Small-displacement monochromator for microdiffraction experiments

Abstract

We describe the design, construction, and performance of the MHATT-CAT microdiffraction x-ray monochromator. This monochromator is specially engineered for x-ray microdiffraction experiments with a high brilliance undulator source. The monochromator passes a small emittance beam, suitable for focusing to submicron size with submilliradian divergence. Over its energy range of 8–22 keV the absolute energy calibration is better than 2 eV and scans of ± 1 keV show no measurable hysterisis. The monochromator operates with a simple water-cooled first crystal and shows no measurable warm-up time. Horizontal linear bearings allow the monochromator crystals to be rapidly inserted or removed from the beam. Slits before and after the monochromator work to pass broad bandpass or monochromatic x-ray beams at the same vertical height. The monochromatic beam direction is adjusted so the monochromatic and broad bandpass beams are coaxial. The design and performance of the monochromator allows efficient collection of microdiffraction data when coupled to a nondispersive Kirkpatrick–Baez focusing mirror pair.

3D X-Ray Crystal Microscope

“…In this configuration, a polychromatic (i.e., white) X-ray beam passes by the side of an insertable scanning monochromator [8] and is focused to a submicrometer spot by a non-dipersive Kirpatrick± Baez mirror pair. As the white beam probes the sample, a complete diffraction pattern is generated at an X-ray sensitive charge coupled device (CCD) for each illuminated grain.…”

“…[9,10] To determine the full stress/strain tensor (including the dilatation) for a grain, the energy of one of the reflections in the pattern is determined by inserting the monochromator into the incident beam and performing an energy scan of the reflection. [8] At present, the location of individual crystal grains along the beam path can be determined with~2±5 lm resolution through the use of geometrical triangulation as illustrated schematically in Figure 1c. [8] The 3D resolution is linked to the spatial resolution along the beam, and although triangulation procedures can be improved, other methods are presently under development that will provide substantially better depth resolution.…”

“…[8] At present, the location of individual crystal grains along the beam path can be determined with~2±5 lm resolution through the use of geometrical triangulation as illustrated schematically in Figure 1c. [8] The 3D resolution is linked to the spatial resolution along the beam, and although triangulation procedures can be improved, other methods are presently under development that will provide substantially better depth resolution. Two beamlines based on the general principles described here have been commissioned to date;…”

The three-dimensional X-ray crystal microscope: A new tool for materials characterization

“…[1,2,3] This microscope is possible due to major technical advances in X-ray sources, detectors, and optics. [4,5] Ironically, the 3-D X-ray crystal microscope uses the oldest X-ray diffraction method: Laue diffraction. Laue diffraction is used to solve an intrinsic problem associated with conventional microdiffraction: sample rotations complicate the spatial mapping of crystalline properties below 5 m. Indeed, as described in Reference 1, diffraction with monochromatic X-rays requires substantial rotations of the sample to achieve a Bragg condition.…”

Local strain redistribution in a coarse-grained nickel-based superalloy subjected to shot-peening, fatigue or thermal exposure investigated using synchrotron X-ray Laue microdiffraction

“…Three methods were developed for that purpose: switching from polychromatic mode to tunable-energy monochromatic beam mode [37], using 1D or 2D energy dispersive detectors [31,38] and a crystal filter [39] while remaining in the polychromatic mode. In this study, an energy dispersive point detector was used (see Fig.…”