A quantitative analysis was made of high-resolution He-atom scattering measurements of (111)-c(2 x 8) surfaces. The presence of quarter-order beams, as well as symmetries along [11¯2] and [2¯1¯1], confirmed that the angular distributions arose from 3 equivalent c(2 x 8) domains. The corrugation function which was deduced from the calculations clearly revealed that the 2 rest atoms within the unit cell were buckled; as had previously been suggested by scanning tunnelling microscopic data. Intensity analyses of diffraction scans which had been obtained above and below the order-order transition (1050K) suggested that, above the transition, the first-layer atoms were shifted, to hexagonal diamond sites, from their normal bulk positions.

D.Farías, G.Lange, K.H.Rieder, J.P.Toennies: Physical Review B, 1997, 55[11], 7023-33