A low-noise X-band microwave source with digital automatic frequency control for electron paramagnetic resonance spectroscopy

We report a new design of microwave source for X-band electron paramagnetic resonance spectrometer.The microwave source is equipped with a digital automatic frequency control circuit.The parameters of the digital automatic frequency control circuit can be flexibly configured for different experimental conditions,such as the input powers or the quality factors of the resonator.The configurability makes the microwave source universally compatible and greatly extends its application.To demonstrate the ability of adapting to various experimental conditions,the microwave source is tested by varying the input powers and the quality factors of the resonator.A satisfactory phase noise as low as-135 d Bc/Hz at 100-k Hz offset from the center frequency is achieved,due to the use of a phase-locked dielectric resonator oscillator and a direct digital synthesizer.Continuous-wave electron paramagnetic resonance experiments are conducted to examine the performance of the microwave source.The outstanding performance shows a prospect of wide applications of the microwave source in numerous fields of science.

Electron paramagnetic resonance characterization of aluminum ion implantation-induced defects in 4H-SiC

Deep-level defects in silicon carbide(SiC)are critical to the control of the performance of SiC electron devices.In this paper,deep-level defects in aluminumion-implanted 4H-SiC after high-temperature annealingwere studied using electron paramagnetic resonance(EPR)spectroscopy at temperatures of 77 K and 123 K under different illumination conditions.Results showed that the main defect in aluminum ion-implanted 4H-SiC was the positively charged carbon vacancy(VC+),and the higher the doping concentration was,the higher was the concentration of VC+.Itwas found that the type of material defectwas independent of the doping concentration,although more VC+defects were detected during photoexcitation and at lower temperatures.These results should be helpful in the fundamental research of p-type 4H-SiC fabrication in accordance with functional device development.

Electron paramagnetic resonance studies of the chelate-based ionic liquid in different solvents

The electron paramagnetic resonance spectra of the chelate-based ionic liquid[C_(10)mim][Cu(F_6-acac)_3]in different solvents have been obtained at 120 K.It was found that the values of the^(63)Cu hyperfine coupling constants(A_(IL))of[C_(10)mim][Cu(F_6-acac)_3]in molecular solvents were from 116 to 180 Gauss.Moreover,the A_(IL)values in general ionic liquids are more complicated,and two sets of peaks can often be observed in their electron paramagnetic resonance spectra.Based on the Kamlet-Taft parameters,relative permittivity,the experimental results were discussed in terms of solvation effect and coordination of the solvents.

Developing in situ electron paramagnetic resonance characterization for understanding electron transfer of rechargeable batteries

Electrochemical energy storage devices are pivotal in achieving“carbon neutrality”by enabling the storage of energy generated from renewable sources.To facilitate the development of these devices,it is important to gain insight into the underlying the single-/multi-electron transfer process.This can be achieved through in-time detection under operational conditions,but there are limited tools available for monitoring electron transfer under operando conditions.Electron paramagnetic resonance(EPR)is a powerful technique that can meet these expectations,as it is highly sensitive to unpaired electrons and can detect changes of paramagnetic centres.Despite the long history of in situ electrochemical EPR research,its potential has been surprisingly underutilized due to the need for strict operando cell design under special testing conditions.This review comprehensively summarizes recent efforts to understand energy storage mechanisms using in situ/operando EPR,with the aim of drawing researchers’attention to this powerful technique.After introducing the fundamental principles of EPR,we describe the critical advances made in detecting batteries using operando EPR,along with the remaining challenges and opportunities for future development of this technology in batteries.We emphasize the need for strict operando cell design and the importance of designing experiments that closely mimic real-world conditions.We believe that this review will provide innovative solutions to solve tough problems that researchers may encounter during their battery research,and ultimately contribute to the development of more efficient and sustainable energy storage devices.

Development of 3-actoxymethoxycarbonyl-2,2,5,5-tetramethyl-1-pyrrolidinyloxyl as an electron paramagnetic resonance imaging reagent for in vivo mapping brain oxygen distribution and infarction in ischemic brain

Measurement of oxygen concentration and distribution in brain is essential to understanding the pathophysiology of stroke. Although brain oxygen level is critical for brain tissue survival,

Correlations between trace elements in pyrite and gold mineralization of gold deposits on the North China platform

By studying both the microscopic physical and chemical typomorphic characteristics of typical mineral pyrite samples associated with representative gold deposits on the north-central margin of the North China Platform,this paper seeks to identify macroscopic metallogenic mechanisms of gold deposits and to reveal the formation mechanism of lattice gold in pyrite.Typomorphic characteristics of pyrite reveal that pyrite grain size has a negative correlation with gold content.Cubic pyrite,as the dominant crystal form,contains more gold than pentagonal dodecahedral pyrite.Both pyrite crystal forms and chemical compositions indicate that the replacement style of gold deposit formed in a low saturability,low sulfur fugacity,and at temperatures either much higher or much lower than its best forming temperature;comparatively,that of the quartz vein style of gold deposit occurred under conditions with the best temperature,rich in sulfur,and with high sulfur fugacity.The Au/Ag ratios of the pyrites show that both the replacement and quartz vein styles of deposits are mesothermal and hypothermal,while the Co/Ni ratios of the pyrites indicate that the quartz vein style is of magmatic-hydrothermal origin.The X-ray diffraction intensity of pyrite rich in gold is lower than that of pyrite poor in gold at the quartz vein style.In general,with an increase in gold content in pyrite,the total sum intensityΣI decreases.The pyroelectricity coefficient has a negative correlation trend with the values of(Co+Ni+Se+Te)-As and(Co+Ni+Se+Te)/As.The pyrite pyroelectricity of the replacement style is N-type,indicating that it formed under low sulfur fugacity,while that of the quartz vein style is a mixture of P-N types,indicating that it formed under high sulfur fugacity.On the pyroelectricity-temperature diagram,pyrite of the replacement style is mainly distributed between 200 and 270°C,while that of the quartz vein style varies between 90–118 and274–386°C,demonstrating a multistage forming process.In contrast to previous researchers'conclusions,the authors confirm the existence of lattice gold in pyrites through the use of an electron paramagnetic resonance(EPR)test.Au in the form of Au~+,entering pyrite as an isomorph and producing electron–hole centers,makes the centers produce spin resonance absorption and results in EPR absorption peak II.The intensity of auriferous pyrite absorption peak II has certain direct positive correlations with pyrite gold content.The#I and#III absorption peaks of pyrites possibly result from the existence of Ni^(2+)and/or Cu^(2+).γ1,γ2,andγ3 are the strongest and most typical absorption peaks of the infrared spectra of the pyrites.Generally,with the increase in gold content in the pyrite samples,γ1,γ2,andγ3 tend to shift to higher wavenumbers,and the gold content in the pyrite samples has a positive correlation with their relative absorbance.

Thermoluminescent response of gamma irradiated Na^(+)–Cu^(+) ionexchanged silicate glass in large dose range

The introduction of metals into vitreous matrices is the origin of various interesting phenomena;in particular,the presence of copper ions in glass has been the subject of considerable research because of its numerous applications.The ion-exchange process is primarily used to introduce copper ions into glass matrices.The thermoluminescence(TL)of silicate glass was studied to evaluate its potential as gamma-sensitive material for dosimetric applications;the effect of copper doping on the thermoluminescent sensitivity was investigated using the Cu-Na ion-exchange technique for different concentrations and doping conditions,over a wide dose range of 10 mGy to 100 kGy.The results showed that Cu doping significantly improved the sensitivity of the glasses to gamma radiation.After the ion-exchange,two peaks appeared in the glow curves at approximately 175 and 230°C,respectively,which possibly originated from the Cu^(+) centers,along with a weak TL peak at around 320℃.We also attempted to explain the origin of the observed thermoluminescence by exploiting the Electron paramagnetic resonance(EPR)spectra.The results clearly show quenching of the TL emission with increasing copper concentrations.The present work indicates that the thermoluminescence response of these glasses to gamma rays can be reasonably measured in the range of 0.001-100 kGy.This study also facilitates the understanding of the basic TL mechanism in this glass system.

Chemical and physical characteristics of quartz from gold deposits in the North China platform: relationship to gold mineralization

This paper seeks to identify macroscopic metallogenic mechanisms of various mineral deposits by studying microscopic typomorphic characteristics of typical minerals associated with the deposits and to reveal the mechanism of lattice gold in detail by studying both physical and chemical characteristics of quartz from representative gold deposits in the North China Platform.As part of their extensive research,the authors examine the relationship between trace elements with wall rock,the ore-forming media,and gold immigration of various types of gold deposits,including their salinity,type,temperature.These are key factors to revealing the mineralization mechanism,and indicators for mineral prospecting,exploration,mining,and metallurgical technology.In order to address the questions posed,the following methods were used:field investigations of geology and sampling of the representative gold deposits,physical study and chemical analysis of quartz including,but not limited to,fluid inclusions as well as their compositions and trace elements in quartz,the unit cell parameters,electron paramagnetic resonance spectrum(EPR),and infrared spectroscopic analysis(ISA).As a result of this study,the authors observe the following key findings:unit cell parameters of quartz vary with their contents of foreign elements including gold,paragenetic stage,wall rock type,and other factors;the higher the forming temperature and the lower the gold content in quartz,the smaller the unit cell parameters,and vice versa.Additionally,the EPR absorption lines resulted from the O–Al defect center.The density of these types of hole centers increases and the EPR signal strengthens when the temperature decreases.Based on the findings,the authors conclude that lattice gold exists in quartz.Gold,in the form of Au^(+)and/or Au^(3+),entering quartz and producing an electron–hole center,namely,the O-Au hole center,makes the center produce spin resonance absorption and results in the EPR absorption peak#I.Both unit cell parameters and EPR of quartz can potentially be used in mineral prospecting,relative ore-forming temperature determination,and grade control during mining.

EPR study of charge separation associated states and reversibility of surface bound superoxide radicals in SrTiO_(3) photocatalyst

Understanding the processes of charge generation, transfer and capture is important for the design and synthesis of efficient photocatalysts. In this work, light-induced charge separation and effect of O_(2) on electron transfer processes in SrTiO_(3) were investigated by electron paramagnetic resonance(EPR). It was found that photoinduced electron transfer from O_(2)- to Ti^(4+) produced Ti^(3+) and O- redox radical pairs under vacuum condition. Under oxygen atmosphere, however, surface bound superoxide radicals O_(2)-were formed by electron reduction of adsorbed oxygen at initial photoirradiation stage, and quenched by the reverse electron transfer to Ti^(4+) upon further photoirradiation. Formation of long-lived charge separation associated [Ti^(3+)---O-] species and the reversibility of surface bound superoxide radicals mediating the processes of photogenerated electrons may be accountable for the high activity of SrTiO_(3) in photocatalytic water splitting reaction.

A design of resonant cavity with an improved coupling-adjusting mechanism for the W-band EPR spectrometer

We report a new design of resonant cavity for a W-band electron paramagnetic resonance(EPR)spectrometer.An improved coupling-adjusting mechanism,which is robust,compact,and suits with both solenoid-type and split-pair magnets,is utilized on the cavity,and thus enables both continuous-wave(CW)and pulsed EPR experiments.It is achieved by a tiny metal cylinder in the iris.The coupling coefficient can be varied from 0.2 to 17.9.Furthermore,two pistons at each end of the cavity allow for adjustment of the resonant frequency.A horizontal TE_(011) geometry also makes the cavity compatible with the two frequently used types of magnets.The coupling-varying ability has been demonstrated by reflection coefficient(S_(11))measurement.CW and pulsed EPR experiments have been conducted.The performance data indicates a prospect of wide applications of the cavity in fields of physics,chemistry and biology.

Superoxide and hydrogen peroxide productions by NO-inhibited complex Ⅲ

Complex Ⅲ plays a central role in the mitochondrial respiratory chain transferring electrons from ubiquinol to cytochrome c and pumping protons to the intermembrane space,contributing to the protonmotive force.Furthermore,complex Ⅲ can act as a source of O_(2^(·-))in the presence of ubiquinol and antimycin,an expermiental condition in which the oxidation of the cytochrome b hemes is blocked.The O_(2^(·-))dismutation catalyzed by superoxide dismutase produces H2O2,a known second messenger in redox signalling.Results from our laboratory have shown that NO,released from GSNO or from SPER-NO or generated by mtNOS,inhibits electron transfer at ubiquinone-cytochrome b area producing antimycin-like effects.Thus,both antimycin-and NO-inhibited complex Ⅲ showed a high content of cytochromes b in the reduced state(79 and 71%,respectively)and an enhancement in the ubisemiquinone EPR signal at g=1.99(42 and 35%,respectively).As consequence,O_(2^(·-))and H2O2 productions were increased,being the O_(2^(·-))/H_(2)O_(2) ratio equal to 1.98 in accordance with the stoichiometry of the O_(2^(·-))disproportionation.The interruption of the oxidation of cytochromes b by NO leads to an enhancement of the steady-state concentration of UQH·,allowing cytochrome bc1 complex to act as a source of reactive oxygen species in physiological conditions.

Reduction and pH-responsive performance of nitroxide radical-containing copolymers probed by EPR spectroscopy Dedicated to Professor Chaohui Ye on the occasion of his 80th birthday

Although stimuli-responsive polymers have appeared as promising materials for drug administration,the effectiveness of these materials on various bioinspired stimuli is still open for dispute.In this work,the stimuli-responsive behaviors of radical-containing nonamphiphilic copolymers were investigated using electron paramagnetic resonance(EPR)spectroscopy while altering the pH and reductant concentration.The concentration of radicals in the aqueous solution had a considerable impact on self-assembly.The nitroxide radicals(hydrophobic)were converted to hydroxylamine(hydrophilic)when ascorbic acid(Asc)was added as a reductant,and the assemblies were switched to dissolution with a rate control behavior.The behavior of morphological change was observed in the acidic pH due to the disproportionation reaction of nitroxide radicals forming cationic species.The acquired results give new insights into the colloidal nanoparticles of nonamphiphilic copolymers and encourage the development of comparable responsive nanoparticles with intriguing drug delivery applications.

The Quantum Mechanical Rotation Operators of Spins 5/2 to 7/2

With the creation of logic gates and algorithms for quantum computers and entering our lives, it is predicted that great developments will take place in this area and important efforts are made. Spin rotation processors are quantum mechanical rotation processors and have no classic counterparts. The rotation operators of spin 1/2 are well known and can be found in related textbooks. But rotation operators of other spins greater than 1/2 can be found numerically by evaluating the series expansions of exponential operator obtained from Schr?dinger equation, by evaluation of Wigner-d formula or by recently established expressions in polynomial forms discussed in the text. In a previous paper, rotation operators for spins 1/2 to 2 were published. In this work, explicit symbolic expressions of x, y and z components of rotation operators for spin 5/2, 3 and 7/2 are worked via exponential operator for each element of related spin operators and utilizing simple linear curve fitting process. The procedures gave out exact expressions of each element of the rotation operators.

Ferromagnetic Exchange Coupling in Ni(Ⅱ)Complexes with a Coordinated Boron-Oxamido Radical:A Result of Spin State Transition

A Ni(Ⅱ)coordination complex 1 with a novel boron-oxamido radical ligand was synthesized and isolated.Reactions of 1 with N,N-dimethyl-4-pyridinamine(DMAP)and 4,4'-bpy resulted in 2 and 3,respectively,accompanied by the spin state transition from S=1/2 to S=3/2.Both 2 and 3 were isolated as stable crystals and characterized to feature an S=3/2 spin state,with the S=1 Ni(Ⅱ)atoms ferromagnetically coupled with the ligand-centred radicals,by SQUID measurement and EPR spectroscopy.Complex 3 represents the first example of one-dimensional magnetic chain constructed by S=3/2 Ni(Ⅱ)-radical units.

Surface characterization of metal oxides-supported activated carbon fiber catalysts for simultaneous catalytic hydrolysis of carbonyl sulfide and carbon disulfide

The sol–gel method was used to synthesize a series of metal oxides-supported activated carbon fiber (ACF) and the simultaneous catalytic hydrolysis activity of carbonyl sulfide (COS)and carbon disulfide (CS2) at relatively low temperatures of 60°C was tested.The effects of preparation conditions on the catalyst properties were investigated,including the kinds and amount of metal oxides and calcination temperatures.The activity tests indicated that catalysts with 5 wt.%Ni after calcining at 400°C (Ni(5)/ACF(400)) had the best performance for the simultaneous catalytic hydrolysis of COS and CS2.The surface and structure properties of prepared ACF were characterized by scanning electron microscope-energy disperse spectroscopy (SEM-EDS),Brunauer–Emmett–Teller (BET),X-ray diffraction (XRD),carbon dioxidetemperature programmed desorption (CO2-TPD) and diffuse reflectance Fourier transform infrared reflection (DRFTIR).And the metal cation defects were researched by electron paramagnetic resonance (EPR) method.The characterization results showed that the supporting of Ni on the ACF made the ACF catalyst show alkaline and increased the specific surface area and the number of micropores,then improved catalytic hydrolysis activity.The DRFTIR results revealed that-OH species could facilitate the hydrolysis of COS and CS2;-COO and-C–O species could facilitate the oxidation of catalytic hydrolysate H2S.And the EPR results showed that high calcination temperature conditions provide more active reaction center for the COS and CS2 adsorption.