High-sensitivity ethanol vapor detection using In<sub>2</sub>O<sub>3</sub>@ZnO core-shell nanomeshes fabricated <i>via</i> block copolymer templating.

Abstract

Metal-oxide semiconductor nanowires are promising building blocks for high-performance gas sensors due to their high specific surface area and tunable electronic properties. In this work, we adapted a single-step synthesis based on block copolymer templates to fabricate indium oxide (In₂O₃) nanowires subsequently coated with a thin layer of zinc oxide (ZnO) <i>via</i> atomic layer deposition (ALD). The optimized core-shell heteronanostructures, featuring a 10 nm-thick ZnO shell and annealed at 400 °C, exhibited a markedly enhanced electrical response measured as a resistance ratio in the absence and presence of ethanol vapors (<i>R</i> ₀/<i>R</i> ≈ 245 at 100 ppm), as well as high sensitivity (≈2.28 ppm^-1) in the 10-100 ppm range as compared to bare In₂O₃ nanowires (response ≈ 120, sensitivity ≈ 1.01 ppm^-1). This increase in response and sensitivity is related to the electronic structure of the In₂O₃@ZnO heterostructure. Additionally, the core-shell configuration shows promising long-term stability, maintaining high response performance in both dry and ambient humidity conditions. The structural characterization revealed a highly porous and interconnected nanowire architecture of the sensing material and showed that high-temperature annealing significantly improves the crystallinity of both the In₂O₃ core and the ZnO shell. The combination of high sensitivity and robust response underscores the potential of these porous core-shell heteronanostructures with a high surface-to-volume ratio for low-concentration detection of ethanol and potentially also other volatile organic compounds, offering a promising avenue for advanced gas-sensing applications.