Switch of p-n electricity of reduced-graphene-oxide-flake stacked films enabling room-temperature gas sensing from ultrasensitive to insensitive

The p-n-p double transformation and ultrasensitive-insensitive gas sensing of reduced-graphene-oxide-flake stacked films (rGOFSFs) were controlled by changing the annealing temperature from 100 to 400 °C on a sodium silicate substrate, as a result of the competition between the thermal reduction, decomposition, and diffusion of Na, as determined from comprehensive microstructure characterization. The slightly reduced p-type GOFSF showed ultrasensitive gas sensing at room temperature (RT), with a response of 58% to 1 ppm ethanol and a high detection limit (sub-ppm). Interestingly, the rGOFSF can become n-type and insensitive to gas sensing, with a low response of −0.5% to 50 ppm ethanol, by simply increasing the annealing temperature to 200-300 °C. The capability of controlling carrier types and ultrasensitivity-insensitivity transition to gas is useful for developing nanodiodes and RT gas sensors.