Papers by Keyword: Grazing Incidence

Abstract: Synchrotron X-ray Topography with grazing incidence geometry is useful for discerning defects at different depths below the crystal surface, particularly for 4H-SiC epitaxial wafers. However, the penetration depths measured from X-ray topographs are much larger than the theoretical values. In order to interpret this discrepancy, we simulate topographic contrast of dislocations based on two of the most basic contrast formation mechanisms – orientation contrast and kinematical contrast. Orientation contrast considers merely the displacement fields associated with dislocations while kinematical contrast also takes the diffraction volume into account. The diffraction volume is defined by the effective misorientation around dislocations and the rocking curve width for particular diffraction vector. Ray Tracing Simulation has been carried out to visualize dislocation contrast for both models, taking into account the photoelectric absorption of X-ray beams inside the crystal. Results show that orientation contrast plays the key role in determining both the contrast and X-ray penetration depths for different types of dislocations.

Abstract: The multireflection grazing incident X-ray diffraction (MGIXD) is used to determine a stress gradient in thin surface layers (about 1-20 μm for metals). In this work two theoretical developments of this method are presented. The first procedure enables determination of c/a parameter in hexagonal polycrystalline materials exhibiting residual stresses. In the second method, the influence of stacking faults on the experimental data is considered. The results of both procedures were verified using X-rays diffraction.

Abstract: The present work deals with the evaluation of the residual-stress profile in expanded-austenite by successive removal steps using GI-XRD. Preliminary results indicate stresses of several GPa's from 111 and 200 diffraction lines. These stresses appear largest for the 200 reflection. The strain-free lattice parameter decayed smoothly with depth, while for the compressive stress a maximum value is observed at some depth below the surface. Additionally a good agreement was found between the nitrogen profile determined with GDOES analysis and the strain-free lattice parameter from XRD.

Abstract: Collecting reliable data is crucial in the research of residual stresses in thin films using X-ray diffraction. The parallel beam geometry has advantage of reliability compared to focusing beam geometry. Though care must be taken to the alignment. A small alignment error may cause a significant error in the stress value. We will show the sensitivity for the misalignment of the parallel beam optics, discuss requirements on hardware alignment and demonstrate a software correction for the presence of remaining hardware errors.

Abstract: Al2O3 ceramic plates of diameter 166 mm and thickness 5 mm were subjected to frictional loading regimes. The resultant residual stress effect in the material was analyzed using the sin2y and AP methods based on a modified measurement condition for the pole angle y and the azimuth angle F on a 4 cycle goniometer. Furthermore, the frictional loading of the Al2O3 plates lead to clear differences in the residual stress state near the surface. An underlying correlation was observed between the residual stress state of the Al2O3 material and its residual strength with this effect being ascribed to the magnitude of frictional load applied.

Abstract: Nuclear resonant scattering (NRS) methods allow to determine diffusion coefficients and jump directions. The capability to measure the diffusion mechanism in ordered intermetallics on atomic scale by mean of NRS was shown in various experiments and in different geometries (transmission [1,2], Bragg [3], grazing incidence [4]). A combination of NRS and grazing incidence geometry can be used as a very sensitive tool to investigate thin films or near-surface-regions [4]. Fe3Si with a D03 structure stable at high temperature and with a well known diffusion mechanism was chosen for this investigation.

Abstract: The structure of thin films of tungsten-carbon, deposited onto monocrystalline silicon substrates by reactive magnetron sputtering (argon + benzene) in a wide range of preparation parameters has been investigated by GISAXS. Substrates were in a fixed position relative to the two adjacent cylindrical magnetrons. Benzene partial pressure was varied from 1% to 10% of the total working gas pressure. A series of samples were prepared, with the substrate held at room temperature and 400°C, and the substrate potential held at floating potential or biased -70 V with respect to the discharge plasma. The bulk particle contribution to the scattering was investigated outside of the specular plane, applying a two dimensional CCD detector. For higher values of benzene partial pressure, the generated films consist of densely packed tungsten carbide grains in an amorphous, carbon rich matrix, while, in some cases, the lower benzene pressure resulted in isolated carbon rich particles in tungsten carbide. From earlier work it is known that the preparation parameters influence the film’s chemical composition, the relatively complex dependence of particle sizes on benzene partial pressure can be explained as a function of the relative carbon content.