A. Bruson

Structural and magnetic profiles in Fe/Si multilayers

Abstract Iron-silicon multilayers were prepared by vacuum evaporation and characterized by cross-sectional electron microscopy, electron diffraction, in situ electrical measurements and low-angle X-ray scattering. Mossbauer spectroscopy measurements carried out on samples with different silicon and iron thicknesses showed a distribution of the magnetic moments of the iron atoms. The Mossbauer spectra are analysed with reference to those of Fe-Si amorphous and crystalline alloys. They show iron atoms in a pure bcc crystalline phase, in a bcc crystalline phase with a silicon atom as a first neighbour, in an amorphous magnetic phase with a large hyperfine field distribution and in an amorphous non-magnetic phase. A Jaccarino-Walker type hypothesis allows us to propose a model for structural and magnetic profile of the layers which is consistent with neutron scattering and Mossbauer spectroscopy data.

Polarized neutron study of Fe/Si multilayers

Abstract A low-angle neutron scattering study has been carried out on Fe/Si multilayers. It is shown that the flipping ratio of the satellites is not constant, which can be explained by the presence of a non-magnetic interlayer between Fe and Si. A simple step-model analysis shows that the thickness of the Fe-Si alloyed interlayer is about 15A, which is consistent with previous Mossbauer measurements.

Interference effect in non-specular scattering from multilayers interpretation of the rocking curves

Abstract Non specular scattering of X-rays occuring at the periodic interfaces of Si/Ge multilayers produce interference effects. These effects are shown experimentally from rocking curves (ω-scans) ad from scans of the detector for fixed positions of the sample (θ2-scans). Peaks in θ2-scans and broad wings in ω-scans are explained by simple considerations on the phase-shifts of the incident and scattered waves. A generalization of Groces and Sinhas relation is proposed.

Determination of Short-Range Motion of Hydrogen in Amorphous Silicon Multilayers by Low-Angle Neutron Scattering

The diffusion coefficient of hydrogen in amorphous silicon deposited at 77 K has been measured by monitoring the decay of the low-angle neutron scattering intensity during annealing of Si:H/Si:D/Si:H/Si:D/... multilayers. Diffusion coefficient values ranging from 1 10-19 cm2/s to 5 10-19 cm2/s have been obtained for annealing temperatures between 250 °C and 300 °C. These very low values confirm recent experiments of Shinar et al. and show that the motion of hydrogen atoms may be impeded by microstructures in amorphous silicon.

Study of the hydrogen stability in evaporated amorphous Si1−xSnx:H (0≤x≤0.2) alloys by neutron scattering and exodiffusion measurements

Exodiffusion and low‐angle neutron scattering experiments are used to investigate the influence of tin on the hydrogen stability in evaporated amorphous Si1−xSnx (0≤x≤0.2) alloys. The neutron diffraction experiments, which are performed on Si1−xSnx:H/Si1−xSnx:D/... multilayers, consist in following the decay of the diffracted intensity during thermal treatments. Both studies give information on the structure of the alloys and show that the hydrogen stability decreases with increasing tin concentration.

Evidence of hydrogen modulation in amorphous germanium prepared by reactive evaporation

Reactive evaporation of germanium under a flow of hydrogen atoms on substrates maintained at liquid‐nitrogen temperature allows us to obtain a‐Ge:H thin films and multilayers. The material contains a considerable amount of polygermane bonds and is porous, as shown by low angle x‐ray scattering performed on Ge/Ge:H/... multilayers. The stability of hydrogen is measured by resistivity measurements and by effusion experiments. Finally, low angle neutron scattering shows that it is possible to modulate hydrogen in Ge/Ge:H/Ge/Ge:D/... multilayers with 40 A thick layers.

Interpretation of transmission electron microscope images of amorphous silicon/germanium and silicon/iron multilayers

We show that the observed contrast in transmission electron microscope images of multilayer specimens composed of amorphous materials can be understood in terms of the scattering of electrons passing through the material. This leads us to develop a simple method of analyzing the image contrast to give quantitative information about the thicknesses of individual layers, which cannot be obtained by any other technique. The results of this analysis for images of silicon/germanium and silicon/iron multilayers are in good agreement with the results of small‐angle x‐ray scattering and the readings of quartz thickness monitors during the deposition of the layers. The accuracy of the thickness measurements we obtain from transmission electron microscope images is 7% for the average layer thickness of a single component and 10% for the thickness of individual layers when the layer thickness is about 4 nm, which is comparable to the accuracy which can be attained for crystalline layers.

Evidence for amorphous multilayered silicon obtained by deposition under modulated pressure of hydrogen

A new method of fabrication of layered structure of silicon is presented. The silicon was evaporated continuously under a modulated pressure of hydrogen. A contrast was dense and less dense silicon layers is evidenced by low‐angle x‐ray scattering and cross‐sectional electron microscopy.