AVS 49th International Symposium
    Surface Science Tuesday Sessions
       Session SS2-TuM

Paper SS2-TuM8
Ultrathin Transition Metal Films on W Surfaces - Conditions for Surface Alloy Formation

Tuesday, November 5, 2002, 10:40 am, Room C-110

Session: Diffusion & Growth on Metal Surfaces
Presenter: T.E. Madey, Rutgers, The State University of New Jersey
Authors: J. Block, Chalmers University of Technology and Gothenburg University, Sweden
E. Schroder, Chalmers University of Technology and Gothenburg University, Sweden
J.J. Kolodziej, Rutgers, The State University of New Jersey
J.W. Keister, North Carolina State University
J.E. Rowe, North Carolina State University
T.E. Madey, Rutgers, The State University of New Jersey
Correspondent: Click to Email
We report theory and experiment for the formation of alloy layers in the growth of transition metal films on W surfaces. When W(111) is covered by monolayer films of certain metals (Pt, Pd, Ir, Rh, Au), followed by annealing to T>750 K, the surface becomes covered with three-sided pyramids of nanometer-scale dimensions, having {211} planes as facet sides. High resolution soft x-ray photoelectron spectroscopy using synchrotron radiation is employed to study metal films (Pt, Pd, Ir, Rh) on W(111) and W(211). Surface core level shifts of 4f@sub 7/2@ photoemission peaks indicate that single physical monolayers of these metals are stable against thermal rearrangement. In contrast, when multilayer films of Pd, Pt, Ir, Rh are annealed above 700-1000 K, tungsten atoms diffuse into the overlayer to form alloy films. We also characterize ultrathin Pd and Pt films on W(211) by first-principles density-functional theory (DFT) methods. Both to confirm the formation of alloy from theory and to help characterize the alloy, we present studies of Pd and Pt films with included W atoms. The DFT methods allow us to suggest the energetically preferred structures. We studied both pseudomorphically-grown alloy films and alloy films with the atomic positions locally optimized by minimizing the Hellmann-Feynman forces. The DFT calculations are consistent with the experimental observations.