SURFACE-STATES DUE TO FE ATOMS DEPOSITED ON A TIO2 SURFACE-COATED WITH A POROUS SIO2 FILM

hA thin SiO2 film 20 Angstrom in thickness has been deposited on the T iO2 surface by a sputtering technique. In the SiO2-coated TiO2 electro de, a current density at -1.0 V is reduced to one-third that of the ba re TiO2 electrodes. This indicates that on average one-third of the Ti O2 surface is in contact with an electrolyte solution through pores of the SiO2 film. Electronic structures at the interfaces of TiO2-electr olytic solution and TiO2-SiO2-electrolytic solution are investigated b y means of the conductance method and isothermal capacitance transient spectroscopy. The electrochemical depositions of Fe atoms on the surf aces of the bare and the SiO2-coated TiO2 electrodes result in the for mation of new surface states. The Fe-related surface states are distri buted in the range 0.45-0.75 eV below the bottom of the conduction ban d. The bandwidth of the Fe-related surface states at the SiO2-coated T iO2 electrode is slightly wider than that at the bare TiO2 electrode. The energy distribution of Fe-related surface states is varied with th e number of Fe atoms. This implies that the surface-state band origina tes from electronic interactions inside Fe microclusters.