X-ray diffraction study of stresses and textures in strongly oriented thin films
Résumé
X-ray diffraction techniques for analysis of thin polycrystalline films have been well-developed and they are routinely used when often low-angle incidence setup is applied instead or in addition to symmetrical scans. For strongly oriented films more different asymmetric scans and/or reciprocal space mapping are required. The so-called sin2ψ method is usually used for determination of residual stress while simple texture indices are calculated or ω scans (rocking curves) measured for fast characterization of preferred orientation. Measurement of stresses in highly textured films can be complicated by limitations in both hkl and angular ranges. For cubic materials, quite simple, crystallite group method can be applied. However, for non-cubic systems this may be complicated by uncertain ratio of lattice parameters. Various measurements as well as techniques were performed for different materials like cubic TiN films, nanocrystalline ZnO films, several phases of hexagonal ferrites. We have applied a combination of different scans to characterize both the so-called out-of-plane orientation and in-plane orientation of the films. Sometimes, the only way of stress determination was comparison of results for films and corresponding powders. Fast reciprocal-space mapping by placing a 2D detector close to the sample was also used. In this configuration, the continuous theta-2theta scan fully probes a long stripe in a reciprocal space. Such measurement can be performed for different sample azimuths. The obvious advantage of this approach is a possibility to quickly visualise the intensity in reciprocal space and to compare the obtained images with the simulations based on some expected phase/texture/stress model giving semi-quantitative results.
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