STRUCTURAL DETERMINATION OF AN INTERMIXED (1X2) AU FILM ON PD(110) BYDYNAMICAL LOW-ENERGY ELECTRON-DIFFRACTION ANALYSIS

The geometric structure of a (1 x 2) Au film on Pd(110) has been deter mined by dynamical low-energy electron-diffraction analysis. The conce ntration profile of Au in the surface region is determined in the anal ysis, and the results clearly reveal the presence of intermixed layers beneath two layers of essentially pure Au. As for the optimum geometr y of the film, the topmost layer is of the missing-row type, the secon d layer is row-paired by 0.10 angstrom, the third layer is rumpled by 0.07 angstrom, and the first three interlayer spacings are relaxed by DELTAd12 = -6.6%, DELTAd23 = + 5.1%, and DELTAd34 = + 3.6% relative to the bulk-truncated substrate. (Deeper interlayer spacings are at or n ear the bulk value.) The optimum geometry of the intermixed Au film di ffers considerably from that of the (1 x 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 a nd Pd.