Decomposition of Methylthiolate Monolayers on Au(111) Prepared from Dimethyl Disulfide in Solution Phase

FERNANDO P. COMETTO; VICENTE A. MACAGNO; PATRICIA P. OLIVERA; EDUARDO M. PATRITO; HUGO ASCOLANI; GUILLERMO ZAMPIERI

JOURNAL OF PHYSICAL CHEMISTRY C

AMER CHEMICAL SOC

Año: 2010 vol. 114 p. 10183 - 10194

1932-7447

We investigated the formation and stability of layers of methylthiolate prepared on the Au(111) surface by the method of immersion in an ethanolic solution of dimethyl disulfide (DMDS). The surface species were characterized by electrochemical reductive desorption and high-resolution photoelectron spectroscopy. Both techniques confirmed the formation of a methylthiolate monolayer at short immersion times (around 1 min). As the immersion time increased, the electrochemical experiments showed the disappearance of the ethylthiolate reductive desorption current peak and the appearance of a current peak at ca. -0.9 V which was attributed to sulfur species. At long immersion times, the XPS measurements showed two main components for the S 2p signal: a component at ca. 161 eV which corresponds to atomic sulfur and a component at ca. 162 eV which we attributed to polysulfide species. We propose that the breakage of the S-C bond of methylthiolate is esponsible for the appearance of sulfur species on the surface. Density functional theory (DFT) alculations were performed to identify the elementary steps that may lead to the decomposition of methylthiolate. We ound that the cleavage of the S-C bond is only activated by the oxidative dehydrogenation of the methyl group of methylthiolate. Thio-oxymethylene, SCH2O, is the key intermediate leading to the breakage of the S-C bond because it decomposes into atomic sulfur and formaldehyde with an activation energy barrier of only 1.1 kcal/mol.-0.9 V which was attributed to sulfur species. At long immersion times, the XPS measurements showed two main components for the S 2p signal: a component at ca. 161 eV which corresponds to atomic sulfur and a component at ca. 162 eV which we attributed to polysulfide species. We propose that the breakage of the S-C bond of methylthiolate is esponsible for the appearance of sulfur species on the surface. Density functional theory (DFT) alculations were performed to identify the elementary steps that may lead to the decomposition of methylthiolate. We ound that the cleavage of the S-C bond is only activated by the oxidative dehydrogenation of the methyl group of methylthiolate. Thio-oxymethylene, SCH2O, is the key intermediate leading to the breakage of the S-C bond because it decomposes into atomic sulfur and formaldehyde with an activation energy barrier of only 1.1 kcal/mol.