontology and archaeology. It offers a roadmap of novel complementary techniques that can be used in the exploration of entrapped organic material in flint.

The technologically important frequency range for the application of electrostrictors and piezoelectrics is tens of Hz to tens of kHz. Sm3+- and Gd3+-doped ceria ceramics, excellent intermediate-temperature ion conductors, have been shown to exhibit very large electrostriction below 1 Hz. Why this is so is still not understood. While optimal design of ceria-based devices requires an in-depth understanding of their mechanical and electromechanical properties, systematic investigation of the influence of dopant size on frequency response is lacking. In this report, the mechanical and electromechanical properties of dense ceria ceramics doped with trivalent lanthanides (RE0.1Ce0.9O1.95, RE = Lu, Yb, Er, Gd, Sm, and Nd) were investigated. Youngs, shear, and bulk moduli were obtained from ultrasound pulse echo measurements. Nanoindentation measurements revealed room-temperature creep in all samples as well as the dependence of Youngs modulus on the unloading rate. Both are evidence for viscoelastic behavior, in this case anelasticity. For all samples, within the frequency range f = 0.15150 Hz and electric field E ≤ 0.7 MV/m, the longitudinal electrostriction strain coefficient (|M33|) was 102 to 104-fold larger than expected for classical (Newnham) electrostrictors. However, electrostrictive strain in Er-, Gd-, Sm-, and Nd-doped ceramics exhibited marked frequency relaxation, with the Debye-type characteristic relaxation time τ ≤ 1 s, while for the smallest dopantsLu and Yblittle change in electrostrictive strain was detected over the complete frequency range studied. We find that only the small, less-studied dopants continue to produce useable electrostrictive strain at the higher frequencies. We suggest that this striking difference in frequency response may be explained by postulating that introduction of a dopant induces two types of polarizable elastic dipoles and that the dopant size determines which of the two will be dominant.

Mature red blood cells (RBCs) lack internal organelles and canonical defense mechanisms, making them both a fascinating host cell, in general, and an intriguing choice for the deadly malaria parasite Plasmodium falciparum (Pf), in particular. Pf, while growing inside its natural host, the human RBC, secretes multipurpose extracellular vesicles (EVs), yet their influence on this essential host cell remains unknown. Here we demonstrate that Pf parasites, cultured in fresh human donor blood, secrete within such EVs assembled and functional 20S proteasome complexes (EV-20S). The EV-20S proteasomes modulate the mechanical properties of naïve human RBCs by remodeling their cytoskeletal network. Furthermore, we identify four degradation targets of the secreted 20S proteasome, the phosphorylated cytoskeletal proteins β-adducin, ankyrin-1, dematin and Epb4.1. Overall, our findings reveal a previously unknown 20S proteasome secretion mechanism employed by the human malaria parasite, which primes RBCs for parasite invasion by altering membrane stiffness, to facilitate malaria parasite growth.

The facile fabrication of free-floating organic nanocrystals (ONCs) was achieved via the kinetically controlled self-assembly of simple perylene diimide building blocks in aqueous medium. The ONCs have a thin rectangular shape, with an aspect ratio that is controlled by the content of the organic cosolvent (THF). The nanocrystals were characterized in solution by cryogenic transmission electron microscopy (cryo-TEM) and small-angle X-ray scattering. The ONCs retain their structure upon drying, as was evidenced by TEM and atom force microscopy. Photophysical studies, including femtosecond transient absorption spectroscopy, revealed a distinct influence of the ONC morphology on their photonic properties (excitation energy transfer was observed only in the high-aspect ONCs). Convenient control over the structure and function of organic nanocrystals can enhance their utility in new and developed technologies.

Dimensional change in a solid due to electrochemically driven compositional change is termed electro-chemo-mechanical (ECM) coupling. This effect causes mechanical instability in Li-ion batteries and solid oxide fuel cells. Nevertheless, it can generate considerable force and deformation, making it attractive for mechanical actuation. Here a Si-compatible ECM actuator in the form of a 2 mm diameter membrane is demonstrated. Actuation results from oxygen ion transfer between two 0.1 µm thick Ti oxide\Ce0.8Gd0.2O1.9 nanocomposite layers separated by a 1.5 µm thick Ce0.8Gd0.2O1.9 solid electrolyte. The chemical reaction responsible for stress generation is electrochemical oxidation/reduction in the composites. Under ambient conditions, application of 5 V DC produces actuator response within seconds, generating vertical displacement of several µm with calculated stress ≈3.5 MPa. The membrane actuator preserves its final mechanical state for more than 1 h following voltage removal. These characteristics uniquely suit ECM actuators for room temperature applications in Si-integrated microelectromechanical systems.

We find significant differences between degradation and healing at the surface or in the bulk for each of the different APbBr3 single crystals (A = CH3NH3+, methylammonium (MA); HC(NH2)2+, formamidinium (FA); and cesium, Cs+). Using 1- and 2-photon microscopy and photobleaching we conclude that kinetics dominate the surface and thermodynamics the bulk stability. Fluorescence-lifetime imaging microscopy, as well as results from several other methods, relate the (damaged) state of the halide perovskite (HaP) after photobleaching to its modified optical and electronic properties. The A cation type strongly influences both the kinetics and the thermodynamics of recovery and degradation: FA heals best the bulk material with faster self-healing; Cs+ protects the surface best, being the least volatile of the A cations and possibly through O-passivation; MA passivates defects via methylamine from photo-dissociation, which binds to Pb2+. DFT simulations provide insight into the passivating role of MA, and also indicate the importance of the Br3- defect as well as predicts its stability. The occurrence and rate of self-healing are suggested to explain the low effective defect density in the HaPs and through this, their excellent performance. These results rationalize the use of mixed A-cation materials for optimizing both solar cell stability and overall performance of HaP-based devices, and provide a basis for designing new HaP variants.

Biological organisms are inherently complex. Although investigations of the function and design of living organisms have existed since the dawn of science, only in recent years have the tools existed to extend such studies to the nanoscale. Progress in nanomechanics of biological systems has enabled our understanding of intricate mechanical designs which nature has optimized for specific functions. This review provides an overview of the field of bionanomechanics, emphasizing the manner in which fundamental mechanical concepts are expressed in the design of a wide spectrum of biological specimens. We show that diverse species exploit common concepts to achieve desired function; a principle that extends over large scales of size and mechanical properties. The powerful techniques that enable such studies, particularly atomic force microscopy and instrumented nanoindentation, as well as common analytical approaches are given special attention.

The transformations of biomass burning brown carbon aerosols (BB-BrC) over their diurnal lifecycle are currently not well studied. In this study, the aging of BB tar proxy aerosols processed by NO3 under dark conditions followed by photochemical OH reaction and photolysis were investigated in tandem flow reactors. The results show that O3 oxidation in the dark diminishes light absorption of wood tar aerosols, resulting in higher particle single-scattering albedo (SSA). NO3 reactions augment the mass absorption coefficient (MAC) of the aerosols by a factor of 2-3 by forming secondary chromophores, such as nitroaromatic compounds (NACs) and organonitrates. Subsequent OH oxidation and direct photolysis both decompose the organic nitrates (ONs, representing bulk functionalities of NACs and organonitrates) in the NO3-aged wood tar aerosols, thus decreasing the particle absorption. Moreover, the NACs degrade faster than the organonitrates by photochemical aging. The NO3-aged wood tar aerosols are more susceptible to photolysis than to OH reactions. The photolysis lifetimes for the ONs and for the absorbance of the NO3-aged aerosols are on the order of hours under typical solar irradiation, while the absorption and ONs lifetimes towards OH oxidation are substantially longer. Overall, nighttime aging via NO3 reactions increases the light absorption of wood tar aerosols and shortens their absorption lifetime under daytime conditions.

We demonstrate the formation of uniform and oriented metal-organic frameworks using a combination of anion-effects and surface-chemistry. Subtle but significant morphological changes result from the nature of the coordinative counter-anion of the following metal salts: NiX2 with (X = Br-, Cl-, NO3-, and OAc-). Crystals could be obtained in solution or by template surface growth. The latter resulting in truncated crystals that resemble a half-structure of the solution-grown ones. The oriented surface-bound metal-organic frameworks (sMOFs) are obtained via a one-step solvothermal approach, rather than in a layer-by-layer approach. The MOFs are grown on Si/SiOx substrates modified with an organic monolayer or on glass substrates covered with a transparent conductive oxide (TCO). Regardless of the different morphologies, the crystallographic packing is nearly identical and is not affected by the type of anion, nor by solution versus the surface chemistry. A propeller-type arrangement of the non-chiral ligands around the metal center affords a chiral structure with two geometrically different helical channels in a 2:1 ratio with the same handedness. To demonstrate the accessibility and porosity of the macroscopically-oriented channels, a chromophore (resorufin sodium salt) was successfully embedded into the channels of the crystals by diffusion from solution, resulting in fluorescent crystals. These "colored" crystals displayed polarized emission (red) with a high polarization ratio because of the alignment of these dyes imposed by the crystallographic structure. A second-harmonic generation (SHG) study revealed Kleinman-symmetry forbidden non-linear optical properties. These surface-bound and oriented SHG-active MOFs have the potential for use as single non-linear optical (NLO) devices.

Solid-state electronic transport (ETp) via the electron-transfer copper protein azurin (Az) was measured in Au/Az/Au junction configurations down to 4 K, the lowest temperature for solid-state protein-based junctions. Not only does lowering the temperature help when observing fine features of electronic transport, but it also limits possible electron transport mechanisms. Practically, wire-bonded devices-on-chip, carrying Az-based microscopic junctions, were measured in liquid He, minimizing temperature gradients across the samples. Much smaller junctions, in conducting-probe atomic force microscopy measurements, served, between room temperature and the protein's denaturation temperature (similar to 323 K), to check that conductance behavior is independent of device configuration or contact nature and thus is a property of the protein itself. Temperature-independent currents were observed from similar to 320 to 4 K. The experimental results were fitted to a single-level Landauer model to extract effective energy barrier and electrode-molecule coupling strength values and to compare data sets. Our results strongly support that quantum tunneling, rather than hopping, dominates ETp via Az.

The bivalve hinge ligament holds the two shells together. The ligament functions as a spring to open the shells after they were closed by the adductor muscle. The ligament is a mineralized tissue that bears no resemblance to any other known tissue. About half the ligament is composed of a protein-rich matrix, and half of long and extremely thin segmented aragonite crystals. Here we study the hinge ligament of the pearl oyster Pinctada fucata. FIB SEM shows that the 3D organization is remarkably ordered. The full sequence of the major protein component contains a continuous segment of 30 repeats of MMMLPD. There is no known homologous protein. Knockdown of this protein prevents crystal formation, demonstrating that the integrity of the matrix is necessary for crystals to form. X-ray diffraction shows that the aragonite crystals are more aligned in the compressed ligament, indicating that the crystals may be actively contributing to the elastic properties. The fusion interphase that joins the ligament to the shell nacre is composed of a prismatic mineralized tissue with a thin organic-rich layer at its center. Nanoindentation of the dry interphase shows that the elastic modulus of the nacre adjacent to the interphase gradually decreases until it approximates that of the interphase. The interphase modulus slightly increases until it matches the ligament. All these observations demonstrate that the ligament shell complex is a remarkable biological tissue that has evolved unique properties that enable bivalves to open their shell effectively innumerable times during the lifetime of the animal.Statement of significance - The hinge ligament shell complex is a unique functioning structural tissue whose elastic properties enable the shell to open without expending energy. Methionine-rich proteins are not known elsewhere raising fundamental questions about secondary and tertiary structures contributing to its elastic properties. The segmented and extremely thin aragonite crystals embedded in this matrix may also have unexpected elastic materials properties as they flex during compression. The structure of the interphase comprises a fascinating biological joint that connects two very different materials. The interphase materials, including the nacre, are graded with respect to elastic modulus so as to approximately match the connecting components. The interphase incorporates a thin organic rich layer that presumably functions as a gasket. This study raises many fundamental questions relevant to the diverse fields of protein chemistry, biomineralization and biological materials. (C) 2019 Published by Elsevier Ltd on behalf of Acta Materialia Inc.

Organic photovoltaics enable cost-efficient, tunable, and flexible platforms for solar energy conversion, yet their performance and stability are still far from optimal. Here, we present a study of photoinduced charge transfer processes between electron donor and acceptor organic nanocrystals as part of a pathfinding effort to develop robust and efficient organic nanocrystalline materials for photovoltaic applications. For this purpose, we utilized nanocrystals of perylenediimides as the electron acceptors and nanocrystalline copper phthalocyanine as the electron donor. Three different configurations of donor-acceptor heterojunctions were prepared. Charge transfer in the heterojunctions was studied with Kelvin probe force microscopy under laser or white light excitation. Moreover, detailed morphology characterizations and time-resolved photoluminescence measurements were conducted to understand the differences in the photovoltaic processes of these organic nanocrystals. Our work demonstrates that excitonic properties can be tuned by controlling the crystal and interface structures in the nanocrystalline heterojunctions, leading to a minimization of photovoltaic losses.

Since scorpions exist almost all over the world, some expected body differences exist among the species: undoubtedly, the most evident is the shape and size of their pincers or chelae. The scorpion chela is a multifunctional body component (e.g. attack/defense, mating and protection from the environment) that leads to the development of different stresses in the cuticle. How such stresses in the cuticle are accommodated by different chelae shape and size is largely unknown. Here we provide new comparative data on the hierarchical structure and mechanical properties of the chela cuticle in two scorpion species: Scorpio Maurus Palmatus (SP) that has a large chela and Buthus Occitanus Israelis (BO), with a slender chela. We found that the SP exocuticle is composed of four different sublayers whereas the BO exocuticle displays only two sublayers. These structures are different from the exocuticle morphologies in crustaceans, where the Bouligand morphology is present throughout the entire layer. Moreover, the scorpion chela cuticle presents an exclusive structural layer made of unidirectional fibers arranged vertically towards the normal direction of the cuticle. Nanoindentation measurements were performed under dry conditions on transversal and longitudinal planes to evaluate the stiffness and hardness of the different chela cuticle layers in both scorpions. The chela cuticle structure is a key factor towards the decision of the scorpion whether to choose to sting or use the chela for other mechanical functions. Statement of Significance: Many arthropods such as lobsters, crabs, stomatopods, isopods, and spiders have been the subject of research in recent years, and their hierarchical structure and mechanical properties extensively investigated. Yet, except for a limited number of pre-1980 publications, comparatively little work has been devoted to the terrestrial scorpion. The scorpion chela is a multifunctional part of the body (e.g. attack/defense, mating and protection from the environment) that involves the development of various stresses in the cuticle. How these stresses in the chela cuticle are managed by different chelae shape and size is still unknown. The lack of a single study that integrates morphological characterization of the entire hierarchical structure of the scorpion chela cuticle, and local mechanical properties, significantly affects the scientific knowledge regarding important structural approaches that can be used by nature to maximize functionality.

Protozoan pathogens secrete nanosized particles called extracellular vesicles (EVs) to facilitate their survival and chronic infection. Here, we show the inhibition by Plasmodium berghei NK65 blood stage-derived EVs of the proliferative response of CD4(+) T cells in response to antigen presentation. Importantly, these results were confirmed in vivo by the capacity of EVs to diminish the ovalbumin-specific delayed type hypersensitivity response. We identified two proteins associated with EVs, the histamine releasing factor (HRF) and the elongation factor 1 alpha (EF-1 alpha) that were found to have immunosuppressive activities. Interestingly, in contrast to WT parasites, EVs from genetically HRF- and EF-1 alpha-deficient parasites failed to inhibit T cell responses in vitro and in vivo. At the level of T cells, we demonstrated that EVs from WT parasites dephosphorylate key molecules (PLC gamma 1, Akt, and ERK) of the T cell receptor signalling cascade. Remarkably, immunisation with EF-1 alpha alone or in combination with HRF conferred a long-lasting antiparasite protection and immune memory. In conclusion, we identified a new mechanism by which P. berghei-derived EVs exert their immunosuppressive functions by altering T cell responses. The identification of two highly conserved immune suppressive factors offers new conceptual strategies to overcome EV-mediated immune suppression in malaria-infected individuals.

Gddoped ceria (CGO), one of the most extensively studied oxygen ion conductors, is a low dielectric constant/low mechanical compliance material exhibiting large nonclassical electrostriction. The electromechanical response of the microelectromechanical devices with CGO films as an active material described previously can not be attributed exclusively to electrostriction. Here it is shown that, below 1 Hz, in addition to electrostriction (secondharmonic response), there is a strong contribution of the electrochemomechanical effect (ECM, first harmonic response). ECM is the change in mechanical dimensions of ionic and mixed ionicelectronic conductors as a result of a change in chemical composition induced by an electric field. In batteries, the presence of ECM is highly detrimental. In ceria at room temperature, it was considered to be negligible because of slow oxygen diffusion. This work demonstrates ECM actuation at ambient temperature and moderate electric field (

Young's, shear and bulk moduli of Ce _1-xSm _xO _2-x/2 (x ≤ 0.55) were studied using ultrasonic time of flight and nanoindentation techniques. Sound velocity measurements, corrected for sample porosity, demonstrate decrease in the unrelaxed ceramic moduli with increasing Sm-content. Room temperature creep under indenter load-hold, as well as time-dependent material stiffness, reveal a transition from prominent anelasticity in the fluorite phase to prominent elasticity in the double fluorite phase. This supports rearrangement of elastic dipoles under anisotropic stress, which occurs more readily when oxygen vacancies are not ordered on the crystal lattice, as the source of ceria anelastic behavior.

Symmetry-imposed restrictions on the number of available pyroelectric and piezoelectric materials remain a major limitation as 22 out of 32 crystallographic material classes exhibit neither pyroelectricity nor piezoelectricity. Yet, by breaking the lattice symmetry it is possible to circumvent this limitation. Here, using a unique technique for measuring transient currents upon rapid heating, direct experimental evidence is provided that despite the fact that bulk SrTiO3 is not pyroelectric, the (100) surface of TiO2-terminated SrTiO3 is intrinsically pyroelectric at room temperature. The pyroelectric layer is found to be ≈1 nm thick and, surprisingly, its polarization is comparable with that of strongly polar materials such as BaTiO3. The pyroelectric effect can be tuned ON/OFF by the formation or removal of a nanometric SiO2 layer. Using density functional theory, the pyroelectricity is found to be a result of polar surface relaxation, which can be suppressed by varying the lattice symmetry breaking using a SiO2 capping layer. The observation of pyroelectricity emerging at the SrTiO3 surface also implies that it is intrinsically piezoelectric. These findings may pave the way for observing and tailoring piezo- and pyroelectricity in any material through appropriate breaking of symmetry at surfaces and artificial nanostructures such as heterointerfaces and superlattices.

Nanometer-sized structures, surfaces and sub-surface phenomena have played an enormous role in science and technological applications and represent a driving-force of current interdisciplinary science. Recent developments include the atomic-scale characterization of nanoparticles, molecular reactions at surfaces, magnetism at the atomic scale, photoelectric characterization of nanostructures as well as two-dimensional solids. Research and development of smart nanostructured materials governed by their surface properties is a rapidly growing field. The main challenge is to develop an accurate and robust electronic structure description. The density of surface-related trap states is analyzed by transient UV photoconductivity and temperature-dependent admittance spectroscopy. An advanced application of thin films on shaped substrates is the deposition of catalytic layers on hollow glass microspheres for hydrogen storage controlled exothermal hydrolytic release. Surface properties of thin films including dissolution and corrosion, fouling resistance, and hydrophilicity/hydrophobicity are explored to improve materials response in biological environments and medicine. Trends in surface bio-functionalization routes based on vacuum techniques, together with advances in surface analysis of biomaterials, are discussed. Pioneering advances in the application of X-ray nanodiffraction of thin film cross-sections for characterizing nanostructure and local strain including in-situ experiments during nanoindentation are described. Precise measurements and control of plasma properties are important for fundamental investigations and the development of next generation plasma-based technologies. Critical control parameters are the flux and energy distribution of incident ions at reactive surfaces; it is also crucial to control the dynamics of electrons initiating non-equilibrium chemical reactions. The most promising approach involves the exploitation of complementary advantages in direct measurements combined with specifically designed numerical simulations. Exciting new developments in vacuum science and technology have focused on forward-looking and next generation standards and sensors that take advantage of photonics based measurements. These measurements are inherently fast, frequency based, easily transferrable to sensors based on photonics and hold promise of being disruptive and transformative. Realization of Pascal, the SI unit for pressure, a cold-atom trap based ultra-high and extreme high vacuum (UHV and XHV) standard, dynamic pressure measurements and a photonic based thermometer are three key examples that are presented.

Self-lubricating films are of immense importance in various tribological applications. Nanoparticles are often used as the lubricating component in such films. Inorganic fullerene-like (IF) nanoparticles of WS2 have been used in the past for variety of tribological applications including for self-lubricating polymer and metallic films. IF nanoparticles from MoS2 with superior tribological behavior were reported in the past. However, such nanoparticles, which are available in minute amounts, were not applied for self-lubricating coatings in the past. In the current work, inorganic fullerene-like nanoparticles of MoS2 (IF-MoS2) were co-evaporated with titanium (cobalt) on metal substrates. The films were characterized by different techniques and were shown to have good adhesion to the underlying substrate. Furthermore, tribological tests indicated that such coatings exhibit improved friction coefficient (roughly 0.1) and very small wear under relatively high load.

Creating sub-micron hotspots for applications such as heat-assisted magnetic recording (HAMR) is a challenging task. The most common approach relies on a surface-plasmon resonator (SPR), whose design dictates the size of the hotspot to always be larger than its critical dimension. Here, we present an approach which circumvents known geometrical restrictions by resorting to electric field confinement via excitation of a gap-mode (GM) between a comparatively large Gold (Au) nano-sphere (radius of 100 nm) and the magnetic medium in a grazing-incidence configuration. Operating a lambda = 785 nm laser, sub-200 nm hot spots have been generated and successfully used for GM-assisted magnetic switching on commercial CoCrPt perpendicular magnetic recording media at laser powers and pulse durations comparable to SPR-based HAMR. Lumerical electric field modelling confirmed that operating in the near-infrared regime presents a suitable working point where most of the light's energy is deposited in the magnetic layer, rather than in the nano-particle. Further, modelling is used for predicting the limits of our method which, in theory, can yield sub-30 nm hotspots for Au nano-sphere radii of 25-50 nm for efficient heating of FePt recording media with a gap of 5 nm. Published by AIP Publishing.

Microstructure Grains Dislocations Friction Wear Lubrication.Evolution of deformation microstructure and nanohardness of Ag and Ni after friction in the BL regime was studied. All friction tests were conducted under lubricated conditions using a pin-on-disk rig. Pure fee metals such as Ag and Ni, with different SFE (16 and 125 mJm(-2), respectively), were chosen as pin materials. Cross sectional transmission electron microscopy (TEM) lamellae were prepared from the pins using a focused ion beam (FIB). Using TEM, we analysed the regions of the pins that are in steady state after friction; the friction coefficient (mu) and hardness (H-s) remained unchanged with deformation in the BL regime. After the wear tests, the specimens were cross-sectioned in longitudinal and transverse directions (parallel and perpendicular to the direction of friction). Nanoindentations were performed using a Berkovich diamond tip. A gradient of grain sizes during the friction of Ag and Ni in BL regime was revealed by TEM imaging. Deformation twinning followed by limited recovery within the surface of Ag led to the formation of a relatively thick top layer of ultra-fine equiaxial grains. Thermally activated processes for the rearrangement and annihilation of dislocations are accelerated during the friction of Ni due to high SFE and contact temperature. Cross-sectional microstructures observed normal and parallel to the direction of friction are dissimilar. Steady state values of grain size, d(s), and hardness, H-s, after friction in lubricated conditions are explained by the balance between hardening and dynamic recovery in surface layers, and they strongly depend on the SFE and temperature. A correlation between the wear properties (wear coefficient) and total work of deformation during nanoindentation shows a similarity in the nano- and microscales in lubricated friction.

Electromechanical response of 1.5 μm thick 2 mm diameter self-supported films (membranes) of 20 mol% Gd-doped ceria with Ti electrodes was measured at two temperatures (25 and 75 °C) as a function of direct (U _DC) and alternating (U _AC, 20 Hz) voltages. The films assumed a soup-panbowl shape and application of the external voltage resulted in a uniform vertical shift of the flat area. In the absence of superimposed U _DC, U _AC induces electromechanical response at the 1st and 2nd harmonics at both temperatures. The amplitude of the 2nd harmonic is proportional to U _AC ² at these temperatures and it is independent of U _DC, which identifies it as due to the electrostriction effect. Direct measurement of the built-in bias via minimization of the 1st harmonic response, as well as electrical impedance and IV measurements indicate that, although asymmetry of the contacts may contribute to the appearance of the 1st harmonic, it is insufficient to explain it. Based on the fact that the force-displacement curve of the membrane measured with AFM is hysteretic, we hypothesize that the 1st harmonic response is related to the non-linear mechanical deformation of the buckled film.

The incorporation of proteins as functional components in electronic junctions has received much interest recently due to their diverse bio-chemical and physical properties. However, information regarding the energies of the frontier orbitals involved in their electron transport (ETp) has remained elusive. Here we employ a new method to quantitatively determine the energy position of the molecular orbital, nearest to the Fermi level (E-F) of the electrode, in the electron transfer protein Azurin. The importance of the Cu(ii) redox center of Azurin is demonstrated by measuring gate-controlled conductance switching which is absent if Azurin's copper ions are removed. Comparing different electrode materials, a higher conductance and a lower gate-induced current onset is observed for the material with smaller work function, indicating that ETp via Azurin is LUMO-mediated. We use the difference in work function to calibrate the difference in gate-induced current onset for the two electrode materials, to a specific energy level shift and find that ETp via Azurin is near resonance. Our results provide a basis for mapping and studying the role of energy level positions in (bio)molecular junctions.

In this paper, we demonstrate the formation of hybrid nanostructures consisting of two distinctive components mainly in a one-to-one ratio. Thermolysis of inorganic nanotubes (INT) and closed-cage, inorganic fullerene-like (IF) nanoparticles decorated with a dense coating of metallic nanoparticles (M = Au, Ag, Pd) results in migration of relatively small NPs or surface-enhanced diffusion of atoms or clusters, generating larger particles (ripening). AuNP growth on the surface of INTs has been captured in real time using in situ electron microscopy measurements. Reaction of the AuNP-decorated INTs with an alkylthiol results in a chemically induced NP fusion process at room temperature. The NPs do not dissociate from the surfaces of the INTs and IFs, but for proximate IFs we observed fusion between AuNPs originating from different IFs.

Human brain wrinkling has been implicated in neurodevelopmental disorders and yet its origins remain unknown. Polymer gel models suggest that wrinkling emerges spontaneously due to compression forces arising during differential swelling, but these ideas have not been tested in a living system. Here, we report the appearance of surface wrinkles during the in vitro development and self-organization of human brain organoids in a microfabricated compartment that supports in situ imaging over a timescale of weeks. We observe the emergence of convolutions at a critical cell density and maximal nuclear strain, which are indicative of a mechanical instability. We identify two opposing forces contributing to differential growth: cytoskeletal contraction at the organoid core and cell-cycle-dependent nuclear expansion at the organoid perimeter. The wrinkling wavelength exhibits linear scaling with tissue thickness, consistent with balanced bending and stretching energies. Lissencephalic (smooth brain) organoids display reduced convolutions, modified scaling and a reduced elastic modulus. Although the mechanism here does not include the neuronal migration seen in vivo, it models the physics of the folding brain remarkably well. Our on-chip approach offers a means for studying the emergent properties of organoid development, with implications for the embryonic human brain.

We report here a unique and efficient methodology for the surface functionalization of closed-cage inorganic fullerene-like (IF) nanoparticles and inorganic nanotubes (INTs) composed of two-dimensional nanomaterials of transition-metal chalcogenides (MS ₂; M = W or Mo). The first step is the physical coverage of these robust inorganic materials with monodispersed and dense monolayers of gold, silver, and palladium nanoparticles. The structural continuity at the interface between the IF/INT and the metallic nanoparticles is investigated. Lattice matching between these nanocrystalline materials and strong chemical affinity lead to efficient binding of the metallic nanoparticles onto the outer sulfide layer of the MS ₂-based structures. It is shown that this functionalization results in narrowing of the IF/INT optical band gap, increased work function, and improved surface-enhanced Raman scattering. In the second step, functionalization of the surface-bound nanoparticles is carried out by a ligand-exchange reaction. This ligand exchange involving the tetraoctylammonium bromide capping layer and an alkyl thiol enhances the solubility (∼10×) of the otherwise nearly insoluble materials in organic solvents. The scope of this method is further demonstrated by introducing a ruthenium(II) polypyridyl complex on the surface of the surface-bound AuNPs to generate fluorescent multicomponent materials.

Inorganic fullerene-like closed-cage nanoparticles of MoS2 and WS2 (IF-MoS2; IF-WS2), are synthesized in substantial amounts and their properties are widely studied. Their superior tribological properties led to large scale commercial applications as solid lubricants in numerous products and technologies. Doping of these nanoparticles can be used to tune their physical properties. In the current work, niobium (Nb) doping of the nanoparticles is accomplished to an unprecedented low level (

We report here a new methodology for the formation of freestanding nanotubes composed of individual gold nanoparticles (NPs) cross-linked by coordination complexes or porphyrin molecules using WS ₂ nanotubes (INT-WS ₂) as a template. Our method consists of three steps: (i) coverage of these robust inorganic materials with monodispersed and dense monolayers of gold NPs, (ii) formation of a molecular AuNP network by exposing these decorated tubes to solutions containing a ruthenium polypyridyl complex or meso-tetra(4-pyridyl)porphyrin, and (iii) removal of the INT-WS ₂ template with a hydrogen peroxide solution. Nanoindentation of the template-free AuNP tubes with atomic force microscopy indicates a radial elastic modulus of 4 GPa. The template-free molecular AuNP tubes are characterized using scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, and micro-Raman spectroscopy. The methodology provides a convenient and scalable strategy for the realization of molecular AuNP tubes with a defined length and diameter, depending on the dimensions of the template.

Organic crystalline materials are used as dyes/pigments, pharmaceuticals, and active components of photonic and electronic devices. There is great interest in integrating organic crystals with inorganic and carbon nanomaterials to create nanocomposites with enhanced properties. Such efforts are hampered by the difficulties in interfacing organic crystals with dissimilar materials. Here, an approach that employs organic nanocrystallization is presented to fabricate solution-processed organic nanocrystal/carbon nanotube (ONC/CNT) hybrid materials based on readily available organic dyes (perylene diimides (PDIs)) and carbon nanotubes. The hybrids are prepared by self-assembly in aqueous media to afford free-standing films with tunable CNT content. These exhibit excellent conductivities (as high as 5.78 ± 0.56 S m⁻¹), and high thermal stability that are superior to common polymer/CNT hybrids. The color of the hybrids can be tuned by adding various PDI derivatives. ONC/CNT hybrids represent a novel class of nanocomposites, applicable as optoelectronic and conductive colorant materials.

Friction at hydrophobic surfaces in aqueous media is ubiquitous (e.g., prosthetic implants, contact lenses, microfluidic devices, biological tissue) but is not well understood. Here, we measure directly, using a surface force balance, both normal stresses and sliding friction in an aqueous environment between a hydrophilic surface (single-crystal mica) and the stable, molecularly smooth, highly hydrophobic surface of a spin-cast fluoropolymer film. Normal force versus surface separation profiles indicate a high negative charge density at the water-immersed fluoropolymer surface, consistent with previous studies. Sliding of the compressed surfaces under water or in physiological-level salt solution (0.1 M NaCl) reveals strikingly low boundary friction (friction coefficient mu approximate to 0.003-0.009) up to contact pressures of at least 50 atm. This is attributed largely to hydrated counterions (protons and Na+ ions) trapped in thin interfacial films between the compressed, sliding surfaces. Our results reveal how frictional dissipation may occur at hydrophobic surfaces in water and how modification of such surfaces may suppress this dissipation.

The chiral-induced spin selectivity (CISS) effect entails spin-selective electron transmission through chiral molecules. In the present study, the spin filtering ability of chiral, helical oligopeptide monolayers of two different lengths is demonstrated using magnetic conductive probe atomic force microscopy. Spin-specific nanoscale electron transport studies elucidate that the spin polarization is higher for 14-mer oligopeptides than that of the 10-mer. We also show that the spin filtering ability can be tuned by changing the tip-loading force applied on the molecules. The spin selectivity decreases with increasing applied force, an effect attributed to the increased ratio of radius to pitch of the helix upon compression and increased tilt angles between the molecular axis and the surface normal. The method applied here provides new insights into the parameters controlling the CISS effect. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license

In this study, we explored the feasibility of employing Gd-doped ceria (GDC) thin films (12 μm) as functional, mechanically reliable material for microelectromechanical systems (MEMS). Self-supported structures, based on microscopic-scale GDC membranes, bridges, and cantilevers, were fabricated using Si-compatible processes and materials. With voltages of different amplitudes and frequencies and a variety of metal electrodes, we monitored structural stability and device response. The membrane-based structures displayed much higher stability under voltage and better mechanical robustness than those based on bridges or cantilevers. At low frequencies (a few Hz), the use of Ti contacts resulted in observable displacement of the membranes in the presence of moderately low voltage (≤10 V/1.6 μm), while Al, Cr, and Ni contacts did not provide such functionality. Although for all contact metals tested, formation of a blocking layer at room temperature is evident, for the case of Ti, the barrier height is much lower. In view of the fact that the crystallographic space group of weakly doped GDC is Fm-3 m, the electromechanical response of the microfabricated GDC membranes is most likely electrostrictive, but a strict proof is not yet available. At high frequencies (>100 kHz), the membranes produce lateral displacement as large as several microns due to Joule heating, i.e., a thermo-electromechanical response.

Heat-assisted magnetic recording (HAMR) is often considered the next major step in the storage industry: it is predicted to increase the storage capacity, the read/write speed and the data lifetime of future hard disk drives. However, despite more than a decade of development work, the reliability is still a prime concern. Featuring an inherently fragile surface-plasmon resonator as a highly localized heat source, as part of a near-field transducer (NFT), the current industry concepts still fail to deliver drives with sufficient lifetime. This study presents a method to aid conventional NFT-designs by additional grazing-incidence laser illumination, which may open an alternative route to high-durability HAMR. Magnetic switching is demonstrated on consumer-grade CoCrPt perpendicular magnetic recording media using a green and a near-infrared diode laser. Sub-500 nm magnetic features are written in the absence of a NFT in a moderate bias field of only μ₀H = 0.3 T with individual laser pulses of 40 mW power and 50 ns duration with a laser spot size of 3 μm (short axis) at the sample surface - six times larger than the magnetic features. Herein, the presence of a nanoscopic object, i.e., the tip of an atomic force microscope in the focus of the laser at the sample surface, has no impact on the recorded magnetic features - thus suggesting full compatibility with NFT-HAMR.

Cotton is a promising basis for wearable smart textiles. Current approaches that rely on fiber coatings suffer from function loss during wear. We present an approach that allows biological incorporation of exogenous molecules into cotton fibers to tailor the materials functionality. In vitro model cultures of upland cotton (Gossypium hirsutum) are incubated with 6-carboxyfluoresceinglucose and dysprosium1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acidglucose, where the glucose moiety acts as a carrier capable of traveling from the vascular connection to the outermost cell layer of the ovule epidermis, becoming incorporated into the cellulose fibers. This yields fibers with unnatural properties such as fluorescence or magnetism. Combining biological systems with the appropriate molecular design offers numerous possibilities to grow functional composite materials and implements a material-farming concept.

The riddle of anomalous polar behavior of the centrosymmetric crystal of α-glycine is resolved by the discovery of a polar, several hundred nanometer thick hydrated layer, created at the {010} faces during crystal growth. This layer was detected by two independent pyroelectric analytical methods: (i) periodic temperature change technique (Chynoweth) at ambient conditions and (ii) contactless X-ray photoelectron spectroscopy under ultrahigh vacuum. The total polarization of the surface layer is extremely large, yielding ≈1 μC·cm^-2, and is preserved in ultrahigh vacuum, but disappears upon heating to 100 °C. Molecular dynamics simulations corroborate the formation of polar hydrated layers at the sub-microsecond time scale, however with a thickness of only several nanometers, not several hundred. This inconsistency might be reconciled by invoking a three-step nonclassical crystal growth mechanism comprising (i) docking of clusters from the supersaturated solution onto the evolving crystal, (ii) surface recognition and polar induction, and (iii) annealing and dehydration, followed by site-selective recrystallization.

Classical electrostriction, describing a second-order electromechanical response of insulating solids, scales with elastic compliance, S, and inversely with dielectric susceptibility, ε. This behavior, first noted 20 years ago by Robert Newnham, is shown to apply to a wide range of electrostrictors including polymers, glasses, crystalline linear dielectrics, and relaxor ferroelectrics. Electrostriction in fluorite ceramics of (Y, Nb)-stabilized δ-Bi₂O₃ is examined with 16%-23% vacant oxygen sites. Given the values of compliance and dielectric susceptibility, the electrostriction coefficients are orders of magnitude larger than those expected from Newnham's scaling law. In ambient temperature nanoindentation measurements, (Y, Nb)-stabilized δ-Bi₂O₃ displays primary creep. These findings, which are strikingly similar to those reported for Gd-doped ceria, support the suggestion that ion conducting ceramics with the fluorite structure, a large concentration of anion vacancies and anelastic behavior, may constitute a previously unknown class of electrostrictors.

Chiral helicene, a fully conjugated system without stereogenic carbon, can filter spins effectively at room temperature, a consequence of the chiral-induced spin-selectivity effect. The chirality dictates the spin of the electrons transferred through helicene, and magnetoresistance devices based on these molecules show antisymmetric magnetoresistance versus H plots.

The internet has influenced all aspects of modern society, yet likely none more than education-opening new possibilities for how, where, and when we learn. Nanoscience and nanotechnology have developed over a similar time frame as the rapid growth of the internet and thus the use of the internet for nanoscience education serves as an interesting paradigm for internet-enabled education in general. In this chapter we give an overview of use of internet in nanoeducation, first in terms of available resources, then by describing the technological, philosophical, and pedagogical approaches. In order to illustrate the concepts, we describe as example a for-credit nanoscience curriculum which the authors developed recently as part of an international team.

The simple process of a liquid wetting a solid surface is controlled by a plethora of factors - surface texture, liquid droplet size and shape, energetics of both liquid and solid surfaces, as well as their interface. Studying these events at the nanoscale provides insights into the molecular basis of wetting. Nanotube wetting studies are particularly challenging due to their unique shape and small size. Nonetheless, the success of nanotubes, particularly inorganic ones, as fillers in composite materials makes it essential to understand how common liquids wet them. Here, we present a comprehensive wetting study of individual tungsten disulfide nanotubes by water. We reveal the nature of interaction at the inert outer wall and show that remarkably high wetting forces are attained on small, open-ended nanotubes due to capillary aspiration into the hollow core. This study provides a theoretical and experimental paradigm for this intricate problem.

The remarkable optoelectronic and especially photovoltaic performance of hybrid organic-inorganic perovskite (HOIP) materials drives efforts to connect materials properties to this performance. From nano-indentation experiments on solution-grown single crystals we obtain elastic modulus and nano-hardness values of APbX(3) (A = Cs, CH3NH3; X = I, Br). The Young's moduli are similar to 14, 19.5, and 16 GPa, for CH3NH3PbI3, CH3NH3PbBr3, and CsPbBr3, respectively, lending credence to theoretically calculated values. We discuss the possible relevance of our results to suggested self-healing, ion diffusion, and ease of manufacturing. Using our results, together with literature data on elastic moduli, we classified HOIPs amongst the relevant material groups, based on their elastomechanical properties.

Young's moduli of selected amino acid molecular crystals were studied both experimentally and computationally using nanoindentation and dispersion-corrected density functional theory. The Young modulus is found to be strongly facet-dependent, with some facets exhibiting exceptionally high values (as large as 44 GPa). The magnitude of Young's modulus is strongly correlated with the relative orientation between the underlying hydrogen-bonding network and the measured facet. Furthermore, we show computationally that the Young modulus can be as large as 70-90 GPa if facets perpendicular to the primary direction of the hydrogen-bonding network can be stabilized. This value is remarkably high for a molecular solid and suggests the design of hydrogen-bond networks as a route for rational design of ultra-stiff molecular solids.

Despite the tremendous progress made in the design of supramolecular and inorganic materials, it still remains a great challenge to obtain uniform structures with tailored size and shape. Metal-organic frameworks and infinite coordination polymers are examples of rapidly emerging materials with useful properties, yet limited morphological control. In this paper, we report the solvothermal synthesis of diverse metal-organic (sub)-microstructures with a high degree of uniformity. The porous and thermally robust monodisperse crystalline solids consist of tetrahedral polypyridyl ligands and nickel or copper ions. Our bottom-up approach demonstrates the direct assembly of these materials without the addition of any surfactants or modulators. Reaction parameters in combination with molecular structure encoding are the keys to size-shape control and structural uniformity of our metal-organic materials.

Cephalaspidean gastropods are common marine mollusks with a unique digestive apparatus containing 3 hardened plates of millimeter size inside the muscular esophageal crop (gizzard). The gizzard plates are reported to either grind or crush shelled prey. The current study aims at better understanding the manner in which the gizzard plates of the cephalaspid Philine quadripartita function in the overall digestion process by relating their structural and mechanical properties. Philine quadripartita possesses 3 gizzard plates which have one of the common configurations of cephalaspidean gizzard plates: two paired plates that are mirror images of each other and one smaller unpaired plate. We used micro-CT to characterize the gizzard musculature, the food which is present at different stages of the digestion process and the working surface of the gizzard plates. We show that the gizzard plates are used to crush the shelled prey, and that the functional mode of the small unpaired plate is different from the larger plates. All 3 plates are composed of a mixture of amorphous calcium carbonate and amorphous calcium phosphate embedded in a chitinous matrix. The proportions of these two mineral phases vary systematically within the plate. The plates have a complex layered structure, whose elastic moduli and hardness also vary in a continuous systematic manner. We observed that the stiffest layer is below the working surface, unlike most teeth where the stiffest layer is at the surface. Rigorous analysis of the elasticity indices of the gizzard plates as compared with sea urchin teeth and synthetic calcite provided insights into the connection between the biological function and the mechanical properties of biological composites. Specifically, we show that materials used for grinding require harder surfaces to avoid excessive wear compared to materials for crushing, whereas both of these functions require high toughness.

Potential future use of bacteriorhodopsin (bR) as a solid-state electron transport (ETp) material requires the highest possible active protein concentration. To that end we prepared stable monolayers of protein-enriched bR on a conducting HOPG substrate by lipid depletion of the native bR. The ETp properties of this construct were then investigated using conducting probe atomic force microscopy at low bias, both in the ground dark state and in the M-like intermediate configuration, formed upon excitation by green light. Photoconductance modulation was observed upon green and blue light excitation, demonstrating the potential of these monolayers as optoelectronic building blocks. To correlate protein structural changes with the observed behavior, measurements were made as a function of pressure under the AFM tip, as well as humidity. The junction conductance is reversible under pressure changes up to ∼300 MPa, but above this pressure the conductance drops irreversibly. ETp efficiency is enhanced significantly at >60% relative humidity, without changing the relative photoactivity significantly. These observations are ascribed to changes in protein conformation and flexibility and suggest that improved electron transport pathways can be generated through formation of a hydrogen-bonding network.

Poly(3-hydroxybutyrate) (PHB) nanocomposites containing environmentally-friendly tungsten disulphide inorganic nanotubes (INT-WS ₂) have been successfully prepared by a simple solution blending method. The dynamic and isothermal crystallization studies by differential scanning calorimetry (DSC) demonstrated that the INT-WS₂ exhibits much more prominent nucleation activity on the crystallization of PHB than specific nucleating agents or other nanoscale fillers. Both crystallization rate and crystallinity significantly increase in the nanocomposites compared to neat PHB. These changes occur without modifying the crystalline structure of PHB in the nanocomposites, as shown by wide-angle X-ray diffraction (WAXS) and infrared/Raman spectroscopy. Other parameters such as the Avrami exponent, the equilibrium melting temperature, global rate constant and the fold surface free energy of PHB chains in the nanocomposites were obtained from the calorimetric data in order to determine the influence of the INT-WS₂ filler. The addition of INT-WS₂ remarkably influences the energetics and kinetics of nucleation and growth of PHB, reducing the fold surface free energy by up to 20%. Furthermore, these nanocomposites also show an improvement in both tribological and mechanical (hardness and modulus) properties with respect to pure PHB evidenced by friction and nanoindentation tests, which is of important potential interest for industrial and medical applications.

Scratch resistance and friction are core properties which define the tribological characteristics of materials. Attempts to optimize these quantities at solid surfaces are the subject of intense technological interest. The capability to modulate these surface properties while preserving both the bulk properties of the materials and a well-defined, constant chemical composition of the surface is particularly attractive. We report herein the use of a soft, flexible underlayer to control the scratch resistance of oxide surfaces. Titania films of several nm thickness are coated onto substrates of silicon, kapton, polycarbonate, and polydimethylsiloxane (PDMS). The scratch resistance measured by scanning force microscopy is found to be substrate dependent, diminishing in the order PDMS, kapton/polycarbonate, Si/SiO₂. Furthermore, when PDMS is applied as an intermediate layer between a harder substrate and titania, marked improvement in the scratch resistance is achieved. This is shown by quantitative wear tests for silicon or kapton, by coating these substrates with PDMS which is subsequently capped by a titania layer, resulting in enhanced scratch/wear resistance. The physical basis of this effect is explored by means of Finite Element Analysis, and we suggest a model for friction reduction based on the "cushioning effect" of a soft intermediate layer.

Conducting Probe AFM. CP-AFM, was used to follow how chemical etching, oxidation, and sulfurization affect the surface nanoscale electrical characteristics of polycrystalline Cu(In,Ga)Se₂ (CIGS) thin films. Band bending at grain boundaries (GBs) on the surface was studied and analyzed by CP-AFM - measured photocurrents. We find that both oxidation and sulfurization can passivate the GBs of the CIGS films; oxidation increases n-type band bending, which impedes the transport of photogenerated electrons, while sulfurization increases p-type band bending at GBs, which helps this transport. Differences in effects between surface terminations by sulfide, selenide and oxide were analyzed. The effects of these treatments on the electrical activity of the GBs of the films, as well as the importance of the use of chemical bath deposition of the CdS buffer, are explained within a defect surface chemistry model.

The effect of hydration on the mechanical properties of osteonal bone, in directions parallel and perpendicular to the bone axis, was studied on three length scales: (i) the mineralized fibril level (~100. nm), (ii) the lamellar level (~6. μm); and (iii) the osteon level (up to ~30. μm).We used a number of techniques, namely atomic force microscopy (AFM), nanoindentation and microindentation. The mechanical properties (stiffness, modulus and/or hardness) have been studied under dry and wet conditions. On all three length scales the mechanical properties under dry conditions were found to be higher by 30-50% compared to wet conditions. Also the mechanical anisotropy, represented by the ratio between the properties in directions parallel and perpendicular to the osteon axis (anisotropy ratio, designated here by AnR), surprisingly decreased somewhat upon hydration. AFM imaging of osteonal lamellae revealed a disappearance of the distinctive lamellar structure under wet conditions. Altogether, these results suggest that a change in mineralized fibril orientation takes place upon hydration.

The microstructure and the phase composition of the interfaces of Al-1050/Al-1050 and Al-1050/Mg-AZ31 magnetic pulse welding (MPW) joints were characterized by SEM and TEM analyses. The mechanical properties were tested by nanoindentation. Properties of the Al-1050/Al-1050 interface joint were established. The interface is almost free from Al3Fe precipitates, which are present in the base metal. The hardness value is higher than that of the base metal; however, values of the Young's modulus of the interface and base metal are similar. It was suggested that the interface evolution in the Al-1050/Al-1050 system includes local melting and rapid solidification of the base materials. A wavy shaped heterogeneous interface was detected in the Al-1050/Mg-AZ31 joints. Some areas are free from visible intermetallic phases (IMPs), while others contain pockets of relatively coarse intermetallic precipitates. The presence of a relatively large fraction of globular porosity at the interface indicates that local melting takes place in the course of MPW. TEM characterization of regions free of IMPs at the interface reveals regions consisting of fcc supersaturated Al-Mg solid solution, apparently formed as a result of local mechanical alloying during MPW. In other regions, the composition and structure correspond to the Mg17Al12 phase, which was probably formed by local melting and rapid solidification.

Disulfide bond formation in secretory proteins occurs primarily in the endoplasmic reticulum (ER), where multiple enzyme families catalyze cysteine cross-linking. Quiescin sulfhydryl oxidase 1 (QSOX1) is an atypical disulfide catalyst, localized to the Golgi apparatus or secreted from cells. We examined the physiological function for extracellular catalysis of de novo disulfide bond formation by QSOX1. QSOX1 activity was required for incorporation of laminin into the extracellular matrix (ECM) synthesized by fibroblasts, and ECM produced without QSOX1 was defective in supporting cell-matrix adhesion. We developed an inhibitory monoclonal antibody against QSOX1 that could modulate ECM properties and undermine cell migration.

The influence of dopant size and oxygen vacancy concentration on the room temperature elastic modulus and creep rate of ceria doped with Pr⁴⁺, Pr³⁺, Lu³⁺, and Gd³⁺, is investigated using a nanoindentation technique. Measurements are conducted with both fast (15 mN s^-1) and slow (0.15 mN s^-1) loading modes, including a load-hold stage at 150 mN of 8 s and 30 s, respectively. Based on the data obtained using the fast loading mode, it is found that: 1) the dopant size is a primary determinant of the elastic modulus - the larger dopants (Pr³⁺ and Gd³⁺) produce lower unrelaxed moduli which are independent of the oxygen vacancy concentration. 2) The rearrangement of point defects is the major source of room temperature creep observed during load-hold. Pr ³⁺- and Gd³⁺-doped ceria display the higher creep rates: due to their large size, they repel oxygen vacancies (V_O), thereby promoting the formation of O₇-Ce_Ce-V_O complexes that are capable of low temperature rearrangement. Lower creep rates are observed for Pr⁴⁺- and Lu³⁺-doped ceria: the former has no vacancies and the latter, immobile vacancies. 3) Nanoindentation is a practical technique for identifying materials with labile point defects, which may indicate useful functionality such as high ionic conductivity, large electrostriction, and inelasticity. Nanoindentation measurements performed on ceria doped with Pr⁴⁺, Pr³⁺, Lu³⁺, Gd ³⁺ demonstrate that the rearrangement of point defects may be a major source of creep at room temperature. Nanoindentation is shown to be an effective technique for identifying materials with labile point defects, which may point to practical functionality such as high ionic conductivity, large electrostriction, and inelasticity.

Surface pyroelectricity: Centrosymmetric crystals of α-glycine display an anomalous quadrupole-like pyroelectric current. This observation implies the formation of water-glycine hybrid polar layers at the (010) faces of the α-glycine crystals (see picture).

A methodology leading to facile self-assembly of crystalline aromatic arrays in dilute aqueous solutions would enable efficient fabrication and processing of organic photonic and electronic materials in water. In particular, soluble 2D crystalline nanosheets may mimic the properties of photoactive thin films and self-assembled monolayers, covering large areas with ordered nanometer-thick material. We designed such solution-phase arrays using hierarchical self-assembly of amphiphilic perylene diimides in aqueous media. The assemblies were characterized by cryogenic transmission electron microscopy (cryo-TEM), revealing crystalline order and 2D morphology (confirmed by AFM studies). The order and morphology are preserved upon drying as evidenced by TEM and AFM. The 2D crystalline-like structures exhibit broadening and red-shifted absorption bands in UV-vis spectra, typical for PDI crystals and liquid crystals. Photophysical studies including femtosecond transient absorption spectroscopy reveal that two of the assemblies are superior light-harvesters due to excellent solar spectrum coverage and fast exciton transfer, in one case showing exciton diffusion comparable to solid-state crystalline systems based on perylene tetracarboxylic dianhidride (PTCDA).

This study describes a new method for fabrication of thin composite films using physical vapor deposition (PVD). Titanium (Ti) and hybrid films of titanium containing tungsten disulphide nanoparticles with inorganic fullerene-like structure (Ti/IF-WS₂) were fabricated with a modified PVD machine. The evaporation process includes the pulsed deposition of IF-WS₂ by a sprayer head. This process results in IF-WS₂ nanoparticles embedded in a Ti matrix. The layers were characterized by various techniques, which confirm the composition and structure of the hybrid film. The Ti/IF-WS₂ shows better wear resistance and a lower friction coefficient when compared to the Ti layer or Ti substrate. The Ti/IF films show very good antireflective properties in the visible and near-IR region. Such films may find numerous applications, for example, in the aerospace and medical technology.

An important challenge of modern materials science and nanoscience is to develop ways to alter the mechanical properties of an interface in a controlled fashion. Doing this while preserving the bulk properties of a material and maintaining a fixed chemical composition and reactivity of the interface is particularly attractive. In this work, the creation of substrates with tunable stiffness has been achieved by coating a soft polymer with an adherent, crack-free oxide overlayer whose thickness is varied from 8 to 70 nm. Specifically, amorphous titania with controlled, variable, thickness was deposited on polydimethylsiloxane (PDMS), and the surface mechanical properties were characterized using atomic force microscope (AFM)-based nanoindentation. The force/deformation curves can be quantitatively reproduced using a finite element analysis (FEA) modeling protocol. The FEA modeling facilitates predictability and enables the design of surfaces with independently customized chemical and mechanical properties.

Halogen bonding between complementary organic monolayers was directly observed in an organic environment using force spectroscopy. This non-covalent interaction is significantly affected by the nature of the organic media. We also demonstrated the effect of lateral packing interactions on the optical properties of the monolayers.x

Viscoelasticity is a complex yet important phenomenon that drives material response at different scales of time and space. Burgeoning interest in nanoscale dynamic material mechanics has driven, and been driven by two key techniques: instrumented nanoindentation and atomic force microscopy. This review provides an overview of fundamental principles in nanoindentation, and compares and contrasts these two techniques as they are used for characterization of viscoelastic processes at the nanoscale.

The mechanical and structural properties of the sublayers of osteonal lamellae were studied. Young's modulus (E) of adjacent individual lamellae was measured by nanoindentation of parallel slices every 1-3 μm, in planes parallel and perpendicular to the osteon axis (OA). In planes parallel to the OA, the modulus of a lamella could vary significantly between sequential slices. Significant modulus variations were also sometimes found on opposing sides of the osteonal canal for the same lamella. These results are rationalized by considerations involving the microstructural organization of the collagen fibrils in the lamellae. Scanning electron microscope imaging of freeze fractured surfaces revealed that the substructure of a single lamella can vary significantly on the opposing sides of the osteonal axis. Using a serial surface view method, parallel planes were exposed every 8-10 nm using a dual-beam microscope. Analysis of the orientations of fibrils revealed that the structure is rotated plywood like, consisting of unidirectional sublayers of fibrils of several orientations, with occasional randomly oriented sublayers. The dependence of the measured mechanical properties of the lamellae on the indentation location may be explained by the observed structure, as well as by the curvature of the osteonal lamellae through simple geometrical-structural considerations. Mechanical advantages arising from the curved laminate structure are discussed.

We used atomic force microscope (AFM) to acquire high-resolution images of collagen type I triple-helices under ambient conditions in tapping mode. Angles between consecutive fixed-length segments were measured and analyzed to yield persistence length and elastic constant. Changing the segment length allowed exploring the mechanics at various scales. Understanding the mechanical properties of collagen molecules could serve to elucidate mechanisms of complex mechanical properties of interest in nanomedicine and nanotechnology.

We report here a finite element simulation of the compression of inorganic WS ₂ hollow nanoparticles. The particle was modeled as a multilayered polyhedron to investigate the effect of the unique onion-like and highly faceted structure in the mechanical response. The simulation revealed the central role of the faceted structure of the WS ₂ nanoparticles in the mode of failure. The stress magnitude and distribution was shown to be size dependent, as predicted from previously published experimental results. Moreover, the simulation points to the influence of the layered structure on the energy release during compression loading via interlayer shear.

High-density ceramics of ceria doped with 0, 3, 5, 10, 15 and 20 mol.% Gd and with grain sizes exceeding 1.5 μm were investigated by nanoindentation. The deduced elastic moduli are independent of Gd content and remain close to the value reported for bulk ceramics (210 ± 5% GPa). All ceramics exhibit transient creep with displacement proportional to the 1/3 power of the time. For 0.05 < x < 0.2, the derived creep magnitude parameter decreases linearly with increasing Gd content. These results strongly suggest that defect rearrangement influences the measurements.

A synthetic route for preparation of inorganic WS ₂ nanotube (INT)-colloidal semiconductor quantum dot (QD) hybrid structures is developed, and transient carrier dynamics on these hybrids are studied via transient photoluminescence spectroscopy utilizing several different types of QDs. Measurements reveal efficient resonant energy transfer from the QDs to the INT upon photoexcitation, provided that the QD emission is at a higher energy than the INT direct gap. Charge transfer in the hybrid system, characterized using QDs with band gaps below the INT direct gap, is found to be absent. This is attributed to the presence of an organic barrier layer due to the relatively long-chain organic ligands of the QDs under study. This system, analogous to carbon nanotube-QD hybrids, holds potential for a variety of applications, including photovoltaics, luminescence tagging and optoelectronics. This journal is

The photovoltaic performance of solar cells, based on a Cu(In _1-xGa _x)Se ₂ (CIGS) absorber layer, is directly correlated with Ga composition. We have used scanning capacitance microscopy and conducting probe atomic force microscopy (CP-AFM) to provide microscopic electrical characterization of CIGS films with different Ga content. We found p- to n-type inversion at grain boundaries of the polycrystalline CIGS film, especially for Ga-poor compositions. The fraction of grain boundaries undergoing inversion dramatically decreased for Ga compositions above x = 0.32, the composition corresponding to a sharp efficiency drop of the complete cells. CP-AFM measurements showed a marked current drop at grain boundaries as the Ga composition rose above x = 0.32.

Solid-state electron transport (ETp) via a monolayer of immobilized azurin (Az) was examined by conducting probe atomic force microscopy (CP-AFM), as a function of both temperature (248-373K) and applied tip force (6-15 nN). At low forces, ETp via holo-Az (with Cu²⁺) is temperature-independent, but thermally activated via the Cu-depleted form of Az, apo-Az. While this observation agrees with those of macroscopic-scale measurements, we find that for holo-Az the mechanism of ETp at high temperatures changes upon an increase in the force applied by the tip to the proteins; namely, above 310 K and forces >6 nN ETp becomes thermally activated. This is in contrast to apo-Az, where increasing applied force causes only small monotonic increases in currents due to decreased electrode separation. The distinct ETp temperature dependence of holo- and apo-Az is assigned to a difference in structural response to pressure between the two protein forms. An important implication of these CP-AFM results (of measurements over a significant temperature range) is that for reliable ETp measurements on flexible macromolecules, such as proteins, the pressure applied during the measurements should be controlled or at least monitored.

Friction and wear of copper rubbed with lubrication in wide range of loads and sliding velocities were studied. The results of friction and wear experiments are presented as the Stribeck curve where the boundary lubrication (BL), mixed (ML) and elasto-hydrodynamic lubrication (El-IL) regions are considered. The structural state of subsurface layers in different lubricant regions is studied by X-ray photoelectron spectroscopy, optical, transmission and scanning microscopy analysis. Dislocation density of dislocations in El-IL and BL lubricant regimes was determined. Nanohardness at thin surface layers rubbed under different lubricant regimes is compared. The dominant friction and wear mechanisms in different lubrications regions are discussed.

A strategy for clustering of native lipid membranes is presented. It relies on the formation of complexes between hydrophobic chelators embedded within the lipid bilayer and metal cations in the aqueous phase, capable of binding two (or more) chelators simultaneously Fig. 1. We used this approach with purple membranes containing the light driven proton pump protein bacteriorhodopsin (bR) and showed that patches of purple membranes cluster into mm sized aggregates and that these are stable for months when incubated at 19°C in the dark. The strategy may be general since four different hydrophobic chelators (1,10-phenanthroline, bathophenanthroline, Phen-C10, and 8-hydroxyquinoline) and various divalent cations (Ni²⁺, Zn²⁺, Cd²⁺, Mn²⁺, and Cu²⁺) induced formation of membrane clusters. Moreover, the absolute requirement for a hydrophobic chelator and the appropriate metal cations was demonstrated with light and atomic force microscopy (AFM); the presence of the metal does not appear to affect the functional state of the protein. The potential utility of the approach as an alternative to assembled lipid bilayers is suggested.

The effect of oxygen and argon partial pressures (P _O2, P _Ar) in a Zr vacuum arc on plasma ion current density J _p, arc voltage V _arc, deposition rate v _d, and selected coating properties was determined. A d.c. arc current of I _arc=100A was initiated between a Zr cathode and a grounded anode. Cathode spots produced a plasma jet, which entered a 1/8 torus macroparticle (MP) filter. The plasma was guided by a d.c. magnetic field through an aperture to a glass substrate or a flat disk probe, mounted on a rotatable holder. J _p was measured with the probe, negatively biased to V _b=-60V. Coating thickness was measured using a profilometer, and coating properties were investigated using optical microscopy, energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), nano-indentation and optical analysis. The discharge electrical characteristics and the coating deposition rate were found to be significantly influenced by P _O2 and P _Ar. J _p and v _d increased with P _Ar until a maximum at P _Ar=0.27Pa and decreased with P _O2. V _arc decreased with both P _Ar and P _O2. The changes in J _p, V _arc, and v _d, with P _Ar were larger at larger P _O2. The J _p, V _arc, and v _d dependencies suggest that addition of Argon increased the Zr ion emission from the cathode, possibly because Ar ion bombardment reduced Zr surface oxidation and improved plasma conductivity. Zirconium Oxide (ZrO ₂) coatings were transparent and had colored interference rings. Well adhered, MP-free ZrO ₂ coatings were deposited with P _O2≥1.07Pa. Coatings deposited with P _O2=1.07Pa+P _Ar=0 were amorphous, whereas those deposited with P _O2=1.07Pa+P _Ar=0.27Pa had some degree of a monoclinic phase. Furthermore, the refractive index (n) and extinction coefficient (k) slightly decreased, from 2.22 to 2.17, and from 0.03 to 0.01, respectively and coating hardness (H) and Young's Modulus (E) decreased from ~12.9 to ~11.6GPa and from ~153 to ~136GPa respectively when P _Ar=0.27Pa was added to a P _O2=1.07Pa environment.

Compositional uniformity of Cu(In,Ga)Se ₂ (CIGS) solar cells was studied, using thin cross sections of complete cells prepared by focused ion beam (FIB) and examined in the transmission electron microscope (TEM). This methodology revealed the compositional variations at the nm-scale. The Ga and In compositions vary not only between neighboring grains, but also inside individual single crystal grains along their growth direction, which explains the electrical non-uniformity seen in electron beam-induced current (EBIC) measurements. The improved compositional uniformity with increase in sample preparation temperature correlates with higher solar cell efficiency.

Variations in Young's modulus of individual lamellae around a single bone osteon have been measured in three orthogonal planes by nanoindentation. The objective of these measurements was to establish a correlation between the mechanical properties and the microstructure of the osteonal lamellae. When indentation was performed in a plane perpendicular to the osteon axis (OA), the modulus of the lamella closest to the canal appears to be higher than the modulus of all other lamellae. No such difference was observed in planes parallel to the OA. However, in the parallel planes, an unexpected asymmetry in modulus was detected on opposing sides of the canal, potentially supporting the validity of the rotated plywood structure model of bone lamellae. Finally, based on the experimentally measured Young's modulus values, most osteonal lamellae appear to exhibit structural anisotropy.

Nanoindentation has become a common technique for measuring the hardness and elastic-plastic properties of materials, including coatings and thin films. In recent years, different nanoindenter instruments have been commercialised and used for this purpose. Each instrument is equipped with its own analysis software for the derivation of the hardness and reduced Young's modulus from the raw data. These data are mostly analysed through the Oliver and Pharr method. In all cases, the calibration of compliance and area function is mandatory. The present work illustrates and describes a calibration procedure and an approach to raw data analysis carried out for six different nanoindentation instruments through several round-robin experiments. Three different indenters were used, Berkovich, cube corner, spherical, and three standardised reference samples were chosen, hard fused quartz, soft polycarbonate, and sapphire. It was clearly shown that the use of these common procedures consistently limited the hardness and reduced the Young's modulus data spread compared to the same measurements performed using instrument-specific procedures. The following recommendations for nanoindentation calibration must be followed: (a) use only sharp indenters, (b) set an upper cut-off value for the penetration depth below which measurements must be considered unreliable, (c) perform nanoindentation measurements with limited thermal drift, (d) ensure that the load-displacement curves are as smooth as possible, (e) perform stiffness measurements specific to each instrument/indenter couple, (f) use Fq and Sa as calibration reference samples for stiffness and area function determination, (g) use a function, rather than a single value, for the stiffness and (h) adopt a unique protocol and software for raw data analysis in order to limit the data spread related to the instruments (i.e. the level of drift or noise, defects of a given probe) and to make the H and E _r data intercomparable.

Multiwalled nanotubes and nanoparticles of metal dichalcogenides express unique mechanical and tribological characteristics. A widely studied member of this class of materials is the WS2 nanotube whose structure consists of layers of covalent W-S bonds joined by the van der Waals interactions between the sulfur layers which mediate any interlayer sliding or compression. One of the intriguing aspects of these structures is the response of these layers under mechanical stress. Such internal degrees of freedom can profoundly impact on the overall mechanical response. The fact that the internal structure of these nanotubes is well characterized enables a full treatment of the problem. Here, the authors report an experimental and modeling study of the radial mode of deformation. Three independent atomic force microscope experiments were employed to measure the nanomechanical response using both large (radius=100 nm) and small (radius=3-15 nm) probe tips. Two different analytical models were applied to analyze the results. The modulus values derived from the analytical models were used as initial input for a finite element analysis model to yield a refined value of this parameter. The obtained values compare favorably with density functional tight binding calculations. The results indicate a strong influence of interwall shear on the radial modulus. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3549132]

Two-dimensional porous networks self-assembled in solution are rare, while maintaining the solution-phase network structure upon casting on solid supports presents a major challenge. We report on oligoarylacetylene bearing amphiphilic perylene diimide moieties that self-assemble into a two-dimensional porous network in aqueous solution that can be cast on surfaces, while maintaining the porous structure. The networks were characterized by cryogenic electron microscopy (cryo-TEM and cryo-SEM), and by atomic force microscopy, revealing formation of thin porous films (4-nm thick). The network can be cast on various solid surfaces, preserving its solution-phase structure. The design motif utilizing an oligoarylacetylene backbone with interacting amphiphilic pendants appears to be of wide utility for formation of novel assembly patterns. Copyright (C) 2010 John Wiley & Sons, Ltd.

Spin-based properties, applications, and devices are commonly related to magnetic effects and to magnetic materials. Most of the development in spintronics is currently based on inorganic materials. Despite the fact that the magnetoresistance effect has been observed in organic materials, until now spin selectivity of organic based spintronics devices originated from an inorganic ferromagnetic electrode and was not determined by the organic molecules themselves. Here we show that conduction through double-stranded DNA oligomers is spin selective, demonstrating a true organic spin filter. The selectivity exceeds that of any known system at room temperature. The spin dependent resistivity indicates that the effect cannot result solely from the atomic spin-orbit coupling and must relate to a special property resulting from the chirality symmetry. The results may reflect on the importance of spin in determining electron transfer rates through biological systems.

The local Young modulus of dry dentin viewed as a hierarchical composite was measured by nano-indentation using two types of experiments, both in a continuous stiffness measurement mode. First, tests were performed radially along straight lines running across highly mineralized peritubular dentin sections and through less mineralized intertubulars dentin areas. These tests revealed a gradual decrease in Young's modulus from the bulk of the peritubular dentin region where modulus values of up to ∼40-42. GPa were observed, down to approximately constant values of ∼17. GPa in the intertubular dentin region. A second set of nano-indentation experiments was performed on the facets of an irregular polyhedron specimen cut from the intertubular dentin region, so as to probe the modulus of intertubular dentin specimens at different orientations relative to the tubular direction. The results demonstrated that the intertubular dentin region may be considered to be quasi-isotropic, with a slightly higher modulus value (∼22. GPa) when the indenting tip axis is parallel to the tubular direction, compared to the values (∼18. GPa) obtained when the indenting tip axis is perpendicular to the tubule direction.

Interactions between the walls in multiwalled nanotubes are key to determining their mechanical properties. Here, we report studies of radial deformation of multiwalled WS₂ nanotubes in an atomic force microscope. The experimental results were fitted to a finite element model to determine the radial modulus. These results are compared with density-functional tight-binding calculations of a double-walled tube. Good agreement was obtained between experiment and calculations. The results indicate the importance of the sliding between layers in moderating the radial modulus. A plateau in the deformation curves is seen to have atomistic origins.

Friction and wear of copper rubbed in the presence of lubricants over a wide range of loads and sliding velocities were studied. The results of friction and wear experiments in the boundary lubrication (BL) and elastohydrodynamic lubrication (EHL) regimes are briefly considered. The structural state of subsurface layers in different lubricant regions is studied by optical, transmission and scanning microscopy analysis. Dislocation density and Burgers vector of individual dislocations in EHL and BL lubricant regimes were determined. A laminated structure with thin and elongated grains is formed in the EHL region. A range of nanocrystalline structures with grain sizes of 20-100 nm is formed in the surface layers in the BL region. Strong plastic deformation (SPD) of thin surface layers under friction is accompanied by formation of shear bands in sublayers of contact spots. Nanohardness at thin surface layers is compared for surfaces rubbed under different lubricant regimes. The hardness of thin surface layers saturates after repeated sliding of Cu and is close to the hardness of nanocrystalline Cu produced by various SPD processes.

The sea urchin tooth is a mosaic of calcite crystals shaped precisely into plates and fibers, cemented together by a robust calcitic polycrystalline matrix. The tooth is formed continuously at one end, while it grinds and wears at the opposite end, the sharp tip. Remarkably, these teeth enable the sea urchin to scrape and bore holes into rock, yet the teeth remain sharp rather than dull with use. Here we describe the detailed structure of the tooth of the California purple sea urchin Strongylocentrotus purpuratus, and focus on the self-sharpening mechanism. Using high-resolution X-ray photoelectron emission spectromicroscopy (X-PEEM), scanning electron microscopy (SEM), EDX analysis, nanoindentation, and X-ray micro-tomography, we deduce that the sea urchin tooth self-sharpens by fracturing at discontinuities in the material. These are organic layers surrounding plates and fibers that behave as the "fault lines" in the tooth structure, as shown by nanoindentation. Shedding of tooth components at these discontinuities exposes the robust central part of the tooth, aptly termed "the stone", which becomes the grinding tip. The precise design and position of the plates and fibers determines the profile of the tooth tip, so as the tooth wears it maintains a tip that is continually renewed and remains sharp. This strategy may be used for the top-down or bottom-up fabrication of lamellar materials, to be used for mechanical functions at the nano- and micrometer scale. Five white, calcitic teeth are at the center of a sea urchin, shown upside down. Using these teeth sea urchins can bore into rocks, whereby the teeth are seen to self-sharpen with use rather than dull. Here, the self-sharpening mechanism is described, in which the continuously growing teeth wear at pre-determined locations near the tip, and thus renew and maintain a sharp tip profile.

Despite many recent research efforts, the influence of grain boundaries (GBs) on device properties of CuIn_1-xGa_xSe₂ solar cells is still not fully understood Here, we present a microscopic approach to characterizing GBs in polycrystalline CuIn_1-xGa _xSe₂ films with x = 0.33. On samples from the same deposition process we applied methods giving complementary information, i.e., electron backscatter diffraction (EBSD), electron-beam induced current measurements (EBIC), conductive atomic force microscopy (c-AFM), variable-temperature Kelvin probe force microscopy (KPFM), and scanning capacitance microscopy (SCM). By combining EBIC with EBSD, we find a decrease in charge-carrier collection for non-σ3 GBs, while σ 3 GBs exhibit no variation with respect to grain interiors. In contrast, a higher conductance of GBs compared to grain interiors was found by c-AFM at low bias and under illumination. By KPFM, we directly measured the band bending at GBs, finding a variation from - 80 up to + 115 mV. Depletion and even inversion at GBs was confirmed by SCM. We comparatively discuss the apparent differences between the results obtained by various microscopic techniques.

The potential for manipulation and control inherent in molecule-based motors holds great scientific and technological promise. Molecules containing the azobenzene group have been heavily studied in this context. While the effects of the cis-trans isomerization of the azo group in such molecules have been examined macroscopically by a number of techniques, modulations of the elastic modulus upon isomerization in self-assembled films were not yet measured directly. Here, we examine the mechanical response upon optical switching of bis[(1,1'-biphenyl)-4-yl]diazene organized in a self-assembled film on Au islands, using atomic force microscopy. Analysis of higher harmonics by means of a torsional harmonic cantilever allowed real-time extraction of mechanical data. Quantitative analysis of elastic modulus maps obtained simultaneously with topographic images show that the modulus of the cis-form is approximately twice that of the trans-isomer. Quantum mechanical and molecular dynamics studies show good agreement with this experimental result, and indicate that the stiffer response in the cis-form comprises contributions both from the individual molecular bonds and from intermolecular interactions in the film. These results demonstrate the power and insights gained from cutting-edge AFM technologies, and advanced computational methods.

In this work chromium-rich coatings impregnated with fullerene-like (IF)-WS₂ nanoparticles were deposited on stainless steel substrates. The coatings were obtained from a trivalent chromium bath at pH 2 by galvanostatic electrodeposition. Zinc and cobalt salts were added to the aqueous solution in small amounts serving as cationic growth promoters. Photodeposition of tin-palladium nanoparticles was used as seeding enhancer for the co-deposition of the fullerene-like nanoparticles. The coatings were characterized by a number of techniques and were found to show a decreasing gradient of the IF nanoparticles towards the film-substrate interface. Tribological tests showed that in contrast to the substrate and the pure metal coating, the IF-containing films exhibit low friction and wear.

Nickel-titanium (NiTi) alloys combine several remarkable characteristics, among them are shape-memory, superelasticity, great strain recovery, good biocompatibility, and corrosion resistance. These render them well suited to a wide range of medical applications, such as cardiovascular stents, laparoscopy, and dental applications such as NiTi endodontic files (EFs) used for root canal treatment, which are the focus of this work. Unfortunately, fatigue-induced and incidental failure of NiTi EFs is not uncommon, which may lead to severe medical consequences. Here we examine the effects of cobalt coatings with impregnated fullerene-like WS₂ nanoparticles on file fatigue and failure. Dynamic x-ray diffraction, nanoindentation and torque measurements all indicate a significant improvement in the fatigue resistance and time to breakage of the coated files, stemming from reduced friction between the file and the surrounding tissue. These methods are possibly applicable to a variety of NiTi-based medical devices where fatigue and consequent failure are of relevance.

A nanostructure, being either an Inorganic Fullerene-like (IF) nanostructure or an Inorganic Nanotube (INT), A1-x-Bx-chalcogenide are described. A being a metal or transition metal or an alloy of metals and/or transition metals, B being a metal or transition metal B different from that of A and x being ≤0.3. A process for their manufacture and their use for modifying the electronic character of A-chalcogenide are described.

Medicine's prime concern is first not to harm, thereafter elongate and benefit lifespan. The vast technological advances of the last decade permit implementation of minimal invasive medicine in the different medical disciplines. Laparoscopic procedures and intubations, stents insertion and joint replacement had become commonplace in the operating rooms. Overcoming wear and frictional forces in order to elevate treatment efficiency and diminish unwanted side effects is now a rising challenge in designing new medical appliances. Here, two kinds of self-lubricating metal coatings with impregnated fullerene-like (IF) nanoparticles of W ₂ are presented: cobalt films deposited on NiTi substrate (foils and orthodontic wires) and nickel films deposited on orthodontic wires made of stainless steel. Tribological and mechanical tests provide strong evidence for the efficacy of the coatings in reducing the static and kinetic friction. It is concluded that the use of these self-lubricating coatings may have important impact on ubiquitous medical procedures.

One of the most important steps in the process of viral infection is a fusion between cell membrane and virus, which is mediated by the viral envelope glycoprotein. The study of activity of the glycoprotein in the post-fusion state is important for understanding the progression of infection. Here we present a first real-time kinetic study of the activity of gp41 (the viral envelope glycoprotein of human immunodeficiency virus-HIV) and its two mutants in the post-fusion state with nanometer resolution by atomic force microscopy (AFM). Tracking the changes in the phosphatidylcholine (PC) and phosphatidylcholine-phosphatidylserine (PC:PS) membrane integrity over one hour by a set of AFM images revealed differences in the interaction of the three types of protein with zwitterionic and negatively charged membranes. A quantitative analysis of the slow kinetics of hole formation in the negatively charged lipid bilayer is presented. Specifically, analysis of the rate of roughness change for the three types of proteins suggests that they exhibit different types of kinetic behavior. (C) 2010 Elsevier B.V. All rights reserved.

Objectives: The small volume of human dentin available for sample preparation and the local variations in its microstructure present a real challenge in the determination of their mechanical properties. The main purpose of the present study was to develop a new procedure for the preparation and mechanical testing of small-scale specimens of biomaterials such as dentin, so as to probe local mechanical properties as a function of microstructure. Methods: Ultra short laser pulses were used to mill a block of dentin into an array of 16 μm size dentin pillars. These could then be individually tested in compression with an instrumented nanoindenter fitted with a 30 μm wide flat punch. Results: The laser-based pillar preparation procedure proved effective and reliable. Data was produced for the mechanical properties of a first set of dry dentin micro-pillars. Significance: This novel experimental approach enables the preparation and compression of micron-scale samples with well-defined microstructure. For dentin, this means samples containing a relatively small number of well-defined parallel tubules, with a distinct orientation relative to the applied load. The ability to isolate the separate effects of microstructural parameters on the mechanical properties is of major significance for future substantiation of theoretical models.

Enzymatic processing of extracellular matrix (ECM) macromolecules by matrix metalloproteases (MMPs) is crucial in mediating physiological and pathological cell processes. However, the molecular mechanisms leading to effective physiological enzyme-ECM interactions remain elusive. Only scant information is available on the mode by which matrix proteases degrade ECM substrates. An example is the enzymatic degradation of triple helical collagen II fragments, generated by the collagenase MMP-8 cleavage, during the course of acute inflammatory conditions by gelatinase B/MMP-9. As is the case for many other matrix proteases, it is not clear how MMP-9 recognizes, binds and digests collagen in this important physiological process. We used single molecule imaging to directly visualize this protease during its interaction with collagen fragments. We show that the initial binding is mediated by the diffusion of the protease along the ordered helix on the collagen 3/4 fragment, with preferential binding of the collagen tail. As the reaction progressed and prior to collagen degradation, gelatin-like morphologies resulting from the denaturation of the triple helical collagen were observed. Remarkably, this activity was independent of enzyme proteolysis and was accompanied by significant conformational changes of the working protease. Here we provide the first direct visualization of highly complex mechanisms of macromolecular interactions governing the enzymatic processing of ECM substrates by physiological protease.

Nanoindentation testing has been used to analyze local mechanical parameter changes across interfaces formed between the solder and the Cu substrate and also in the eutectic solder, in miniature lead-free soldered joints. Effects of plastic deformation and aging were investigated. The lead-free solder alloy used in this study is commercially available and has nominal composition by weight of 99.3% Sn and 0.7% Cu. During aging, the joints were exposed to 150°C for 1000h in an inert atmosphere. Tensile testing of as-soldered miniature joints shows strong positive dependence of the plastic flow stresses on strain rate, meaning that the stresses increase with strain rate. Similar behavior was observed for aged miniature soldered joints with ∼10% decrease in the level of maximum stresses, compared to as-soldered joints.Indentation hardness and modulus were measured in soldered joint components, in the as-soldered, aged conditions, and tensile tested with strain rates in the range of 1.8×10^-3-1.8×10^-1s^-1. Scanning electron and optical microscopy were employed to analyze the fracture paths and microstructure of the as-soldered and aged miniature joints, as well as the location and shape of the indentations. The measured indentation hardness and modulus agreed well with previous studies on similar alloys. The tested modulus of the intermetallic phase in the eutectic area exhibited a considerable reduction as compared to the intermetallic phase at the interface between the solder and the Cu substrate. Strain rate strongly influences local mechanics: for both as-soldered and deformed miniature joints; close to the fracture face in the eutectic solder, the indentation modulus values were 53% higher and hardness more than 100% higher in joints exposed to the highest strain rate relative to the smallest rate.

Inorganic layered materials can form hollow multilayered polyhedral nanoparticles. The size of these multi-wall quasi-spherical structures varies from 4 to 300 nm. These materials exhibit excellent tribological and wear-resisting properties. Measuring and evaluating the stiffness of individual nanoparticle is a non-trivial problem. The current paper presents an in situ technique for stiffness measurements of individual WS₂ nanoparticles which are 80 nm or larger using a high resolution scanning electron microscope (HRSEM). Conducting the experiments in the HRSEM allows elucidation of the compression failure strength and the elastic behavior of such nanoparticles under uniaxial compression.

WS₂ inorganic nanotubes (INT) and inorganic fullerene-like nano-particles (IF) are well-known for their high mechanical strength and as superior solid lubricants. The outermost WS₂ layer is considered to be fully bonded; thus, it was suggested that the interactions of these WS₂ nanostructures with their surroundings are governed by purely van der Waals (vdW) interactions. However, in the case of IF-WS₂ nanoparticles, the faceted surface may contain sites with nonsaturated coordination, which, in turn, react with the surrounding media. Gold nanoparticles(GNP) wereusedas probesforthe IF-WS₂ surfacedefects,mapped by both scanning and transmission electron microscopy. The interaction between the GNP and the reactive surface was investigated using INT-WS₂ as a model and was characterized by atomic force microscopy (AFM).

Monolayer self-assembly (MSA) was discovered owing to the spectacular liquid repellency (lyophobicity) characteristic of typical self-assembling monolayers of long tail amphiphiles, which facilitates a straightforward visualization of the MSA process without the need of any sophisticated analytical equipment. It is this remarkable property that allows precise control of the self-assembly of discrete, well-defined monolayers, and it was the alternation of lyophobicity and lyophilicity (liquid affinity) in a system of monolayer-forming bifunctional organosilanes that allowed the extension of the principle of MSA to the layer-by-layer self-assembly of planed multilayers. On this basis, the possibility of generating at will patterned monolayer surfaces with lyophobic and lyophilic regions paves the way to the engineering of molecular templates for site-defined deposition of materials on a surface via either precise MSA or wetting-driven self-assembly (WDSA), namely, the selective retention of a liquid repelled by the lyophobic regions of the pattern on its lyophilic sites. Highly ordered organosilane monolayer and thicker layer-by-layer assembled structures are shown to be ideally suited for this purpose. Examples are given of novel WDSA and MSA processes, such as guided deposition by WDSA on lyophobic-lyophilic monolayer and bilayer template patterns at elevated temperatures, from melts and solutions that solidify upon cooling to the ambient temperature, and the possible extension of constructive nanolithography to thicker layer-by-layer assembled films, which paves the way to three-dimensional (3D) template patterns made of readily available monofunctional n-alkyl silanes only. It is further shown how WDSA may contribute to MSA on nanoscale template features as well as how combined MSA and WDSA modes of surface assembly may lead to composite surface architectures exhibiting rather surprising new properties. Finally, a critical evaluation is offered of the scope, advantages, and limitations of MSA and WDSA in the bottom-up fabrication of surface structures on variable length scales from nano to macro

The key to functionalize of engineered molecularly nanometer thick films lies in the ability to reproducibly control their structure. A number of factors influence the film morphology of self-assembled films on solid or liquid surfaces, such as the structure of the molecules/particles, wetting, solvent hydrodynamics, and evaporation. An important example is the deposition of amphiphilic molecules from a volatile solution, self-assembled onto a water surface at monolayer coverage. Upon evaporation, a myriad of microscopic two-dimensional (2D) crystallites forms a ruptured film lying in random orientation on the surface, resulting in "2D powders." Here we present a general technique, employing linearly polarized laser pulses and varying solvent composition to influence the assembly of molecules such as poly-benzyl-L-glutamate and alamethicin on water surfaces, resulting in ultrathin molecular films with aligned regions that point in the same direction, though macroscopically separated. The experimental results are tentatively explained by a mechanism that is based on excluded volume forces and "kick model" for the effect of laser pulses to induce molecular rotation that eventually results in an aligned pattern when the system is at a collective state.

We propose a new experimental approach for the study of Young's modulus and the strength of dentin, using micro sized pillar-like specimens tested under compression using a nanoindenter apparatus fitted with a flat punch indenter. Dentin micro pillars were prepared by ablation with ultra short laser pulses, and subsequently compressedwith a 30 μmdiameter flat punch. Tubule orientation is found to affect the compression behavior of dry dentine in air, more so for Young's modulus than for strength.We propose to fit these results with adaptations of fiber composite theoretical models.

Adsorption-induced magnetization of binding PbS self-assembled nanoparticles (NP) on GaAs surfaces by an organic linker was studied. The magnetization is anisotropic and the magnetic moment reaches saturation for a magnetic field of 2000 Oe applied parallel to the surface. The results also show the dependence of the measured magnetic moment on the density of 4.2 nm diameter PbS nanoparticles, when the field is applied parallel to the surface. The observed dependence of anisotropy on the alignment of the linking molecule, relative to the surface normal, indicates that the anisotropy is caused by the attachment of the organic to the NPs. The orientation of the organic molecule relative too the NPs surface normal is found to coincide with the direction of the magnetic anisotropy.

A study was conducted to investigate how different kinds of calcite crystals in the sea urchin tooth work together as an effective grinding tool. The study showed that the polycrystalline matrix has a higher elastic modulus and hardness than the single crystalline needles and plates, and that the working surface is smooth. It ascribed the unique properties of the matrix to a combination of a very high Mg content, the lack of orientation of the nanocrystals, and their very small size. The single crystals contain relatively high concentrations of Mg, and presumably like other echinoderm crystals, occluded proteins that reduce the brittleness of the calcite and allow it to deform in a plastic manner and fracture with conchoidal cleavage. The study proposed that it is the unusually high hardness and modulus of the Mg-enriched matrix that is mainly responsible for the ability to grind the rocky substrate, whereas the arrays of calcite needles and plates act as a support framework for the polycrystalline matrix.

Mechanical properties of peritubular dentin were investigated using scanning probe microscopy techniques, namely Nanoindentation and Band Excitation. Particular attention was directed to the possible existence of a gradient in these properties moving outward from the tubular lumen to the junction with the intertubular dentin. Finite element analysis showed that the influence of the boundaries is small relative to the effects observed. Thus, these results strongly support the concept of a lowering of modulus and hardness from the tubular exterior to its periphery, which appear to correlate with graded changes in the mineral content.

The versatility of scanning probe microscopy, as evidenced in the capability for high-resolution imaging, mechanical measurements, and electrical probing, has great utility in biological research. This short review outlines both the strengths and weaknesses of the technique. A few examples of recent and notable applications give the reader a sense of the power of the technique and potential for contribution to the field.

In this chapter, a perspective is given on some aspects of electron flow through molecular bridges. The advent of molecular electronics, drive to understand charge transfer in biological systems, and functioning of devices such as organic lightemitting diodes and dye-sensitized solar cells all require deeper understanding of this topic. Application of SPM to such studies has opened the possibility of true single-molecule measurements, but has also introduced a number of artifacts and complications into the work, notably perturbations due to the force and local electric field applied by the tip. Additional chapters in this book provide specific studies of electron flow in thiolated hydrocarbons and of electrical and electromechanical measurements on biomolecules. Here, SPM measurements on two specific systems-electron flow through DNA, and STM measurements of isolated molecules on a semiconductor surface, are developed in detail. These studies are presented in the general context of electron flow measurements through single molecules, and are compared with parallel, non-SPM techniques. The strength of SPM to combine imaging with the electrical measurement is emphasized.

The cylindrical geometry of nanotubes dictates a strong anisotropy of their physical properties. In practice, the difficulty in extracting individual components of the elastic tensor has limited the available information to only very partial and indirect experimental data. Here, the interlayer shear (sliding) modulus (C₄₄) of single multiwalled WS₂ nanotubes was studied by atomic force microscopy bending tests. The observed value of 2 GPa agrees well with the value of 4 GPa obtained for density functional tight binding calculations for 2H-MoS₂. This value of the shear modulus represents a much higher degree of anisotropy than that obtained for carbon nanotubes and enables assignment of the mode of shear deformation.

Geoinspired synthetic chrysotile nanotubes both stoichiometric and 0.67 wt % Fe doped were characterized by transmission electron microscopy and electron diffraction. Bending tests of the synthetic chrysotile nanotubes were performed using the atomic force microscope. The nanotubes were found to exhibit elastic behaviour at small deformations (below ca. 20 nm). Young's modulus values of (159±125) GPa and (279±260) GPa were obtained from the force-deflection curves using the bending equation for a clamped beam under a concentrated load, for the stoichiometric and the Fe doped chrysotile nanotubes, respectively. The structural modifications induced by Fe doping altered the mechanical properties, with an apparent dependence of the latter on the number of constituting walls of the nanotubes.

The multidomain zinc endopeptidase matrix metalloproteinase-9 (MMP-9) is a recognized therapeutic target in autoimmune diseases, vascular pathologies, and cancer. Despite its importance, structural characterization of full-length pro-MMP-9 is incomplete. Here, we report the structural model of full-length pro-MMP-9 and, in particular, the molecular character of its unique proline-rich and heavily O-glycosylated (OG) domain. Using a powerful combination of small-angle X-ray scattering and single-molecule imaging, we demonstrate that pro-MMP-9 possesses an elongated structure with two terminal globular domains connected by an unstructured OG domain. Image analysis highlights the flexibility of the OG domain, implicating its role in the varied enzyme conformations and in facilitating independent movements of the terminal domains. This may endorse recognition, binding, and processing of substrates, ligands, as well as receptors and marks this domain as an additional target for the design of selective regulators.

IF-MO_1-xNb_xS₂ nanoparticles have been synthesized by a vapor-phase reaction involving the respective metal halides with H₂S. The IF-MO_1-xNb_xS₂ nanoparticles, containing up to 25% Nb, were characterized by a variety of experimental techniques. Analysis of the powder X-ray powder diffraction, X-ray photoelectron spectroscopy, and different electron microscopy techniques shows that the majority of the Nb atoms are organized as nanosheets of NbS₂ within the MoS₂ host lattice. Most of the remaining Nb atoms (3%) are interspersed individually and randomly in the MoS₂ host lattice. Very few Nb atoms, if any, are intercalated between the MoS₂ layers. A sub-nanometer film of niobium oxide seems to encoat the majority of the nanoparticles. X-ray photoelectron spectroscopy in the chemically resolved electrical measurement mode (CREM) and scanning probe microscopy measurements of individual nanoparticles show that the mixed IF nanoparticles are metallic independent of the substitution pattern of the Nb atoms in the lattice of MoS₂ (whereas unsubstituted IF-MoS₂ nanoparticles are semiconducting). Furthermore the IF-MO_1-xNb_xS₂ nanoparticles are found to exhibit interesting single electron tunneling effects at low temperatures.

The superior performance of certain polycrystalline (PX) solar cells compared to that of corresponding single-crystal ones has been an enigma until recently. Conventional knowledge predicted that grain boundaries serve as traps and recombination centers for the photogenerated carriers, which should decrease cell performance. To understand if cell performance is limited by grain bulk, grain surface, and/or grain boundaries (GBs), we performed high-resolution mapping of electronic properties of single GBs and grain surfaces in PX p-CdTe/n-CdS solar cells. Combining results from scanning electron and scanning probe microscopies, viz., capacitance, Kelvin probe, and conductive probe atomic force microscopies, and comparing images taken under varying conditions, allowed elimination of topography-related artifacts and verification of the measured properties. Our experimental results led to several interesting conclusions: 1) current is depleted near GBs, while photocurrents are enhanced along the GB cores; 2) GB cores are inverted, which explains GB core conduction. Conclusions (1) and (2) imply that the regions around the GBs function as an extension of the carrier-collection volume, i.e., they participate actively in the photovoltaic conversion process, while conclusion (2) implies minimal recombination at the GB cores; 3) the surface potential is diminished near the GBs; and 4) the photovoltaic and metallurgical junction in the n-CdS/p-CdTe devices coincide. These conclusions, taken together with gettering of defects and impurities from the bulk into the GBs, explain the good photovoltaic performance of these PX cells (at the expense of some voltage loss, as is indeed observed). We show that these CdTe GB features are induced by the CdCl ₂ heat treatment used to optimize these cells in the production process.

The mechanical properties of materials and particularly the strength are greatly affected by the presence of defects; therefore, the theoretical strength (≈10% of the Young's modulus) is not generally achievable for macroscopic objects. On the contrary, nanotubes, which are almost defect-free, should achieve the theoretical strength that would be reflected in superior mechanical properties. In this study, both tensile tests and buckling experiments of individual WS₂ nanotubes were carried out in a high-resolution scanning electron microscope. Tensile tests of MoS₂ nanotubes were simulated by means of a density-functional tight-binding-based molecular dynamics scheme as well. The combination of these studies provides a microscopic picture of the nature of the fracture process, giving insight to the strength and flexibility of the WS₂ nanotubes (tensile strength of ≈16 GPa). Fracture analysis with recently proposed models indicates that the strength of such nanotubes is governed by a small number of defects. A fraction of the nanotubes attained the theoretical strength indicating absence of defects.

The electrical conduction through three short oligomers (26 base pairs, 8 nm long) with differing numbers of GC base pairs was measured. One strand is poly(A)-poly(T), which is entirely devoid of GC base pairs. Of the two additional strands, one contains 8 and the other 14 GC base pairs. The oligomers were adsorbed on a gold substrate on one side and to a gold nanoparticle on the other side. Conducting atomic force microscope was used for obtaining the current versus voltage curves. We found that in all cases the DNA behaves as a wide band-gap semiconductor, with width depending on the number of GC base pairs. As this number increases, the band-gap narrows. For applied voltages exceeding the band-gap, the current density rises dramatically. The rise becomes sharper with increasing number of GC base pairs, reaching more than 1 nA/nm² for the oligomer containing 14 GC pairs.

In this contribution we report on an in situ enzymatic self-assembly of a polyaniline (PAN) monolayer on modified hydroxyl-terminated surfaces. The consecutive assembly steps consist of a chemical deposition of 3-aminopropyltrimethoxysilane (APT) as a coupling agent with a positively-charged amine end group. The next step involved an electrostatic adhesion of sulfonated polystyrene (SPS) followed by electrostatic adhesion of anilinium. In situ enzymatic polymerization of the anilinium monolayer took place using horseradish peroxidase (HRP) enzyme and its substrate H ₂O₂. The assembly steps were characterized by variable angle spectroscopic ellipsometry (VASE), UV-Vis-NIR spectroscopy, contact angle measurements, X-ray photoelectron spectroscopy (XPS), contact potential difference (CPD) and scanning force microscopy (SFM). The SFM measurements were divided between ex situ analysis in which morphology of the obtained layers was determined, and in situ analysis which provided information on the dynamic process of the enzymatic polymerization.

The interfacial strength between carbon nanotubes and a polymer matrix increases dramatically when the carbonnanotube surface is chemically modified. As individual nanotubes are pulled from a polymer matrix, a transition from pullout to fracture occurs (see Figure) at a critical nanotube embedded length, with chemically modified nanotubes showing a smaller critical length than unmodified ones.

Carbon nanotubes^{1, 2} can be distinctly metallic or semiconducting depending on their diameter and chirality³. Here we show that continuously varying the chirality by mechanical torsion⁴ can induce conductance oscillations, which can be attributed to metalsemiconductor periodic transitions. The phenomenon is observed in multiwalled carbon nanotubes, where both the torque⁵ and the current are shown to be carried predominantly by the outermost wall^{6, 7}. The oscillation period with torsion is consistent with the theoretical shifting⁸ of the corners of the first Brillouin zone of graphene across different sub-bands allowed in the nanotube. Beyond a critical torsion, the conductance irreversibly drops due to torsional failure, allowing us to determine the torsional strength of carbon nanotubes. Carbon nanotubes could be ideal torsional springs for nanoscopic pendulums^{4, 9, 10}, because electromechanical detection of motion could replace the microscopic detection techniques used at present. Our experiments indicate that carbon nanotubes could be used as electronic sensors of torsional motion in nanoelectro-mechanical systems¹¹.

The subject of this volume, Scanning Probe Microscopy, by its nature brings us to the molecular or atomic realm, or minimally into nanometer-scale phenomena. This chapter deals with the fabrication of small features on solid surfaces, aided by the scanning probe microscope (SPM) tip. Whereas lithography was developed to create small structures, and is continually undergoing improvements to reduce the size scale and improve fidelity, reproducibility, and speed, most lithographic procedures treat the surface as a formable mold, into which features are etched or grown with spatial resolution aided by the blocking properties of a resist. The procedures described here use the surface as template for subsequently grown structures the surface is built upon rather than carved into. Further, in contrast to conventional lithographic processes, this can essentially be thought of as resistless lithography, since the organic coating on the silicon substrate is not used to \u201cblock\u201d chemical access to the silicon, but rather serves as a template for the growth of surface structures, by chemical specificity of subsequent reactions. In this case, the organic coating consists of a self-assembled monolayer (SAM) film. The wide range of surface chemical modifications that can be controllably performed on such films lends flexibility to this technique that is not available with other lithographic processes.In order to provide a sound overview of this field, brief discussions of the principle ingredients will be made - silane-based SAMs, and scanned-probe based anodic oxidation at a silicon surface. Subsequently, several examples of the application of this technique will be given, in order to give a feeling for the extent of different possibilities, and to demonstrate the philosophy of the approach. Particular care will be given to the experimental aspects of the work, such as the non-trivial problem of performing surfaceanalytical chemistry at the nanoscale. The goal of this chapter is thus to present the scientific basis behind a new approach for performing surface chemistry at the nanoscale, rather than to propose a technologically sophisticated lithographic procedure.

The Young's modulus of WS2 nanotubes is an important property for various applications. Measurements of the mechanical properties of individual nanotubes are challenging because of the small size of the tubes. Lately, measurements of the Young's modulus by buckling of an individual nanotube using an atomic force microscope(1) resulted in an average value of 171GPa. Tensile tests of individual WS2 nanotubes were performed experimentally using a scanning electron microscope and simulated tensile tests of MoS2 nanotubes were performed by means of a density-functional tight-binding (DFTB) based molecular dynamics (MD) scheme. Preliminary results for WS2 nanotubes show Young's modulus value of ca. 162GPa, tensile strength value of ca. 13GPa and average elongation of ca. 12%. MD simulations resulted in elongation of 19% for zigzag and 17% for armchair MoS2 single wall nanotubes. Since MoS2 and WS2 nanotubes have similar structures the same behavior is expected for both, hence there is a good agreement regarding the elongation of WS2 nanotubes between experiment and simulation.

A C₃-symmetric tridentate hexahydroxamate ligand molecule was specially synthesized and used for coordination self-assembly of branched multilayers on Au surfaces precoated with a self-assembled monolayer (SAM) of ligand anchors. Layer-by-layer (LbL) growth of multilayers via metal-organic coordination using Zr⁴⁺ ions proceeds with high regularity, adding one molecular layer in each step, as shown by ellipsometry, wettability, UV-vis spectroscopy, and atomic force microscopy (AFM). The branched multilayer films display improved stiffness, as well as a unique defect self-repair capability, attributed to cross-linking in the layers and lateral expansion over defects during multilayer growth. Transmetalation, i.e., exposure of Zr ⁴⁺-based assemblies to Hf⁴⁺ ions, was used to evaluate the cross-linking. Conductive atomic force microscopy (AFM) was used to probe the electrical properties of the multilayers, revealing excellent dielectric behavior. The special properties of the branched layers were emphasized by comparison with analogous multilayers prepared similarly using linear (tetrahydroxamate) ligand molecules. The process of defect annihilation by bridging over defective areas, attributed to lateral expansion via the excess bishydroxamate groups, was demonstrated by introduction of artificial defects in the anchor monolayer, followed by assembly of two layers of either the linear or the branched molecule. Analysis of selective binding of Au nanoparticles (NPs) to unblocked defects emphasized the superior repair mechanism in the branched layers with respect to the linear ones.

Trimethoxy-[11-(2-nitrobenzyloxy)undecyl]silane (1) and trimethoxy-[17-(2-nitrobenzyloxy)heptadecyl]silane (2) have been used for the covalent assembly of siloxane-based photopatternable monolayers. Exposing the monolayers to UV light (312 ± 10 nm) results in the generation of reactive hydroxyl-terminated monolayers without affecting the film quality. The new monolayers, deprotection chemistry, and the effect of photoinduced headgroup lift-off on the monolayer microstructure have been studied in detail by a full complement of physicochemical techniques, including optical (UV-vis) spectroscopy, ellipsometry, aqueous contact angle (CA) measurements, X-ray photoelectron spectroscopy (XPS), synchrotron X-ray reflectivity (XRR), and atomic force microscopy (AFM and AFM-force spectroscopy). AFM-force spectroscopy was used to analyze hydrogen-bond interactions as a function of the nature of the solid-liquid interface. AFM-force spectroscopy indicates a hydrogen-bond energy for photodeprotected monolayers of 8.2 kJ mol ^-1 (∼2 kcal mol ^-1). Scanning electron microscopy (SEM) revealed that treatment of photopatterned monolayers with ZnEt ₂ solutions resulted in well-defined ∼2 μm × 2 μm features of 10 Å thick ZnO layers.

Potential variations on semiconductor surfaces are often mapped using a combination of constant current topographic and local surface photovoltage (SPV) imaging. SPV imaging provides a direct measurement of surface-potential variations at large lateral distances from a charged defect or adsorbate. However, directly above the defect, variations in the SPV signal need to be interpreted in terms of surface screening, traps, and band bending. We have examined these effects using isolated oxygen atoms on a GaAS(110) surface, which is free of surface states. We interpret variations in the SPV signal in terms of a simple electrostatic model which considers the oxygen-induced Coulomb potential and corresponding image potential, both of which affect the surface density of states.

Scanning tunneling microscopy and surface photovoltage images are reported for isolated dye molecules on the GaAs(1 1 0) surface. Profound differences in the molecular images are observed for different experimental conditions. Specifically, contrast variations with changing bias polarity and magnitude, and for different substrate doping type are examined. Several mechanisms are considered to describe the observations including direct and resonant tunneling, and switching of charges between molecular states in the band gap and the energy bands of the GaAs. This treatment enables both assignment of the molecular charge state polarity, and clarification of the mechanism for current flow.

Individual multiwalled carbon nanotubes were controllably wetted by polyethylene glycol, glycerol, and water. A Wilhelmy force balance approach was used to calculate contact angles at the nanotube-polyethylene glycol and nanotube-glycerol interfaces, allowing examination of the contact angle dependence on the nanotube diameter. Water, however, exhibited a significantly larger interaction with the nanotube, which could only be explained by allowing for internal wetting of the open carbon nanotube structure. This internal wetting angle is smaller than the external one.

This paper summarizes and discusses the limited statistically significant, currently available, experimental data for the tensile strength of individual nanotubes of any sort. Only three such data sets currently exist: two for multi-wall carbon nanotubes and one for multi-wall WS₂ nanotubes. It is shown here that Weibull-Poisson statistics accurately fits all strength data sets and thus seems to apply at the nano-scale as well as it does at the micro- and macro-scales. The significance and trends of the Weibull shape and scale parameters, and their relation to the specific structural features of the different nanotubes, are discussed in each case. More recent fracture analyses are also discussed and, in that context, the role of defects in quasi-perfect structures in relation to the theoretical strength is examined.

Individual multi-walled carbon nanotube pullout experiments were used to measure the adhesion strength at a nanotube-epoxy polymer interface. The interfacial strength was found, as expected, to increase when the nanotubes were chemically treated to induce strong bonding with the polymer matrix. At long nanotube embedment lengths within the polymer, the nanotubes were seen to fracture in preference to failure at their interface with the polymer. Interfacial mechanics models are applied to the data to describe interfacial adhesion at the nano-level.

The wetting properties and surface characteristics of individual carbon nanotubes are elucidated by immersing the nanotube into various organic liquid. The resultant force acting on the nanotube can be used to evaluate a liquid contact angle at the nanotube surface from classical methods. This technique was shown to be accurate enough to discern differences in wetting behavior due to both structural and chemical changes in the nanotube structure.

Pullout experiments were performed at the nanoscale using an atomic force microscope, to assess the interfacial adhesion between multi-walled carbon nanotubes and a matrix of polyethylene-butene. Fracture energy for the nanotube-polymer interface was calculated from the measured pullout forces and embedded lengths. The results suggest the existence of a relatively strong interface, with higher fracture energy for smaller diameter nanotubes.

Quasi-amorphous BaTiO3 thin films demonstrate pyroelectricity and piezoelectricity of a magnitude of 5-15% of bulk BaTiO3, despite the fact that X-ray and electron diffraction data do not reveal detectable crystallites in this material. Therefore, the pyroelectric and piezoelectric effects must be attributed to a local dipole ordering, which is induced by the high compressive stress in the films. The non-crystalline films were prepared by passing amorphous BaTiO3 layers deposited on a Si(I 0 0) substrate through a temperature gradient. (C) 2003 Elsevier B.V. All rights reserved.

The single-crystal outperformance of thin film polycrystalline (PX) CdTe/CdS solar cells was analyzed. The defect density of grains was reduced by gettering of defects at the grain boundaries (GB). Scanning capacitance microscopy (SCM) alongwith scanning Kelvin probe microscopy (SKPM) characterize the grain surface electrically. The results show that the separation and collection of photogenerated charge carriers was enhanced by CdTe GB.

The Young's modulus of WS₂ nanotubes is an important property for various applications. Measurements of the mechanical properties of individual nanotubes are challenged by their small size. In the current work, atomic force microscopy was used to determine the Young's modulus of an individual multiwall WS₂ nanotube, which was mounted on a silicon cantilever. The buckling force was measured by pushing the nanotube against a mica surface. The average Young's modulus of an individual WS₂ nanotube, which was calculated by using Euler's equation, was found to be 171 GPa. First-principle calculations of the Young's modulus of MoS₂ single-wall nanotubes using density-functional-based tight-binding method resulted in a value (230 GPa) that is close to that of the bulk material. Furthermore, the diameter dependence of the Young's modulus in both zigzag and armchair configuration was studied and was found to approach the bulk value for nanotubes with few-nanometer diameters. Similar behavior is expected for WS ₂ nanotubes. The mechanical behavior of the WS₂ nanotubes as atomic force microscope imaging tips gave further support for the measured Young's modulus.

Complementary, single-strands of DNA (ssDNA), one bound to a gold electrode and the other to a gold nanoparticle were hybridized on the surface to form a self-assembled, dsDNA bridge between the two gold contacts. The adsorption of a ssDNA monolayer at each gold interface eliminates non-specific interactions of the dsDNA with the surface, allowing bridge formation only upon hybridization. The technique used, in addition to providing a good electrical contact, offers topographical contrast between the gold nanoparticles and the non-hybridized surface and enables accurate location of the bridge for the electrical measurements. Reproducible AFM conductivity measurements have been performed and significant qualitative differences were detected between conductivity in single- and double-strand DNA. The ssDNA was found to be insulating over a 4 eV range between ±2 V under the studied conditions, while the dsDNA, bound to the gold nanoparticle, behaves like a wide band gap semiconductor and passes significant current outside of a 3 eV gap.

Coordination self-assembly of bishydrpxamate-based metal-organic multilayers on gold employing a layer-by-layer (LbL) approach was investigated. It is shown that the solution chemistry of the participating metal ion has a marked influence on the composition and properties of the multilayers. Use of Ce⁴⁺ and particularly zirconium(IV) acetylacetonate (Zr(acac) ₄) solutions in the ion-binding step of multilayer construction leads to multilayers with a near-stoichiometric metal ion-to-ligand ratio, suggesting a structure close to that predicted by a simple coordination self-assembly scheme. On the other hand use of a ZrCl₄ solution as the source of metal ions in the multilayer construction leads to a multilayer with greater thickness and a large excess of Zr(IV), evenly distributed between the organic layers. In the latter case, a ratio of ca. 1:2 between the excess Zr and oxygen, as well as long-term Zr⁴⁺ binding experiments showing deposition of ZrO₂, suggest the formation of a zirconia-type nanophase between the bishydroxamate organic repeat units during multilayer self-assembly. Hence, while the multilayer prepared using Zr(acac)₄ solution appears to represent a "true" coordination-based structure, the one prepared using ZrCl₄ is best described as a composite organic-ceramic multilayer. Composite multilayers prepared in this way display different properties from those of the stoichiometric ones, such as improved dielectric behavior and higher stiffness. Even greater mechanical stability is obtained with multilayers constructed using alternate binding of ZrCl₄ and Ce⁴⁺, The concept of LbL formation of coordination-based composite organic-ceramic structures may be useful in obtaining nanometer-scale structures with tunable properties.

The static and dynamic wetting measurements of an individual multiwalled carbon nanotubes (MWCNTs) were discussed. The possibility of adapting the Wilhelmy balance method to perform measurements of the static and dynamic wetting characteristics of single carbon nanotubes using a range of simple liquids in air was shown. It was observed that the increased attractive force during removal of carbon nanotubes from the liquids could be used to evaluate the mechanical distortion of the liquid meniscus. A method was also developed to monitor the forces acting on individual carbon nanotubes during their immersion into and retraction from liquids in air.

Stepped conical structures have been produced at the surface of poly(ethylene glycol) by contacting a single, relatively short carbon nanotube attached to an AFM tip with the molten polymer surface, followed by polymer cooling. Cooling of the polymer melt in the nanotube vicinity is the most likely mechanism for these ziggurat-like structural formations. Simple heat transfer calculations confirm the effect of the nanotube length on the propensity for local solidification of the polymer.

Two methods are described for experimental determination of interfacial strengths of carbon nanotubes (CNT) in a polymer matrix. These SPMbased techniques allow realtime monitoring of the dynamics of a single pullout event. A comparison and contrast of these different techniques is presented here. Correlations found with the tube diameter give insights as to the nature of the CNTpolymer interaction.

Type conversion in CdS in CdTe/CdS solar cells was disproved. CdS and high-resistance SnO₂ layer in USF cells were found to be electronically similar, rationalizing the need for a HR layer in cells with very thin CdS for supporting the junction photovoltage, without reducing the cell's blue response. Most importantly, combined XS SCM and SKPM of CdTe/CdS cells show that the photovoltaic and metallurgical functions coincide.

The direct characterization of a single grain boundary (GB) and a single grain surface in solar cell-quality CdTe was performed using scanning probe microscopy. It was found that scanning capacitance microscopy could be used to study polycrystalline electronic materials. The presence of a barrier for hole transport across GB in solar-cell quality CdTe was also observed.

The magnitude of pyroelectricity in highly stressed quasi-amorphous thin films was analyzed. The amorphous BaTiO₃ layers were deposited by radio frequency (RF) magnetron oxygen plasma sputtering. The stress in the BaTiO₃ films was measured by the substrate curvature method. It was found that the films that passed through the temperature gradient showed large pyroelectric effect over the temperature range of 20-150 °C.

CdS quantum particles (QPs) assembled at predetermined distances from a gold substrate are prepared within a Langmuir-Blodgett film that forms an organic host matrix. The system is characterized by controlled surface charging (CSC) in X-ray photoelectron spectroscopy (XPS) and complementary methods, successfully resolving the discrete QP layers. A quantitative study of substrate-QPs charge-transfer channels is provided by laser-intensity dependent contact potential difference (CPD) measurements. The extracted electron-transfer rate constants exhibit marked differences in electron transfer from the film toward the substrate versus the backward process. The charging of the hybrid film was found to be either negative or positive depending on the intensity of the laser that photoexcites the QPs.

A composite surface comprising evenly distributed silicon oxide islands on a gold substrate is described. The composite surface is prepared by evaporation of a thin (50 nm) gold layer on oxide-free (H-passivated) silicon, followed by thermal diffusion of Si through the Au layer, gradually forming islands of SiO₂ on the Au surface. The rate of Si diffusion through the Au, and hence, the rate of SiO₂ island formation, is controlled by the annealing temperature, the Si crystallographic face, the Au film thickness, and the contacting atmosphere. The Au-SiO₂ composite surfaces can be used in applications requiring substrates patterned on a mesoscopic scale, while exposing two chemically dissimilar phases. One such application is shown here, namely, the formation of thiol-silane monolayers, for which the distribution of the different molecules in the resultant monolayer is determined by the substrate composition. The XPS controlled surface charging (CSC) method is used to establish a site-selective adsorption. The SiO₂ islands are found to be rather labile, shifting and aggregating upon self-assembly of alkanethiol molecules on the Au exposed areas. Pretreatment of the islands with a long-chain silane stabilizes the morphology.

The measurement of the force required to separate a carbon nanotube from a solid polymer matrix was discussed. The reproducible nanopullout experiments were performed by using atomic force microscopy during the analysis. The results showed that the polymer matrix in close vicinity of the carbon nanotube was able to withstand stresses, causing considerable yield in a bulk polymer specimen.

A strong Bragg peak, attributed to regular corrugation in a crystalline film, was detected in a series of self-assembled supramolecular complexes of bifunctional bolaamphiphiles of different lengths, with divalent ions of Pb and Cu, at the air - aqueous interface. This peak has a d spacing half that of the proposed corrugation-repeat length of ca. 82 Å, which is not a multiple of the long lattice spacing of the crystalline structure, and is susceptible to film compression. This corrugation is interpreted in terms of unfavorable interactions between the polar aqueous surface and the nonpolar hydrocarbon part of the bolaamphiphiles. To establish the nature of the corrugation, grazing-incidence X-ray diffraction and specular X-ray reflectivity with synchrotron radiation were applied, as well as scanning force microscopy of films deposited on mica.

Carbon nanotube nanocomposites containing well-dispersed and aligned single- and multi-walled nanotubes have been fabricated by an extrusion method and their impact and hardness properties determined. The impact resistance of the polymer matrix has been improved considerably by the inclusion of the highly flexible and elastic nanotubes. The Knoop hardness reached a maximum at 90 deg to the orientation of the reinforcement, which demonstrated the direction of maximum strength, is in the extrusion flow direction. New techniques to investigate the adhesion of carbon nanotubes to a polymer matrix are described and recently produced data are presented. The measured interfacial shear strengths for multi-walled carbon nanotube nanocomposites is found to be very high, a result which is in agreement with earlier conjectures.

The complex issues involved in the development of template-controlled chemical processes that would allow the planned self-assembly of an entire functioning electric circuit of nano-metric dimensions pose new and far more difficult scientific challenges. To have real impact on future nanotechnologies, a useful bottom-up nano-fabrication methodology should thus be capable of dealing satisfactorily of the given issues. This paper reports on a series of proof-of-concept experiments carried out with the purpose of demonstrating the practical feasibility of a comprehensive all-chemical nanofabrication strategy that can, in principle, meet the requirements.

Inorganic nanotubes of WS₂ have been investigated by high-resolution transmission electron microscopy, and scanning tunneling microscopy, providing support for the theoretical prediction of correlation of bandgap with diameter.

An experimental technique for probing the adhesion of carbon nanotubes to a polymer matrix was described. The nanotube-polymer interaction was quantified by detaching individual single-walled carbon nanotube bundles and multiwalled-carbon nanotube from an epoxy matrix using a scanning probe microscope tips. These experiments were used for the calculation of the nanotube-polymer interfacial shear strength.

Direct, spatially resolved, mechanical measurements on the transcrystalline phase formed near high modulus carbon fibers embedded in α-isotactic polypropylene are reported. A scanning force microscope has been implemented with two nonstandard modifications in order to probe both the Young's modulus and shear modulus at varying directions with respect to the lamellae growth direction. The experiments show an unequivocal anisotropy in both moduli, which varies with radial distance from the fiber. The results can be interpreted in terms of morphology of the polymer molecules and lamella stacks. The different probe size for the two measurements enables a separation of molecular and lamellae order.

Direct, spatially resolved, mechanical measurements on the transcrystalline phase formed near high modulus carbon fibers embedded in alpha -isotactic polypropylene are reported. A scanning force microscope has been implemented with two nonstandard modifications in order to probe both the Young's modulus and shear modulus at varying directions with respect to the lamellae growth direction. The experiments show an unequivocal anisotropy in both moduli, which varies with radial distance from the fiber. The results can be interpreted in terms of morphology of the polymer molecules and lamella stacks. The different probe size for the two measurements enables a separation of molecular and lamellae order.

Two methods for the synthesis of CdTe nanoparticles in zirconia sol-gel films are demonstrated. The nanoparticles were obtained by chemical reduction of Te(IV) using reducing agent (hydrazine) or tin chloride. Particle sizes ranging from 6 to 20 nm in diameter could be prepared by varying the experimetal parameters. The size and crystalline structure of the particles were characterized by optical absorption, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The film morphology was characterized by scanning force microscopy. The film obtained by SnCl₂ method is smooth and homogeneous. The dense structure of CdTe nanoparticles of a few nm in diameter is revealed. The films prepared with hydrazine are porous as a result of evolution of the decomposition gaseous products during the reduction. Advantages and disadvantages of the two methods are discussed.

The relation between the mechanical properties and the lamellar morphology of the α-isotactic polypropylene transcrystalline interphase in a fiber composite was investigated by means of nanometric shear and directional indentation measurements, using scanning force microscopy. Measurements were performed along directions parallel and perpendicular to the transcrystalline growth direction. A key finding is the inversion of the shear modulus anisotropy ratio from 2.3 to 0.5 as the crystal grows away from the fiber. On the basis of this finding, an improved view of the hierarchical lamellar and molecular order of the transcrystalline layer is proposed.

Capacitance due to geometric influence of the finite tip shape and influence of distant surface points can lead to artifacts in scanning Kelvin probe microscopy (SKPM) images. These artifacts appear as features in the SKPM image which are due only to tip/surface geometry and not to true surface potential variations. They can also cause blurring of real features. Such effects are most prominent for samples with rich topography. We present here a method for identifying and removing these artifacts, and demonstrate it for a gold sample with rich topography relative to the nearly flat surface potential fluctuations. (C) 2000 American Vacuum Society. [S0734-2101(00)11104-2].

Oriented crystalline monolayers, ~ 14 Å thick, of a 2 x 2 Ag⁺ grid complex, self-assembled at the air-solution interface starting from an waterinsoluble ligand 3,6-bis[2-(6-phenylpyridine)]pyridazine spread on silver-ion-containing solutions, were examined by grazing-incidence X-ray diffraction and specular X-ray reflectivity using synchrotron radiation. The monolayer structure was refined, including a determination of the positions of the counterions, with the SHELX-97 computer program. The monolayers were transferred from the interface onto various solid supports and visualized by scanning force microscopy, and characterized by X-ray photoelectron spectroscopy in terms of molecular structure. On surface compression, the initial selfassembled monolayer undergoes a transition to a crystalline bilayer in which the two layers, almost retaining the original arrangement, are in registry. Such a phase transition is of relevance to the understanding of crystal nucleation.

Constructive nanolithography is a nanofabrication method where an electrically conducting atomic force microscopy (AFM) tip is used to nondestructively inscribe chemical information on the exposed outer surface of an organized organic monolayer, thus converting it into a patterned template for spatial control of the surface self-assembly of various selected organic and inorganic nanoentities. The experimental results demonstrating the practical feasibility of a versatile generic approach to constructive nanolithography are reported.

The effectiveness of constructive nanolithography as a versatile approach to the in situ chemical fabrication of spatially-defined silver structures on thiol-top-functionalized silane monolayer templates was investigated. Metallic silver nanoparticles were generated at selected surface sites by either wet chemical or tip-induced electrochemical reduction of the surface-bound metal ions. A simple change of experimental conditions such as the tip material, composition of the template surface and the composition of the ambient atmosphere resulted in different, yet useful mode of nanoelectrochemical surface patterning, which points to the versatility and wide applicability of the method.

X-ray photoelectron spectroscopy (XPS), an essentially macroscopic probe, is used to analyze mesoscopic systems at a lateral resolution given by the substrate structure. The method is based on controlled differential charging of multi-component surfaces, using a simple, commonly available XPS function, the electron flood gun. This new approach is applied here to a novel composite surface comprising SiO₂ clusters on a {111} gold substrate, onto which different molecules are self-assembled to form a mixed organic monolayer. The method allows direct correlation of adsorbed molecules with surface sites, by analyzing XPS line shifts, which reflect local potential variations resulting from differential surface conductivity. This provides a powerful tool for resolving complex ultrathin films on heterogeneous substrates, on a length scale much smaller than the probe size.

Friction and wear behavior of new nanomaterial - inorganic fullerene-like (IF) WS2 supramolecules has been compared with layered solid lubricants MoS2 and WS2. Lubrication mechanism of IF nanoparticles and tribochemistry of contact have been studied. The main advantages of IF nanoparticles lies in their round shape and the absence of dangling bonds. Velocity accommodation modes under friction with solid lubricant powders were considered. The main lubrication mechanism of contact with IF nanoparticles appears to be rolling friction.

In recent years, a variety of methodologies and samples have been proposed for removing the effect of tip shape from scanning probe microscope (SPM) images. Despite the importance of such procedures in obtaining accurate representation of the surface topography, they are not generally applied, nor have they become readily available to the average SPM user. This paper contrasts the two major categories of methodology for extracting the tip shape and subsequently eroding this shape from an image. Several commonly available samples are used as examples and/or proposed as standards. It is seen that the unique considerations of a specific measurement will guide which protocols are used, and that misdirected application of the techniques can give misleading results.

Recently, new structural formulations of metal dichalcogenides have resulted in greatly enhanced lubricant properties, placing the mechanisms of lubrication for this class of materials under closer scrutiny. In this work, scanned probe microscope techniques have been used to probe the surface on a nanoscale, comparing friction and adhesion at specific surface sites. In addition, the role of interlayer shear and subsurface defects in moderating friction are examined. (C) 1999 Elsevier Science B.V. All rights reserved.

Functionalized organic monolayers are excellent candidates for the preparation of templates with selectable surface chemical properties. A versatile selfassembly approach is reported to the in situ chemical generation of spatially defined surface nanostructures (see Figure). The patterning process used allows the nanoscale inscription of chemical information on the surface of functionalized organic monolayers.

The assembly, orientation, and structural features of nanoscale tubes composed of cyclic peptides, formed at the air-water interface, were detected by grazing incidence X-ray diffraction (GIXD). The peptide cyclo-[(L-Phe-D- N-MeAla-)₄] (1) exhibits two-dimensional crystallinity in which the plane of the peptide ring is parallel to the water interface. The peptide cyclo-[(L- Trp-D-Leu)₃-L-Ser-D-Leu] (2) forms predominantly planar aggregates composed of several tubes, lying with their long axes parallel to the air-water interface. In contrast, the peptide cyclo-[(L-Trp-D-Leu)₄] (3) exhibits a very low tendency to form ordered two-dimensional arrays of nanotubes. Films of peptides 2 and 3 as well as their mixtures with the phospholipid DPPA were transferred onto a solid support and visualized by scanning force microscopy (SFM).

WS₂ nanotubes a few microns long were attached to microfabricated Si tips and tested afterwards in an atomic force microscope by imaging a "replica" of high aspect ratio, i.e., deep and narrow grooves. These WS₂ nanotube tips provide a considerable improvement in image quality for such structures when compared with commercial ultrasharp Si tips. The nanotube tip apex shape was extracted by blind reconstruction from an image of Ti spikes, showing a smooth cylindrical profile up to the end.

A scanning force microscope was fitted with an elongated, blade-like tip, with which nanoindentations were performed in the transcrystalline isotactic polypropylene phase grown from the surface of high-modulus carbon fibers. The anisotropic Young's modulus was evaluated by measuring the force-penetration curve of the indentation and the tip topography, as a function of the indentation depth. The modulus is 1.6-3 times higher when the longer axis of the indenting tip is perpendicular to the transcrystalline growth direction than when it is parallel to that direction. We discuss possible options for the lamellar arrangement in a transcrystalline isotactic polypropylene layer and, based on the present experimental data, propose a most likely model.

CdS quantum dots (QDs) have been electrodeposited onto textured gold substrates from a nonaqueous electrolyte containing Cd(ClO₄)₂ and elemental S. The initial deposit consisted of very small (about 3 nm) nanocrystals of CdS which were partially oriented with the Au substrate. With increasing deposit thickness, the crystal size increased and the degree of orientation decreased. Photocurrent spectroscopy and I-V spectroscopy, using a conducting scanning force microscope tip, were used to measure the CdS bandgap variations due to size quantization. The latter method also revealed room temperature conductivity peaks assigned to Coulomb charging of the QDs and evidence for charge tunneling into higher discrete energy levels.

Structural studies on Langmuir films of C50H102, nylon-6,6 polymer and its oligomeric analog provide information on the crystallization behavior of these substances in thin layers. While a nylon-6,6 oligomer and C50H102 form stable crystalline monolayers with the chains aligned mainly normal to the water surface, nylon-6,6 polymer assembles into a fibrous multilayer film (see SFM micrograph).

We fabricate sub-micron sized diode and transistor structures (down to 100 nm in diameter) inside CuInSe2 crystals by inducing thermally assisted electromigration of mobile dopants. This is achieved by applying an electric field via a small area contact to the crystals, using a conducting Atomic Force Microscope tip. The structures are characterized by nm scale scanning spreading resistance and scanning capacitance measurements to reveal the inhomogeneous doping profiles, that result from the electric field action. Calculations suggest that the smallest of the structures that we made are very close to the lower size limit of possible p/n/p devices.

Oriented crystalline films, ~11-20 Å thick, of metal ion complexes of the grid type [Co₄L₄]⁸⁺·8PF₆^- and [Ag₉L₆]⁹⁺ 9·CF₃SO₃^-, based on various ligands L, were prepared in-situ at the air-aqueous solution interface by the interaction of the free ligand molecules spread onto aqueous solutions containing Co²⁺ or Ag⁺ ions. The structure of the complex architectures composed of a 2 x 2 Co²⁺ grid coordinated to four ligand molecules and a 3 x 3 Ag⁺ grid coordinated to six ligand molecules as well as their molecular organization in thin films were characterized by grazing incidence synchrotron X-ray diffraction (GIXD) and specular X-ray reflectivity (XR) measurements performed at the air-aqueous solution interface and by UV, X-ray photoelectron spectroscopy (xPs), and scanning force microscopy (SFM) after film transfer onto various solid supports. The results open perspectives toward an implementation of the air-water interface for the self-assembly and subsequent deposition of organized arrays of complex inorganic architectures onto solid support.

Oriented crystalline thin films of alpha,omega-tetracosanedioic acid metal salts form in situ at the air-liquid interface, following the simple procedure described here. It is shown that the Cd2+ and Pb2+ metal ions have a dramatic influence on the packing of the diacid molecules, which self-assemble as multilayer domains approximately 50 Angstrom thick, with the molecules and bound ions perfectly ordered laterally over distances up to 1000 Angstrom. These oriented crystallites preserve their integrity upon transfer to a mica support and can be used to prepare quantum dots (see following communication).

We show how sub-μm sized transistor structures (down to 50 nm cross section) can be fabricated by thermally assisted electromigration of mobile dopants inside the semiconductor CuInSe₂. Small device structures are fabricated by application of an electric field to the sample via the contact, defined by a conducting atomic force microscope tip. The structures are characterized by nm scale scanning spreading resistance and scanning capacitance measurements to reveal the inhomogeneous doping profiles created by the electric field.

The tribological properties of textured WS₂, MoS₂ and WSe₂ films, which were prepared using an ultra-thin interlayer of Ni/Cr (van der Waals rheotaxy technique) on quartz substrate, were determined in ambient conditions. Using scanning force microscope adapted for tribological measurements, very low (0.04 and below) friction coefficients and little wear were measured on flat areas of the films. Macroscopic (engineering) tribological measurements, using the reciprocating ball on flat tribometer, exhibit somewhat higher friction coefficients. Compactization of the films under the load and little wear were observed for the films even after a few hundred cycles. X-ray photoelectron spectroscopy of the WS₂ film after the wear experiment confirmed that some oxidation took place within the wear track, but the overall integrity of the film was preserved. These measurements indicate that highly textured films of this kind are promising candidates for tribological coatings, where oil-free lubrication is required.

Evaporation of metals, like W, Mo, V, and In, in the presence of water vapor and subsequent sulfidization has yielded bulk quantities of nested fullerenes, nanotubes, and structures with negative curvature (inorganic fullerene-like-IF). Dissolving alkali-metal salts into the water source afforded alkali-metal intercalation and staging (n = 6) of the IF structures after sulfidization. The intercalated moieties were found to be stable in air and even in water. The intercalated IF structures could be dispersed in alcoholic suspensions, and electrophoretic deposition from the suspensions yielded thin films of the IF particles. The films of intercalated IF showed respectable and time-invariant photoeffects. Furthermore, low adhesion and robust tips for scanning probe microscopy were prepared by depositing intercalated IF film on Si tips. Other applications, which are currently investigated, are briefly mentioned.

We describe a novel approach based on atomic force microscopy to determine the dihedral contact angle of a liquid polymer on top of a solid substrate. By cross-linking the polymer in an ion beam, the polymer surface becomes amenable to AFM imaging. This sample preparation enables us to take topography scans of the polymer in a solid state. The cross section of the contact area of a polymer drop and the substrate can then be utilized to determine the contact angle between polymer and substrate. Extremely low contact angles in the range 2-8° are reproducibly measured. Control measurements carried out with optical phase modulated interference microscopy gave contact angles well comparable to the AFM results. We use our method in a study of polymer dewetting on top of a network of itself.

Solid lubricants fill a special niche in reducing wear in situations where the use of liquid lubricants is either impractical or inadequate, such as in vacuum, space technology or automotive transport. Metal dichalcogenides MX₂ (where M is, for instance, Mo or W and X is S or Se) are widely used as solid lubricants. These materials are characterized by a layered structure with weak (van der Waals) inter-layer forces that allow easy, low-strength shearing. Within the past few years, hollow nanoparticles (HNs) of MX₂ with structures similar to those of nested carbon fullerenes and nanotubes have been synthesized. Here we show that these materials can act as effective solid lubricants: HN-WS₂ outperforms the solid lubricants 2H-MoS₂ and 2H- WS₂ in every respect (friction, wear and lifetime of the lubricant) under varied test conditions. We attribute the outstanding performance of HN-WS₂ to its chemical inertness and the hollow cage structure, which imparts elasticity and allows the particles to roll rather than to slide.

New observations on the effect of surface morphology (corrugation) on the structure of vapor-deposited ice are presented. Amorphous quartz and single-crystal Si(100) were used as substrates. Water was deposited on the bare substrates and on the substrates covered with organized organic thin films (OOTF). By coating the substrates with mixed organic monolayers, controlled corrugation was achieved, without affecting the chemical nature of the surface. Information on the surface corrugation on different scales was obtained by atomic force microscopy and wettability measurement techniques. The ice phase was determined by in situ infrared absorption measurements. Correlation was observed between the surface roughness on a scale that is characteristic for the distance between ice nucleation centers and the deposited ice structure. Molecular dynamics simulations could reproduce the experimental observations and provide an insight into its origin.

Optical and electrical properties of films of CdSe quantum dots epitaxially electrodeposited onto gold have been measured by modulated optical spectroscopy, liquid junction photoresponse spectroscopy and local current-voltage spectroscopy using a metallized scanning probe tip. The blue shift in the bandgap resulting from quantum confinement in the quantum dots has been measured by all these techniques. Large differences in the charge collection efficiency between the first and subsequent layers of dots have been measured and explained by the positive role of grain boundaries in enhancing collection efficiency in these films. Single electron transfer through the dots has been observed and explained by the large charging energies of the very small (45nm) dots.

A correlation is presented between the crystalline structure of monolayers and multilayers of α,ω-alkanediols HO-(CH₂)_n-OH (n = 16, 18, 19, 21, 22, 23, 24, 30) at the air-water interface and their function as ice nucleators. Structural elucidation was carried out by the following methods: grazing incidence X-ray diffraction, scanning force microscopy, cryo-transmission electron microscopy and external reflection Fourier transform-infrared spectroscopy.

Thin films of metal dichalcogenide compounds with a layered structure, such as MoS₂ (WSe₂), play an important role in a number of technologies, like solid lubrication, experimental photovoltaic cells, etc. Such films usually adopt a type-I texture, in which case the c-axis of the crystallites is parallel to the substrate plane. However, for the aforementioned applications, type-II texture, where the c-axis of the crystallite is perpendicular to the substrate, is required. We have recently demonstrated a novel growth technique (Van der Waals rheotaxy, VdWR) which yields a crystalline film having exclusively type-II texture on amorphous, (quartz) substrate. In the present work superior crystalline, optical and electronic properties of the overlying WSe₂ (WS₂) film together with an improved adhesion of the film to the quartz substrate are obtained by replacing the ultra thin Ni film with a Ni/Cr film.

Structure, morphology, and mechanical properties of mono- and several-layer structures of amphiphiles or pure n-alkane crystallites generated by spontaneous self-assembly on aqueous subphase have been analyzed by scanning force microscopy (SFM). Pure-component and heterogeneous mixtures of molecules were allowed to spread and self-assemble without compression on an aqueous subphase. The self-assembled films were transferred to an atomically smooth mica substrate by drainage for measurement using SFM. Results were compared with a variety of techniques including cryo-transmission electron microscopy, grazing incidence X-ray diffraction. X-ray reflectivity, and reflectance/absorption infrared spectroscopy. Whereas the collaborative techniques provide spatially-averaged information, we find that the SFM accesses both individual crystallites and amorphous material, thus providing unique information on the morphology, number of layers, and complementary structural features.

Micrometer-sized homojunction structure can be formed by applying strong electric pulses, at ambient temperatures, to Li-doped, floating zone n-Si. Two such junctions, arranged back to back, act as a transistor, as evidenced by electron-beam-induced current and current-voltage measurements. The structures are created during a time ranging from ∼100 ms to a few seconds, depending on the size of the structure. The phenomenon is similar to what was observed earlier in CuInSe₂ and was explained there by thermally assisted electromigaration of Cu. In the case of Si doped with Li we can use secondary-ion-mass spectrometry to detect the redistribution of Li after electric-field application. Such a redistribution is needed found and corresponds to an n⁺-p-n structute with the p region extending at least ∼20 μm into the bulk of Si. Structures created in Si doped with Li in this way are stable for at least 13 months after their creation. We ascribe this to the large difference between Li diffusivity at the local temperature that is reached during structure formation (∼400°C; 10^-8 cm²/s) and at room temperature (∼10^-15 cm²/s).

We present recent results of the study of surface properties and quantum efficiency (QE) of CsI photocathodes prepared on various substrates. Microanalysis methods provide laterally resolved surface morphology and chemical composition of the photoemissive film. Integral measurements of the QE of CsI were done with a monochromator system and a RICH device. It was shown that CsI films deposited on large area Ni- or Ni-Au-coated printed circuit electrodes have a uniform crystalline structure and an average QE close to that reached on polished stainless steel. The films have a good stability in air over periods of Ih. On a microscopic scale of 3-30 mu m, the films exhibit nonuniform emission properties correlated with variations in the chemical composition.

The conductance of isolated CdSe quantum dots (QDs) of 4 nm diameter, epitaxially electrodeposited on gold substrates, has been studied using a scanning force microscope with a metallized tip to perform current-voltage spectroscopy. The band gaps of the dots have been measured and correlated with the QD size distribution. Reproducible peaks in the room-temperature conductance spectra are interpreted as transport of single electrons through the quantum dots. The roles of both Coulomb charging and interlevel spacing are considered.

We demonstrate quartz micropipette and optical fiber based structures with unique applications for scanned probe microscopy. These probes are produced by drawing, cantilevering, and polishing tapered micropipettes and optical fibers and have significantly greater potential functionality than any other currently available scanning tip. We present normal force, contact mode imaging of a selection of surfaces, operating these probes with different commercial instruments for atomic force microscopy (AFM). With their very sharp tips, ultrahigh aspect ratios, and readily adjustable force constants and resonance frequencies, the probes present an attractive alternative to conventional microfabricated cantilevers that are currently in routine use with AFM. Bent quartz optical fiber probes also enable simple integration of near-field scanning optical microscopy and AFM.

Spreading of the bolaamphiphile alpha,omega-docosanediol, HO(CH2)(22)OH, on water results in spontaneous aggregation into embryonic 3-D crystallites. These crystallites have been analyzed by cryo-transmission electron microscopy, scanning force microscopy, X-ray reflectivity, and external reflection Fourier transform infrared spectroscopy. The molecules are aligned in an almost perpendicular fashion in a rectangular cell, and the crystallites are about five molecular layers thick.

The spontaneous aggregation of the bolaamphiphile α,ωdocosanediol into embryonic threedimensional crystallites at the airwater interface can be inhibited by additives. A study with the aim of determining the necessary properties of such supplements is reported, which uses additives with molecular recognition properties and methods such as Xray reflectivity, cryotransmission electron microscopy, and atomic force microscopy in order to detect structural changes at the nanometer level.

The scanning force microscope (SFM, also known as atomic force microscope, AFM) has achieved widespread usage and commercialization much more rapidly than the related scanning tunneling microscope (STM). This is due to the applicability of the technique to virtually any surface. Measurements may be made in vacuum, in ambient, under solution, on conducting and nonconducting surfaces alike. Progress in the field has been marked by expansion into diverse areas spurring equipmental developments which have enabled increased performance for the new applications. This review briefly introduces this microscope, then highlights some recent advances, and assesses their significance.

The friction of a clean diamond tip on diamond (111) and (100) surfaces is studied using an ultrahigh vacuum force microscope that simultaneously measures forces parallel and perpendicular to the surface. The 30 nm radius diamond tip is fabricated by chemical vapor deposition. The attractive normal force curve between the tip and surface agrees well with calculated dispersion interactions. The frictional force exhibits periodic features, which on the (100) surface are tentatively associated with a 2 X 1 reconstructed surface convoluted over an asymmetric tip shape. The (111) surface shows features that cannot be simply related to the surface structure. As the tip is scanned back and forth along a line, the same features are observed in each direction, but offset, suggesting the presence of a conservative force independent of the direction of motion as well as a nonconservative force. The friction is approximately congruent-to 3 X 10(-9) N independent of loads up to 1 X 10(-7) N.

The advantages and limitations of using the AFM for studies of materials properties on a small scale is discussed. Alternate analysis methods for calculating interfacial energies from AFM force versus tip-surface distance curves are compared. These values have been calculated in the past by relying only on the maximum pull-off force. Uncertainty regarding the chemical nature and physical structure of the tip at the atomic scale makes such estimates unreliable. It is shown that integrating the experimental force versus distance data to estimate adhesive energy can provide additional information on the nature of the contact. This sample approach has been applied to several published experiments. The results show that in most cases failure of the adhesive bond between tip and flat is mediated by a contaminant layer.

In this paper it is demonstrated that glass micropipettes have unique applicability as force probes for a variety of imaging conditions and a variety of scanned tip microscopies. These probes are characterized in terms of the parameters that determine their force characteristics. Measurements are presented showing that one can readily achieve force constants of 10 N/m and it is anticipated that a reduction in this force constant by two orders of magnitude can be achieved. Such probes can be produced simply with a variety of geometries that permit a wide range of force imaging requirements to be met. Specifically, the glass micropipette probes reported in this paper are readily produced with apertures at the tip and can thus be applied to near-field scanning optical microscopy (NSOM). This opens the possibility of the long-awaited development of a universal feedback mechanism for NSOM.