CM04.04.08 : Micro Grain Analysis in Plastic Deformed Silicon by 2nd-Order X-Ray Diffraction

5:00 PM–7:00 PM Apr 3, 2018

PCC North, 300 Level, Exhibit Hall C-E

Gabriel Dina2 Ariel Gonzalez2 Sergio Morelhao2 1 Stefan Kycia2

2, University of Guelph, Guelph, Ontario, Canada
1, University of Sao Paulo, Sao Paulo, , Brazil

Plastic deformation of otherwise perfect crystals is an unlikely process to be used for production of optical X-ray components due to the detrimental impact of resulting mechanically induced defects would have on the coherence of the diffracted X-ray waves [1]. However, if controlled, such defects in plastically deformed crystals can enable optics solutions that may outperform current options. Understanding the micro-grain structure of plastically deformed crystals is a key for this goal. Particularly interesting optical components for high energy X-rays are the Laue monochromators. At synchrotron beamlines they are preferred over standard Bragg monochromators when using high energy X-rays above 30keV. Advantages of using a bent Laue monochromator include increasing the rocking curve width, and hence, the intensity, as a result of the spread in d-spacing and the change in Bragg plane orientation. Furthermore, Laue monochromators do not demand large crystal beam footprints and allow the focusing of X-rays, which results in increased intensity on a sample or detector. Moreover, plastically deformed Laue crystals versus the more widely used elastically bent design, have the benefits of not needing complicated bender mechanisms and freedom to choose any sagittal and meridional curvature corresponding to the desired shape that meets the exact optical specifications [2].
We have developed high quality curved plastic deformed silicon Laue monochromator crystal. We characterized the crystal at the Cornell High Energy Synchrotron Source and the Canadian Light Source. The crystal monochromator enabled a wide band pass, high throughput monochromatic beam focussed down to 300um seven meters from the monochromator. The micro grain structure is the limiting factor to the fous size and throughput. In order to characterize and understand the limiting nature of the plastic disorder in the crystal, we took advantage of non-traditional multiple beam diffraction technique.
Second-order X-ray diffraction (SOXRD) processes are three-dimensional in nature and capable of probing the relative misorientation between perfect crystal domains [3]. In silicon, forbidden reflections such as the 002 reflection allows observation of SOXRD alone, without intensity contributions from the direct first-order diffraction. In this work, we use a multi-axis diffractometer for mapping the two-dimensional intensity distribution around a few SOXRD from the {111} family of planes in a plastically bent (001) silicon wafer. Each one of these SOXRD takes place at different azimuths, probing the relative grain misorientation along distinct in-plane directions. As we scan the beam footprint across the curvature of the wafer, the evolution of grain misorientation is figured out.

[1] K. Nakajima et al. Nat Mater. 4, 47 (2005).
[2] H. C. Kang et al. Phys. Rev. Lett. 96, 127401 (2006).
[3] S. L. Morelhão, L. P. Cardoso. J. Appl. Cryst. 29, 446 (1996).