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).

Rationalizing the formation of binary mixed thiol self-assembled monolayers

“…This point was also very concluded in our recent investigation on the thiol SAM formation reaction paths analysis. [36] The surface is indeed found to be affected by adsorption of the thiol radicals. No barrierless adatom formation was observed, however Au-atoms were pulled out of the surface.…”

“…[30][31][32][33][34] It should be noted that the adsorption of thiol molecules cannot be generalized to one model, since the polarization of the sulphur atom is very sensible to the thiol chain; at least this is what we would like to show in results presented here. This means that the adsorption process involving S-H bond breaking [35][36][37][38] and or adatom adsorption [39][40][41][42] is expected to be dependent of the type of thiol.…”

Nanoparticle Assembling through Click Chemistry Directed by Mixed SAMs for Magnetic Applications

“…This value is further used as a reference value in order to quantify the stabilization of the SAM mixture. 30,54,55 ΔE ads is the lowest for all segregated mixtures whatever the S-CC/S-CH 3 molar ratio ( Figure 6). It shows that intermolecular interactions are thermodynamically favored in segregated mixtures.…”

The Role of a Double Molecular Anchor on the Mobility and Self‐Assembly of Thiols on Au(111): The Case of Mercaptobenzoic Acid

“…[1,2] It has also been shown that thiol mobility is reduced as van der Waals interactions among adsorbed molecules increase, which resultsi nadecrease of the size of the ordered domains, af act observed for alkanethiols as af unction of the hydrocarbon chain length. It is well-known that the adsorptionp rocess results in the formationo fo rdered molecular domains, the size of which depends on the temperature, thus reflecting the surface mobilityo fa dsorbed thiol species on the Au(111)s urface.…”