Dynamical low-energy electron-diffraction investigation of lateral displacements in the topmost layer of Pd(110).

Based on He-atom diffraction evidence for an order-disorder transition on Pd(110) at 230 K, other authors have proposed a model in which the atoms of the topmost layer are displaced laterally by 0.7 Å along the [001] direction, with the directions of the displacements correlated at T<230 >K, but largely uncorrelated at T>230 K. To test this model, we have examined the proposed ordered phase by dynamical low-energy electron-diffraction analysis. Our results favor a nonlaterally displaced geometry, with a contraction of 4.4±1.5% in the first interlayer spacing and an expansion of 1.5±1.5% in the second interlayer spacing, but do not conclusively rule out the possibility of lateral displacements