Chalcogenide-based van der Waals-layered materials for enhanced electronic and electromechanical properties

Abstract

Since the successful isolation of graphene via mechanical exfoliation at room temperature, other van der Waals (vdW)-layered or quasi-2D materials have gained significant interest in the scientific and technological communities. Quasi-2D (q2D) materials have been shown to unlock a wide variety of unusual and useful thermoelectric, electronic, optoelectronic, electromechanical, and sensing properties (among others) offering several advantages over conventional bulk 3D materials. From an application standpoint however, between the large band gap of hexagonal boron nitride and the zero band gap of graphene, the semiconductor space is mostly limited to Transition Metal Dichalcogenides (TMDCs) - which are semiconductors. There are several ways to improve the diversity of semiconducting 2D or q2D materials, which can lead not only to new materials, but to new phenomena and applications as well; these include alloying, doping, layering (heterostructuring), or discovering and manufacturing new 2D or q2D materials altogether. In the quest for new, versatile, and multi-functional q2D materials, this thesis presents computational studies based on vdW-corrected density functional theory addressing several directions of increasing the range of electronic and electromechanical properties of chalcogenide-based 2D or q2D materials. These studies pertain to group IV monochalcogenides, bilayer and bulk TMDC heterostructures, and surface-doped TMDCs, and have led, respectively, to (i) the discovery of 39 new and potentially synthesizable monochalcogenides, (ii) understanding the range of band gaps and piezoelectric coeffecients achievable in bilayer TMDCs and the effects of interlayer registry, and (iii) elucidating the physical origins of the p-type doping measured in molybdenum ditelluride in ambient air