Initial gas exposure effects on monolayer pentacene field-effect transistor studied using four gallium indium probes

Abstract In this study, we report that the electrical transport property in monolayer pentacene is highly sensitive to a small amount of exposure to gaseous molecules of oxygen, nitrogen, and argon, by using independently-driven four gallium indium (GaIn) probes. Liquid metal GaIn probes have been used as non-destructive conductivity electrodes for monolayer OFET films in a vacuum chamber. We carried out the fabrication of monolayer pentacene and the four-probe measurement without exposure to atmospheric air. Four GaIn probes were used in situ to measure conductivity in the channel separately from the overall characteristics including contact resistance at the electrode probes. The results demonstrate that oxygen exposure of 1 L ( 10 − 6 Torr s) reduces mobility to 8% of the original value in the monolayer film, and the reduction is irreversible, i.e., mobility does not recover its original value after the evacuation of gaseous molecules. Physisorption of gaseous molecules is involved in the gas exposure effects, because chemically inert gases of nitrogen and argon also reduce the mobility. Taking these findings together with the results of photoelectron spectroscopy and atomic force microscopy measurements, we assume that the reduction is attributed to the physisorption at grain boundaries formed by the coalescence of monolayer islands.