Electronic structure and orientation of anthracene on Ag(111)

Abstract

Spectroscopic techniques based on photoabsorption and photoemission, i.e. near edge X-ray absorption fine structure (NEXAFS) and angular-resolved photoemission (ARUPS) using synchrotron radiation, as well as inverse photoemission (IPES) have been employed to obtain information on the molecular orientation and electronic structure of thin films of anthracene adsorbed on Ag(111) surfaces. By measuring the polarisation dependence of the (Cls →π∗) transitions in the NEXAFS spectra, we find a parallel orientation of the molecular plane with respect to the substrate. The angular behaviour of the adsorbate-induced photoemission bands corroborates this result, and additionally a complete mapping of the valence levels and an improved assignment for the bands extended over a large binding energy region emerges. The unoccupied π ∗ levels levels have been studied by inverse photoemission and have been compared with MO calculations, as well as with electron transmission gas phase measurements (ETS). A well ordered (4 × 4) structure is observed in LEED investigations.