HYDROGEN AND HUMIDITY SENSING PROPERTIES OF C-60 THIN-FILMS

We discuss the sensing properties of C-60 thin films towards reducing gases and humidity. C-60 thin films were sublimed onto alumina substra tes with platinum interdigitated contacts, and a platinum heating elem ent was deposited on the substrate back face. The electrical responses of the C-60 films towards 1000 ppm of hydrogen, ethyl alcohol and car bon monoxide were measured both in dry and humid air, in the temperatu re range between 50 and 300 degrees C. At 300 degrees C we observe a r eversible increase of the current in the presence of hydrogen, while t he water vapour causes a reversible decrease in the current. We sugges t that the response to hydrogen may be due to a chemical reaction betw een the oxygen molecules trapped in the film and the hydrogen, reducin g the concentration of oxygen-based electron traps in the C-60, hence increasing the conductivity. The reduction in conductivity in the pres ence of humidity is probably due to the formation of extra trap states by water molecules in the film.