Two-dimensional surface alloys: Copper on W(100)

Structural transformations when up to two monolayers of Cu are adsorbed on W(100) and then annealed have been studied by ion scattering spectroscopy, low energy electron diffraction (LEED), Auger electron spectroscopy (AES), work function changes and thermal desorption spectroscopy (TDS). Adsorption at 300 K produces epitaxial growth up to two monolayers, but annealing the surface at ≈700 K induces coverage-dependent structural transformations. In the coverage range 0.2 4 He + collected at various scattering geometries show that this structure consists of a coplanar two-dimensional double-spaced Cu−W surface alloy. AES demonstrates that there is no significant bulk alloying. Annealing at θ=0.75 produces a p(2×2) structure which disorders at 900 K, while with higher Cu coverages the LEED patterns after annealing show disordering and domain formation. These results provide a structural basis for a coherent reinterpretation of the data produced by Bauer and coworkers for the same system.