Integrated Calendar

A new type of transmission electron microscopes operating at electron energies between 80keV and 20keV has been developed to obtain structural and electronic properties of advanced low-dimensional material at the atomic scale. It allows to undercut most of the materials knock-on damage thresholds and enables sub-Angstroem resolution in an 4000x4000 pixels, single-shoot image down to 40keV by correcting not only the geometrical aberrations of the objective lens but also its chromatic aberration. During the imaging process, the interaction of the beam electrons with the low-dimensional material can, nevertheless, results in changes of the atomic structure due to ionization and radiolysis, and sophisticated sample preparation methods are employed to reduce these effects. In this talk, we briefly outline key instrumental and methodological developments and report on structural properties of low-dimensional materials. We not only determine the structure of the pristine material but also use the electron beam to engineer defined properties. Thus, we show for instance the dynamics of extended defects in MoTe2 and WS2 and the creation of a commensurate charge density wave (CDW) in a monolayer 1T-TaSe2, as well as properties of MnPS3, and moreover the dynamics and bond order changing of dirhenium molecule in single-walled carbon nanotubes. Finally we intercalate bilayer graphene by lithium and study in-situ lithiation and delithiation between bilayer graphene, identify single Li atoms as well as the structure of the new high density crystalline Li- phase.

Over a century ago, various experiments both in gravitropism and phototropism, revealed that plants respond to an integrated history of stimuli rather than responding instantaneously. Particularly, experimental observations have shown that plants respond identically to different combinations of stimuli - intermittent in time or with reciprocal ratios of intensity and duration - as long as the total dose of these stimuli is the same. Current mathematical descriptions of the kinematics of tropic
responses are instantaneous and limited to constant stimuli. In this work we adopt the well-established approach of response theory, which describes the non-trivial input-output relationship of a signal transducer, in this case a plant turning an external stimulus into a growth response. This model is experimentally tractable, allowing a quantitative description of the ability of plants to integrate stimuli over time, laying the foundation for an understanding of decision-making in plant tropisms.

Engineering next-generation materials that can grow into efficient multitasking agents, move rapidly, or discern environmental cues greatly benefits from inspiration from biological systems. In the first part of my talk, I will present a geometrical theory that explains the biomineralization-inspired growth and form of carbonate-silica microarchitectures in a dynamic reaction-diffusion system. The theory predicts new self-assembly pathways of intricate morphologies and thereby guides the synthesis of light-guiding optical structures. The second part is dedicated to a soft matter analog of controlled actuation and complex sensing in living systems. Specifically, I will introduce a continuum framework of a simple hydrogel system that is activated upon transport and reaction of chemical stimuli. The hydrogel exhibits unique cascades of mechanical and optical responses, suggesting that common gels have a much larger sensing space than currently employed. The theoretical work presented in my talk is intimately connected to modern materials science. The effective convergence of theory and experiment paves the way for optimized hard or soft biomimetic materials for applications ranging from bottom-up manufacturing to soft robotics.