Determination of (1 x 1) and (1 x 2) structures of Pt thin films on Pd(110) by dynamical low-energy electron-diffraction analysis.

Geometric structures of (1×1) and (1×2) Pt thin films on Pd(110) have been determined by dynamical lowenergy electron-diffraction analysis. The (1×1) structure is found to exhibit relaxations in the first two interlayer spacings of Δd12=-11.0% and Δd23=6.6% at a Pt coverage of one monolayer, and relaxations of Δd12=-6.6% and Δd23=4.4% at two monolayers. As for the (1×2) structure, the top three layers are found to be Pt. The topmost layer is of the missing-row type, the second layer is slightly row paired (0.06 Å), and the third layer is significantly rumpled (0.23 Å). Relaxations in the first four interlayer spacings are found to be Δd12=-9.5%, Δd23=-8.0%, Δd34=-7.3%, and Δd45=2.2%. Except for a significantly less contracted first interlayer spacing, the (1×2) structure of the Pt film mimics the (1×2) structure of bulk Pt(110).