Synchrotron X-ray tomography provides scientists a powerful tool for obtaining three-dimensional, high-resolution images of ordered materials. But successfully performing synchrotron tomography typically involves a complex and tedious process. For instance, the selected sample and its containment vessel must be rotated together in tiny incremental steps under a focused X-ray beam, over a full 360-degree rotation. And during this full rotation an extremely precise alignment between the crystalline lattice and rotational axis must be continuously maintained. Failure to meet this challenging protocol frequently introduces errors that seriously degrade the tomographic images.
In pursuit of a more efficient and reliable approach, a research team recently combined dark-field X-ray microscopy (DFXM) with a technique called structured illumination. This combination allows the sample and sample environment to remain stationary throughout the imaging process, resulting in quicker setup times, faster data collection, and a more robust path to achieving high-quality 3D images. The new imaging technique was performed on a pnictide superconductor at beamline 6-ID-C of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science user facility at DOE’s Argonne National Laboratory.
The experimental results demonstrate the practicality of the less complex, yet still powerful, modified DFXM technique, opening up a new approach for scientists to obtain accurate 3D imaging at sub-micrometer resolutions.
3D imaging generally entails using some sort of rotation or translation. Medical CT scanners, for example, revolve an X-ray beam and detectors around a stationary patient. During each revolution the X-rays image a “slice” of the patient's interior, and a computer then combines multiple slices to form a three-dimensional body image.
Synchrotron tomography reverses this process by fixing the X-ray beam's direction, which then scans an incrementally rotating sample. Unfortunately, this arrangement introduces complexities that frequently lead to imaging errors. This is partly due to the sophisticated equipment that rotates with the sample, such as containment vessels for maintaining the sample at high or low temperatures, at extreme pressures, or within high magnetic fields. A servomotor then rotates both the sample and containment vessel, a complicated arrangement that not only requires long setup times but also provides multiple paths for mechanical deviations.
Another difficulty is the precise rotational alignment required. During conventional DFXM imaging a crystalline sample must be rotated around a lattice direction called the momentum-transfer vector. The slightest misalignments between this vector and the sample's rotational axis during the experiment degrades the tomographic images.
To overcome the problems associated with conventional 3D synchrotron tomography, the researchers employed a modified form of dark-field X-ray microscopy. Normally, DFXM uses an X-ray lens to focus the X-ray beam, which subsequently diffracts from a crystalline sample to form Bragg peaks (high-intensity interference spots) that pass through an objective lens to reach a 2D imaging detector. To obtain 3D images from this setup, the sample must be rotated. However, the researchers avoided sample rotation by systematically attenuating the X-ray beam used for DFXM.
The resulting arrangement is illustrated in Fig. 1a. None of the depicted components rotate. Instead, a focused X-ray beam intercepts a coded aperture that attenuates, or shapes, the incident beam as the aperture moves linearly as indicated. The aperture consists of distinct gold lines that intermittently block the focused X-rays utilizing a unique binary code design (Fig. 1b). The attenuated X-rays subsequently diffract from a selected sample region and are then magnified by an objective lens before entering a detector. By combining numerous 2D diffraction images as a function of aperture position, a 3D view of the sample region is formed that reveals distinct lattice orientations, strains, and larger mesoscale structures.
The research team tested their 3D imaging approach on a copper-doped, barium-iron-arsenide belonging to a family of compounds with unusual electronic, magnetic, and superconducting properties. The sample was imaged at a temperature just below 90 kelvin where it undergoes a tetragonal-to-orthorhombic structural transition, with a Bragg peak selected to isolate one of these orthorhombic domains (inset of Fig. 1a). The resulting 3D images of this domain appear in Fig. 1c.
This study demonstrates that supplementing DXFM with structured illumination allows high-resolution 3D imaging of crystalline compounds without sample rotation. This technique can also reveal the electronic and magnetic features in many ordered compounds, including single crystals and polycrystals, and potentially in quasicrystals and crystalline multilayers. The researchers anticipate that improved apertures will allow even higher-resolution 3D imaging for a wide range of materials and sample environments. – Philip Koth
See: D. Gursoy1, K.A. Yay2, E. Kisiel1,3, M. Wojcik1, D. Sheyfer1, A. Last4, M. Highland1, I.R. Fisher2, S. Hruszkewycz1, Z. Islam1, “Dark-field X-ray microscopy with structured illumination for three-dimensional imaging,” Commun Phys 8, 34 (2025)
Author affiliations: 1Argonne National Laboratory; 2Stanford University/SLAC National Accelerator Laboratory; 3University of California San Diego; 4Karlsruhe Institute of Technology
This research used resources of the Advanced Photon Source and the Center for Nanoscale Materials, US Department of Energy (DOE) Office of Science User Facilities and is based on work supported by Laboratory Directed Research and Development (LDRD) funding from Argonne National Laboratory, provided by the Director, Office of Science, of the US DOE under Contract No. DE-AC02-06CH11357. The work of M.H. and S.H. was supported by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Science and Engineering Division. The work of K.A.Y. and I.R.F. on crystal growth and characterization received support from the DOE, Office of Science, BES, under contract DE-AC02-76SF00515.
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