第一性原理研究闪锌矿结构MnSb和MnBi半金属性和磁性的稳定性

采用基于第一性原理的全势能线性缀加平面波方法对闪锌矿结构MnSb和MnBi的电子结构进行自旋极化计算。闪锌矿结构MnSb和MnBi处于晶格平衡时都是半金属性的,并且它们自旋向下电子能带带隙分别是1.32eV 和1.27eV。闪锌矿结构MnSb和MnBi的自旋总磁矩都为4.00μB/formula,总磁矩主要来源于Mn的原子磁矩,Sb和Bi的原子磁矩对总磁矩的贡献很小而且为负值,它们具有明显的铁磁性特征. 使晶体晶格在±10%的范围内发生各向同性形变,对闪锌矿结构MnSb和MnBi的电子结构进行计算. 计算结果表明,当晶格各向同性形变分别为-1 % ~ 10 %和-4 % ~10 %时,闪锌矿结构MnSb和MnBi仍然保持半金属铁磁性,并且总磁矩都稳定于4.00μB/formula.     

第一性原理研究闪锌矿结构MnSb和MnBi半金属性和磁性的稳定性

采用基于第一性原理的全势能线性缀加平面波方法对闪锌矿结构MnSb和MnBi的电子结构进行自旋极化计算.闪锌矿结构MnSb和MnBi处于晶格平衡时都是半金属性的,并且它们自旋向下电子能带带隙分别是1.32 eV和1.27 eV.闪锌矿结构MnSb和MnBi的自旋总磁矩都为4.00μB/formula,总磁矩主要来源于Mn的原子磁矩,Sb和Bi的原子磁矩对总磁矩的贡献很小而且为负值,它们具有明显的铁磁性特征.使晶体晶格在±10％的范围内发生各向同性形变,对闪锌矿结构MnSb和MnBi的电子结构进行计算.计算结果表明,当晶格各向同性形变分别为-1％～10％和-4％～10％时,闪锌矿结构MnSb和MnBi仍然保持半金属铁磁性,并且总磁矩都稳定于4.00μs/formula.     

第一性原理研究闪锌矿结构MnSb和MnBi半金属性和磁性的稳定性

采用基于第一性原理的全势能线性缀加平面波方法对闪锌矿结构MnSb和MnBi的电子结构进行自旋极化计算。闪锌矿结构MnSb和MnBi处于晶格平衡时都是半金属性的,并且它们自旋向下电子能带带隙分别是1.32eV 和1.27eV。闪锌矿结构MnSb和MnBi的自旋总磁矩都为4.00μB/formula,总磁矩主要来源于Mn的原子磁矩,Sb和Bi的原子磁矩对总磁矩的贡献很小而且为负值,它们具有明显的铁磁性特征. 使晶体晶格在±10%的范围内发生各向同性形变,对闪锌矿结构MnSb和MnBi的电子结构进行计算. 计算结果表明,当晶格各向同性形变分别为-1 % ~ 10 %和-4 % ~10 %时,闪锌矿结构MnSb和MnBi仍然保持半金属铁磁性,并且总磁矩都稳定于4.00μB/formula.     

F原子吸附TiO_2:Mn(001)稀磁半导体薄膜电子结构和磁性的第一性原理计算

利用第一性原理方法计算Mn离子掺杂纯净TiO2(001)和F原子吸附的TiO2(001)薄膜的形成能、态密度和磁矩.F原子吸附明显降低TiO2∶Mn薄膜体系的形成能.F原子的吸附导致Mn离子的磁矩减小,而表面O原子的磁矩增大.表面O原子的磁矩主要来源于O原子p x和p y轨道的自旋极化,研究表明表面吸附F原子更有利于Mn离子的掺杂,在一定程度上有利于获得结构稳定的铁磁态半金属特性的TiO2∶Mn薄膜.     

第一性原理研究闪锌矿结构CrSe和CrAs半金属铁磁性的稳定性

运用第一性原理的全势能线性缀加平面波方法对闪锌矿结构CrSe和CrAs的电子结构进行自旋极化计算。闪锌矿结构CrSe和CrAs处于晶格平衡时都具有半金属性,它们自旋向下的电子能带带隙分别为3.38eV 和1. 79eV,同时,它们的自旋总磁矩分别为4.00和3.00μB/formula。自旋总磁矩主要来源于Cr的原子磁矩,Se和As的原子磁矩对总磁矩的贡献很小而且为负值,因而它们具有明显的铁磁性特征. 使晶体晶格在±10%的范围内发生各向同性形变,对闪锌矿结构CrSe和CrAs的电子结构进行计算. 计算结果表明,当晶格各向同性形变分别为-4 % ~ 10 %和-2 % ~10 %时,闪锌矿结构CrSe和CrAs仍然保持半金属铁磁性,并且总磁矩都稳定于4.00和3.00μB/formula.     

第一性原理研究闪锌矿结构CrSe和CrAs半金属铁磁性的稳定性

运用第一性原理的全势能线性缀加平面波方法对闪锌矿结构CrSe和CrAs的电子结构进行自旋极化计算.闪锌矿结构CrSe和CrAs处于晶格平衡时都具有半金属性,它们自旋向下的电子能带带隙分别为3.38 eV和1.79 eV,同时,它们的自旋总磁矩分别为4.00和3.00μ_B/formula.自旋总磁矩主要来源于Cr的原子磁矩,Se和As的原子磁矩对总磁矩的贡献很小而且为负值,因而它们具有明显的铁磁性特征.使晶体晶格在±10%的范围内发生各向同性形变,对闪锌矿结构CrSe和CrAs的电子结构进行计算.计算结果表明,当晶格各向同性形变分别为-4%～10%和-2%～10%时,闪锌矿结构CrSe和CrAs仍然保持半金属铁磁性,并且总磁矩都稳定于4.00和3.00μ_B/formula.     

CrO_2块体及其(001)和(100)表面的电子结构和磁性质

基于密度泛函理论的第一性原理计算,我们研究了CrO_2块体以及其(100)和(001)表面的磁性和电子结构.CrO_2(100)表面中表面层Cr原子向内收缩,而(001)表面中的表面层Cr原子却向外伸展;越往内层,原子驰豫幅度越小.由于表面效应.表面层原子的磁矩有了大幅的提升,其中(100)表面中表面层Cr原子的磁矩最高,为3.03μB.电子结构计算表明,CrO_2(100)和(001)表面均保持了块体中良好的半金属性,并且半金属带隙在(100)表面中受到了进一步的拓宽,因此具有更稳定的半金属性     

晶格均匀体形变对闪锌矿结构CaC和 SrC半金属性和磁性的影响

采用基于第一性原理的全势能线性缀加平面波方法计算闪锌矿结构CaC和SrC的电子结构.计算结果表明,锌矿结构CaC和SrC是自旋向上电子为非金属性的半金属,其半金属隙分别为0.83 eV和0.81 eV.磁性的计算分析表明,CaC和SrC的晶胞总磁矩都为2.00μ_B,C的原子磁矩较强,Ca和Sr的原子磁矩较弱.使晶格均匀体形变△a/a₀限于±15%,在此范围内计算CaC和SrC的电子结构.计算研究表明,当闪锌矿结构CaC和SrC的晶格常数分别为0.490 nm—0.661 nm和0.539 nm—0.707 nm时,它们的半金属性不变,晶胞总磁矩仍然为2.00μ_B.     

第一原理研究界面弛豫对InAs/GaSb超晶格界面结构、能带结构和光学性质的影响

通过广义梯度近似的第一原理全电子相对论计算, 研究了不同界面类型InAs/GaSb超晶格的界面结构、电子和光吸收特性. 由于四原子界面的复杂性和低对称性, 通过对InAs/GaSb超晶格进行电子总能量和应力最小化来确定弛豫界面的结构参数. 计算了InSb, GaAs型界面和非特殊界面(二者交替)超晶格的能带结构和光吸收谱, 考察了超晶格界面层原子发生弛豫的影响.为了证实能带结构的计算结果, 用局域密度近似和Hartree-Fock泛函的平面波方法进行了计算. 对不同界面类型InAs/GaSb超晶格的能带结构计算结果进行了比较, 发现界面Sb原子的化学键和离子性对InAs/GaSb超晶格的界面结构、 能带结构和光学特性起着至关重要的作用.     

Cr含量对ZB型半金属铁磁体Cr_xZn_(1-x)Se磁电性能的影响

使用基于密度泛函理论的第一性原理方法,优化了闪锌矿结构的Cr_xZn_(1-x)Se(x=0.000,0.125,0.250和0.375)的2×2×2超胞的几何结构,计算了其自旋极化的态密度和能带结构、离子磁矩、电荷分布等磁电性能,详细分析了Cr含量对Cr_xZn_(1-x)Se磁电性能的影响.结果表明,Cr掺杂后ZB型ZnSe具有明显的半金属特性;当x=0.125,0.250和0.375时,Cr_xZn_(1-x)Se均有较宽的半金属带隙,从而可能具有较高的居里温度;当x=0.125时,Cr_xZn_(1-x)Se的半金属性最稳定;x=0.125,0.250和0.375时,Cr_xZn_(1-x)Se的超胞磁矩分别为整数磁矩4.0,8.0和12.0μ_B,而具有整数磁矩是半金属铁磁体非常重要的特征之一.Cr_xZn_(1-x)Se的半金属性和磁性主要来源于Cr离子的自旋极化,Cr离子的电子结构为Cr e_g~2↑e_g~1↓t_(2g)~3↑.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.