The dissertation is devoted to the study of local chemical, adsorption and mechanical functionalization of two-dimensional structures based on graphene and black phosphorene. Methods of density functional theory and pseudopotential from the first principles have been used.
Two-dimensional semiconducting materials represent the thinnest semiconductors, holding novel properties, such as the absence of surface dangling bonds, sizable band gaps, high flexibility, and ability of artificial assembly. However, there are still some obstacles prohibiting the practical applications of two-dimensional semiconducting materials, one of which is to improve the device performance. Improving the properties of two-dimensional materials is an important step in implementing their multifunctional applications. Therefore, to well understand the factors affecting the device performance is highly desired. In order to identify new factors influencing the electronic and photonic properties of two-dimensional semiconductor materials by computational experiment using the author's program code, the following investigations were performed: calculated the spatial distributions of valence electron densities, the densities of electron states, the band gap widths, the Coulomb potentials along selected directions, the charge values in materials in regions of different sizes, the dielectric matrices, the macroscopic permittivities and absorption spectra.
It is established that the combination of non-functionalized and functionalized sections of graphene according to a pre-planned pattern in one structure gives controlled changes of electronic properties.
The redistribution of electric charge in the plane of graphene-like combined C/CH and C/CF structures with the formation of regions of different sign is stated.
It is determined that the fluorination process as a functionalization effect causes the redistribution of electric charge between separate sections of two-dimensional combined C/CFH structures with different concentrations of fluorine atoms.
It is shown that as the degree of fluorination increases, the two-dimensional combined C/CFH structure as a photonic crystal weakens the passage of an electromagnetic wave in the direction of perturbation.
The peak wavelength in the adsorption spectrum of a two-dimensional combined C/CH structure as a photonic crystal at 0% fluorination in the direction corresponding to the soft X-ray region (0,82 nm) was estimated. Subsequent fluorination process leads to a shift of the peaks in the region of ultraviolet radiation.
It is established that the effect of static pressure on the combined C/CH structure as a photonic crystal leads to the rearrangement of the electron density in the direction of covalent C-H bonds, which causes a change in the band gap, anisotropy of dielectric properties at different directions of the electric field of the perturbing electromagnetic wave and shift of peaks in the absorption spectrum.
It is determined that the bend deformation as a functionalization effect leads to an increase in the charge difference in the combined curved C/CH, C/CF, C/CCl structures and to an increase of the band gap width compared to the undeformed ones.
It is recorded that the functionalization of the black phosphorene monolayer by urea molecules leads to the redistribution of electric charge and the formation of areas of different sign.
The nonmonotonic nature of the change in the band gap of the black phosphorene monolayer depending on the adsorption distance of urea molecules was revealed. This affects its conductivity, which can be changed by controlling the localization of the adsorbed molecules.
Keywords: functionalization, two-dimensional semiconductor materials, photonic crystal, graphene, black phosphorene, electronic properties, photonic properties, electron density functional, pseudopotential from the first principles.
