Spatially resolved MoOx phases by the laser oxidation of MoO2: a possible route for all-molybdenum oxide devices

Abstract

MoO₂ thin films were subjected to a laser localized oxidation process that allowed us to obtain different well defined MoO_x phases. In particular, the spatially resolved MoO₂, α-MoO₃, β-MoO₃, amorphous a-MoO₃, and Mo₄O₁₁ regions were obtained as a function of the laser power and the distance to the laser focus. The origin of this spatial phase separation was investigated through a careful and exhaustive Raman mapping study covering several micrometres away from the laser focus and taking into account the thermochemical properties of the species involved. It was found that a sublimation/deposition process, driven by the different vapour pressures of the species, was responsible for the phase separation. At higher laser powers, a solid state reaction was observed to contribute as well. In the laser annealed tracks, distant lateral sidebands of oxide deposition were observed with composition that depended on the laser power and the distance to the centre of the track. The electrical measurements between the irradiated and non-irradiated regions showed a strong rectifying behaviour, revealing a transformation from metal-like to semiconducting Mo oxide phases, which may open the way to the development of laser written all-oxide electronic circuits.