Molecular orientation of 2-mercaptobenzoxazole adsorbed on Cu(100) surface

The long range ordered p(2x2) self-assembled monolayer formed by dosing 2-mercaptobenzoxazole (MBO, C7H5NOS) on the Cu(100) surface at room temperature has been investigated by means of near edge X-ray adsorption fine structure (NEXAFS) technique at the sulphur K-edge. NEXAFS S-K-edge spectra have been recorded at different incident photon angles with respect to the Cu(100) surface, using linearly polarised synchrotron radiation. A clear spectral feature has been observed close to the absorption edge, with higher intensity at grazing incidence, assigned to the sigma*(S-C) resonance, corresponding to the transition from the S Is core level to the sigma*(S-C) antibonding molecular state. The angular dependence of the sigma*(S-C) resonance intensity clearly indicates that the S-C axis is nearly perpendicular to the surface (13 degrees +/- 13 degrees), confirming the major role of S in bonding to the surface, and the influence of the pi-pi interaction between the molecules in driving the almost upright position at saturation coverage. (c) 2005 Elsevier B.V. All rights reserved.