Atomic structure of the annealed Ge(111) surface

A model for the atomic structure of the annealed Ge(111) 2×8 surface is proposed on the basis of intensity measurements in which the fractional order beams are attributed to a ripplelike distortion of (at least) the top two double layers in a manner consistent with charge density wave (Peierls) instabilities or compresive stress deformations derived from distributed rehybridization. The distortion is similar to that suggested for the annealed Si(111) 7×7 surface from a similar analysis. The superlattice is actually an 8×8 unit cell; the observed 2×8 reconstruction follows from selected structure factor cancellations owing to the specific topography of the distortion.