Shedding Light on the Interfacial Structure of Low-Coverage Alkanethiol Lattices

Abstract

A comprehensive description of the self-assembly process of alkanethiols on Au( 111) is presented, focused on the initial formation of the lying down phases. Low-coverage monolayers are prepared by the disintegration of Au 144 (RS) 60 nanoclusters on the reconstructed (22 × √3)-Au(111) surface.The method provides a limited number of thiols together with a large excess of gold adatoms. Scanning tunneling microscopy and density functional theory calculations were employed to study the transition between low to high thiolate coverage phases. The process involves different lattices and surface transformations, including thiyl radicals on the herringbone reconstruction, radicalinduced herringbone lifting, and the formation of energetically similar metastable phases formed by RS-Au-RS moieties. Results also show that the transition is slow, and different surface structures can coexist on the same sample. Along the process, the first source of Au adatoms to form the RS-Au-SR moieties is the lifting of the herringbone reconstruction because of the lower energetic cost to extract the extra Au atom. However, for hexanethiol (and shorter alkanethiols) at low coverage, additional Au adatoms must be taken from terraces leading to vacancy islands. This process can be entirely suppressed by growing the lying down phases in the presence of an excess of Au adatoms. Taken together, our results shed light on the elusive initial steps of thiol adsorption on clean reconstructed Au, showing that the RS-Au-SR staple motif is also present at the interface of low-coverage self-assembled monolayers.

Functional Group Effects on the Electrochemical Properties of Carboranethiol Monolayers on Au(111) As Studied by Density Functional Theory: Implications for Organic Electronics

“…This finding was also reported in previous theoretical studies . In addition, the phenomenon that a gold atom being pulled up by the thiol terminal as a result of Au–S bond formation mimics the adatom model used to explain the experimental observations regarding self-assembly of thiolates on Au(111). − …”

Unraveling the Causes of the Instability of Aun(SR)x Nanoclusters on Au(111)

“…Our experimental data indicate that the AuNCs protected by RS-Au-SR units decompose into Au islands and LD phases containing RS-Au-SR moieties upon interaction with the Au surface. We have recently shown that the most stable configurations for H-T and H-H phases are described, in both cases, by a (8 × 2√3) rect unit cell . The optimized structures are shown in Figure a,b, respectively.…”

“…We have recently shown that the most stable configurations for H-T and H-H phases are described, in both cases, by a (8 × 2√3) rect unit cell. 43 The optimized structures are shown in Figure 2a,b, respectively.…”

How far the chemistry of self-assembled monolayers on gold surfaces affects their work function?

“…24,25,36 More recently, van der Waals interactions between the molecular chains were also included in the DFT models with various functions. 20,[40][41][42][43][44] The considered supercells aiming to describe the SAM on gold are usually rather small in order to significantly reduce the computational cost, thus restricting the exploration of the complex relative conformations and orientations of the co-adsorbed molecules in long range. In addition, under experimental conditions the presence of contaminants adds a supplemental and hardly incontrollable dipole contribution that blurs the WF values.…”