`A new UK Surface X-Ray Diffraction (SXRD) Facility for SRS Station 9.4'

R. McGrath^a,G. Thornton^b, T. Turner ^c and D. Norman^c

^aSurface Science Research Centre, The University of Liverpool

^bSurface Science Research Centre and Chemistry Department, Manchester University

^cCLRC Daresbury Laboratory

A new surface x-ray diffraction chamber has been built for use on SRS station 9.4. The chamber incorporates several useful features including an Auger electron spectroscopy (AES) analyser, a low energy electron diffraction (LEED) system, a sample transfer system and a computer-controlled pumping system. On-line reference manuals for the chamber and analysis suite have been provided (see the SRS facility station 9.4 WWW pages). The system is available for general users and has attracted several new applicants.

The metal oxide experiments involved the TiO₂(110)-(1x1) and SrTiO₃(1x1) surfaces. The details of the TiO₂(110)-(1x1) surface relaxation were measured [1], the first structural determination of an oxide surface, and agree well with the predictions of first principles calculations. The relaxation is modified by an epitaxial Cu(111) overlayer, which results in large displacements of the surface anions. The structure of the TiO₂(110)-(2x1)-HCOO adsorption system was also measured. Data were obtained from TiO₂(110)-Cu(111)-S to assess the effect of an adsorbate on the metal-metal oxide interface. Finally, the structure of the clean SrTiO₃(100) surface has been determined.

The metal surface experiments involved the measurement of the Ni(100)(2x2)p4g-N reconstruction and its removal by coadsorption of potassium. The in-plane reconstruction was determined to be d_xy=0.30¬± 0.01 ˆÖ, which is less than that suggested by photoelectron diffraction and surface extended x-ray absorption fine structure measurements of the same system. Reasons for these discrepancies have been discussed [2]. We have also shown that this reconstruction is removed by coadsorption of alkali metals and provided an interpretation of this effect in terms of a balance of adsorbate-induced surface stresses [3].

References

[1] Relaxation of TiO2(110)-(1x1) using surface x-ray diffraction
G. Charlton, P.B. Howes, C.L. Nicklin, C. Norris, P. Steadman, J.S.G. Taylor, C.A. Muryn, S.P. Harte, J.R. Mercer, R. McGrath, D. Norman, T.S. Turner,G. Thornton
Phys. Rev. Lett., 78 (1997) 495-498.

[2].The Ni(100)(2x2)p4g-N reconstruction determined by surface x-ray diffraction.
E. Dudzik, A.G. Norris, R. McGrath, G. Charlton, G. Thornton, B. Murphy, T.S. Turner, and D. Norman
Surface Science 433/435 (1999) p.317-321

[3].Potassium-induced removal of the Ni(100)(2x2)-p4g-N reconstruction using surface x-ray diffraction.
E. Dudzik, A.G. Norris, R. McGrath, G. Charlton, G. Thornton, B. Murphy, T.S. Turner, and D. Norman
Phys. Rev. B 58 (1998) 12659-12662.

EPSRC Assessment of final report:

Scientific and/or technological merit: Very significant contribution to the field, Alpha 4
Management and use of resources: Excellent.