Sequential Infiltration Synthesis of Nano-porous and Electrically Conductive In2O3 for Water Remediation

Abstract

Sequential infiltration synthesis (SIS) is derivative of atomic layer deposition (ALD) that expands the morphological palate of materials to enable an even greater variety of applications. During SIS, a vapor phase precursor reversibly and selectively adducts with a polymer matrix. By controlling the polymer moieties, precursor chemistry, and reaction parameters such as time, temperature, and pressure, the process can yield precise deposition and high growth rates (equivalent to > 30 nm/cycle) in complex matrices that are 100s of nanometers thick. In our work, we leverage those parameters to deposit nano-porous In2O3 electrodes for water remediation. Electrified water treatment has the potential to greatly improve energy and cost efficiency over current methods. SIS has been used previously to create well-defined nano-porous structures, yet there has not been a report of an electrode developed via SIS. Our work describes how amorphous InOHx clusters deposited by SIS combine to form an interconnected and electrically conductive network of crystalline In2O3. Changes in optical parameters, probed by spectroscopic ellipsometry, reveal that the oxygen annealing burns off the polymer and leads to partial densification of the film. XRD and TEM further demonstrate the development of a crystalline network of In2O3 with grain sizes of approximately 20 nm. Additional annealing in forming gas yields resistivity values on the order of 10-3 Ω*m. Aside from the annealing conditions, the microstructure of the In2O3 network also influences electrical properties. Using SIS to control the volume fraction of In2O3 in PMMA, annealed samples were prepared with porosity ranging from 30-80% In2O3. As the amount of In2O3 increases, Hall measurements reveal that the resistivity decreases and the mobility increases, which suggests that the prevalence of charge conduction pathways within the In2O3 film can be controlled. We demonstrate nano-porous In2O3 films with tunable electrical properties and further highlight the opportunity to precisely control properties of In2O3 for applications such as water remediation.