This MRI grant is for the acquisition of a nano-scale resolution X-ray computed tomography (nano-CT) instrument that provides 3D volumetric imaging within opaque structures at 50 nm resolution. Nano-CT offers a unique set of capabilities compared to other imaging techniques and other available X-ray CT instruments. The particular nano-CT provides visualization inside materials and devices with 50 nm or 150 nm resolution with large 3D fields of view of 15 µm and 60 µm, respectively. This is the highest X-ray CT resolution available outside of large-scale synchrotron facilities. The high resolution is obtained even with soft materials, such as polymers, through a combination of a Fresnel zone plate objective and Zernike phase contrast imaging. Compared to techniques using sectioning, nano-CT is non-destructive and sample remains intact. Furthermore, the imaging is done in ambient or controlled environments without vacuum. These features combined with the nano-CT?s long working distance enable in-situ, in-operando, and time-history (4D) imaging. The nano-CT will be used in a wide array of projects across the colleges of science and engineering at Carnegie Mellon, with the enabled research falling into the major themes of: a) Energy and the environment, b) Micro/Nano materials and fabrication, and c) Biomedical and life sciences.
The nano-CT will be a unique resource at Carnegie Mellon and at the regional and national levels, attracting external users from academia, industry, and national labs. The nano-CT will be installed alongside an existing custom micro-CT that offers a maximum resolution of 0.5-1 µm and large fields of view. These combined instruments will form a versatile multi-scale CT imaging facility, with imaging length scales ranging five orders of magnitudes, O(10 nm) to O(1 mm). This comprehensive facility will be advertised through a dedicated website and an annual user group meeting will be held to promote information exchanges and collaborations between the diverse set of users. In addition, workshops will be held to introduce industry to X-ray CT and nano-CT. The nano-CT will result in the training of a large number of student researchers from diverse areas, inspiring interdisciplinary collaborations. The nano-CT and its data will be integrated into existing outreach efforts and classes. To support this effort, a fixed number of zero user cost scans will be made available annually for education and outreach activities.
With the support of a National Science Foundation Major Research Infrastructure award, a nano-scale resolution X-ray computed tomography (nano-CT) instrument was acquired and installed at Carnegie Mellon University, where it currently operates as a user facility. The instrument is the UltraXRM-L200 manufactured by Xradia, Inc. The nano-CT enables the 3D imaging of materials, including their internal structure, at resolutions as high as 50 nm. In a large field of view imaging mode, the instrument can image sample within a 65 micrometer field view with 150 nm resolution. The high resolution is achieved using a series of advanced X-ray optics, including a monocapillary condenser and Fresnel zone plate objective. The UltraXRM-L200 allows conventional X-ray absorption imaging that distinguishes materials by their atomic number, density, and thickness. The instrument also features a Zernike phase contrast imaging mode for resolving low atomic number organic, polymer, and biological materials that are difficult to observe by X-ray absorption. By rotating samples small increments between sequential 2D radiograph images, a volumetric, 3D image of the material can be computationally reconstructed. A key advantage of X-ray imaging is that it can be performed in ambient and controlled environments, enabling in-situ and in-operando imaging of materials and devices. In addition, the method does not destroy the sample and thus complete images can be generated as a function of time or according to progress through a sequence of events. As there is currently only a handful of such instruments available, the nano-CT at Carnegie Mellon represents an important regional and national asset. The nano-CT facility is used by research groups from across the Carnegie Mellon campus and users from outside the university to advance scientific and engineering knowledge in a wide variety of research areas. For example, the nano-CT imaging is being applied to understand the complex material structure and transport processes in energy materials, including battery and fuel cell electrodes. In one project, the nano-CT imaging is being used to resolve the hierarchical structure of carbon-based catalysts that are being developed to replace the Pt catalyst presently used in fuel cells for electric vehicles. Through morphological analysis, the nano-CT data provides insight into the impact of material specifications and processing on the resulting structure. In addition, the geometrical data from the nano-CT is used to generate computational models of gas transport and reaction that are applied to optimizing electrode architectures for better performance. The nano-CT is also being applied to understanding material structures in batteries. A study has been performed to elucidate how conductive additives included in the positive electrodes of Li-ion batteries increase the electrical connectivity of the oxide materials used for energy storage. The nano-CT has also spurred new research activities on imaging techniques, including methods for the correction and segmentation of Zernike phase contrast images using optics based models and new techniques for in-situ and in-operando imaging.
