The Role of Gold Adatoms and Stereochemistry in Self-Assembly of Methylthiolate on Au(111)

Abstract

On the basis of high resolution STM images and DFT modeling, we have resolved low- and high-coverage structures of methylthiolate (CH(3)S) self-assembled on the Au(111) surface. The key new finding is that the building block of all these structures has the same stoichiometry of two thiolate species joined by a gold adatom. The self-arrangement of the methylthiolate-adatom complexes on the surface depends critically on their stereochemical properties. Variations of the latter can produce local ordering of adatom complexes with either (3 x 4) or (3 x 4 square root(3)) periodicity. A possible structural connection between the (3 x 4 square root(3)) structure and commonly observed (square root(3) x square root(3))R30 degrees phase in methylthiolate self-assembled monolayers is developed by taking into account the reduction in the long-range order and stereochemical isomerization at high coverage. We also suggest how the observed self-arrangements of methylthiolate may be related to the c(4 x 2) phase of its longer homologues.

Photoemission core-level shifts reveal the thiolate-Au(111) interface

“…We note that the results from the core-level spectroscopy conform to the energetic argument in the preference for the MeS-Au-SMe structure over alternative adsorption models. 22 It is also consistent with experimental STM, 23 IR, 24 GIXRD, 25 and NEXAFS ͑Ref. 26͒ data.…”

“…22 Although there is an uncertainty concerning the ability of state-of-the-art DFT methods to predict small energy differences ͓in particular, for reconstructed RS / Au͑111͒ systems, as the cohesive energy of gold is underestimated by ϳ15%͔ the structure based on RS-Au-RS units is consistent with the bulk of experimental data. RS-Au-SR complexes bonded to Au͑111͒ has been observed at different coverages by STM, 23 calculations of the infrared ͑IR͒ vibrational signatures match the experimental data, 24 simulations of the GIXRD maps 25 are in agreement with experiments and calculations for the RS-Au-RS structure compare favorably with sulfur K-edge near-edge x-ray absorption fine-structure ͑NEXAFS͒ measurement. 26 It has also been suggested that the RS-Au-RS structure might be consistent with normal-incidence XSW data.…”

Destabilization of Ag nanoislands on Ag(100) by adsorbed sulfur

“…Alkanethiols on Au(111) form clusters with Au atoms that can be described as M(SR) 2 , where R is an alkyl group. [9][10][11][12] These are analogous to MS 2 . On Ni(111), a triangular Ni 3 S 3 cluster has been identified, although its role in coarsening was not studied.…”

Thiolate adsorption on Au(${\bm {hkl}}$hkl) and equilibrium shape of large thiolate-covered gold nanoparticles

“…19,21,22 The same configuration, including Au adatoms bonded to two RS-groups, has been named the "standard model" for close-packed methylthiolate self-assembled monolayers on Au(111), 23 as it has been found in several experimental and theoretical studies for this system. [24][25][26][27] Such bonds between two S atoms and a Au adatom appear due to low reactivity of Au atoms in the close-packed (111) surface, and are expected to be less likely in stepped or kinked surfaces, where undercoordinated Au atoms form significantly stronger bonds to S. Moreover, the strong steric repulsions associated with adsorption of longer molecules will result in grafting densities of the order of 1 nm −2 or less, 28 where it is unlikely that thiolate groups from two different molecules will bind to the same Au atom.…”