Seebeck gas sensors

点击翻译按钮获取中文摘要

The proposed project in focused on the investigation of the mechanisms, which affect the Seebeck coefficient in metal oxides. To a major part, it analyses nanocrystalline films with a particle size smaller or equal to the film thickness and their manipulation by annealing, gas environment and ultraviolet illumination. Single crystalline represents a reference material as well as a model system with well-defined geometry for reliable determination of materials parameter and the analysis of specific interaction mechanisms with a gas environment. Nanostructured films, in comparison to the bulk materials, have the advantage of possessing a high concentration of grains and grain boundaries. In a nanostructured semiconductor with intrinsic surface accumulation of carriers, these grain boundaries lower the thermal conductivity but on the other side, increase the electrical conductivity of the material with a positive impact on the thermoelectric properties. These characteristics are intrinsic properties for several indium containing compounds such as InN, InAs, and In2O3. For the project we propose to investigate nanocrystalline based on In2O3 as thermoelectric, gas sensitive material. The electronic transport phenomena in the particles, at the surface and at grain boundaries, which contribute to the gas detection phenomena, are investigated by specific variation of particle size, doping and systematic manipulation of the particle surfaces. The major instrument will be the adjustment of the Fermi level (work function) and the surface band bending by specific gas adsorption. The reference values will be obtained by in situ photoelectron spectroscopy.By using optimized nanoparticle films, these effects will be used for highly-sensitive Seebeck gas sensor systems. A major goal will be the investigation of a phenomenon that has been observed in nanocrystalline films. In specific film the Seebeck coefficient unexpectedly decreased while the electric resistance increased. By controlling the conditions where this effect appears, simple sensor structures can be designed which record two electric, gas sensitive parameters independently. It enables to improve the performance of commercial metal oxide gas sensors regarding selectivity on specific gases and enable the implementation of self-calibration schemes, which would prolong the service life of sensor devices remarkably.