Electronic structure of 1,3,5,7-cyclooctatetraene chemisorbed on Si(001)-2×1 at 300 K studied by PES, NEXAFS, and resonant valence band spectroscopy

The electronic structure of 1,3,5,7-cyclooctatetraene, an antiaromatic molecule, adsorbed on Si(001)-2×1 at 300 K has been investigated by a combination of core-level spectroscopies using synchrotron radiation. Si 2p and C 1s photoemission spectroscopy (PES) are used to follow the reaction of silicon surface states and the formation of Si-C bonds. C 1s near-edge X-ray absorption fine structure (NEXAFS) spectroscopy shows that p bonds survive after chemisorption. The orientational order of the free p bonds is deduced from the angular dependence of the NEXAFS spectra; performed on a single domain (vicinal) surface, this study indicates that multiple adsorption geometries are actually adopted by the chemisorbed molecules. Finally, resonant valence band spectroscopy gives the binding energy position of the occupied p band of the chemisorbates, information that may be useful for the interpretation of scanning tunneling microscopy images.