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 (PdSe
₂
) and molybdenum disulfide (MOS
₂
), used as the channel of back-gate field-effect transistors. Air pressure can control the carrier polarity in PdSe
₂
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 MoS
₂
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
^-
/nm
²
fluence can significantly change the transistor characteristics. Finally, the field emission currents from both PdSe
₂
and MoS
₂
nanoflakes are measured. The first experimental observation of the gate modulation of the field emission current from a MoS
₂
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.