Research in Dr.Weinstein's laboratory involves experimental studies of high-pressure optical properties related to the intrinsic and defect states in semiconductor materials - particularly IV, III-V and II-VI crystals, alloys, and nanostructures composed of single and multiple constituents. Electronic and vibrational excitations are probed using a number of techniques, including Raman scattering, photoluminescence, and other visible/IR spectroscopies carried out as a function of pressure up to ½ megabar (7.5 million psi) using specialized room temperature and cryogenic diamond-anvil cells. Phenomena of interest include: solid-solid phase transitions in bulk crystals, multilayers, and other types of nanostructures; coupled phonon and electron excitations; confinement and interface effects; disorder and localization in dilute alloys; far-infrared magnetospectroscopy of 2D electron and impurity states. Some recent and on-going projects deal with pressure-induced de-localization of N-pair states in dilute GaAs_1-xN_x alloys; electron-phonon and phonon-phonon coupling in hybrid II-VI/III-V colloidal nanoparticles; pressure-tuning of resonant anharmonicity and phonon lifetimexss in ZnS, ZnSe, and CuI; and, most recently, the effects of pressure on excitonic transitions in the organic semiconductor α-PTCDA (perylene tetracarboxylic dianhydride).

Current Work

Recent efforts have been directed towards researching anharmonic effects in different isotopic copositions of ZnS and ZnSe. Below is a graph from a poster presented at HPSP-XI in San Fransisco in 2004. To see the full power point poster click here

This figure shows the Raman Spectra of 68Zn32S from 50 - 800 cm-1. The yellow shadded region shows the original region of interest. More recent measurements where preformed to look at the changes in the difference mode line-shape.

Caught in the Act: Phase transition of a ⁶⁸Zn³²S crystal from a large- to a small- band gap semiconductor at 152kbar (2.3 million lbs./sq. in.) inside the sample chamber of a diamond anvil cell. Note diamond facets.

These two photos show a piece of PTCDA (perylene tetracarboxylic dianhydride) held in the Diamond anvil cell at Room Tempature. The pressures are at 1 kbar and 15 kbars measured using the ruby's R1 line. There is an obvious change in length between the two pressures. This change in length can be used to calculate the bulk modulus.

P = 1 kbar at T = RT	P = 15 kbars at T = RT.

In these figures we see the difference in the raman spectra between Bulk and nano silicon. Where the Bulk spectrum shows a sharp peak at 520 cm^-1 the spectra from the nano particles has a peak that is asymetric with a higher linear background to lower energy.

Raman spectra of nano Si particles taken at atmospheric pressure and room tempature.	Raman spectra of bulk Si taken at atmospheric pressure and room tempature.

These spectra where taken by Alham Hmadouch in our lab as an REU student in 2004.


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