Photoemission study of the modification of the electronic structure of transition-metal overlayers on TiO2 surfaces -: III.: Ni on TiO2(001) and Cu on TiO2(110)

The electronic states of the Ni overlayers on TiO2 (001) surface and Cu overlayers on TiO2, (110) surface have been investigated using angle-resolved and resonant photoemission spectroscopy with synchrotron radiation. In the Ni/ TiO2 (001) system, an in-gap emission from the reduced Ti3+ 3d(1) state appears at 1.2 eV below E-F for the initial Ni deposition. Upon further deposition, the emission grows and is evolved to a spectrum of Ni metal, with forming no Fermi edge, suggesting the formation of small Ni clusters on TiO2 (001). In the Cu/TiO2 (110) system, Cu grows in a Stranski-Krastanov mode. Two in-gap emissions from the reduced Ti3+ 3d(1) state and oxidized Cu+ 3d(10) or Cu2+ 3d(9) state are observed at 0.8 and 2.8 eV below E-F, respectively, for the initial Cu deposition, giving convincing evidence that there is significant charge transfer between Cu and the substrate. Upon further deposition, the emission in the band-gap region is evolved to a spectrum of Cu metal, though delayed completion of the Fermi edge is observed. Such delay can be explained by finite cluster size effects. (C) 2004 Elsevier B.V. All rights reserved.