X-ray diffraction study of multilayer W(001) surface reconstruction.

The clean W(001) surface undergoes a reconstruction upon cooling below 300 K which produces a (square root 2 x square root 2) R45 degree two-dimensional periodicity [1]. Systematic extinctions in the LEED pattern show that surface W atoms are laterally displaced in the 110 > directions in the reconstructed phase [2,3]. A detailed model of the surface geometry has been developed, based largely on LEED intensity analyses [4,5], and has been used in numerous calculations of the stability of this surface [6]. Displacements of only top layer atoms, however, have been considered in these studies. In the present work, we have extended previous surface x-ray diffraction techniques [7], by using non-grazing geometry, to allow study of the three- dimensional character of the reconstructed W(001) surface.