The effect of reconstruction on reflection high-energy electron diffraction intensities was investigated for 512 different models of the As terminated GaAs(001)2 x 4 surface. Each model consisted of a different arrangement of twisted titled dimers of the same type. Corresponding rocking curves for elastic diffraction of 12.5keV electrons incident in turn in the [010], [110] and [¯110] azimuths were computed and compared with experimental data. It was shown that the theoretical intensity of the specular diffracted beam was quite different for the reconstructed and unreconstructed surfaces. Causes of these differences in intensity were explained and intensity peaks due to secondary Bragg diffraction of fractional order beams were identified in the specular beam rocking curve for one particular model. For each incident beam azimuth, many different models of the reconstruction give rise to identical rocking curves. Consequently there was only a small number of distinct curves. This grouping effect was explained in terms of the possible values of the structure factor for scattering by surface atoms. In particular it was shown that the incident electrons were insensitive to atomic displacements which were parallel to the incident beam azimuth. Preliminary models were presented for which the agreement with experiment was best for all three azimuths, but overall the results suggest that further models need to be considered to solve the surface structure.

The Effect of Reconstruction on RHEED Intensities for the GaAs(001)2 x 4 Surface M.G.Knibb, P.A.Maksym: Surface Science, 1988, 195[3], 475-98