A study on adatom transport through (√3 × √3)–R30°–CH₃S self-assembled monolayers on Au(111) using first principles calculations

Abstract

Self-assembled monolayers on Au(111) have outstanding chemical, electrical, and optical properties, and Au adatoms seem to play a key role in these properties. Still, the fundamental understanding of adatom transport inside the self-assembled structure is very thin. In this paper we use first-principles calculations to reveal new details about the migration mechanism of Au adatoms in the presence of a CH3S self-assembled structure on Au(111). We study the inclusion of Au adatoms inside a well-packed (√3 × √3)-R30°-CH3S self-assembled lattice and present atomistic models supporting adatom migration by means of a hopping mechanism between pairs of CH3S species. Our calculations reveal that the transport of Au adatoms is slowed down inside the molecular network where the kinetic barrier for adatom migration is larger than on the clean Au surface. We attribute the hindered mobility of Au adatoms to the fact that adatom transport involves the breaking and making of Au-S bonds. Our results form a basis for further understanding the role played by defect transport in the properties of molecular assemblies.

Does the S−H Bond Always Break after Adsorption of an Alkylthiol on Au(111)?

“…The evidenced role of gold surface defects and particularly Au adatoms may hold the key to the characterization of the thiolate geometry. Indeed, several recent experimental and theoretical studies indicate that thiolate‐induced reconstruction may also occur on the Au(111) surface …”

Formation Mechanism of Metal–Molecule–Metal Junctions: Molecule-Assisted Migration on Metal Defects

“…Very recent Monte Carlo models 109 showed slower diffusion in close-packed SAMs. To summarise, the molecule unbinding energies estimated by breaking van der Waals interactions between molecules in monolayers (Fig.…”

Molecular Description of Grafted Supramolecular Assemblies on Gold Surfaces: Effect of Grafting Points and Chain Lengths

“…In addition, the transport of Au adatoms at the interface leads to the breaking and making of Au–S bonds. 24 …”

“…At the gold–sulfur interface, the covalent interaction requires the formation of gold–thiolate (RS–Au) bond(s). Sulfur-metal interfacial chemistry has been investigated by numerous techniques such as scanning tunneling microscopy, low-energy electron diffraction, and X-ray spectroscopic techniques, and first-principles calculations. , The reader is redirected to significant works in this field. ,− Different binding modes have been suggested for the S–Au bond: , a classical view involving monothiolate bonding on an Au atom of the Au(111) surface, a disulfide bonding, a complex involving an Au adatom and a thiolate (Au–SR), and a polymeric chain structure where monothiolates are bridging Au adatoms. In addition, the transport of Au adatoms at the interface leads to the breaking and making of Au–S bonds …”

“…In addition, the transport of Au adatoms at the interface leads to the breaking and making of Au−S bonds. 24 Because the sulfur−gold chemistry is complex in terms of diversity of the adsorption sites, binding, presence, and transport of Au adatoms, we take the route of defining a model system: an Au(111) gold surface in which only the chain length of alkylthiols spacer of the surface-immobilized host and the number of grafting points involving the formation of covalent thiolate−Au (S−Au) bonds with the substrate will vary. We assume that the variety of Au−S bonding will be implicitly considered through the number of grafting points.…”