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S. Barth, J. Sama, A. Romano-Rodriguez:
"VLS Growth of In₂O₃ Nanowires via Carbothermal Reduction: Growth Conditions, Structural Characterization and Gas Sensing Properties";
Poster: 2014 MRS Fall Meeting, Boston; 2014-11-30 - 2014-12-05; in: "2014 MRS Fall Meeting - Program", (2014), LL5.37.

In2O3 is a wide band-gap semiconducting material, with a direct gap of about 3.6eV, which is employed as transparent contact in the fabrication of solar cells and light emitting diodes and which is increasingly graining interest in other fields. Furthermore, like other metal oxide (MOX) materials, as SnO2, ZnO, Ga2O3, ..., In2O3 changes its resistance in the presence of different gases, like NO2, CO or NH3, due to the adsorption-desorption of the gas from the surface, where change transfer is involved. To increase the gas response, the use of In2O3 nanowires (NWs) is of interest because of the increased surface-to-volume ratio, which enhances the surface adsorption-desorption effects on the electrical parameters.
In this work we will present the growth of In2O3 NWs, as well as the fabrication and characterization of gas sensors based on individual NWs. The synthesis is carried out in a horizontal furnace using the vapour-liquid-solid (VLS) mechanism. The In is brought into the gas phase using the carbothermal reduction of In2O3 in the presence of graphite powder, and the transport and growth is promoted using Ar and O2 as carrier gases, the latter in low concentrations. The morphology of the grown material varies from thin layer to bundles of NWs as a function of the O2 concentration in the gas phase, of the flow of gas used, of the vacuum level in the furnace, of the furnace and substrate temperatures and of the In2O3 precursor power to substrate distance. For this, Si or Al2O3 substrates, covered with a discontinuous layer of Au, have been used to promote the growth. The samples have been structural, chemically, electrically and optically characterized to determine the correlation with the growth conditions.
NWs have been removed from the substrate and have been transferred to prepatterned Si substrates wit interdigitated electrodes and have been contacted using Focused Electron and Focused Ion Beam techniques to allow electrical and gas sensing characterisation. Responses to different gases and to simultaneous UV-light exposure have been measured in a self-constructed gas testing chamber and using SMUs for the electrical measurements.
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.