SUPERFICIAL OXIDATION OF MOLYBDENUM AT HIGH-PRESSURE AND LOW-TEMPERATURE - RHEED AND AES ANALYSES OF THE MOLYBDENUM OXIDE FORMATION

Numerous studies relate to the interaction of the molybdenum surface with oxygen at low pressure and high temperature. They give results about oxygen chemisorption, surface facetting and the epitaxial formation of MoO2 crystallites. This work deals with the interaction of Mo(100), Mo(110) and Mo(111) surfaces with oxygen at high pressure (10(4) Pa) and low temperature (620-820 K). RHEED and AES analyses results prove that, in these oxidation conditions: MoO2 and non-stoichiometric molybdenum oxide such as Mo4O11 are not evidenced in any of the molybdenum oxidation steps. The MoO3 phase nucleates directly from any Mo surface. The structure and orientation of MoO3 nuclei are characterized in relation with the parent molybdenum surface. Some MoO3 nucleation and growth mechanisms are proposed, involving the specific properties of the MoO3 phase and the structure of molybdenum surfaces.