The role of water in surface charge transport on tin dioxide as revealed by the thermal dependence of conductance

The presence of water on an oxide surface can dramatically alter its electrical properties with important consequences for electrical measurements by scanning probe microscopy, and for the use of semiconducting oxides in sensing applications. Here, the thermal dependence of the surface conductance of tin dioxide is interpreted by combining equilibrium carrier statistics with the Grotthuss mechanism for proton hopping. The functional form of this charge transport model is fit to experimental conductance data for tin dioxide. Next, the important energy parameters in the model are computed with electronic structure methods. Comparing the values of the energy parameters obtained by fitting to those obtained from electronic structure calculations yields new insight into the surface charge transport in tin dioxide. In particular, it is found that mobile protons, freed by the dissociative adsorption of water on the [110] surface, are an essential component of the observed thermal dependence of surface conductance in tin dioxide.