No abstract

Fast highly-sensitive room-temperature semiconductor gas sensor based on the nanoscale Pt-TiO 2 -Pt sandwich, Sensors and Actuators B: Chemical (2014), http://dx. AbstractDevelopment 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-TiO 2 -Pt sandwich. The sensor consists of a thin (~30 nm) nanocrystalline TiO 2 layer with ~10 nm grains, placed between the bottom Pt electrode layer and top Pt electrode shaped as a long narrow (width w down to 80 nm) stripe. If we decrease w to ~100 nm and below, the sensor exposed to air with 1% H 2 exhibits the increase of response (R air / ) up to ~ 10 7 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 TiO 2 layer, combinedPage 2 of 41 A c c e p t e d M a n u s c r i p t 2 with onset of the hot-electron-temperature instability when the tiny grains are subjected to high electric field.

We study electron transport in quasi-one-dimensional metallic wires. Our aim is to compare an impurity-free wire with rough edges with a smooth wire with impurity disorder. We calculate the electron transmission through the wires by the scattering-matrix method, and we find the Landauer conductance for a large ensemble of disordered wires. We first study the impurity-free wire whose edges have roughness with a correlation length comparable with the Fermi wavelength. Simulating wires with the number of the conducting channels (N c ) as large as 34-347, we observe the roughness-mediated effects which are not observable for small N c (∼ 3-9) used in previous works. First, we observe the crossover from the quasi-ballistic transport to the diffusive one, where the ratio of the quasi-ballistic resistivity to the diffusive resistivity is ∼N c independent of the parameters of roughness. Second, we find that transport in the diffusive regime is carried by a small effective number of open channels, equal to ∼6. This number is universal-independent of N c and of the parameters of roughness. Third, we see that the inverse mean conductance rises linearly with the wire length (a sign of the diffusive regime) up to the length twice larger than the electron localization length. We develop a theory based on the weak-scattering limit and semiclassical Boltzmann equation, and we explain the first and second observations analytically. For the impurity disorder we find a standard diffusive behavior. Finally, we derive from the Boltzmann equation the semiclassical electron mean free path and we compare it with the quantum mean free path obtained from the Landauer conductance. They coincide for the impurity disorder; however, for the edge roughness they strongly differ, i.e., the diffusive transport in the wire with rough edges is not semiclassical. It becomes semiclassical only for roughness with a large correlation length. The conductance then behaves like the conductance of the wire with impurities, also showing the conductance fluctuations of the same size.