Electrochemical intercalation of perchlorate ions in HOPG: an SFM/LFM and XPS study

Highly oriented pyrolitic graphite (HOPG) in perchloric acid was adopted as a model system in order to elucidate the electrochemical anion intercalati on process in graphite. The effects of the intercalation process were studi ed in terms of the changes in surface friction and on the electronic struct ure of the HOPG. Lateral force microscopy (LFM) combined with cyclic voltam metry (CV) and X-ray photoelectron spectroscopy (XPS) indicated that the sp ecific adsorption of perchlorate ions is responsible for changes in frictio n occurring in proximity of the steps on the HOPG surface. The friction cha nges reversibly within a narrow potential window preceding intercalation. A fter an intercalation and deintercalation cycle the change of the friction at a step is irreversible. No change in the friction could be observed on t he basal plane. The binding energies in the C 1s, O 1s and Cl 2p XPS spectr a of the intercalated compound are shifted relative to those of the non-int ercalated host and adsorbed perchlorate ions, which is attributed to a shif ted Fermi level. (C) 2001 Elsevier Science B.V. All rights reserved.