Coverage-dependent faceting of Au chains on Si(557)

The structural and electronic phase diagrams of Au on Si(557) are established using scanning tunneling microscopy (STM) and angle-resolved photoemission. Five phases consisting of altogether seven facets are observed in the submonolayer regime. With increasing Au coverage one observes Si(111)7×7+Si(112), Si(557)-Au, Si(111)5×2-Au+Si(335)-Au, Si(111)√3×√3-Au+Si(335)-Au, and Si(111)√3×√3-Au+Si(5 5 11)-Au. The relative surface areas of the five phases and seven facets are determined accurately by depositing a Au wedge ranging from 0 to 0.7 monolayer and performing automatic pattern recognition on large-scale STM images. Angle-resolved photoemission spectra are decomposed into contributions from the five phases. The Fermi wave vectors and the band filling of various facets are identified. Using Si(557)-Au as reference we find a coverage of three Au chains per unit cell for the frequently studied Si(111)5×2-Au surface (instead of the widely used value of two Au chains). Likewise a coverage of two Au chains per unit cell is found for Si(553)-Au (instead of one Au chain), in agreement with x-ray diffraction. A structural model with three Au rows per unit cell is developed for Si(111)5×2-Au using density-functional-theory calculations.