Advanced tomography techniques for inorganic, organic, and biological materials
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Introduction Imaging from the atomic to the bulk scale to understand system dynamics and connectivity is a common need for nearly all science fields. For example, in biology, visualizing molecularscale metabolic flow within individual cells as well as in the context of a whole plant is a grand challenge. This requires similar multiscale three-dimensional (3D) imaging approaches as those needed in materials science to link atomic-structure defects to crack propagation and component failure in jet engines or to understand mechanistic details of how chemical changes affect the nanoscale morphology of solid phases leading to reduced capacity of battery systems or activity and selectivity loss in catalysts. The ability to visualize the whole system intact with low resolution, such as with x-ray microcomputed tomography, and then sequentially zoom in with increasing spatial resolution and narrower field-ofview using x-ray nanotomography1 or electron tomography approaches,2 promises new paradigms for interrogating not only static systems, but also systems perturbed or evolving over time.
Tomography using x-rays and electrons The mathematical basis of tomography—3D imaging using two-dimensional (2D) projections acquired from different
perspectives—has been known for almost 100 years.3,4 For tomography, a series of projections of the specimen, conventionally 50–150, are acquired by tilting the specimen relative to the probing beam or vice versa, while recording an image at each tilt step. Subsequently, these 2D images are aligned and reconstructed, or back-projected, to create the 3D volume, conventionally a 3D intensity map of a specific contrast mode. Technological limitations prevented immediate implementation and application from the 1920s to 1950s. The first groundbreaking experiments for tomography using x-rays occurred in the early 1960s,5 while those using electrons occurred later in the same decade.6–8 Since then, much progress and impact has been realized specifically for the analysis of complex 3D materials where conventional 2D imaging approaches may lead to erroneous interpretations of structure or function, as illustrated in Figure 1. While tomography has been historically dominated by biological applications because of the complexity of cells, its relevance and scope in the development of advanced materials has dramatically increased due to progress in materials science. In recent years, materials research across the disciplinary boundaries of biology, chemistry, and physics is increasing, which has pushed the development of this approach. For instance, expanding from the initial conventional bright-field
James E. Evans, Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, USA; [email protected] Heiner Friedrich, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, The Netherlands; [email protected] doi:10.1557/mrs.2016.134
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• www.mrs.org/bulletin MRShttps://www.cambridge.org/core. BULLETIN • VOLUME 41 • JULY 2016University © 2016 Materials D
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