Electrical transport in two-dimensional PdSe2 and Mos2 nanosheets

We investigate the effect of pressure and gas species on the electrical transport in nanosheets of palladium diselenide (PdSe2) and molybdenum disulfide (MOS2), used as the channel of back-gate field-effect transistors. Air pressure can control the carrier polarity in PdSe2 devices and the dominant n-type conduction in a high vacuum can reversibly transform in p-type transport at atmospheric pressure. Structural defects facilitate gas adsorption, which widens the hysteresis of the transfer characteristics. For Mos2 the hysteresis has a monotonic dependence on gas adsorption energy. We investigate the effect of low-energy electron irradiation and find that few tens e-/nm2 fluence can significantly change the transistor characteristics. Finally, the field emission currents from both PdSe2 and Mos2 nanoflakes are measured. The first experimental observation of the gate modulation of the field emission current from a Mos2 monolayer is reported. Such a finding constitutes the proof-of-concept of a field-effect transistor based on field emission and paves the way for new applications of 2D materials in vacuum electronics.