Influence of defects and impurities on the properties of 2D materials

Abstract: Graphene, the thinnest material with a stable 2D structure, is a potential alternative for silicon-based electronics. However, zero band gap of graphene causes a poor on-off ratio of current thus making it unsuitable for logic operations. This problem prompted scientists to find other suitable 2D materials. Creating vacancy defects or synthesizing hybrid 2D planar interfaces with other 2D materials, is also quite promising for modifying graphene properties. Experimental productions of these materials lead to the formation of possible defects and impurities with significant influence in device properties. Hence, a detailed understanding of the effects of impurities and defects on the properties of 2D systems is quite important.In this thesis, detailed studies have been done on the effects of impurities and defects on graphene, hybrid graphene/h-BN and graphene/graphane structures, silicene and transition metal dichalcogenides (TMDs) by ab-initio density functional theory (DFT). We have also looked into the possibilities of realizing magnetic nanostructures, trapped at the vacancy defects in graphene, at the reconstructed edges of graphene nanoribbons, at the planar hybrid h-BN graphene structures, and in graphene/graphane interfaces. A thorough investigation of diffusion of Fe adatoms and clusters by ab-initio molecular dynamics simulations have been carried out along with the study of their magnetic properties. It has been shown that the formation of Fe clusters at the vacancy sites is quite robust. We have also demonstrated that the quasiperiodic 3D heterostructures of graphene and h-BN are more stable than their regular counterpart and certain configurations can open up a band gap. Using our extensive studies on defects, we have shown that defect states occur in the gap region of TMDs and they have a strong signature in optical absorption spectra. Defects in silicene and graphene cause an increase in scattering and hence an increase in local currents, which may be detrimental for electronic devices. Last but not the least, defects in graphene can also be used to facilitate gas sensing of molecules as well as and local site selective fluorination.