Correlation between High Gas Sensitivity and Dopant Structure in W-doped ZnO

The proverbial ``canary in a coal mine'' is truly a thing of the past; nowadays zinc oxide is a key material in solid-state gas sensors, yet the mechanism by which doping can improve its performance is not fully understood. The authors use two-dimensional photoelectron diffraction to study thin films of tungsten-doped ZnO, and find clear evidence for substitution of segregated W atoms into Zn sites in the subsurface layer, which drastically improves the sensing response. This insight into the surface's structure-function relationship suggests how best to prepare these films for this important application.