hA thin SiO2 film 20 Angstrom in thickness has been deposited on the TiO2 surface by a sputtering technique. In the SiO2-coated TiO2 electrode, a current density at -1.0 V is reduced to one-third that of the bare TiO2 electrodes. This indicates that on average one-third of the TiO2 surface is in contact with an electrolyte solution through pores of the SiO2 film. Electronic structures at the interfaces of TiO2-electrolytic solution and TiO2-SiO2-electrolytic solution are investigated by means of the conductance method and isothermal capacitance transient spectroscopy. The electrochemical depositions of Fe atoms on the surfaces of the bare and the SiO2-coated TiO2 electrodes result in the formation of new surface states. The Fe-related surface states are distributed in the range 0.45-0.75 eV below the bottom of the conduction band. The bandwidth of the Fe-related surface states at the SiO2-coated TiO2 electrode is slightly wider than that at the bare TiO2 electrode. The energy distribution of Fe-related surface states is varied with the number of Fe atoms. This implies that the surface-state band originates from electronic interactions inside Fe microclusters.