Integrated Nanostructured Systems

Optical and high-pressure studies of the vibrational and electronic properties of semiconductor nanostructures; effects of nanoscale geometry on phase stability; confined effects and coupled excitations for lattice modes and electronic levels; impurity and defect states in confined geometries.

In recent years, Weinstein’s group has investigated the effects of nanoscale geometry on the stability of semiconductor systems against high-pressure structural phase transitions. The systems studied have ranged from GaAs/AlAs superlattices to ZnSe nanoparticles and nanorods. It is found that the phase transitions generally commence in nanoscale domains having a minimum nucleation size. In ZnSe the nucleation process results in similar disorder in both bulk and nanoparticle systems.

Anharmonic coupling of optical phonon modes is another area of current interest. Pressure is used to tune the coupling between different modes. Hybrid nanoparticle systems, e.g., InP/CdS, have been studied because of the possibilities they present for cross interface anharmonic coupling. The effects of surfactant and disorder at nanoparticle surfaces in enhancing mode mixing are also of interest. Other studies of phonon anharmonicity have been carried out on bulk ZnS and CuI.

Other research includes work on dilute nitrogen GaAlAs:N alloys in bulk and confinement structures. Particularly, studies of the effects of pressure on the extent of localization of N-pair states were carried out. The initial localization is extreme and on the nanoscale, but under hydrostatic compression certain states selected by energy become extended.

High resolution Raman scattering system; diamond-anvil pressure cells for room temperature and cryogenic work; hybrid micro-macro optical probing capability; wire-bonder.

B. A. Weinstein, "Spectroscopy under Pressure in Semiconductor Nanoparticles", Physica Status Solidi (b), 244(1), 368-379 (2007). http://dx.doi.org/10.1002/pssb.200672542

B. A. Weinstein, S. R. Stambach, T.M. Ritter, J. Maclean, D. Wallis, "Evidence of Selective De-localization of N-pair States in Dilute GaAs_1-xN_x", Phys. Rev. B68, 035336(1-9) (2003). http://prola.aps.org/abstract/PRB/v68/i3/e035336

I. L. Kuskovsky, G. F. Neumark, J. G. Tischler and B. A. Weinstein, "Resonant Donor Defect as Cause of Compensation in p-type ZnSe: Photoluminescence under Hydrostatic Pressure", Phys. Rev. B, Rapid Comm. 63, 161201(1-5), (2001). http://prola.aps.org/abstract/PRB/v63/i16/e161201

V. Iota and B. A. Weinstein, "Effects of Pressure on the Zn Vacancy in ZnSe: Essential Role of Lattice Relaxation for a Basic C_3v Defect", Phys. Rev. Lett. 81, 4955-4958 (1998). http://prola.aps.org/abstract/PRL/v81/i22/p4955_1

L.J. Cui, U.D. Venkateswaran, B.A. Weinstein and F.A. Chambers "Polymorphic Stability of AlAs/GaAs Superlattices at High Pressure", Phys. Rev. B45, 9248-9265 (1992). http://prola.aps.org/abstract/PRB/v45/i16/p9248_1

A. Patra, R.E Tallman, B.A. Weinstein, "Effect of Crystal Structure and Dopant Concentration on the Luminescence of C^r3 in Al₂O₃ Nanocrystals", Optical Materials 27, 1396-1401 (2005). doi:10.1016/j.optmat.2004.10.002

J. Serrano, A. Cantarero, M. Cardona, N. Garro, R. Lauck, R. E. Tallman, T. M. Ritter, and B. A. Weinstein, "Raman Scattering in β-ZnS", Phys. Rev. B69, 014301(1-12) (2004). http://link.aps.org/abstract/PRB/v69/e014301

S.A. Choulis, T.J.C. Hosea, S. Tomic, M. Kamal-Saadi, A. Adams, E. O’Reilly, P. Klar, B.A. Weinstein, "Electronic Structure of In_yGa_1-yAs_1-xN_x/GaAs Multiple Quantum Wells in Dilute-N Regime from Pressure and k.p Studies", Phys. Rev. B66, 165321-29 (2002). http://prola.aps.org/abstract/PRB/v66/i16/e165321

T. M. Ritter, B. A. Weinstein, R. M. Park and M. C. Tamargo, "Emergence of Deep Levels in n-Type ZnSe Under Hydrostatic Pressure" Phys. Rev. Lett. 76, 964-967 (1996). http://prola.aps.org/abstract/PRL/v76/i6/p964_1

R. Ziolo, E. Giannelis, B. A. Weinstein, M. O’Horo, B. Ganguly, V. Mehrotra, M. Russell, D. R. Huffman, "Matrix-mediated Synthesis of Nanocrystalline ggr-Fe₂O₃: A New Optically Transparent Magnetic Material", Science 257, 219-223 (1992). http://www.sciencemag.org/cgi/reprint/257/5067/219.pdf