Electronic structure of high- and low-temperature c(2x2)-Na/Al(001) phases from angle-scanned ultraviolet photoemission

The electronic states of Na on Al(001) have been studied by angle-scanned ultraviolet photoelectron spectroscopy. In the initial stage of Na deposition at room temperature, the Al(001) sp surface state is found to be rapidly quenched. From the linear decrease in intensity with coverage, the scattering cross section for electrons in this zone-center surface state scattering off Na surface impurities has been determined. For the two structurally different c(2X2) phases formed at low temperature and at room temperature, the surface-state dispersions along the <(Gamma)over bar> (M) over bar and <(Gamma)over bar> (X) over bar directions of the surface Brillouin zone have been measured and compared to the corresponding results from the clean Al(001) surface. Opposite energy shifts and distinctly different effective masses have been found for the electronic states in the two c(2X2) phases.