An X-ray scattering study was made of the orientational epitaxy which was exhibited by the hexagonally reconstructed (001) surface. At 1685K, the reconstructed surface layer underwent a continuous rotational transformation with respect to the underlying bulk, and exhibited a mean-field behavior. A second, discontinuous rotational, transformation was observed at 1580K. These results were inconsistent with the predictions of current theory, and led to the proposal of a mean-field description of rotational transformations.

D.Gibbs, G.Grübel, D.M.Zehner, D.L.Abernathy, S.G.J.Mochrie: Physical Review Letters, 1991, 67[22], 3117-20