A medium energy ion scattering study of the structure of Sb overlayers on Cu(111)

Using 100 keV H+ ions, medium energy ion scattering (MEIS) has been applied to a study of Sb overlayers on Cu(111). Upon deposition of 10 ML of Sb at room temperature, considerable intermixing of Sb and Cu occurs in thick (100 Angstrom) overlayers, forming a partially ordered alloy phase, of composition Cu3Sb. Heating to 200 degrees C produces a second ordered alloy phase with reduced Sb content, whilst heating to 305 degrees C diffuses excess Sb into the bulk and produces an ordered Cu(111)(root 3 x root 3)R30 degrees-Sb surface phase with 0.33 ML Sb. Comparison of blocking curves obtained from this phase with the results of simulations for a range of model structures leads to the conclusion that the Sb atoms substitute outermost layer Cu atoms, but this surface alloy layer is laterally displaced so that all constituent atoms occupy hcp hollow sites relative to the underlying Cu(111) substrate. In this stacking faulted surface layer, the layer spacings of the Sb and Cu atoms relative to the outermost underlying Cu surface layer have been determined to be 2.52 +/- 0.13 Angstrom and 2.05 +/- 0.09 Angstrom respectively. Some aspects of the methodology for the application of MEIS to surface structure determination and structural parameter precision estimation are addressed. (C) 1999 Elsevier Science B.V. All rights reserved.