Stepped silicon templates for quantum wire structures

During the twenty-year development of synchrotron radiation sources for X-ray diffraction, the application to surfaces and interfaces has been a primary motive for the technological advances. The experimental techniques, which are now well-developed, are described in the introduction of this paper. A recent application has been to understand the quantum physics of one-dimensional electronic structures. Here a vicinal semiconducting surface, Si(557), is used as a template to grow ordered arrays of metallic wires by evaporation of gold. The structure of the resulting Au/Si(557) surface is determined from three-dimensional X-ray diffraction measurements. The data directly mandate a single Au atom per unit cell, which allows the use of 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. This structure is found from theoretical band structure calculations to be consistent with the I D metallic behavior seen by photoemission.