2D nanocrystal heterostructures - novel production methods and device applications

Abstract

This thesis primarily investigates an approach to realise a variety of functional heterostructures based on van der Waals (vdW) nanocrystalline lms produced through the mechanical abrasion of bulk powders. This novel production technique represents the next step in the evolution of scalable production routes which can take advantage of vdW materials and their heterostructures whilst preserving the high electronic and optical quality of the individual crystals. To demonstrate the e cacy of this method, a slew of di erent device architectures are developed, including photovoltaics, triboelectric nanogenerators, strain sensors, capacitive pressure sensors and thermistors. All exhibit either superior or comparable performance to analogous systems within the literature, and show great potential for future optimised vdW heterostructure devices. The secondary focus of this thesis is the incorporation of talc dielectrics as a potentially clean and atomically at alternative substrate to hexagonal boron nitride (hBN) for few-layer transition metal dichalcogenide (TMDC) eld-e ect transistors (FETs) and for excitonic TMDC monolayers. It is found that talc-based TMDC FETs show small hysteresis which does not strongly depend on back gate sweep rate as well as have negligible leakage current for the dielectric thicknesses studied. Furthermore, it is found that photoluminescent (PL) emission from monolayer TMDC materials using talc as a substrate have narrow linewidths reduced to as little as 10 meV which, in addition to the high intensity PL emission, suggests that talc can be used to preserve the intrinsic excitonic properties of the TMDC. Additionally, the spontaneous doping properties of talc allow for the room-temperature observation of trions in all of the TMDC/talc devices studied.