Raman spectroscopy under pressure in semiconductor nanoparticles

Abstract

A brief survey of recent high-pressure Raman investigations and associated studies of nanoparticle systems is given, and the consequences for understanding the vibrational properties and stability of these systems are reviewed. The results of new pressure-Raman experiments on colloidal ZnSe nanorods, highpurity bulk 68 Zn 76 Se crystals, and colloidal InP/CdS core/shell nanoparticles are presented. The nanorod and bulk ZnSe spectra are compared for similar pressure cycles. Evidence is found for the early stages of nucleation of the zincblende-rocksalt transition in the bulk crystals, and for the effects of non-uniform surface contact forces in the nanorod ensemble. Similarities and differences between the post-transition spectra of both types of samples are discussed. The InP/CdS core/shell nanoparticles exhibit a structured Raman line-shape that contains contributions from LO-and TO-like modes of the InP cores and from an overlapping manifold of CdS shell modes. Our results indicate that pressure acts to decrease this overlap. Cross-interface mechanical coupling is considered for describing the pressure-induced line-shape changes.

Structural stability and Raman scattering of ZnSe nanoribbons under high pressure

“…The broadening effect occurs at notable lower pressure (5-6 GPa) for the ZnSe nanoribbons than for the bulk ZnSe (normally ∼11 GPa). In the Raman spectra at lower pressure the broadening of the peaks can be associated with non-homogeneous surface strains or the effect of interparticle dipole-dipole coupling on phonon modes in the ZnSe nanoribbons [26]. In our experiments, as the pressure is gradually released to the lowest pressure, the original peaks corresponding to the ZB phase reappear, thus confirming the reversible transition between the ZB and RS phases for the ZnSe nanoribbons.…”

“…These Raman peaks related to the TO modes become very weak and invisible above 14.8 GPa. The related report [26] pointed out that the broadening of the peaks under pressure is higher than expected for the mixing of resonant three phonons. The possible reasons for this are attributed to disorders and localization in ZnSe associated with primary stages of nucleation of sixfold coordinated domains.…”

Luminescence of II-VI Semiconductor Nanoparticles

“…Among the several techniques used to characterize nanomaterials, Raman spectroscopy is considered to be the most powerful tool to get information on their vibrational and electronic structures [84,85]. In fact, Raman spectroscopy is based on the inelastic scattering of visible light by matter.…”

Structural and chemical disorder in semiconductors under pressure: Evidence in II–VI’s, role of photoactive defects, material predictions

“…The effects of applied hydrostatic pressure on the Raman spectra of semiconductors have been explored by many researchers over the years. [1][2][3][4][5][6][7][8][9] The findings have been important for determining the phonon dispersion ω(q), mode Gruneisen parameters !ðqÞ ¼ À@'n!ðqÞ=@'nV, multiphonon and phonon-plasmon interactions, and high-pressure phase changes in this important and large class of solids. Allied with high-pressure X-ray crystal-structure experiments, [10][11][12][13] and modern ab-initio theory, [14][15][16][17][18] this fruitful body of work is responsible for much of our current understanding of the intrinsic harmonic and anharmonic forces in these solids, their thermal expansion properties vs temperature, and the total energy and comparative stability of their high-pressure equilibrium structures.…”