Structure of double row quantum wires in Au/Si(5Â 5Â 3)

We present a new structure for the quantum-wire surface Au/Si(5 5 3) obtained from three-dimensional X-ray diffraction measurements. We have found the structure has double row of gold, so the wires are two atoms thick. The diffraction pattern is 1 × 1 implying a simple (CTR-only) structure, but disorder is necessary in the model to get a good fit, in the form of a 50-50 splitting of the position of one of the gold sites. A 50% occupied Si adatom is also found, which is a common structural theme of Si(1 1 1) vicinal surfaces. Since there are insufficient available bonds for an adatom to reside in every unit cell, the Au splitting can be seen as a consequence of the alternating presence of the adatoms. No half order diffraction was observed, so any local order of these features must be assumed to be short-range.