NA AND K ON AL(100) STUDIED BY LOW-ENERGY-ELECTRON DIFFRACTION AND HIGH-RESOLUTION CORE-LEVEL SPECTROSCOPY

Experimental results for Na and K deposited at 100 K on the Al(100) su rface using low-energy electron diffraction and high-resolution core-l evel spectroscopy are presented. Our results show that from a coverage of 0.20 monolayers (ML), Na condenses into dense islands with a local Na coverage of 0.50 ML. In the case of K, the overlayer condenses int o islands at a coverage of 0.18 ML, with a local coverage of 0.30 ML. A compilation of various geometric parameters of the present systems a nd of alkalis on Al(111) suggests that the condensation of K on Al(100 ) differs from that of other alkalis on Al systems which undergo conde nsation into two-dimensional islands. Furthermore, all the island-form ing structures display an alkali-alkali distance which is expanded rel ative to the nearest-neighbour distance in the respective alkali metal . The reasons for and implications of this are discussed.