Li‐rich layered oxide cathodes with conventional transition metal cation and unique oxygen anion redox reactions deliver high capacities in Li‐ion batteries. However, the oxygen redox process causes ...the oxygen release, voltage fading/hysteresis, and sluggish electrochemical kinetics, which undermine the performance of these materials. By combining operando quick‐scanning X‐ray absorption spectroscopy with online gas chromatography, the effect of the local electronic structure is elucidated on the reaction mechanism and electrochemical kinetics of Li‐rich cathodes. The local electronic structure of Li‐rich cathodes varies with the excess Li (i.e., Li2MnO3 phase) and Ni contents. Compared to the Li‐rich cathodes with higher amounts of Li2MnO3 phase (high excess lithium content (HLC) cathode), those with lower Li2MnO3 contents (low excess lithium content (LLC) cathode) exhibit reversible anion redox reactions and suppressed voltage hysteresis. The cation oxidation process of LLC cathode is kinetically slower than that of HLC cathode and the cation oxidation potential is shifted, likely due to the local coordination associated with different Li/O ratios. The obtained insights into the effect of local electronic structure on the reaction mechanism and kinetics provide a better understanding and control of Li‐rich cathodes.
This research reveals the reaction mechanism and electrochemical kinetics of Li‐rich cathodes using in operando quick‐scanning X‐ray absorption spectroscopy. With the control of Li2MnO3 domain, cation migration and voltage decay were suppressed. The electrochemical stability and kinetics of tradition metal (TM) redox can be tuned by modifying the local coordination structure of Li‐rich cathode.
Lithium dendrite growth dynamics on Cu surface is first visualized through a versatile and facile experimental cell by in operando transmission X-ray microscopy (TXM). Galvanostatic plating and ...stripping cycle(s) are applied on each cell. Upon plating/stripping at ∼1 mA cm–2, mossy lithium is clearly found growing and shrinking on the Cu surface as the application time increases. It is interesting to note that the aspect ratio (height/width) of deposited lithium has increased with charge passed during plating, indicating a faster growing from the base. In addition, the dendritic or mossy lithium has also been observed when various high current densities (25, 12.5, and 6.3 mA cm–2) are applied in different cycles, showing a severe dendritic lithium formation that could be induced by inhomogeneous current distribution. The clear structure of dead lithium is found after the cycling, which also shows a lower efficiency and higher hazard when a higher current density is applied. This work explores TXM as a useful tool for in operando dynamic visualization and quantitative measurement of lithium dendrite, which is difficult to achieve with ex situ measurements and other microscopy techniques. The understanding of the growth mechanism from TXM can be beneficial for the development of safe lithium ion and lithium metal batteries.
Thallium (Tl) is a non-essential metal mobilized through industrial processes which can lead to it entering the environment and exerting toxic effects. Plants are fundamental components of all ...ecosystems. Therefore, understanding the impact of Tl on plant growth and development is of great importance for assessing the potential environmental risks of Tl. Here, the responses of Arabidopsis thaliana to Tl were elucidated using physiological, genetic, and transcriptome analyses. Thallium can be absorbed by plant roots and translocated to the aerial parts, accumulating at comparable concentrations throughout plant parts. Genetic evidence supported the regulation of Tl uptake and movement by different molecular compartments within plants. Thallium primarily caused growth inhibition, oxidative stress, leaf chlorosis, and the impairment of K homeostasis. The disturbance of redox balance toward oxidative stress was supported by significant differences in the expression of genes involved in oxidative stress and antioxidant defense under Tl exposure. Reduced GSH levels in cad2–1 mutant rendered plants highly sensitive to Tl, suggesting that GSH has a prominent role in alleviating Tl-triggered oxidative responses. Thallium down-regulation of the expression of LCHII-related genes is believed to be responsible for leaf chlorosis. These findings illuminate some of the mechanisms underlying Tl toxicity at the physiological and molecular levels in plants with an eye toward the future environment management of this heavy metal.
•Thallium can be absorbed by plant roots and translocated to the aerial part; it accumulates throughout plant tissues at similar concentrations.•Oxidative stress is one of the early responses to Tl exposure and is counteracted through activation of GSH-related metabolism pathways.•Thallium interferes with K homeostasis via down-regulating K channel genes and competing with K for K-related transport pathways.•Thallium inhibits the levels of transcripts encoding subunits of LCHII, thus affecting the photosynthetic activity, and is believed to be responsible for leaf chlorosis symptoms.
In this study, a combination of X‐ray excited optical luminescence (XEOL), time‐resolved XEOL (TR‐XEOL) and the Hanbury‐Brown and Twiss (HB‐T) interferometer at the Taiwan Photon Source (TPS) 23A ...X‐ray nanoprobe beamline for exploring quantum materials is demonstrated. On the basis of the excellent spatial resolution rendered using a nano‐focused beam, emission distributions of artificial micro‐diamonds can be obtained by XEOL maps, and featured emission peaks of a selected local area can be obtained by XEOL spectra. The hybrid bunch mode of the TPS not only provides a sufficiently high peak power density for experiments at each beamline but also permits high‐quality temporal domain (∼200 ns) measurements for investigating luminescence dynamics. From TR‐XEOL measurements, the decay lifetime of micro‐diamonds is determined to be approximately 16 ns. Furthermore, the XEOL spectra of artificial micro‐diamonds can be investigated by the HB‐T interferometer to identify properties of single‐photon sources. The unprecedented strategy of combining XEOL, TR‐XEOL and the HB‐T interferometer at the X‐ray nanoprobe beamline will open new avenues with significant characterization abilities for unraveling the emission mechanisms of single‐photon sources for quantum materials.
The unprecedented strategy of combining XEOL, TR‐XEOL and the HB‐T interferometer at the TPS 23A X‐ray nanoprobe beamline will open new avenues for exploring quantum materials.
X‐ray ptychography, a technique based on scanning and processing of coherent diffraction patterns, is a non‐destructive imaging technique with a high spatial resolution far beyond the focused beam ...size. Earlier demonstrations of hard X‐ray ptychography at Taiwan Photon Source (TPS) using an in‐house program successfully recorded the ptychographic diffraction patterns from a gold‐made Siemens star as a test sample and retrieved the finest inner features of 25 nm. Ptychography was performed at two beamlines with different focusing optics: a pair of Kirkpatrick–Baez mirrors and a pair of nested Montel mirrors, for which the beam sizes on the focal planes were 3 µm and 200 nm and the photon energies were from 5.1 keV to 9 keV. The retrieved spatial resolutions are 20 nm to 11 nm determined by the 10–90% line‐cut method and half‐bit threshold of Fourier shell correlation. This article describes the experimental conditions and compensation methods, including position correction, mixture state‐of‐probe, and probe extension methods, of the aforementioned experiments. The discussions will highlight the criteria of ptychographic experiments at TPS as well as the opportunity to characterize beamlines by measuring factors such as the drift or instability of beams or stages and the coherence of beams. Besides, probe functions, the full complex fields illuminated on samples, can be recovered simultaneously using ptychography. Theoretically, the wavefield at any arbitrary position can be estimated from one recovered probe function undergoing wave‐propagating. The verification of probe‐propagating has been carried out by comparing the probe functions obtained by ptychography and undergoing wave‐propagating located at 0, 500 and 1000 µm relative to the focal plane.
The working of the hard X‐ray ptychography technique at Taiwan Photon Source, with 11–20 nm spatial resolution, is demonstrated. Experimental conditions influencing the results are also discussed.
Time‐resolved X‐ray excited optical luminescence (TR‐XEOL) was developed successfully for the 23A X‐ray nanoprobe beamline located at the Taiwan Photon Source (TPS). The advantages of the TR‐XEOL ...facility include (i) a nano‐focused X‐ray beam (<60 nm) with excellent spatial resolution and (ii) a streak camera that can simultaneously record the XEOL spectrum and decay time. Three time spans, including normal (30 ps to 2 ns), hybrid (30 ps to 310 ns) and single (30 ps to 1.72 µs) bunch modes, are available at the TPS, which can fulfil different experimental conditions involving samples with various lifetimes. It is anticipated that TR‐XEOL at the TPS X‐ray nanoprobe could provide great characterization capabilities for investigating the dynamics of photonic materials.
Time‐resolved X‐ray excited optical luminescence (XEOL) capabilities were developed successfully for the 23A X‐ray nanoprobe beamline at the Taiwan Photon Source, with an excellent spatial resolution of <60 nm. The XEOL spectrum and decay time were simultaneously recorded over three time intervals, including normal (30 ps to 2 ns), hybrid (30 ps to 310 ns) and single (30 ps to 1.72 µs) bunch modes.
This study develops and successfully demonstrates visualization methods for the characterization of europium (Eu)‐doped BaAl2O4 phosphors using X‐ray nanoprobe techniques. X‐ray fluorescence (XRF) ...mapping not only gives information on the elemental distributions but also clearly reveals the valence state distributions of the Eu2+ and Eu3+ ions. The accuracy of the estimated valence state distributions was examined by performing X‐ray absorption spectroscopy (XAS) across the Eu L3‐edge (6.977 keV). The X‐ray excited optical luminescence (XEOL) spectra exhibit different emission lines in the selected local areas. Their corresponding emission distributions can be obtained via XEOL mapping. The emission properties can be understood through correlation analysis. The results demonstrate that the main contribution to the luminescence intensity of the Eu‐doped BaAl2O4 comes from the Eu2+ activator and the emission intensity will not be influenced by the concentration of Eu2+ or Eu3+ ions. It is anticipated that X‐ray nanoprobes will open new avenues with significant characterization ability for unravelling the emission mechanisms of phosphor materials.
It is anticipated that X‐ray nanoprobes will open new avenues with significant characterization ability for unravelling the emission mechanisms of phosphor materials.
Polarization-dependent hard X-ray excited optical luminescence (XEOL) was used to study not only the optical properties but also the crystallographic orientations of a non-polar a-plane ZnO wafer. In ...addition to a positive-edge jump and extra oscillations in the near-band-edge (NBE) XEOL yield, we observed a blue shift of the NBE emission peak that follows the polarization-dependent X-ray absorption near-edge structure (XANES) as the X-ray energy is tuned across the Zn K-edge. This NBE blue shift is caused by the larger X-ray absorption, generating higher free carriers to reduce the exciton-LO phonon coupling, which causes a decrease in the exciton activation energy. The extra oscillations in XANES and XEOL as the polarization is set parallel to the c-axis is attributed to simultaneous excitations of the Zn 4p - O 2pπ -bond along the c-axis and the bilayer σ-bond, whereas only the σ-bond is excited when the polarization is perpendicular to the c-axis. The polarization-dependent XEOL spectra can be used to determine the crystallographic orientations.
In this report, we describe a general methodology to determine the extent of alloying or atomic distribution quantitatively in bimetallic nanoparticles (NPs) by X-ray absorption spectroscopy (XAS). ...The structural parameters determined in these studies serve as a quantitative index and provide a general route to determine the structural aspects of the bimetallic NPs. We have derived various types of possible structural models based on the extent of alloying and coordination number parameters of bimetallic NPs. We also discussed the nature of homo- and heterometallic interactions in bimetallic NPs based on the extent of alloying. Herein, we use carbon-supported platinum−ruthenium bimetallic nanoparticles to demonstrate the proposed methodology, and this can be extended further to get more insights into the alloying extent or atomic distribution of other bimetallic systems. The results demonstrated in this paper open up methods to determine the atomic distribution of bimetallic NPs, which is an extremely important parameter that strongly influences the physicochemical properties of NPs and their applications.
PDF
