Formation and Structural Analysis of a Surface Alloy: Al(111)-(2 × 2)-Na

Abstract

The Al(111)-(2 \ifmmode\times\else\texttimes\fi{} 2)-Na phase formed by adsorption of one-half monolayer Na at 300 K is shown to be a surface alloy. Quantitative agreement is achieved between the results of structure determinations by low energy electron diffraction, surface extended x-ray adsorption fine structure, and total energy calculations. The first four layers of the structure are shown to consist of a Na-Al-Na sandwich on a reconstructed Al substrate layer. It is suggested that the formation of the structure involves surface steps as sources of Al atoms.