Figure 1.

(a) Optical image of an FET with a multilayer MoS₂ channel on a SiO₂/Si substrate. The transport properties between the source and drain contacts were measured as functions of the gate voltage. (b) I_ds–V_g curves for V_ds = 0.1 V in vacuum and air with varying values of pressure. The scan rate for the measurement of the I_ds–V_g curves was approximately 1.0 V/s. The hysteresis increases with increasing air pressure. The sweep directions are indicated by the arrows. (c) I_ds–V_g curves for V_ds = 0.1 V measured under different environmental conditions. The influence of nitrogen, oxygen, air (RH = 18%), and humid nitrogen (RH = 80%) are compared. Small temperature variation and environmental gas change the on-state current (I_ds at V_g = 40 V). Therefore, for the sake of enhancing the visibility of the hysteresis, some of the curves are vertically scaled such that the on-state currents shown in the figure nearly coincide with each other. The sweep directions are indicated by the arrows. (d) I_ds–V_g curves for V_ds = 0.1 V measured after evacuating humid nitrogen for various periods of time using a turbo-molecular pump. The hysteresis decreases slowly; however, it persists even after pumping for 10 h. The curves are offset vertically for clarity.