Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5423823 | Surface Science | 2009 | 4 Pages |
Abstract
Low energy ion scattering spectroscopy (LEISS) has been used to characterize the evolution of ordered structures of S on the Pd(1Â 1Â 1) surface during annealing. During exposure of the Pd(1Â 1Â 1) surface to 0.7Â L H2S at 300Â K-conditions that produce the S(â3Â ÃÂ â3)R30 overlayer-the intensity of the Pd LEIS signal decreases and a feature assigned to adsorbed S appears as the adsorbed layer forms. When the surface is held at 300Â K after exposure to H2S is stopped, the LEIS Pd intensity partially recovers and the S signal weakens, presumably as surface S atoms assume their equilibrium positions in the S(â3Â ÃÂ â3)R30 overlayer. Subsequent annealing of the S(â3Â ÃÂ â3)R30 structure at 700Â K causes it to convert into a S(â7Â ÃÂ â7)R19 overlayer, whose LEIS spectrum is identical to that of clean Pd(1Â 1Â 1). The absence of LEIS evidence for S atoms at the exposed surface of the S(â7Â ÃÂ â7)R19 overlayer is at odds with published models of a mixed Pd-S top layer. Despite the similarity of the LEIS spectra of Pd(1Â 1Â 1) and Pd(1Â 1Â 1)-S(â7Â ÃÂ â7)R19, their activities for dissociative hydrogen adsorption are very different-the former readily adsorbs hydrogen at 100Â K, while the latter does not-suggesting that S exerts its influence on surface chemistry from subsurface locations.
Related Topics
Physical Sciences and Engineering
Chemistry
Physical and Theoretical Chemistry
Authors
James B. Miller, Andrew J. Gellman,