Electronic structure of multilayer allotropes of 2D silicon carbide
The transition from bulk material to low-dimensional structures (2D, 1D) is accompanied not only by the appearance of new electrophysical properties, but also by a change in the symmetry of the elementary lattice caused by the violation of long-range order in one or several crystallographic directions. Therefore, of a particular interest is the study of the phenomenon of allotropy in 2D and quasi-2D crystals. In the present work, on the basis of quantum chemical calculations from first principles, we studied the size-depended allotropy and the structure-dependent properties of low-dimensional silicon carbide (SiC), obtained on the basis of SiC monolayers with a stoichiometric composition of 1:1. It has been established that 2D allotropes of SiC form a family of semiconductor structures with a different band structure (both direct-band- and non-direct-band-semiconductors) and charge properties. A deeper analysis of the geometric and energy parameters made it possible to establish the possibility of the sustainable existence of four topological 2D SiC types, differing in the way and order of alternation of layers, and the allotropic modifications obtained are not characteristic of bulk material. Accounting for the spatial separation of the charge as a result of the formation of a covalent polar bond between the carbon and silicon atoms that made up the structure allowed detecting the formation of an effective charge within the monolayer. After the analysis of the magnitude and sign of the specific surface charge, a correlation was established between this parameter and the geometry of the optimized structure. Thus, taking into account the charge properties of 2D SiC, it is possible to trace structural changes in the system, identify a specific allotrope, and establish the order in which the monolayers are laid. Characteristic patterns in the charge distribution are a prerequisite for the production of composite materials based on 2D allotropes of SiC.