Dispersed Nanoelectrodes for High Performance Gas Sensors
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Dispersed Nanoelectrodes for High Performance Gas Sensors Antonio Tricoli and S.E. Pratsinis Particle Technology Laboratory, Institute of Process Engineering, Department of Mechanical and Process Engineering, ETH Zurich, CH-8092 Zurich, Switzerland
ABSTRACT Integration of nanoparticles in electronic devices such as sensors, actuators, batteries, solar and fuel cells is a key technological development for advancing their performance and miniaturization. Frequently, however, the benefit of nanoscale is lost by poor electrical conductivity through such nanoparticle structures. As a result, it is challenging to achieve both attractive conductivity and maximal performance by the device. Recently it was demonstrated that flame-made nanoparticles can be directly deposited onto substrates to form porous thick films of controlled thickness for application as gas sensors. The mechanical stability of FSPdeposited layers can be greatly increased by in situ annealing showing compatibility even with fragile CMOS-based substrates. Here, a novel asymmetric electrode assembly is described that greatly reduces the resistance of a nanostructured layer and maximizes its performance: Nanoparticles with tailored conductivity (e.g. Ag, CuO, Au) serving as electrodes are stochastically deposited by a scalable technique either below or above a functional (e.g. SnO2, TiO2, WO3) film decreasing the effective length of the resistive components. As the distance between electrodes is at the nanoscale, the total film resistance is drastically decreased. The feasibility of this assembly is demonstrated with solid state sensors having controlled resistance and exceptionally high sensitivity. INTRODUCTION Nanoparticles are powerful functional components with the potential of remarkably increasing the performance of several devices. Often their integration in standard electrical components is difficult due to the poor conductivity through interparticle boundaries. Tailoring of the total resistance through such a nanoparticle films is challenging and is usually obtained by increasing the particle size. This compromise between functionality and conductivity limits the realization of the full potential of nanoparticles that is often obtained with size below 10 nm. An alternative is the utilization of nanowires1 that however do not have the same properties of the nanoparticles. In fact, both attempts to tame the resistance of nanoparticle films results in lower performances as reported for gas sensors2 and solar cells,1 to name a few. Recently, it was suggested that a way out from the size/conductivity dilemma is the integration of two types of nanoparticles.3 A first type, also called nanoelectrodes, is utilized to tailor the total resistance of the nanoparticle film. The second type supplies the functionality and its size can be (nearly) arbitrary decreased. For example, utilizing CuO nanoparticles as nanoelectrodes the resistance of SnO2 nanoparticles films was decreased up to 5 orders of magnitude.3
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Here, we apply the same approach to optimize
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