Faceting and nanoscale faceting of surfaces around (113)

We have studied, by means of scanning tunneling microscopy and low-energy electron diffraction, the Ge(115), (114), and (112) surfaces. It turns out that none of these surfaces is stable because after being thoroughly annealed all of them facet completely: both (115) and (114) to (113) and (117), while (112) to (113) and (7 7 13). We find that the two stable surfaces, (117) and (7 7 13), in turn consist of nanoscale facets of (001) and (113) as well as (113) and (111), respectively. On the basis of these and our previous observations, we suggest that the γ plot of germanium has marked cusps at 〈113〉, and that in many cases as studied here the edges as well as corners connecting the nanoscale facets may generally have negative contributions to the specific surface free energy of stable high index germanium surfaces.