The composition and reconstruction of the GaP{100}-(4 x 2) surface was studied by time-of-flight scattering and recoiling spectrometry and low energy electron diffraction. Time-of-flight spectra of scattered and recoiled neutrals plus ions were collected as a function of crystal azimuthal rotation angle δ and primary beam incident (polar) angle α. Compositional analysis of the surface was obtained from 4keV Ne+ scattering and recoiling spectra. Structural analysis was obtained from the azimuthal anisotropy of the δ-scans and the features of the α-scans using both 4keV Ne+ and Kr+ for scattering and recoiling. The azimuthal δ-scans were simulated by means of a shadow cone focusing model and a classical ion trajectory model. The totality of these data showed that the (4 x 2) reconstruction of GaP was a Ga missing-row-trimer P dimer structure in which every fourth Ga<0¯11> row was missing, the Ga atoms were trimerized along the <011> azimuth, and the 2nd-layer P atoms exposed in the <0¯11> troughs were dimerized. This model was consistent with all of the data, was autocompensated, and had Ga intratrimer spacings of 3.2Å and P intradimer spacings of 2.7Å. The results of the simulations suggest that the two end Ga atoms of the trimers were relaxed downward by a minimum of 0.2Å. A missing-row-dimer model, similar to that proposed for the GaAs (4 x 2) structure, in which every fourth Ga <011> row was missing and Ga dimers formed along <011>, was also considered. This missing-row-dimer model was inconsistent with large portions of the experimental data and the simulations. The results were discussed in terms of the differences in the chemical bonds of phosphorus and arsenic.

Composition and Reconstruction of the GaP{100}-(4 x 2) Surface. M.M.Sung, J.W.Rabalais: Surface Science, 1996, 365[1], 136-48