A number of similar DAS reconstructions have also been observed on Si (111) in non-equilibrium conditions in a (2 n + 1)×(2 n + 1) pattern and include 3×3, 5×5 and 9×9 reconstructions. The preference for the 7×7 reconstruction is attributed to an optimal balance of charge transfer and stress, but the other DAS-type reconstructions can be obtained under conditions such as rapid quenching from the disordered 1×1 structure.