S在Cu(111)表面吸附的第一性原理研究*

基于广义梯度近似的投影缀加平面波(Projector augmented wave) 赝势和具有三维周期性边界条件的超晶胞模型,采用第一原理方法计算并分析了由于S吸附所形成的S/Cu(111)界面体系的吸附结构、吸附能和局域电子结构,考虑了不同覆盖度（1,0.25ML）下S在不同吸附位置的吸附特性. 结果表明：S原子倾向于吸附在高对称的fcc位与hcp位;由于S的负电性而使S/Cu吸附能随覆盖度的减小而增加, 与之相应,S-Cu键长随覆盖度的减小而缩短. DOS图、Bader电荷分析表明杂化主要发生在S的3p态和表面Cu原子的3d态之间,表层近邻的Cu原子向S转移的电子数随覆盖度增加而减小,这表明S与Cu(111)面有强的相互作用.     

H_2S,HS自由基以及S原子在Fe(111)表面吸附的密度泛函研究

采用广义梯度近似下的密度泛函理论方法,研究了不同覆盖度下H2S,HS自由基以及S原子在Fe(111)表面的吸附结构和吸附特性,计算了吸附能、功函数、差分电荷密度、态密度和电荷布居,讨论了覆盖度对表面吸附的影响作用,对比分析了H2S,HS自由基,S在Fe(111)表面的吸附强弱.研究结果表明:随着覆盖度的增大,吸附物与表面的作用力逐渐减弱;H2S,HS自由基,S三者与Fe(111)表面的作用力大小依次为:H2SHSS,表面容易形成FexSy腐蚀产物膜,只是随着覆盖度的不同,其致密度将发生变化.各吸附物在低指数晶面上的吸附结果表明:Fe(111)面吸附作用最强,而Fe(110)和Fe(100)吸附作用相对较弱,二者吸附能相差不大.     

二维Ti_2CO_2单层吸附H_2S分子的第一性原理研究

采用第一性原理计算方法研究了H_2S分子在二维单层Ti_2CO_2表面上的吸附以及外加应变和电场对其性质的调制,发现该吸附为物理吸附,其吸附强度几乎不受外加拉伸应变的影响,而外加电场使H_2S分子的吸附增强.同时,通过单层Ti_2CO_2表面不同结构(如水分子修饰、官能团掺杂、氧官能团空位)对H_2S分子吸附性质影响的研究表明:(1)表面吸附的水分子促进H_2S分子的吸附,其吸附强度随H_2O分子数增多而增强;(2)官能团OH掺杂浓度低于0.22 ML时,促进H_2S分子的吸附,而较高浓度OH掺杂使H_2S分子吸附减弱;官能团F掺杂对H_2S分子吸附强度几乎没有影响;(3)含氧空位的Ti_2CO_2表面与H_2S分子相互作用较强,吸附能高达-1.06 eV,且电子结构改变明显.     

分子团簇表面吸附敏化ZnO纳米线的第一性原理研究

ZnO纳米线作为新型太阳能电池结构的重要组成部件之一, 其导电能力直接影响到太阳能电池的性能. 采用密度泛函理论平面波超软赝势方法, 计算并分析了C₂H₆O(乙醇)、 C₆H₅FS(4-氟苯硫酚)、 C₇HF₇S(4-(三氟甲基L)-2, 3, 5, 6-四氟硫代苯酚) 等小分子吸附的六边形结构\langle0001angle ZNWs (ZnO 纳米线) 的几何结构、 吸附能和电子结构. 首先, 通过几何优化得到了不同基团吸附的ZNWs的稳定结构, 同时吸附能计算结果表明C₇HF₇S吸附的体系结构最为稳定, 且吸附呈现放热反应; 其次, 为研究表面敏化对导电性能的影响, 计算了不同小分子基团吸附下的能带结构和态密度, 并利用能带理论分析了表面吸附敏化对禁带宽度的调控机理, 结果分析表明小分子表面吸附敏化对ZNWs的电学性能有一定的影响, 其中C₇H₇FS和C₆H₅FS分子均发生了不同程度的电荷转移.     

硫原子在镍基合金825(001)面吸附的第一性原理研究

元素硫在镍基合金表面吸附产生严重的电化学腐蚀,为从原子尺度研究硫腐蚀机理,采用第一性原理方法,构建并优化了镍基合金825的晶胞结构模型,计算分析了S原子在镍基合金825耐蚀性较差面(001)晶面的吸附及电子转移情况.结果表明:Ni原子占据顶角, Cr原子和Fe原子对称占据面心是镍基合金825稳定的晶胞结构;原子S在镍基合金825(001)面上最稳定的吸附位为四重穴位,吸附能为-6.51 eV; S吸附前后的态密度(DOS)和二维电荷差分密度图(DCD)对比发现,镍基合金825中Fe与S之间电荷偏移明显,形成离子键,易生成腐蚀产物Fe_xS_y. S的吸附对镍基合金825中Cr原子的电子分布影响不大,且合金中Cr和Ni抑制了合金中Fe与S之间的相互作用,从而提高了合金耐蚀性.     

Au(111)表面甲基联二苯丙硫醇盐单层膜的原子结构

利用第一性原理研究了甲基联二苯丙硫醇盐(BP3S)单体、虚拟Au表面BP3S的分子链和单层膜及BP3S/Au(111)吸附系统的原子结构.计算表明BP3S单体呈对称结构,两苯环夹角为35°±10°.首先BP3S单体在虚拟Au(111)表面自组装成稳定的单一分子链.然后在虚拟Au(111)表面,分子链错位排列自组装成两种稳定的单层膜.在虚拟Au(111)-(3~(1/2)×7~(1/2))和Au(111)-(3~(1/2)×13~(1/2))表面,分子链与虚拟表面夹角分别为60°和30°.最后把两种稳定的单层膜吸附在Au(111)表面的四个吸附位,计算表明只有桥位和顶位稳定,且桥位的吸附能比顶位的吸附能低.比较吸附前后BP3S单层膜的结构变化,可知其变化不大,这说明吸附系统的结构参数主要取决于单层膜内的相互作用,衬底对其的影响不大.     

S钝化GaAs(100)表面的电子特性

用TB-LMTO方法研究单层的S原子在理想的GaAs (100) 表面的化学吸附, 对GaAs(100)表面是Ga-和As-中断两种情况分别进行考虑. 计算了S原子在不同位置的吸附能、吸附体系与清洁的GaAs(100)表面的层投影态密度, 以及电子转移情况. 结果表明, 两种情况下S原子都是桥位吸附最稳定, S-Ga相互作用比S-As稍强, S钝化GaAs(100)表面可以取得明显的钝化效果.     

覆盖度对S原子在Ir(001)表面吸附性质的影响

采用第一性原理方法模拟了覆盖度对S原子在Ir(001)表面吸附能和电子结构的影响。结果表明：在覆盖度0.50 ML以下,S原子吸附在Hollow空位最稳定,且吸附能几乎不随覆盖度变化;在覆盖度0.66 ML以上吸附能随覆盖度增加而减小。吸附体系金属表面d带电子结构随覆盖度变化与O/Pt(111)吸附体系相似。这些结果与Hammer-Nørskov模型吻合。     

S在Pt皮肤Pt_3Ni(111)面吸附的第一性原理研究

采用基于密度泛函理论的第一性原理方法,计算并分析了S原子在Pt皮肤Pt3Ni(111)面不同位置的吸附特性.结果表明:S原子在Pt皮肤Pt3Ni的fcc位吸附最强,吸附能为5.49eV;与S原子在纯净的Pt(111)表面吸附相比较,S原子在Pt皮肤Pt3Ni(111)面相应吸附位置的吸附能变小,与近邻Pt原子形成的S-Pt键变长,表明掺杂的Ni会减小相应位点S原子的吸附能,降低体系对S原子的吸附能力,进而减弱S吸附对体系催化能力的影响;态密度分析发现,S原子的吸附使得Pt基催化剂的催化活性降低,主要是S的2p电子引起的;这些结果将为后续研究Pt基合金电极抗S中毒效果以及探究S原子吸附后Pt3Ni的活性位提供依据.     

H2S、HCN、PH3在FeO（100）表面吸附的密度泛函理论研究

基于密度泛函理论研究了H2S、HCN、PH3 在FeO(100)表面的吸附行为,其吸附位点主要考虑四个：Fe-top(铁顶位)、O-top(氧顶位)、Hollow(空位)、Bridge(桥位)。结果表明H2S吸附在O-top吸附位点的吸附能最小,为-1.02ev,即在该位点的吸附体系最稳定。当HCN吸附在FeO(100)表面时,各吸附位点的稳定顺序为Hollow>Fe-top>Bridge>O-top。PH3 的最稳定的吸附位点与H2S的一致,为O-top吸附位点,其吸附能为-1.11ev。当H2S吸附在O-top吸附位点时,H2S与FeO（100）表面的电荷转移量最多,说明该吸附构型最稳定,而HCN吸附在FeO(100)表面,在Hollow吸附位点的电荷转移量最多,也即该吸附位点属于最稳定吸附位点。PH3与FeO（100）表面之间的电荷转移量最多的吸附位点与H2S的相同。当H2S和PH3吸附在O-top吸附位点时,吸附后的态密度曲线整体向低能级移动,峰值降低,其吸附结构变得更加稳定。而HCN吸附在Hollow位点时,吸附后的HCN态密度曲线向能量更低的区域移动,吸附体系变得更稳定。     

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.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

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.