Synergistic effects of codecoration of oxide nanoparticles on the gas sensing performance of In2O3 nanorods

n-In2O3 nanorods codecorated with n-Fe2O3 and p-Co3O4 nanoparticles were synthesized by the thermal evaporation of In2S3 powders in an oxidizing atmosphere followed by the solvothermal deposition of Fe2O3 and Co3O4 nanoparticles, and their ethanol gas sensing properties were examined. The p-Co3O4-decorated n-In2O3 nanorods exhibited stronger and faster response to ethanol gas than the n-Fe2O3-decorated n-In2O3 nanorods due to the larger modulation of the conduction channel width and interfacial potential barrier height, and stronger catalytic activity of p-Co3O4 than n-Fe2O3. Furthermore, the codecorated In2O3 nanorod sensor exhibited significantly stronger and faster response to ethanol gas than its mono-oxide nanoparticle-decorated counterparts under the condition of the same total amount of the decorating nanoparticles. The origin of the synergistic effects of codecoration on the ethanol sensing properties of the In2O3 nanorod sensor is not the formation of compounds or nanoalloys between the oxides but the formation of a large number of the p-n junctions between the two different types of decorating oxides, i.e., Fe2O3-Co3O4 p-n junctions in addition to the Co3O4-In2O3 p-n junctions.