Determination of Quality Factor for Highly Overcoupled EPR Resonators

We reported determination of the loaded quality factor (Q) of highly overcoupled (dielectric, loop-gap, and cavity) resonators used in time-domain electron paramagnetic resonance. We introduced a microwave absorber into resonators and achieved critical-coupling. Due to the deep “Q-dip” of critical-coupling, we can easily determine the loaded Q as low as 10. The loaded Q of resonators with and without the microwave absorber was examined under various overcoupling conditions. We found that the radiation Q (Q _r) can be calculated from the loaded Q of the resonator that contains the microwave absorber. We proposed a simple model that represents the loaded Q of the overcoupled resonator in terms of two parameters, Q ₀ and Q _r. Q ₀ is the effective unloaded Q of the resonator determined for the critically coupled resonator without the microwave absorber and is independent of a degree of coupling. The model can be applied to overcoupling in which the coupling parameter (Q ₀/Q _r) is in the range of 1 to ca. 20.     

Quantitative investigation of the two-photon absorption of Ruby-laser-light in various semiconductors

With aQ-switched Ruby-laser (h v _L =1.785 eV), the two-photon absorption (TPA) coefficient of various semiconductors is determined. The gap energy,E _g , of these substances is lying in the range ofh v _L <E _g <2hv _L . For all measurements the same experimental setup is used, and for the evolution of the data the real, time-dependent intensity of the laser pulse is taken. Thus, the existing discrepancies between the TPA-coefficients as determined by various authors with different experimental techniques can be settled.     

3D Flake‐Like Bi2Te3 with Outstanding Lightweight Electromagnetic Wave Absorption Feature

Flake‐like semiconductors with strong interfacial polarization exhibit excellent electromagnetic absorption properties. To the best of the knowledge, 3D flake‐like Bi₂Te₃ is never reported as effective MAMs (microwave absorption materials). Herein, it is first introduced the novel lightweight microwave absorption of 3D flake‐like Bi₂Te₃ synthesized by a simple hydrothermal process. Compared with the traditional research objects, the obtained Bi₂Te₃ possessed prominent absorbing ability at a rather thin thickness (1.0 mm), which will draw much attention to new‐materials for electromagnetic wave absorption.     

Remanent microwave absorptin in Y−Ba−Cu−O at low magnetic fields

Polycrystalline samples of YBa₂Cu₃O₇ were studied by the microwave absorption technique at the low magnetic fields in the temperature range from 5 to 80 K. The direct microwave absorption and the field modulated microwave absorption were measured at 77 K. Analysis of the microwave absorption curves indicates that the field penetration into the sample starts from the lowest values of applied magnetic field within the whole temperature range.     

Level splitting in semimagnetic semiconductors under spin-magnetophonon resonance conditions

The splitting of electronic levels in quantum wells of semimagnetic semiconductors typically characterized by large effective g factors is analyzed theoretically. They are found to be capable of supporting resonance, provided the Zeeman spin-level splitting is equal to the energy of the longitudinal optical phonon ?ω_‖. The resonance condition can be written as ?ω_‖ = gμ_B B. This condition can be satisfied by choosing the magnetic field Bsuch that the sum of the energies of the lowest spin level and the optical phonon coincides with the energy of the highest level. It is shown that these two degenerate energy levels should experience mutual repulsion. The magnitude of the corresponding splitting depends on both the electron-phonon and spin-orbit interactions in semiconductors; moreover, it turns out substantially lower than the Zeeman energy gμ_B B. Resonant passage of light through and its reflection from a quantum well are considered as one of possible ways to observe this energy level splitting.     

On theg-value shift and intersystem crossing in photo-excited radical-triplet systems

The electron paramagnetic resonance (EPR) signals of photoexcited quartet (Q₁) states for zinc(II) tetra-tert-butyl-phthalocyanine (ZnPc) ligated by 3- and 4-(N-nitronyl-nitroxide) pyridine radicals (3-NOPy, 4-NOPy) were observed in toluene solution at room temperature by means of X-band (9.4 GHz) time-resolved EPR (TREPR) spectroscopy. Theg values of Q₁ in the ZnPc-3-NOPy and ZnPc-4-NOPy complexes were found to beg=2.0025 andg=2.0036, respectively. The obtainedg value (2.0036) for ZnPc-4-NOPy is in good agreement with the value (g=2.0037) of the Q₁ state calculated under the strong-exchange limit. Theg value (2.0025) is just an average of the Q₁ and D₁ (g=2.0013) states for ZnPc-3-NOPy. Theg value of Q₁ for zinc(II) meso-tetraphenylporphine (ZnTPP) ligated by 3-NOPy showed a slight shift (g=2.0027) at X-band and no shift (g=2.0031) at W-band from the calculatedg value (g=2.0031) (J. Fujisawa, Y. Iwasaki, Y. Ohba, S. Yamauchi, K. Koga, S. Karasawa, M. Fuhs, K. Möbius, S. Weber, Appl. Magn. Reson. 21, 483–493, 2001). These changes in theg value were found to originate from an averaging of the TREPR spectra over the Q₁ and photoexcited doublet (D₁) states via a fast intersystem crossing (ISC) process. The ISC rates between these two states were estimated by means of numerical calculations with the modified Bloch equations as 1.2·10⁸ and 6·10⁷ s^?1 for the ZnTPP-3-NOPy complex at the X- and W-bands, respectively. The lower limit of the ISC rate was obtained as 10⁹s^?1 for the ZnPc-3-NOPy complex and the higher limit was found to be 3.1·10⁸ s^?1 for the ZnPc-4-NOPy complex.     

A new approach to calculate the gluon polarization

We derive the Leading-Order (LO) master equation to extract the polarized gluon distribution G(x,Q ²)=xδg(x,Q ²) from polarized proton structure function, g^p₁(x,Q²)g^{p}_{1}(x,Q^{2}). By using a Laplace-transform technique, we solve the master equation and derive the polarized gluon distribution inside the proton. The test of accuracy which is based in our calculations on two different methods, confirms that we achieve to the correct solution for the polarized gluon distribution. To determine the polarized gluon distribution xδg(x,Q ²) more accurately, we only need to have more experimental data on the polarized structure functions, g₁^p(x,Q²)g_{1}^{p}(x,Q^{2}). Our result for polarized gluon distribution is in good agreement with some phenomenological models.     

Microwave absorption studies of MgB2 superconductor

Microwave absorption studies have been carried out on MgB₂ superconductor using a standard X-band EPR spectrometer. The modulated low-field microwave absorption signals recorded for polycrystalline (grain size ∼ 10 μm) samples suggested the absence of weak-link character. The field dependent direct microwave absorption has been found to obey a ✓H dependence with two different slopes, which indicated a transition from strongly pinned lattice to flux flow regime.     

Anomalous X-ray scattering studies on superionic glassy (As2Se3)-(AgX) systems (X = halides)

Anomalous X-ray scattering experiments for glassy room-temperature superionic conductors (As₂Se₃)_0.4 (AgI)_0.6 and (As₂Se₃)_0.4(AgBr)_0.6 were performed close to the As, Se, Ag, and Br K edges using a third-generation synchrotron radiation facility, ESRF. The differential structure factors, Δ_iS(Q), were obtained from detailed analyses, indicating that Δ_AsS(Q) and Δ_SeS(Q) of both the glassy superionic semiconductors are similar to those of glassy As₂ Se₃ except the prepeak in Δ_SeS(Q). The Δ_AgS(Q) spectrum of (As₂Se₃)_0.4 (AgI)_0.6 looks molten salt-like. However, the Δ_Ag S(Q) of (As₂Se₃)_0.4(AgBr)_0.6 glass have quite different features from that of (As₂Se₃)_0.4 (AgI)_0.6 glass in the low Q range, and the Δ_BrS(Q) has even a pre-shoulder around 13 nm^? 1 unlike molten salts. In the differential pair distribution functions Δ_ig(r) obtained from the Fourier transforms of Δ_iS(Q), the first peaks of Δ_Asg(r) and Δ_Seg(r) show no correlation with those of Δ_Agg(r) and Δ_Brg(r), and vice versa. From these results, it can be concluded that a pseudo-binary mixture of the As₂Se₃ network matrix and AgX-related ionic conduction pathways is a good structural model for these superionic glasses. Differences between the AgBr- and AgI mixtures were found in the second-neighbor structures around the Ag atoms, which may reflect those in the crystal structures of the AgX salts.     

Giant red shift of the absorption spectra due to nonstoichiometry in GdCoO<Subscript>3–δ</Subscript>

The GdCoO_3–δ perovskite is a semiconductor with the energy gap E _g ≈ 0.5 eV from electrical transport measurements. It reveals unusual optical absorption spectra without transparency window expected for semiconductors. Instead we have measured the narrow transmittance peak at the photon energy ε₀ = 0.087 eV. To reconcile the transport and optical data we have studied the effect of oxygen vacancies on the electronic structure of the GdCoO_3–δ. We have found that oxygen vacancies result in the in-gap states inside the charge-transfer energy gap of the GdCoO₃. It is a multielectron effect due to strong electron correlations forming the electronic structure of the GdCoO_3–δ. These in-gap states decrease the transparency window and result in a narrow absorption minimum. The predicted temperature dependence of the absorption spectra has been confirmed by our measurements.     

Hysteresis phenomena in charging of Si Mosfet in quantizing magnetic field

We report the observation of nonequilibrium processes of charging in 2D electron layer in Si MOSFET. There were investigated the hysteresis variations of a 2D-layer charge Q_S with a gate voltage V_g or with a magnetic field H, and the hysteresis of a gate potential U_g vs magnetic field at Q_S = Const. At sufficiently low temperature T < 1K the relaxation time of a nonequilibrium state is much higher than 10³ sec. The observed phenomena may be explained qualitatively in frame of a surface potential randomness conception.     

Microwave absorption in the Kondo lattice of CeB6 in strong magnetic fields

The characteristic features of microwave (30–120 GHz) magnetoabsorption in the magnetic Kondo lattice of CeB₆ at liquid-helium temperatures in strong magnetic fields are investigated. It is discovered that the absorption structure is the result of the superposition of the ESR of the cerium 4 f electrons, which has a pronounced doublet structure, and features whose position does not depend on the radiation frequency and which are associated with transitions in the magnetic phase diagram of CeB₆. The character of the absorption in the vicinity of the ESR can be linked to the splitting of the ² F _5/2 state in the crystal field; here the g factor is substantially renormalized from g=2.06±0.03 to g=1.83±0.03 as the temperature decreases from 4.2 K to 1.8 K, respectively. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 6, 431–435 (25 March 1996)     

Far-infrared absorption of MgO: Fe2+ in magnetic fields

We have measured the far-infrared absorption of iron-doped MgO in the wavenumber region 10–200 cm^?1 and in magnetic fields up to 6 T. Absorption peaks found at 107.0 and 110.5 cm^?1 are assigned to magnetic dipole transitions between the spin-orbit Г_5g groundstate (J = 1) and the Г_3g, Г_4g excited states (J = 2) of the Fe²⁺ -ion at a cubic site. The observed magnetic field dependence shows that Г_4g is the higher excited level, so that the crystal field order of the levels is not changed by the reduction of the spin-orbit splitting attributed to a dynamic Jahn-Teller effect. An additional absorption peak at 33.4 cm^?1 is found to split in magnetic field.In iron-doped KMgF₃ absorption peaks at 52 and 87 cm^?1 that have previously been attributed to the same transitions of Fe²⁺ are found to remain unshifted and unsplit in magnetic fields up to 6 T.     

Improvement of the polishing treatment for niobium surfaces of superconducting cavity resonators

For superconducting cavities made from niobium sheet, which are interesting in the field of accelerator applications, smooth and defect free inner surfaces are needed to achieve a high unloadedQ along with high accelerating field strength. These can be obtained using chemical polishing procedures. Whereas normally a mixture of HF, HNO₃, and H₃PO₄ is applied, we chose the known bath containing HF, HNO₃, and H₂SO₄ and worked above 50 °C. The surface quality was judged by visual inspection using a light microscope as well as by microwave measurements of one spherical resonator. The new method gave less grain boundary etching and, with high field levels, an enlarged unloadedQ.     

Field-theory methods in coagulation theory

Coagulating systems are systems of chaotically moving particles that collide and coalesce, producing daughter particles of mass equal to the sum of the masses involved in the respective collision event. The present article puts forth basic ideas underlying the application of methods of quantum-field theory to the theory of coagulating systems. Instead of the generally accepted treatment based on the use of a standard kinetic equation that describes the time evolution of concentrations of particles consisting of a preset number of identical objects (monomers in the following), one introduces the probability W(Q, t) to find the system in some state Q at an instant t for a specific rate of transitions between various states. Each state Q is characterized by a set of occupation numbers Q = {n ₁, n ₂, ..., n _g , ...}, where n _g is the total number of particles containing precisely g monomers. Thereupon, one introduces the generating functional Ψ for the probability W(Q, t). The time evolution of Ψ is described by an equation that is similar to the Schrödinger equation for a one-dimensional Bose field. This equation is solved exactly for transition rates proportional to the product of the masses of colliding particles. It is shown that, within a finite time interval, which is independent of the total mass of the entire system, a giant particle of mass about the mass of the entire system may appear in this system. The particle in question is unobservable in the thermodynamic limit, and this explains the well-known paradox of mass-concentration nonconservation in classical kinetic theory. The theory described in the present article is successfully applied in studying the time evolution of random graphs.     

Some comments on the diffusion of particles in stochastic r.f. fields

The form of the distribution functionf (P _i, Q_i,t) is determined in terms of the integralW of the diffusion equation and of the initial distribution functionf ₀(P _i, Q_i, t).W gives the probability of the occurrence of a particle in the phase space P_i, Q_k.The Hamiltonian function of the particle and the distribution functionf obtained in the above way are used for establishing the value of the absorbed energy and the rate of absorption in the case of the homogeneous magnetostatic fields. We discuss the conservative r.f. field-particle system (also in the nonlinear approximation), the effect of the nonlinearity of the diffusion tensor and the meaning of the resonance for the rate of absorption. We discuss also shortly the effect of the external stochastic field on the stability of plasma, already mentioned in earlier literary sources.The author wishes to thank Dr. J. Lacina for valuable discussions.     

Optical and ESR studies of an air absorption band in CsI:Na after X-ray irradiation

We have studied the nature of the defect giving rise to a near IR absorption band (717 nm) in X irradiated CsI:Na by measuring its linear dichroism, its magnetic circular dichroism and its change due to the resonance microwave. The defect (g₆ = 1.96, g_⊥ = 2.23 with axis near 〈100〉) involves a Na⁺ ion and an excess electron.     

NiSi金属栅电学特性的热稳定性研究

研究了NiSi金属栅的各种电学特性及其热稳定性，提出一个物理模型用于解释当形成温度大于500 ℃时NiSi功函数随退火温度升高而增大的现象.测量了不同退火温度形成的NiSi材料的方块电阻，当退火温度大于400 ℃时，方块电阻达到最小，并在400—600 ℃范围内稳定.比较各种温度下形成的NiSi材料X射线衍射谱的变化，说明温度在400—600 ℃范围内NiSi相为最主要的成分.制备了以NiSi为金属栅的金属氧化物半导体电容.通过等效氧化层电荷密度及击穿电场E_bd的分布研 关键词： 金属栅 NiSi 炉退火 快速热退火     

Microwave hall field inertia due to dielectric relaxation time

The magnetoresistive e.m.f. caused by microwave was measured as a function of _m in wide (3 cm – 4mm) range wave length. It has been found that Maxwell relaxation time does not influence the microwave Hall field lag in semiconductors. The discussion of these results is presented.     

EPR and ENDOR Investigation of Rhodosemiquinone in Bacterial Reaction Centers Formed by B-Branch Electron Transfer

In photosynthetic bacteria, light-induced electron transfer takes place in a protein called the reaction center (RC) leading to the reduction of a bound ubiquinone molecule, Q_B, coupled with proton binding from solution. We used electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) to study the magnetic properties of the protonated semiquinone, an intermediate proposed to play a role in proton coupled electron transfer to Q_B. To stabilize the protonated semiquinone state, we used a ubiquinone derivative, rhodoquinone, which as a semiquinone is more easily protonated than ubisemiquinone. To reduce this low-potential quinone we used mutant RCs modified to directly reduce the quinone in the Q_B site via B-branch electron transfer (Paddock et al. in Biochemistry 44:6920–6928, 2005). EPR and ENDOR signals were observed upon illumination of mutant RCs in the presence of rhodoquinone. The EPR signals had g values characteristic of rhodosemiquinone (g _x  = 2.0057, g _y  = 2.0048, g _z  ~ 2.0018) at pH 9.5 and were changed at pH 4.5. The ENDOR spectrum showed couplings due to solvent exchangeable protons typical of hydrogen bonds similar to, but different from, those found for ubisemiquinone. This approach should be useful in future magnetic resonance studies of the protonated semiquinone.