Naidych B. Crystal structure and thermodynamic parameters of the thin-film condensates for II-VI, IV-VI systems.

The principles of constructing of the adequate models for clusters of IV-VI, II-VI semiconductor compounds and solid solutions based on the Pb-Cd-Te system in order to analyze the subsequent influence of the surface on the structural and thermodynamic characteristics of such materials were proposes in dissertation. The energy ΔE, enthalpy ΔH, Gibbs free energy ΔG, and entropy ΔS for the cubic phases of IV-VI compounds (PbS, PbSe, PbTe and Pb0.9Cd0.1Te) and sphalerite phases for the II-VI compounds (CdS, CdSe, CdTe) were calculated on the basis of the density functional method for wide temperature range (20-1000) K. Taking into account the prevailing directions of growth of Pb0,9Cd0,1Te thin films, the cluster models were proposed based on X-ray analysis data, and the corresponding surface reconstruction was performed. It was shown that an area of high electron density gradient arises around the cadmium atom, which gives rise the clearly express of ionic bonds.The electronic density distribution maps for the developed cluster models were constructed and its redistribution was established due to the formation of chemical bonds on the cluster surface.The temperature dependences of isochoric Cv and isobaric Cp molar capacities were investigated on the basis of comparison of values of experimental measurements and ab initio calculations.The relation of the contribution of internal atoms to the total number of atoms in the built clusters in the analysis of the electron density of states is determined. The increase of the contribution of surface atoms to the formation of electron-electron density with increasing the spatial dimensions of the cluster was shown. The key role of surface states for determining for the values of thermodynamic and energy characteristics of the studied semiconductor binary and ternary systems and the contribution of cadmium inclusions to the Pb-Cd-Te solid solution in the conduction band and valence band.The values of the minimum sizes of clusters for performing the calculations from the first principles and the correct description of the material characteristics.