Interaction of methanol with ZnO surfaces at low temperatures

Adsorption and condensation of methanol on polar (0001) faces of zinc oxide were studied by XPS and UPS. The results indicate that adsorbed CH₃OH is partly transformed to a precursor of a methoxy species at temperatures at low as 105 K. Adsorption saturates only at a coverage of about two monolayers. This double layer seems to become oriented by the structural influence of the (0001) face and stabilized by hydrogen bridge bonds. The sticking coefficient is of the order of 10^?2 while the condensation coefficient on top of the oriented double layer is as low as 10^?3. TDS on a polycrystalline ZnO film supports this model. No other species than CH₃OH occurred in desorption.