Nanoporous SnO2 Film Gas Sensor Formed by Anodic Oxidation

Nanoporous SnO2 films on SiO2/Si substrate with one-dimensional (1D) nanochannels were fabricated by anodic oxidation, and their gas sensing properties were investigated. For this, Sn films of similar to 600 nm thick were deposited on SiO2/Si substrate by thermal evaporation and anodized in an electrolyte of 0.3 M oxalic acid. Subsequent annealing at 700 degrees C completely transformed amorphous anodic oxide into crystalline SnO2, which was confirmed by X-ray diffraction. During annealing, both 1D nanoporous structure and adhesion to the substrate were maintained. The pore shape was more or less spherical, and the channel diameter and wall thickness were similar to 50 and similar to 20 nm, respectively. The Pt-patterned nanoporous SnO2 film sensor responded to H-2, NH3, and CO gases with a relatively short response time. It showed the highest gas response (S) of similar to 52 toward 1.0% H-2/air at 400 degrees C and exhibited the linear concentration dependence and high selectivity toward H-2 against CO or NH3. The sensing performance of the nanoporous SnO2 film sensor was compared with that of the thermally oxidized SnO2 film sensor without the anodizing step and commercial SnO2 powder sensor.