The use of scanning tunnelling microscopy and reflection high-energy electron diffraction showed convincingly, for the first time, that molecular beam epitaxially grown GaAs(001)-(2 x 4) , , and  phases all had the same outermost surface layer unit cell. This consisted of two As dimers and 2 dimer vacancies. On the basis of the scanning tunnelling microscopic and reflection high-energy electron diffraction observations, and dynamic reflection high-energy electron diffraction calculations, a structural model was proposed which was consistent with the various results.

T.Hashizume, Q.K.Xue, J.Zhou, A.Ichimiya, T.Sakurai: Physical Review Letters, 1994, 73[16], 2208-11