a b s t r a c tAtomically thin MoS 2 /graphene vertical heterostructures are promising candidates for nanoelectronic and optoelectronic technologies. In this work, we studied the optical and electronic properties of n doped single layer MoS 2 on p doped bilayer graphene vdW heterostructures. We demonstrate a non-uniform strain between two different orientation angles of MoS 2 monolayer on top of epitaxial bilayer graphene. A significant downshift of the E 1 2g mode, a slight downshift of the A 1g mode, and photoluminescence shift and quenching are observed between two MoS 2 monolayers differently oriented with respect to graphene; This could be mostly attributed to the strain-induced transition from direct to indirect bandgap in monolayer MoS 2 . Moreover, our theoretical calculations about differently-strained MoS 2 monolayers are in a perfect accordance with the experimentally observed behavior of differently-oriented MoS 2 flakes on epitaxial bilayer graphene. Hence, our results show that straininduced bandgap engineering of single layered MoS 2 is dependent on the orientation angle between stacked layers. These findings could be an interesting novel way to take advantage of the possibilities of MoS 2 and deeply exploit the capabilities of MoS 2 /graphene van der Waals heterostructures.© 2016 Elsevier Ltd. All rights reserved.Ever since the technique to isolate stable single-layer graphene was reported, the study of two-dimensional (2D) materials has gained a lot of research interest. Hence, a broad family of 2D materials like graphene, transition metal dichalcogenides (TMDCs), and topological insulators have been explored so far [1]. For the sake of exploring their fundamental interfacial interactions and conceiving novel electronic functionalities, vertical heterostructures composed of 2D materials stacked together by van der Waals (vdW) forces have attracted a great attention lately [2]. Among these combined structures, the MoS 2 /graphene heterostructure, among other heterostructures combining graphene with different layered 2D materials [3], shows a promising potential for next generation nanoelectronic and optoelectronic devices thanks to the outstanding carrier mobilities on one hand and the excellent optical responsivities on the other hand [4e6].However, research work about the structural quality, the band alignment and the optical emission properties of MoS 2 /graphene or graphene/MoS 2 vdW heterostructures are still limited. The exploration of such characteristic properties are fundamental to make possible the assembling of MoS 2 with graphene, pave the way for the realization of a well-ordered MoS 2 /graphene structure, and enable opportunities for a wide spectrum of optoelectronic functionalities. Inspirations of this present work arise from the fact that some of the theoretical calculations have predicted the crossover between a direct and indirect bandgap of MoS 2 originating from the modification of interlayer orientation [7e9]. Since the properties of MoS 2 /graphene heterostructure depend st...