Nucleation, growth, and deformation of one-dimensional Ge nanostructures on the Si(5512)-2 x 1 surface

Evolution of the strained Ge-nanofacet, self-assembled on the Si(5 5 1 2)-2 x 1 template held at 530 degrees C, has been observed in the atomic scale using scanning tunneling microscopy. Initially, a Ge pi-bonded chain is formed on the preferential adsorption site, a dimer-adatom row at the (225) subunit in a (5 5 1 2) unit, which results in subunit-switching between (3 3 7) and (2 2 5). By repeated subunit-switchings, the seed of sawtooth-like facet, that is, a single (1 1 3) subunit, is sorted out at the center of double (2 2 5) subunits. Then, the stable (1 1 3) facet expands until the (1 1 2) [or (3 3 5)] facet on the other side of sawtooth-like facet borders on the edge of the next (113) facet, and, in the end, the one-dimensional (1 D) nanofacet with high aspect-ratio and well-defined cross-section (average width: 14 nm, and height: 0.58 nm) is completed at 1.5 monolayer (ML) of Ge coverage. At higher substrate temperature. 600 degrees C, the cross-section of nanofacet becomes smoother with additional faces (1 1 1) and (2 2 5), while its height becomes less uniform. When the anisotropic stress relaxation arrives at the limit with additional Ge, the (1 1 3) facet starts to have 2 x 2 structure and lose 1 D symmetry. Finally, at 4 MLs of Ge coverage, it converts into a Ge but with faces, (1 1 3), (1 1 2), (1 5 3 2 3), and (3 1 5 2 3). (C) 2008 Elsevier B.V. All rights reserved.