Anomalous interplanar expansion at the (0001) surface of Be

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 Å. The size of this expansion is large compared to that of close-packed fcc (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.