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Department of Physics

Final Report 1999

 Summary of Final Report on EPSRC Grant GR/K45250

 

Quantitative Structure Determination for Molecular Adsorbates Using Backscattering Photoelectron Diffraction

 

This research grant was concerned with the development and use of scanned-energy mode photoelectron diffraction (PhD) and exploited the BESSY synchrotron radiation facility in a Warwick-Berlin collaboration involving the group of Prof.A.M.Bradshaw of the Fritz Haber Institute. The work has involved some advances in the methodology of the technique, notably in the extension to a wider range of substrates including Si and Pd as well as Cu and Ni, and has included the solution of a substantial range of distinct adsorption structural problems. A total of 22 papers has been published, including one general review.

 

The main structures solved include:

1. Determination of the local adsorption site of CO on Ni(111) as a function of coverage and coadsorption with O and K. These results confirm the pereference for hollow site adsorption in contraction to conventional wisdom based on mis-interpretation of data on the C-O stretching vibrational frequency which had been taken to imply bridge site occupation on the bare surface and atop adsorption when coadsorbed with O. Similar results were also found for NO on Ni(111) at low coverage and corrected the results of an earlier diffuse LEED study.

2. Structure determination for CO on Pd(111) at different coverages. Here too we see behaviour similar to that for CO on Ni(111), again in clear contradiction to prior interpretation of vibrational spectroscopic data.

3. A detailed study of the local adsorption site of benzene on Ni(111) at different coverages, demonstrating both an orientation and a site change as the coverage increases.

4. Determination of the local adsorption geometry of the simplest amino acid, glycine, on Cu(110) through the use of both O 1s and N 1s PhD. The adsorption geometry is consistent with bonding through both the oxygens of the carboxyl group (the group occupying bridging sites on the close-packed <110> rows) and through the amino group (with the N off-atop).

5. Determination of the local geometries of both intact NH3 (off-atop) and the NHx (short-bridge) species formed by NH/oxygen interaction on Cu(110). The origin of the low symmetry site for ammonia is unclear, but s consistent with independent ESDIAD studies.

6. Identification of the bonding geometry of CN on Ni(110). Despite evidence that at electrochemical surfaces CN bonds end-on as might be expected by the similarity between CO and CN-, our study, combining C 1s and N 1s PhD data as well as N K-edge NEXAFS, shows clearly that the C-N axis is aligned along <100>, perpendicular to the close-packed direction with the whole molecule occupying a local hollow site. This geometry is quite different to all previous suggestions, but is the first true structure determination for this species on any surface.

7. Determination of a series of metal-on-metal adsorption structures, notably of Cu(100)c(2x2)-Mn and of the earliest stages of psuedomorphic growth of fcc Fe films for the Cu(111)/Fe and Cu(110)/Fe [10] systems.

8. Identification of the local bonding geometries of NH2 and OH on Si(100)(2x1) including a demonstration that these adsorbates suppress the Si-Si dimer asymmetry of the clean surface reconstruction.

References

  1. R.Davis, D.P.Woodruff, Ph.Hofmann. O.Schaff, V.Fernandez, K.-M.Schindler, V.Fritzsche and A.M.Bradshaw 'Local structure determination for low coverage CO on Ni(111)' J.Phys.:Condens.Matter 8 (1996) 1367-79
  2. O.Schaff, V.Fernandez, Ph.Hofmann, K-M.Schindler, A.Theobald, V.Fritzsche, A.M.Bradshaw, R.Davis and D.P.Woodruff 'Coverage-dependent changes in the adsorption geometry of benzene on Ni(111)' Surface Sci. 348(1996) 89-99
  3. V.Fernandez, K-M.Schindler, O.Schaff, Ph.Hofmann, A.Theobald, A.M.Bradshaw, V.Fritzsche, R.Davis and D.P.Woodruff 'Structure determination of a CO/O coadsorption phase on Ni(111)' Surface Sci. 351 (1996) 1-12
  4. C.J.Hirschmugl, K-M.Schindler, O.Schaff, V.Fernandez, A.Theobald, Ph.Hofmann, A.M.Bradshaw, R.Davis, N.A.Booth, D.P.Woodruff and V.Fritzsche 'Quantitative structure determination of an NHx species adsorbed on Cu(110)' Surface Sci. 352-354 (1996) 232-237
  5. D.P.Woodruff, R.Davis, N.A.Booth, A.M.Bradshaw, C.J.Hirschmugl, K-M.Schindler, O.Schaff, V.Fernandez, A.Theobald, Ph.Hofmann and V.Fritzsche 'An integrated approach to adsorbate structure determination using photoelectron diffraction: direct 'imaging' and quantitative simulation' Surface Sci. 357/358 (1996) 19-27
  6. M.E.Davila, M.C.Asensio, D.P.Woodruff, K-M.Schindler, O.Schaff, K-U.Weiss, V.Fritzsche and A.M.Bradshaw 'A scanned-energy mode photoelectron diffraction study of the structure of Ni(111)(2x2)-O' Surface Sci. 359 (1996) 185-197
  7. R.Toomes, A.Theobald, R.Lindsay, T.Giebel, O.Schaff, R.Didszuhn, D.P.Woodruff, A.M.Bradshaw and V.Fritzsche 'Photoelectron diffraction determination of the structure of the Cu(100)c(2x2)-Mn surface phase' J.Phys.:Condens.Matter 8 (1996) 10231-10240
  8. V.Fernandez, T.Giebel, O.Schaff, K-M.Schindler, A.Theobald, C.J.Hirschmugl, S.Bao, A.M.Bradshaw, C.Baddeley, A.F.Lee, R.M.Lambert, D.P.Woodruff and V.Fritzsche, 'A photoelectron diffraction study of the Pd{111}(Ö 3xÖ 3)R30° -CO chemisorption phase' Z.phys.Chemie 198 (1997) 73-85
  9. N.Franco, J.Avila, M.E.Davila, M.C.Asensio, D.P.Woodruff, O.Schaff, V.Fernandez, K.-M.Schindler, V.Fritzsche and A.M.Bradshaw 'The local structure of NH2 on Si(100)(2x1) and its effect on the asymmetry of the Si surface dimers' Phys.Rev.Lett. 79 (1997)673-676
  10. A.Theobald, S.Bao, V.Fernandez, K.-M.Schindler, O.Schaff, V.Fritzsche, A.M.Bradshaw, N.Booth and D.P.Woodruff 'A photoelectron diffraction study of the structure of ultrathin iron films on Cu(110)' Surf.Sci. 385 (1997) 107-114
  11. N.Franco, J.Avila, M.E.Davila, M.C.Asensio, D.P.Woodruff, O.Schaff, V.Fernandez, K.-M.Schindler, V.Fritzsche and A.M.Bradshaw 'Structure determination of Si(100)(2x1)/NH2 using scanned-energy mode photoelectron diffraction' J.Phys.:Condens.Matter 9 (1997) 8419-8432
  12. N.A.Booth, R.Davis, D.P.Woodruff, C.Hirschmugl, K.-M.Schindler, O.Schaff, V.Fernandez, A.Theobald, Ph.Hofmann, A.M.Bradshaw and V.Fritzsche 'Structure determination of ammonia on Cu(110) - a low-symmetry adsorption site' Surf.Sci. 387 (1997) 152-159
  13. R.Davis, R.Toomes, D.P.Woodruff, O.Schaff, V.Fernandez, K.-M.Schindler, Ph.Hofmann, K.-U.Weiss, R.Dippel, V.Fritzsche and A.M.Bradshaw 'Quantitative structural study of the coadsorption of CO and K on Ni(111) using photoelectron diffraction' Surf.Sci. 393 (1997) 12-23
  14. N.A.Booth, D.P.Woodruff, O.Schaff, T.Giebel, R.Lindsay, P.Baumgartel and A.M.Bradshaw 'Determination of the local structure of glycine adsorbed on Cu(110)' Surf.Sci. 397 (1998) 258-269
  15. C.J.Baddeley, A.F.Lee, R.M.Lambert, T.Giebel, O.Schaff, V.Fernandez, K.-M.Schindler, A.Theobald, C.J.Hirschmugl, R.Lindsay, A.M.Bradshaw and D.P.Woodruff, 'Photoelectron diffraction study of a catalytically active layer: C2H2 on Pd{111}' Surf.Sci. 400 (1998) 166-175
  16. N.Franco, J.Chrost, J.Avila, M.C.Asensio, C.Muller, E.Dudzik, A.J.Patchett, I.T.McGovern, T.Giebel, R.Lindsay, V.Fritzsche, A.M.Bradshaw and D.P.Woodruff, 'Structural determination for H2O adsorption on Si(100)(2x1) using scanned-energy mode photoelectron diffraction' Appl.Surf.Sci. 123 (1998) 219-222
  17. R.Lindsay, A.Theobald, T.Giebel, O.Schaff, A.M.Bradshaw, N.A.Booth and D.P.Woodruff, 'The structure of NO on Ni(111) at low coverage' Surf.Sci. 405 (1998) L566-572
  18. T.Giebel, O.Schaff, C.J.Hirschmugl, V.Fernandez, K.-M.Schindler, A.Theobald, S.Bao, W.Berndt, A.M.Bradshaw, C.Baddeley, A.F.Lee, R.M.Lambert and D.P.Woodruff, 'A photoelectron diffraction study of ordered structures in the chemisorption system Pd{111}-CO', Surf.Sci. 406 (1998) 90-102
  19. N.A.Booth, R.Davis, D.P.Woodruff, D.Crysostomou, T.McCabe, D.R.Lloyd, O.Schaff, V.Fernandez, S.Bau, K-M.Schindler, R.Lindsay, J.T.Hoeft, R.Terborg, P.Baumgartel and A.M.Bradshaw, 'CN coordination in the adsorption system Ni(110)c(2x2)-CN: an unexpected geometry', Surf.Sci. 416 (1998) 448-45
  20. A.Theobald, V.Fernandez, O.Schaff, Ph.Hofmann, K-M.Schindler, V.Fritzsche, A.M.Bradshaw and D.P.Woodruff, 'The structure of adsorbed Fe on Ni{111}' Phys.Rev.B. 58 (1998) 6768-6771
  21. A.Theobald, O.Schaff, C.J.Hirschmugl, V.Fernandez, K-M.Schindler, M.Polcik, A.M.Bradshaw and D.P.Woodruff, 'A photoelectron diffraction study of ultrathin Fe films on Cu{111}' Phys.Rev.B 59 (1999) 2313-9
  22. D.P.Woodruff 'Quantitative determination of molecular adsorbate structures' in Chemisorption and Reactivity on Supported Clusters and Thin Films, eds R.M.Lambert and G.Pacchioni (Kluwer Ac.Pubs., Dordrecht, Netherlands, 1997)pp193-214