Are 4-Mercaptobenzoic Acid Self Assembled Monolayers on Au(111) a Suitable System to Test Adatom Models?

Abstract

The adsorption of 4-mercaptobenzoic acid (MBA) has been studied on Au(111) by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), electrochemical techniques, and density functional theory (DFT) calculations. Results show that MBA molecules adsorb on the Au surface via a thiolate bond, arranged in a (√3×4) lattice with coverage θRS = 0.25. DFT data show the strong effect of aromatic ring interactions in stabilizing the adsorbed molecules. The total absence of vacancy islands upon thiol adsorption and the surface coverage of gold islands after desorption are difficult to conciliate with the usual gold-adatom models for thiol adsorption. This is an important issue, as the strongest evidence for the existence of gold-adatom complexes arises from MBA-capped Au nanoparticles. Our results raise an interesting point as regards the validity of making a straightforward parallel between the thiol–Au interface in single crystal surfaces and in monolayer-protected clusters.

AFM Imaging of Mercaptobenzoic Acid on Au(110): Submolecular Contrast with Metal Tips

“…The distances, sizes and corrugations in our measurements indicate that MBA molecules adsorb in a nearly planar orientation on Au(110), contrary to what has been reported for other surfaces. [46][47][48][49][50] Further details of the molecular structure are resolved in constant height measurements of the tunneling current and the frequency shift. The tunneling-current map ( Fig.…”

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

“…[a] M. C. Rodríguez Gonzµlez (4-MBA)S AMs on Au(111)b yu sing different techniques. [15,16] Our results showed that this molecule initially forms ordered domainsw ith a( 4 p 3) lattice with two molecules per unit cell and surface coverage q = 0.25 and then undergoes ap hase transition to reach q = 0.33, which is av alue consistentw ith the c(4 2) lattice. [16] On the other hand, 4-MBA adsorbs on the Au(110) from the gaseous phase forming dimerics tructures that are nearly parallel to the Au surface, forming a( 5 4) lattice with q = 0.20.…”

“…Similar STM images taken on 4-MBA covered substrates showl arger domains, which can reach 50 nm in size (Figure 1f), consisting of molecular rows separated by 0.69 AE 0.02 nm. [15,16,18] To estimate the surfacec overage of the 2-MBA on the Au(111), surface reductived esorption measurements were performed. [15,16,18] To estimate the surfacec overage of the 2-MBA on the Au(111), surface reductived esorption measurements were performed.…”

“…In this case 4-MBAm olecules are clearly observed within each row,s eparated by 0.47 AE 0.02 nm (Figure 1g), yieldingt he well-known (4 p 3) lattice with as urfacec overage q = 0.25 that has been observedf or different aromatic thiols. [15,16,18] To estimate the surfacec overage of the 2-MBA on the Au(111), surface reductived esorption measurements were performed. [19] Typical electroreduction curveso f2 -MBA SAMs on Au(111)y ield as mall peak with ap eak potential E p = À0.47 V (Figure 2, full red line).…”

6-Mercaptopurine Self-Assembled Monolayers on Gold (001)-Hex: Revealing the Fate of Gold Adatoms

“…[7][8] The failure of small aromatic thiols to form staple moieties has been explained considering their lower coverage and adsorption energy compared to alkanethiols (they do not compensate the energy cost to extract the Au atoms from the terraces). 9 Similar arguments 4 have been used to explain the absence of staples when 6-mercaptopurine (6MP, Figure 1), a small aromatic thiol of relevance for the treatment of some leukemias and autoimmune conditions because of its role as purine antagonist 10 , is adsorbed on the Au(111) 7 and Au(001)-(1×1) surfaces. 11 However, there is also another possible reason for this behavior: a low chemical affinity of the aromatic molecules to the Au adatoms, a fact that could also explain the formation of Au islands rather than vacancy Au islands.…”