SXPS and XANES Studies of Interface Reactions of Organic Molecules on Sulfide Semiconductors

XPS, Static SIMS and NEXAFS Spectroscopic Investigation of Thiol Adsorption on Metals and Metal Sulfides

“…By contrast, for monolayer coverage, both π* peaks were of significantly lower intensity relative to the σ* continuum structure for a 15 o angle of incidence than for 90 o , with the difference greater for the lower energy (=N-) π* peak. This behaviour is similar to that observed for MBT adsorbed on CdS, and is indicative of a tilted upright orientation (8). It also indicates that the surface prepared by gentle abrasion was indeed sufficiently flat to result in a significant 'average' alignment.…”

“…These observations are consistent with some interaction between the N and metal atoms for both the monolayer and multilayer in each system. The features of N K-edge spectra for pyrrole derivatives, MBT, MBT-metal complexes and MBT adsorbed on CdS have been described and interpreted by Szargan and co-workers (4,5,8,21,22), and on the basis of those studies, the peaks observed near 399 and 401 eV can be assigned to N 1s transitions to (=N-) and (=N δ+ ≈) 2pπ* states, respectively, and the peak near 407-408 eV to transitions to 2pσ* states. Pavlychev et al (23) showed that the intensity of the ~401 eV 2pπ* peak relative to that of the ~407 eV 2pσ* continuum structure was greater for pyrrole than for polypyrrole.…”

“…Angle-dependent N K-edge spectra. Determination of the orientation of adsorbed molecules by means of angle-dependent NEXAFS spectroscopy is now a well-established technique ( 16) that has been used to obtain orientation information for MBT adsorbed on CdS wafers (4,8). Clearly, in order to establish the orientation of an adsorbate on a surface, that surface must be as flat as possible, and preferably a single crystal plane.…”

“…The interaction of MBT with a number of metal and metal sulfide surfaces has been investigated extensively by various surface analytical techniques (1)(2)(3)(4)(5)(6)(7)(8), theoretical approaches (9)(10)(11)(12) and thermochemical measurements (13), but several questions remain unanswered. In some cases, it has been concluded that chemisorption of the MBT to the metal atoms in the surface layer occurred via the exocyclic S only, and did not involve the N atom.…”

“…In some cases, it has been concluded that chemisorption of the MBT to the metal atoms in the surface layer occurred via the exocyclic S only, and did not involve the N atom. For adsorption on CdS (1010) surfaces, however, a density functional theory investigation showed that chemisorption should occur via both the N and exocyclic S atoms to adjacent Cd atoms in the CdS surface (8,11). In most cases, it has been concluded that the chemisorbed MBT radicals are aligned more nearly perpendicular than parallel to the substrate surface.…”