title: Does the S-H Bond Always Break after Adsorption of an Alkylthiol on Au(111)?
abstract: The reaction mechanism for the formation of alkyl thiol self-assembled monolayers (SAM) on Au(111) is still not clearly understood. Especially, the role of defects on the chemisorption process is an important goal to be addressed. In this work, different minimum energy reaction paths for R-SH dissociation of thiols (with long and short chains and dithiol species) adsorbed on gold adatom are calculated by using periodic density functional theory (DFT). Our results show a lower energy barrier for the RS-H bond dissociation when two thiols are adsorbed per adatom. In addition, in contrast with the formation of an adatom at the Au(111) which has been shown to depend on the alkyl chain length, the activation energy of the RS-H bond dissociation of thiols adsorbed on an adatom was shown to be independent of the alkyl chain length. The presented results and derived hypothesis support the model that thiols with long alkyl chain thiols mainly adsorb molecularly on Au(111), while for short alkyl chain thiols the S-H bond breaks. This result is explained by the fact that short-chain thiols have lower interchain interaction energies and are thus more mobile compared to the long alkyl chain thiols on the Au(111) surface. This feature enables the short chains to reach adequate geometries, driven by entropy, which could deform the Au(111) more drastically and probably pull Au atoms out from surface to form adatoms. With these results a new mechanism is proposed for the formation of alkyl chain thiols on Au(111).
authors: Institut Charles Gerhardt Montpellier, UMR5253 UM/CNRS/ENSCM, 8 Rue de l'Ecole Normale, 34296, Montpellier, France.
authors: Hazar
authors: H
authors: Guesmi
authors: Sorbonne Université, UPMC Univ Paris 06, UMR 7197, Laboratoire de Réactivité de Surface - Casier 178, 4 Place Jussieu, 75252, Paris, France.|Present address: Faculty of Sciences, Division of Theoretical Chemistry, Vrije Universiteit Amsterdam, de Boelelaan 1083, 1081 hv, Amsterdam, The Netherlands.
authors: Noelia B
authors: NB
authors: Luque
authors: Institut für Theoretische Chemie, Ulm University, Albert-Einstein-Allee 11, 89081, Ulm, Germany.|Instituto de Física Enrique Gaviola (IFEG), Universidad Nacional de Córdoba - CONICET, Argentina.
authors: Elizabeth
authors: E
authors: Santos
authors: Sorbonne Universités, UPMC Univ Paris 06, UMR 7574, CNRS, Collège de France, Laboratoire de Chimie de la Matière Condensée de Paris - Casier 174, Collège de France, 4 Place Jussieu, 75252, Paris Cedex 05, France.
authors: Frederik
authors: http://orcid.org/0000-0002-6760-6176
authors: F
authors: Tielens
keywords: S−H bond; adatoms; density functional calculations; reaction mechanisms; self-assembled monolayers