| Abstract
| - Although self-assembled monolayers made of long chains of n-alkanethiols [CH3(CH2)n-1SH] on Au(111)have been extensively studied in the past, the driving forces behind the appearance of the (3 × 2√3) superlatticeobserved at full coverage are still not completely understood. To focus on the role played by the sulfurheadgroup minimizing the interactions between chains and to prevent a possible X-ray-induced damage, wehave carried out a He atom diffraction study of the adsorption of the shortest (n = 1) thiol radical, obtainedby dissociative adsorption of (CH3S)2, on the Au(111) surface. Contrary to current literature reports, domainsof the hexagonal (√3 × √3)R30° structure are observed to convert into the well-ordered(3 × 2√3) superstructure after annealing times of a few hours. The observation of peaks forbidden by the(3 × 2√3) model proposed by Fenter et al. (Fenter, P.; Eberhardt, A.; Eisenberger, P. Science1994, 266,1216) suggests a distortion of the symmetry of the unit cell. The observed chemisorption and physisorptionenergies were in good agreement with the literature.
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