Epitaxial MoO x nanostructures on TiO 2(1 1 0) obtained using thermal decomposition of Mo(CO) 6

Abstract

Stoichiometric and highly-defective TiO 2(1 1 0) 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 °C 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 °C led to the elimination of Mo as MoO 3 and to the formation of a transformed layer of stoichiometry of Ti (1− x) Mo x O 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(1 1 0) substrate to Mo(CO) 6 vapours at 450 °C in an O 2 atmosphere it was possible to obtain a MoO 2 epitaxial ultrathin layer, whose photoelectron diffraction data demonstrate that is pseudomorphic to the substrate.