B. A. Weinstein

•   Effects of applied pressure on phonon and electron states in solids

•   High pressure structural phase-transitions in tetrahedral semiconductors

•   Pressure-induced deep defects, disorder, and electron localization in crystals

•   Photo-induced crystallization in amorphous Se and chalcogenide glasses

•   Anharmonic resonant phonon interactions in semiconductors

•   Studies of the above phenomena by Raman scattering, other spectral probes,

            and by novel diamond-anvil cell high pressure experiments

            In Professor Weinstein's research, Raman scattering, photoluminescence, and other visible and infrared spectroscopy experiments are focused on the phonon and electron excitations in semiconductor crystals, alloys, nanostructures, and glasses. Diamond-anvil cells are employed to probe the hydrostatic-pressure dependence of these excitations and to investigate the structural phase transitions in the different materials.  The most recent studies by Weinstein’s group have explored: correlation between pressure-softening of TA phonons and phase changes, pressure effects in the novel perovskite BaZrS3, and precipitate formation and plasticity under applied pressure in II-VI crystals. (See Selected Publications below.)

          Earlier work by Weinstein on phonons, anharmonic interactions, and phase changes in Group IV, III-V, and II-VI crystals led to an understanding of the effects of pressure on the dispersion of the optic- and acoustic- phonon branches in these materials across the Brillouin Zone. Subsequent research on the high-pressure phase changes in epitaxial multilayers revealed superpressing driven by interlayer constraints, behavior that bears on the growth (at 1 atm.) of metastable strained-layer systems.  Studies of intrinsic and defect electron states explored how applied pressure tunes the extended-localized nature of impurities in n-type ZnSe and of N-pairs in GaAs1-xNx, and how pressure enhances the lattice relaxation of Zn-vacancies in ZnS.  Another area of Weinstein’s interest has been the properties of chalcogenide glasses at both ambient and elevated pressures. Experiments on amorphous Se films show that photo-crystallization is promoted by as-grown interface strain, and studies on several As- and Ge- chalcogenide glasses and crystals find connections between the network dimensionality of bonding and photoelastic behavior.

          Professor Weinstein has made significant contributions to high-pressure experimentation by pioneering the use of the modern diamond-anvil cell for Raman scattering and other optical studies. He also advanced cryogenic pressure research, developing tunable low-temperature diamond-anvil cells, including an apparatus patented with R. J. Chen for far infrared magnetospectroscopy.