No abstract

The Raman spectra of surface regions of bulk Cu2ZnSnS4 (CZTS) samples with different Cu and Zn cation content were obtained and the differences in the spectra are attributed to statistical disorder effects in the cation sublattice. This disorder in the Cu and Zn sublattices may initiate a change of the crystal symmetry from kesterite‐type $({I\bar 4})$ to $({I\bar 42m})$ space group. The investigated CZTS crystals grown at high temperature are characterised by the co‐existence of regions with different composition ratio of Cu/(Zn + Sn) which results in kesterite and disordered kesterite phases. The presence of a disordered phase with ${I\bar 42m}$ symmetry is reflected in the appearance of a dominant broadened A‐symmetry peak at lower frequency than the peak of the main A‐symmetry kesterite mode at 337 cm–1. We suppose that due to a small energy barrier between these phases the transition from one phase to the other can be stimulated by optical excitation of Cu2ZnSnS4. The analysis of the Raman spectra measured under different excitation conditions has allowed obtaining first (to our knowledge) experimental evidence of the existence of such optically induced structural transition in CZTS. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Resonant Raman scattering spectra of glass-embedded CdS 1−x Se x nanocrystals are measured and complemented with TEM and optical absorption as well as photoluminescence data. The selectivity of the resonant Raman process not only for the size, but also for the composition of nanocrystals within the ensemble, is directly observed in the dependence of phonon band frequency, linewidth and shape on the excitation wavelength.

The Raman spectra of CdS 1-x Se x nanocrystals, embedded in a borosilicate glass matrix, are studied, CdSlike and CdSe-like LO phonon frequencies being used to determine the nanocrystal composition. The Raman lineshape is analyzed taking account of confinement-related phonons with nonzero wavevector, surface phonon modes, glass matrix pressure and disorder effects.

Effects of tin doping on crystallization of amorphous silicon were studied using Raman scattering, Auger spectroscopy, scanning electron microscopy, and X-ray fluorescence techniques. Formation of silicon nanocrystals (2–4 nm in size) in the amorphous matrix of Si1−xSnx, obtained by physical vapor deposition of the components in vacuum, was observed at temperatures around 300 °C. The aggregate volume of nanocrystals in the deposited film of Si1−xSnx exceeded 60% of the total film volume and correlated well with the tin content. Formation of structures with ∼80% partial volume of the nanocrystalline phase was also demonstrated. Tin-induced crystallization of amorphous silicon occurred only around the clusters of metallic tin, which suggested the crystallization mechanism involving an interfacial molten Si:Sn layer.

We discuss the Raman scattering of thermally oxidized gallium selenide (GaSe) and indium selenide (InSe) single crystals. It has been established that the oxidation mechanisms of these compounds are rather different. For InSe, an increase of the oxidation temperature leads to the formation of (SeO 4 ) complexes. For GaSe, it is characteristic that only Ga 2 O 3 is formed as an oxygen-containing phase during the oxidation. The presence of the Me 2 Se 3 phase (where Me is Ga or In) in its own oxide is common for both of the semiconductors.

A Raman spectroscopic study of Cu2ZnSnS4 (CZTS) nanocrystals (NCs) produced by a “green” synthesis in aqueous solutions is reported.

The aim of this study is to establish reliable spectroscopic fingerprints of compounds that may form as secondary phases in Cu2ZnSnS4 (CZTS) nanocrystals (NCs) synthesized by “green” colloidal chemistry directly in aqueous solutions or during post-processing of NC films for photovoltaic applications. For this purpose, we investigated a series of binary and ternary compound NCs synthesized under the same conditions as the quaternary CZTS NCs. The capabilities of combined Raman and X-ray photoemission (XPS) spectroscopy are used to identify these compounds formed separately and define spectral fingerprints for distinguishing them as possible secondary phases in the spectra of CZTS NCs. Besides the conventional analysis of element ratios and chemical shifts of the core-level peaks in the XPS spectra, the careful analysis of Auger lines and modified Auger parameters is applied to distinguish otherwise similar spectral contributions of different compounds. In the case of Cu x S NCs, the binding energy separation between the Cu2p3/2 and S2p3/2 core-levels is used as the additional fingerprint. As a criterion of a certain crystal structure in Raman spectroscopy, we rely not only on frequency positions of particular phonon modes but also on selective probing of different compounds at different (resonant) excitation wavelengths. The reasons of controversial previous reports on Raman spectra of Cu x S are revealed, and characteristic Raman spectra of Sn-poor Cu–Sn–S and Sn-poor Zn–Sn–S are proposed. For Cu–Zn–S, a mixture of Cu x S and ZnS is formed under the given mild conditions rather than ternary compounds or alloys.