The influence of step sites on the bonding of benzenethiol on Au surfaces

The influence of step sites on benzenethiol adsorption on Au surfaces has b een studied using high resolution electron energy loss spectroscopy, X-ray photoelectron spectroscopy and thermal desorption spectroscopy. At all expo sures, the absence of a S-H stretching vibration indicates that the sulphyd ryl hydrogen is lost during adsorption on Au(322) at 300 K, The formation o f benzenethiolate is confirmed by C 1s and S 2p core level data. In contras t to the Au(111) surface, the introduction of defects consisting of monatom ic (100) steps separating (111) microterraces five atoms wide, leads to the thiolate surface intermediate adopting a coverage dependent bonding geomet ry. At low exposures, the phenyl ring is tilted away from the (111)microter races while at saturation coverage a more flat-lying orientation is preferr ed. Consideration of core level and vibrational data, supported by thermal stability studies, suggests that this unusual behaviour can be attributed t o the existence of inequivalent adsorption sites. (C) 2000 Published by Els evier Science B.V. All rights reserved.