Spontaneously Formed Sulfur Adlayers on Gold in Electrolyte Solutions: Adsorbed Sulfuror Gold Sulfide?

P.G. LUSTEMBERG; C. VERICAT; G. A. BENITEZ; M.E. VELA; N. G. TOGNALLI; A. FAINSTEIN; M.L. MARTIARENA; R.C. SALVAREZZA

Journal Physical Chemistry C

American Chemical Society

Año: 2008 vol. 112 p. 11394 - 11402

1932-7447

High coverage S phases (surface coverage  0.33), spontaneously formed by immersion of Au(111) in Na2S aqueous solutions at room temperature, have been studied by scanning tunneling microscopy (STM), X- ray photoelectron spectroscopy (XPS), surface enhanced Raman spectroscopy (SERS), electrochemistry, and density functional theory (DFT) calculations. XPS data show no evidences of a AuS phase, as no oxidized gold is detected. Voltammetric data are also inconsistent with the formation of a AuS phase with 0.5 stoichiometry. In situ and ex situ SERS measurements of S-covered nanostructured gold substrates demonstrate that the surface species present at the gold surface consist of a mixture of chemisorbed S and polysulfide species, as already proposed based on in situ STM images. A DFT surface model that is energetically feasible and reproduces well the experimental STM images is presented. The proposed model involves only a small rearrangement of the upper Au layer and coexistence of monomeric and polymeric S. Therefore, the high coverage S phase should be described as a mixture of monomeric and polymeric chemisorbed sulfur rather than as an extended 2D AuS phase. 0.33), spontaneously formed by immersion of Au(111) in Na2S aqueous solutions at room temperature, have been studied by scanning tunneling microscopy (STM), X- ray photoelectron spectroscopy (XPS), surface enhanced Raman spectroscopy (SERS), electrochemistry, and density functional theory (DFT) calculations. XPS data show no evidences of a AuS phase, as no oxidized gold is detected. Voltammetric data are also inconsistent with the formation of a AuS phase with 0.5 stoichiometry. In situ and ex situ SERS measurements of S-covered nanostructured gold substrates demonstrate that the surface species present at the gold surface consist of a mixture of chemisorbed S and polysulfide species, as already proposed based on in situ STM images. A DFT surface model that is energetically feasible and reproduces well the experimental STM images is presented. The proposed model involves only a small rearrangement of the upper Au layer and coexistence of monomeric and polymeric S. Therefore, the high coverage S phase should be described as a mixture of monomeric and polymeric chemisorbed sulfur rather than as an extended 2D AuS phase.2S aqueous solutions at room temperature, have been studied by scanning tunneling microscopy (STM), X- ray photoelectron spectroscopy (XPS), surface enhanced Raman spectroscopy (SERS), electrochemistry, and density functional theory (DFT) calculations. XPS data show no evidences of a AuS phase, as no oxidized gold is detected. Voltammetric data are also inconsistent with the formation of a AuS phase with 0.5 stoichiometry. In situ and ex situ SERS measurements of S-covered nanostructured gold substrates demonstrate that the surface species present at the gold surface consist of a mixture of chemisorbed S and polysulfide species, as already proposed based on in situ STM images. A DFT surface model that is energetically feasible and reproduces well the experimental STM images is presented. The proposed model involves only a small rearrangement of the upper Au layer and coexistence of monomeric and polymeric S. Therefore, the high coverage S phase should be described as a mixture of monomeric and polymeric chemisorbed sulfur rather than as an extended 2D AuS phase.