Holographic Atomic Images from Surface and Bulk W(110) Photoelectron Diffraction Data

Although Gabor originally proposed using electrons in holography to form atomic-resolution images, it is only very recently that photoelectron diffraction data have been discussed as a practical method for achieving this. Such data enable recording both the amplitudes and phases of the scattered waves (relative to a direct reference wave), thus in principle permitting the holographic reconstruction of atomic positions. Photoelectron holography thus holds much promise of at least providing approximate starting structures that can be refined by more conventional comparisons of multiple-scattering calculations with experiment via R-factors. Criteria for optimizing the taking of such data and their holographic photoelectron diffraction patterns have been measured for surface and bulk core-level-shifted W 4f{sub 7/2} photoemission from W(110) on ALS beamline 7.0, yielding a data set of unprecedented size and quality. These data have been compared to multiple scattering theory, and used as a test case, since the W(110) surface is known not to exhibit significant relaxation in its interlayer spacings relative to the bulk. The authors have analyzed these experimental and theoretical results holographically in order to demonstrate the capabilities and limitations of photoelectron holography as a structural probe.