| AVS 57th International Symposium & Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS2-TuM |
| Session: | Aromatic Molecular Films |
| Presenter: | W.W. Pai, National Taiwan Univ. |
| Authors: | W.W. Pai, National Taiwan Univ. H.T. Jeng, Academia Sinica, Taiwan C.-M. Cheng, National Synchrotron Radiation Research Center, Taiwan C.-H. Lin, National Taiwan Univ. X.D. Xiao, Hong Kong Univ. of Sci. and Tech. A.D. Zhao, Hong Kong Univ. of Sci. and Tech. X.Q. Zhang, Hong Kong Univ. of Sci. and Tech. G. Xu, City Univ. of Hong Kong X.Q. Shi, City Univ. of Hong Kong M.A. Van Hove, City Univ. of Hong Kong C.-S. Hsue, National Tsing Hua Univ., Taiwan K.-D. Tsuei, National Synchrotron Radiation Research Center, Taiwan |
| Correspondent: | Click to Email |
We demonstrate the charge state of C60 on a Cu(111) surface can be made optimal, i.e., forming C603- as required for superconductivity in bulk alkali-doped C60, purely through interface reconstruction rather than with foreign dopants [1]. We link the origin of the C603- charge state to a reconstructed interface with ordered (4 × 4) 7-atom vacancy holes in the surface. In contrast, C60 adsorbed on unreconstructed Cu(111) receives a much smaller amount of electrons. Specifically, we used multiple techniques of scanning tunneling microscopy and spectroscopy (STM/STS), angle-resolved and angle-integrated photoemission spectroscopy(AR-,AI-PES), ab initio calculations, and low-energy electron diffraction I-V analysis(LEED I-V) to convincingly establish the C603- charge state and the reconstructed interface model. With STM, in-situ monitoring of C60 growth at ~400 K revealed that each C60 removes 7 atoms. STS showed the LUMO band sits nearly at the Fermi energy when the interface is reconstructed, or ~0.8 eV above the Fermi energy at unreconstructed interface. AI-PES indicated the initial charge state of C60 over reconstructed interface is already close to C603- because very few extra K atoms are needed to reach maximal LUMO spectra intensity. AR-PES showed two hole-like bands crossing Kbar that account for most of the charge transfer, and a shallow electron-like band near Γbar. An extensive LEED I-V analysis using a total fitting range of ~3500 eV and 33 independent beams resolved the preferred structure model as the unfaulted fcc 7-atom monolayer vacancy model. We obtained a very good Pendry factor of ~0.27. Finally, although the C60 has an optimal doping level for bulk superconductivity, we did not observe surface superconductivity down to ~5 K. Our result adds a new dimension in understanding functional molecular thin films; it illustrate a definitive interface structure-doping effect that affects the electronic properties of molecule-electrode contact.
[1] Woei Wu Pai et al., Phys. Rev. Lett. 104, 036103 (2010)