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

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 ∼B ², consistent with the 2D Mott VRH transport.