Symmetry and Electronic Structure of Benzene Adsorbed on Single-Domain Ge(100)-(2×1) and Ge/Si(100)-(2×1)

Abstract

The electronic structure of benzene adsorbed on single-domain Ge(100)-(2×1) and on a single-domain Ge monolayer grown on Si(100)-(2×1) has been investigated by angle-resolved ultraviolet photoemission spectroscopy (ARUPS) using linearly polarized synchrotron radiation and by temperature-programmed desorption (TPD) spectroscopy. For benzene chemisorption on both surfaces C2v adsorption symmetry is found on the basis of the ARUPS data. The detailed analysis indicates a flat-lying molecule which is di-σ-bonded to a Ge−Ge dimer and which exhibits a 1,4-cyclohexadiene-like electronic structure. The similarity of the ARUP spectra for benzene on Ge(100), on Ge/Si(100), and on Si(100) indicates nearly identical electronic structures. Benzene TPD spectra on a Ge monolayer on Si(100) show two desorption peaks at 311 and 369 K which are interpreted as desorption from terrace and step sites, respectively. Similarly, benzene desorption on Ge(100) leads to desorption peaks at about 230 and 250 K, again interpreted as desorption of chemisorbed benzene from terrace and step sites. Additionally, a weakly bound benzene species is found on Ge(100) which desorbs between 155 and 220 K and which is absent on the other surfaces. ARUPS data indicate C1 adsorption symmetry and an electronic structure similar to that of gas-phase benzene for this species.