Observation of photoexcitation of Fe-oxide grown on TiO2(100) by visible light irradiation

Electronic excitation of materials is of fundamental and technological importance and interest in terms of photoinduced phase transition, photovoltaics, and photocatalysis. In the present study, photoexcitation of Fe2 O 3 epitaxially grown on rutile TiO2(100) was investigated with conversion electron Mossbauer spectroscopy (CEMS) under dominantly visible-light irradiation. 57Fe was deposited on the substrate at a substrate temperature of 973 K, and the resulting film was characterized by RHEED and XPS. After deposition of Fe on TiO2(100), it was found that Fe was oxidized to Fe 3+, and the structure was analyzed to be the rhombohedral phase of Fe2 O 3. While the CEMS spectrum without light irradiation showed a quadrupole splitting of 0.80 mm/s with an isomer shift of +0.25 mm/s, an additional component with a quadrupole splitting of 0.85 and an isomer shift of +0.67 mm/s was observed under light irradiation. The latter component corresponds to a reduced state of Fe at the octahedral site surrounded by oxygen atoms. The lifetime of this photoexcited state is discussed.