Nanostructured MoSx-based thin films obtained by electrochemical reduction

The in situ electrochemical deposition of nanostructured MoSx (x = 1.5-1.7) based thin films on various substrates from aqueous solutions is reported. The as-deposited amorphous films transform on annealing into crystalline ones as revealed by a stepwise high temperature X-ray diffraction (XRD). Both Raman spectroscopy and XRD crystal structure analyses confirmed the formation of inorganic fullerene-MoSx nanoparticles (IF-MoSx). The as-deposited thin films have a featureless surface morphology, but after annealing either a nanotube or a nanorod structure along with numerous smaller nanoballs appear at the surface. An investigation by transmission electron microscopy unearths the presence of nanoballs, nanoribbons, and nanotubes throughout the annealed MoSx thin films. The size of the nanoballs is in the range of 5-10 nm. The nanotubes have a diameter of 10-400 nm, and a length of up to several micrometers as evidenced by SEM. The catalytic effect of transition metals on the growth of nanotubes is noticed. The temperature-induced transformation from amorphous to crystalline structured MoSx films results in a large lowering of the coefficient of friction under sliding against corundum in ambient air of 50% relative humidity.