  Chemically _ driven isothermal close space vapour transport was used to
prepare pure MoO2 films which were eventually converted to MoO3 by annealing in
air. According to temperature_dependent Raman measurements, the MoO2/MoO3 phase
transformation was found to occur in the 225 _ 350 oC range; no other phases
were detected during the transition. A clear change in composition and Raman
spectra, as well as noticeable modifications of the band gap and the absorption
coefficient confirmed the conversion from MoO2 to MoO3. An extensive
characterization of films of both pure phases was carried out. In particular, a
procedure was developed to determine the dispersion relation of the refractive
index of MoO2 from the shift of the interference fringes the used SiO2/Si
substrate. The obtained refractive index was corrected taking into account the
porosity calculated from elastic backscattering spectrometry. The Debye
temperature and the residual resistivity were extracted from the electrical
resistivity temperature dependence using the Bloch _ Gruneisen equation. MoO3
converted samples presented very high resistivity and a typical semiconducting
behaviour. They also showed intense and broad luminescence spectra, which were
deconvoluted considering several contributions; and its behaviour with
temperature was examined. Furthermore, surface photovoltage spectra were taken
and the relation of these spectra with the photoluminescence is discussed.
