Theoretical characterization of the indium tin oxide surface and of its binding sites for adsorption of phosphonic acid monolayers

A study was carried out to present the first theoretical characterization of a model indium tin oxide (ITO) surface and of the nature of the binding sites that determine the adsorption of phosphonic acid (PA) monolayers. The advantage of the approach is to provide from the theory side core-level energies calculated at the quantum-mechanical level for specific atom types, which leads on the experimental side to unambiguous assignments of the various peak components in the XPS spectra. The capability of the methodology to describe the PA binding was demonstrated through a comparison with experimental XPS spectra. The results of the study confirm that, under the typical reaction conditions, PA adsorption on ITO takes place predominantly through bidentate/tridentate binding, which involves P-O-In bonds. First-principles calculations also were shown to be underway to characterize the work function modifications induced by self-assembly of various PA molecules on ITO.