Highly responsive and selective NO gas sensing based on room temperature sputtered nanocrystalline WO3/Si thin films

Abstract

This study investigates the nitric oxide (NO) gas sensing performance of room temperature sputtered nanocrystalline WO3 thin films deposited on Si substrate in a single step without heat treatment. The prepared WO3/Si sample properties have been systematically characterized for crystallographic, surface morphology, elemental, and chemical bonding analysis by XRD, FE-SEM, EDS, and XPS techniques, respectively. It has been observed that the thin film samples have a nanocrystalline structure with a granular-like porous morphology, and the presence of oxygen or metal vacancies/defects contributes to improving the sensing response of a target gas. The gas sensing performance of WO3 thin film deposited over Si (WO3/Si) has been recorded at various crucial parameters such as different operating temperatures (200–325 °C), gas concentrations (3–100 ppm), and target gases (H2S, CO, NH3, NO, and NO2). The maximum sensor response for 100 ppm concentration of NO gas was achieved at an operating temperature of 250 °C with a response time of ∼172 s and a recovery time of ∼86 s. At the optimal operating temperature of 250 °C, the lowest NO gas concentration was measured as low as 3 ppm. The calculated theoretical detection limit for NO gas at this concentration was determined to be 167 ppb. Further, the sample shows long-term stability over a period of 33 days and preserves the same value of sensor response. The selectivity performance tested for various gases clearly indicates that our sample is highly selective towards NO gas. This improved sensing performance can be attributed to the granular-like porous structure and excessive oxygen vacancies on the sample surface. The underlying sensing mechanism for superior response to NO gas has also been discussed. These results demonstrate the potential application of nanocrystalline WO3/Si thin film prepared at room temperature for the development of high-performance and cost-effective single-material-based metal oxide gas sensors.