Two-dimensional materials “beyond graphene”, including transition metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN), and 2D layers of pure elements, like phosphorus, have shown some exceptional properties. They offer great choices for various applications, ranging from electronics and optoelectronics to catalysis and energy storage. In the laboratories, these atomically thin samples are commonly obtained by mechanical exfoliation, i.e. the scotch-tape method, therefore are very limited in sizes. Larger samples can be produced by chemical vapor deposition growth, however, this often leads to many interfaces in the layered materials such as edges and grain boundaries, as well as dislocations and defects. Furthermore, in order to make an optoelectrical device out of these materials, it usually requires transferring the 2D material from its native growth substrate to the final device substrate that can be corrugated, and this step can introduce further distortions such as stresses and strains.
Understanding and managing interfaces and distortions in 2D materials are extremely important to maintain high performance in optoelectrical devices. These imperfections fortunately do not always degrade the material properties, but sometimes bring new physics and even useful functionality. In this project, we focus on defects and stress in light-emitting 2D layered materials. With the aid of various microscopic techniques, including AFM, STEM and STM, we will investigate how the imperfections in the 2D materials affect the performance of 2D based light-emitting devices such as LEDs and single photon emitters.
Please note that for PhD projects advertised as “awaiting funding”, we anticipate that the majority of decisions will be made in December 2019.