MoO3 films grown on polycrystalline Cu: Morphological, structural, and electronic properties

In this work, the authors investigated MoO₃ films with thickness between 30 nm and 1 μm grown at room temperature by solid phase deposition on polycrystalline Cu substrates. Atomic force microscopy, scanning electron microscopy, and scanning tunneling microscopy revealed the presence of a homogenous MoO₃ film with a "grainlike" morphology, while Raman spectroscopy showed an amorphous character of the film. Nanoindentation measurements evidenced a coating hardness and stiffness comparable with the copper substrate ones, while Auger electron spectroscopy, x-ray absorption spectroscopy, and secondary electron spectroscopy displayed a pure MoO₃ stoichiometry and a work function Φ MoO₃ = 6.5 eV, 1.8 eV higher than that of the Cu substrate. MoO₃ films of thickness between 30 and 300 nm evidenced a metallic behavior, whereas for higher thickness, the resistance-temperature curves showed a semiconducting character.