In this study, the effects of growth interruptions on the formation of the interfaces in GaAs∕AlAs multilayers are investigated. For that purpose, a series of different samples has been manufactured with molecular-beam epitaxy. The introduction of growth interruptions of 50 s after the deposition of the layer leads to a change in the morphological properties of the interfaces, in particular their correlation length. These modifications due to the growth interrupt are analyzed with diffuse X-ray scattering. As a result of the measurements, an extension of the lateral correlation length can be proved. By contrast, the vertical correlation of the interfaces is not affected.
AbstractX-ray scattering is used to investigate the surface dynamics on Au(111) during Ar+ ion irradiation. During 500 eV Ar+ ion irradiation, we observe the three regimes of step retraction, quasi-layer-by-layer removal and three dimensional rough erosion, analagous to molecular beam epitaxy. The quasi-layer-by-layer sputtering regime has been studied to identify similarities and differences in surface evolution during ion irradiation and molecular beam epitaxy. X-ray measurements suggest that 500 eV Ar+ ion irradiation does not lead to stable adatom island formation. Also, in contrast to molecular beam epitaxy, adatom detachment and diffusion seems important in describing the surface kinetics during ion irradiation.
AbstractWe describe measurements on the magnetic properties of Co-Cu superlattices in which the Co layer thickness was fixed at 20 Å and the Cu thickness was varied from 4 Å to 24 Å. The samples were grown on Ge-buffered (110) GaAs by molecular beam epitaxy. X-ray scattering and in-situ RHEED indicate that the multilayers are oriented in the (111) direction with the Co layers stacked in an fcc arrangement. Our interest in this series of samples lies in their unusual hysteresis curves which show distinct transitions. We have found that the appearance of these transitions is directly related to the Cu thickness, indicating the presence of complex spin configurations as a consequence of competing interactions. The results are not consistent with a simple RKKY antiferromagnetic coupling.
AbstractInAs/GaAs superlattices with thin (0.5–1 monolayer) δ-InAs insertions were grown by molecular beam epitaxy at low (150–200°C) temperature. The as-grown samples contained up to 1020 cm−3 arsenic antisite defects. Transmission electron microscopic study revealed no extended defect and showed that the real thickness of δ-InAs insertions is 3–4 monolayers. This thickness seems to be due to short-range roughness of the growth surface. Low diffuse scattering and extended interference picture were observed for such superlattices by x-ray diffraction study. Superlattices of two-dimensional cluster sheets were produced by annealing of the δ-InAs/GaAs superlattices at 500–600°C. Precipitation of excess arsenic at InAs δ-layers was found to be accompanied by enhanced In-Ga intermixing, roughening the InAs δ-layers, and smoothing the x-ray interference picture. No evidence for any self-ordering in the system of nanoscale As clusters was revealed using x-ray mapping in reciprocal space.
Reciprocal Space Expansion in the Analysis of X-Ray Scattering Intensities from Liquid Carbon Tetrachloride