Electronic structure of nickel nano-structures on titanium dioxide and copper : photoemission study.
Date of Issue2010
School of Physical and Mathematical Sciences
It is very critical in the subject of surface science to discriminate the initial- and final-state effects in photoemission of supported (or isolated) metal clusters. In this thesis, Auger parameter analysis is applied to separate the contributions of the initial- and final-state effect to the binding energy shift observed. The comparison made on TiO2(001) and TiO2(110) surfaces demonstrates the importance of substrate contributions to the initial-state effect. The further analysis helps us to assign initial-state effect to a combination of eigenvalue shift in surface core-level shift and charge transfer between the Ni clusters and the TiO2 substrates. The cluster size effect and interfacial charge transfer have a collective impact on the electronic structure of Ni clusters on the TiO2 surfaces. The variation of the triplet atomic states in Ni satellite features can be used to trace the electron transfer mechanism when the dimension of Ni nano-clusters is modified because the Ni 3d electron population varies with scaling the dimension size. The correlation enhancement of electrons in Ni nano-clusters due to the confinement in reduced dimension has been observed. Both the size and shape of nano-clusters show strong influence on the Ni 2p satellite structures. Apart from the 6-eV satellite, a 3-eV satellite structure emerges in Ni 2p3/2 photoemission spectra for small clusters due to the existence of 3E and 3T triplet states. However, the 3-eV satellite becomes weakened in larger clusters due to the increased electron population in 3d level, which is achieved through the electron transfer from the free-electron-like 4sp states to the unhybridized pure 3d spin down states.