Structural aspects of the interaction of methyl thiol and dimethyldisulphide with Ni(111)

Abstract

A combination of "ex-edge and surface extended x-ray absorption fine stmcture (NEXAFS and SEXAFS), normal incidence x-ray standing wavefield absorption (NIXSW) and (laboratory-based) x-ray photoelectron spectroscopy and diffraction (XPS and XPD) has been used to investigate the local phases and associated structures resulting from the interaction of methylthiol (CH3SH) and dimethyldisulphide ((CH3S)x-DMS) with Ni( 1 I I). The interaction was followed by adsorbing at low temperature and observing the effects of sequential heating cycles to up to 373 K. At the lowest temperature DMS appears to be intact on the surface, but at slightly higher temperatures, up to at least 223 K. a second molecular species is formed which is also obtained by the thiol adsorption, even at 153 K. This is identified as methylthiolate (CHJS-) and appears to be bonded (through the S atom) to the hollow sites on the surface with a S-Ni bondlength of 2.24 A, essentially equal occupation of both (fcc and hcp) hollow sites is found. Both XAFS and XPD indicate that this species shows a substantial tilt angle of the S-C symmetry axis away from the surface normal; the situation is somewhat similar to that reported for the same species on Pt(l!l) on the basis of C K-edge NEXAFS and vibmional spectmscopy, and compmtive S K-edge NEXAFS measurements for R(1 I I) are also reported here. The tilted geometry found on both Ni and Pt surfaces contrasts with the perpendicular orientation found on Cu(l1 I). Heating the Ni(1 I I) surface to 373 K converts the thiolate species to a third state which we identify as atomic sulphur. Buth SEXAFS and NEXAFS show that this final species has lhe same local geometry as that found in earlier studies of atomic S on Ni(l I I): in pmiicular, while the S-Ni nearest-neighbour spacing is similar to that of the thialate, the S in this phase ippears to peneme the top Ni layer.

A density functional study of the adsorption of methane-thiol on the (111) surfaces of the Ni-group metals: I. Molecular and dissociative adsorption

“…Above room temperature methane desorption has been observed, leaving S on the surface. For lower coverage it was suggested [37] that the adsorption of CH 3 S induces a surface layer reconstruction similar to that reported for methane-thiolate adsorption on Cu(111) [38] and for the adsorption of atomic sulfur on Ni(111) [39]. For the more open Ni(100) surface it was reported [40] that alkanethiols start to decompose at low temperatures to form adsorbed thiolates and that further heating results in the formation and desorption of alkanes, olefins and hydrogen and leaves sulfur adsorbed on the surface.…”

The adsorption site and orientation of CH3S and sulfur on Ni(001) using angle-resolved X-ray photoelectron spectroscopy

“…An alternative method is demonstrated in Fig. 3B, Fernfindez et al [18] have shown that the methyl group in CHaS on Ni(lll) at 100 K is tilted toward the surface. Assuming that the orientation is also azimuthally averaged, the C Is photoemission is not expected to show any angular anisotropy.…”

X-ray Photoelectron Spectroscopy Sulfur 2p Study of Organic Thiol and Disulfide Binding Interactions with Gold Surfaces

“…5 This is consistent with studies of methanethiolate species chemisorbed onto W, Ru, Ni, Cu, and Ag single-crystal surfaces. [28][29][30][31][32][33] detected in lower coordination sites than the hollow sites (e.g., bridge sites). 28,29 In all cases where the S 2p3/2 BE was measured it was observed to decrease in the order unbound thiol or disulfide > thiolate in hollow site > thiolate in low-coordination site.…”