Wenbing Yun

Non invasive, multiscale 3D X-Ray characterization of porous functional composites and membranes, with resolution from MM to sub 50 NM

We describe a novel x-ray computer tomography (CT) system for high contrast, non invasive 3D imaging of internal structures of functional ceramics, composites and polymeric membranes. System is capable of multi-length scale imaging from mm to sub 50 nm spatial resolutions and requires little or no sample preparation or staining. Relatively large samples with thickness from several mm to several microns may be imaged at high resolution. Examples using functional composites and membranes from SOFC (solid oxide fuel cell) and PEM (proton exchange membranes) fuel cell to derive direct information such as porosity and catalytic membrane degradation will be discussed. The key to the novel laboratory CT technology lies in utilizing proprietary x-ray optics with Fresnel Zone plates, and innovative high resolution, high contrast detectors.

Nondestructive Reconstruction and Analysis of Solid Oxide Fuel Cell Anodes using X-ray Computed Tomography at sub-50 nm Resolution

X-ray computed tomography (XCT) is applied to non-destructively image the three-dimensional (3D) microstructure of a solid oxide fuel cell (SOFC) with a solid yttria-stabilized zirconia (YSZ) electrolyte and porous nickel and YSZ (Ni-YSZ) anode. The x-ray microscope uses the 8 keV Cu-Kα line from a laboratory x-ray source with a condenser optic lens and an objective Fresnel zone plate lens providing spatial resolution of 42.7 nm. The data is visualized as 3D images and post-processed as binary images to obtain structural parameters. Porosity is calculated using a voxel counting method and tortuosity is evaluated by solving the Laplace equation. The 3D representation of the microstructure is used to calculate true structural and transport parameters and optimization through a detailed mass transfer and electrochemical study. Simulation of multi-component mass transport and electrochemical reactions in the microstructure using XCT data as geometric input illustrates the impact of this technique on SOFC modeling.

Advantages of intermediate X-ray energies in Zernike phase contrast X-ray microscopy.

Understanding the hierarchical organizations of molecules and organelles within the interior of large eukaryotic cells is a challenge of fundamental interest in cell biology. Light microscopy is a powerful tool for observations of the dynamics of live cells, its resolution attainable is limited and insufficient. While electron microscopy can produce images with astonishing resolution and clarity of ultra-thin (<1 μm thick) sections of biological specimens, many questions involve the three-dimensional organization of a cell or the interconnectivity of cells. X-ray microscopy offers superior imaging resolution compared to light microscopy, and unique capability of nondestructive three-dimensional imaging of hydrated unstained biological cells, complementary to existing light and electron microscopy. Until now, X-ray microscopes operating in the water window energy range between carbon and oxygen k-shell absorption edges have produced outstanding 3D images of cryo-preserved cells. The relatively low X-ray energy (<540 eV) of the water window imposes two important limitations: limited penetration (<10 μm) not suitable for imaging larger cells or tissues, and small depth of focus (DoF) for high resolution 3D imaging (e.g., ~1 μm DoF for 20 nm resolution). An X-ray microscope operating at intermediate energy around 2.5 keV using Zernike phase contrast can overcome the above limitations and reduces radiation dose to the specimen. Using a hydrated model cell with an average chemical composition reported in literature, we calculated the image contrast and the radiation dose for absorption and Zernike phase contrast, respectively. The results show that an X-ray microscope operating at ~2.5 keV using Zernike phase contrast offers substantial advantages in terms of specimen size, radiation dose and depth-of-focus.

X‐ray Microscopy for Interconnect Characterization

X‐ray computed tomography (XCT) offers powerful non‐destructive three dimensional imaging capability widely used in diverse fields, including medical diagnosis, biomedical and material research, geology, petrology, and archeology. XCT with micrometer resolution is being rapidly adopted for semiconductor packaging process development and failure analysis by creating virtual cross sections without the time consuming destructive cross sectioning processes. Thanks to rapid advancements in x‐ray imaging technology, XCT with 30 nm and 50 nm resolution (nanoXCT) has been developed using synchrotron and laboratory x‐ray sources, respectively. The nanoXCT can image internal structures of semiconductor IC devices that are fabricated using the latest IC manufacturing technology. This new capability is very valuable to the characterization of semiconductor interconnects for process development and failure analysis. We will present the design, specification, and operation of the nanoXCT. 2D and 3D tomographic reconstr...

X-ray microscopy for NDE of micro- and nano-structrues (Invited Paper)

X-ray imaging offers a number of unique properties that are favorable for NDE applications, including large penetration depth, elemental specificity, and relatively low radiation damage. While direct-projection type x-ray systems with a few um resolution have been widely deployed, recent advances in x-ray optics and imaging methodology have lead to lens-based x-ray microscopes with better than 60-nm resolution, and with integrated 3D imaging and material analysis capabilities. Used independently or in combination with established techniques based on visible light and electron microscopy, these new high-resolution x-ray systems introduces many attractive new capabilities for studying structures at micrometer to tens-of-nm scale.

Calculation of x-ray refraction from near-edge absorption data only

Near-edge x-ray absorption resonances provide information on molecular orbital structure; these resonances can be exploited in x-ray spectromicroscopy to give sub-50-nanometer resolution images with chemical state sensitivity. At the same time, radiation damage sets a limit to the resolution that can be obtained in absorption mode. Phase contrast imaging may provide another means of chemical state imaging with lower radiation dose. We describe here the use of experimentally measured near-edge absorption data to estimate near-edge phase resonances. This is accomplished by splicing the near-edge data into reference data and carrying out a numerical integration of the Kramers-Kronig relation.

Scattering imaging method in transmission x-ray microscopy

We present a x-ray microscopy technique based on structured illumination in a microscope that characterizes the size of the subresolution-limit features. The technique is effective for characterizing fine structures substantially beyond the Rayleigh resolution of the microscope. We carried out optical experiments to demonstrate the basic principle of this new technique. Experimental results show good agreement with theoretical predictions. This technique should find a wide range of important imaging applications with a feature size down to nanometer scale, such as oil and gas reservoir rocks, advanced composites, and functional nanodevices and materials.

Advances toward submicron resolution optics for x-ray instrumentation and applications

Sigray’s axially symmetric x-ray optics enable advanced microanalytical capabilities for focusing x-rays to microns-scale to submicron spot sizes, which can potentially unlock many avenues for laboratory micro-analysis. The design of these optics allows submicron spot sizes even at low x-ray energies, enabling research into low atomic number elements and allows increased sensitivity of grazing incidence measurements and surface analysis. We will discuss advances made in the fabrication of these double paraboloidal mirror lenses designed for use in laboratory x-ray applications. We will additionally present results from as-built paraboloids, including surface figure error and focal spot size achieved to-date.

A New Type of Super Bright Laboratory X-ray Source

We are developing a revolutionary new type of x-ray source that is designed to be more than 10X brighter than the brightest rotating anode x-ray source currently available. Additionally, the new x-ray source will have substantially wider selection of characteristic x-ray energies than are abailable using the current x-ray source technologies. The outstanding performance is achieved with patent pending x-ray source technology that incorporates the outstanding thermal and material properties of diamond as part of the microstructured anode, creates large thermal gradients within the microstructure and; and accumulates x-rays generated from a linear array of x-ray sub-sources.