Structure of Quantum Wires in $\mathrm{Au}/\mathrm{Si}\left(557\right)$

The structure of the $\mathrm{Au}/\mathrm{Si}\left(557\right)$ surface is determined from three-dimensional x-ray diffraction measurements, which directly mandate a single Au atom per unit cell. We use a “heavy atom” method in which the Au atom images the rest of the structure. Au is found to substitute for a row of first-layer Si atoms in the middle of the terrace, which then reconstructs by step rebonding and adatoms. The structure is consistent with the 1D metallic behavior seen by photoemission.