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Issue 9, 2008
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Methylthiolate on Au(111): adsorption and desorption kinetics

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Abstract

Low energy electron diffraction, Auger electron spectroscopy, X-ray photoelectron spectroscopy and line of sight mass spectrometry have been used to study the adsorption and desorption of dimethyldisulfide (DMDS) on Au(111). At 300 K adsorption is dissociative, forming a chemisorbed adlayer of methylthiolate with a 1/3 ML, (√3 × √3)R30°, structure. At 100 K adsorption is molecular, with dissociation to form the 1/3 ML (√3 × √3)R30° methylthiolate structure occurring at 138–160 K. A physisorbed DMDS layer, with a coverage of 1/6 ML of DMDS, forms on top of the (√3 × √3)R30° chemisorbed MT surface for T ≤ 180 K, with multilayers forming for T ≤ 150 K. In temperature programmed desorption, multilayers of DMDS desorbed with zero order kinetics and an activation energy of 41 kJ mol−1; the physisorbed layer desorbed with first order kinetics, exhibiting repulsive lateral interactions with an activation energy which varied from 63 kJ mol−1 (θ = 0) to 51 kJ mol−1 (θ = 1); the chemisorbed methylthiolate layer desorbed associatively as DMDS via the physisorbed layer, the activation energy for the reaction, 2 methylthiolate → physisorbed DMDS, exhibiting repulsive lateral interactions with an activation energy which varied from 65 kJ mol−1 (θ = 0) to 61 kJ mol−1 (θ = 1). The physisorbed disulfide layer explains the pre-cursor state adsorption kinetics observed in sticking probability measurement, while its relatively facile formation provides a mechanism by which thiolate self-assembled monolayers can become mobile at room temperature.

Graphical abstract: Methylthiolate on Au(111): adsorption and desorption kinetics

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Article information


Submitted
10 Oct 2007
Accepted
14 Dec 2007
First published
21 Jan 2008

Phys. Chem. Chem. Phys., 2008,10, 1336-1346
Article type
Paper

Methylthiolate on Au(111): adsorption and desorption kinetics

M. G. Roper and R. G. Jones, Phys. Chem. Chem. Phys., 2008, 10, 1336
DOI: 10.1039/B715682K

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