Abstract
Development of fast highly-sensitive semiconductor gas sensors operating at room temperature, which would be compatible with semiconductor technology, remains a challenge for researchers. Here we present such sensor based on a nanoscale Pt–TiO2–Pt sandwich. The sensor consists of a thin (∼30nm) nanocrystalline TiO2 layer with ∼10nm grains, placed between the bottom Pt electrode layer and top Pt electrode shaped as a long narrow (width w down to 80nm) stripe. If we decrease w to ∼100nm and below, the sensor exposed to air with 1% H2 exhibits the increase of response (Rair/RH2) up to ∼107 and decrease of the reaction time to only a few seconds even at room temperature. The sensitivity increase is due to a nontrivial non-ohmic effect, a sudden decrease (by three orders of magnitude) of the electrical resistance with decreasing w for w∼100nm. This non-ohmic effect is explained as a consequence of two nanoscale-related effects: the hydrogen-diffusion-controlled spatially-inhomogeneous resistivity of the TiO2 layer, combined with onset of the hot-electron-temperature instability when the tiny grains are subjected to high electric field.
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