Correlation between atomic composition and gas sensing properties in tungsten–iron oxide thin films

Mixed tungsten and iron oxide thin films were prepared with reactive RF sputtering. The electrical response of thin films of W–Fe oxides toward CO, NO2, ozone and ethanol was investigated. Moreover, XPS technique was employed to study the chemical composition of the samples’ surfaces and the depth profile through the whole thickness of the films. The oxidation states of W and Fe were determined from the photoelectron spectra. Iron addition always increases the response towards ozone, carbon monoxide and ethanol. For nitrogen dioxide, the introduction of iron concentrations lower than 10% produce an enhancement in the response.