Figure 2.

(a) I_ds–V_g curves measured at various temperatures for a device that is different from that used for acquiring the data shown in the other figures. The thickness of the MoS₂ flake of this device was measured to be ~5 nm. The channel length and width are L = 4.5 μm and W = 13.8 μm, respectively. In this measurement, V_ds was maintained at 1 V. The sample was cooled in helium gas for heat exchange. At 240 K, the hysteresis due to the charge trapping related to the adsorbed molecules completely disappears. The curves are offset vertically for clarity. (b) The threshold gate voltages V_th1, V_th2 (open triangles), and ΔV_th = V_th2 − V_th1 (filled circles) as functions of relative humidity. These data were obtained using humid nitrogen at 760 Torr as the environmental gas. The flattening of ΔV_th with decreasing humidity is explained in terms of the limited measuring range of the humidity sensor. The humidity dependence of V_th1 and V_th2 indicates the dominance of the hole-trapping effects of water molecules in the hysteresis of the transfer characteristics.