The Ge(0 0 1) surface

Although germanium (Ge) (0 0 1) has a relatively small surface unit cell, this surface displays a wealth of fascinating phenomena. The Ge(0 0 1) surface is a prototypical example of a system possessing both a strong short-range interaction due to dimerization of the surface atoms, as well as an energetically weaker, long-range interaction related to the ordering of the dimers. In this review, I show how the key energetic parameters that govern the thermodynamic behavior of Ge(0 0 1) are extracted from scanning tunneling microscopy measurements. These energetic parameters are used to interpret several surface phase transitions: the 2D equilibrium shape evolution of islands and vacancy islands; the order-disorder c(4×2)→(2×1) phase transition; the orientational phase diagram; and, the faceting of [0 1 0] oriented steps. Particular attention is paid to the differences between Ge (0 0 1) and the closely related and technologically important silicon (Si) (0 0 1) surface.