Angular-Resolved X-Ray Absorption Study of Alkanethiols on III-V(110) Surfaces D. Zerulla 1 , K.H. Hallmeier 1 , and T. Chassé 1,2 1 Wilhelm-Ostwald-Institut für Physikal. u. Theoret. Chemie, Univ. Leipzig, Linnéstr. 2, D-04103 Leipzig 2 Institut für Oberflächenmodifizierung e.V., Permoserstr. 15, D-04308 Leipzig , Germany The XANES-measurements were carried out at the beamlines HE-TGM2 and PM5 of the BESSY I storage ring. The spectra were recorded in partial electron yield mode at a pressure of 5-8x10 -10 mbar. The retard potential of the partial yield detector was typically set to 50V. All spectra were normalized with respect to the incident photon flux, and the independently recorded background curve. Self-assembled monolayers (SAMs) were prepared by adsorption from millimolar solutions of thiols . Fig. 1: Angular dependent C K absorption spectra (electron yield mode) from HDT on GaP(110). Fig. 1 displays a set of C K XANES of a monolayer prepared by adsorption of hexa- decanethiol (HDT) on GaP(110). The absorption spectra in the figure were recorded at several incidence directions of the soft X- ray photons with respect to the surface normal while keeping the azimuthal orientation of the polarization vector parallel to the [001] surface direction strictly. The broad peak at the highest photon energy, close to 296eV, is attributed to the C-C(*) resonance. The sharp peak at the photon energy of about 290eV, close to the C K edge, corresponds to the C- H(*) resonance, mainly [1]. The third peak feature, which may be observed at about 2 eV higher energy compared to the latter, is much smaller in intensity. This peak feature appears much stronger in the absorption spectra for the shorter thiols, suggesting an origin due to the C-S bonds at the end of the alkyl chains. A peak shape analysis of the C K absorption spectra has been performed in order to obtain quantitative data [2]. In the special case of the C-C(*) resonance and determination of its intensity, the exact position and width of this edge are not critical to the fit because this high energy peak is situated well above the threshold already.