Nanotek and Expo

Biography

Biography: Lun Dai

Abstract

Monolayer MoS₂ with fascinating mechanical, electrical and optical properties has generated enormous scientific curiosity and industrial interest. Hexagonal boron nitride (h-BN), an insulating isomorph of graphene with boron and nitrogen atoms occupying the two nonequivalent sub-lattices is relatively inert and expected to be free of charged surface states and dangling bonds. Moreover, h-BN possesses a smaller lattice mismatch (1.4%) with MoS₂. Therefore, using h-BN as substrate may provide a possibility of investigating intrinsic properties of monolayer MoS₂. In this work, we have devised and realized a high-yield and convenient method to synthesize monolayer MoS₂ directly on h-BN flakes via a dual-temperature-zone atmospheric-pressure chemical vapor deposition (CVD) method. Compared with that grown on SiO₂/Si substrate, the monolayer MoS₂ grown on h-BN exhibits enhanced photoluminescence (PL) and Raman signals as well as the smaller intensity ratio of E_2g to A_1g. Besides, its A_1g Raman mode exhibits clear stiffening, whereas its E_2g mode exhibits a negligible shift. We have calculated the PL intensity as function of both the h-BN thickness and the PL wavelength based on light ray propagation in multilayer structure. The theoretical analysis and experimental results suggest that the improved optical property of monolayer MoS₂ on h-BN results mainly from the weaker doping effect from the h-BN substrate, rather than the optical interference effect suggested previously.