PHONON STIFFENING INDUCED BY COPPER INTERCALATION IN MONOLAYER GRAPHITE ON NI(111)

The intercalation of copper underneath a graphite monolayer (IL IG) fo rmed an Ni(111) has been investigated by means of HREELS, Auger spectr oscopy and LEED. The softening of the graphite phonon modes in the cas e of the MG/Ni(111) system, caused by a strong interaction with the Ni substrate, is removed after intercalation of copper. The correspondin g phonon dispersion curves are very similar to those of bulk graphite and the C(KVV) Auger spectra resemble very much those of classical gra phite intercalated compounds. This demonstrates that the observed, sti ffening is a consequence of a smaller charge transfer from the copper atoms into the pi-states of graphite.