Surface reconstruction and relaxation of Al(110)-c(2X2)-Na

The surface structure of the Al(110)-c(2 x 2)-Na phase, formed by adsorptio n of 0.5 ML Na on Al(110) at room temperature, is shown by analysis of exte nsive low-energy electron diffraction measurements to contain Na atoms in t wofold substitutional sites formed by displacement of 0.5 ML Al atoms from the first layer of the substrate. The reconstructive adsorption leads to st rong perturbations of the substrate extending to the fifth Al layer. A larg e rumpling (0.15 Angstrom) of the third Al layer is found, together with a smaller rumpling (0.06 Angstrom) of the fifth layer. Al atoms in the third Al layer, which are directly below Na atoms, exhibit enhanced vibrations as compared to the remaining atoms of the layer.