MoOx (x ≤ 2) ultrathin film growth from reactions between metallic molybdenum and TiO2 surfaces

Abstract Exposures to oxygen at room temperature and annealings under vacuum were carried out on deposits obtained from molybdenum interacting with (1 1 0) TiO 2 surfaces in order to obtain molybdenum oxide ultra thin films. Exposures to oxygen at room temperature show that the interfacial molybdenum oxide layers resulting from the TiO 2 /Mo interactions are inactive towards oxygen whereas the metallic molybdenum clusters, which grew on top of the interfacial layers, oxidise into MoO 3 . Besides, during annealings under vacuum, substrate oxygen anions can diffuse into the deposit. Thus, between 400 and 500°C, molybdenum oxide layers are progressively oxidised into MoO 2 . Moreover, from the annealing temperature, it is possible to control the film oxidation and to select its stoichiometry. At higher temperatures, MoO 2 layers oxidise, leading to MoO 3 clusters which sublimate restoring a clean TiO 2 surface. As concerns the metallic clusters, if they are exposed to air and then oxidised in MoO 3 prior to annealing, they sublimate below 300°C.