Anisotropic oscillations arising from steps have also been observed by Hofmann et al. , on Be(1010) surface close to the surface defects and steps. They have found oscillations in two directions with a periodicity of approx. 4.7 Å and 10.0 Å along and perpendicular to the stacking line, respectively. The anisotropicity may be tracked back to its unusual Fermi surface plot -the Be(10 10) possesses a disconnected surface-state pocket around a distant Ā point (shown on the Fig. ). Such a pocket causes the plane-wave-like ripples of charge density (visible in Fig. ) instead of the expected circular-wave pattern, thus showing a sig- nificant anisotropy. At the same time, geometry dictates the character of the Fermi surface. In fact, in the case of the Be(0001), a circular, perfectly isotropic Fermi contour was observed. This feature of Be(10 10) Fermi surface has been reflected in the following formula of total charge density at a distance along y-axis from a step, derived by Hofmann et al., :