Electronic Conductivity of Nanoporous Indium Oxide Derived from Sequential Infiltration Synthesis

Sequential infiltration synthesis (SIS) is a vapor phase synthetic method that enables the selective nucleation and growth of metal oxides within polymer volumes. The expanding palette of SIS materials and process designs enables tunability of the resulting material properties. We derive porous indium oxide thin films from the SIS of indium oxide using trimethyl indium and H2O2 in polymethyl methacrylate films and observe the strong effect of SIS and post-deposition processing, which affords 7 orders of magnitude of tunability in electrical resistivity. While as-deposited hybrid nanocomposites show no measurable conductivity, high-temperature treatment in O2 removes the polymer matrix and creates a porous nanocrystalline In2O3 film with resistivities ranging from 103 to 105 Ω*cm, with lower resistivity correlated to larger grain sizes. Subsequent annealing in H2 decreases the resistivity of films to less than 10–2 Ω*cm. A clear correlation between increasing In2O3 volume fraction, grain size, and carrier mobility is observed, which arises from increased percolation pathways, path length, and contact area in nanocrystalline In2O3 films. This wide tunability demonstrates the importance of understanding growth mechanisms and processing conditions for functional materials development.