THE SURFACE STRUCTURES OF Pd(100)-(1×1) AND c(2×2)-K

Abstract

The surface structure of the Pd (100)- c (2×2)-K phase formed by adsorption of K at room temperature has been determined by quantitative analysis of low-energy electron-diffraction (LEED) intensity-energy measurements. K atoms occupy four-fold hollow sites on a slightly perturbed substrate. The vertical distance between the K layer and the first Pd layer is determined to be 2.13±0.06 Å, which corresponds to an effective hard-sphere radius of 1.83 Å for the adsorbed K atoms. The second Pd layer is rumpled with a splitting of 0.04 Å between two bilayers. An analysis of LEED intensities measured for the clean Pd(100) surface confirms previous reports of an expansion of the first interlayer spacing. Adsorption of K in the c (2×2) structure results in a reduction of this expansion from 5% to 1%.