Interaction of oxygen with Mo(100), Mo(110), and Mo(111) surfaces. RHEED and AES analyses of the molybdenum oxide nucleation and growth

Abstract

A study of the nucleation and growth of MoO 3 generated by interaction of oxygen with Mo(100), Mo(110), and Mo(111) single crystalline surfaces is investigated at high oxygen pressure (10 4 Pa) and low temperature (620 to 820 K). The results of RHEED and AES analyses prove that under these oxidation conditions, MoO 3 nucleates directly from the metal without intermediate formation of MoO 2 or nonstoichiometric molybdenum oxide such as Mo 4O 11. The structure and orientation of MoO 3 nuclei are characterized in relation with the parent molybdenum surface. On the Mo(110) and Mo(111) surfaces, which are faceting, the nucleation and growth of MoO 3 takes place by successive structural steps. On the Mo(100) surface, epitaxial relations induce the formation of MoO 3(010) plates oriented onto the Mo surface, which stabilizes and makes passive the Mo(100) surface. The features of the nucleation and growth of MoO 3 are interpreted as linked respectively to structural relations of the metal-oxide interface and to preferential diffusion paths of oxygen through MoO 3.