It is now well established that the clean surface of diamond structure silicon undergoes reconstructions characterised by dimer formation in the top surface layer. Also found on many diamond surfaces are stacking faults, rings and chains of atoms and adatoms. These structures have the effect of reducing the number of dangling bonds and increasing the surface repeat distance as described above.
A great deal of attention has been paid to reconstructions of the diamond silicon surface in particular. In vacuum and at ambient temperature, this surface forms a 2 1 unit cell with a surface energy of 0.098eV/Å . Upon heat treatment, an intermediate 5 5 surface develops which then converts to a 7 7 reconstruction [89, 90, 91] with an energy of 0.092eV/Å . Both the 5 5 and 7 7 surfaces involve complex combinations of adatoms, dimers and stacking faults. Other surfaces have been investigated by ab initio techniques, such as reconstructions of the Si-I (311) and (001) surfaces[92, 93] where even higher surface energies 0.138eV/Å and 0.126eV/Å are reported. Concurrent advances in both experimental and computational methods have allowed for even these high-order reconstructions to be studied in great detail. The family of reconstructions of Si-I(111) has now been studied up to n=3 by first principles methods [91, 94].
The germanium (100) surface also reconstructs by the formation of dimers. It is found that high order reconstructions characterises this surface with the most stable states being 2 2 and 4 1 unit cells forming symmetric buckled dimer formations.