AVS 46th International Symposium
    Surface Science Division Wednesday Sessions
       Session SS1-WeM

Paper SS1-WeM6
Ordered Alloying of Pd with the Mo(001) Surface

Wednesday, October 27, 1999, 10:00 am, Room 606

Session: Surface Structure
Presenter: M.S. Altman, Hong Kong University of Science and Technology, P.R. China
Authors: D. Wu, Hong Kong University of Science and Technology, P.R. China
Z.Q. He, Hong Kong University of Science and Technology, P.R. China
M.S. Altman, Hong Kong University of Science and Technology, P.R. China
W.K. Lau, Hong Kong University of Science and Technology, P.R. China
C.T. Chan, Hong Kong University of Science and Technology, P.R. China
Correspondent: Click to Email
The interaction of Pd with the Mo(001) surface has been studied with low energy electron microscopy (LEEM) and diffraction (LEED), and first principles total energy calculations. A significant change of surface morphology is revealed by LEEM during the development of a Pd-induced c(2x2) periodic structure. The creation of a large number of islands upon Pd deposition is consistent with the formation of a subsitutional alloy. Accommodation of Pd in excess of the ideal c(2x2) coverage leads to the formation of a c(2x8) structure, although with no apparent change of surface morphology. The c(2x8) structure is stable at the interface between Mo and thicker Pd overlayers. Theoretical calculations demonstrate that the substitutional alloy is energetically favored compared to an overlayer structure at half monolayer coverage. Proliferation of antiphase domain walls in the c(2x2) subsitutional alloy is proposed to explain the c(2x8) periodic structure. Theoretical calculations indicate that a pseudomorphic Pd overlayer is more stable than substitutional alloys at one monolayer coverage, and that the Pd-covered Mo(001) surface would be unstable with respect to faceting to the (112) orientation if the pseudomorphic growth can be realized. However, experiment reveals that there is a kinetic limitation to the formation of the pseudomorphic structure and that faceting is preempted by the formation of more complex surface alloy structures.