The Electronic Structure of Ag(110)c(4$\times$4)C$_{60}$ and Au(110)(6$\times$5)C$_{60}$

We use direct (UPS) and inverse photoemission spectroscopy (IPS) to examine the occupied and unoccupied electronic structure of C$_{60}$ adsorbed on Ag(110). In addition, the unoccupied electronic structure of C$_{60}$ adsorbed on Au(110)2$\times$1 is investigated by IPS. Two distinct coverage regimes, monolayer and multilayer, are found for both systems. First layer C$_{60}$ chemisorbs, forming an ordered overlayer on each substrate: Ag(110)c(4$\times$4)C$_{60}$ and Au(110)(6$\times$5)C$_{60}$. The unoccupied electronic structures of these ordered overlayer systems are indistinguishable within the limitations of the measurement. In each case the unoccupied levels move down in energy from the multilayer positions and the lowest unoccupied molecular orbital is pinned to E$_{F}$. In the occupied region of Ag(110)c(4$\times$4)C$_{60}$ peaks also move towards E$_{F}$ in comparison to multilayer data. This combined observation irrefutably points to final state effects being of relevance in both spectroscopies. Charge transfer from Ag(110) into first layer C$_{60}$ molecules is directly observed by UPS. The interaction of first layer C$_{60}$ molecules with the substrate is further evidenced by a broadening of C$_{60}$ features, ascribed to a splitting of molecular orbitals. The work functions of Ag(110)c(4$\times$4)C$_{60}$ and Au(110)(6$\times$5)C$_{60}$ are found to be equal to that of bulk C$_{60}$.

By: D. Purdie, H. Bernhoff and B. Reihl

Published in: Surface Science, volume 364, (no 3), pages 279-86 in 1996

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