MODIFICATION OF THE ELECTRON SPECTRUM AND VIBRATIONAL PROPERTIES OF AMORPHOUS-CARBON BY COPPER DOPING

The near-gap electron spectrum and the effective charge distribution i n graphite-like carbon nanoclusters of simple geometry in a-C: H conta ining a single Cu atom are calculated in the tight-binding approximati on. Only the coupling between pi electrons of the constituent C atoms and one valence s electron of the Cu atom is taken into account. The b inding energy of the Cu atom in the clusters and the static dipole mom ent of the clusters are calculated. The results are invoked to interpr et the experimentally observed activation of the Raman G band in the I R spectrum of a-C : H : Cu as a consequence of a lowering of the symme try of the graphite-like clusters due to copper intercalation. Experim ental data on the time dependence of the G band intensity during isoth ermal annealing of a-C : H: Cu are presented. The data suggest the pos sibility of reversible transfer of Cu atoms between the impurity state s in the copper-carbon clusters and the impurity states in the purely copper clusters. The average activation energies of direct and reverse transfer are estimated from the experiment. (C) 1998 American Institu te of Physics.