W_(20)O_(58)(010)表面氢吸附机理的第一性原理研究

采用基于密度泛函理论的第一性原理平面波超软赝势方法,在广义梯度近似下,研究了W_(20)O_(58)晶胞、W_(20)O_(58)(010)表面结构及其氢吸附机理.计算结果表明:W_(20)O_(58)晶体理论带隙宽度为0.8 eV,为间接带隙,具有金属性.W_(20)O_(58)晶体中W—O共振较强,以共价键居多.W_(20)O_(58)(010)表面有WO终止(010)表面和O终止(010)表面,表面结构优化后使得W—O键长和W—O—W键角改变,从而实现表面弛豫.分别计算了H_2分子吸附在WO终止(001)表面和O终止(001)表面的WO-L-O_(1c),WO-V-O_(1c),WO-L-O_(2c),WO-V-O_(2c),O-L-O_(1c)和O-V-O_(1c)六种吸附构型,其中WO-L-O_(1c),WO-V-O_(1c)和WO-L-O_(2c)这三种吸附构型不稳定;而WO-V-O_(2c),O-L-O_(1c)和O-V-O_(1c)这三种吸附构型都很稳定,H_2分子都解离成两个H原子,吸附能均为负值,分别为-1.164,-1.021和-3.11 eV.WO-V-O_(2c)吸附构型的两个H原子分别吸附在O和W原子上;O-L-O_(1c)吸附构型的两个H原子,一个与O原子成键,另一个远离了表面.其中O-V-O_(1c)吸附构型最稳定,两个H原子失去电子,为O原子提供电子.分析其吸附前后的态密度,H的1s轨道电子与O的2p,2s轨道电子相互作用,均形成了一些较强的成键电子峰,两个H原子分别与O_(1c)形成化学键,最终吸附反应生成了一个H_2O分子,同时产生了一个表面氧空位.     

NH3分子在LiH(100)表面吸附的第一性原理研究

采用第一性原理方法研究了NH3分子在LiH(100)晶面的表面吸附情况. 通过研究LiH(100) /NH3体系的吸附位置、吸附能和电子结构,发现NH3分子在Li3N (100)晶面主要是化学吸附,初始位置为NH3分子中N-H键在Li顶位时失去一个H原子,并在LiH(110)面形成NH2基,其吸附能为0.511 eV,属于强化学吸附,吸附作用最强. 此时NH2基与附近H原子和Li原子之间为离子键作用,NH2基中N—H键为共价键;NH3分子中另一个H原子与LiH表面的一个H原子形成一个H2分子逸出表面. H2分子中H-Ｈ键为明显的共价键.     

三氧化钨表面氢吸附机理的第一性原理研究

采用基于密度泛函理论的第一性原理平面波超软赝势方法,在广义梯度近似下,研究了立方WO_3,WO_3(001)表面结构及其氢吸附机理.计算结果表明立方晶体WO_3理论带隙宽度为0.587 eV.WO_3(001)表面有WO终止(001)表面和O终止(001)表面两种结构,表面结构优化后W—O键长和W—O—W键角改变,从而实现表面弛豫;WO终止(001)表面和O终止(001)表面分别呈现n型半导体特征和p型半导体特征.分别计算了H原子吸附在WO终止(001)表面和O终止(001)表面的H—O_(2c)—H,H—O_(2c)…H—O_(2c),H—O_(1c)—H和H—O_(1c)…H—O_(1c)四种吸附构型,其中H—O_(1c)—H吸附构型的吸附能最小,H—O键最短,H失去电子数最多,分别为-3.684 eV,0.0968 nm和0.55e,此吸附构型最稳定.分析其吸附前后的态密度,带隙从吸附前的0.624 eV增加到1.004 eV,价带宽度基本不变.H的1s轨道电子与O的2p,2s轨道电子相互作用,在-8和-20 eV附近各形成了一个较强的孤立电子峰,两个H原子分别与一个O_(1c)原子形成化学键,最终吸附反应生成了一个H_2O分子,同时产生了一个表面氧空位.     

NH3分子在LiH（100）表面吸附的第一性原理研究

采用第一性原理方法研究了NH₃分子在LiH（100）晶面的表面吸附情况.通过研究LiH（100）/NH₃体系的吸附位置、吸附能和电子结构,发现NH₃分子在LiH（100）晶面主要是化学吸附,初始位置为NH₃分子中N-H键在Li顶住时失去一个H原子,并在LiH（100）面形成NH₂基,其吸附能为0.511 eV,属于强化学吸附,吸附作用最强.此时NH₂基与附近H原子和Li原子之间为离子键作用,NH₂基中N—H键为共价键;NH₃分子中另一个H原子与LiH表面的一个H原子形成一个H₂分子逸出表面.H₂分子中H-H键为明显的共价键.     

LiH晶体在空气中腐蚀的理论研究

用CASTEP软件包中的GGA/RPBE基组,采用平面波超软赝势方法,计算了空气中主要成分H2O、O2、CO2、HCl、N2在LiH表面的最佳吸附方式,优化结构后的离解能、布居数和态密度.由吸附前后的态密度(DOS)图和电子转移数可知,H2O、O2发生的是化学吸附,CO2、HCl、N2发生的是物理吸附.     

N2H4在NiFe(111)合金表面吸附稳定性和电子结构的第一性原理研究

采用基于色散校正的密度泛函理论进行了第一性原理研究, 详细分析了肼(N₂H₄)在Ni₈Fe₈/Ni(111)合金表面稳定吸附构型的吸附稳定性和电子结构及成键性质. 通过比较发现, 肼分子以桥接方式吸附在表面的两个Fe原子上是最稳定的吸附构型, 其吸附能为-1.578 eV/N₂H₄. 同时发现, 肼分子在这一表面上吸附稳定性的趋势为: 桥位比顶位吸附更有利, 且在Fe原子上比在Ni原子上的吸附作用更强. 进一步分析了不同吸附位点上稳定吸附构型的电子结构、电荷密度转移以及电子局域化情况. 结果发现: 相同吸附位点的电子态密度图基本一致, 并且N原子的p轨道和与之相互作用的表面原子的d轨道之间存在态密度上的重叠; 吸附后电荷密度则主要从肼分子转移到表面原子之上; 在电子局域化函数切面图中也发现吸附后电子被局域到肼分子的N原子和相邻的表面原子之间. 这些电子结构的表征都充分说明肼分子与表面原子之间通过电荷转移形成了强烈的配位共价作用.     

Aun(n=2,3,4)团簇与乙醇分子相互作用的第一性原理研究

利用密度泛函理论研究了Au_n(n=2,3,4)团簇与乙醇分子的吸附机理.研究结果表明:Au_n(n=2,3,4)团簇分别能够吸附1到n个乙醇分子,生成Au_n-(C₂H₆O)_1-n配合物;Au₄团簇吸附乙醇分子有多种构型,通过分析吸附能和Mulliken电荷分布,确定了4个乙醇分子的吸附顺序及相应的稳定构型;Au_n(n=3,4)团簇在吸附最后一个乙醇分子时改变了前面Au—O成键的作用模式,而是选择Au—H成键;作为吸附主体的金团簇和被吸附的乙醇分子在吸附前后构型变化都很少,它们之间的吸附作用为弱相互作用. 关键词： 金团簇 乙醇分子 密度泛函理论     

LiH晶体在空气中腐蚀的理论研究

用CASTEP软件包中的GGA／RPBE基组，采用平面波超软赝势方法，计算了空气中主要成分H2O、O2、CO2、HCl、N2在LiH表面的最佳吸附方式，优化结构后的离解能、布居数和态密度．由吸附前后的态密度（DOS）图和电子转移数可知，H2O、O2发生的是化学吸附，CQ、HCl、N2发生的是物理吸附．     

第一性原理研究O2和H2O在ZnO (101 ̅0)表面上的吸附行为

运用基于密度泛函理论(DFT)的第一性原理方法研究了O2和H2O单分子在ZnO (101 ̅0)表面上的吸附行为。吸附位点主要考虑了表面的Zn顶位和Zn桥位,同时也考虑了其它可能的吸附行为。对于O2在ZnO (101 ̅0)表面上的吸附设计了9个模型,H2O在ZnO (101 ̅0)表面上的吸附设计了12个模型。通过形成能计算发现,O2在表面上的吸附为正值,H2O的吸附为负值。O2和H2O单分子在表面上发生分子吸附,未见解离形态。对于O2吸附最稳定的结构是O2分子与表面相邻的Zn原子形成了Znslab1-Oads1-Oads2-Znslab2桥连键。其它较为稳定的结构是Oads1原子迁移到下一个表面重复晶胞的O原子位置附近,在表面上形成了Znslab1-Oads1键,同时Oads2原子扩散至表面沟渠上方。对于H2O吸附,不论以何种方式吸附结构都比较稳定。其中最稳定的构型是Oads迁移到下一个表面重复晶胞的O原子位置附近,形成了Znslab1-Oads键以及Oslab3-H氢键。另外较稳定的构型是Oads迁移到ZnO (101 ̅0)表面台阶上方,形成了Znslab1-Oads键以及Oslab1-H氢键。     

H2O在SrTiO3-(001)TiO2表面上吸附和解离的密度泛函理论研究

利用密度泛函理论研究了0.25单层(ML),0.5ML,0.75ML和1ML吸附率下H2O在SrTiO3-(001)TiO2表面上的吸附行为.比较了不同吸附率下分子吸附和解离吸附的稳定性,利用微动弹性带(nudged elastic band)方法计算了H2O的解离势垒.结果表明:在低吸附率(0.25ML和0.5ML)时,H2O表现为解离吸附;在0.75ML吸附率下,分子吸附和解离吸附同时存在;而在全吸附(吸附率为1ML)时,分子吸附更稳定.基于对H2O分子与表面之间以及H2O分子之间的电荷转移和相互作用的分析,讨论了吸附率对H2O吸附和解离的影响.     

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.