Subsurface strain in the Ge(001) and (111) surfaces and comparison to silicon.

The subsurface strain associated with surface reconstruction was measured for the Ge(001)-c(4x2) and Ge(111)-c(2x8) surfaces using high energy ion scattering. In the case of the Ge(001) surface we find the equivalent of ~3 monolayers displaced by more than 0.12angstroms, in accord with dimer models of the surface reconstruction. For the Ge(111) surface displacements are observed in off-normal incidence, indicating large displacements perpendicular to the surface or other reconstructions, such as a stacking fault configuration. The relationship between subsurface strain and stacking fault models is also discussed.