Binding Modes of Fluorinated Benzylphosphonic Acids on the Polar ZnO Surface and Impact on Work Function

The interfaces formed between a zinc-terminated polar zinc oxide (0002) surface and a series of chemisorbed fluorinated benzylphosphonic acids have been studied at the density functional theory level. The results indicate that there occur substantial changes in the adsorption energy and surface work function whether the binding mode is bidentate or tridentate. Also, the trends and magnitude of the various factors that determine the total modifications in work function markedly vary between the two binding modes. We have also calculated the oxygen core-level binding energy shifts of the PO3 moiety with respect to the oxygen atoms in bulk ZnO; good agreement is obtained between the calculated values of the core-level binding energy shifts for the tridentate binding mode and available X-ray photoelectron spectroscopy data.