Li <i>K</i>-edge XAS spectra of Li₂O.

<p>The spectra were collected on fresh surface, the same spot with 0.5 hour soft x-ray exposure, and 12 hours of soft x-ray exposure.</p

Soft x-ray irradiation effect on Li₂O₂ revealed by Li <i>K</i>-edge XAS spectra.

<p>(top) The XAS spectrum of Li₂O₂ evolves towards that of the Li₂O upon increasing the radiation exposure. The top spectrum is the first one collected from spot A. From top to bottom, the first ten spectra were collected every ten minutes, with an hour of x-ray exposure at the same spot to maximize the dosage, then the measurements resumed with again ten minute each spectrum. The bottom red spectrum is collected on Li₂O for comparison. (bottom) Li₂O₂ Li <i>K</i>-edge XAS spectrum measured from a new spot B on the same sample stored in the ultra-high vacuum chamber for one week.</p

O <i>K</i>-edge XAS spectra of Li₂O₂, Li₂CO₃, and Li₂O.

<p>O <i>K</i>-edge XAS spectra of Li₂O₂, Li₂CO₃, and Li₂O.</p

Soft x-ray irradiation effect on Li₂CO₃ revealed by Li <i>K</i>-edge XAS spectra.

<p>The XAS lineshape of Li₂CO₃ (from top to bottom) evolve towards that of Li₂O (red) after exposed to the soft x-rays. Each spectrum was taken with 10 minute x-ray exposure. The bottom panel shows the Li₂CO₃ Li <i>K</i>-edge XAS spectrum collected from a new spot B on the same sample.</p

Crystal structure of Li₂O₂, Li₂CO₃, and Li₂O.

<p>Red (largest) spheres represent oxygen atoms, green (smaller) spheres represent lithium atoms and purple (smallest) spheres are carbon atoms. Li-O polygons are drawn for better view.</p

Thermal stability and unfolding pathways of hyperthermophilic and mesophilic periplasmic binding proteins studied by molecular dynamics simulation

<p>The ribose binding protein (RBP), a sugar-binding periplasmic protein, is involved in the transport and signaling processes in both prokaryotes and eukaryotes. Although several cellular and structural studies have been reported, a description of the thermostability of RBP at the molecular level remains elusive. Focused on the hyperthermophilic <i>Thermoytoga maritima</i> RBP (tmRBP) and mesophilic <i>Escherichia coli</i> homolog (ecRBP), we applied molecular dynamics simulations at four different temperatures (300, 380, 450, and 500 K) to obtain a deeper insight into the structural features responsible for the reduced thermostability of the ecRBP. The simulations results indicate that there are distinct structural differences in the unfolding pathway between the two homologs and the ecRBP unfolds faster than the hyperthermophilic homologs at certain temperatures in accordance with the lower thermal stability found experimentally. Essential dynamics analysis uncovers that the essential subspaces of ecRBP and tmRBP are non-overlapping and these two proteins show different directions of motion within the simulations trajectories. Such an understanding is required for designing efficient proteins with characteristics for a particular application.</p

Mussel-Inspired Conductive Polymer Binder for Si-Alloy Anode in Lithium-Ion Batteries

The excessive volume changes during cell cycling of Si-based anode in lithium ion batteries impeded its application. One major reason for the cell failure is particle isolation during volume shrinkage in delithiation process, which makes strong adhesion between polymer binder and anode active material particles a highly desirable property. Here, a biomimetic side-chain conductive polymer incorporating catechol, a key adhesive component of the mussel holdfast protein, was synthesized. Atomic force microscopy-based single-molecule force measurements of mussel-inspired conductive polymer binder contacting a silica surface revealed a similar adhesion toward substrate when compared with an effective Si anode binder, homo-poly­(acrylic acid), with the added benefit of being electronically conductive. Electrochemical experiments showed a very stable cycling of Si-alloy anodes realized via this biomimetic conducting polymer binder, leading to a high loading Si anode with a good rate performance. We attribute the ability of the Si-based anode to tolerate the volume changes during cycling to the excellent mechanical integrity afforded by the strong interfacial adhesion of the biomimetic conducting polymer

Reducing Exciton Binding Energy by Increasing Thin Film Permittivity: An Effective Approach To Enhance Exciton Separation Efficiency in Organic Solar Cells

Photocurrent generation in organic solar cells requires that excitons, which are formed upon light absorption, dissociate into free carriers at the interface of electron acceptor and donor materials. The high exciton binding energy, arising from the low permittivity of organic semiconductor films, generally causes low exciton separation efficiency and subsequently low power conversion efficiency. We demonstrate here, for the first time, that the exciton binding energy in B,O-chelated azadipyrromethene (BO-ADPM) donor films is reduced by increasing the film permittivity by blending the BO-ADPM donor with a high dielectric constant small molecule, camphoric anhydride (CA). Various spectroscopic techniques, including impedance spectroscopy, photon absorption and emission spectroscopies, as well as X-ray spectroscopies, are applied to characterize the thin film electronic and photophysical properties. Planar heterojunction solar cells are fabricated with a BO-ADPM:CA film as the electron donor and C₆₀ as the acceptor. With an increase in the dielectric constant of the donor film from ∼4.5 to ∼11, the exciton binding energy is reduced and the internal quantum efficiency of the photovoltaic cells improves across the entire spectrum, with an ∼30% improvement in the BO-ADPM photoactive region

High-Capacity, Aliovalently Doped Olivine LiMn_{1–3<i>x</i>/2}V_<i>x</i>□_<i>x</i>/2PO₄ Cathodes without Carbon Coating

A substantial amount of Mn²⁺ has been aliovalently substituted by V³⁺ in cation-deficient LiMn_{1–3<i>x</i>/2}V_<i>x</i>□_<i>x</i>/2PO₄ (0 ≤ <i>x</i> ≤ 0.20) by a low-temperature (<300 °C) microwave-assisted solvothermal (MW-ST) process. The necessity of a low-temperature synthesis to achieve higher levels of doping is demonstrated as the solubility of vanadium decreases with the formation of impurity phases on heating the samples to ≥575 °C. Soft X-ray absorption spectroscopy reveals enhanced Mn–O hybridization in the vanadium-doped samples, which is believed to facilitate an increase in capacity with increasing vanadium content in the lattice. For example, a high capacity of 155 mAh/g is achieved above a cutoff voltage of 3 V without any carbon coating for the <i>x</i> = 0.2 sample. The vanadium substitution enhances the overall kinetics of the material by lowering the charge-transfer impedance and increasing the lithium-diffusion coefficient

Probing LaMO₃ Metal and Oxygen Partial Density of States Using X‑ray Emission, Absorption, and Photoelectron Spectroscopy

We examined the electronic structure in LaMO₃ perovskite oxides (M = Cr, Mn, Fe, Co, Ni) by combining information from X-ray emission, absorption, and photoelectron spectroscopy. Through first-principles density functional theory simulations, we identified complementary hybridization features present in the transition metal and oxygen X-ray emission spectra. We then developed a method for the self-consistent alignment of the emission data onto a common energy scale using these features, providing a valuable supplementary technique to photoelectron spectroscopy for studying the partial density of states in perovskites. The combined information from X-ray emission and absorption was used to explore trends in electronic structure characteristics under the Zaanen–Sawatzky–Allen frameworknamely the extent of metal–oxygen hybridization, band gap, and charge-transfer gap. We further established a method that allows for the experimental determination of the occupied and unoccupied band positions relative to the oxide Fermi level, as well as on an absolute energy scale