Enhancing exciton diffusion in monolayer W S2 with h- BN bottom layer

We investigated two-dimensional (2D) exciton diffusion in monolayer WS2 on both SiO2 and hexagonal boron nitride (h-BN) layers to identify the exciton diffusion enhanced by the h-BN bottom layer using spatially resolved photoluminescence imaging combined with time-resolved spectroscopy. The WS2 on the h-BN bottom layer shows an exciton diffusion coefficient of 38cm2/s, which is almost 1.7 times that of WS2 on the SiO2 layer. Electrostatic force microscopy confirms that the increase in the 2D exciton diffusion is mainly due to the reduction in the charge impurities and traps on the h-BN surface compared to the SiO2 surface.