Structure and properties of potassium on Pd(100) surface

Abstract

The adsorption of K on Pd(100) was investigated using LEED, EELS, work function and thermal desorption measurements. Adsorbed potassium on Pd(100) formed two well-ordered structures, p(2×2) at θK=0.25, and c(2×2) at monolayer coverage. This latter corresponds to a surface concentration of 6.7×1014 K atoms/cm2. The work function of Pd decreased to a minimum at a coverage of 2.7×1014 K atoms/cm2 and then increased toward the value of metallic potassium. The metallization began at∼1.5 monolayer. The activation energy of desorption decreased from 240 kJ/mol at zero coverage to 108 kJ/mol for monolayer coverage. Adsorption of K on Pd(100) produced four loss features (at 19.4, 18.4, 3.5 and 2.6 eV) in the EEL spectrum which were attributed to K(3p)→K(4s), K(3p)→Pd Fermi level, Pd d-band→K(4s) electron transitions and to a s-derived plasmon loss in metallic potassium.