The role of Rh dispersion in gas sensing effects observed in SnO2 thin films

Highlights: • Rh influence on the response of SnO₂ gas sensors is analyzed. • Surface modification with Rh provides the improvement of gas sensor performance. • An explanation of the observed effects has been proposed. • It was assumed that atomic–dispersed state of Rh is the most active one in gas–sensing effects. • New approaches and additional studies are required. -- Abstract: In the present work the effect of surface modification by rhodium on the conductivity response of the SnO₂ films to reducing gases such as CO and H₂ and oxidizing gas ozone was analyzed. SnO₂ films, subjected to surface modification, were deposited by spray pyrolysis, while Rh was deposited using a micro electron beam evaporation. The thickness of the Rh coating varied in the range of 0–0.1 ML. It was found that there is an optimal thickness of Rh, which gives an improvement in the sensor response and a decrease in the recovery time. An explanation of the observed effects was proposed. It was assumed that the atomically dispersed state of rhodium is most active in gas–sensing effects. The transformation from the atomic state to the cluster state reduces the efficiency of the surface functionalization of SnO₂ with rhodium.