Epitaxial MoO_x nanostructures on TiO_2(110) obtained using thermal decomposition of Mo(CO)_6

摘要

Stoichiometric and highly-defective TiO_2(110) surfaces (called as yellow and blue, respectively) were exposed to Mo(CO)_6 vapours in UHV and in a reactive O_2 atmosphere. In the case of yellow-TiO_2, an O_2 reactive atmosphere was necessary to obtain the Mo(CO)_6 decomposition at 450℃ with deposition of MoO_x nanostructures where, according to core level photoemission data, the Mo~(+4) state is predominant. In the case of blue-TiO_2 it was possible to obtain Mo deposition both in UHV and in an O_2 atmosphere. A high dose of Mo(CO)_6 in UHV on blue-TiO_2 allowed the deposition of a thick metallic Mo layer. An air treatment of this sample at 580℃ led to the elimination of Mo as MoO_3 and to the formation of a transformed layer of stoichiometry of Ti_((1-x))Mo_xO_2 (where x is close to 0.1) which, according to photoelectron diffraction data, can be described as a substitutional near-surface alloy, where Mo~(+4) ions are embedded into the titania lattice. This embedding procedure results in a stabilization of the Mo~(+4) ions, which are capable to survive to air exposure for a rather long period of time. After exposure of the blue-TiO_2(110) substrate to Mo(CO)_6 vapours at 450℃ in an O_2 atmosphere it was possible to obtain a MoO_2 epitaxial ultrathin layer, whose photoelectron diffraction data demonstrate that is pseudomor-phic to the substrate.