Diode type Ag–TiO2 hydrogen sensors

The use of diode type noble metal–metal oxide gas sensors is spreading due to their unique gas sensing properties such as ultra high responses, reproducibility and long life time. In this paper, hydrogen and oxygen detection using Ag–TiO2–Ti diodes is reported. The I–V characteristics of these diodes are highly sensitive to the partial pressure of hydrogen contamination in the surrounding atmosphere. Reducing atmosphere alters the population of pre-adsorbed oxygen species on silver surface, thereupon, the energy barrier height established at the Ag–TiO2 junction reduces and the junction behaves as an ohmic contact in a highly reducing atmosphere. This reversible transition from Schottky to ohmic behaviour was modelled qualitatively and quantitatively based on the hydrogen–silver interaction. The model was experimentally confirmed. It was also shown that the fabricated Ag–TiO2–Ti devices are good oxygen sensors at low O2 contamination in argon atmosphere.