Full-field Transmission X-ray Microscopy Research Articles

Laboratory High-Contrast X-ray Microscopy of Copper Nanostructures Enabled by a Liquid-Metal-Jet X-ray Source.

High-resolution imaging of Cu/low-k on-chip interconnect stacks in advanced microelectronic products is demonstrated using full-field transmission X-ray microscopy (TXM). The comparison of two lens-based laboratory X-ray microscopes that are operated at two different photon energies, 8.0 keV and 9.2 keV, shows a contrast enhancement for imaging of copper nanostructures embedded in insulating organosilicate glass of a factor of 5 if 9.2 keV photons are used. Photons with this energy (Ga-Kα radiation) are generated from a Ga-containing target of a laboratory X-ray source applying the liquid-metal-jet technology. The 5 times higher contrast compared to the use of Cu-Kα radiation (8.0 keV photon energy) from a rotating anode X-ray source is caused by the fact that the energy of the Ga-Kα emission line is slightly higher than that of the Cu-K absorption edge (9.0 keV photon energy). The use of Ga-Kα radiation is of particular advantage for imaging of copper interconnects with dimensions from several 100 nm down to several 10 nm in a Cu/SiO2 or Cu/low-k backend-of-line stack. Physical failure analysis and reliability engineering in the semiconductor industry will benefit from high-contrast X-ray images of sub-μm copper structures in microchips.

Unveiling the Inner Structure of Micrometric Hollow Polymeric Fibers Using Synchrotron X-Ray Nanotomography.

In this study, a novel application of synchrotron X-ray nanotomography based on high-resolution full-field transmission X-ray microscopy for characterizing the structure and morphology of micrometric hollow polymeric fibers is presented. By employing postimage analysis using an open-source software such as Tomviz and ImageJ, various key parameters in fiber morphology, including diameter, wall thickness, wall thickness distribution, pore size, porosity, and surface roughness, were assessed. Electrospun polycaprolactone fibers with micrometric diameters and submicrometric features with induced porosity via gas dissolution foaming were used to this aim. The acquired synchrotron X-ray nanotomography data were analyzed using two approaches: 3D tomographic reconstruction and 2D radiographic projection-based analysis. The results of the combination of both approaches demonstrate unique capabilities of this technique, not achievable by other available techniques, allowing for a full characterization of the internal and external morphology and structure of the fibers as well as to obtain valuable qualitative insights into the overall fiber structure.

Automatic marker-based alignment method for a nano-resolution full-field transmission X-ray microscope

Driven by the development of X-ray optics, the spatial resolution of the full-field transmission X-ray microscope (TXM) has reached tens of nanometers and plays an important role in promoting the development of biomedicine and materials science. However, due to the thermal drift and the radial/axial motion error of the rotation stage, TXM computed tomography (CT) data are often associated with random image jitter errors along the horizontal and vertical directions during CT measurement. A nano-resolution 3D structure information reconstruction is almost impossible without a prior appropriate alignment process. To solve this problem, a fully automatic gold particle marker-based alignment approach without human intervention was proposed in this study. It can automatically detect, isolate, and register gold particles for projection image alignment with high efficiency and accuracy, facilitating a high-quality tomographic reconstruction. Simulated and experimental results confirmed the reliability and robustness of this method.

Nanoscale chemical imaging with structured X-ray illumination.

High-resolution imaging with compositional and chemical sensitivity is crucial for a wide range of scientific and engineering disciplines. Although synchrotron X-ray imaging through spectromicroscopy has been tremendously successful and broadly applied, it encounters challenges in achieving enhanced detection sensitivity, satisfactory spatial resolution, and high experimental throughput simultaneously. In this work, based on structured illumination, we develop a single-pixel X-ray imaging approach coupled with a generative image reconstruction model for mapping the compositional heterogeneity with nanoscale resolvability. This method integrates a full-field transmission X-ray microscope with an X-ray fluorescence detector and eliminates the need for nanoscale X-ray focusing and raster scanning. We experimentally demonstrate the effectiveness of our approach by imaging a battery sample composed of mixed cathode materials and successfully retrieving the compositional variations of the imaged cathode particles. Bridging the gap between structural and chemical characterizations using X-rays, this technique opens up vast opportunities in the fields of biology, environmental, and materials science, especially for radiation-sensitive samples.

In-house design hard X-ray transmission microscope at SSRF

A hard X-ray full field transmission X-ray microscopy (TXM) based on zone plate optics has been constructed at BL18B beamline at Shanghai Synchrotron Radiation Facility (SSRF). This beamline aims to the frontier science issues demands in many fields including nanomaterials, energy and life sciences, providing advanced nanostructure characterization for submicron-sized samples. It uses a bending-magnet source and works in the range of energies from 5 keV to 14 keV. The achieved spatial resolution of TXM imaging is 20 nm. This paper describes the details of the design, characterization, stability testing, TXM, CT and 2D TXM-XANES performance of this beamline.

Mapping Heterogeneity of Pristine and Aged Li- and N-Mnhcf Cathode by Synchrotron-Based Energy-Dependent Full Field Transmission X-ray Microscopy.

Manganese hexacyanoferrate is a promising cathode material for lithium and sodium ion batteries, however, it suffers of capacity fading during the cycling process. To access the structural and functional characteristics at the nanometer scale, fresh and cycled electrodes are extracted and investigated by transmission soft X-ray microscopy, which allows chemical characterization with spatial resolution from position-dependent x-ray spectra at the Mn L-, Fe L- and N K-edges. Furthermore, soft X-rays prove to show superior sensitivity toward Fe, compare to hard X-rays. Inhomogeneities within the samples are identified, increasing in the aged electrodes, more dramatically in the Li-ion system, which explains the poorer cycle life as Li-ion cathode material. Local spectra, revealing different oxidation states over the sample with strong correlation between the Fe L-edge, Mn L-edge, and N K-edge, imply a coupling between redox centers and an electron delocalization over the host framework.

Refractive axicon for X-ray microscopy applications: design, optimization, and experiment.

In a full-field transmission X-ray microscopy (TXM) setup, a condenser X-ray optical element is used to illuminate the sample by condensing the X-ray beam delivered by the synchrotron storage ring. On-going and future upgrades of synchrotron facilities to diffraction-limited storage rings will pose new challenges to these TXM setups, such as much smaller X-ray beams on the condenser. Here, we demonstrate that a refractive axicon can be used as an X-ray beam shaper to match the ring-shaped aperture of the condenser. Aiming at more efficient use of the incoming X-ray intensity, we explore several axicon designs both analytically and with numerical simulations. The axicons were produced by two-photon polymerization 3D printing on thin silicon nitride membrane substrates. The first characterization of the axicon was carried out at the TOMCAT beamline of the Swiss Light Source (Switzerland).

Feature detection network-based correction method for accurate nano-tomography reconstruction.

Driven by the development of advanced x-ray optics such as Fresnel zone plates, nano-resolution full-field transmission x-ray microscopy (Nano-CT) has become a powerful technique for the non-destructive volumetric inspection of objects and has long been developed at different synchrotron radiation facilities. However, Nano-CT data are often associated with random sample jitter because of the drift or radial/axial error motion of the rotation stage during measurement. Without a proper sample jitter correction process prior to reconstruction, the use of Nano-CT in providing accurate 3D structure information for samples is almost impossible. In this paper, to realize accurate 3D reconstruction for Nano-CT, a correction method based on a feature detection neural network, which can automatically extract target features from a projective image and precisely correct sample jitter errors, is proposed, thereby resulting in high-quality nanoscale 3D reconstruction. Compared with other feature detection methods, even if the target feature is overlapped by other high-density materials or impurities, the proposed Nano-CT correction method still acquires sub-pixel accuracy in geometrical correction and is more suitable for Nano-CT reconstruction because of its universal and faster correction speed. The simulated and experimental datasets demonstrated the reliability and validity of the proposed Nano-CT correction method.

A Procedure for the Characterization of Monocapillary X-Ray Lenses as Condensers for Full-Field Transmission X-Ray Microscopes

Monocapillary x-ray lenses (MXRLs) are mostly used as condensers in full-field transmission x-ray microscopy (TXM) based on synchrotron radiation or laboratory x-ray tubes. The performance of the condenser has a significant impact on the imaging quality of the TXM. In this paper, a procedure for the characterization of the MXRL as a condenser is presented. The procedure mainly includes two parts: optical measurement and x-ray tests. From the test results of the characterization procedure, it can be seen that a relatively high-performance condenser can be screened out from a series of MXRLs drawn by an electric furnace. This is also fed back to the manufacturing process, and therefore, the technology of manufacturing the condenser can be gradually optimized. Moreover, the method of characterizing the performance of the condenser designed for synchrotron radiation TXM by laboratory x-ray tubes is proposed to be used in this procedure, which effectively reduces the manufacturing time of high-performance condensers for synchrotron radiation TXM.

Exploring spectroscopic X-ray nano-imaging with Zernike phase contrast enhancement

Spectroscopic full-field transmission X-ray microscopy (TXM-XANES), which offers electrochemical imaging with a spatial resolution of tens of nanometers, is an extensively used unique technique in battery research. However, absorption-based bright-field imaging has poor detection sensitivity for nanoscale applications. Here, to improve the sensitivity, we explored spectroscopic X-ray nano imaging with Zernike phase contrast (ZPC-XANES). A pinhole-type Zernike phase plate, which was optimized for high-contrast images with minimal artifacts, was used in this study. When the absorption is weak, the Zernike phase contrast improves the signal-to-noise ratio and the contrast of images at all energies, which induces the enhancement of the absorption edge step. We estimated that the absorption of the samples should be higher than 2.2% for reliable spectroscopic nano-imaging based on XANES spectroscopy analysis of a custom-made copper wedge sample. We also determined that there is a slight absorption peak shift and sharpening in a small absorption sample due to the inflection point of the refractive index at the absorption edge. Nevertheless, in the case of sub-micron sized cathode materials, we believe that better contrast and higher resolution spectroscopic images can be obtained using ZPC-XANES.

Optimizing the energy bandwidth for transmission full-field X-ray microscopy experiments.

Full-field transmission X-ray microscopy (TXM) is a very potent high-resolution X-ray imaging technique. However, it is challenging to achieve fast acquisitions because of the limited efficiency of the optics. Using a broader energy bandwidth, for example using a multilayer monochromator, directly increases the flux in the experiment. The advantage of more counts needs to be weighed against a deterioration in achievable resolution because focusing optics show chromatic aberrations. This study presents theoretical considerations of how much the resolution is affected by an increase in bandwidth as well as measurements at different energy bandwidths (ΔE/E = 0.013%, 0.27%, 0.63%) and the impact on achievable resolution. It is shown that using a multilayer monochromator instead of a classical silicon double-crystal monochromator can increase the flux by an order of magnitude with only a limited effect on theresolution.

Characterization of Polycrystalline Cathode Materials in Five Dimensions (5D)

Thermal stability is one of the most desired features for large-scale energy applications, such as batteries used in electronics and electric vehicles. Thermal runaway, heat generation, and gas release are likely to happen for batteries under thermal abuse conditions, leading to severe performance degradation and safety risks. Although the decomposition of electrolytes at high temperatures has been widely studied in the community, a systematic and in situ study of the intrinsic instability of the cathodes in Li ion batteries is lacking. Polycrystalline nickel-rich Li layered oxides (LiNi x Mn y Co1-x-y O2, NMC) were chosen as the platform materials considering the recent improvements in specific capacity but also the rising safety concerns in Ni-rich cathodes.Here we used one of state-of-the-art techniques in microscopy: the full-field transmission X-ray microscope (TXM) to capture the 3D tomography of charged NMC particles, together with the X-ray absorption near edge structure (XANES) spectroscopic capability for Ni oxidation state. Moreover, we performed the XANES-3DTXM measurements during the whole process of heating the NMC cathodes from room temperature up to 250°C, which enables us to monitor the full evolution of NMC secondary particles in real time in 5 dimensions (3D spatial + tunable X-ray energy + temperature).This in situ XANES-3DTXM approach allows us to observe the real-time morphological and chemical evolution at elevated temperatures. The large field of view and reasonably high spatial resolution offer the capability to analyze NMC cathodes at different length scales, ranging from voids of tens of nanometers, to cracks of hundreds of nanometers, to secondary particles of tens of micrometers.With quantification of morphological (e.g., relative volume change, porosity, crack propagation) and chemical (e.g., the oxidation state of Ni, local charge distribution) characteristics as a function of temperature and time, the fundamental degradation mechanisms in polycrystalline nickel-rich Li layered oxides under thermally abuse conditions are thereupon unveiled. Based on these analyses and discoveries, we proposed to alter the primary particle arrangement as an effective solution to alleviate the thermal issues in nickel-rich Li layered oxides.Figure: Schematic of the in situ heating setup, 3D rendering of a NMC secondary particle, and selected morphology section and Ni oxidation state mapping at different temperatures. Figure 1

Deep-learning-based image registration for nano-resolution tomographic reconstruction.

Nano-resolution full-field transmission X-ray microscopy has been successfully applied to a wide range of research fields thanks to its capability of non-destructively reconstructing the 3D structure with high resolution. Due to constraints in the practical implementations, the nano-tomography data is often associated with a random image jitter, resulting from imperfections in the hardware setup. Without a proper image registration process prior to the reconstruction, the quality of the result will be compromised. Here a deep-learning-based image jitter correction method is presented, which registers the projective images with high efficiency and accuracy, facilitating a high-quality tomographic reconstruction. This development is demonstrated and validated using synthetic and experimental datasets. The method is effective and readily applicable to a broad range of applications. Together with this paper, the source code is published and adoptions and improvements from our colleagues in this field are welcomed.

A passive characterization method of the single-bounce ellipsoidal capillary for the full field transmission X-ray microscopy

A passive characterization method to evaluate the quality of the single-bounce ellipsoidal capillary (SBEC) for the full field transmission X-ray microscopy was designed. The simulation model was established by measuring the outer diameter of the SBEC. The simulated shape of the focusing ring consisted with that from the experiment. This passive characterization method could be used evaluate efficiently the quality of SBEC and provide a guidance for SBEC manufacturing.

Simulation of optical properties of ellipsoidal monocapillary X-ray optics with inner-surface imperfections

Ellipsoidal monocapillary x-ray optics are used as condenser lenses in full-field transmission x-ray microscopy. The numerical aperture (NA) of the ellipsoidal monocapillary is designed to match that of the x-ray zone plate objective. In practice, monocapillaries have inner-surface errors that lead to mismatches between the monocapillary and the zone plate. In this study, mathematical models of monocapillaries with elliptic cross-section deformation and centreline straightness errors were developed, respectively. Furthermore, the optical properties of these monocapillaries were simulated based on a ray-tracing method. The simulation provides a qualitative picture of the NA and illumination angle distributions of the ellipsoidal monocapillary with inner-surface errors, and it is useful for predicting the inner-surface imperfections from the x-ray ring behind the monocapillary.

Zone plate-based full-field transmission X-ray microscopy beamline design at nearly diffraction-limited synchrotron radiation facility

With the development of full-field transmission X-ray microscopy (TXM) for research in biology, life science, material science and physics, zone plate-based full-field TXM is becoming a powerful tool for obtaining quantitative internal structural and chemical information at the nanoscale when combined with spectroscopic imaging. For the TXM beamline design, the best choice is to match the phase space needed by the zone plate from the source point. However, for the nearly diffraction-limited synchrotron radiation sources, it is not easy to fully match the needed phase space due to its low-emittance. Using redshift radiation from an undulator, under consideration of experimental requirements and the heat load effect, this paper describes the design of TXM beamline at the nearly diffraction-limited High Energy Photon Source (HEPS). In this design, not only sufficient illumination angle can be acquired, but also a nearly annular illumination can be obtained to match the illumination required for zone plate imaging. Furthermore, about two times photon flux can be obtained at source point and the photons can be fully used in this design using redshift undulator radiation. The presented design can also be informative for the same kind of beamline design at other nearly diffraction-limited synchrotron photon sources.

The Diamond I13 full-field transmission X-ray microscope: a Zernike phase-contrast setup for material sciences

The I13 transmission X-ray microscope at Diamond Light Source (DLS) has been designed to cover a broad range of energies and field of views. The beamline operates on an undulator source, and a multilayer monochromator can be used to work at a larger bandwidth to enable faster acquisitions. The experimental design includes large working distances for the optics to allow installing in situ sample environments. This paper presents the current state of the experimental system and shows some of the latest results.

Versatile compact heater design for in situ nano-tomography by transmission X-ray microscopy.

A versatile, compact heater designed at National Synchrotron Light Source-II for in situ X-ray nano-imaging in a full-field transmission X-ray microscope is presented. Heater design for nano-imaging is challenging, combining tight spatial constraints with stringent design requirements for the temperature range and stability. Finite-element modeling and analytical calculations were used to determine the heater design parameters. Performance tests demonstrated reliable and stable performance, including maintaining the exterior casing close to room temperature while the heater is operating at above 1100°C, a homogenous heating zone and small temperature fluctuations. Two scientific experiments are presented to demonstrate the heater capabilities: (i) in situ 3D nano-tomography including a study of metal dealloying in a liquid molten salt extreme environment, and (ii) a study of pore formation in icosahedral quasicrystals. The progression of structural changes in both studies were clearly resolved in 3D, showing that the new heater enables powerful capabilities to directly visualize and quantify 3D morphological evolution of materials under real conditions by X-ray nano-imaging at elevated temperature during synthesis, fabrication and operation processes. This heater design concept can be applied to other applications where a precise, compact heater design is required.

Mesoscale Chemomechanical Interplay of the LiNi0.8Co0.15Al0.05O2 Cathode in Solid-State Polymer Batteries

Presently, the challenges faced by batteries are twofold. Firstly, they are expected to possess high energy and power density for powering zero emission electric vehicles. Secondly, they are also expected to be inexpensive and safe for deployment in electric vehicles and consumer applications. A potential candidate ideally suited for this case are solid-state polymer lithium-ion batteries coupled with layered nickel-rich oxides such as LiNi0.8Co0.15Al0.05O2 (NCA) or LiNi1−x−yCoxMnyO2 (NCM). Replacing the non-aqueous, liquid electrolytic solution that is comprised of flammable components, with a solid-state electrolyte such as an inexpensive polymer is highly advantageous. However, layered nickel-rich oxides such as NCA are not only known for their high reversible capacity, but also their inherent structural and thermal instability at charged state, which leads to several degradation mechanisms including intergranular cracking. While this phenomenon has been studied extensively for lithium-ion batteries consisting of a non-aqueous, liquid electrolyte, it has not been studied for solid polymer batteries. Secondary NCA particles harvested from cycled NCA-poly(ethylene oxide) batteries were subjected to a combination of two- and three-dimensional full-field transmission X-ray microscopy (2D/3D-FF-TXM) and high resolution broad ion beam- and focuses ion beam milling-scanning electron microscopy (BIB-/FIB-SEM). Doing so, the complex chemomechanical interplay within the hierarchically structured lithium-ion battery was investigated to reveal morphological defects and chemical heterogeneity in the secondary particles. Intergranular cracking was found to be extremely apparent after only a few cycles. It was found, that the absence of liquid electrolyte severely affects transport in fractured particles and may also hastens and accelerates fracture due to lower uniformity in current density. Intergranular cracks significantly increase diffusion path lengths of both charge carriers, electrons and lithium ions. While in liquid lithium-ion batteries, electrolyte filling the cracks should maintain lithium ion transport pathways but not electron transport pathways, in solid-state batteries, intergranular cracking compromises not only the electronic pathways, but also the ionic pathways. Eventually, intergranular cracking in polymer batteries seems to lead to isolated and inactivated primary grains within the core of secondary particles. Figure 1

X-ray-Powered Micromotors.

Light-powered wireless manipulation of small objects in fluids has been of interest for biomedical and environmental applications. Although many techniques employing UV-vis-NIR light sources have been devised, new methods that hold greater penetrating power deep into medium are still in demand. Here, we develop a method to exploit X-rays to propel half-metal-coated Janus microparticles in aqueous solution. The Janus particles are simultaneously propelled and visualized in real-time by using a full-field transmission X-ray microscope. Our real-time observation discovers that the propulsive motion follows the bubble growth enhanced by water radiolysis near the particle surface under X-ray irradiation. We also show that the propulsion speed is remotely controlled by varying the radiation dose. We expect this work to open opportunities to employ light-powered micro/nanomotors in opaque environments, potentially by combining with medical imaging or nondestructive testing.