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

Geometric structures of (1[times]1) and (1[times]2) Pt thin films on Pd(110) have been determined by dynamical low-energy electron-diffraction analysis. The (1[times]1) structure is found to exhibit relaxations in the first two interlayer spacings of [Delta][ital d][sub 12]=[minus]11.0% and [Delta][ital d][sub 23]=6.6% at a Pt coverage of one monolayer, and relaxations of [Delta][ital d][sub 12]=[minus]6.6% and [Delta][ital d][sub 23]=4.4% at two monolayers. As for the (1[times]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 A), and the third layer is significantly rumpled (0.23 A). Relaxations in the first four interlayer spacings are found to be [Delta][ital d][sub 12]=[minus]9.5%, [Delta][ital d][sub 23]=[minus]8.0%, [Delta][ital d][sub 34]=[minus]7.3%, and [Delta][ital d][sub 45]=2.2%. Except for a significantly less contracted first interlayer spacing, the (1[times]2) structure of the Pt film mimics the (1[times]2) structure of bulk Pt(110).