Au-Induced Faceting of Si(5 5 12)

Abstract

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 (≤0.1 ML, 400–500°C), Au 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 (∼0.15 ML) and higher (0.5–2 ML) coverages are the (337) and (225) planes, which are tilted 0.7° down [towards (111)] and 1.1° 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°C). These include (113)+(7 7 15) planes at very low coverage (0.05 ml) and (113)+(5 5 11) planes at higher coverage (∼1 ML), where (113) is tilted up by 5.3° and (7 7 15) and (5 5 11) are tilted down by 2.9° and 2.2°, 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).