Na2ZrFe(PO4)3─A Rhombohedral NASICON-Structured Material: Synthesis, Structure and Na-Intercalation Behavior.

A NASICON-structured earth-abundant mixed transition metal (TM) containing Na-TM-phosphate, viz., Na2ZrFe(PO4)3, has been prepared via a sol-gel route using a low-cost Fe3+-based precursor. The as-prepared material crystallizes in the desired rhombohedral NASICON structure (space group: R3̅c) at room temperature. Synchrotron X-ray diffraction (XRD), transmission electron microscopy, X-ray absorption spectroscopy, etc., have been performed to determine the crystal structure, associated details, composition, and electronic structures. In light of the structural features, as one of the possible functionalities of Na2FeZr(PO4)3, Na-intercalation/deintercalation has been examined, which indicates the occurrence of reversible electrochemical Na-insertion/extraction via Fe2+/Fe3+ redox at an average potential of ∼2.5 V. The electrochemical data and direct evidences from operando synchrotron XRD indicate that the rhombohedral structure is preserved during Na-insertion/extraction, albeit within a certain range of Na-content (i.e., ∼2-3 p.f.u.), beyond which rhombohedral → monoclinic transformation takes place. Within this range, Na-insertion/extraction takes place via solid-solution pathway, resulting in outstanding cyclic stability, higher Na-diffusivity, and good rate-capability. To the best of the authors' knowledge, this represents the first in-depth structural, compositional, and electrochemical studies with Na2ZrFe(PO4)3, along with the interplay between those, which provide insights into the design of similar low-cost materials for various applications, including sustainable electrochemical energy storage systems.

Extreme UV Resist Exhibiting Synergism between Chemical and Physical Crosslinking Mechanisms.

Carbon-fluorine bonds in fluorinated molecules can undergo homolytic cleavage reactions when electrons are injected, and the resulting radicals combine to form network structures characterized by reduced solubility. This crosslinking chemistry suggests a new category of patterning materials that function under electron beam (e-beam) and extreme ultraviolet (EUV) lithographic conditions. Although this chemistry enables the production of 50 nm or smaller-sized features of simple fluoroalkylated polymers, it is limited by the need for relatively large amounts of irradiation energy to achieve required solubility changes. Therefore, this study was undertaken to devise a sensitivity-enhancing strategy based on a synergistic combination of radical crosslinking and hydrogen-bonding interactions between highly fluoroalkylated copolymers. An alternating copolymer was synthesized using tert-butoxystyrene and a fluoroalkylated maleimide, the former of which produces active hydrogens through catalytic acidolysis reactions. When the polymer was blended with a catalytic amount of a photoacid generator and subjected to lithographic patterning tests under e-beam and EUV irradiation, the deprotection reactions of tert-butoxy moieties proceeded at room temperature and led to a solubility decrease. We presume the small number of hydroxyl moieties produced formed an intermolecular hydrogen-bonding network, which acted synergistically with the covalent crosslinks generated by C-F bonds. When 30 nm features of copolymer thin films were fabricated by EUV lithography, sensitivity was improved by 25-34% without significant deterioration of pattern quality, especially line-edge roughness. These results demonstrate that EUV resists with improved patterning capabilities can be achieved by combining catalytic acidolysis reactions and noncatalytic crosslinking chemistry.

Near-field infrared nanoscopic study of EUV- and e-beam-exposed hydrogen silsesquioxane photoresist.

This article presents a technique of scattering-type scanning near-field optical microscopy (s-SNOM) based on scanning probe microscopy as a nanoscale-resolution chemical visualization technique of the structural changes in photoresist thin films. Chemical investigations were conducted in the nanometer regime by highly concentrated near-field infrared on the sharp apex of the metal-coated atomic force microscopy (AFM) tip. When s-SNOM was applied along with Fourier transform infrared spectroscopy to characterize the extreme UV- and electron-beam (e-beam)-exposed hydrogen silsesquioxane films, line and space patterns of half-pitch 100, 200, 300, and 500 nm could be successfully visualized prior to pattern development in the chemical solutions. The linewidth and line edge roughness values of the exposed domains obtained by s-SNOM were comparable to those extracted from the AFM and scanning electron microscopy images after development. The chemical analysis capabilities provided by s-SNOM provide new analytical opportunities that are not possible with traditional e-beam-based photoresist measurement, thus allowing information to be obtained without interference from non-photoreaction processes such as wet development.

Synchrotron radiation based X-ray techniques for analysis of cathodes in Li rechargeable batteries.

Li-ion rechargeable batteries are promising systems for large-scale energy storage solutions. Understanding the electrochemical process in the cathodes of these batteries using suitable techniques is one of the crucial steps for developing them as next-generation energy storage devices. Due to the broad energy range, synchrotron X-ray techniques provide a better option for characterizing the cathodes compared to the conventional laboratory-scale characterization instruments. This work gives an overview of various synchrotron radiation techniques for analyzing cathodes of Li-rechargeable batteries by depicting instrumental details of X-ray diffraction, X-ray absorption spectroscopy, X-ray imaging, and X-ray near-edge fine structure-imaging. Analysis and simulation procedures to get appropriate information of structural order, local electronic/atomic structure, chemical phase mapping and pores in cathodes are discussed by taking examples of various cathode materials. Applications of these synchrotron techniques are also explored to investigate oxidation state, metal-oxygen hybridization, quantitative local atomic structure, Ni oxidation phase and pore distribution in Ni-rich layered oxide cathodes.

Investigation of correlative parameters to evaluate EUV lithographic performance of PMMA.

Investigations to evaluate the extreme ultraviolet (EUV) lithographic performance of 160 nm thick poly(methyl methacrylate) with 13.5 nm wavelength EUV light were performed using a synchrotron radiation source at Pohang Light Source-II (PLS-II). The single system enabled the determination of the sensitivity, contrast, linear absorption coefficient, critical dimension, and line edge roughness of polymer thin films through tests and measurements. The experimental findings were also compared to theoretical results and those of previously reported studies. According to the results of the dose-to-clear test and transmission measurements, the critical dimension of a line and space pattern (>50 nm) via interference lithography with 250 nm pitch grating agreed well with the results calculated using the lumped parameter model. The experimental results demonstrated that the equipment and test protocol can be used for EUV material infrastructure evaluation in academia and in industry.

Universal Alignment of Graphene Oxide in Suspensions and Fibers.

Graphene oxide (GO) has become a key component for high-performance carbon-based films or fibers based on its dispersibility and liquid crystallinity in an aqueous suspension. While the superior performance of GO-based fiber relies on their alignment at the submicrometer level, fine control of the microstructure is often hampered, in particular, under dynamic nature of GO-processing involving shear. Here, we systemically studied the structural variation of GO suspensions under shear conditions via in situ rheo-scattering and shear-polarized optical microscope analysis. The evolution of GO alignment under shear is indeed complex. However, we found that the shear-dependent structural equilibrium exists. GO showed a nonlinear structural transition with shear, yet there is a "universal" shear threshold for the best alignment, resulting in graphene fiber achieved an improvement in mechanical properties by ∼54% without any chemical modification. This finding challenges the conventional concept that high shear stress is required for the good alignment of particles and their best performance.

Perfluoroalkylated alternating copolymer possessing solubility in fluorous liquids and imaging capabilities under high energy radiation.

A highly fluorinated alternating polymer, P(RFMi-St), possessing improved thermal properties and patterning capabilities over perfluoroalkyl polymethacrylates under high energy radiation was achieved with semi-perfluorododecyl maleimide (RFMi) and styrene (St). RFMi could be synthesised efficiently via a Mitsunobu reaction condition and copolymerised with St by free radical and reversible-deactivation radical polymerisation protocols. P(RFMi-St) showed a satisfactory glass-transition temperature (108 °C) and intermolecular cross-linking behaviour under electron-beam and commercially more important extreme UV (λ = 13.5 nm) irradiation. The exposed regions lost their solubility, resulting in the successful formation of mechanically non-deteriorated negative-tone images down to 50 nm. In addition, P(RFMi-St) could be solution-processed with chemically non-damaging fluorous liquids, which enabled the polymer to be applied effectively on top of an organic semiconductor layer as a dielectric material (dielectric constant 2.7) for the organic field-effect transistor fabrication.

Zernike phase-contrast full-field transmission X-ray nanotomography for 400 micrometre-sized samples.

Full-field X-ray nanotomography based on a Fresnel zone plate offers a promising and intuitive approach to acquire high-quality phase-contrast images with a spatial resolution of tens of nanometres, and is applicable to both synchrotron radiation and laboratory sources. However, its small field of view (FOV) of tens of micrometres provides limited volume information, which primarily limits its application fields. This work proposes a method for expanding the FOV as the diameter of the objective zone plate, which provides a 400 µm FOV at below 500 nm resolution with Zernike phase contrast. General applications of large-volume nanotomography are demonstrated in integrated circuit microchips and Artemia cysts. This method can be useful for imaging/analyzing industrial and biological samples where bulk properties are important or the sample is difficult to section.

Approaches to synthesize MgO nanostructures for diverse applications.

Magnesium oxide remained interesting from long time for several important phenomena like; defect induced magnetism, spin electron reflectivity, broad laser emission etc. Moreover, nanostructures of this material exhibited suitability for different kinds of applications ranging from wastewater treatment to spintronics depending upon their shape and size. In this way, researchers had grown nanostructures in the form of nanoparticles, thin films, nanotubes, nanowalls, nanobelts. Though nanoparticles and thin films are well known form of nanostructures and wide variety of synthesis approaches are available, however, limited methodology for other nanostructures are available. In order to grow these nanostructures in an optimized way an understanding of these methods is essential. Thus, this review article depicts an overview of various approaches for design of different kinds of nanostructures.

X-ray nanotomography of dry colloidal packings.

Random packings are crucial in understanding arrangement and geometry of particles. Random packings of dry small particles may be subject to adhesion or friction, as expected theoretically and numerically. We explore experimentally random packings of dry colloids with X-ray nanotomography that directly provides three-dimensional structural and geometric information of dry colloidal packings. We find that dry colloidal packings, as characterized by contact number and packing density, are quite consistent with adhesive loose packings that significantly deviate from random loose packings for hard spheres. This study may offer direct evidence for adhesive loose packings comprising dry small particles, as proven by X-ray nanotomography.

MgO Thin Film Growth on Si(001) by Radio-Frequency Sputtering Method.

Herein, sputtering duration and annealing temperature effects on the structure and local electronic structure of MgO thin films were studied using synchrotron radiation based X-ray diffraction and X-ray absorption spectroscopic investigations. These films were grown at substrate temperature of 350 °C by varying sputtering duration from 25 min to 324 min in radio frequency (RF) sputtering method followed by post-deposition annealing at 400, 600 and 700 °C for 3 h. These films were amorphous upto certain sputtering durations, typically upto 144 min and attains crystallization thereafter. This kind of behavior was observed at all annealing temperature. The textured coefficient of crystalline films envisaged that the orientation was affected by annealing temperature. Coordination of Mg2+ ions was more distorted in amorphous films compared to crystalline films. Moreover, onset of molecular oxygen are absorbed at low annealing temperature on these films.

Local Electronic Structure of Calcite Investigated Using X-ray Absorption Spectroscopy at Different Span of Time.

For the present work, calcite nanoparticles was synthesized from calcium nitrate by annealing precursor at 300, 400, 500 and 600°C. Ca K-edge near edge X-ray absorption fine structure measurements revealed spectral features characteristics to the amorphous phase of calcium carbonate at 300 and 400°C. At 500 and 600°C, the spectra were analogues to the calcite phase of calcium carbonate. Simulation of extended X-ray absorption fine structure spectra envisaged that both coordination number and bond distance for Ca-O bonds decreased with annealing temperature. Both parameters attained values close to standard calcite when annealed at 600°C. The spectral features at Ca L-, O K- and C K-edge near edge X-ray absorption fine structure appeared at same positions for different ages, which envisaged the occurrence of almost same local electronic structure for different span of times.

Soft X-ray Absorption Spectroscopic Investigation of Li(Ni0.8Co0.1Mn0.1)O2 Cathode Materials.

Herein, we report the soft X-ray absorption spectroscopic investigation for Li(Ni0.8Co0.1Mn0.1)O2 cathode material during charging and discharging. These measurements were carried out at the Mn L-, Co L-, and Ni L-edges during various stages of charging and discharging. Both the Mn and Co L-edge spectroscopic measurements reflect the invariance in the oxidation states of Mn and Co ions. The Ni L-edge measurements show the modification of the oxidation state of Ni ions during the charging and discharging process. These studies show that eg states are affected dominantly in the case of Ni ions during the charging and discharging process. The O K-edge measurements reflect modulation of metal-oxygen hybridization as envisaged from the area-ratio variation of spectral features corresponding to t2g and eg states.

Development of XANES nanoscopy on BL7C at PLS-II.

X-ray absorption near-edge structure (XANES) imaging is a powerful tool to visualize the chemical state distribution of transition-metal-based materials at synchrotron radiation facilities. In recent years, the electrochemical working rechargeable battery has been the most studied material in XANES imaging owing to the large increase of portable electronics and electric vehicles. This work acknowledges the importance of battery analysis and has developed the XANES imaging system on BL7C at Pohang Light Source-II (PLS-II). BL7C employs an undulator taper configuration to obtain an energy band >130 eV near the K-absorption edge of the target element with a minimum energy interval >0.2 eV. While measuring energy-dependent images, the zone plate translation maintains the best focus, and then various data processes such as background correction, image registration and clustering allow single XANES spectrum extraction and chemical distribution mapping. Here, the XANES imaging process is described, the XANES spectrum quality is identified and the chemical states of the partially charged cathode material used in lithium-ion batteries as an application example are examined.

Correlating the size and cation inversion factor in context of magnetic and optical behavior of CoFe2O4 nanoparticles.

Herein, the size dependent behavior of cobalt ferrite nanoparticles was investigated using synchrotron radiation based techniques. Scanning electron micrographs revealed the enhancement of particle/crystallite size with increase of annealing temperature. Moreover, the shape of these particles also changed with increase of crystallite size. Saturation magnetization increased with increase of crystallite size. The higher saturation magnetization for larger crystallite size nanoparticles was attributed to a cation distribution similar to that of bulk CoFe2O4. The optical band-gap of these nanoparticles decreased from 1.9 eV to 1.7 eV with increase of crystallite size. The enhancement of the optical band-gap for smaller crystallites was due to phenomena of optical confinement occurring in the nanoparticles. Fe L Co L-edge near edge extended X-ray absorption fine structure (NEXAFS) measurements showed that Fe and Co ions remain in the 3+ and 2+ state in these nanoparticles. The results obtained from Fe & Co K-edge X-ray absorption near edge structure (XANES)-imaging experiments further revealed that this oxidation state was possessed by even the crystallites. Extended X-ray absorption fine structure (EXAFS) measurements revealed distribution of Fe and Co ions among tetrahedral (A) and octahedral (B) sites of the spinel structure which corroborates the results obtained from Rietveld refinement of X-ray diffraction patterns (XRD). X-ray magnetic circular di-chroism (XMCD) measurements revealed negative exchange interaction among the ions situated in tetrahedral (A) and octahedral (B) sites. Theoretical and experimental calculated magnetic moments revealed the dominancy of size effects rather than the cation redistribution in the spinel lattice of CoFe2O4 nanoparticles.

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.

X-ray beam-position feedback system with easy-to-use beam-position monitor.

X-ray beam-position stability is indispensable in cutting-edge experiments using synchrotron radiation. Here, for the first time, a beam-position feedback system is presented that utilizes an easy-to-use X-ray beam-position monitor incorporating a diamond-fluorescence screen. The acceptable range of the monitor is above 500 µm and the feedback system maintains the beam position within 3 µm. In addition to being inexpensive, the system has two key advantages: it works without a scale factor for position calibration, and it has no dependence on X-ray energy, X-ray intensity, beam size or beam shape.

Early commissioning results for spectroscopic X-ray Nano-Imaging Beamline BL 7C sXNI at PLS-II.

For spectral imaging of chemical distributions using X-ray absorption near-edge structure (XANES) spectra, a modified double-crystal monochromator, a focusing plane mirrors system and a newly developed fluorescence-type X-ray beam-position monitoring and feedback system have been implemented. This major hardware upgrade provides a sufficiently stable X-ray source during energy scanning of more than hundreds of eV for acquisition of reliable XANES spectra in two-dimensional and three-dimensional images. In recent pilot studies discussed in this paper, heavy-metal uptake by plant roots in vivo and iron's phase distribution in the lithium-iron-phosphate cathode of a lithium-ion battery have been imaged. Also, the spatial resolution of computed tomography has been improved from 70 nm to 55 nm by means of run-out correction and application of a reconstruction algorithm.

Carbon contamination analysis and its effect on extreme ultra violet mask imaging performance using coherent scattering microscopy/in-situ accelerated contamination system.

The coherent scattering microscopy/in-situ accelerated contamination system (CSM/ICS) is a developmental metrology tool designed to analyze the impact of carbon contamination on the imaging performance. It was installed at 11B EUVL beam-line of the Pohang Accelerator Laboratory (PAL). Monochromatized 13.5 nm wavelength beam with Mo/Si multilayer mirrors and zirconium filters was used. The CSM/ICS is composed of the CSM for measuring imaging properties and the ICS for implementing acceleration of carbon contamination. The CSM has been proposed as an actinic inspection technique that records the coherent diffraction pattern from the EUV mask and reconstructs its aerial image using a phase retrieval algorithm. To improve the CSM measurement accuracy, optical and electrical noises of main chamber were minimized. The background noise level measured by CCD camera was approximately 8.5 counts (3 sigma) when the EUV beam was off. Actinic CD measurement repeatability was <1 A (3 sigma) at 17.5 nm line and space pattern. The influence of carbon contamination on the imaging properties can be analyzed by transferring EUV mask to CSM imaging center position after executing carbon contamination without a fine alignment system. We also installed photodiode and ellipsometry for in-situ reflectivity and thickness measurement. This paper describes optical design and system performance observed during the first phase of integration, including CSM imaging performance and carbon contamination analysis results.