Fabrication of Mo oxide and metallic Mo thin film deposited by chemical vapor transport and their optical and electrical properties

Abstract

MoO3, one of the transition metal oxides has attracted a considerable attention in many industrial applications such as photochromic, electrochromic, sensor, catalysis and microbatteries due to its superior characteristics. Recently, many deposition techniques have been developed to deposit Mo oxide thin films including chemical vapor deposition, evaporation, sol-gel coating, various wet chemistry methods, RF magnetron sputtering, and pulsed laser deposition. Despite the variety of synthesis techniques, there are significant need for improvement in the deposition of large area chromigenic film, that is simple, low-cost and environtment-friendly. In this study, Mo oxide thin films were successfully fabricated by chemical vapor transport of volatile MoO3(OH)2(g) and dehydration to Mo oxided phase during hydrogen reduction at various temperatures for various holding times with subsequent annealing under O2 at 400oC for various maintaining times. The MoO2 thin film revealed good adhesion onto the various substrates. At the XPS spectra of the sample deposited at 500oC for 5min, it was confirmed that the thin film was composed three phases of MoO2, Mo4O11 and Mo13O33. On going the annealing, the ratio of the MoO3 phase became higher and fully transformed to the MoO3 phase after 60 min. The transmittance band broadened and red-shifted with increasing annealing time, and the thin films simultaneously became more transparent. Due to reduced oxygen vacancy. The index of refraction is around 1.55 with a flat dispersion curve across the visible. The band gap energy increased to approximately 3.5 eV the transformation from MoO2 to MoO3 with increasing the annealing time. Also, it was considered that the annealing of the deposited MoO2 thin film produces three microstructural changes such as increase of density, improvement of crystallinity. In the metallic Mo thin film deposition, thin film with well adhesion onto the substrate was homogeneously deposited at various temperatures and subsequent reduction at various conditions. Phase change as the deposition time increase was confirmed by XRD and microstructure analysis. It was considered that the exhaustion of source materials for deposition, MoO3(OH)2 by reduction from MoO3 powder to MoO2 powders and simultaneous reduction to metallic Mo phase affected the phase change of the thin film during deposition.