The surface structures formed by Na adsorption on Al(1 1 0)

The surface structures formed by the adsorption of Na on Al(1 1 0) at room temperature have been studied by low energy electron diffraction (LEED) and core-level photoemission spectroscopy (CLS). With increasing Na coverage in the submonolayer region the following sequence of adsorbed phases is observed: (3×2), c(2×2), (3×1), (4×1), and (2×1). For the well-ordered c(2×2) and (4×1) phases, the detailed surface structures have been determined by LEED. The c(2×2) phase has been shown previously [1] to contain 0.5 monolayer (ML) Na atoms located in substitutional sites formed by displacement of 0.5 ML Al atoms. In the present work it is shown that the (4×1) phase consists of 0.25 ML Na adsorbed in substitutional sites and 0.5 ML Na adsorbed in low-symmetry sites on the first Al layer. Based on CLS measurements, and the structures determined for the c(2×2) and (4×1) phases, models are presented for the partially disordered (3×2), (3×1), and (2×1) phases. Finally, it is found that Na adsorption beyond 1 ML leads to the growth of a distinct, second layer of Na atoms on top of the mixed Al/Na layer.