Superior sensor performance from Ag@WO3 core-shell nanostructure

WO3, Ag-WO3 mixture and Ag@WO3 core-shell nanostructure materials were prepared by a hydrothermal process. Material characterization included UV-Vis spectroscopy, XRD, XPS, and TEM imaging. Gas sensors fabricated using the samples were mainly characterized by the response to alcohol vapor. It was found that the Ag@WO3 core-shell nanostructure provides greatly enhanced chemical sensor performance. Specifically, the sensor response towards 500 ppm alcohol vapor increases from 44 for pure WO3 and 52 for Ag-WO3 mixture to 154 for the Ag@WO3 core-shell structure; response and recovery time are shortened considerably from 3 and 15 s for pure WO3, 12 and 7 s for the Ag-WO3 mixture to 2 and 4 s for the Ag@WO3 core-shell nanostructure. Moreover, optimum sensor working temperature lowered from 370 °C to 340 °C. It appears that the Ag@WO3 core-shell nanostructure results in an effective Schottky junction enhanced sensor while the Ag-WO3 mixture does not. The significant downshift in the Ag 3d XPS chemical shift for the Ag@WO3 core-shell nanostructure sample confirms that the sensor performance improvement is due to Schottky junction formation at the Ag/WO3 interface.