Electron Spin States Research Articles

X-ray and Nuclear Spectroscopies to Reveal the Element-Specific Oxidation States and Electronic Spin States for Nanoparticulated Manganese Cyanidoferrates and Analogs

In this publication, the potential non-gadolinium magnetic resonant imaging agent—nanoparticulate K2Mn[Fe(CN)6]—its comparison sample KFe[Co(CN)6], as well as their reference samples were measured and analyzed using Mn, Co and Fe L-edge X-ray absorption spectroscopy (L XAS). From the information obtained, we conclude that K2Mn[Fe (CN)6] has a high spin (hs)-Mn(II) and a low spin (ls)-Fe(II), while KFe[Co(CN)6] has an hs-Fe(II) and an ls-Co(III). In these Prussian blue (PB) analog structures, the L XAS analysis also led to the conclusion that the hs-Mn(II) in K2Mn[Fe(CN)6] or the hs-Fe(II) in KFe[Co(CN)6] bonds to the N in the [M(CN)6]4−/3− ions (where M = Fe(II) or Co(III)), while the ls-Fe(II) in K2Mn[Fe(CN)6] or the ls-Co(III) in KFe[Co(CN)6] bonds to the C in the [M(CN)6]4−/3− ion, suggesting the complexed metalloligand [Mn(II) or Fe(II)] occupies the N-bound site in PB. Then, nuclear resonant vibrational spectroscopy (NRVS) was used to confirm the results from the L XAS measurements: the Mn(II), Eu(III), Gd(III), Fe(II) cations complexed by [M(CN)6]n−-metalloligand all take the N-bound site in PB-like structures. Our NRVS studies also prove that iron in the K2Mn[Fe(CN)6] compound has a 2+ oxidation state and is surrounded by the C donor atoms in the [M(CN)6]n− ions.

Exploring the physical behavior of surface-functionalized two-dimensional Tungsten carbide/nitride MXenes

In this article, we present a study of the properties of two-dimensional (2D) derivatives of MAX phases, namely W2XT2 (X = C, N; T = O, F) MXenes, which have become hot spots of research for their intriguing physical properties. In pursuing this first-principles study, we realized W2X pristine MXene by eliminating the Ga atomic layer from the W2GaX MAX phase, which is then functionalized with oxygen and fluorine. These materials exhibit electronic states above the Fermi level primarily of W-d nature, indicating their metallic nature similar to the parent MAX phases. The distribution of up and down spin electronic states is highly symmetrical, depriving the W2XT2 MXenes of spontaneous magnetization. They demonstrated prominent optical properties where the W2NF2 exhibits approximately 70% reflection of infrared (IR) light, while W2CF2 reflects around 47%. On the contrary, W2NO2 and W2CO2 reflect 33% and 20% of the incident IR light, respectively. At an energy of 0 eV, the refractive indices recorded for W2CF2, W2CO2, W2NF2, and W2NO2 were 5.11, 2.29, 8.56, and 3.47, respectively. When exposed to IR light, they showed remarkable ultraviolet (UV) light absorption of 23.62 × 104 cm−1 and 20.71 × 104 cm−1 for W2NF2 and W2CF2, respectively. The absorption of IR light by W2CO2 and W2NO2 was relatively smaller, with values of 12.52 × 104 cm−1 and 8.30 × 104 cm−1, respectively. The interesting optical characteristics of the W2XT2 MXene make them promising for utilization in advanced optical devices.

On readout and initialisation fidelity by finite demolition single shot readout

Abstract Ideal projective quantum measurement makes the system state collapse in one of the observable operator eigenstates | ϕ α ⟩ , making it a powerful tool for preparing the system in the desired pure state. Nevertheless, experimental realisations of projective measurement are not ideal. During the measurement time needed to overcome the classical noise of the apparatus, the system state is often (slightly) perturbed, which compromises the fidelity of initialisation. In this paper, we propose an analytical model to analyse the initialisation fidelity of the system performed by the single-shot readout. We derive a method to optimise parameters for the three most used cases of photon counting based readouts for NV colour centre in diamond, charge state, nuclear spin and low temperature electron spin readout. Our work is of relevance for the accurate description of initialisation fidelity of the quantum bit when the single-shot readout is used for initialisation via post-selection or real-time control.

Optimizing the Electron Spin States of Na4Fe3(PO4)2P2O7 Cathodes via Mn/F Dual‐Doping for Enhanced Sodium Storage

AbstractA NASICON‐type Mn/F dual‐doping Na4Fe3(PO4)2P2O7 cathode material is successfully synthesized via a spray drying method. A medium‐spin of Fe is measured by DFT calculation, X‐ray absorption near edge structure (XANES), temperature‐dependent magnetization susceptibility (M−T) measurement, and electron paramagnetic resonance (EPR) tests. It indicates that the eg orbital occupation of Fe2+ can be finely regulated, thus optimizing the bond strength between the oxidation and reduction processes. Furthermore, from UV−vis DRS and four‐point probe conductivity measurements, it can be seen that, after adjusting the electron spin states, the band gap of the material has decreased from 1.01 to 0.80 eV, and the electronic conductivity has increased from 8.5 to 24.4 µS cm−1, thereby leading to competitive electrochemical performance. The as‐optimized Na4Fe3(PO4)2P2O7 displays both excellent rate performance (121.0 and 104.9 mAh g−1 at 0.1 C and 5 C, respectively) and outstanding cycling stability (88.5% capacity retention after 1000 cycles at 1 C). The results indicate that this low‐cost Mn/F dual‐doping Na4Fe3(PO4)2P2O7 cathode can be a competitive candidate material for sodium‐ion batteries.

Modulation of electronic spin state and construction of dual-atomic tandem reaction for enhanced pH-universal oxygen reduction

Combining both advances of electronic spin state modulation and tandem reaction mechanism, an atomic-level dual iron-copper catalyst is designed for enhanced oxygen reduction capability. Herein, the intense interaction between the iron-copper site and its coordination environment can not only controls the flow of external charge at the atomic level, but regulates the internal 3d electron configuration. These modulations can optimize the orbital interaction and pair hardness (ηDA) between the acceptor and the donor, and achieves a fast tandem reaction kinetics, thereby surmounting the limitation of Scaling Relation. The as-prepared bimetal catalyst validates a high ORR activity and stability, which even exceed those of the benchmark Pt/C in pH-universal electrolytes. Meanwhile, Fe,Cu/N-C driven Zn-air batteries in alkaline and neutral electrolytes show prominent performance with peak power densities of 173.7 mW cm−2 and 86.5 mW cm−2. This work provides a useful design principle for developing or optimizing other efficient ORR catalysts.

Correlation Study of the Spin-Orbit State-Resolved Scattering of Al(2P) in Oxidation Reaction and Nonreactive Collision.

Spin-orbit coupling plays an important role in chemical reactivity, especially in reactions that require the change of electron spin states. However, it is difficult to measure and analyze the reaction dynamics between spin-orbit splitting states, particularly for splitting states with a small energy difference. In this study, we find that nonreactive scattering of spin-orbit splitting states can provide complementary information that is overlooked in chemical reaction studies. Here, the oxidation reactivities of spin-orbit Al(2P1/2,3/2) states with small energy difference of 112 cm-1 are clearly distinguished in the high rotational AlO(v = 0 and 1, N) products at low collision energy of 507 cm-1 using a laser ablation crossed-beam and time-sliced ion velocity mapping technique, in conjunction with state-selected nonreactive scattering studies. For both the AlO(v = 0 and 1) channels, the spin-orbit relative reactivity σ3/2/σ1/2 increases with the increase of rotational level N of AlO products. However, for AlO(v = 0), the reactivity of the Al(2P3/2) excited state is consistently lower than that of the Al(2P1/2) ground state, whereas for AlO(v = 1), the reactivity of Al(2P3/2) is higher than that of Al(2P1/2) at a higher rotational state. The relative reactivity of spin-orbit split Al(2P) states at different scattering angles shows a more pronounced enhancement of forward scattering relative to side and backward scattering for Al(2P3/2) when a higher rotationally excited AlO is produced. Nonreactive scattering studies of Al(2P) suggest that the Al(2P3/2) state is deexcited to the ground Al(2P1/2) state at the sideways and backward scattering directions, and the deexcitation is supposed to reduce the reactivity of the excited Al(2P3/2) at the corresponding direction.

Spin state-tailored tetrahedral and octahedral cobalt centers on millimetric Co-Al oxide catalysts as dual sites for synergistic peroxymonosulfate activation

Rationally developing millimetric metal catalysts with tailored electron function is crucial for water decontamination, but challenges remain due to insufficient understanding on their electronic structure engineering and the underlying mechanism. Here, through constructing bonded Co-O-Al unit sites on the millimetric γ-Al2O3 spheres, we report a feasible and scalable strategy of modulating the 3d electron configurations and spin states of supported tetrahedral and octahedral cobalt cations just by adjusting the radius of support curvature. The tetrahedral and octahedral cobalt centers with tailored electron spin states showed a synergism in peroxymonosulfate activation to generate SO4• and reactive oxygen (O*), in which the latter was converted into 1O2 and O2•. The electronic structure-oriented spin catalysis affected the formation of reactive species and the pathway of pollutant degradation. This work will stimulate the design and mass production of macroscopic spin catalysts with superior activity, reusability and stability for catalytic water purification.

Electronic structure and spin state regulation of vanadium nitride via a sulfur doping strategy toward flexible zinc-air batteries

Owing to the distinctive structural characteristics, vanadium nitride (VN) is highly regarded as a catalyst for oxygen reduction reaction (ORR) in zinc-air batteries (ZABs). However, VN exhibits limited intrinsic ORR activity due to the weak adsorption ability to O-containing species. Here, the S-doped VN anchored on N, S-doped multi-dimensional carbon (S-VN/Co/NS-MC) was constructed using the solvothermal and in-situ doping methods. Incorporating sulfur atoms into VN species alters the electron spin state of vanadium in the S-VN/Co/NS-MC for regulating the adsorption energy of vanadium sites to oxygen molecules. The introduced sulfur atoms polarize the V 3dz2 electrons, shifting spin-down electrons closer to the Fermi level in the S-VN/Co/NS-MC. Consequently, the introduction of sulfur atoms into VN species enhances the adsorption energy of vanadium sites for oxygen molecules. The *OOH dissociation transitions from being unspontaneous on the VN surface to a spontaneous state on the S-doped VN surface. Then, the ORR barrier on the S-VN/Co/NS-MC surface is reduced. The S-VN/Co/NS-MC demonstrates a higher half-wave potential and limiting current density compared to the VN/Co/N-MC. The S-VN/Co/NS-MC-based liquid ZABs display a power density of 195.7 mW cm−2, a specific capacity of 815.7 mA h g−1, and a cycling stability exceeding 250 h. The S-VN/Co/NS-MC-based flexible ZABs are successfully employed to charge both a smart watch and a mobile phone. This approach holds promise for advancing the commercial utilization of VN-based catalysts in ZABs.

First principles studies of adsorption of H2S on vacancy defected and transition metal-doped phosphorene-graphene heterostructures

ABSTRACT The adsorption stability, geometry, and electronic and magnetic properties of H2S adsorbed on pristine, vacancy defected, and transition metal (TM)-doped phosphorene-graphene (PG) heterostructures were calculated using density functional theory. In pristine and vacancy defected PG systems, the interaction between H2S and the heterostructure was weak, and the mechanism was physical adsorption. After TM-doping (Ti, V, Cr, Mn, Co, and Ni), the strong orbital hybridisation between the dopant and H2S significantly enhanced the interaction between H2S and the doped heterostructures, and the physisorption mechanism of H2S changed to chemical adsorption. The adsorption energy and desorption time of H2S molecules on Mn-doped PG heterostructures was suitable, which can be applied as sensors to detect H2S gas. The density of states of Cr- and Mn-doped PG heterostructures exhibited asymmetric electron spin states, indicating the existence of magnetic moments. Thus, introducing defects and TM dopants on PG heterostructures can improve H2S sensitivity, providing a theoretical basis for developing gas detection sensors.

Artificial Neural Network-Based Density Functional Approach for Adiabatic Energy Differences in Transition Metal Complexes.

During the past decades, approximate Kohn-Sham density functional theory schemes have garnered many successes in computational chemistry and physics, yet the performance in the prediction of spin state energetics is often unsatisfactory. By means of a machine learning approach, an enhanced exchange and correlation functional is developed to describe adiabatic energy differences in transition metal complexes. The functional is based on the computationally efficient revision of the regularized, strongly constrained, and appropriately normed functional and improved by an artificial neural network correction trained over a small data set of electronic densities, atomization energies, and/or spin state energetics. The training process, performed using a bioinspired nongradient-based approach adapted for this work from the particle swarm optimization, is analyzed and discussed extensively. The resulting machine learned meta-generalized gradient approximation functional is shown to outperform most known density functionals in the prediction of adiabatic energy differences for a diverse set of transition metal complexes with varying local coordinations and metal choices.

Direct observation of chirality-induced spin selectivity in electron donor-acceptor molecules.

The role of chirality in determining the spin dynamics of photoinduced electron transfer in donor-acceptor molecules remains an open question. Although chirality-induced spin selectivity (CISS) has been demonstrated in molecules bound to substrates, experimental information about whether this process influences spin dynamics in the molecules themselves is lacking. Here we used time-resolved electron paramagnetic resonance spectroscopy to show that CISS strongly influences the spin dynamics of isolated covalent donor-chiral bridge-acceptor (D-Bχ-A) molecules in which selective photoexcitation of D is followed by two rapid, sequential electron-transfer events to yield D•+-Bχ-A•-. Exploiting this phenomenon affords the possibility of using chiral molecular building blocks to control electron spin states in quantum information applications.

Topological Design and Synthesis of High-Spin Aza-triangulenes without Jahn-Teller Distortions.

The atomic doping of open-shell nanographenes enables precise tuning of their electronic and magnetic states, which is crucial for their promising potential applications in optoelectronics and spintronics. Among this intriguing class of molecules, triangulenes stand out with their size-dependent electronic properties and spin states, which can also be influenced by the presence of dopant atoms and functional groups. However, the occurrence of Jahn-Teller distortions in such systems can have a crucial impact on their total spin and requires further theoretical and experimental investigation. In this study, we examine the nitrogen-doped aza-triangulene series via a combination of density functional theory and on-surface synthesis. We identify a general trend in the calculated spin states of aza-[n]triangulenes of various sizes, separating them into two symmetry classes, one of which features molecules that are predicted to undergo Jahn-Teller distortions that reduce their symmetry and thus their total spin. We link this behavior to the location of the central nitrogen atom relative to the two underlying carbon sublattices of the molecules. Consequently, our findings reveal that neutral centrally doped aza-triangulenes have one less radical than their undoped counterparts, irrespective of their predicted symmetry. We follow this by demonstrating the on-surface synthesis of π-extended aza-[5]triangulene, a large member of the higher symmetry class without Jahn-Teller distortions, via a simple one-step annealing process on Cu(111) and Au(111). Using scanning probe microscopy and spectroscopy combined with theoretical calculations, we prove that the molecule is positively charged on the Au(111) substrate, with a high-spin quintet state of S = 2, the same total spin as undoped neutral [5]triangulene. Our study uncovers the correlation between the dopant position and the radical nature of high-spin nanographenes, providing a strategy for the design and development of these nanographenes for various applications.

Dual Breaking of Molecular Orbitals and Spatial Symmetry in an Optically Controlled Ferroelectric.

As particles carry quantified energy, photon radiation enables orbital transitions of energy levels, leading to changes in the spin state of electrons. The resulting switchable structural bistability may bring a new paradigm for manipulating ferroelectric polarization. However, the studies on molecular orbital breaking in the ferroelectric field remain blank. Here, for the first time, a new mechanism of ferroelectrics-dual breaking of molecular orbitals and spatial symmetry, demonstrated in a photochromic organic crystal with light-induced polarization switching, is formally proposed. By alternating the ultraviolet/visible light irradiation, the states of electron spin and the radial distribution p atomic orbitals experience a change, showing a reversible switch from "shoulder-to-shoulder" form to a "head-to-head" form. This reflects a reversible conversion between π and σ bonds, which induces and couples with the variation of spatial symmetry. The intersection of spatial symmetry breaking and molecular orbital breaking in ferroelectrics present in this work will be more conducive to data encryption and anticounterfeiting.

Modulating the electronic spin state of atomically dispersed iron sites by adjacent zinc atoms for enhanced spin-dependent oxygen electrocatalysis

Modulating the electronic spin state of atomically dispersed iron sites by adjacent zinc atoms for enhanced spin-dependent oxygen electrocatalysis

Unraveling the Photophysical Characteristics, Aromaticity, and Stability of π-Extended Acene-Quinodimethyl Thioamides†.

Poly-aromatic systems that contain quinodimethyl (QDM) units are appealing for several photonic and spintronic applications owing to the unique electronic structure, aromaticity, and spin state(s) of the QDM ring. Herein, we report the synthesis and characterization of novel QDM-based chromophores 1-3, which exhibit unique photo-excited behavior and aromaticity. Extending the aromatic core with a biphenyl/phenanthryl- and a pyrrolo-fragment led to reducing the optoelectronic bandgap and modulating the photophysics QDM 1-3. Yet, QDM 2 and 3 suffer from "aromaticity imbalance" and become relatively unstable compared to the parent compound QDM 1. Further assessment of local aromaticity using computational tools revealed that the pseudo-quinoidal ring B is the main driving force allowing to easily populate the excited triplet state of these chromophores. The present study provides complementary guidelines for designing novel non-classical poly-aromatic systems.

Effect of high magnetic field treatment on the microstructure and mechanical properties of Ti-48Al-2Cr-2Nb alloy prepared by powder-hot isostatic pressing

The microstructure and mechanical properties of Ti-48Al-2Cr-2Nb alloy prepared by powder-hot isostatic pressing have been adjusted by high magnetic field treatment. Results show high magnetic field treatment not just refines the duplex microstructures but increases the proportion of CSL boundaries for the γ phase, and accordingly improves the strength and elongation of Ti-48Al-2Cr-2Nb alloy. Particularly, the ultimate tensile strength increases to 440 MPa and the room elongation increases from 0.4% to 1% after holding for 3 h at 1260℃ in the 10 T magnetic field. Magnetoplastic effect, changing the dislocation characteristics due to the transformation of electron spin state, well clarifies the alteration of microstructures features and the improvement of mechanical properties of TiAl alloys. This work points out the significant role of high magnetic field treatment on the regulation of the microstructure and mechanical properties of TiAl alloys.

Magnetic carbon fiber/reduced graphene oxide film for electromagnetic microwave absorption

Adding 10 wt% carbon fiber (CF) into graphene oxide (GO) dispersion were performed to fabricate CF10/reduced graphene oxide (rGO) film without the use of surfactants, binders or polymer matrices. The all-carbon CF10/rGO film possesses plausible tensile strength over one page of regular A4 printing paper and improved room-temperature ferromagnetism compared with the as-assembled rGO film, with saturation magnetization of about 0.327 emu/g and coercivity of about 100.4 Oe. The CF10/rGO composite with 50 wt% filler loading exhibits a good electromagnetic wave (EMW) absorption performance in the measured frequency range of 2–18 GHz. A minimal reflection loss reaches −34.3 dB@6.2 GHz (C-band), −35.4 dB@9.6 GHz (X-band), and −33.7 dB@13.1 GHz (Ku-band) with a thickness of 3.0 mm, 2.0 mm and 1.5 mm, respectively. The enhanced complex permittivity and permeability causing by the introduction of CF in rGO film are in favor of achieving an excellent impedance matching characteristic between the carbon materials and the air, responsible for more amount of EMW incidence; furthermore, localized electronic spin states and multi-relaxation processes arisen from the topological defects, oxygen-containing groups, and interfaces are ascribed to the enhanced microwave attenuation ability.

A Theoretical Analysis of the Differential Chemical Reaction Results Caused by Chirality Induction.

The theory of electron spin has been proposed for a century, but the study of quantum effects in biological molecules is still in its infancy. Chirality-induced spin selectivity (CISS) is a very modern theory that can explain many biochemical phenomena. In this paper, we propose a new theoretical model based on CISS theory and quantum chemistry theory, which can well explain the theoretical explanation of the chiral selectivity of chiral proteins. Moreover, this theory can predict the spin state of corresponding chiral molecules. Taking the L-DOPA and AADC enzymes as examples, this theoretical model elucidates the AADC enzyme's chiral catalysis selectivity and successfully predicts the spin state of L-DOPA and D-DOPA's valence electrons.

Phase transition engineering of nanoporous pyrite-phase NiSe2 foam by phosphorus doping for robust pH-universal hydrogen evolution

The present non-precious hydrogen-evolving electrocatalysts deliver high catalytic activity either in acidic or basic media but very few simultaneously exhibit superb catalytic efficiency and stability for hydrogen evolution reaction (HER) in a wide pH range, especially for pyrite-phase materials (e.g., CoS2, NiSe2), probably due to their high kinetic energy barriers of initial water dissociation process. Herein, we report a phase transition engineering of pyrite-phase porous NiSe2 into NiP1.86Se0.14 by heavy phosphorus doping, which performs excellently as a pH-universal electrocatalyst for HER. In this material, P atom replaces the sub-selenium atom in NiSe2 to modulate the electronic structures and spin states of Ni sites with lower d-band center, thus promoting sluggish hydrogen adsorption, water adsorption, and dissociation dynamics. As a result, this catalyst exhibits superior hydrogen-evolving catalytic activity in multiple media in terms of relatively low overpotentials of 56.8 and 79 mV at a current density of 10 mA cm−2 in 0.5 M H2SO4 and 1.0 M KOH, respectively. Particularly, this porous NiP1.86Se0.14 shows good stability toward hydrogen evolution in both acidic and alkaline media, with little variation in potentials after continuous operation for approximately 80 and 70 h at 30 mA cm−2. This work may provide a promising solution to address the poor catalytic HER activity and instability of transition metal selenides under alkaline conditions.

Rh19-: A high-spin super-octahedron cluster.

Probing atomic clusters with magic numbers is of supreme importance but challenging in cluster science. Pronounced stability of a metal cluster often arises from coincident geometric and electronic shell closures. However, transition metal clusters do not simply abide by this constraint. Here, we report the finding of a magic-number cluster Rh19- with prominent inertness in the sufficient gas-collision reactions. Photoelectron spectroscopy experiments and global-minimum structure search have determined the geometry of Rh19- to be a regular Oh‑[Rh@Rh12@Rh6]- with unusual high-spin electronic configuration. The distinct stability of such a strongly magnetic cluster Rh19- consisting of a nonmagnetic element is fully unveiled on the basis of its unique bonding nature and superatomic states. The 1-nanometer-sized Oh-Rh19- cluster corresponds to a fragment of the face-centered cubic lattice of bulk rhodium but with altered magnetism and electronic property. This cluster features exceptional electron-spin state isomers confirmed in photoelectron spectra and suggests potential applications in atomically precise manufacturing involving spintronics and quantum computing.