Bondar I. Effect of the crystal structure inhomogeneities on electronic properties of a hexagonal modification of niobium dichalcogenide and graphene

The presented thesis is focused on the study of peculiarities in low-temperature behavior of the graphene derivatives and hexagonal modification of niobium diselenide with the low-dimensional structure imperfections, identification of their common features and potentialities for a controlled tuning of their electronic properties in smart applications. Structural analysis and numerical experiments have shown a close relationship between singularities on the measured temperature dependences of linear themal expansivities (LTE) and of calculated ratios of rms displacements (RMSD). In this way, novel information about atomic interactions in highly anisotropic materials can be obtained and verified. In addition, a comprehensive analysis of RMSD evolution with temperature allowed us to find the temperature ranges of planar stability in the materials under study and, thus, the condictions for nanoformations occurrence. For the first time, anisotropic expansion along different crystal lattice directions was analysed in layered crystals, constituted by both monoatomic planes, and multilayer “sandwiches”. Numerical experiment, using original computational technique, within a tight-binding approximation, has elucidated effect of next-to-nearest neighbour atomic coupling on electronic properies of graphene with vacancy imperfections, which is manifested in evolution of the local densities of states (LDOS) of carriers due to formation of dangling bonds at vacancies. It was also shown, that step-edges in the thin graphene nanofilms result in growth of LDOS near Fermi level.