M. Ya. Valakh

Resonant Raman scattering study of CdSe nanocrystals passivated with CdS and ZnS

CdSe nanocrystals (NCs) were obtained from cadmium sulfate and sodium selenosulfate in aqueous gelatin solutions. A near-bandgap emission of CdSe NCs was noticeably enhanced after passivation with CdS or ZnS. Resonant Raman scattering spectra of the passivated NCs revealed new peaks attributed to the formation of the sulfide shells around CdSe cores. The peaks observed for the CdSe/CdS core–shell NCs near 280 cm−1 were attributed to LO vibrations within a thin CdS passivating layer. Observation of the peak in the same frequency range for CdSe/ZnS is discussed within an assumption of alloying at the core–shell interface. Notable changes in the Raman spectra at different excitation wavelengths and shell parameters were attributed to the resonant and size-selective nature of the Raman process.

Polarized Raman scattering analysis of Cu2ZnSiS4 and Cu2ZnSiSe4 single crystals

The polarized Raman spectra of the Cu2ZnSnSe4 and Cu2ZnGeSe4 single crystals were measured for various in-plane rotation angles on the basal (1 1 2) crystal facet. The position of up to 15 (for Cu2ZnSnSe4) and 16 (for Cu2ZnGeSe4) Raman peaks was determined in the spectral region 50–300 cm−1. From the analysis of the experimental dependence of the intensity of the Raman peaks with the rotation angle, a symmetry assignment for most of the detected modes and an estimation of numerical values of Raman tensor elements were derived. The kesterite type structure of Cu2ZnSnSe4 and Cu2ZnGeSe4 single crystals was established by the quantity of the observed nonpolar A and polar B (TO+LO) symmetry modes.

Spectral features above LO phonon frequency in resonant Raman scattering spectra of small CdSe nanoparticles

We report unusual spectral features in the resonant Raman scattering spectra of colloidal CdSe nanoparticles as small as 2–3 nm. High-frequency shoulders of the longitudinal optical phonon peak and its overtones were observed and their dependence on the excitation wavelength, temperature, nanoparticle size, and surface passivation with ZnS shell studied. As the probable origin of the uncommon spectral feature the participation of acoustic phonons and manifestation of the density of surface-related vibrational states is discussed.

OPTICAL AND ELECTRON PARAMAGNETIC RESONANCE STUDY OF LIGHT-EMITTING SI+ ION IMPLANTED SILICON DIOXIDE LAYERS

Thermally grown SiO2 on Si substrates implanted with Si+ ions with a dose of 6×1016 cm−2 were studied by the techniques of photoluminescence, electron paramagnetic resonance (EPR), and low-frequency Raman scattering. Distinct oxygen-vacancy associated defects in SiO2 and nonbridging oxygen hole centers were identified by EPR. The luminescence intensity in the 620 nm range was found to correlate with the number of these defects. The low-frequency Raman scattering technique was used to estimate the average size of the Si nanocrystallites formed after the implantation and thermal annealing at T>1100 °C, which are responsible for the photoluminescence band with a maximum at 740 nm. The intensity of this band can be significantly enhanced by an additional treatment in a low-temperature rf plasma.

Optically Induced Structural Transformation in Disordered Kesterite Cu 2 ZnSnS 4

The kesterite-structured semiconductor Cu2ZnSnS4 is one of the most promising compound for earth-abundant low-cost solar cells. One of the complex problem on this way deals with its stoichiometry. In this work Raman spectra of Cu-rich Cu2ZnSnS4 crystals are discussed in connection with the non-stoichiometric composition and disordering within the cation sublattice of the kesterite. The shift of the main A-peak from 338 to 331 cm−1 and its broadening are attributed here to transition from the kesterite (I

Microscopic and optical investigation of Ge nanoislands on silicon substrates

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Structural transformations and silicon nanocrystallite formation in SiOx films

symmetry) to the disordered kesterite structure (I

The influence of shell parameters on phonons in core-shell nanoparticles: a resonant Raman study

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Resonant Raman study of phonons in high-quality colloidal CdTe nanoparticles

2m symmetry). It is shown that this transition may also be driven by an intense light, which could stimulate transformation of Cu+-ion to Cu2+-ions and facilitates generation of CuZn-defects on 2d-crystalographic positions.

Nanostructured Silver Substrates With Stable and Universal SERS Properties: Application to Organic Molecules and Semiconductor Nanoparticles

We investigate self-assembled nanoislands in heteroepitaxial GeSi systems by means of atomic force microscopy and micro-Raman scattering techniques. We show that the surface diffusion of Si atoms from the substrate to the islands is strongly enhanced when the temperature increases, giving rise to a wider stability range of pyramid-shaped volumes.