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J. Sama, S. Barth, A. Romano-Rodriguez:
"Gas Sensing Properties of In₂O₃ Nanowires Grown via Carbothermal Reduction";
Vortrag: 2014 MRS Fall Meeting, Boston; 30.11.2014 - 05.12.2014; in: "2014 MRS Fall Meeting - Program", (2014).

Metal oxide (MOX) materials, like SnO2, In2O3, ZnO, ..., are employed in the development and fabrication of solid state gas sensors due to the well-known interaction between the MOX surface and the different gases, which leads to a variation in the electrical characteristics of the metal oxides. In fact, several commercial gas sensors of different providers worldwide are based on them. Generally, the gas sensing properties are a consequence of the adsorption-desorption processes that take place at the surface of the MOX in which the oxygen-poor surface plays a key role in the sensing mechanism. Different accepted models for the sensing have been presented and are commonly accepted to interpret the observed gas sensing behavior.
MOX nanowires (NWs) have emerged in the last two decades as a step forward in the development of gas sensors, when compared to thin or thick film MOX materials, due to their high aspect ratio. Especially monocrystalline materials have become important to achieve effective and known interactions of their surface in gas sensors.
Among the different MOX materials, In2O3 is receiving relatively little attention due to the fact that its synthesis window is much more reduced than that of SnO2 or ZnO, and that it leads to either semiconducting or metallic behavior, being its reproducibility of the material complicated. For sensing applications, In2O3, however, shows some interesting features like a low level of detection of NOx compounds in air and a reduced sensitivity to CO, which gives rise to an enhanced selectivity as compared to the 2 above-mentioned compounds.
In this work we will present the synthesis of In2O3, as well as the fabrication and characterization of gas sensors based on them. The synthesis is carried out in a horizontal furnace using the carbothermal reduction process from In2O3 and graphite powders, and using Ar and O2 as carrier gases. Depending on the concentration of O2 in the gas phase, on the flow used, on the vacuum level in the furnace and on the furnace and substrate temperatures, either continuous layers or bundles of NWs have been synthesized on Au-seeded Si or Al2O3 substrates. NWs have been removed from the surface where they grew, have been dispersed on prepatterned Si substrates and have been contacted using Focused Electron and Focused Ion Beam techniques. Characterisation towards the different gases has been carried out on a self-constructed gas testing chamber.
The material´s growth, structural and electrical characteristics will be presented as a function of the growth conditions and the correlation with the gas sensing properties discussed with the view on published sensing mechanisms.