AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS3+MC-TuM

Paper SS3+MC-TuM10
Application of a Direct Method in Surface X-ray Crystallography

Tuesday, October 3, 2000, 11:20 am, Room 210

Session: Technique Innovations: Experiment, Theory and Simulation
Presenter: P.F. Lyman, University of Wisconsin, Milwaukee
Authors: P.F. Lyman, University of Wisconsin, Milwaukee
R. Harder, University of Wisconsin, Milwaukee
D.K. Saldin, University of Wisconsin, Milwaukee
C.-Y. Kim, Lucent Technologies
K.W. Evans-Lutterodt, Lucent Technologies
Correspondent: Click to Email
The electron density of the near-surface region of a crystal could be recovered from x-ray scattering data if the phases of the scattered radiation were known. In the case of surface scattering, the diffracted intensities arise from the square of a linear combination of bulk and surface amplitudes. Since the phases and amplitudes of the bulk component can be calculated accurately, it is possible to use the bulk scattering as a reference wave, and to thereby estimate the phases of the surface component, in analogy with holography. We have developed an algorithm to estimate the most likely set of surface phases, and to thereby recover the electron density of the near-surface region. We present preliminary applications of this method to (2x1)-reconstructed Ge(001) surfaces. It has been shown that the (001) face of Ge or Si can be passivated by 1 ML of a group V element. Although there is general acceptance of the existence of symmetric group V dimers for most adsorbate/substrate combinations, a controversial result of asymmetric Sb dimers for the Sb/Ge(001) system was concluded from an x-ray scattering study: Each Sb dimer was found to have shifted along the axis of the Sb-Sb bond.@footnote 1@ However, a number of first-principles calculations have found no evidence for the shift. We will use our direct reconstruction algorithm on experimental x-ray scattering data to address the possibility of shifted dimers in a model-independent way. @FootnoteText@ @footnote 1@ M. Lohmeier, H.A. van der Vegt, R.G. van Silfhout, E. Vlieg, J.M.C. Thornton, J.E. Macdonald and P.M.L.O. Scholte, Surf. Sci. V. 275, p.190 (1992).