J. Am. Chem. SOC. 1995,117, 12344-12345
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A Novel Surface Structure: Rh( l l l ) - ( J 7 x J7)R19.1°-P W. Liu. K. C. Wong, and K. A. R. Mitchell* Department of Chemistry, Uniuersip of British Columbia 2036 Main Mall. Vancouuer British Columbia. Canada V6T IZI Receiued August 7. 1995 The interactions of electronegative species with transition metal surfaces can yield a wide range of structural arrangements, and the methods of surface structure determination, especially low-energy electron diffraction (LEED), are giving important new information.' Structures with the (J7xJ7)R19.1° translational symmetry are providing considerable interest. in part because they represent the upper end of complexity for current structural analyses, when no other information is available, and they can show distinctive chemistries compared with simpler systems. Examples include the J7 structures formed by I on pt( I I I ) and S on Ru(000 I ) which have been indicated respectively by scanning tunneling microscopy' and LEED crystallography' to have simple chemisorption arrangements without substantial modifications to the metallic structures; but in contrast the J7 structures formed by S on Pd( I 1 1): Cu(l11).5 and Ag(l1 appear much more challenging. There have been frequent suggestions that the latter systems involve mixed sulfur-metal overlayers and, in particular, that the structures for the S/Cu(I 1 I ) and S/Ag(l I I ) cases relate to the ( I I I ) plane of the bulk compounds Cu?S and Ag?S,'.'' but confirmation has proven hard to obtain. Another case in point is the Rh(l1 I)(J7xJ7)R19.1°-P surface, which is highly stable and the work here shows that it has a novel structural arrangement. Discussions of this structure. its implications for other J 7 systems, and possible links between this structural type and chemical propenies provide the subject of this communication. The Rh(l11)-(~7~~7)R19.1~-Psurface was prepared under ultrahigh-vacuum conditions (base pressure 2 x IO-"' Torr) by exposing a clean, well-ordered single-crystal of rhodium in the ( I I I ) orientation to approximately 4.8 ( I L = IO-h Torr s) PHI at room temperature. followed by a flash annealing to loo0 "C. The surface was assessed with standard surface science procedures, including Auger electron spectroscopy, throughout the cleaning and preparation steps. A sharp LEED pattem is obtained from this surface, and its high stability is shown by a number of observations including its persistence over long periods (weeks) in the vacuum chamber, as well as the difficulty of its removal under typical ion bombardment conditions. Intensity-versus-energy ( I ( @ ) curves were measured with a video system for 12 inequivalent diffracted beams with appropriate beam averaging, smoothing, and normalization for normal incidence and for energies up to 252 eV (total energy range 1438 eV). The analysis was done with multiple-scanering calculations in the context of tensor LEED' using the R-factor ( R p ) introduced by Pendry;* the potential of the solid was approximated with the muffin-tin model with the electron ~~
(11 Somorjai. G.A. Annu. fleu P11y.v. Chrm. 1994. 45. 721. (2)Schardt. B. C.: Yau. S. L.: Rinaldi. F. S&nw 1989. 243. 1050. (3) Sklarek. W.: Schwennicke. C.: Jurgens. D.; Pfnilr. H. Surf Sci. 1995.
I. .I .IIJ .. I .. (4) (a) Patterson. C. H.:Lambert. R. M. Su$ Sci. 1987. 187. 339. (b) Gellman. A. J.: Dunphy. J. C.: Salmeron. M. Lanjimuir 1992. 8. 534. (cl Forks. J. G.: Gellman. A. J.: Dunphy. J. C.: Salmeron. M. .Su$ Sci. 1992. 27Y. 68. (d) Grillo. M. E.: Stampfl. C.: Bcmdt. W. S t o f k i . 1994.317. 84. (51 (a) Domangc. J. L.: Oudar. J. Surf Sri. 1968. 11. 124. ( h l Prince. N. P.: Seymour. D. L.: Ashwin. M. J.: McConville. C. F.: Woodruff. D. P.: Jones. R. G. St,$ Sci. 1990. 230. 13. (cl Rum. L.: Stenrgaard. I.: Berenhacher. F.: Laegsgaard. E. U l r m ~ n i u m m p1992. ~ 42-44. 498. lh) Schwaha. K.: Spencer. N. D.: Lamben. R. M. .Su$ Sci. 1979. 81.
Figure 1. The Rh(l1 I ) - ( J ~ x J ~ ) R I ~ . I " -surface P stmcturc with an
indication of atom designations used in the lex!. The 3-fold rotation axes are located at the centers of atoms Rhl. Rh?. and Rhs.
