I. Pape

Analysis of grazing incidence X-ray diffuse scatter from Co–Cu multilayers

Abstract Grazing incidence diffuse X-ray scattering data from a Co–Cu multilayer with stepped interfaces grown by molecular beam epitaxy on a copper silicide buffer on a silicon substrate has been analysed using a computer code based on a fractal interface within the distorted wave Born approximation. We have extended the theory to include the scattering from a stepped interface and have shown that a single set of structural parameters can be used to obtain an excellent agreement between simulation and experimental data taken under very different X-ray optical conditions. The symmetry of the diffuse scatter on rotation about the surface normal can be explained if it arises from step bunching at the ends of extensive flat terraces. These steps have a self-affine nature, enabling the fractal model to be used successfully.

Evaluation of polishing damage in alumina

Abstract Grazing incidence X-ray scattering and line focus acoustic microscopy have been applied to the study of grinding, lapping and polishing processes on alumina. Changes as a function of polishing time in the near-surface density, measured from the critical angle for total external reflection of X-rays, were related to changes in the bearing area and surface morphology. No relation was found between the micrometre-scale roughness measured by a stylus instrument and the integrated diffuse scatter, the latter being related to the nanometre-scale roughness on the top of the polished mesas remaining after grain pull-out during the grinding and lapping process. The surface acoustic wave velocity was also found to vary with polishing time. These changes cannot be ascribed to changes in roughness and are believed to measure changes in the residual crack density.

The relation of structure to giant magnetoresistance in Co/Cu multilayers

The X-ray diffuse scatter at low angle and around the 111 Bragg peak has been measured from a series of Co/Cu superlattices grown by molecular-beam epitaxy on niobium-buffered sapphire substrates. We have found the conformal roughness to fall linearly with increase in giant magnetoresistance (GMR). The GMR also rises as the mosaic spread falls.

Grazing incidence X-ray scattering measurement of silicate glass surfaces

Grazing incidence X-ray scattering measurements have been performed on a series of silicate glass specimens. We show that it is possible to deduce the true roughness using a Born wave approximation (BWA) analysis, provided that the data are corrected for the effects of the diffuse scatter not emerging from the sample surface. The method is valid provided that the lateral correlation length is approximately known and it holds even in the presence of an electron density gradient at the surface. Agreement within experimental error is found with the interface parameters deduced from full simulations of the specular and diffuse scatter using the distorted wave Born approximation (DWBA). We suggest that the analysis may be appropriate for production line quality control of glassy ceramic materials.

Giant magnetoresistance and interface structure of Cu/Co multilayers grown by MBE on Si(111) substrates with copper-silicide buffers

Abstract Grazing incidence specular and diffuse synchrotron X-ray scattering has been used to study the interface structure of Cu/Co multilayers grown by MBE on Si(111) substrates with a thin copper silicide buffer layer. For similar values of GMR, the roughness is found to be significantly greater than that of Co/Cu multilayers grown on sapphire with a Nb buffer. The roughness has a very long in-plane correlation length and the off-set in the peaks of diffuse and specular scatter is interpreted as arising from terracing of the multilayers.

Influence of step-bunching on grazing incidence diffuse x-ray scattering

An asymmetry in the grazing incidence diffuse x-ray scatter from a 420 A silver film grown on an offcut (111) silicon substrate has been interpreted as arising from fractal-like step-bunching of terraces at the substrate-layer interface. The variation of diffuse scatter with the component of scattering vector normal to the film surface indicates the presence of different lateral correlation lengths for the two interfaces.

Triple-axis X-ray diffraction study of polishing damage in III-V semiconductors

SummaryTriple-axis X-ray diffraction has been performed on a series of GaAs and InP crystals polished by different techniques. Symmetric-reflection reciprocal space maps show that the lattice strain normal to the surface does not vary with sample preparation but that the tilt distribution does vary greatly. Asymmetric reflections, which probe the in-plane strain distribution, reveal that the lattice strains are again constant for GaAs, although there is some variation in the InP data at high tilt distribution

High resolution X-ray scattering from nanotechnology materials

The application of X-ray scattering to the non-destructive determination of physical properties of nanostructured materials is illustrated through use of three example systems. High resolution parallel beam powder diffraction is used to measure particle size and melting temperature in Sn nanoparticles while full reciprocal space mapping allows the mosaic distribution of Co in epitaxial Ag films to be determined. The in-plane correlation length associated with steps on Ag surfaces and the period of artificial gratings are measured by grazing incidence scattering.

Magnetization Process in Co/Cr/Co Trilayers with Ferro- and Antiferromagnetic Interlayer Coupling

Magnetization process was studied in Co/Cr/Co trilayers. B-H hysteresis loops, domain patterns and different types of domain walls were correlated with the interlayer exchange coupling strength. For dCr < 10 A, a cross-tie character of walls indicates a strong ferromagnetic coupling between the cobalt sublayers, which is decreasing rapidly above 10 A of Cr. In ultra high vacuum deposited samples with dCr about 15 A, both stepped hysteresis loops and a patch domain pattern indicate an antiferromagnetic coupling.