Off‐resonance Raman analysis of wurtzite CdS ground to the nanoscale: structural and size‐related effects

Abstract

Different techniques were used to follow the transformation of CdS platelets during grinding and under hydrostatic pressure. X-ray diffraction and transmission electron microscopy revealed that the platelets included zinc blende (cubic) CdS nanodomains dispersed in a wurtzite (hexagonal) single-crystalline matrix. Extended grinding led to a decrease of the grain size and to a progressive transformation of the hexagonal stacking into a cubic one. The same phase transition was observed up to 9 GPa under hydrostatic pressure.Off-resonance Raman spectra collected at different stages of the transition led us to connect band groups that were usually overlooked (in resonance conditions) or considered separately. They all probe the stacking disorder and their intensity can be related to the density of stacking faults. Off-resonance Raman spectroscopy offers a way of probing the optical properties of CdS (and, more generally, layered semiconductors) as a function of the structure and of the confinement of vibrations by structural defects.

Room temperature ferromagnetism in Mn doped CdS nanowires

“…Additional Raman peaks at 280 cm À1 and 900 cm À1 have also been observed for Mn doped CdS nanowires, the farmer can be attributed to the surface phonon mode and the later can be attributed to multiphonon Raman scattering (3LO) of CdS. The assignment of the Raman scattering peaks is in great agreement with the earlier reports [38][39][40][41][42][43]. It is significant to note that the intensity of multiphonon features can be efficiently enhanced and tuned by increasing the Mn doping concentration in CdS:Mn nanowires.…”

A Density Functional Theory Study of Raman Modes of Hydrogenated Cadmium Sulphide Nanoparticles

“…The study of the size dependence of CdS NPs is an exciting research area since it provides tunable physical and chemical properties. However, few reports are available on the experimental study of vibrational dynamics of CdS [22][23] and the literature is still lacking on its counterpart using density functional theory-based calculations.…”

Phonon Spectra of Small Colloidal II-VI Semiconductor Nanocrystals

“…No trace of 2TO or 2SO band was detected, what can be the result of the dominance of Fröhlich mechanism in electron-phonon coupling in II-VI compounds. The resonant phonon Raman spectrum of NCs smaller than 2 nm is shown to be dominated by a broad feature similar to the SO mode of larger NCs or phonon density of states of a bulk crystal.The understanding of the phonon spectrum of semiconductor nanocrystals (NCs), electron-phonon coupling (EPC), dependence of the phonon spectra on the NC size, surfacebound moieties, and extended environment is of a large fundamental and application significance [1][2][3][4][5][6][7][8][9][10][11] due to the determinant role phonons play in the optical and electrical properties of semiconductor nanostructures [12,13]. Though a number of in-depth studies have addressed the phonon spectra of colloidal [14][15][16][17][18][19][20], glass-embedded [21][22][23] NCs, and epitaxial nanostructures [24][25][26], a significant divergence of the results exists concerning both the nature of the modes and their response to such factors as size, surface conditions, properties of the hosting medium and so forth.…”