Electronic and Transport Properties of Novel Two Dimensional Materials

The family of 2D layered materials has gained enormous attention of materials scientists and researchers from other fields of science. This stems from the fact that 2D monolayers (1Ls) can exhibit remarkably different electronic properties than their bulk counterparts. Moreover, stacking different 1Ls, results in yet different electronic properties than these of the 1Ls. Recently, among others, van der Waals heterostructures (vdW HS) of transition-metal dichalcogenides (TMDC) have been extensively studied due to their type-II band alignment.
This thesis summarizes four different theoretical studies on layered 2D materials. The first study investigates the potential existence of a new family of bulk layered materials with chemical formula XY3 (where X = group 14; Y = group 15). The low cleavage energies indicate the potential exfoliation as mono- and bi- layers (2Ls), where most of the exfoliated layers are thermally and dynamically stable. Interestingly, many 1Ls and 2Ls show strong quantum confinement and turn into indirect semiconductors, unlike bulks which are all metals. Such metal to semiconductor transition was previously known for noble-metal dichalcogenides. Next study shows one of the potential applications of XY3, that is, single-material logical junction for gas sensing applications. A device that consists of metallic multilayers (3L) as electrodes and semiconducting 1L as scattering region. To do so, one of the exemplary materials (SnP3) was picked to construct a single-material device. The results combining density functional theory (DFT) and non-equilibrium Green’s function (NEGF) calculations revealed that SnP3 is an ideal material for gas sensing applications, especially for poisonous NO gas molecules. For NO molecules, this device showed a negative differential resistance (NDR) at small bias voltages.
Moreover, electronic properties of vdW TMDC HS were investigated for the HS having up to six layers. In this part, it was essentially studied how the electron and hole states in heterobilayer (HBL), namely MoS2/WSe2, will change as a function of additional electron/hole layers. We found that additional electron layers will result in equal delocalization of electron states among all layers forming conduction bands. However, additional hole layers do not alter the holes states distribution much, i.e., hole states stay localized at HBL+1L (WSe2).
The last study, in this thesis, focused on understanding the interplay between the so- called atomic collapse states and moiré potential in twisted bilayer graphene (tBLG) systems. It was found that individual graphene layers did host collapse states. However, moiré potential in tBLG may destroy the collapse states, although tBLG systems have similar band dispersion as in graphene.
The knowledge acquired from the findings presented in this thesis can provide new potential candidates as well as some helpful insights into electronic properties of existing layered materials, for their applications in the future nano(opto)electronic devices.