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

Abstract

The dynamics of the self-assembly process of thiol molecules on Au(111) is affected by the interplay between molecule-substrate and molecule-molecule interactions. Therefore, it is interesting to explore the effect of a second anchor to the gold surface, in addition to the S atom, on both the order and the feasibility of phase transitions in self-assembled monolayers. To assess the role of an additional O anchor, we have compared the adsorption of two mercaptobenzoic acid isomers, 2-mercaptobenzoic acid (2-MBA) and 4-mercaptobenzoic acid (4-MBA), on Au(111). Results from scanning tunneling microscopy, X-ray photoelectron spectroscopy, electrochemical techniques, and density functional theory calculations show that the additional O anchor in 2-MBA hinders surface mobility, reducing domain size and impeding the molecular reorganization involved in phase transition to denser phases on the Au(111) substrates. This knowledge can help to predict the range order and molecular density of the thiol SAM depending on the chemical structure of the adsorbate.

Interfacial Acid–Base Equilibria and Electric Fields Concurrently Probed by In Situ Surface-Enhanced Infrared Spectroscopy

“…To put these numbers into context, the density of singlecomponent 4-MBA SAMs has been reported to be between 4 and 6 molecules/nm 2 (the density of our SAMs could not be unambiguously determined by SEIRAS or electrochemical measurements). 33,77,78 It is therefore reasonable to assume an average density of 2.5 molecules of 4-MBA/nm 2 for our 1:1 SAMs, which is roughly half that of the total charge density. Using this value, the drop in the value of σ from low to high pD levels is only 60% of the change expected for the deprotonation of almost every carboxylic acid.…”

Dynamics of RS-(Au-SR)x Staple Motifs on Metal Surfaces: From Nanoclusters to 2D Surfaces

“…For thiolated molecules, in contrast, bi-and tri-coordinated sulfur− metal complexes exhibit six times larger activation barriers than the metal adatom. 48 This is reasonable because the mobility of the sulfur−metal complexes such as RS-Au-SR and Au-(SR)-Au-SR should be limited due to the additional S-metal bonds 10,49 and also by the larger binding energy of the entire species on the Au(111) surface (E b ,Table 3). 50 Thus, we propose that RS-Au, RS, and Au adatoms are the predominant species involved in mass transport from the AuNC to the Au(111) surface, according to the following steps…”

Faradaic Impedimetric Immunosensor for Label-Free Point-of-Care Detection of COVID-19 Antibodies Using Gold-Interdigitated Electrode Array

“…However, biosensors based on Faradaic detection using a [Fe(CN) 6 ] −3/4 redox system are reported to have limitations arising from baseline signal drifts which are often not adequately addressed and can therefore compromise the reliability of the devices. Plausible origin of baseline signal drift for gold-electrode-based electrochemical biosensors has been attributed to etching of the gold by cyanide and chloride ions from [Fe(CN) 6 ] −3/4 in phosphate-buffered saline [55][56][57][58][59], oxidation of thiolate head groups [60][61][62], spontaneous dissociation of Au-S bonds [63][64][65][66], Oswald ripening of the thiolate SAM [67,68], and reorganization of defects (pinholes and collapsed sites) in the SAM [62,64,69,70]. Thus, a better fundamental understanding of the origin of the baseline signal drift is required in order to address this challenge.…”