It was recalled that, when Ge atoms were deposited onto an (001) Si substrate, dimer vacancies were created in the strained system. At sufficiently high concentrations, interactions between the vacancies caused them to line up; resulting in a 2 x n reconstruction. By analyzing thermal fluctuations around the ideal 2 x n structure, using scanning tunnelling microscopy and transfer matrix theory, the form of the dimer vacancy-vacancy interaction was determined, together with a value for its magnitude.

X.Chen, F.Wu, Z.Zhang, M.G.Lagally: Physical Review Letters, 1994, 73[6], 850-3