A first-principle prediction on the magnetism and electronic structure of Ti-doped CoO with two O vacancies

The electronic structure and magnetism in Co₁₄Ti₂O₁₄ systems are investigated by using the first-principles calculations. The system of 2 × 2 × 2 Co₁₄Ti₂O₁₆ supercell doped with Ti at 9 and 11 position shows a half-metallic character with a high spin polarization. Based on the above system, we remove two O atoms to form two O vacancies. The two O vacancies near Ti have a huge effect on the electronic structure and magnetic properties of Co₁₄Ti₂O₁₄ system. When O vacancies locate at 1 and 3 positions, the system shows a half-metallic character. For the O vacancies at 6 and 8 positions, the system shows a semiconducting character. The system with O vacancies at 9 and 11 positions is a typical spin gapless semiconductor.     

Analysis of TiO2 photocatalysis in a pulsed discharge system for phenol degradation

Photocatalysis of supported TiO₂ film photocatalyst in a pulsed discharge system for phenol degradation was studied in this paper. The obtained results revealed that the supported TiO₂ film with anatase structure had preferable photocatalytic activity in the pulsed discharge system. Phenol degradation and main byproduct generation were better in the discharge/TiO₂ system. The photocatalyst prepared with eight times dipping process had higher photocatalytic activity than other photocatalysts and testified a preferable photocatalyst condition in the pulsed discharge system. Furthermore, the supported TiO₂ photocatalyst kept photocatalytic activity after using five times in the pulsed discharge system.     

The determination of the neél point in the diluted ferromagnetic chain system CsNiF3 (2% Mg)

The pure CsNiF₃ is known to be a very good example of a ferromagnetic chain system with planar anisotropy. In continuation of the studies on the pure system here results for a diamagnetically diluted one-dimensional system, Cs(Ni_98%Mg_2%)F₃, are presented for the first time. The susceptibility shows qualitatively the same behaviour as the pure system but the maximum in χ is shifted by 10% to lower temperatures. This corresponds to the findings of elastic neutron scattering experiments where the magnetic Bragg reflections for the diluted system disappear at a T_N, which is only 90% of T_N of the pure system.     

Temperature and frequency dependence of AC electrical properties of Zn and Ni doped CoFe2O4 nanocrystals

Abstract

We have investigated the structure and the electrical properties of CoFe₂O₄, Ni_0.5Co_0.5Fe₂O₄ and Zn_0.5Co_0.5Fe₂O₄ nanoparticles, prepared through a chemical pyrophoric reaction technique. The study of the dielectric constant reveals evidence of Rabinkin and Novikova polarisation in the system. The increased value of the dielectric constant at low frequency is attributed to the presence of interfacial and dipolar polarisation in the system. The impedance for Zn_0.5Co_0.5Fe₂O₄ nanoparticles is found to decrease with increase in temperature, indicating the presence of a temperature-dependent electrical relaxation process in the system. Nyquist plots have been fitted using parallel combinations of grain boundaries resistance and grain boundaries capacitance. The activation energy is estimated from Nyquist plots, dc and ac conductivity data using the Arrhenius relation. This is indicating that the same type of charge carrier is responsible for the relaxation and the conduction processes in the system. Ac conductivity curves follow a double power law, as proposed by Jonscher. The conduction mechanism with temperature is mainly due to the large polaronic hopping in the system.     

Design and evaluation of a Blu-ray pickup head system for determining the tilt angle and displacement of the test plane

We present an optical system design for determining the tilt angle and displacement of the test plane. The proposed optical system consists of a Blu-ray pickup head and a pigtailed laser diode with a uniform Gaussian beam. The optical system is evaluated by two optical design software packages, Code V and LightTools. A quadrant detector is used to detect the relative relationship of the V_A, V_B, V_C and V_D output signals, which can be used to measure the tilt angle and displacement on the test plane. Both the tilt angle and displacement on the test plane can be determined from the change in the beam shape on the quadrant detector. The proposed system can generate a circular uniform beam shape to reduce the misjudgment and to enhance the measurement accuracy. Various simulation cases are presented in detail to show the feasibility of the proposed system.     

弱吸收多层薄膜消光系数的反演

从窄带干涉滤光片的峰值透射率测量可以直接反演出弱吸收薄膜的消光系数，从而得到一种能简易而又精确地评价多层薄膜微弱吸收的新方法. 推导了弱吸收窄带干涉滤光片的吸收表达式， 阐述了确定弱吸收薄膜消光系数的基本原理.以离子束溅射的Ta₂O5/SiO₂波分复用滤光片为例，分析了这种评价方法的基本精度. 关键词： 光学测试 离子束溅射 光学薄膜干涉滤光片 消光系数     

Polarization-dependent intensity transmittance of optical systems

The intensity transmittance α of a linear nondepolarizing optical system is investigated as a function of the state of polarization of the incident light. For totally polarized incident light the state of polarization is completely described by a single complex variable χ. In the χ-plane, the loci of incident polarizations that experience equal attenuation or amplification [α(χ)=constant] upon passing through the system constitute a family of nonintersecting coaxal circles. The zero-radius point circles of the coaxal family represent two orthogonal polarizationsχ _max andχ _min that pass through the system with maximum and minimum transmittances, respectively. Simple elegant expressions are derived for α in terms of the propertiesχ _max,χ _min;α _max andα _min of the system. When χ is expressed in terms of the azimuth and the ellipticity of the polarization ellipse a generalized version of Malus' law is obtained which is applicable to any optical system. Special cases of optical systems are discussed. The condition that a Jones matrix represents an active system is derived. Such a system may amplify polarization states inside a circular domain in the complex χ-plane and attenuate all other states. The results for totally polarized incident light are used to derive the polarization-dependent intensity transmittance of the system for unpolarized and partially polarized incident light. A new set of three parameters is introduced to describe the state of polarization of partially polarized light. The polarization-dependent intensity transmittance is completely determined by four real quantities which can be measured photo-ellipsometrically.     

Localization in a system of N coupled chains

The behaviour of a quantum particle moving in a system of N coupled chains parallel to each other and packed into a bundle is investigated in the presence of weak disorder. This system may be thought of as a model of an anisotropic thin wire. The dependence of the localization length r_loc on N and t_⊥ is studied (t_⊥ is the interchain exchange integral characterizing the strength of the interchain tunneling). For t_⊥ < t_c ≅ h/τ the localization length r_loc increases proportionally to lt_⊥/(t_τ −t_⊥) attaining a plateau value of the order of Nl (τ is the relaxation time and 1 the mean free path for elastic scattering). Such a behaviour may be called a transition from the Mott localization regime to the Thouless localization regime. It may be considered as a precursor of the insulator-metal transition (r_loc → ∞) occuring for t_⊥ → t_c in the quasi-1d system (N → ∞).     

Direct Monitoring of Thickness and Refractive Index of Optical Thin Film Deposited on Fiber End-face

We propose a system for depositing thin films on waveguides which enables low-temperature deposition and precise control of the refractive index and film thickness. It is composed of a conventional ion-beam sputtering (IBS) system and a new system for directly monitoring film characteristics during deposition. We controlled refractive indices over a wide range from 1.52 to 1.97 by moving the sputtering targets (SiO₂ and Si₃N₄) in the IBS system. The refractive index or film thickness was in-situ monitored by observing the optical power reflected from the end-face of a monitoring fiber set in the deposition chamber. Antireflection coating films were successfully deposited on a fiber end-face and a laser diode chip facet with low reflectivity from 0.05 to 0.07%. This deposition system is attractive for constructing highly functional optical devices for future photonic networks.     

A Raman system for multi-gas-species analysis in power transformer

We have built a complete Raman detection system for multi-trace-gas diagnosis, which is suitable for analyzing the dissolved gases in electric power system. In the system, a high-sensitivity CCD device connected to a spectrometer is used as the detection unit of the Raman system. A near-confocal cavity is used for improving the detection sensitivity of the system. In the effective spectral range of about 570–710 nm, Raman spectra of eight typical gases are achieved by using this Raman system. The detection limits for different gases have been obtained: 126 ppm for CO₂, 21 ppm for CH₄, 63 ppm for C₂H₄, 42 ppm for C₂H₂, 96.6 ppm for H₂. The detectability of the system satisfies the requirements of gas diagnosis in power transformer.     

New optical absorption spectra of Cu2 molecules produced by the gas evaporation technique

A study was conducted on the optical absorption spectra ranging from 233 to 285 nm, which were taken in a region close to the source of evaporation of Cu, in low-pressure helium gas of 100 Torr. Eight band systems for Cu₂ dimers designated as system 1 through 8 were identified. The spectroscopic constants for the band origins were derived as follows: [vtilde] ≈ 42 200 cm^?1 for system 1, [vtilde]₀₀ = 41 604.74cm^?1 for system [vtilde]₀₀ = 39 606.70cm^?1 for system [vtilde]₀₀ = 38 124.32cm^?1 for system 4, [vtilde]₀₀ = 38 048.65 cm^?1 for system 5, 98, [vtilde]₀₀ = 36 834.22cm^?1 for system 6, [vtilde]₀₀ = 36 341.55 cm^?1 for system 7 and [vtilde]₀₀ = 36 174.99cm^?1 for system 8. For all cases in which vibrational constants of the lower state could be determined, it was found that the transition originated from the ground state of Cu₂.     

Simple kinetic model of symmetry breaking

We consider a dynamical system described by a set of random variablesN| _i(t) and depending on a parameterR controlling its stability. IfR < R _c the system is stable and theN _i have some symmetry properties in the statistical sense (i.e., with respect to time averaging). IfR > R _c the system is unstable and the nonlinear dynamics of theN _i may lead to an asymptotic stationary state which does not possess the symmetries of the stable system. We show that the dynamics of symmetry breaking resembles a phase transition in the limit of many variables.     

Mass spectrometric and thermodynamic studies of vapor-phase growth of In(1−x)GaxP

A time-of-flight mass spectrometer was coupled directly to an open tube vapor growth system. The vapor composition and the processes occurring during the deposition of In_(1?x)Ga_xP alloys were studied. It was found that the vapor species present in this system are InCl, GaCl, HCl, PH₃, P₂, P₄ and H₂. The deviations from the chemical equilibrium in the system were determined and measured.A chemical equilibrium model was set and used to calculate the equilibrium partial pressures of all species under a wide range of experimental conditions. These calculations were used to predict successfully the proper conditions for growth of desired In_(1?x)Ga_xP alloys.     

Growth of yttrium iron garnet single crystals in Na2O-B2O3 flux system in air

Detailed studies of growth of yttrium iron garnet (YIG) in the flux system Na₂O-B₂O₃ were made to delineate the phase stability regions of YIG and the neighbouring crystalline phases, and a tentative working diagram of Na₂O-B₂O₃-YIG in air was drawn from the results of small batch crystal growth runs and solubility studies. The occurrence of a rather narrow field of YIG crystallization in this system was explained on the basis of relative solubilities of different oxides constituting YIG. Several long-time growth runs with some typical compositions were carried out in this system to evaluate its suitability for bulk growth of YIG crystals. The system, although possessing some inherent advantages, was found to suffer from limitations because of which the maximum size of the self-nucleated crystals grown hardly exceeded 2.00 mm.     

Anomalous thermal conductivity of single crystal Cu2Te2O5Cl2

A strong increase of the thermal conductivity is observed at the phase transition (T _c=18.2 K) in Cu₂Te₂O₅Cl₂ single crystal. This behavior is compared with that of the spin-Peierls system NaV₂O₅, where a similar experimental observation has been made, and the conventional spin-Peierls system CuGeO₃, where a modest kink in the thermal conductivity curve has been observed. The strong increase of the thermal conductivity atT _c in Cu₂Te₂O₅Cl₂ could be partially attributed to the opening of the energy gap in the magnetic excitation spectrum evident from the magnetic susceptibility measurements. However, the main reason for the anomaly of the thermal conductivity could be explained by a strong spin-lattice coupling in this system, which what is in agreement with the preliminary X-band electron spin resonance measurement.     

Preparation and mechanism of formation of hematite particles in the Fe-HNO3 system

The mechanism of formation of hematite particles in the Fe-HNO₃ system is investigated by introduction of a small amount of PO₄³⁻ ions to the system. The intermediate species in the reaction, 6-line ferrihydrite, is successfully obtained. The transformation of 6-line ferrihydrite to hematite is investigated. The results show that Fe(II) in the Fe-HNO₃ system can catalyze the dissolution of 6-line ferrihydrite, leading to the rapid formation of hematite.     

Formation of a system of InGaAs quantum wires in a gallium arsenide matrix

The formation of a system of one-dimensional quantum conductors in porous multilayer In_xGa_1?xAs/GaAs structures with a two-dimensional charge-carrier gas in the In_xGa_1?xAs layers is discussed. The transition from the single-crystalline to porous matrix is studied with scanning atomic force microcopy. A decrease in the dimensionality of the electron-hole gas in the objects, i.e., a transition from the two-dimensional to a one-dimensional system, is established by analyzing the dependences of the position and width of a spectral line in the photoluminescence spectra on the etching time. Both multilayer periodic superlattices and a structure with a single In_xGa_1?xAs layer located near the surface of gallium arsenide are studied. The electrophysical characteristics of electrons in the porous superlattices are measured as functions of temperature. They confirm the formation of a new structure and indicate a change in the mechanism of electron scattering in the quasi-one-dimensional transport channels formed in the system.     

Triaxial strain effect on the electron transport performance and absorption spectrum of ZnO

The effect of triaxial strain on the electron transport performance and absorption spectrum of ZnO has been rarely reported. In this paper, the generalized gradient approximation plane wave ultrasoft pseudopotential + U method based on the spin density functional theory is adopted to solve this problem. The first-principle method is utilized to study the triaxial strain on the electron transport performance and absorption spectrum of ZnO. Results show that the binding energy of Zn₃₆O₃₆ is 2.14 eV when the system is unstrained and relatively stable. The formation energy of the Zn₃₆O₃₆ system increases with the increase in tensile or compressive strain, and the system stability decreases. The formation energy of the O-vacancy system is smaller compared with the same orders of magnitude of tensile or compressive strain. The formation energy of O-vacancy system is smaller, and the structure is stable when the system is tensile strain. Specifically, the absorption spectrum of the Zn₃₆O₃₅ system has the optimal redshift and intensity when the tensile strain is 5%. The electron mobility of the Zn₃₆O₃₆ system along the y direction (G → F) is relatively large when the compressive strain is −5%, the band gap of the system is wide, and the blueshift of the absorption spectral distribution is obvious. This work has a certain theoretical guidance for the design and preparation of novel ultraviolet light detectors or improvement of the electron transmission performance.     

Coherent antistokes raman scattering instrument for diagnostics of laser-induced processes

Summary A nonintrusive diagnostic system is described which permits simultaneous measurement of number density and temperature of small molecules in hostile environments such as photo-chemical reactors where laser induced processes occur. This system is formed by a frequency-doubled Nd:YAG laser which is partially used to excite a broad-band dye laser. The system utilizes a collinear beam arrangement, the signals are detected with an intensified photodiode array after proper filtering and wavelength separation through a 60° prism and a monochromator. Calibration measurements have been performed on small molecules (SiH₄, NH₃, C₂H₂, C₂H₄, C₂H₆) involved in the IR laser-induced photosynthesis of ceramic powders (Si₃N₄ and SiC). The effect of nonresonant background in number density measurements due to carrier gases used in flow reactors has been carefully investigated in cell experiments. The strong temperature dependence of the envelope of the vibrorotational Raman active band detected under rather low resolution is demonstrated in band contour calculations performed on hydrocarbons (C₂H₂ and C₂H₂). To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

High Field ESR System and Its Application to the Study of Quantum Spin Systems

Developments of the high field ESR system in Kobe University is presented. Using Gunn oscillators and backward traveling oscillators (BWO), we can cover the frequency region from 30 to 1183.6 GHz with the use of InSb detector. Pulsed magnetic field up to 30 T is available and we are now trying to extend the field up to 40 T. Temperature range is from 1.8 to 300 K. Using this system, we studied S=1/2 ladder like system Cu₂(C₅H₁₂N₂)₂Cl₄, and found a new magnetic transition at 10.1 T at 1.8 K. The temperature dependence of ESR in Cu₂(C₅H₁₂N₂)₂CI₄ shows g-shift below 8 K which corresponds to the maximum of the magnetic susceptibility. The g-shift below 8 K suggests the increase of the quantum fluctuation in the system, and the role of the quantum fluctuation in Cu₂(C₅H₁₂N₂)₂CI₄ is discussed.