Trapping of Charged Gold Adatoms by Dimethyl Sulfoxide on a Gold Surface

Abstract

We report the formation of dimethyl sulfoxide (DMSO) molecular complexes on Au(111) enabled by native gold adatoms unusually linking the molecules via a bonding of ionic nature, yielding a mutual stabilization between molecules and adatom(s). DMSO is a widely used polar, aprotic solvent whose interaction with metal surfaces is not fully understood. By combining X-ray photoelectron spectroscopy, low temperature scanning tunneling microscopy, and density functional theory (DFT) calculations, we show that DMSO molecules form complexes made by up to four molecules arranged with adjacent oxygen terminations. DFT calculations reveal that most of the observed structures are accurately reproduced if, and only if, the negatively charged oxygen terminations are linked by one or two positively charged Au adatoms. A similar behavior was previously observed only in nonstoichiometric organic salt layers, fabricated using linkage alkali atoms and strongly electronegative molecules. These findings suggest a motif for anchoring organic adlayers of polar molecules on metal substrates and also provide nanoscale insight into the interaction of DMSO with gold.

Negative‐Imaging of Citrate Layers on Gold Nanoparticles by Ligand‐Templated Metal Deposition: Revealing Surface Heterogeneity

“…Given that Au adatoms are present on a gold surface, the binding mode of deprotonated citrate anions (H 2 Cit − , HCit 2− , and Cit 3− ) is more diverse than the previously proposed mode associated with the binding of the two oxygen atoms of the central carboxylate group to the defect‐free metallic surface of AuNPs . To a Au adatom can each oxygen atom of a carboxylate group coordinate through monodentate binding mode to form a AuO bond.…”

“…Strong citrate adsorption, [66] experimentally verified on AuNPs in the previous studies, [17,67,68] is better understood on the basis of the surface Au adatom -carboxylate complex which the bond energy is expected to be in the range of chemisorption [32,33] by the positive charge of Au adatom. [45][46][47] Surplus Au(0) atoms, produced by stoichiometric imbalance during crystallization of the atoms to form a nanocrystal, are likely bound on the metallic surface of AuNPs in the form of Au adatom.…”

“…Oxoanions such as citrate do interact weakly with metallic Au(0), and even water molecules compete with citrate anions in binding on a metallic Au(111) . In general, however, the bond energy of Au(I)‒X is larger than that of Au(0)‒X, and the binding energy of citrate carboxylate to the AuNP surface can be in the range of chemisorption owing to the positively charged low‐coordinated Au adatom . Therefore, it is the Au adatom that causes the strong citrate adsorption on AuNPs, with bond energy of Au‒carboxylate similar to the metal‒oxygen bond energies determined between metal cation and acetate (median energy range: 10‒25 kcal mol −1 ) …”

“…[44] In general, however, the bond energy of Au(I)-X is larger than that of Au(0)-X, [32] and the binding energy of citrate carboxylate to the AuNP surface can be in the range of chemisorption owing to the positively charged low-coordinated Au adatom. [45][46][47] Therefore, it is the Au adatom [48] that causes the strong citrate adsorption on AuNPs, [17,25] with bond energy of Au-carboxylate similar to the metal-oxygen bond energies determined between metal cation and acetate (median energy range: 10-25 kcal mol −1 ). [49] Another study shows that Au(I) ions are chemisorbed on gold surfaces based on the computational result of Møller−Plesset second order perturbation theory (MP2).…”

Imaging on-surface hierarchical assembly of chiral supramolecular networks

“…36 However, the distance between the molecules (1.2 nm) is larger than the one found in anthracene chains on Au (0.85 nm), 44 suggesting the presence of bridging Cu adatoms, 36,38 usually not visible in STM images. [54][55][56] Since the adatoms are expected to sit closer to the substrate than the molecular protruding lobes, they cannot be detected by constant-height AFM. Moreover, the observed distorted shape of diffusing chains (see below) suggests an important intermolecular interaction, supporting metal-organic coordination.…”