High-Resolution 3D Imaging Microscopy Using Hard X-Rays
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High-Resolution 3D
Imaging Microscopy Using Hard X-Rays Christian G. Schroer, Peter Cloetens, Mark Rivers, Anatoly Snigirev, Akahisa Takeuchi, and Wenbing Yun
Abstract The key strength of hard x-ray full-field microscopy is the large penetration depth of hard x-rays into matter, which allows one to image the interior of opaque objects. Combined with tomographic techniques, the three-dimensional inner structure of an object can be reconstructed without the need for difficult and destructive sample preparation. Projection microscopy and microtomography are now routinely available at synchrotron radiation sources. The resolution of these techniques is limited by that of the detector to 1 m or slightly less. X-ray images and tomograms at higher spatial resolution can be obtained by x-ray optical magnification, for example, by using parabolic refractive x-ray lenses as a magnifying optic. Combining magnifying x-ray imaging with tomography allows one to reconstruct the three-dimensional structure of an object, such as a microprocessor chip, with resolution well below 1 m. In x-ray scanning microscopy, the sample is scanned through a small-diameter beam. The great advantage of scanning microscopy is that x-ray analytical techniques such as fluorescence analysis, diffraction, and absorption spectroscopy can be used as contrast mechanisms in the microscope. In combination with tomography, fluorescence analysis makes it possible to reconstruct the distribution of different chemical elements inside an object (fluorescence microtomography), while combining absorption spectroscopy with tomography yields the distribution of different oxidation states of atomic species. Keywords: hard x-rays, three-dimensional imaging microscopy, tomography.
Micro- and Nanotomography for 3D Imaging with Hard X-Rays The geometric structure of crystalline materials is studied routinely by x-ray and neutron diffraction. Many thousands of inorganic, organic, and biological systems have been analyzed in this way. Structure determination by diffraction often reaches atomic resolution. However, when the system has no long-range order, other techniques are needed. Electron transmission microscopy is one such technique and has been in use for more than 50 years. Electron microscopy reaches atomic resolution, but is hampered by the need for sophisticated sample preparation; this is time-consuming and prone to generating artifacts. In addition, the sample must be high-vacuum compatible, which is a MRS BULLETIN/MARCH 2004
(44 Å) and oxygen (23 Å); carbon and nitrogen atoms in biological tissue generate absorption contrast, whereas water is still reasonably transparent for x-rays. This technique is mainly used to produce twodimensional (2D) micrographs. As described in a number of articles,1 this method is well developed and provides lateral resolution down to 25 nm; however, because it is mainly a 2D technique requiring thin samples, it will not be considered here. We concentrate on hard x-rays where microscopy has been aided by the construction of ded
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