Photoemission study of the modification of the electronic structure of transition-metal overlayers on TiO2 surfaces: I. Fe on TiO2(1 1 0)

The electronic states of the Fe overlayers on TiO2(1 1 0) surfaces have been investigated using normal-emission and resonant photoelectron spectroscopy with synchrotron radiation. It was found that Fe grows in a Stranski–Krastanov mode. At low coverages, Fe deposition on TiO2(1 1 0) is supposed to create surface Ti3+(3d1) ions leading to the same in-gap emission as that is produced by surface oxygen vacancies of TiO2. At high coverages, Fe-induced in-gap emission is evolved into a bulk Fe spectrum. However, at the beginning, a Fermi edge is not observed, indicating that the small Fe clusters of non-metallic nature are formed. A sharp Fermi edge is formed at higher coverages, indicating that the cluster becomes metallic as the size increases.