The high-order commensurate phase of the clean (001) surface at about 100K was studied by using surface X-ray diffraction techniques. A quantitative structural analysis demonstrated the relevance of the periodic lattice distortion model, but the detailed displacement pattern was closer to a square wave than a sine wave. This was tentatively attributed to a specific bonding; similar to that seen in W(001).

D.M.Smilgies, P.J.Eng, I.K.Robinson: Physical Review Letters, 1993, 70[9], 1291-4