Seebeck gas sensors

本项目主要研究影响金属氧化物中塞贝克系数的机理。主要分析了粒径小于或等于薄膜厚度的纳米晶薄膜及其在退火、气体环境和紫外线照射下的操作。单晶是一种标准材料，也是一种具有良好定义的几何结构的模型系统，用于可靠地确定材料参数和分析与气体环境的特定相互作用机制。与块状材料相比，纳米结构薄膜的优点是具有较高的晶粒浓度和晶界。在具有载流子固有表面积累的纳米结构半导体中，这些晶界降低了热导率，但另一方面，增加了材料的导电性，对热电性能产生了积极的影响。这些特性是一些含铟化合物如InN、InAs和In2O3的固有特性。本课题拟研究基于In2O3的纳米晶热电气敏材料。通过颗粒尺寸的特定变化、掺杂和颗粒表面的系统操作，研究了颗粒中、表面和晶界处的电子输运现象，这些现象有助于气体检测现象。主要的仪器将是调节费米能级（功函数）和表面带弯曲的特定气体吸附。参考值将通过原位光电子能谱法得到。通过使用优化的纳米颗粒薄膜，这些效应将用于高灵敏度的塞贝克气体传感器系统。一个主要目标将是研究在纳米晶体薄膜中观察到的一种现象。在特定薄膜中，塞贝克系数意外地减小，而电阻增加。通过控制这种效应出现的条件，可以设计简单的传感器结构，分别记录两个电、气敏参数。它能够提高商用金属氧化物气体传感器在特定气体选择性方面的性能，并能够实现自校准方案，这将显着延长传感器设备的使用寿命。

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.