Environmentally Controlled Charge Carrier Injection Mechanisms of Metal/WS₂ Junctions

Here we report on a novel, noninvasive route for operando tailoring of the charge transport properties of metal/WS₂ contacts without the negative impacts to two-dimensional materials arising from conventional doping methods. The doping level of thin WS₂ flakes supported on insulating mica is susceptible to local charge variations induced by the presence of a hydration layer between mica and WS₂. We demonstrate, via the use of several complementary scanning probe techniques, that the direct control of the state and thickness of this intercalated water film controls the charge injection properties of Pt/WS₂ nanocontacts. A switch from unipolar to ambipolar transport was achieved by environmentally controlling the thickness of the intercalated water. We show that the effect persists even for multilayer flakes and that it is completely reversible, opening a new route toward the realization of novel electronics with environmentally controllable functionalities.