A detailed microscopic description was developed for the Si(111)/Cu(5 x 5) reconstruction. One guide to the nature of this structure was an X-ray standing-wave determination of the registration of the Cu with respect to the Si substrate. When the Cu was located mainly in H3 and substitutional sites, the buckled Si(111) bi-layer changed into an almost-planar hexagonal Cu2Si layer. The straightened bond-angles, and an associated increase in the lateral lattice constant, gave rise to an hexagonal network of discommensurations with a period which was approximately equal to 5.5 times the unit-cell parameter of Si. Complete tiling of the surface required 3 types of twisted (±3º) domains; 2 of which were rotationally equivalent.

J.Zegenhagen, E.Fontes, F.Grey, J.R.Patel: Physical Review B, 1992, 46[3], 1860-3