An STM and XPS study of the chemisorption of methyl mercaptan at a Cu(110)surface

XP spectra of a Cu(1 1 0) surface exposed to methyl mercaptan at 290 K show the presence of an adsorbate assigned to mercaptide, CH3S(a). Scanning tun neling microscopic (STM) images show that the formation of the adsorbed mer captide (CH3S(a)) is accompanied by a restructuring of the surface. The rec onstructed surface is characterized by very narrow terraces (typically 10-1 5 Angstrom wide) oriented mainly in the [1 (1) over bar 0] direction with a 'zig-zag' structure. Higher resolution images of the terraces reveal an at omic scale structure with a c(2 X 2) unit cell, each cell containing two br ight features. The combination of STM and X-ray photoelectron spectroscopy (XPS) shows that the c(2 X 2) structure is complete at a surface concentrat ion of similar to 5X10(14) cm(-2), consistent with the c(2 X 2) unit cell c ontaining two equivalent mercaptide species. On heating to 450 K the mercap tide dissociates to give chemisorbed sulfur adatoms and the desorption of a ll of the surface carbon. The STM images show that following the decomposit ion of the mercaptide adlayer the copper surface regains its original struc ture of broad terraces (typically 100-200 Angstrom wide), though an adlayer of chemisorbed sulfur atoms is now present. (C) 2001 Elsevier Science B.V. All rights reserved.