Gas sensing properties of hydrogenated amorphous silicon films

Gas sensing experiments on hydrogenated amorphous silicon (a Si:H) films have been performed. We show that a-Si:H exhibits a low-temperature gas response that is distinctly different from the more familiar combustive gas response operative on heated metal-oxide surfaces. In particular, we show that at room temperature and above, a-Si:H samples exhibit a dissociative gas response which has first been observed on hydrogenated diamond (HD) samples. Whereas this dissociative gas response disappears at HD surfaces upon evaporation of the adsorbed surface electrolyte layer, a gas response with a similar cross sensitivity profile is observed on a-Si:H surfaces that persists up to the original deposition temperature of the a-Si:H films. We argue that this latter kind of gas response is due to a coordinative gas response that takes place when surface H-atoms of the a-Si:H film enter the coordination sphere of adsorbed analyte gas molecules.