Au-Induced Nanostructuring of Vicinal Si Surfaces

The deposition of extremely small amounts of metal onto vicinal semiconductor surfaces can cause dramatic changes in morphology on a nanometer scale. Recently this has been exploited to self-assemble arrays of atomic chains that exhibit bands with intriguing one--dimensional (1-d) metallic behavior. Depositing Au onto a vicinal Si(111) sample tilted either towards or away from the $[11\overline 2 ]$ can produce an array of 1--d chains running along the $[1\overline 1 0]$direction. To investigate the nanofaceting underlying chain formation, we have measured the surface morphology of several miscuts as a function of Au coverage using scanning tunneling microscopy. Samples oriented 3.8\r{ }, 8\r{ }, and 12.5\r{ } from [111] towards $[11\overline 2 ]$ have been measured with Au coverages ranging from less than 0.06~ML up to 0.5~ML. All surfaces exhibit nanofacets with orientations that depend critically on Au coverage. On the 8\r{ } sample, while the exact nature of the surface morphology depends on Au coverage, below 0.32~ML all surfaces incorporate (775)-Au nanofacets. Similarly, (775)-Au facets are also observed on the 3.8\r{ } sample. At 0.17~ML the surface consists of (111)7x7 and (775)--Au nanofacets. At 0.4 ML the (111) terraces transform from 7x7 to a 5x2, and the surface consists of Si(111)5x2--Au terraces separated by (775)-Au facets. The persistence of the (775)-Au facet reinforces the idea that it represents a low energy facet on these Au modified vicinal surfaces.