Direct contacting of 2D nanosheets by metallic nanoprobes

We present a simple and fast methodology to realize metal contacts on two-dimensional nanosheets. In particular, we perform a complete characterization of the transport properties of MoS₂ monolayer flakes on SiO₂/Si substrates by using nano-manipulated metallic tips as metallic electrodes directly approached on the flake surface. We report a detailed experimental investigation of transport properties and contact resistance in back-gated field-effect transistor in which the Si substrate is used as the gate electrode. Moreover, profiting from the n-type conduction as well as the high aspect ratio at the edge of the MoS₂ flakes, we also explored the possibility to exploit the material as a field emitter. Indeed, by retracting one of the metallic probes (the anode) from the sample surface, it has been possible to switch on a field emitted current by applying a relatively low external electric field of few tens of Volts for cathode-anode separation distance below 1µm. Experimental data are then analyzed in the framework of Fowler-Nordheim theory and its extension to the two-dimensional limit.