Full-field Transmission X-ray Research Articles

Analysis and Correction of Dynamic Geometric Misalignment for Nano-Scale Computed Tomography at BSRF.

Due to its high spatial resolution, synchrotron radiation x-ray nano-scale computed tomography (nano-CT) is sensitive to misalignments in scanning geometry, which occurs quite frequently because of mechanical errors in manufacturing and assembly or from thermal expansion during the time-consuming scanning. Misalignments degrade the imaging results by imposing artifacts on the nano-CT slices. In this paper, the geometric misalignment of the synchrotron radiation nano-CT has been analyzed by partial derivatives on the CT reconstruction algorithm and a correction method, based on cross correlation and least-square sinusoidal fitting, has been reported. This work comprises a numerical study of the method and its experimental verification using a dataset measured with the full-field transmission x-ray microscope nano-CT at the beamline 4W1A of the Beijing Synchrotron Radiation Facility. The numerical and experimental results have demonstrated the validity of the proposed approach. It can be applied for dynamic geometric misalignment and needs neither phantom nor additional correction scanning. We expect that this method will simplify the experimental operation of synchrotron radiation nano-CT.

Quantified abundance of magnetofossils at the Paleocene–Eocene boundary from synchrotron-based transmission X-ray microscopy

The Paleocene-Eocene boundary (∼55.8 million years ago) is marked by an abrupt negative carbon isotope excursion (CIE) that coincides with an oxygen isotope decrease interpreted as the Paleocene-Eocene thermal maximum. Biogenic magnetite (Fe3O4) in the form of giant (micron-sized) spearhead-like and spindle-like magnetofossils, as well as nano-sized magnetotactic bacteria magnetosome chains, have been reported in clay-rich sediments in the New Jersey Atlantic Coastal Plain and were thought to account for the distinctive single-domain magnetic properties of these sediments. Uncalibrated strong field magnet extraction techniques have been typically used to provide material for scanning and transmission electron microscopic imaging of these magnetic particles, whose concentration in the natural sediment is thus difficult to quantify. In this study, we use a recently developed ultrahigh-resolution, synchrotron-based, full-field transmission X-ray microscope to study the iron-rich minerals within the clay sediment in their bulk state. We are able to estimate the total magnetization concentration of the giant biogenic magnetofossils to be only ∼10% of whole sediment. Along with previous rock magnetic studies on the CIE clay, we suggest that most of the magnetite in the clay occurs as isolated, near-equidimensional nanoparticles, a suggestion that points to a nonbiogenic origin, such as comet impact plume condensates in what may be very rapidly deposited CIE clays.

Analysis and calibration of stage axial vibration for synchrotron radiation nanoscale computed tomography.

Synchrotron radiation nanoscale computed tomography (SR nano-CT) is a powerful analysis tool and can be used to perform chemical identification, mapping, or speciation of carbon and other elements together with X-ray fluorescence and X-ray absorption near edge structure (XANES) imaging. In practical applications, there are often challenges for SR nano-CT due to the misaligned geometry caused by the sample stage axial vibration. It occurs quite frequently because of experimental constraints from the mechanical error of manufacturing and assembly and the thermal expansion during the time-consuming scanning. The axial vibration will lead to the structure overlap among neighboring layers and degrade imaging results by imposing artifacts into the nano-CT images. It becomes worse for samples with complicated axial structure. In this work, we analyze the influence of axial vibration on nano-CT image by partial derivative. Then, an axial vibration calibration method for SR nano-CT is developed and investigated. It is based on the cross correlation of plane integral curves of the sample at different view angles. This work comprises a numerical study of the method and its experimental verification using a dataset measured with the full-field transmission X-ray microscope nano-CT setup at the beamline 4W1A of the Beijing Synchrotron Radiation Facility. The results demonstrate that the presented method can handle the stage axial vibration. It can work for random axial vibration and needs neither calibration phantom nor additional calibration scanning. It will be helpful for the development and application of synchrotron radiation nano-CT systems.

Operando Imaging of Electrochemical Phase Transitions in LiNi0.8Co0.15Al0. 05O2 secondary Particles

The observation in dynamic conditions of electrochemical transformations relevant to energy storage creates the opportunity of identifying design rules that directly reflect the veiled electrochemical reaction mechanisms which are controlled by kinetics under load. Under the intrinsic limitations of ex-situ methods, opening the circuit to harvest multiple samples of interest at the different stages of reaction can lead to relaxation of the materials to a different, thermodynamically stable state. In addition, these operandoobservations must occur at multiple scales, but are particularly critical at the individual cathode particle level, where incomplete reactions and failure are prone to occur. In this study, we focused on LiNi0.8Co0.15Al0.05O2 (NCA)-based cathode materials, which are one of the leading candidates for use in high energy density Li-ion batteries for electric vehicle applications. This material offers high storage, but still presents limitations vis-à-vis capacity loss and concurrent increases in impedance. We adopted operando 2D full field transmission X-ray microscopy (FF TXM) coupled with X-ray absorption near edge spectroscopy (XANES) to follow the chemical and microstructural evolution at the secondary particles of NCA with sub-30 nm spatial resolution. Chemical phase maps from quantitative analysis of pixel-by-pixel X-ray absorption near edge structure spectra and morphological information of optical-density images at the post-absorption-edge region were obtained at the different state of charge as shown in Figure 1. As a result, this work successfully revealed the existence of kinetically-induced inhomogeneities during the electrochemical phase transition, and their morphological consequences, within a secondary particle, at nanoscale spatial resolution during an electrochemical reaction. We believe the rich insight provided by high resolution spectro-microscopy could inform the design of optimized architectures and the projection of performance using continuum models. Figure 1. A. Charge galvanostatic profile of operando Li metal half cell with an NCA composite cathode. The cell charged to capacity of 350 mAh·g-1 with cycling rate of C/15 (C was defined as the current density to achieve the theoretical capacity in 1 hour). Chemical maps were obtained at different state-of-charges (SOCs), labeled as 1 ~ 9, indicated as blue outlined circles. B. A map of white line peak positions for a secondary particle at SOC 5. Higher white line peak position indicates more oxidazed area. Figure 1

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.

Overview of nanoscale NEXAFS performed with soft X-ray microscopes.

Today, in material science nanoscale structures are becoming more and more important. Not only for the further miniaturization of semiconductor devices like carbon nanotube based transistors, but also for newly developed efficient energy storage devices, gas sensors or catalytic systems nanoscale and functionalized materials have to be analysed. Therefore, analytical tools like near-edge X-ray absorption fine structure (NEXAFS) spectroscopy has to be applied on single nanostructures. Scanning transmission X-ray microscopes (STXM) as well as full-field transmission X-ray microscopes (TXM) allow the required spatial resolution to study individual nanostructures. In the soft X-ray energy range only STXM was used so far for NEXAFS studies. Due to its unique setup, the TXM operated by the Helmholtz-Zentrum Berlin (HZB) at the electron storage ring BESSY II is the first one in the soft X-ray range which can be used for NEXAFS spectroscopy studies which will be shown in this review. Here we will give an overview of the different microscopes used for NEXAFS studies and describe their advantages and disadvantages for different samples.

Mapping metals incorporation of a whole single catalyst particle using element specific X-ray nanotomography.

Full-field transmission X-ray microscopy has been used to determine the 3D structure of a whole individual fluid catalytic cracking (FCC) particle at high spatial resolution and in a fast, noninvasive manner, maintaining the full integrity of the particle. Using X-ray absorption mosaic imaging to combine multiple fields of view, computed tomography was performed to visualize the macropore structure of the catalyst and its availability for mass transport. We mapped the relative spatial distributions of Ni and Fe using multiple-energy tomography at the respective X-ray absorption K-edges and correlated these distributions with porosity and permeability of an equilibrated catalyst (E-cat) particle. Both metals were found to accumulate in outer layers of the particle, effectively decreasing porosity by clogging of pores and eventually restricting access into the FCC particle.

Nanoscale morphological and chemical changes of high voltage lithium-manganese rich NMC composite cathodes with cycling.

Understanding the evolution of chemical composition and morphology of battery materials during electrochemical cycling is fundamental to extending battery cycle life and ensuring safety. This is particularly true for the much debated high energy density (high voltage) lithium–manganese rich cathode material of composition Li1 + xM1 – xO2 (M = Mn, Co, Ni). In this study we combine full-field transmission X-ray microscopy (TXM) with X-ray absorption near edge structure (XANES) to spatially resolve changes in chemical phase, oxidation state, and morphology within a high voltage cathode having nominal composition Li1.2Mn0.525Ni0.175Co0.1O2. Nanoscale microscopy with chemical/elemental sensitivity provides direct quantitative visualization of the cathode, and insights into failure. Single-pixel (∼30 nm) TXM XANES revealed changes in Mn chemistry with cycling, possibly to a spinel conformation and likely including some Mn(II), starting at the particle surface and proceeding inward. Morphological analysis of the particles revealed, with high resolution and statistical sampling, that the majority of particles adopted nonspherical shapes after 200 cycles. Multiple-energy tomography showed a more homogeneous association of transition metals in the pristine particle, which segregate significantly with cycling. Depletion of transition metals at the cathode surface occurs after just one cycle, likely driven by electrochemical reactions at the surface.

Evolution of Chemical and Morphological Changes of High Capacity Electrode Materials Across Multiple Lengths Scales

Understanding and quantifying the changes in chemical composition as well as morphology of battery materials under electrochemical cycling is fundamental to their long cycle life and safety1-2. This is particularly true for high energy density lithium-manganese rich cathodes which transitions from a high voltage layered–layered phase to a defect type spinel phase under constant electrochemical cycling. In this study we combine the full-field transmission X-ray microscopy (TXM) and the X-ray absorption near edge structure (XANES) to spatially resolve and map the accompanying chemical phase change and morphology of a high voltage lithium-ion cathode composition, Li1.2Mn0.525Ni0.175Co0.1O2, (LMR-NMC)3 at a resolution down to 30 nm over a fields-of-view of several tens of microns. 2D TXM-XANES imaging was conducted on a series of samples recovered at different stages of the battery cycling, showing that the material experiences phase segregation of various transition metal species from the particle bulk to surface4. Energy-resolved 3D morphology and quantification analysis with elemental information suggested that the distribution of three transition metal is heterogeneous and the surface of material particle constantly evolves with electrochemical cycling with varied average concentration of Mn, Co and Ni compared to particle internal.These results will be compared with results obtained from confocal ex-situ Raman mapping for pristine and cycled LMR-NMC composite cathodes. Raman results provide important information regarding the chemical homogeneity of the electrodes with respect to active material, binder and carbon additive distribution and their changes under high voltage electrochemical cycling. Florian Meirer, Jordi Cabana, Yijin Liu, Apurva Mehta, Joy C. Andrews and Piero Pianetta, J. Synchrotron Rad,. 18, 773 (2011).Wen-Chin Chen, Yen-Fang Song, Chun-Chieh Wang, Yijin Liu, Darius T. Morris,Piero A. Pianetta, Joy C. Andrews, Hung-Chun Wud and Nae-Lih Wu, J. Mater. Chem. A 1, 10847. (2013).Surendra K. Martha, Jagjit Nanda, Gabriel Veith Nancy J. Dudney, J Power Sources 199, 220 (2012)Fei fei Yang et al. Under preparation (2014)

Structural characterization of colloidal crystals and inverse opals using transmission X-ray microscopy

A nondestructive tomographic technique was used to determine the crystallographic information of colloidal crystals comprising of polystyrene (PS) microspheres, as well as their silver inverse opals. The properties of the colloidal crystals, such as defects, grain size, grain boundaries, stacking sequence, and grain orientation, were determined using the full field transmission X-ray microscopy (TXM) with a spatial resolution of 50nm. The PS microspheres (500–750nm) which underwent a vertical electrophoresis process to form a face-centered cubic (fcc) close-packed structure with an ABCABC packing sequence. In addition, the colloidal crystal exhibited multiple grains, and an orientation variation of 6.1° in the stacking direction between two neighboring grains.

Nanoscale spectroscopy and tomography with the HZB X-ray microscope: Applications in materials and life sciences

The full-field transmission X-ray microscope at the electron storage ring BESSY II allows nanoscale spectroscopy as well as correlative fluorescence and nanoscale tomographic imaging of frozen-hydrated adherent cells. Reconstructions of tilt series permit the visualization of the sub-cellular structures in mammalian cells and plant cells. Quantitative information about package densities of cell organelles in the cytoplasm is possible. We present an overview of recent results in materials and life sciences obtained with the HZB X-ray microscope.

NEXAFS spectromicroscopy of suspended carbon nanohorns

We demonstrate that near-edge X-ray-absorption fine-structure spectroscopy combined with full-field transmission X-ray microscopy can be used to study the electronic structure of suspended carbon nanohorns. Based on reports of electronic structure calculations additional spectral features observed in the π region of the NEXAFS spectrum recorded on the carbon nanohorns were associated to the presence of the pentagonal rings and the folding of the graphene sheet.

Observation of Nickel Oxidation Using Transmission X-ray Microscopy

Changes in the microstructure of solid oxide fuel cell electrodes have been known to contribute to performance degradation. One degradation mechanism is the conversion of the nickel to nickel oxide in the anode. This conversion causes a volume increase and can increase stresses in the anode which could lead to performance loss. In order to study the reaction kinetics for nickel oxidation, a full field transmission x-ray microscope was used to image the reaction in situ. The conversion can be monitored based on the optical density of the sample and complete conversion can be confirmed with x-ray absorption near edge spectroscopy. The conversion data is used to calculate reaction rates as a function of temperature and activation energies for the reactions.

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.

Full-field transmission x-ray imaging with confocal polycapillary x-ray optics

A transmission x-ray imaging setup based on a confocal combination of a polycapillary focusing x-ray optic followed by a polycapillary collimating x-ray optic was designed and demonstrated to have good resolution, better than the unmagnified pixel size and unlimited by the x-ray tube spot size. This imaging setup has potential application in x-ray imaging for small samples, for example, for histology specimens.

Three-dimensional reconstruction and analysis of an entire solid oxide fuel cell by full-field transmission X-ray microscopy

An entire active region of an anode-supported solid oxide fuel cell was structurally analyzed by X-ray computed nano-tomography using full-field transmission X-ray microscopy (NANO-TXM). A total three-dimensional volume of ∼38,500 μm3 was imaged, from which Ni–YSZ anode functional layer (∼3650 μm3) and LSM–YSZ cathode functional layer (∼4100 μm3) volumes were reconstructed. These were among the largest-volume electrode reconstructions ever reported, while at the same time exhibiting high spatial resolution of 50 nm. Comparison with electrode microstructures measured using other imaging methods demonstrates that the larger NANO-TXM-measured volumes provided significantly more accurate phase connectivity information. A microstructure-based electrochemical model prediction agreed well with the measured full-cell electrochemical data. The results suggest that low LSM connectivity and slow oxygen reduction reaction kinetics in the cathode were a major limitation to the overall cell performance.

In situ hard X-ray microscopy of self-assembly in colloidal suspensions

An experimental setup combining full-field transmission X-ray microscopy (TXM) and microradian X-ray diffraction (μradXRD) is tested for the in situ study of self-organization of colloidal dispersions of anisotropic particles. Averaged structural information of the samples is determined by μradXRD and local morphology is determined by TXM. Utilization of hard X-rays (12.2 keV) and the ease of switching from diffraction mode to microscopy mode makes such a setup a unique tool, especially for the study of opaque colloidal systems. We demonstrate diffraction patterns together with real space images of the following morphologies: smectic structures in the sediment of colloidal silica rods, the reorientation of a smectic phase of goethite particles in an elevated magnetic field and an interface region between isotropic and ordered phases in a dispersion of colloidal hematite cubes.

A 30 nm-resolution hard X-ray microscope with X-ray fluorescence mapping capability at BSRF

A full-field transmission X-ray microscope (TXM) operating continuously from 5 keV to 12 keV with fluorescence mapping capability has been designed and constructed at the Beijing Synchrotron Radiation Facility, a first-generation synchrotron radiation facility operating at 2.5 GeV. Spatial resolution better than 30 nm has been demonstrated using a Siemens star pattern in both absorption mode and Zernike phase-contrast mode. A scanning-probe mode fluorescence mapping capability integrated with the TXM has been shown to provide 50 p.p.m. sensitivity for trace elements with a spatial resolution (limited by probing beam spot size) of 20 µm. The optics design, testing of spatial resolution and fluorescence sensitivity are presented here, including performance measurement results.

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

Full-field transmission X-ray microscopy is a unique non-destructive technique for three-dimensional imaging of specimens at the nanometer scale. Here, the use of zone-doubled Fresnel zone plates to achieve a spatial resolution better than 20 nm in the hard X-ray regime (8-10 keV) is reported. By obtaining a tomographic reconstruction of a Ni/YSZ solid-oxide fuel cell, the feasibility of performing three-dimensional imaging of scientifically relevant samples using such high-spatial-resolution Fresnel zone plates is demonstrated.

X-ray absorption spectroscopy by full-field X-ray microscopy of a thin graphite flake: Imaging and electronic structure via the carbon K-edge

We demonstrate that near-edge X-ray-absorption fine-structure spectra combined with full-field transmission X-ray microscopy can be used to study the electronic structure of graphite flakes consisting of a few graphene layers. The flake was produced by exfoliation using sodium cholate and then isolated by means of density-gradient ultracentrifugation. An image sequence around the carbon K-edge, analyzed by using reference spectra for the in-plane and out-of-plane regions of the sample, is used to map and spectrally characterize the flat and folded regions of the flake. Additional spectral features in both π and σ regions are observed, which may be related to the presence of topological defects. Doping by metal impurities that were present in the original exfoliated graphite is indicated by the presence of a pre-edge signal at 284.2 eV.