標題: Photoemission and photoabsorption study of C-60 adsorption on Cu(111) surfaces
作者: Tsuei, KD
Yuh, JY
Tzeng, CT
Chu, RY
Chung, SC
Tsang, KL
光電工程學系
Department of Photonics
公開日期: 15-十二月-1997
摘要: We have carried out an extensive study of C-60 adsorption on Cu(111) surfaces using low-energy electron diffraction, photoemission, and x-ray-absorption spectroscopy. It is found that in valence-band photoemission a state forms right below the Fermi energy for an annealed, well-ordered monolayer, similar to the case of K-doped C-60. This peak disperses across the Fermi energy at off normal emission geometry. The spectra of carbon core-level photoemission show that the line shape is highly asymmetric with a metalliclike tail. The carbon near-edge absorption spectra show that the lowest unoccupied molecular orbital (LUMO) is attenuated, and a clear Fermi edge jump appears at the absorption onset. This evidence indicates that charge transfers from the substrate to the C-60 molecular orbitals and the overlayer becomes metallic. The amount of charge transfer can be determined to be 1.5-2 electrons per molecule from both the area of the occupied LUMO in photoemission and the peak shift in near-edge absorption spectra. It has been reported that many metal surfaces with originally different work functions covered by a monolayer of C-60 have a similar work function of about 5 eV. We suggest that the measured work functions are due to the metallic C-60 overlayers and are similar regardless of the metal substrates. This is in line with the reported alignment of monolayer energy levels to substrate Fermi energy. Since the work functions are similar, the energy levels with respect to the vacuum level are also similar. Finally we compare near-edge x-ray-absorption with inverse photoemission spectroscopy to address the screening effects.
URI: http://hdl.handle.net/11536/144
ISSN: 1098-0121
期刊: PHYSICAL REVIEW B
Volume: 56
Issue: 23
起始頁: 15412
結束頁: 15420
顯示於類別:期刊論文