Graphene-WS2 heterostructures by a lithography free method: their electrical properties

Abstract

We have developed a lithography free technique for the fabrication of two-dimensional (2D) material based heterostructures. We fabricated graphene-WS2 heterostructured devices using a transmission electron microscope grid as a shadow mask and their electrical transport characteristics were studied by electrical and magneto transport measurements. Graphene was directly deposited on a Si/SiO2 substrate by radio frequency plasma enhanced chemical vapor deposition. WS2 was synthesized by first depositing WO3 followed by sulfurization. The temperature dependence of the resistance and magnetoresistance are measured for graphene, WS2, and graphene-WS2 heterostructure. At low temperatures, the transport is found to follow the variable-range hopping (VRH) process, where logarithmic R exhibits a T−1/3 temperature dependence, an evidence for the 2D Mott VRH transport. The measured low-field magnetoresistance also exhibits a quadratic magnetic field dependence ∼B2, consistent with the 2D Mott VRH transport.