Structural determination of an intermixed (1×2) Au film on Pd(110) by dynamical low-energy electron-diffraction analysis

The geometric structure of a (1 × 2) Au film on Pd(110) has been determined by dynamical low-energy electron-diffraction analysis. The concentration profile of Au in the surface region is determined in the analysis, and the results clearly reveal the presence of intermixed layers beneath two layers of essentially pure Au. As for the optimum geometry of the film, the topmost layer is of the missing-row type, the second layer is row-paired by 0.10 Å, the third layer is rumpled by 0.07 Å, and the first three interlayer spacings are relaxed by Δd 12 = −6.6%, Δd 23 = +5.1%, and Δd 34 = +3.6% relative to the bulk-truncated substrate. (Deeper interlayer spacings are at or near the bulk value.) The optimum geometry of the intermixed Au film differs considerably from that of the (1 × 2) missing-row reconstruction of bulk Au(110), but can be rationalized in terms of conservation of volume density as a response to the 4.8% lattice mismatch between Au and Pd.