Compact and versatile neutron imaging detector with sub-4μm spatial resolution based on a single-crystal thin-film scintillator

A large and increasing number of scientific domains pushes for high neutron imaging resolution achieved in reasonable times. Here we present the principle, design and performance of a detector based on infinity corrected optics combined with a crystalline Gd₃Ga₅O₁₂ : Eu scintillator, which provides an isotropic sub-4 µm true resolution. The exposure times are only of a few minutes per image. This is made possible also by the uniquely intense cold neutron flux available at the imaging beamline NeXT-Grenoble. These comparatively rapid acquisitions are compatible with multiple high quality tomographic acquisitions, opening new venues for in-operando testing, as briefly exemplified here.

Detailed and Direct Observation of Sulfur Crystal Evolution During Operando Analysis of a Li-S Cell with Synchrotron Imaging

Herein, we present a detailed investigation of the electrochemically triggered formation and dissolution processes of α- and β-sulfur crystals on a monolithic carbon cathode using operando high-resolution synchrotron radiography (438 nm/pixel). The combination of visual monitoring with the electrical current response during cyclic voltammetry provides valuable insights into the sulfur formation and dissolution mechanism. Our observations show that the crystal growth process is mainly dictated by a rapid equilibrium between long-chain polysulfides on one side and solid sulfur/short-chain polysulfides on the other side, which is consistent with previous studies in this field. The high temporal and spatial resolution of synchrotron imaging enables the observation of different regimes during the sulfur formation and dissolution process. The appearance of short-chain polysulfides after the first anodic CV peak initiates a rapid dissolution process of α-sulfur crystals on the cathode. The increase in the long-chain lithium polysulfide concentration at the cathode surface during charge results in an increased crystal growth rate, which in turn produces imperfections in α- and β-sulfur crystals. There are strong indications that these defects are fluid inclusions, which may trap dissolved polysulfides and therefore reduce the electrochemical cell capacity.

Multidimensional Integrated Chalcogenides Nanoarchitecture Achieves Highly Stable and Ultrafast Potassium-Ion Storage

Potassium-ion batteries (KIBs) have come into the spotlight in large-scale energy storage systems because of cost-effective and abundant potassium resources. However, the poor rate performance and problematic cycle life of existing electrode materials are the main bottlenecks to future potential applications. Here, the first example of preparing 3D hierarchical nanoboxes multidimensionally assembled from interlayer-expanded nano-2D MoS₂ @dot-like Co₉ S₈ embedded into a nitrogen and sulfur codoped porous carbon matrix (Co₉ S₈ /NSC@MoS₂ @NSC) for greatly boosting the electrochemical properties of KIBs in terms of reversible capacity, rate capability, and cycling lifespan, is reported. Benefiting from the synergistic effects, Co₉ S₈ /NSC@MoS₂ @NSC manifest a very high reversible capacity of 403 mAh g^-1 at 100 mA g^-1 after 100 cycles, an unprecedented rate capability of 141 mAh g^-1 at 3000 mA g^-1 over 800 cycles, and a negligible capacity decay of 0.02% cycle^-1 , boosting promising applications in high-performance KIBs. Density functional theory calculations demonstrate that Co₉ S₈ /NSC@MoS₂ @NSC nanoboxes have large adsorption energy and low diffusion barriers during K-ion storage reactions, implying fast K-ion diffusion capability. This work may enlighten the design and construction of advanced electrode materials combined with strong chemical bonding and integrated functional advantages for future large-scale stationary energy storage.

Interfacial Processes and Influence of Composite Cathode Microstructure Controlling the Performance of All-Solid-State Lithium Batteries

All-solid-state lithium-ion batteries have the potential to become an important class of next-generation electrochemical energy storage devices. However, for achieving competitive performance, a better understanding of the interfacial processes at the electrodes is necessary for optimized electrode compositions to be developed. In this work, the interfacial processes between the solid electrolyte (Li₁₀GeP₂S₁₂) and the electrode materials (In/InLi and Li_xCoO₂) are monitored using impedance spectroscopy and galvanostatic cycling, showing a large resistance contribution and kinetic hindrance at the metal anode. The effect of different fractions of the solid electrolyte in the composite cathodes on the rate performance is tested. The results demonstrate the necessity of a carefully designed composite microstructure depending on the desired applications of an all-solid-state battery. While a relatively low mass fraction of solid electrolyte is sufficient for high energy density, a higher fraction of solid electrolyte is required for high power density.

Phase-contrast synchrotron microtomography reveals the internal morphology of a new fossil species of the <i>Corticaria</i>-<i>sylvicola</i>-group (Coleoptera: Latridiidae)

Corticaria amberica sp. nov. (Coleoptera: Latridiidae) from Baltic amber is described and illustrated using the features of the male genitalia. To study these features, phase-contrast synchrotron microtomography was used for the first time with a member of this family. A literature-based checklist of fossil and subfossil Latridiidae is provided. The following new synonymy is established: Latridius alexeevi Bukejs, Kirejtshuk & Rücker, 2011 = Latridius usovae Sergi & Perkovsky, 2014 syn. nov. New fossil records for the species Latridius alexeevi Bukejs, Kirejtshuk & Rücker, Latridius jantaricus Borowiec, Revelieria groehni Sergi, Perkovsky & Reike, and Corticarina palaeominuta Reike are also presented.

In operando monitoring of the state of charge and species distribution in zinc air batteries using X-ray tomography and model-based simulations

A novel combination of in operando X-ray tomography and model-based analysis of zinc air batteries is introduced.

Kinetics, energetics, and electronic coupling of the primary electron transfer reactions in mutated reaction centers of Blastochloris viridis

Femtosecond spectroscopy in combination with site-directed mutagenesis has been used to study the dynamics of primary electron transfer in native and 12 mutated reaction centers of Blastochloris (B) (formerly called Rhodopseudomonas) viridis. The decay times of the first excited state P* vary at room temperature between of 0.6 and 50 ps, and at low temperatures between 0.25 and 90 ps. These changes in time constants are discussed within the scope of nonadiabatic electron transfer theory using different models: 1) If the mutation is assumed to predominantly influence the energetics of the primary electron transfer intermediates, the analysis of the room temperature data for the first electron transfer step to the intermediate P(+)B(A)(-) yields a reorganization energy lambda = 600 +/- 200 cm(-1) and a free energy gap Delta G ranging from -600 cm(-1) to 800 cm(-1). However, this analysis fails to describe the temperature dependence of the reaction rates. 2) A more realistic description of the temperature dependence of the primary electron transfer requires different values for the energetics and specific variations of the electronic coupling upon mutation. Apparently the mutations also lead to pronounced changes in the electronic coupling, which may even dominate the change in the reaction rate. One main message of the paper is that a simple relationship between mutation and a change in one reaction parameter cannot be given and that at the very least the electronic coupling is changed upon mutation.

Electron transfer dynamics of Rhodopseudomonas viridis reaction centers with a modified binding site for the accessory bacteriochlorophyll

Femtosecond spectroscopy in combination with site-directed mutagenesis was used to study the influence of histidine L153 in primary electron transfer in the reaction center of Rhodopseudomonas viridis. Histidine was replaced by cysteine, glutamate, or leucine. The exchange to cysteine did not lead to significant changes in the primary reaction dynamics. In the case of the glutamate mutation, the decay of the excited electronic level of the special pair P* is slowed by a factor of 3. The exchange to leucine caused the incorporation of a bacteriopheophytin b instead of a bacteriochlorophyll b molecule at the BA site. As a consequence of this chromophore exchange, the energy level of the electron transfer state P+BA- is lowered to such an extent that repopulation from the next electron transfer intermediate state P+HA- takes place, resulting in a long-lasting P+BA- population. The observed differences in time constants are discussed in the scope of nonadiabatic electron transfer theory considering the influence of the amino acids at position L153 and the chromophore exchange on the energy level of the intermediate state P+BA-. The results show that the high efficiency of primary electron transfer is reduced substantially, if the energy level of P+BA- is lowered or raised by several hundred wave numbers.

Spectroscopic characterization of reaction centers of the (M)Y210W mutant of the photosynthetic bacterium Rhodobacter sphaeroides

The tyrosine-(M)210 of the reaction center of Rhodobacter sphaeroides 2.4.1 has been changed to a tryptophan using site-directed mutagenesis. The reaction center of this mutant has been characterized by low-temperature absorption and fluorescence spectroscopy, time-resolved sub-picosecond spectroscopy, and magnetic resonance spectroscopy. The charge separation process showed bi-exponential kinetics at room temperature, with a main time constant of 36 ps and an additional fast time constant of 5.1 ps. Temperature dependent fluorescence measurements predict that the lifetime of P(*) becomes 4-5 times slower at cryogenic temperatures. From EPR and absorbance-detected magnetic resonance (ADMR, LD-ADMR) we conclude that the dimeric structure of P is not significantly changed upon mutation. In contrast, the interaction of the accessory bacteriochlorophyll BA with its environment appears to be altered, possibly because of a change in its position.

The accessory bacteriochlorophyll: a real electron carrier in primary photosynthesis

The primary electron transfer in reaction centers of Rhodobacter sphaeroides is studied by subpicosecond absorption spectroscopy with polarized light in the spectral range of 920-1040 nm. Here the bacteriochlorophyll anion radical has an absorption band while the other pigments of the reaction center have vanishing ground-state absorption. The transient absorption data exhibit a pronounced 0.9-ps kinetic component which shows a strong dichroism. Evaluation of the data yields an angle between the transition moments of the special pair and the species related with the 0.9-ps kinetic component of 26 +/- 8 degrees. This angle compares favorably with the value of 29 degrees expected for the reduced accessory bacteriochlorophyll. Extensive transient absorbance data are fully consistent with a stepwise electron transfer via the accessory bacteriochlorophyll.