InxGa1-xAs (x = 0.53-0.93) based PIN photodiodes (PDs) were fabricated using a metal-organic chemical vapor deposition system. Current density vs. voltage (J-V) measurements showed that as the In content increased from 0.53 to 0.88, the reverse current density at -0.5 V decreased from 9.60 x 10- 2 to 0.56 x 10- 2 mA center dot cm- 2, while the ideality factor increased from 1.51 to 2.12, indicating enhanced trap-assisted recombination. Temperature dependent J-V analysis revealed that the Ea,c values for In0.83Ga0.17As and In0.88Ga0.12As were close to half of the bandgap energy, indicating that Shockley-Read-Hall recombination is the dominant mechanism. From deep level transient spectroscopy, H1 and E2 defects appeared at higher In content, with the H1 defect density increasing from 1.68 x 1013 to 3.60 x 1013 cm- 3. This increased in H1 defect density led to a significant decrease in detectivity from 1.30 x 1010 to 5.55 x 109 cm center dot Hz1/2/W.

C-H terminated nanometer scale diamonds (d = 1 to 15 nm) are synthesized from 1-fluoroadamantane at high pressure (6-8 GPa) and high temperature (500-1500 °C) in a multianvil press. High resolution transmission electron microscopy, X-ray diffraction, Raman, diffuse reflectance Fourier transform infrared, and X-ray absorption spectroscopies demonstrate the excellent crystallinity and atomically flat C-H terminated surfaces of nanodiamonds with (111) and (110) facets. The importance of hydrogen to the synthesis of nanodiamond and its faceting is discussed. Following vacancy generation, annealing and oxidation of the nanodiamonds, optically detected magnetic resonance and electron spin resonance coherence times (T2 = 0.9 and 2.1 μs) of nitrogen vacancy (NV) centers are measured. The obtained T2 values are equivalent to the shallow NV centers (depth <10 nm) in bulk diamond crystals and larger nanocrystals prepared by mechanical milling.

Disordered rock-salt (DRX) cathodes have emerged as promising candidates for low-cost, high-energy lithium-ion batteries that are free of nickel and cobalt. However, their practical use is hindered by rapid capacity and voltage degradation during cycling. This degradation has largely been attributed to chemical instability at high charge states, where unstable oxygen oxidation leads to oxygen loss, electrolyte decomposition, and transition metal dissolution. Recently, mechanical instability has been recognized as a key issue, driven by large volume changes in DRX particles that induce composite electrode-level cracks and pores. Here, through combined in situ and ex situ characterization with density functional theory calculations and machine learning applied to a model DRX compound, Li1.2Mn0.6Nb0.2O2, we demonstrate that irreversible oxygen loss triggers cascading lattice expansion in DRX, establishing strong coupling between chemical and mechanical instabilities that leads to composite electrode damage and accelerated performance degradation. Notably, we show that this coupled degradation pathway can be significantly mitigated by employing a highly concentrated electrolyte, which suppresses oxygen loss and stabilizes the DRX structure. These findings provide a more complete understanding of DRX degradation and highlight electrolyte engineering as a key strategy to improve the durability of high-energy DRX cathodes across material, composite electrode, and cell levels.

A large challenge in determining the physics of helimagnetic SrFeO3 is in stabilizing the stoichiometric chemical phase over long enough time scales to conduct extensive measurements. Degradation in SrFeO3 manifests mainly as a crossover from metallic to insulating behavior. Using a combination of electronic transport and density functional theory, we show that this degradation is dominated by oxygen loss, possibly on the order of one percent. We further demonstrate that high quality SrFeO3 thin films can be stabilized long-term by combining a nanoscale band insulator capping layer with an ex situ ozone anneal. We show that this produces a nearly-pristine cation sublattice and preserves metallicity for at least several weeks. These results establish a reliable pathway for producing chemically stable SrFeO3 thin films, enabling reproducible studies of its unusual helimagnetism.

This work presents an experimental and analytical way to elucidate the origin of magnetism in nitrogen-doped graphene (NG) through advanced synchrotron-based techniques. Here, we use a combination of controlled synthesis and synchrotron-based X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES), and X-ray magnetic circular dichroism (XMCD) to investigate the electronic and magnetic structures of NG. By controlling the thermal parameters of synthesis, we create distinct nitrogen-bonding and defect environments in the NG matrix, enabling us to correlate the chemistry and local magnetism of nitrogen-doped graphene. XAS was used to probe the evolution of unoccupied states and bonding, whereas XES provides additional insight into the occupied electronic states and the chemical environment of the nitrogen species, distinguishing between pyridine-, pyrrole-, and graphite-type bonding. XMCD was used to reveal spin polarization at the carbon and nitrogen K-edges. This study shows that the graphitic nitrogen bonding structure is responsible for the observed magnetization, and thus the magnetic properties of graphene originate intrinsically from the nitrogen-defect-induced electronic structure. Our results connect the scale of C-N bond configurations to the macroscale phenomenon of magnetism and offer a path forward for creating magnetic materials from metal-free carbon. Our approach provides an important platform for studying magnetism in low-dimensional graphene-based systems.

X-ray magnetic circular dichroism (XMCD) and resonant inelastic X-ray scattering with magnetic circular dichroism (RIXS-MCD) provide unparalleled insights into the electronic and magnetic dynamics of complex materials. However, interpreting their spectra in mixed-valence systems remains challenging due to intricate many-body interactions and enhanced charge fluctuations. In this study, by utilizing the Anderson impurity model with a full consideration of charge transfer (CT), many-body core-valence exchange correlation (CVEC) effects, and Jahn-Teller (JT) distortions, we systematically investigate the XMCD and RIXS-MCD spectra for a prototypical mixed-valence ferromagnet, La0.7Sr0.3MnO3 film. We demonstrate that simple calculation with limited CT effects fails to capture characteristic substructures observed experimentally. In contrast, an adequate treatment of CT and CVEC effects yields a more consistent description of both XMCD and RIXS-MCD spectra, providing practical guidance for the interpretation of dichroic x-ray spectroscopies in mixed-valence transition-metal oxides. Furthermore, we discuss the role of the JT effect in Mn3+ ions in the determination of their spectra. Although X-ray magnetic circular dichroism (XMCD) and resonant inelastic X-ray scattering with magnetic circular dichroism (RIXS-MCD) provide insights into the electronic and magnetic dynamics of complex materials, interpreting spectra from mixed-valence systems is challenging due to the presence of many-body interactions and enhanced charge fluctuations. Here, the authors use an Anderson impurity model that takes into account charge transfer (CT), many-body core-valence exchange correlation (CVEC) effects and Jahn-Teller (JT) distortions, discussing the role of the JT effect in Mn3+ ions in the determination of their spectra and showing that an adequate treatment of charge transfer and many-body core-valence exchange correlation effects yields a more consistent description of both XMCD and RIXS-MCD data.

Determining the electronic structure of transition metal complexes with non-innocent ligands is challenging, both experimentally and theoretically. In this study, we investigate the electronic structure of iron corrole nitrosyl (Fe[TPC](NO), TPC = meso-triphenylcorrole) using a combination of Fe L-edge and K pre-edge X-ray absorption spectroscopy (XAS), Kβ X-ray emission spectroscopy (XES), and multiconfigurational calculations. A key debate revolves around the distribution of radical character on the ligand and the spin/oxidation state of the iron center. The experimental spectra reveal that the Fe center adopts a low-spin configuration, characterized as either FeII or FeIII with strong π back-bonding and little spin polarization. Calculations identified Fe[TPC](NO) primarily as {FeNO}6 with a corrole3-, where the {FeNO}6 unit exhibits FeIII character. However, no localized hole was found in the iron t2g orbital due to strong covalent mixing with NO π* orbitals. The occupation of the Fe 3d z 2 orbital, and thus the radical character on the corrole ligand, is highly sensitive to the axial ligand environment. This was supported by wavefunction analysis over varying Fe-NO distances and comparison with iron corrole chloride (Fe[TPC]Cl), which displayed significant radical character on the corrole ligand due to the weak axial ligand. These findings provide critical insights into ligand non-innocence and covalency in metal corrole systems, offering a foundation for understanding other highly covalent transition metal systems.

Abstract Proton-coupled electron transfer (PCET) is foundational to catalysis, bioenergetics, and energy conversion, yet directly observing the interplay between electronic redistribution, protonation, and solvent reorganization remains challenging. We combine femtosecond optical spectroscopy, ultrafast N K-edge X-ray absorption spectroscopy, and time-resolved X-ray solution scattering to capture the steps of a sequential PCET reaction in water with atomic-site specificity. Using a ruthenium polypyridyl model complex, we resolve the electron redistribution upon photoinduced metal-to-ligand charge transfer and subsequent ( ~ 460 ps) protonation at a ligand nitrogen, as well as the concomitant rearrangement of the first-solvation-shell. Combined with advanced electronic structure and molecular dynamics simulations, our measurements reveal a marked localization of the excited-state electron density at the protonated N site, together with a switch from N···HO to NH···O hydrogen-bonds. These results establish a multimodal X-ray framework for mechanistic insight into PCET and its control in catalysis, artificial photosynthesis, and biological energy flow.

High-temperature, high-pressure (HPHT) nanodiamond (ND) hosts nitrogen-vacancy (NV) centers, solid-state qubits that enable room-temperature quantum sensing by all-optical magnetometry, electrometry, and thermometry. However, the covalent surface functionalization of nanoscale diamond remains largely limited to carboxylate-based chemistries. Amine termination is particularly attractive because theoretical studies predict suppression of midgap states and extended electron-spin coherence times. Recently, chemical activation of alcohol-terminated NDs to alkyl bromides (ND-Br) using SOBr2 has enabled nucleophilic substitution through a carbocation intermediate, allowing formation of simple amine terminations. Here, we evaluate whether sterically demanding amines can form covalent diamond-nitrogen bonds on ND-Br surfaces. ND-Br was reacted with branched, linear, and cyclic amines, including polyethylenimine, diethylenetriamine, and melamine. X-ray spectroscopies were used to confirm successful and to probe the resulting electronic structure at the diamond-amine interface. These results expand the chemical toolbox for tuning diamond surface dipoles and electron affinity, providing new pathways for engineering nanodiamond surfaces for quantum sensing and photocatalysis applications.

Utilizing anion redox reaction is crucial for developing the next generation of high-energy density, low-cost sodium-ion batteries. However, the irreversible oxygen redox reaction in Na-ion layered cathodes, which leads to voltage fading and reduced overall lifespan, has hindered their practical application. In this study, we incorporated selenium as a synergistic redox active center of oxygen to improve the stability of Na-ion cathodes. Our redesigned cathode maintains stable voltage by demonstrating reversible oxygen redox while significantly suppressing the redox activity of manganese. The anionic redox contribution capacity of the selenium-doped Na0.6Li0.2Mn0.8O2 cathode remains as high as 84% after 50 cycles, while the pristine Na0.6Li0.2Mn0.8O2 cathode experiences a reduction to 39% of its initial capacity. Our X-ray photoelectron spectroscopy data and computational analysis further revealed that selenium doping participates in redox as Se+4/5 which stabilizes the charged state and increases the energy step for O-O dimerization, thus improving the stability and lifespan of Na0.6Li0.2Mn0.8O2 cathodes. Our findings highlight the potential of redox coupling design to address the issue of voltage fade caused by irreversible anionic redox.

The use of anionic redox has become a new paradigm for improving the energy density of rechargeable batteries, which is essential for improving the market competitiveness of sodium-ion batteries. However, issues such as voltage attenuation and cycling stability degradation persist in layered oxide anion redox cathode materials. In this study, we systematically investigate the classic Na-ion cathode material Na0.6Li0.2Mn0.8O2, and the primary causes of voltage decay are identified as the activation of cations and the reduction in anion redox activity. In addition, the activation of cations is closely associated with anion reactions. Through the application of sophisticated multiscale synchrotron absorption spectroscopy and imaging techniques, we have identified a pronounced pattern of spatially dependent degradation in the evolution of redox couples, which is more evident from the material's surface to its core. With this understanding, we introduced a surface fluorination approach that modulates the local chemical coordination environment. This strategy increases the formation energy of surface oxygen vacancies and locks transition metals oxide state. Consequently, it enables more reversible anionic redox reactions, which block the spatial progression of degradation and mitigates voltage decay.

Disordered rock-salt oxides and oxyfluorides are promising positive electrode materials for high-performance lithium-ion batteries free of nickel and cobalt. However, conventional synthesis methods rely on post-synthesis pulverization to achieve cycling-appropriate particle sizes, offering limited control over particle microstructure and crystallinity. This accelerates degradation and complicates secondary particle processing. Here we present a synthesis strategy that enhances nucleation while suppressing particle growth and agglomeration across various disordered rock-salt compositions, including lithium-manganese-titanium oxide, lithium-manganese-niobium oxide, and lithium-nickel-titanium oxide systems. Applied to Li1.2Mn0.4Ti0.4O2, this method yields highly crystalline, well-dispersed sub-200 nm particles that form homogeneous electrode films with stable cycling behavior. Tested in cells with lithium metal as the counter electrode, these electrodes deliver ~200 mAh/g with 85% capacity retention relative to the first cycle after 100 cycles (20 mA/g, 1.5-4.8 V), and an average discharge voltage loss of 4.8 mV per cycle, compared to 38.6% retention and 7.5 mV loss per cycle for electrodes derived from pulverized solid-state particles. This approach suggests a route to enhance the performance and durability of disordered rock-salt electrodes for sustainable lithium-ion batteries.

Rare-earth nickelates exhibit valuable behavior for neuromorphic computing at low temperature: Building blocks for biologically inspired microelectronic neurons like electrically driven insulator-metal transitions (IMTs), negative differential resistance, and self-oscillations have been shown up to 230 K for SmNiO3 and NdNiO3. EuNiO3 raises the IMT far above room temperature (460 K) but high-quality thin films are challenging to synthesize. Here, we explore the epitaxial stabilization of EuNiO3 using pulsed laser deposition. X-ray diffraction reciprocal space maps, x-ray absorption spectroscopy, and transmission electron microscopy show that higher growth temperature (800 degrees C) reduces oxygen vacancy concentrations in EuNiO3. Pseudomorphic EuNiO3 is demonstrated on both SrLaAlO4 and NdGaO3 substrates, and LaNiO3 buffer layers are incorporated to facilitate future vertical device fabrication. In contrast to bulk thermodynamic predictions, the greater oxidation and crystallinity at higher temperature we observe indicates that epitaxial substrates can stabilize EuNiO3 at O-2 pressures less than 1 atm. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Soft X-ray absorption spectroscopy of first row transition elements at their respective L-edges provides important information about the oxidation and spin states of the metal centers. However, the associated sample damage in radiation-sensitive samples substantially alters the electronic and chemical structures of redox-active metal centers. Here, we measure the soft X-ray spectrum of the model MnIII(acac)3 complex containing a redox-active MnIII metal center in an octahedral environment with a superconducting transition-edge sensor detector. To reduce the secondary damage resulting primarily from the diffusion of radicals and electrons, the spectra are collected at 30 K and 80 K on solid samples. Starting from the first scan, we detect the contribution of X-ray induced sample damage leading to a change in the MnII intensity. However, at low temperatures, particularly at 30 K, we do not observe a gradual increase in the radiation damage with successive scans with the X-ray beam at the same spot. At our estimated dose of 90 kGy, we find 62% of MnIII(acac)3 is still intact at 30 K. However, at room temperature, we see a gradual increase in radiation damage with increasing numbers of scans at the same spot, which is consistent with the possibility of increased diffusion rates of secondary radicals and electrons as noted in other studies.

Understanding the behavior of confined water at liquid-solid interfaces is central to numerous physical, chemical, and biological processes, yet remains experimentally challenging. Here, we utilize shallow nitrogen-vacancy (NV) centers in diamond to investigate the nanoscale dynamics of interfacial water confined between the diamond surface and an overlying fluorinated oil droplet. Using NV-based nuclear magnetic resonance protocols selectively sensitive to 1H and 19F, we independently track water and oil near the interface under ambient conditions. Comparing opposite sides of a doubly-implanted diamond membrane - one exposed to oil, the other not - we uncover a slow, multi-day process in which the interfacial water layer is gradually depleted. This desorption appears to be driven by sustained interactions with the fluorinated oil and is supported by molecular dynamics simulations and surface-sensitive X-ray spectroscopies. Our findings provide molecular-level insight into long-timescale hydration dynamics and underscore the power of NV-NMR for probing liquid-solid heterointerfaces with chemical specificity.

Proton-coupled electron transfer (PCET) is foundational to catalysis, bioenergetics, and energy conversion, yet capturing and disentangling the coupled motions of electrons, protons, and solvent has remained a major experimental challenge. We combine femtosecond optical spectroscopy, site-specific ultrafast soft X-ray absorption spectroscopy, and time-resolved X-ray scattering with advanced calculations to disentangle the elementary steps of PCET in solution. Using a ruthenium polypyridyl model complex, we directly resolve photoinduced electron redistribution, ligand-site protonation within 100 ps, and the accompanying solvent reorganization. This unified multi-modal approach provides an orbital-level, atomistic picture of PCET, showing how electronic, nuclear, and solvation degrees of freedom can be separated experimentally. Our results establish a general X-ray framework for understanding and ultimately controlling PCET in catalysis, artificial photosynthesis, and biological energy flow.

Oxygen redox in transition metal oxide cathodes is typically expected to occur at higher voltages. Here, we report an unexpected low-voltage oxygen redox mechanism in the archetypal LiCoO2 (LCO) cathode. This mechanism is triggered by changes to the local atomic structure from a subtle phase change within the first 10% of delithiation. Our results indicate the formation of delocalized electron holes at oxygen 2p orbitals resulting in a reduction of cobalt ions via ligand-to-metal charge transfer. This reduction causes an anomalous change in LCO’s magnetic response with delithiation. This observation provides fundamental insight into the mechanism behind anion redox, offering a fresh perspective to take advantage of this additional redox center.

The electronic structure of oxyhemoglobin has been controversial since the discovery of the compound's diamagnetism in 1936. This study uses partial fluorescence yield Fe L-edge X-ray absorption spectroscopy (XAS) in the 3s→2p fluorescence on oxyhemoglobin solutions, measured using a transition-edge sensor detector, to obtain a quantitative experimental description of the electronic structure of the O2-bound iron site. The spectrum is very different from typical low-spin FeII and FeIII heme spectra, and multiplet simulations indicate a mixed ground configuration with ∼57% low-spin FeIII and ∼43% low-spin FeII character. This is also very different from the FeII character found for the picket-fence porphyrin model complex. The oxyhemoglobin L-edge XAS data further show that the O2 ligand engages in a weak σ- but strong π-bond with the iron ion, leading to the overall strong Fe-O2 bond required for O2 transport.

Understanding the behavior of confined water at liquid-solid interfaces is central to numerous physical, chemical, and biological processes, yet remains experimentally challenging. Here, shallow nitrogen-vacancy (NV) centers in diamond serve as sensors to investigate the nanoscale dynamics of interfacial water confined between the diamond surface and an overlying fluorinated oil droplet. With the help of nuclear magnetic resonance (NMR) protocols selectively sensitive to 1H and 19F, NVs are used to probe water and oil near the interface under ambient conditions. Comparing opposite sides of a doubly-implanted diamond membrane - one exposed to oil, the other not - a slow, multi-day process is uncovered in which the interfacial water layer is gradually depleted. This desorption appears to be driven by sustained interactions with the fluorinated oil and is supported by molecular dynamics simulations and surface-sensitive X-ray spectroscopies. These findings provide molecular-level insight into long-timescale hydration dynamics and underscore the power of NV-NMR for probing liquid-solid heterointerfaces with chemical specificity.