Enhancement of CO gas sensing properties in ZnO thin films deposited on self-assembled Au nanodots

We present an excellent detection of carbon monoxide (CO) gas using Al-doped ZnO nanostructured thin films deposited on self-assembled Au nanodots (ZnO/Au thin films). We formed the self-assembled Au nanodots by annealing a thin Au layer with a thickness of 2 nm at a moderate temperature of 500 °C prior to the growth of the main ZnO layer via the sputtering method. We observed an enhancement of CO gas sensing response in the ZnO/Au gas sensors by the insertion of a thin Au nucleation layer, especially showing a high maximum sensitivity to CO at 250 °C and a low CO detection limit of 5 ppm in dry air. In addition, the ZnO/Au thin film CO gas sensors displayed fast response and recovery behaviors. The observed improvement in gas sensing properties is mainly attributed to the effective formation of ZnO nanostructured morphology having a high specific surface-reaction area via self-assembled Au nanodots. These results along with a simple fabrication process demonstrate that the ZnO thin films deposited on self-assembled Au nanodots are very promising for low-cost and high-performance CO gas sensors.