Single-Crystal Studies of Molecular and Atomic Adsorption on Transition-Metal Oxides

Abstract

Photoemission spectroscopy has been used to study the interaction of inorganic molecules and metals with well characterized single-crystal surfaces of transition-metal oxides. Stoichiometric, nearly perfect surfaces of maximal valency oxides are generally inert, with most adsorption activity resulting from the presence of surface defects. Stoichiometric surfaces of lower oxides range from weakly adsorbing (e.g., O₂ or H₂O on Ti₂O₃), where defects greatly enhance reaction, to highly reactive (e.g., SO₂ on Ti₂O₃), where defects play little if any role. The reaction of metals with oxide surfaces is governed largely by the relative oxygen affinities of the respective oxides, although point defects also play an important role, particularly for relatively inert metals.