Response to ethanol of thin films based on Mo and Ti oxides deposited by sputtering

We have obtained nanosized thin films of titanium and molybdenum oxide with different doping by radio-frequency (RF) sputtering from two targets: Ti (99.5%)–Mo (0.5%) and Mo (98.6%)–Ti (1.4%). The depositions were performed in reactive atmosphere and annealing treatments were performed at temperatures up to 800 °C. The titania layers resulted to be even more stoichiometric as annealing temperature increased. The small part of Mo proved useful to prevent exaggerated grain coalescence. Mo segregated at the surface and partially sublimated as MoO3. Regarding the Mo-based thin films, we have obtained MoO3:Ti layers just after the deposition, while as the annealing temperature is increased there is a partial sublimation of the oxide leaving titania agglomerates not interconnected. All the layers resulted to be n-doped semiconductors and were tested as chemo-resistive gas sensors. The layers had a very high capability to sense ethanol, the detection limit being lower than 10 ppm.