Epitaxial MoOx nanostructures on TiO2(110) obtained using thermal decompositionof Mo(CO)(6)

Stoichiometric and highly-defective TiO2 (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-TiO2, an O-2 reactive atmosphere was necessary to obtain the MO(CO)6 decomposition at 450 degrees C with deposition of Moo, nanostructures where, according to core level photoemission data, the Mo+4 state is predominant. In the case of blue-TiO2 it was possible to obtain Mo deposition both in UHV and in an 02 atmosphere. A high dose Of MO(CO)(6) in UHV on blue-TiO2 allowed the deposition of a thick metallic Mo layer. An air treatment of this sample at 580 degrees C led to the elimination of Mo as MoO3 and to the formation of a transformed layer of stoichiometry of Ti(1-x)MoxO2 (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-TiO2 10) substrate to MO(CO)(6) vapours at 450 degrees C in an O-2 atmosphere it was possible to obtain a MoO2 epitaxial ultrathin layer, whose photoelectron diffraction data demonstrate that is pseudomorphic to the substrate. (c) 2006 Elsevier B.V. All rights reserved.