R. Jiménez-Díaz

Dissipated power in metal oxide nanowires (rNW<45 nm) often causes important self-heating effects and as a result, undesired aging and failure of the devices. Nevertheless, this effect can be used to optimize the sensing conditions for the detection of various gaseous species, avoiding the requirement of external heaters. In this letter, the sensing capabilities of self-heated individual SnO2 nanowires toward NO2 are presented. These proof-of-concept systems exhibited responses nearly identical to those obtained with integrated microheaters, demonstrating the feasibility of taking advantage of self-heating in nanowires to develop ultralow power consumption integrated devices.

The responses of individual ZnO nanowires to UV light demonstrate that the persistent photoconductivity (PPC) state is directly related to the electron-hole separation near the surface. Our results demonstrate that the electrical transport in these nanomaterials is influenced by the surface in two different ways. On the one hand, the effective mobility and the density of free carriers are determined by recombination mechanisms assisted by the oxidizing molecules in air. This phenomenon can also be blocked by surface passivation. On the other hand, the surface built-in potential separates the photogenerated electron-hole pairs and accumulates holes at the surface. After illumination, the charge separation makes the electron-hole recombination difficult and originates PPC. This effect is quickly reverted after increasing either the probing current (self-heating by Joule dissipation) or the oxygen content in air (favouring the surface recombination mechanisms). The model for PPC in individual nanowires presented here illustrates the intrinsic potential of metal oxide nanowires to develop optoelectronic devices or optochemical sensors with better and new performances.

We present a set of criteria to optimize photodetectors based on n-type metal oxide nanowires and a comparison methodology capable of overcoming the present lack of systematic studies dealing with such devices. The response of photoconductors is enhanced following different fabrication strategies, such as diminishing the distance between the electrical contacts, increasing the width of the photoactive area, or improving the electrical mobility of the nanomaterials. The validity of the theoretical background is verified by experimental results obtained with devices based on ZnO nanowires. The performances of our devices show that the normalized gain of single ZnO nanowire-based photodetectors exceeds those of thin films.

Abstract The role of oxygen diffusion in the response of individual SnO 2 nanowires to this gas is studied. Different oxygen partial pressures lead to strong changes of their electrical resistance, even at room temperature. Since surface models fail to explain the experimentally observed long‐term resistance transients, it is necessary to make a description of the interaction mechanisms between oxygen species and SnO 2 nanowires by taking ion diffusion into account. Our model correctly describes the experimentally measured dependence of the nanowire resistance with oxygen partial pressure, and it can be applied to the characterization of other metal oxide materials.