Seminarium "Teoria i Modelowanie Nanostruktur"

Graphene, a two dimensional system exhibits exceptional electronic and physical properties, which have led to the extremely extensive research activities and wide range of proposed applications in nano-electronics and other fields. However, it has been recently predicted theoretically that other group IV elements (Si, Ge, Sn) can be stabilized in the form of honeycomb two-dimensional lattices and soon such materials have been really synthetized and silicene, germacene, and stanene have been born. Soon has been reported that the binary alloys of group IV elements (SiC, SiGe, etc.) can be also stabilized in a form of honeycomb monolayers. Motivated by these developments, we have undertaken extensive ab initio (in the frame work of the density functional theory) studies of cohesive and electronic properties of the whole plethora of the honeycomb monoatomic systems. We have employed the VASP numerical package to compute phase diagrams and electronic band structures of the following systems: Si-Si (silicene), Ge-Ge (germacene), Sn-Sn (stanene) and the binary alloys Si-C, Ge-C, Sn-C, Si-Ge, Si-Sn, and Ge-Sn. For the phase diagram calculations, we consider so-called high buckled and low buckled structures.The alloys containing C, Si-C, Ge-C, and Sn-C, have nearly flat low buckled equilibrium phase and the equilibrium energy of this phase is considerably lower than of the high buckled phase. It is in contrary to all other alloys where the energetic differences are rather small. It strongly suggests that such structures could be transformed into each other under suitable stress. Si-C, Ge-C, and Sn-C alloys have also large energy gap (roughly 2 eV), whereas all other systems have zero or minimal energy gap.