Atomic Layer Deposition of SnO2-Coated Anodic One-Dimensional TiO2 Nanotube Layers for Low Concentration NO2 Sensing

The continuous emission of nitrous oxides contributes to the overall air pollution and deterioration of air quality. In particular, an effective NO 2 sensor capable of low concentration detection for continuous monitoring is demanded for safety, health, and wellbeing. The sensing performance of a metal oxide-based sensor is predominantly influenced by the availability of surface area for O 2 adsorption and desorption, efficient charge transport, and size or thickness of the sensing layer. In this study, we utilized anodic one-dimensional (1D) TiO 2 nanotube layers of 5 μm thick which offer large surface area and unidirectional electron transport pathway as a platform to accommodate thin SnO 2 coatings as a sensing layer. Conformal and homogeneous SnO 2 coatings across the entire inner and outer TiO 2 nanotubes were achieved by atomic layer deposition with a controlled thickness of 4, 8, and 16 nm. The SnO 2 -coated TiO 2 nanotube layers attained a higher sensing response than a reference Figaro SnO 2 sensor. Specifically, the 8 nm SnO 2 -coated TiO 2 nanotube layer has recorded up to ten-fold enhancement in response as compared to the blank nanotubes for the detection of 1 ppm NO 2 at an operating temperature of 300 °C with 0.5 V applied bias. This is attributed to the SnO 2 /TiO 2 heterojunction effect and controlled SnO 2 hickness within the range of the Debye length. We demonstrated in this work, a tailored large surface area platform based on 1D nanotubes with thin active coatings as an efficient approach for sensing applications and beyond.