ELECTRONIC-STRUCTURE OF BENZENE ADSORBED ON SINGLE-DOMAIN SI(001)-(2X1) - A COMBINED EXPERIMENTAL AND THEORETICAL-STUDY

Benzene adsorption on a single-domain Si(001)-(2X1) surface has been s tudied by thermal desorption spectroscopy (TPD) and angle-resolved pho toelectron spectroscopy (ARUPS) using linearly polarized synchrotron r adiation. Angle-resolved photoemission spectra for the saturated benze ne layer exhibit well-defined polarization and azimuthal dependencies compatible with a flat-lying benzene molecule with local C-2 upsilon s ymmetry. Based on these results two structure models are proposed. Fir st-principles density functional cluster calculations have been perfor med for each of these structures, Total energy minimization and a deta iled comparison of the experimental ARUPS spectra with the one-particl e spectra of the model clusters leads to a 1,4-cyclohexadienelike adso rption complex with a flat-lying benzene molecule which is di-sigma bo nded to the two dangling bonds of a single Si-Si surface dimer. Especi ally, one of the unoccupied 1 e(2u) (pi) orbitals of the free benzene molecule shifts down (by about 3 eV) and evolves into the highest occ upied molecular orbital (HOMO) of the chemisorbed molecule. (C) 1998 A merican Institute of Physics. [S0021-9606(98)03213-9].