Work function analysis of gas sensitive WO3 layers with Pt doping

In this paper platinum (Pt) doped tungsten trioxide (WO3) layers have been investigated. The structures were prepared in the standard thick film technology. A scanning electron microscope (SEM) was used for the microstructure analysis of the gas sensitive layers. The work function was examined by using a scanning Kelvin probe (SKP). The Kelvin probe is a non-contact and non-destructive method to provide work function measurements and surface analysis. This tool is very sensitive to any surface potential changes of the investigated material. The measurements preformed by using the SKP shows that the screen printed WO3 layers were very homogenous and no significant defects are present. The Pt dopants added to the gas sensitive layer created small clusters on the surface of the WO3 grains. The presence of those additives changes the potential barrier between the metal oxide crystals and caused a decrease of the sensing layer conductance at low dopants concentration, until the exceed of the percolation threshold. Moreover, due to the introduction of additives a change in the activation energy was observed which has influence on the sensor parameters and resulted in increase of the sensitivity to isopropyl alcohol.