E. A. Romanov

Structure and Properties of ZnSe Nanocomposite Thin Films

The structure and electrophysical and optical properties of semiconductor ZnSe nanocomposite thin films are studied. These films are obtained by discrete thermal evaporation in an ultrahigh vacuum. ZnSe films are synthesized in various structural states in the condensation temperature range 2–200°C. The optical spectra of these films are studied in the visible region.

Structure and properties of ZnSxSe1−x thin films deposited by thermal evaporation of ZnS and ZnSe powder mixtures

Interest to ZnSxSe1−x alloys is due to their band-gap tunability varying S and Se content. Films of ZnSxSe1−x were grown evaporating ZnS and ZnSe powder mixtures onto SiO2, NaCl, Si and ITO substrates using an original low-cost method. X-ray diffraction patterns and Raman spectroscopy, show that the lattice structure of these films is cubic ZnSe-like, as S atoms replace Se and film compositions have their initial S/Se ratio. Optical absorption spectra show that band gap values increase from 2.25 to 3 eV as x increases, in agreement with the literature. Because S atomic radii are smaller than Se, EXAFS spectra confirm that bond distances and Se coordination numbers decrease as the Se content decreases. The strong deviation from linearity of ZnSe coordination numbers in the ZnSxSe1−x indicate that within this ordered crystal structure strong site occupation preferences occur in the distribution of Se and S ions. The behavior is quantitatively confirmed by the strong deviation from the random Bernoulli distribution of the three sight occupation preference coefficients of the strained tetrahedron model. Actually, the ternary ZnSxSe1−x system is a bi-binary (ZnS+ZnSe) alloy with evanescent formation of ternary configurations throughout the x-range.

EXAFS SPECTROSCOPY STUDY OF THE ATOMIC STRUCTURE OF ZnS NANOCOMPOSITE THIN FILMS

The atomic structure of zinc sulfide films obtained by thermal evaporation in ultrahigh vacuum at condensation temperatures of −100°C, −50°C, and 0°C was investigated. Structural states were assessed by means of X-ray diffraction and atomic force microscopy. Fourier transform was used to study the local atomic environment and acquire the structural information (interatomic distances and coordination numbers) by zinc K edge EXAFS spectroscopy.

Structure and properties of nanocrystalline ZnS and ZnSe films

The influence of the condensation temperature on the structure and optical properties of ZnS and ZnSe films is studied. The presence of the hexagonal phase, along with the cubic, is revealed in films deposited on the cleaved NaCl facet. The appearance of the hexagonal phase is explained by the mechanical stress produced at the film-substrate interface.

Characterizing ZnS x Se (1 − x ) films of various compositions via EXAFS spectroscopy

ZnSxSe(1 − x) (x = 0.36, 0.68, and 0.73) films of various compositions are prepared by the thermal deposition of a mixture of zinc sulfide and zinc selenide powders in ultrahigh vacuum. It is shown that the produced films and the source materials are close in chemical composition. The crystal structure of the films is studied via X-ray diffraction. The local atomic environment of selenium and zinc atoms is studied by means of EXAFS spectroscopy.