William M. Harris

Zone-doubled Fresnel zone plates for high-resolution hard X-ray full-field transmission microscopy

The use of zone-doubled Fresnel zone plates for sub-20 nm spatial resolution in full-field transmission X-ray microscopy and tomography at the hard X-ray regime (8–10 keV) is demonstrated.

Three-dimensional mapping of nickel oxidation states using full field x-ray absorption near edge structure nanotomography

The reduction-oxidation cycling of the nickel-based oxides in composite solid oxide fuel cells and battery electrodes is directly related to cell performance. A greater understanding of nickel redox mechanisms at the microstructural level can be achieved in part using transmission x-ray microscopy (TXM) to explore material oxidation states. X-ray nanotomography combined with x-ray absorption near edge structure (XANES) spectroscopy has been applied to study samples containing distinct regions of nickel and nickel oxide (NiO) compositions. Digitally processed images obtained using TXM demonstrate the three-dimensional chemical mapping and microstructural distribution capabilities of full-field XANES nanotomography.

Focused ion beam preparation of samples for X-ray nanotomography.

The preparation of hard material samples with the necessary size and shape is critical to successful material analysis. X-ray nanotomography requires that samples are sufficiently thin for X-rays to pass through the sample during rotation for tomography. One method for producing samples that fit the criteria for X-ray nanotomography is focused ion beam/scanning electron microscopy (FIB/SEM) which uses a focused beam of ions to selectively mill around a region of interest and then utilizes a micromanipulator to remove the milled-out sample from the bulk material and mount it on a sample holder. In this article the process for preparing X-ray nanotomography samples in multiple shapes and sizes is discussed. Additionally, solid-oxide fuel cell anode samples prepared through the FIB/SEM technique underwent volume-independence studies for multiple properties such as volume fraction, average particle size, tortuosity and contiguity to observe the characteristics of FIB/SEM samples in X-ray nanotomography.

Oxidation States Study of Nickel in Solid Oxide Fuel Cell Anode Using X-ray Full-field Spectroscopic Nano-tomography

Identifying the chemical state and coupling with morphological information in three dimensions are of great interest in energy storage materials, which typically involve reduction-oxidation cycling and structural evolution. Here, we apply x-ray nano-tomography with multiple x-ray energies to study oxidation states of nickel (Ni) and nickel oxide phases in Ni-yttria-stabilized zirconia (YSZ), a typical anode material of solid oxide fuel cells (SOFC). We present a method to quantitatively identify the nickel-based oxides from Ni-YSZ anode composite, and obtain chemical mapping as well as associated microstructures at nanometer scale in three dimensions. NiO particles manually placed on a Ni-YSZ composite anode were used for validation of the method, while no nickel oxides were found to be present within the electrode structure as remnants of the cell fabrication process. The application of the method can be widely applied to energy storage materials including SOFCs, Li-ion batteries, and supercapacitors, as...

Characterization of 3D interconnected microstructural network in mixed ionic and electronic conducting ceramic composites

The microstructure and connectivity of the ionic and electronic conductive phases in composite ceramic membranes are directly related to device performance. Transmission electron microscopy (TEM) including chemical mapping combined with X-ray nanotomography (XNT) have been used to characterize the composition and 3-D microstructure of a MIEC composite model system consisting of a Ce0.8Gd0.2O2 (GDC) oxygen ion conductive phase and a CoFe2O4 (CFO) electronic conductive phase. The microstructural data is discussed, including the composition and distribution of an emergent phase which takes the form of isolated and distinct regions. Performance implications are considered with regards to the design of new material systems which evolve under non-equilibrium operating conditions.

Three-Dimensional Microstructural Imaging of Sulfur Poisoning-Induced Degradation in a Ni-YSZ Anode of Solid Oxide Fuel Cells

Following exposure to ppm-level hydrogen sulfide at elevated temperatures, a section of a solid oxide fuel cell (SOFC) Ni-YSZ anode was examined using a combination of synchrotron-based x-ray nanotomography and x-ray fluorescence techniques. While fluorescence measurements provided elemental identification and coarse spatial mapping, x-ray nanotomography was used to map the detailed 3-D spatial distribution of Ni, YSZ, and a nickel-sulfur poisoning phase. The nickel-sulfur layer was found to form a scale covering most of the exposed nickel surface, blocking most fuel reformation and hydrogen oxidation reaction sites. Although the exposure conditions precluded the ability to develop a detailed kinetic description of the nickel-sulfur phase formation, the results provide strong evidence of the detrimental effects of 100 ppm hydrogen sulfide on typical Ni-YSZ anode materials.

In-situ observation of nickel oxidation using synchrotron based full-field transmission X-ray microscopy

An in situ imaging-based approach is reported to study chemical reactions using full-field transmission x-ray microscopy (TXM). Ni particles were oxidized at temperatures between 400 and 850 °C in the TXM to directly observe their morphology change while the chemical composition is monitored by x-ray absorption near edge spectroscopy. Reaction rates and activation energies are calculated from the image data. The goal of this effort is to better understand Ni oxidation in electrode materials. The approach developed will be an effective technique for directly studying chemical reactions of particles and their behavior at the nano-scale.

Comparison of X-ray Nanotomography and FIB-SEM in Quantifying the Composite LSM/YSZ SOFC Cathode Microstructure

Department of Mechanical Engineering, University of Connecticut, Storrs, CT, USA Electrochemical Engineering Group (GGEC), Centre for Interdisciplinary Electron Microscopy, Industrial Energy Systems Laboratory École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland Stanford Synchrotron Radiation Lightsource, Stanford Linear Accelerator Center Menlo Park, CA 94025, USA National Synchrotron Light Source II, Brookhaven National Laboratory Upton, NY 11973, USA

Recent Advancements in 3D X-ray Microscopes for Additive Manufacturing

Three-dimensional X-ray microscopy (XRM) is a powerful sub-surface imaging technique that reveals tomography of three-dimensional microstructure from a range of materials, non-destructively. The nondestructive nature of X-rays has made the technique widely appealing, with the potential for characterizing sample changes in “4D,” delivering 3D microstructural information on physically the same sample over time, as a function of sequential processing conditions or experimental treatments. This has led to a new generation of functional studies with applications and is in a state of rapid expansion [1]. Recently, laboratory-based X-ray sources have been coupled with high resolution X-ray focusing and detection optics from synchrotron-based systems to acquire tomographic datasets with resolution down to 50 nm across a great span of sample dimensions [2]. Additionally, the technique of laboratory based X-ray diffraction contrast tomography has recently become available; allowing the nondestructive routine characterization of 3D crystallographic information on polycrystalline materials in a commercial laboratory X-ray microscope (ZEISS Xradia 520 Versa). Known as laboratory diffraction contrast tomography (LabDCT), this imaging modality will open the way for routine, nondestructive studies of time-evolution of grain structure to complement destructive electron backscatter diffraction (EBSD) end-point characterization. This talk will explore both the implementation of optics in nanoscale and sub-micron laboratory XRM architectures and review in detail several leading applications examples for the field of additive manufacturing including the ability to track changes, in grain size and orientation, over time, e.g. ‘4D’ time lapse studies using LabDCT. XRM for tomography using a laboratory source was used to characterize porosity in additive process control study for various steel input materials and Ti-6Al-4V built with Arcam SEBM. For additional process and material qualification using LabDCT, an example of this capability was used to follow the sintering of copper particles through a series of time-lapsed DCT measurements. XRM tomographic data provides multiscale imaging and visualization for a wide variety of AM materials, even creation of accurate 3D-printed models in biomimetic studies [4-5]. XRM can provide accurate 3D internal structural information critical to aid computational design of next-generation materials.

In situ heater design for nanoscale synchrotron-based full-field transmission X-ray microscopy.

The oxidation of nickel powder under a controlled gas and temperature environment was studied using synchrotron-based full-field transmission X-ray microscopy. The use of this technique allowed for the reaction to be imaged in situ at 55 nm resolution. The setup was designed to fit in the limited working distance of the microscope and to provide the gas and temperature environments analogous to solid oxide fuel cell operating conditions. Chemical conversion from nickel to nickel oxide was confirmed using X-ray absorption near-edge structure. Using an unreacted core model, the reaction rate as a function of temperature and activation energy were calculated. This method can be applied to study many other chemical reactions requiring similar environmental conditions.