Decoration of laser-ablated ZnO nanoparticles over sputtered deposited SnO<inf>2</inf> thin film based formaldehyde sensor

Heterojunction based metal oxide semiconductors have a great potential to detect toxic gases and volatile organic compounds. Here, we report a synthesis technique to obtain ZnO nanoparticles (NPs) via laser ablation method in ambient atmosphere using a nanosecond pulse laser. The laser ablated ZnO NPs were used for the decoration of sputtered deposited SnO2 thin film to realize n-type ZnO/n-type SnO2 heterojunction based formaldehyde (HCHO) gas sensor. Fabricated ZnO/SnO2 sensor shows 3 times higher response (response = 20) to 50 ppm HCHO, faster response-recovery dynamics (τres = 4 s and τrec = 30 s) and better selectivity compared to pristine SnO2 sensor at lower operating temperature (250 °C). The ZnO/SnO2 heterojunction based sensor also can detect < 0.25 ppm HCHO, which allows for lower detectable limit of sub-ppm HCHO. Therefore, the ZnO/SnO2 sensor shows enhanced sensing performance due to oxygen vacancies and n-n heterojunction structures provides more effective electrons for oxygen adsorption which speeds up the electronic transport at the interface of two materials. Synthesis of metal oxide composite NPs using pulse laser ablation method could be a promising alternative rapid route for the fabrication of highly sensitive gas sensors to detect most common indoor air pollutant.