Structure and Morphology of Co Nanoparticles Deposited onto Highly Oriented Pyrolytic Graphite

X-ray photoelectron spectroscopy (XPS) and atomic force microscopy have been used to study Co nanoparticles evaporated onto freshly cleaved highly oriented pyrolytic graphite (HOPG) surfaces. XPS chemical characterization employed symmetrical line shapes and was carried out as functions of the amount of Co deposited and of the time subsequent to deposition. The nominal amounts of evaporated Co ranged from 0.5 to 175 Å. On analyzing the relationships among the Co2p, C1s, and O1s spectra, we found that evaporated Co reacts not only with HOPG surface defects (including oxidized carbon contaminant groups), but also with residual C- and O-containing species present in the vacuum chamber. Both carbide and oxide are produced as surface layers around each nanoparticle, stabilizing them and preventing further coalescence.