Bonding Properties of Isolated Metal Atoms on Two-Dimensional Oxides

We report a systematic comparative dispersion-corrected DFT study of single (K, Au, and Pt) atom adsorption over a wide range of metal-supported oxide ultrathin films (MgO on Ag and Mo, ZnO on Cu, Ag, and Au, SiO2 on Pt and Ru, TiO2 on Ag and Pt, and ZrO2 on Pt and ZrPt). These films include reducible and non-reducible oxides and have been prepared and characterized experimentally, showing very unusual and interesting behavior toward metal atom adsorption. The interaction of K and Au with the metal/oxide substrates is dominated by charge-transfer aspects, where K tends to assume positive charge and Au negative charge. This fact reflects into a general trend where metal-supported oxide films displaying a large work function (i.e., deep empty states) tend to bind K cations strongly, while supports with small work function (i.e., shallow donor states) strongly stabilize Au in anionic form. The correlation between adsorption energy and work function is not strong enough to neglect several other aspects related to chemical and morphological properties of the specific oxide/metal interface. The case of Pt is completely different: here, covalent contributions to the bonding prevail, and the bond strength depends on factors such as the surface morphology and local atomic coordination, rather than the support's work function.