Electron Spin States Research Articles

Modulating the electron spin states of Na2FePO4F cathode via high entropy strategy for enhanced sodium storage and ultra-high cycling stability

Modulating the electron spin states of Na2FePO4F cathode via high entropy strategy for enhanced sodium storage and ultra-high cycling stability

Dual Signature of Chirality Induced Spin Selectivity through Spontaneous Resolution of 2D Metal–Organic Frameworks

AbstractThe Chiral‐Induced Spin Selectivity (CISS) effect has emerged as a fascinating phenomenon within the realm of electron's spin manipulation, showcasing a unique interplay between electron's spin and molecular chirality. Subsequent to its discovery, researchers have been actively involved in exploring the new chiral molecules as effective spin filters. In the realm of observing the CISS effect, the conventional approach has mandated the utilization of two distinct enantiomers of chiral molecules. However, this present study represents a significant advancement by demonstrating the ability to control both spin states of electrons in a single system. In this work, we have demonstrated the preparation of chiral metal–organic frameworks (MOFs) via a “spontaneous resolution” process, obviating the requirement for chiral sources. This resulted in the production of chiral crystals exhibiting opposite handedness (1P and 1M) and these crystals were subsequently employed as a new class of spin filters based on CISS effect. Remarkably, this work signifies the first instance of achieving dual signature of spin selectivity from a single and exclusively achiral system through a spontaneous resolution process. This holds immense potential as it facilitates the production of two distinct spin‐filtering materials from a unified system. Furthermore, we investigated the contact potential differences (CPD) of these chiral crystals and, for the first time, associated it with the preferential spin transport properties. Our findings revealed a correlation between the CPD and the chirality of the crystals, as well as the magnetization orientations of the ferromagnetic substrate, which can be elucidated by the CISS effect. In overall, the significant findings achieved using these robust and easily synthesized MOF crystals without the requirement for chiral medium represent a crucial advancement in enhancing the effectiveness of spin filtering materials to produce spintronic devices.

Dual Signature of Chirality Induced Spin Selectivity through Spontaneous Resolution of 2D Metal-Organic Frameworks.

The Chiral-Induced Spin Selectivity (CISS) effect has emerged as a fascinating phenomenon within the realm of electron's spin manipulation, showcasing a unique interplay between electron's spin and molecular chirality. Subsequent to its discovery, researchers have been actively involved in exploring the new chiral molecules as effective spin filters. In the realm of observing the CISS effect, the conventional approach has mandated the utilization of two distinct enantiomers of chiral molecules. However, this present study represents a significant advancement by demonstrating the ability to control both spin states of electrons in a single system. In this work, we have demonstrated the preparation of chiral metal-organic frameworks (MOFs) via a "spontaneous resolution" process, obviating the requirement for chiral sources. This resulted in the production of chiral crystals exhibiting opposite handedness (1P and 1M) and these crystals were subsequently employed as a new class of spin filters based on CISS effect. Remarkably, this work signifies the first instance of achieving dual signature of spin selectivity from a single and exclusively achiral system through a spontaneous resolution process. This holds immense potential as it facilitates the production of two distinct spin-filtering materials from a unified system. Furthermore, we investigated the contact potential differences (CPD) of these chiral crystals and, for the first time, associated it with the preferential spin transport properties. Our findings revealed a correlation between the CPD and the chirality of the crystals, as well as the magnetization orientations of the ferromagnetic substrate, which can be elucidated by the CISS effect. In overall, the significant findings achieved using these robust and easily synthesized MOF crystals without the requirement for chiral medium represent a crucial advancement in enhancing the effectiveness of spin filtering materials to produce spintronic devices.

Spin-bearing molecules as optically addressable platforms for quantum technologies

Abstract Efforts to harness quantum hardware relying on quantum mechanical principles have been steadily progressing. The search for novel material platforms that could spur the progress by providing new functionalities for solving the outstanding technological problems is however still active. Any physical property presenting two distinct energy states that can be found in a long-lived superposition state can serve as a quantum bit (qubit), the basic information processing unit in quantum technologies. Molecular systems that can feature electron and/or nuclear spin states together with optical transitions are one of the material platforms that can serve as optically addressable qubits. The attractiveness of molecular systems for quantum technologies relies on the fact that molecular structures of atomically defined nature can be obtained in endless diversity of chemical compositions. Crucially, by harnessing the molecular design protocols, the optical and spin (electronic and nuclear) properties of molecules can be tailored, aiding the design of optically addressable spin qubits and quantum sensors. In this contribution, we present a concise and collective discussion of optically addressable spin-bearing molecules – namely, organic molecules, transition metal (TM) and rare-earth ion (REI) complexes – and highlight recent results such as chemical tuning of optical and electron spin quantum coherence, optical spin initialization and readout, intramolecular quantum teleportation, optical coherent storage, and photonic-enhanced optical addressing. We envision that optically addressable spin-carrying molecules could become a scalable building block of quantum hardware for applications in the fields of quantum sensing, quantum communication and quantum computing.

An anisotropic equation of state for solid solutions, with application to plagioclase

SUMMARY This paper presents a framework for building anisotropic equations of state for solid solutions. The framework satisfies the connections between elastic and thermodynamic properties required by Maxwell’s relations. It builds on a recent anisotropic equation of state for pure phases under small deviatoric stresses, adding a dependence on a vector $\boldsymbol {n}$, whose components $n_i$ contain the molar amounts of independent end-members in the solid solution. These end-members may have distinct chemical compositions, site species occupancies or electronic spin states. The high albite-anorthite (C$\bar{\text{1}}$) plagioclase solid solution is used to illustrate the formulation.

Probing the electronic ground state of the nitrogen-vacancy center in nanodiamonds at room temperature

The color centers in diamonds are promising candidates in the context of quantum information science, quantum computation, and spin-based quantum sensors due to their spin-dependent optical transitions. The manipulation and optical readout of electronic spin state is measured using a technique known as optically detected magnetic resonance (ODMR). Here, we discuss the indigenous development of ODMR setup to coherently manipulate and precise readout of spin state of nitrogen-vacancy centers (NV) in nanodiamond at room-temperature. The study involves the confocal mapping of an ensemble of NV centers to measure spin state-dependent optical transition by applying an optical excitation and microwave field simultaneously. The spin state control appears as a dip at 2.87 GHz in the measured emission intensity spectra as a function of microwave frequency. An ODMR contrast of 3.4 % is achieved at the NV center emission maximum of 660 nm and an inhomogeneous dephasing time of 0.03 microseconds. We find an inherent small split in the ODMR dip which is induced by local strain in nanodiamonds. The split becomes stronger while applying an external magnetic field, which forms the basis of NV center-based magnetometry. The results are useful for spin-based microwave-optical quantum transducers, quantum sensing, and quantum memory devices.

Spin Manipulation of Co sites in Co9S8/Nb2CTx Mott-Schottky Heterojunction for Boosting the Electrocatalytic Nitrogen Reduction Reaction.

Regulating the adsorption of an intermediate on an electrocatalyst by manipulating the electron spin state of the transition metal is of great significance for promoting the activation of inert nitrogen molecules (N2) during the electrocatalytic nitrogen reduction reaction (eNRR). However, achieving this remains challenging. Herein, a novel 2D/2D Mott-Schottky heterojunction, Co9S8/Nb2CTx-P, is developed as an eNRR catalyst. This is achieved through the in situ growth of cobalt sulfide (Co9S8) nanosheets over a Nb2CTx MXene using a solution plasma modification method. Transformation of the Co spin state from low (t2g 6eg 1) to high (t2g 5eg 2) is achieved by adjusting the interface electronic structure and sulfur vacancy of Co9S8/Nb2CTx-P. The adsorption ability of N2 is optimized through high spin Co(II) with more unpaired electrons, significantly accelerating the *N2→*NNH kinetic process. The Co9S8/Nb2CTx-P exhibits a high NH3 yield of 62.62µg h-1 mgcat. -1 and a Faradaic efficiency (FE) of 30.33% at -0.40V versus the reversible hydrogen electrode (RHE) in 0.1m HCl. Additionally, it achieves an NH3 yield of 41.47µg h-1 mgcat. -1 and FE of 23.19% at -0.60V versus RHE in 0.1m Na2SO4. This work demonstrates a promising strategy for constructing heterojunction electrocatalysts for efficient eNRR.

Combining electron transfer, spin crossover, and redox properties in metal-organic frameworks

Hofmann coordination polymers (CPs) that couple the well-studied spin transition of the FeII central ion with electron-responsive ligands provide an innovative strategy toward multifunctional metal-organic frameworks (MOFs). Here, we developed a 2D planar network consisting of metal-cyanide-metal sheets in an unusual coordination mode, brought about by infinitely π-stacked redox-active bipyridinium derivatives as axial ligands. The obtained family of materials show vivid thermochromism attributed to electron transfer and/or electronic spin state change processes that can occur either independently or concomitantly. Importantly, the redox activity of the ligands within the structure leads to the quasi-reversible electrochemical reduction reaction on a spin-crossover complex at solid state. These observations have been confirmed via temperature-dependent single-crystal X-ray diffraction, magnetic measurements, Mössbauer, EPR, optical and vibrational spectroscopies as well as quantum chemical calculations.

Constraints on the spin-state transition of siderite from laboratory-based Raman spectroscopy and electrical conductivity under high temperature and high pressure

The vibrational and electrical transport properties of natural siderite are systematically investigated by means of in-situ Raman spectroscopy and alternating current impedance spectroscopy under conditions of 0.6–55.6 GPa, 298–873 K and different hydrostatic environments using a diamond anvil cell (DAC). Upon non-hydrostatic compression, all of these observable characteristic variations of siderite including the appearance of three absolutely new Raman peaks (L’, v4′ and v1′), the disappearance of Raman peaks (T, L and v4) and the discontinuity in the pressure-dependent electrical conductivity can provide robust evidence of electronic spin transitions of Fe2+ from high-spin to mixed-spin to low-spin states at the respective pressures of 42.5 GPa and 48.5 GPa. As far as hydrostatic condition, the electronic spin states from high-spin to mixed-spin to low-spin states occurred at the higher pressures of 45.7 GPa and 50.4 GPa, respectively, which implied the highly sensitive hydrostaticity of electronic spin transition pressures. Upon decompression, the reverse electronic spin transitions from low-spin to mixed-spin to high-spin states were detected at the respective pressures of 47.2 GPa and 28.7 GPa under non-hydrostatic condition, and as well as at the pressures of 49.4 GPa and 25.1 GPa under hydrostatic condition, respectively. The huge pressure hysteresis of 13.8 GPa and 20.6 GPa for the electronic spin state transition was revealed under non-hydrostatic and hydrostatic environments, respectively. In order to explore the effect of temperature on the electronic spin transition, a series of electrical conductivity experiments on siderite were performed over the temperature range of 323–873 K under conditions of three typical pressures of 47.7, 49.8 and 51.6 GPa. Furthermore, the functional relationships between the temperature and pressure describing the high-spin to mixed-spin to low-spin transitions for siderite were successfully established: P1 (GPa) = 39.318 + 0.015 T (K) and P2 (GPa) = 41.277 + 0.018 T (K), respectively. In conclusion, our acquired phase diagram of the electronic spin transition on siderite is beneficial to deep insight into the electronic spin behavior for those of iron-bearing carbonate minerals under high-temperature and high-pressure conditions.

Photophysics of a single quantum emitter based on vanadium phthalocyanine molecules.

Single quantum emitters play a fundamental role in the development of quantum technologies such as quantum repeaters, and quantum information processing. Isolating individual molecules with stable optical emission is an essential step for these applications, especially for those molecules that present large coherence times at room temperature. Among them, vanadium-oxide phthalocyanine (VOPc) molecules stand out as promising candidates due to the large coherence times of their ground state electronic spin, which are on the order of microseconds when measured in the ensemble. However, the optical properties of such VOPc molecules at the single emitter level have not yet been reported. Here we show that single VOPc molecules with stable optical properties at room temperature can be isolated. We find that the optical response of the molecule under laser illumination of different polarizations agrees well with a system having pyramidal C4v symmetry. Furthermore, we provide theoretical calculations that support our experimental findings and provide insight into the role of phonons and the internal electronic structure of the molecule. These results demonstrate that this single paramagnetic molecule can function as a single quantum emitter while displaying optical stability under ambient conditions to have their intrinsic properties investigated.

Transition from amorphous to crystalline in FeW oxides: Alterations in active center spin state to improve OER performance

Amorphous and crystalline catalysts both have their own advantages to reduce the overpotential of OER. However, there is limited research on the relationship between the OER catalytic performance and the crystallinity degree. Herein, this key issue was explored by preparing FeW oxides with varying degrees of crystallinity. DFT combined with practical experimental results indicate that the change in crystalline state not only affects the electronic interactions in Fe-W-O but also the M-O bond lengths, both influencing the spin state of FeW oxides. At the critical temperature of amorphous-to-crystalline transition, a low-spin state of Fe in FeWO-450 is found to optimize the adsorption of intermediates during OER. FeWO-450 exhibits even better performance than commercial noble metal catalysts and numerous catalysts reported in the literature. This work showcases the effect of crystallinity of metal oxides on electron spin and offer a guidance how to improve OER properties by altering the electron spin states.

Identifying Sources of Entanglement Loss in Photodriven Molecular Electron Spin Teleportation.

We report on an electron donor-electron acceptor-stable radical (D-A-R•) molecule in which an electron spin state first prepared on R• is followed by photogeneration of an entangled singlet 1[D•+-A•-] spin pair to produce D•+-A•--R•. Since the A•- and R• spins within D•+-A•--R• are uncorrelated, spin teleportation from R• to D•+ occurs with a maximal 25% efficiency only for the singlet pair 1(A•--R•) by spin-allowed electron transfer from A•- to R•. However, since 1[D•+-A•-] is sufficiently long-lived, coherent spin mixing involving the unreactive 3(A•--R•) population affects entanglement and teleportation within D•+-A•--R•. Pulse electron paramagnetic resonance experiments show a direct correlation between electron spin flip-flops and entanglement loss, providing information for designing molecular materials to serve as nanoscale quantum device interconnects.

Temporal Separation between Lattice Dynamics and Electronic Spin‐State Switching in Spin‐Crossover Thin Films Evidenced by Time‐Resolved X‐Ray Diffraction

AbstractSpin‐crossover (SCO) complexes have drawn significant attention for the possibility to photoswitch their electronic spin state on a sub‐picosecond timescale at the molecular level. However, the multi‐step mechanism of laser‐pulse‐induced switching in solid state is not yet fully understood. Here, time‐resolved synchrotron X‐ray diffraction is used to follow the dynamics of the crystal lattice in response to a picosecond laser excitation in nanometric thin films of the SCO complex [Fe(HB(1,2,4‐triazol‐1‐yl)3)2]. The observed structural dynamics unambiguously reveal a lattice expansion on the 100 picosecond timescale, which is temporally decoupled both from the ultrafast molecular photoswitching process (occurring within 100 fs) and from the delayed, thermo‐elastic (Arrhenius‐driven) conversion (taking place ≈10 ns). These time‐separated dynamics are also manifested by the observation of damped acoustic oscillations in the time evolution of the lattice volume, whereas no such oscillations are observed in the electronic spin‐state dynamics. Overall, these results suggest the existence of a universal behavior whereby the intramolecular energy barrier between low‐spin and high‐spin states acts as an intrinsic dynamical bottleneck in the out‐of‐equilibrium spin‐state switching dynamics of SCO materials.

Promoting Polysulfide Redox Reactions through Electronic Spin Manipulation.

Catalytic additives able to accelerate the lithium-sulfur redox reaction are a key component of sulfur cathodes in lithium-sulfur batteries (LSBs). Their design focuses on optimizing the charge distribution within the energy spectra, which involves refinement of the distribution and occupancy of the electronic density of states. Herein, beyond charge distribution, we explore the role of the electronic spin configuration on the polysulfide adsorption properties and catalytic activity of the additive. We showcase the importance of this electronic parameter by generating spin polarization through a defect engineering approach based on the introduction of Co vacancies on the surface of CoSe nanosheets. We show vacancies change the electron spin state distribution, increasing the number of unpaired electrons with aligned spins. This local electronic rearrangement enhances the polysulfide adsorption, reducing the activation energy of the Li-S redox reactions. As a result, more uniform nucleation and growth of Li2S and an accelerated liquid-solid conversion in LSB cathodes are obtained. These translate into LSB cathodes exhibiting capacities up to 1089 mA h g-1 at 1 C with 0.017% average capacity loss after 1500 cycles, and up to 5.2 mA h cm-2, with 0.16% decay per cycle after 200 cycles in high sulfur loading cells.

Advancing photopolymerization and 3D printing: High-Performance NiII complexes bearing N2O2 Schiff-base ligands as photocatalysts

New high-performance photocatalysts based on metal structures are being developed for polymerization. However, using low-cost metals while ensuring effectiveness is challenging. In this study, two NiII complexes NiL1 and NiL2 were synthesized using N2O2 Schiff-base ligands bearing π-extended rings (naphthaldehyde (H2L1) and phenylsalicylaldehyde (H2L2) groups), respectively. These complexes were characterized by FTIR, UV–Vis and 1H NMR spectroscopy, elemental analysis, cyclic voltammetry, and MALDI-TOF mass spectrometry. NiL1 and NiL2 were evaluated in photoinitiating system as new photocatalysts for the Free Radical Photopolymerization of Ethoxylated (3) Trimethylolpropane Triacrylate (TMPETA) for violet and green light. Three-component systems were employed in the presence of Di-tert-butyl-diphenyl iodonium hexafluorophosphate (Iod) and ethyl dimethylaminobenzoate (EDB). The absorption, luminescence, and redox properties of nickel complexes and ligands were explored and compared for a better understanding of their structure/reactivity relationship. The designed nickel complexes showed good photoinitiation abilities. NiL2 exhibited the highest monomer conversion, and it was investigated in the on–off process under green light irradiation, demonstrating the efficiency of the system in reactivating the polymerization process. An oxidative pathway mechanism was proposed based on free energy, steady state photolysis and electron spin resonance spin trapping experiments. The best system was successfully applied in cationic photopolymerization and 3D printing.

Wireless Powered Microwave-Light Conversion Platform with Dual-Stimulus Nanoresponder Coating for Deep-Seated Photodynamic Therapy.

Traditional external field-assisted therapies, e.g., microwave (MW) therapy and phototherapy, cannot effectively and minimally damage eliminate deep-seated infection, owing to the poor penetrability of light and low reactive oxygen species (ROS) stimulation capability of MW. Herein, an implantable and wireless-powered therapeutic platform (CNT-FeTHQ-TS), in which external MW can be converted into internal light via MW wireless-powered light-emitting chips, is designed to eradicate deep-seated tissue infections by MW-induced deep-seated photodynamic therapy. In application, CNT-FeTHQ-TS is implanted at internal lesions, and the chip emits light under external MW irradiation. Subsequently, CNT-FeTHQ coating in the platform can respond to both MW and light simultaneously to generate ROS and MW-hyperthermia for rapid and precise sterilization at focus. Importantly, MW also improves the photodynamic performance of CNT-FeTHQ by introducing vacancies in FeTHQ to facilitate the photoexcitation process and changing the spin state of electrons to inhibit the complexation of photogenerated electron-hole pairs, which were confirmed by simulation calculations and in situ MW-irradiated photoluminescence experiments. In vivo, CNT-FeTHQ-TS can effectively cure mice with Staphylococcus aureus infection in dorsal subcutaneous tissue. This work overcomes the key clinical limitations of safe energy transmission and conversion for treating deep-seated infections.

Synthesis, Characterization, and Reactivity of Bispidine-Iron(IV)-Tosylimido Species.

Reported are the synthesis and detailed studies of the iron(IV)-tosylimido complexes of two isomeric pentadentate bispidine ligands (bispidines are 3,7-diazabicyclo[3.3.1]nonane derivatives). This completes a series of five tosylimido complexes with comparable pentadentate amine/pyridine ligands, where the corresponding [(L)FeIV═O]2+ oxidants have been studied in detail. The characterization of the two new complexes in solution (UV-vis-NIR, Mössbauer, HR-ESI-MS) shows that these oxidants have an intermediate spin (S = 1) electronic ground state. The reactivities have been studied as oxidants in C-H activation at 1,3-cyclohexadiene and nitrogen atom transfer to thioanisole. For the latter substrate, the entire set of data for the five ligands and for both nitrogen and oxygen atom transfer is now available and the interesting observation is that oxygen atom transfer is, as expected, generally faster than nitrogen atom transfer, with the exception of the two ligands that have four and three pyridine groups oriented parallel to the Fe-O and Fe-N axes. A thorough DFT analysis indicates that this is due to steric effects in the case of the [(L)FeIV═O]2+ species, which are less important in the [(L)FeIV═NTs]2+ compounds due to partial electron transfer from the thioanisole substrate to the iron(IV)-tosylimido oxidant.

Regulating the Critical Intermediates of Dual-Atom Catalysts for CO2 Electroreduction.

Electrocatalysis is a very attractive way to achieve a sustainable carbon cycle by converting CO2 into organic fuels and feedstocks. Therefore, it is crucial to design advanced electrocatalysts by understanding the reaction mechanism of electrochemical CO2 reduction reaction (eCO2RR) with multiple electron transfers. Among electrocatalysts, dual-atom catalysts (DACs) are promising candidates due to their distinct electronic structures and extremely high atomic utilization efficiency. Herein, the eCO2RR mechanism and the identification of intermediates using advanced characterization techniques, with a particular focus on regulating the critical intermediates are systematically summarized. Further, the insightful understanding of the functionality of DACs originates from the variable metrics of electronic structures including orbital structure, charge distribution, and electron spin state, which influences the active sites and critical intermediates in eCO2RR processes. Based on the intrinsic relationship between variable metrics and critical intermediates, the optimized strategies of DACs are summarized containing the participation of synergistic atoms, engineering of the atomic coordination environment, regulation of the diversity of central metal atoms, and modulation of metal-support interaction. Finally, the challenges and future opportunities of atomically dispersed catalysts for eCO2RR processes are discussed.

Boosting the Zn2+ storage capacity of MoO3 nanoribbons by modulating the electrons spin states of Mo via Ni doping

Aqueous zinc-ion batteries (AZIBs) have received considerable potential for their affordability and high reliability. Among potential cathodes, α-MoO3 stands out due to its layered structure aligned with the (010) plane, offering extensive ionic insertion channels for enhanced charge storage. However, its limited electrochemical activity and poor Zn2+ transport kinetics present significant challenges for its deployment in energy storage devices. To overcome these limitations, we introduce a new strategy by doping α-MoO3 with Ni (Ni-MoO3), tuning the electron spin states of Mo. Thus modification can activate the reactivity of Ni-MoO3 towards Zn2+ storage and weaken the interaction between Ni-MoO3 and intercalated Zn2+, thereby accelerating the Zn2+ transport and storage. Consequently, the electrochemical properties of Ni-MoO3 significantly surpass those of pure MoO3, demonstrating a specific capacity of 258 mAh g−1 at 1 A g−1 and outstanding rate performance (120 mAh g−1 at 10 A g−1). After 1000 cycles at 8 A g−1, it retains 76 % of the initial capacity, with an energy density of 154.4 Wh kg−1 and a power density of 11.2 kW kg−1. This work proves that the modulation of electron spin states in cathode materials via metal ion doping can effectively boost their capacity and cycling durability.

Leveraging electron spin driven photocatalytic hydrogen evolution ability of BiVO4 via crystal facet engineering and iron ion infiltration strategies

An electron spin regulated hydrogen evolution reaction (HER) for photocatalyst is significant to understand the underlying photocatalytic mechanism. Here, the iron with gradient distribution in BiVO4 can successfully activate HER of Fe-BiVO4. Mechanical performance calculations indicate that doped Fe3+ replacing V site can form stable chemical structure for BiVO4. Theoretical calculations suggest that the photo-generated electrons migrate from bulk to defect sites in surface layers of Fe-BiVO4. The doped Fe ions effectively improves the carrier transport ability and significantly reduces the carrier recombination probability. Electron spin state change of the 1Fe-BiVO4 (Mag) enhances evidently the current density in photocatalysis, and increases markedly the HER performance compared with that of 1Fe-BiVO4. More importantly, the magnetization further prolongs carrier lifetime and optimizes rate determining step free energy of water dissociation for Fe-BiVO4. Our work opens a new way to understand the effect of magnetic field controlling spin states on photocatalytic HER.