Oxygen etching of Si(5 5 12) and related surfaces

We have used scanning tunneling microscopy to study the oxygen etching behavior of the high index Si(5 5 12) surface, as well as nearby metal-induced facet planes formed by Cu and Au. The (5 5 12) surface is tilted 30.5° away from (0 0 1) towards (1 1 1) and forms a single-domain reconstruction composed of row-like structures. Oxygen etching has been observed for sample temperatures above 700 °C and O2 exposures from 50 to 200 L, where pyramidal islands containing (1 1 3) facets oftentimes occur. As expected, the density of these islands increases at lower temperatures where oxide nucleation is favored. In addition to the clean surface, oxygen etching of metal-adsorbed surfaces that contain (1 1 3) planes has also been investigated. Both Cu and Au are known to cause faceting of the Si(5 5 12) surface: Cu forms sawtooth facets composed of (1 1 3) and (1 1 1) planes, whereas low coverages of Au produce (1 1 3)/(3 3 7) sawtooths. In both cases, oxygen etching at temperatures above 700 °C produces trapezoidal islands that again incorporate (1 1 3) planes. This prevalence of (1 1 3) facets during etching is explained via step pinning at oxide-induced pinning sites.