Au-induced faceting of Si(5512)

The growth of Au on the stable, high-index Si(5 5 12) surface has been studied using scanning tunneling microscopy (STM). At very low coverages and moderate annealing temperatures ( less than or equal to 0.1 ML, 400 500 degreesC), An appears to decorate the underlying Si rows and form an array of rows that maintains the underlying (5 5 12) periodicity of 5.4 nm. For higher annealing temperatures and coverages, however, Au causes faceting to a number of nearby planes. The two primary facets formed at lower (similar to0.15 ML) and higher (0.52 ML) coverages are the (337) and (225) planes, which are tilted 0.7 degrees down [towards (111)] and 1.1 degrees up from (5 5 12), respectively. Both orientations are in fact subunits of the (5 5 12) unit cell, so their presence is not surprising. In addition to these facets, two types of sawtooth morphologies composed of planes oriented further from (5 5 12) are found at very high annealing temperatures (800-900 degreesC). These include (113) + (7 7 15) planes at very low coverage (0.05 ml) and (113) + (5 5 11) planes at higher coverage (similar to 1 ML), where (113) is tilted up by 5.3 degrees and (7 7 15) and (5 5 11) are tilted down by 2.9 degrees and 2.2 degrees, respectively. Au adsorption on Si(5 5 12) therefore results in the formation of five possible facet planes: (113), (225), (337), (5 5 11), and (7 7 15).