Raman spectroscopy under pressure in semiconductor nanoparticles

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, high-purity bulk ⁶⁸Zn⁷⁶Se 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.