Analysis of low-energy electron diffraction spectra for Be(0001) shows that the interplanar spacing between the first and second planes is expanded by 5.8% or 0.10 A. The size of this expansion is large compared to that of close-packed fee (111) surfaces, which show little or no expansion. This large expansion is discussed in terms of the unique bonding of Be. The second and third interplanar spacings show almost no relaxation.

Results from a LEED analysis of NiAl(llO) demonstrate that it possesses a large rippled relaxation away from its hypothetical truncated bulk surface, with the Al sites of the top composite Ni-Al layer being displaced approximately 0.22 A above the Ni sites. The evidence for this rippling is strong, since the agreement achieved between calculated and experimental I-V profiles is of the same quality obtained in better LEED analyses of monatomic surfaces.

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