The atomic geometries of Cs and K adsorbed on Pd(111): the important role of the ionization potential of the substrate for the bonding

Abstract

Detailed LEED analyses provide structural data of the K and Cs overlayers on Pd(111) with (2×2) and (√3×√3)R30° periodicity. The alkali metal (AM)–Pd layer bond lengths and therefore the AM radii turned out to be 0.1 and 0.2 Å smaller on Pd(111) compared to related AM systems on Rh(111) and Ru(0001), respectively. This suggests a stronger AM–substrate bonding on Pd(111) than on Ru(0001) and Rh(111), which is also reflected by the thermal stability of the AM overlayers against desorption. The trend in the AM–substrate bond strengths follows the trend in the ionization potential of the substrates. This effect may support the AM–substrate bonding to be of charge transfer type.