Fabrication of MEMS-based TiO2/SnO2 core-shell nanowires sensor for enhanced H2S sensing

The TiO 2 /SnO 2 core-shell nanowires (NWs) with precisely controlled SnO 2 shell thickness were successfully synthesized via facile hydrothermal method and atomic layer deposition (ALD) process. The innovative approach of integrating ALD with hydrothermal synthesis allowed for the precise tuning of the SnO 2 shell thickness, which is critical for optimizing gas sensing performance. The sensing performance of the prepared sensor was found to be highly dependent on the SnO 2 shell thickness. Notably, the sensor with a 20 nm SnO 2 shell exhibited the highest response (R a /R g ) of 5.9 towards 5 ppm H 2 S at 300 °C, which was approximately three times higher than that of the pristine TiO 2 NWs sensor (∼1.8). This significant enhancement in H 2 S sensing performance can be attributed to the formation of the TiO 2 /SnO 2 heterojunction and the optimal SnO 2 shell thickness, which were further elucidated through chemisorbed oxygen model, heterojunction depletion theory, and bandgap alignment. Additionally, the sensor demonstrated low power consumption (∼100 mW), great selectivity towards H 2 S, fast response/recovery times (25 s and 173 s, respectively), the ability to detect H 2 S at low concentrations (200 ppb), high sensitivity, excellent repeatability and remarkable stability (over 10 months). Therefore, the proposed MEMS-based TiO 2 /SnO 2 core-shell NWs gas sensor provides a promising approach for industrial and environmental monitoring applications.