Stepped surfaces: A challenge for quantitative LEED analysis

Determination of the atomic structure of stepped surfaces by quantitative l ow-energy electron diffraction (LEED) analysis is very difficult when the s pacings between layers parallel to the surface become significantly smaller than about 0.9 Angstrom. For most of the computer programs widely used in LEED crystallography the problem is caused by numerical instabilities and l ack of convergence. However, the CHANGE computer program has had remarkable success on surfaces with interlayer spacings as small as 0.5 Angstrom. Adv antages and disadvantages of this program are briefly discussed. CHANGE is now available to run conveniently on desk-top personal computers.