| Abstract
| - We have used time-of-flight (TOF) direct recoiling spectroscopy (DRS) to follow propanethiol adsorption at300 K from the vapor phase on an Ag(111) surface, for exposures ranging from 10-1 to 105 L. Results showthat the adsorption proceeds with changes in the sticking coefficient, consistent with at least three phases. Atlow exposures, the alkanethiol molecules adsorb with high probability at defect sites, followed by a slowergrowth mode that essentially covers the whole surface. A third change in the sticking coefficient is associatedwith the final saturation stage, corresponding to a thicker layer related to molecules in a more upright orientation.The adsorption kinetics for hexanethiol is similar to that of propanethiol but taking place at higher rates,stressing the importance of the hydrocarbon chain length in the growth process. ISS-TOF measurementsduring thermal desorption show that most of the C, H, and S go away together, suggesting that the moleculesadsorb and desorb from flat regions without S−C bond cleavage. Fitting the desorption maximum at 450 Kwith a first-order desorption curve gives a desorption energy of 1.43 eV. A small final S content that iscorrelated with the initial Ag(111) surface roughness is observed after desorption.
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