Hydrogen and humidity sensing properties of C60 thin films

We discuss the sensing properties of C60 thin films towards reducing gases and humidity. C60 thin films were sublimed onto alumina substrates with platinum interdigitated contacts, and a platinum heating element was deposited on the substrate back face. The electrical responses of the C60 films towards 1000 ppm of hydrogen, ethyl alcohol and carbon monoxide were measured both in dry and humid air, in the temperature range between 50 and 300 °C. At 300 °C we observe a reversible increase of the current in the presence of hydrogen, while the water vapour causes a reversible decrease in the current. We suggest that the response to hydrogen may be due to a chemical reaction between the oxygen molecules trapped in the film and the hydrogen, reducing the concentration of oxygen-based electron traps in the C60, hence increasing the conductivity. The reduction in conductivity in the presence of humidity is probably due to the formation of extra trap states by water molecules in the film.