לוח שנה משולב

A wide range of NCN pincer palladium complexes, [4-tert-2,6-bis(N-alkylimino)phenyl]chloropalladium (alkyl = n-butyl, benzyl, cyclohexyl, t-butyl, adamantyl, phenyl, 4-methoxyphenyl), were readily prepared from trans-(4-tert-butyl-2,6-diformyl-phenyl)chlorobis(triphenylphosphine)palladium via dehydrative introduction of the corresponding alkylimino ligand groups (ligand introduction route) in excellent yields (71-98%). NMR studies on this route for forming pincer complexes revealed the intermediacy of [4-tert-2,6-bis(N-alkylimino)phenyl]chlorobis(triphenylphosphine)palladium which is in equilibrium with the corresponding NCN pincer complexes via coordination/dissociation of the intramolecular imino groups and triphenylphosphine ligands. A series of chiral NCN pincer complexes bearing pyrroloimidazolone units as the trans-chelating donor groups, [4-tert-butyl-2,6-bis{(3R,7aS)-2-phenylhexahydro-1H-pyrrolo[1,2-c]imidazol-1-on-3-yl}phenyl]chloropalladium, were also prepared from the same precursor via condensation with proline anilides in high yields. The catalytic properties of the NCN imino and the NCN pyrroloimidazolone pincer palladium complexes were examined in the Heck reaction and the asymmetric Michael reaction to demonstrate their high catalytic activity and high enantioselectivity. Amphiphilic pincer palladium complexes bearing hydrophilic and hydrophobic side chains on the planar NCN palladium pincer backbone were also designed and prepared via the ligand introduction route. The complexes self-assembled under aqueous conditions to form vesicles with bilayer membranes containing palladium species. The catalytic activity of the vesicles in the Miyaura-Michael reaction in water was investigated.

The acceleration of electrons with high intensity laser pulses offers an efficient and cost effective alternative to classical particle accelerators. The mechanism of laser wakefield acceleration (LWFA) is based on the laser-plasma interaction in underdense plasmas. The laser excites a plasma wave in which the electrons get accelerated, subsequently. Although still in a highly experimental state, recent research indicates a high potential for various applications in basic physics, material sciences, and medicine. Capillary-discharge plasma wave-guides have been applied to confine the laser beam over a higher distance and further increase the electron energy and quality. A new approach for creating a laser waveguide, based on a small scale z-pinch, was recently proposed in collaboration between the Weizmann Institute of Science and the Jena Friedrich Schiller University, Germany. Due to the simple setup without capillary walls, the gas-puff z-pinch provides major advantages over capillary discharges, such as a longer life time. Furthermore, the investigation of the plasma wave-guide using radial observations, which is not possible in the capillary-discharge setup, can provide valuable information about its axial symmetry and the acceleration process itself. An introduction to the mechanism of LWFA and an overview of recent experimental results will be given. Preliminary experimental results of the investigation of a gas-puff z-pinch plasma as a wave-guide for LWFA will be presented.

Nanowires provide fascinating opportunities to study the effects of finite size, of shape anisotropy, and of surface chemical environment on the phase stability in ferroic materials[1] and on optical properties[2,3] and electronic transport within semiconductors. Moreover the integrating of different functional materials within individual nanostructures permits investigation of physical and functional properties where interfaces and surfaces play pivotal roles.
I shall first present our recent work in the proximal probe-based analyses and model calculation results involving ferroelectric polarizations within individual oxide nanowires, and within perovskite nanoshells surrounding selected other materials.[4-7] A range of unusual phenomena are observed, including finite-size evolution of the ferroelectric phase transition temperature with unexpected ferroelectric stability owing to surface chemical environment; enhancements in ferroelectric properties with finite size and with finite curvature; hysteretic current-voltage characteristic; and magnetically-tunable piezoelectricity and ferroelectric coercivity.
In the second part of my talk I shall discuss our recent work involving the electronic and optoelectronic transport within core-shell radial semiconductor heterojunction nanowires, including ultrafast response and hot electron transfer across co-axial interfaces.[8-10] Modulation of the transfer rates, manifested as a large tunability of the voltage onset of negative differential resistance and of voltage-current phase, is achieved using three different modes. The coupling of electrostatic gating, incident photon energy, and the incident photon intensity to transfer rates is facilitated by the combined influences of geometric confinement and heterojunction shape on hot-electron transfer, and by electron-electron scattering rates that can be altered by varying the incident photon flux, with evidence of weak electron-phonon scattering. Dynamic manipulation of this transfer rate permits the introduction and control of a continuously adjustable phase delay over a wide range within a single nanometer-scale device element