Thermal annealing and hydrogen exposure effects on cluster-assembled nanostructured carbon films embedded with transition metal nanoparticles

Abstract

We have studied the morphology and electronic structure of cluster-assembled carbon films containing nickel and titanium nanoparticles by structural probes (transmission electron microscopy) and electronic spectroscopies (x-ray absorption, Auger spectroscopy, and electron energy loss). Vibrational characteristics of the surface have been investigated using high resolution electron energy loss spectroscopy. Nanocomposite carbon-metal films have been grown by supersonic cluster beam deposition of carbon clusters produced in the presence of finely dispersed metal catalysts. Characterization has been performed on pristine, annealed (at 560 K in vacuum), and ${\mathrm{H}}_{2}$ exposed ${(p}_{{\mathrm{H}}_{2}}=1\mathrm{mbar})$ samples. The nanocomposite films are characterized by metallic clusters embedded in a matrix of nanostructured carbon. The carbon structure at the nanoscale depend upon the type of metallic species. The electronic properties of the as-deposited films do not show any evidence of carbide formation. Thermal treatment and ${\mathrm{H}}_{2}$ exposure procedures have different effects on the electronic features inducing a certain degree of bond ordering and a decrease of the available ${\mathrm{sp}}^{2}$ sites, respectively.