Sc掺杂Ca3Si4的电子结构和光学性质

利用基于密度泛函理论的赝势平面波方法对Sc掺Ca3Si4的电子结构和光学性质进行了系统的计算和分析比较.研究结果为块体Ca3Si4是间接带隙半导体,带隙为0.372eV,价带主要是由Si的3s和3p及Ca的3d态电子构成,导带主要是由Ca的3d态电子构成,静态介电常数ε1(0)=19,折射率n0=4.35;吸收系数在能量3.024eV处达到最大峰值1.56×105cm-1.而掺杂Sc变为n型半导体;费米能级附近的导带主要则由Ca的3d态电子和Sc的3d态电子构成,静态介电常数变为ε1(0)=54.58,折射率n0=7.416;吸收系数在能量5.253eV处达到最大峰值1.614×105cm-1.通过掺杂有效调制了Ca3Si4的电子结构和光学性质,计算结果为Ca3Si4光电材料的设计与应用提供了理论依据.     

稀土元素Lu，Sc掺杂GaN光电特性的第一性原理研究

基于密度泛函理论,采用广义梯度近似（GGA+U）平面波超软赝势方法,计算了本征GaN和稀土元素Lu、Sc掺杂GaN体系的电子结构和光学性质.结果表明：计算得到本征GaN的禁带宽度为3.37 eV,与实验值（3.39 eV）接近. Lu掺杂后GaN体系带隙变窄,而Sc掺杂后诱导了深能级杂质,带隙变宽,但仍为直接带隙半导体.掺杂后体系均发生畸变,晶格常数和体积增大,且在费米能级附近产生杂质带. Lu、Sc掺杂GaN体系的静态介电常数较本征GaN（4.50）均有所增大.Lu、Sc掺杂后体系介电常数虚部整体左移,光吸收边往低能方向移动,发生了红移现象.计算结果对稀土元素Lu、Sc掺杂GaN高压光电材料的开发和研究提供了理论依据.     

锰掺杂二硅化铬电子结构和光学性质的第一性原理计算

采用基于第一性原理的密度泛函理论(DFT)赝势平面波方法计算了锰掺杂二硅化铬(CrSi2)体系的能带结构、态密度和光学性件质.计算结果表明末掺杂CrSi2属于间接带隙半导体间接带隙宽度△ER=0.35 eV;Mn掺杂后费米能级进入导带,带隙变窄,且间接带隙宽度△Eg=0.24 eV,CrSi2转变为n型半导体.光学参数发生改变,静态介电常数由掺杂前的ε1(O)=32变为掺杂后的ε1(O)=58;进一步分析了掺杂对CrSi2的能带结构、态密度和光学性质的影响,为CrSi2材料掺杂改件的研究提供r理论依据.     

Co-Cr共掺杂金红石型TiO_2电子结构和光学性质的第一性原理研究

基于密度泛函理论,采用第一性原理赝势平面波方法计算了Co、Cr单掺杂以及Co-Cr共掺杂金红石型TiO2的能带结构、态密度和光学性质.计算结果表明:纯金红石的禁带宽度为3.0eV,Co掺杂金红石型TiO2的带隙为1.21eV,导带顶和价带底都位于G点处,仍为直接带隙,在价带与导带之间出现了由Co 3d和Ti 3d轨道杂化形成的杂质能级;Cr掺杂金红石型TiO2的直接带隙为0.85eV,在价带与导带之间的杂质能级由Cr 3d和Ti 3d轨道杂化轨道构成,导带和价带都向低能级方向移动;Co-Cr共掺杂,由于电子的强烈杂化,使O-2p态和Ti-3d态向Co-3d和Cr-3d态移动,使价带顶能级向高能级移动而导带底能级向低能方向移动,极大地减小了禁带的宽度,也是共掺杂改性的离子选择依据.掺杂金红石型TiO2的介电峰、折射率和吸收系数峰都向低能方向移动;在E2.029eV的范围内,纯金红石的ε2、k和吸收系数为零,掺杂后的跃迁强度都大于未掺杂时的跃迁强度,Co-Cr共掺杂的跃迁强度大于Co掺杂及Cr掺杂,说明Co、Cr共掺杂更能增强电子在低能端的光学跃迁,具有更佳的可见光催化性能.     

Ga掺杂ZnO电子结构和吸收光谱的第一性原理研究

采用第一性原理的平面波赝势方法和广义梯度近似,研究了纤锌矿ZnO掺杂Ga前后的电子结构和光学性质.计算结果表明,ZnO中引入杂质Ga后,导带底主要由Ga4s态和Zn4s态构成,并且Ga4s态跨过费米能级,形成n型半导体.计算得到电子浓度为2.42×10~(21)cm~(-3),掺Ga有效提高了ZnO的载流子浓度.同时ZnO掺Ga后,ZnO的光学带隙从3.47 eV展宽为4.25 eV,并且在可见光区几乎无吸收,是理想的透明导电材料.     

SrSnO3作为透明导电氧化物的第一性原理研究

SrSnO₃是一种钙钛矿结构的宽带隙半导体,透明性高、无毒且价格低廉,是一种有前景的透明导电氧化物的候选者.本文通过第一性原理计算,获得了SrSnO₃的电子结构,着重讨论了SrSnO₃的本征缺陷、外界元素掺杂的缺陷形成能及过渡能级,筛选出适宜的掺杂元素并指出了对应的实验制备环境,进一步根据带边能量位置对其电导性能机制进行了探讨.计算结果表明,SrSnO3是一种基础带隙为3.55 eV、光学带隙为4.10 eV的间接带隙半导体,具有良好的透明性,电子的有效质量轻,利于n型电导.在富金属贫氧条件下,As,Sb掺杂SrSnO₃可以提升n型电导率;SrSnO₃的价带顶位于-7.5 eV处,导带底位于-4.0 eV处,其价带顶和导带底的能量位置均相对较低,解释了其易于n型掺杂而难于p型掺杂,符合宽带隙半导体材料的掺杂规律,最后,Sb掺杂SrSnO₃被提出为有前景的廉价n型透明导电材料.     

N-S共掺杂金红石相TiO2电子结构与光学性质的第一性原理研究

采用基于第一性原理的平面波超软赝势方法研究N和S单掺杂以及N和S共掺杂金红石相TiO2的能带结构,态密度和光学性质.结果表明:N掺杂导致禁带宽度减小为1.43 eV,并且在价带上方形成了一条杂质能带;S掺杂导致费米能级上移靠近导带,直接带隙减小为0.32 eV;N和S共掺杂导致能带结构中出现了两条杂质能带,靠近导带的一条杂质能级距离导带底约0.35 eV,靠近价带的一条杂质能级距离价带顶约0.85 eV,杂质能级主要由N原子的2p轨道和S原子的3p轨道组成.N和S掺杂后不但使TiO2的吸收带产生红移,而且在可见光区具有较大的吸收系数,光催化活性增强.     

Sc掺杂正交相Ca2Si电子结构及光学性质的第一性原理

采用基于第一性原理的密度泛函理论(DFT)赝势平面波方法,对块体及掺Sc的正交相Ca2Si的电子结构和光学性质进行了系统计算.计算结果表明,掺Sc后的Ca2Si能带向低能端偏移,形成n型半导体,正交相结构能隙变为0.6084eV,相比块体Ca2Si带隙加宽了一倍,但仍为直接带隙半导体.Ca2Si掺杂Sc后,正交相导带主要是Ca的4s、3d态和Sc的3d、3p态电子构成,静态介电常数变大,折射率也变大,吸收系数相比块体在低能段基本无变化,在高能段虽吸收系数减小,但仍保持105数量级且大于β-FeSi2的吸收系数,说明Ca2Si在太阳能电池上具有较好的应用前景.通过掺杂有效调制了Ca2Si的电子结构和光学性质,计算结果为Ca2Si光电材料的设计与应用提供了理论依据.     

透明导电氧化物CuScO2的密度泛函理论研究

本文利用基于第一性原理的广义梯度近似方法分析研究透明导电氧化物CuScO2能带结构、态密度和杂质能级．计算结果表明,CuScO2的价带区主要由Cu的3d态和O的2p态构成,而导带区主要由Sc的3d态组成．在进行＋U修正之后,随着U参量的增加,CuScO2的导带区发生分裂导致导带扩大,带隙也随之扩大,表明＋U计算能较好地改进CuSc02带隙值;本文还比较分析了各种掺杂元素在CuSc02的杂质能级,发现Mg原子替位掺杂Sc能有效改善CuScO2的P型导电性能．     

过渡金属W、Mn、V、Ti掺杂二维材料MoSi2N4的第一性原理计算

本文基于密度泛函理论(DFT)的第一性原理计算了W、Mn、V、Ti替位掺杂二维MoSi₂N₄后的几何结构、电子结构以及光学性质的变化.电子结构分析表明W、Mn、W、Ti替位掺杂二维MoSi₂N₄后的禁带宽度分别为1.806 e V、1.003 e V、1.218 e V和1.373 e V;四种过渡金属掺杂后MoSi₂N₄的带隙类型没有发生改变,均为间接带隙半导体;W掺杂后的杂质能级靠近价带顶,费米能级靠近价带顶,为p型半导体,杂质能级为受主能级;Mn掺杂后的杂质能级靠近导带底,费米能级靠近导带底,为n型半导体;V和Ti掺杂后杂质能级位于费米能级附近,为复合中心;光学性质分析表明,在2 e V～4 e V的能量区间内,W掺杂结构的吸收波长为336 nm,体系发生红移;Mn、V和Ti替位掺杂后的吸收波长分别为320 nm、358 nm和338 nm,且掺杂体系均发生蓝移.     

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.