Surface X-ray diffraction experiments were performed on the K-induced super structures on Ag(001). Both, the (2 x 1) and the (3 x 1) superstructure which were formed at K-coverages of about 0.15 and 0.30ML, were found to consist of missing row type reconstructions, where one and two Ag-rows were missing along [1¯10], respectively. In both cases, the K-atoms reside within the large grooves of the missing row structures. For the (2 x 1) structure, it was found the K-atoms were adsorbed on bridge sites relative to second-layer Ag-atoms; there coordinated by six Ag-atoms (4 first-layer Ag-atoms and 2 second-layer Ag-atoms) at a distance of 3.44Å. The consideration of anharmonic displacement factors for the top layer Ag atoms was necessary for the proper description of the structure, leading to a significant better agreement with the data as compared to pure harmonic refinement as expressed by the goodness of fit parameter (0.93 versus 1.67). Allowing for anharmonic displacement parameters, a Ag interlayer spacing d12 was determined which was contracted relative to the bulk spacing by only 3.2% instead of 12.7% if anharmonic contributions were neglected. In the (3 x 1) superstructure, the K-atoms formed staggered double rows along [1¯10], in this way forming a distorted quasi-hexagonal overlayer. The K-atoms were located close to bridge sites to second layer Ag-atoms at a minimum distance of 3.55Å. Additional defects were found in the first Ag-layer. For this more open reconstruction the Ag-interlayer spacing, d12, was contracted by about 10% confirming investigations on fcc (110) surfaces regarding the polarization-induced compression of the interlayer distances.

Surface X-Ray Diffraction on the Potassium-Induced Reconstruction of the Ag(001) Surface. H.L.Meyerheim, S.Pflanz, R.Schuster, I.K.Robinson: Physica B, 1996, 221[1-4], 134-40