X-ray diffraction measurements of the half-order rod intensity profiles arising from the reconstruction of the clean W(001) surface at low temperatures revealed an unexpected modulation with a period corresponding to the layer spacing. It was argued that this could indicate only that the reconstruction involved displacements in at least two layers. The atomic displacements in the second layer were found to be 20% of those in the top layer.

Multilayer Reconstruction of the W(001) Surface. M.S.Altman, P.J.Estrup, I.K.Robinson: Physical Review B, 1988, 38, 5211-4