Tensor LEED analysis for the Cu(111)-(root x root 7)R19.1 degrees-S surface structure

A tensor LEED analysis is reported for the (root 7 x root 7)R19.1 degrees s tructure formed by S at the Cu(lll)surface. A new structural model is found which corresponds to a modified version of the copper sulphide overlayer m odel first proposed by Domange and Oudar. In that model, the topmost layer has 3/7 monolayer each of Cu and S atoms, but the modification involves one S atom per unit mesh moving down to displace a Cu atom from the second met al layer. Relaxations among the topmost Cu atoms result in one S atom being effectively three-fold coordinate while the other two are sixfold coordina te and 12-fold coordinate: the averaged S-Cu bond lengths are indicated to equal 2.19, 2.47 and 2.62 Angstrom respectively. Some discussion is include d of factors that may influence this choice of surface structure. (C) 1999 Elsevier Science B.V. All rights reserved.