Holographic Low Energy Electron Diffraction (holographic LEED), first proposed
by D. K. Saldin and P. L. De Andres,
*Phys. Rev. Lett.* **64**, 1270 (1990),
is a technique for the direct recovery of the 3D
structure of the atomic environment around adsorbate atoms on a surface by an
analysis of the diffuse LEED patterns produced when low energy electrons are
incident on the surface. Using computer algorithms, a 3D real-space image is
reconstructed directly from the measured data of the diffraction pattern.
The electrons reaching a detector directly after scattering from an adsorbate
atom constitute a holographic *reference wave*. Those parts of this reference
wave that are subsequently scattered by substrate atoms constitute an
*object wave*. The diffuse LEED pattern is formed by the interference of
these two waves, and thus constitutes a *hologram*.

Two striking examples of atomic adsorption sites recovered from experimental
diffuse LEED patterns may be seen by clicking on this
link . The method used, later called
Compensated Object- and Reference-wave Reconstruction by an Energy-dependent Cartesian
Transform (CORRECT), was first proposed in the paper by D. K. Saldin and
X. Chen, Phys. Rev. B **52**, 2941 (1995).

The representation of the experimental data on a Cartesian grid in reciprocal
space allows an extension of the method to fractional-order LEED data from
ordered surfaces. A prime example of this was the use of the CORRECT algorithm
to rapidly determine the local atomic structure around prominent adatoms on the
SiC(111) - (3x3) surface. The identification of this element of the surface
by K. Reuter *et al. *
Phys. Rev. Lett. **79**, 4818 (1997).
was a vital first step in the complete solution of the structure some months later
by the same authors by conventional LEED methods.

More recent refinements of the reconstruction algorithm are described in the paper
by A. Seubert, D. K. Saldin, and K. Heinz,
J. Phys.: Condens. Matter **12**, 5527 (2000).

A limitation of the holographic method with an atomic reference-wave source is seen in
the above determination of the SiC(111) - (3x3) structure. The scanning tunneling microscopy
(STM) image below suggested the presence of a single
prominent adatom in each surface unit cell

In fact we have developed just such a method. It is based on a different identification of a reference wave. The idea is applicable to surface x-ray diffraction and also to LEED and is a much more complete solution to the inverse problem in these two fields.