Investigation of the structure of the 2×4 reconstructions of GaAs (001) by analysis of RHEED intensity data

Rocking curves are computed for electrons incident in turn in the [010], [110] and [¯110] azimuths for 512 different models of the reconstruction. Each model corresponds to a different arrangement of twisted tilted dimers. For each incident beam azimuth many of these distinct models give identical rocking curves. This is explained by the possible values of the structure factor for scattering by surface atoms. In particular it is shown that the incident electrons are insensitive to atomic displacements which are parallel to the incident beam azimuth. Preliminary models are presented for which the agreement with experiment is best for all three azimuths. The effects of tuning the displacements within the dimers are considered and finally the intensities of the non-specular beams are briefly discussed.