Two-dimensional (2D) hexagonal boron nitride (h-BN) plays a significant role in nanoscale electrical and optical devices because of its superior properties. However, the difficulties in the controllable growth of high-quality films hinder its applications. In this thesis, we focus on improving the quality of h-BN films with molecular beam epitaxy (MBE), and implementing the as-grown monolayer h-BN films in metal-insulator-metal (MIM) devices. In the first project, i.e., Chapter 2, we present a study of h-BN adlayer growth and provide a strategy towards eliminating these adlayers for the precise control of the number of 2D layers. By varying the growth parameters such as substrate property, nitrogen source composition, and substrate carburization time, we found that the adlayer growth can be controlled by controlling the nucleation and intercalation processes, which is achieved by engineering the defects and impurities on substrate and the activeness of the h-BN edges.
In the second project, i.e., Chapter 3, we report a study of 2D h-BN growth on carburized Ni substrates. It was found that the carburization of Ni substrates with different surface orientations leads to different kinetics of h-BN growth. While the carburization of Ni (100) enhances the h-BN growth, the speed of the h-BN growth on carburized Ni (111) reduces. As grown continuous monolayer h-BN films are used to fabricate Ni/h-BN/Ni MIM devices, which demonstrate a high breakdown electric field of 12.9 MV/cm.
In the last project, i.e., Chapter 4, we report an effective method to synthesize single-crystal monolayer h-BN films. We discovered that electropolishing plays an important role in drastically increasing the speed of h-BN film growth. 1-in2 monolayer single-crystal h-BN films are obtained within 1 hour by MBE. Robust nano capacitors were fabricated using as grown monolayer h-BN films. The nano-capacitance effect and tunneling current mechanism were studied in detail, and the ‘effective distance’ concept is introduced to explain the quantum phenomenon in the van der Waals MIM devices using atomically thin dielectric h-BN films.