XPS STUDY OF THE EARLY STAGES OF DEPOSITION OF NI, CU AND PT ON HOPG

A comparative XPS investigation of the formation of thin layers of tra nsition metals on graphite (HOPG) was carried out. Deposition was perf ormed by ion sputtering a clean metallic target in the preparation cha mber of the spectrometer. The chemical characterization of the interfa ce and the investigation of the growth mechanisms were carried out by examining the binding energies (BE), the full widths at half maximum ( FWHM) and the intensities (I) of the XPS core-level spectra of the dep osited metals and of the substrate as a function of deposition lime. A BE shift of +0.6 eV accompanied by a FWHM increase of about 0.6 eV of the metallic core-level is observed for the smallest amount of deposi ted metal for the three metals, The layer thickness at which the BE an d FWHM of the deposited metals reach the values of the bulk increases in the order of Cu (8 Angstrom)<Ni (12 Angstrom)<Pt (25 Angstrom), The XPS results show that Ni clusters are formed, whereas for Cu the data suggest a layer-by-layer growth. The satellite of the Ni 2p(3/2) leve l is found to be sensitive to the cluster size. The results for Pt ind icate an interfacial reaction with a small charge transfer from Pt to C, and the formation of islands. (C) 1997 Elsevier Science B.V.