ADSORPTION OF CARBON ON NI{100} STUDIED BY SCANNED-ENERGY MODE PHOTOELECTRON DIFFRACTION
R. Terborg1, J.T. Hoeft1, R. Lindsay1,
O. Schaff1,
1Fritz-Haber-Institut der
Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin-Dahlem ,
Germany
2Physics Department, University of
Warwick, Coventry CV4 7AL, England
3University of Wisconsin-Milwaukee,
USA
4Advanced Light Source, Berkeley,
USA
Keywords: metal surfaces, adsorption, surface reconstruction, synchrotron
It is generally believed that the (2x2)p4g reconstruction induced by carbon on Ni{100} is a consequence of the penetration of the C atom into the fourfold symmetric hollow site. This forces the Ni atoms apart and allows the second layer substrate atoms to interact with the adsorbate [1]. Surface stress measurements show a build up of tensile stress at low coverage, with a further increase being relieved by the reconstruction [2]. A key question concerns the structure of the chemisorbed phase prior to the reconstruction. We have therefore carried out scanned energy mode photoelectron diffraction (PhD) measurements of carbon on Ni{100} both at low coverage (0.1 ML) and for the (2x2)p4g phase at 0.5 ML. The measurements were performed on the spectro-microscopy beamline 7.0.1 at the Advanced Light Source in Berkeley. A full analysis of the experimental data using a multiple scattering code gave excellent agreement with previous LEED data [1] for the (2x2)p4g structure and showed that the C atoms occupy a similar near coplanar hollow site in the low coverage, non-reconstructed phase.