STM Study of Surface Species Formed by Methanol Adsorption on Stoichiometric and Reduced ZnO(10(1)over-bar0) Surfaces

Methanol adsorption on the stoichiometric and slightly reduced ZnO(10 (1) over bar0) surfaces has been studied by scanning tunneling microscopy (STM). On the stoichiometric surface it was found that adsorbed methanol formed two types of ordered structures by dissociative adsorption in different modes, one of which was a dominant two-dimensional island structure residing on surface zinc atom rows, while the other was a linear chain structure residing between two surface zinc rows. In addition, a mobile phase of molecularly adsorbed methanol was deduced occupying the areas aside the ordered domains and keeping in equilibrium with the island structure. In contrast to the stoichiometric surface, on the slightly reduced surface, only the linear chain structure was observed as an ordered phase, accompanied by an unusual type of line defects. The STM observations indicated that the drastic change of surface properties occurred oil the whole surface not at the specific sites such as point vacancies.