DETERMINATION OF (1X1) AND (1X2) STRUCTURES OF PT THIN-FILMS ON PD(110) BY DYNAMIC LOW-ENERGY ELECTRON-DIFFRACTION ANALYSIS

Geometric structures of (I X 1) and (I X 2) Pt thin films on Pd(I 10) have been determined by dynamical low-energy electron-diffraction anal ysis. The (1 X 1) structure is found to exhibit relaxations in the fir st two interlayer spacings of DELTAd12 = - 11.0% and DELTAd23 = 6.6% a t a Pt coverage of one monolayer, and relaxations of DELTAd12 = - 6.6% and DELTAd23 = 4.4% at two monolayers. As for the (1 x 2) structure, the top three layers are found to be Pt. The topmost layer is of the m issing-row type, the second layer is slightly row paired (0.06 angstro m), and the third layer is significantly rumpled (0.23 angstrom). Rela xations in the first four inter layer spacings are found to be DETLAd1 2 = - 9.5%, DELTAd23 = - 8.0%, DELTAd34 = - 7.3%, and DELTAd45 = 2.2%. Except for a significantly less contracted first interlayer spacing, the (I X 2) structure of the Pt film mimics the (1 X 2) structure of b ulk Pt(110).