MultiLaue: A Technique to Extract d-spacings from Laue XRD

Abstract

doi:10.1017/S1431927616009764 Microsc. Microanal. 22 (Suppl 3), 2016 © Microscopy Society of America 2016 MultiLaue: A Technique to Extract d-spacings from Laue XRD Zack Gainsforth 1 , Matthew A. Marcus 2 , Nob umichi Tamura 2 and Andrew J. Westphal 1 University of California Berk eley, Space Sciences Laboratory, Berkeley, CA, 91020, USA Lawrence Ber keley Laboratory, Advanced Light Source, Berkeley, CA, 91020, USA Broa d spectrum X-ray Diffraction (XRD) is named Laue after Max von Laue, a nd is the original XRD technique [1]. Today, monochromatic XRD is more common because Bragg's equation allows determination of d-spacings wh ere Laue does not. Laue still remains in use for single crystal system s because it can be used to make very accurate unit cell determination s as well as for strain and orientation mapping. A Laue technique whic h could provide unambiguous determination of lattice spacings, a la Br agg's equation would be a huge leap forward, especially for multiphase samples such as meteorites, interplanetary dust particles and some ge ological specimens. We introduce a new technique we call multiLaue whi ch allows such determination. First an unfiltered Laue pattern is acqu ired. Then a filter is inserted between the radiation source and the s ample – in this case a 100 um thick fused silica wafer – and a new Lau e pattern is acquired. A shield protects the detector from radiation s cattered off the filter. Low energy X-rays are more strongly absorbed by the filter than high energy X-rays so reflections excited by low en ergies are more attenuated relative to those excited by high energies. We developed a computer model simulating the process, and use it to q uantitatively determine the X-ray energy exciting a reflection based o n the reduction of intensity across a set of three filters (100, 200 a nd 300 micron fused silica). We tested multiLaue on a Si chip on beaml ine 12.3.2 at the Advanced Light Source synchrotron. The unfiltered pa ttern is shown in Figure 1. We analyzed 32 reflections (Table 1) and c omputed best fit energies. These are compared with energies based on i ndexation via the XMAS software [2]. The best fit energies matched wel l between 11 and 23 keV, with a mean relative error of 1.9% and a stan dard deviation of the error of 1.4%. This means we can compute d-spaci ngs with an accuracy of 21 keV have large errors. Reflections < 11 keV have a harmonic contribution from the spectrum above 21 keV and also show large errors. Therefore, accurate characterization of the radiati on source, and optics is crucially important to achieving high accurac y quantification. References: [1] Laue, von, M. Physikalische Zeitschr ift, 14, (1913), p. 1075–1079. [2] Tamura, N. In Strain and Dislocaton Gradients from Diffraction Spatially-Resolved Local Structure and Def ects , ed. R. Barabash & G. Ice, (Imperial College Press, London) p. 1 25. [3] The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department o f Energy under Contract No. DE-AC02-05CH11231.