POPRYaHA D. Cluster-Modified Heterostructures with a Nanocluster Subsystem

The dissertation examines cases confirming the potential ability of nanoclusters to functionally modify the properties of a base material. The study of such cases makes it possible to develop criteria for identifying such systems as fundamentally new types of heterosemiconductors – clustered heterostructures. The work reveals the content of the category «cluster-modified materials» and defines their essential characteristics. Theoretical methods for modeling the atomic, electronic, and phonon structures of nanoclusters have been developed based on the electron density functional method, taking into account gradient expansion within the framework of the local electron density approximation. Parameterization using empirical parameters has been applied. The proposed approach minimizes research efforts in determining specific physicochemical characteristics while ensuring sufficient accuracy of results. This approach enables the study of dynamic processes using standard molecular dynamics procedures. Given the advantages of computer modeling of atomic dynamics in nanoclusters, the rehybridization of atomic orbitals during atomic rearrangements (in particular, relaxation) has been taken into account. It has been proven that there is a continuous «updating» of the interaction potential relative to the local energy minimum (instantaneous atomic configuration). Results have been obtained for the structuring of quantum levels, the distribution of electron density, and other physicochemical characteristics of silicon nanoclusters in an isolated state. The nanocluster subsystem is considered as a system of interconnected nanocluster fragments. It is shown that the mechanism of chemical bond formation between nanocluster fragments is realized through the molecular orbitals of the cluster center. It has been demonstrated that the nanocluster subsystem reproduces the properties of atomic nanoclusters, enables the study of their features at the intersection of real and model systems, provides a methodological database for solving practical problems of solid-state electronics, and reveals the relationship between different mechanisms of atomic nanocluster formation both in isolated states and in a matrix environment. Within this approach, the idea is proposed that the cluster center represents a cluster core, while atoms external to this core are defined as surface atoms of the cluster center. It is shown that integration schemes of the equations of motion in molecular dynamics calculations allow the application of interaction potentials between atoms and nanoclusters. Through comparison of real and model nanocluster centers, new possibilities for solving technological problems in solid-state semiconductor electronics, as well as improving the reliability and stability of microelectronic devices, have been identified. Theoretical methods for studying the formation mechanisms and physicochemical properties of silicon nanoclusters are proposed. Deviations from planarity in silicon nanocluster compounds are analyzed.A relatively high stability of pyramidal cluster centers is described, explained by specific electronic effects characteristic of silicon. The following features have been identified: a significant influence of the degree of polyvalency of interatomic bonds on nanocluster stabilization. It has been established that structural stability increases inversely with the number of double bonds. Optimization of cluster geometry has demonstrated the influence of substituents on the redistribution of electron density in various isomeric nanoclusters. It has been shown that the deformation energy of polyhedral structures (PS) depends on the number of planar rings: mechanical stress decreases as their number increases. The deformation energy decreases for polyhedral structures (PS) with an increasing number of four-atom rings. In such PS, certain bond angles n-АС approach the «ideal» value of 109.5° (typical for с-Si). However, further increase in the number of atoms leads to a sharp rise in mechanical stress due to deviations of bond angles in cyclic structures (120° for 6-АС and 135° for 8-АС) in n-АК from tetrahedral values. The lowest deformation energy is characteristic of structures containing five-membered rings in cross-section, confirming the possibility of synthesizing ten-atom PS. Methods for studying the heterojunction pCu₂S–nSi are presented, which are promising for solving problems in modern optoelectronics, particularly in the development of photovoltaic elements (PhE). The proposed technological method is based on the formation of mosaic-type textured copper sulfide layers. Modification of the properties of the pCu₂S–nSi heterojunction is achieved using quasi-metallic nanocluster centers (NCC).