Gas Sensor by Direct Growth and Functionalization of Metal-Oxide/Metal-Sulfide Core-Shell Nanowires on Flexible Substrates.

Abstract

We have developed a novel fabrication method for flexible gas sensors for toxic gases based on sequential wet chemical reaction. In specific, zinc oxide (ZnO) nanowires were locally synthesized and directly integrated on a flexible polymer substrate using localized hydrothermal synthesis methods and their surfaces were selectively functionalized with palladium (Pd) nanoparticles using a liquid phase deposition process. Because the entire processes are conducted in low temperature and mild precursor solution, it can be applied for flexible substrates. Furthermore, the surface of ZnO nanowires was sulfurized by hydrogen sulfide (H2S) gas to form zinc oxide/zinc sulfide (ZnO/ZnS) core-shell nanowires for stable sensing of H2S gas. The locally synthesized ZnO/ZnS core-shell nanowires enable ultra-compact sized device and Pd nanoparticles improve the sensing performance and reduce operating temperature (200 °C). The device shows a high sensitivity ((Ggas-Gair)/Gair × 100 % = 4491 % to 10 ppm), fast response (response/recovery time < 100 secs) to hydrogen sulfide, and outstanding selectivity (> 100 times) to other toxic gases (e.g. carbon monoxide, acetone, ethanol and toluene). Moreover, vertically synthesized nanowires provide long bending path, which reduces the mechanical stresses on the structure. The devices showed stable gas sensing performance under 9 mm positive radius of curvature and 5 mm negative radius of curvature. The mechanical robustness of the device was also verified by numerical simulations which showed dramatic decrease of maximum stress and strain to 4.2% and 5.0%.