Macroscopic and nanoscale faceting of germanium surfaces

By means of scanning tunneling microscopy and low-energy electron diffraction, macroscopic and/or nanoscale faceting of well-annealed Ge(315), (213), (324), (546), (515), (212), and (323) surfaces has been studied. The major results are the following. (i) Ge(21 9 29) is found to be a major stable surface (MAJOR), a stable surface that does not consist of nanofacets of any other stable surfaces, and also to be the last one of germanium that can be found. A detailed model consisting of adatoms, rest atoms, and rebonded atoms has been proposed for the atomic structure of the surface. (ii) For all MAJOR’s the family territory, a stereographic region surrounding the MAJOR within which all surfaces at equilibrium must consist of either large facets or nanofacets of the MAJOR, has been determined, though only roughly. (iii) Ge(10 7 12) is found to be a minor stable surface (MINOR) consisting of nanofacets of the (111) MAJOR, and a model is proposed for its atomic structure. (iv) On the basis of the determined family territories, the specific surface free energies of all MAJOR’s of germanium are obtained through a rough estimation. Among all MAJOR’s Ge(111) and (001) have the lowest specific surface free energies, which, however, are only about 6% and 5% lower than that of unstable germanium surfaces, respectively.