X-ray diffraction measurements of the half-order rod intensity profiles arising from the reconstruction of the clean W(001) surface at low temperature show an unexpected modulation with a period corresponding to the layer spacing. We argue that this can only indicate that the reconstruction involves displacements in at least two layers. The atomic displacements in the second layer are found to be 20% of those in the top layer.

• Received 29 April 1988

DOI:https://doi.org/10.1103/PhysRevB.38.5211