Fast atom diffraction inside a molecular beam epitaxy chamber, a rich combination

- Diffraction is recorded along the [010] direction of the β2(2 × 4) GaAs(001) surface.
- Odd diffraction orders are absent indicating a pseudo symmetry of half a unit cell.
- This is interpreted as due to the As dimer of the terminal layer.
- The FWHM of the scattering profile could also be a way to track the number of layers.
- During growth, oscillations of the elastic diffraction intensity drop to zero.

Two aspects of the contribution of grazing incidence fast atom diffraction (GIFAD) to molecular beam epitaxy (MBE) are reviewed here: the ability of GIFAD to provide in-situ a precise description of the atomic-scale surface topology, and its ability to follow larger-scale changes in surface roughness during layer-by-layer growth. Recent experimental and theoretical results obtained for the He atom beam incident along the highly corrugated [11¯0] direction of the β2(2 × 4) reconstructed GaAs(001) surface are summarized. We also discuss the measurements and calculations for the beam incidence along the weakly corrugated [010] direction where a periodicity twice smaller than expected is observed. The combination of the experiment, quantum scattering matrix calculations, and semiclassical analysis allows structural characteristics of the surface to be revealed. For the in situ measurements of GIFAD during molecular beam epitaxy of GaAs on GaAs surface we analyze the change in elastic and inelastic contributions in the scattered beam, and the variation of the diffraction pattern in polar angle scattering. This analysis outlines the robustness, the simplicity and the richness of the GIFAD as a technique to monitor the layer-by-layer epitaxial growth.

While investigating the [010] direction of the β2(2 × 4) reconstruction of the GaAs surface at 570 °C, the observed diffraction of 400 eV helium atoms shows a complete absence of odd diffraction orders. This is interpreted as a pseudo symmetry of the As dimers of the terminal layer. 275