Electronic structure of biphenyl on Si(100)

We report the study of both occupied and unoccupied electronic states of biphenyl adsorbed on Si 100 by using synchrotron radiation ultraviolet photoemission spectroscopy, x-ray photoemission spectroscopy, and near-edge x-ray absorption fine structure spectroscopy. The results are compared with calculations of the occupied densities of states. Evidence is given of two main effects: i a down shift in energy of the second highest occupied molecular orbital of the strongly chemisorbed configuration at room temperature compared to the weakly chemisorbed configuration at low temperatures and ii an energy splitting of some of the occupied and unoccupied states due to the different interactions of the two phenyl rings of the molecule. The electronic structure of biphenyl on Si 100 appears to be an appropriate test for state of the art experimental and theoretical methods.