New phenomena in the adsorption of alkali metals on Al surfaces

Recent studies of the adsorption and co-adsorption of alkali metals on Al surfaces have revealed a wealth of hitherto unexpected phenomena, including: order-preserving phase transformations between metastable and stable structures; reconstruction of the substrate by adsorption at room temperature; and formation of binary and ternary surface alloys. The results of experimental structural determinations are reviewed, with the major emphasis on Low-Energy Electron Diffraction (LEED) studies of the ordered structures formed by adsorption of the alkalis on Al(111). The experimental results are compared where possible with corresponding results of ab initio calculations of total energy by Scheffler and co-workers. The experiment-theory comparisons provide valuable insight into the adsorption mechanisms, including the possible role of surface steps as both sources and sinks.