反应扩散法制备的PbMo_6S_8超导带的超导特性

本文报道反应扩散法制备Chevrel相PbMo_6S_8超导带材的过程以及带材的超导特性。Mo带与H_2S气体反应生成单相的Mo-S化合物(MoS_2或Mo_2S_3,根据反应温度而定),再与Pb的蒸汽反应生成单相的PbMo_6S_8薄层。PbMo_6S_8超导层的临界温度T_c=13.0—14.5K,转变宽度在0.15—0.20K之间,j_c(6T,4.2K)≈1.9×10~8A/m~2。     

氢分子在Mg2Ni(010)面的吸附与分解

本文采用基于密度泛函理论(DFT)的第一原理赝势平面波(PW-PP)方法,对氢分子在Mg2Ni(010)面的吸附与分解进行了研究,我们发现氢分子以Hor1的方式吸附在表面层Ni原子的顶位时吸附能最高,为0.6769eV,这表明氢分子最可能以Hor1的方式吸附在表面层Ni原子的顶位,此时氢分子跟表面的距离( )和氢分子的键长( )分别为1.6286Å和0.9174Å. 在分子吸附的基础上计算了氢分子沿着选取的反应路径分解时的反应势垒,发现要使氢分子分解需要0.2778eV的活化能,而氢分子分解时的吸附能为0.8390eV,分解后两个氢原子的距离为3.1712Å. 在分子吸附和分解吸附时氢原子跟正下方的Ni原子都有较强的相互作用,氢原子所得到的电子主要来自氢分子正下方的Ni原子.     

室温合成非晶三硫化钼析氢催化剂的性能调制以及其在串联制氢器件中的应用

高催化活性、低成本、良好工艺兼容性以及高稳定性的析氢催化剂是实现一体化光电化学水解制氢器件的关键, 然而传统的贵金属催化剂由于储量稀缺、成本高昂而严重限制了光电化学水解制氢器件的产业化进程. 本文在室温下通过湿法化学合成法制备了高催化活性、成本低廉以及工艺兼容性好的非金属非晶三硫化钼析氢催化剂, 并研究了不同催化剂滴涂量对其催化活性以及串联制氢器件制氢性能的影响. 结果表明, 存在最优化非晶三硫化钼催化剂滴涂量以获得最佳催化活性(10 mA/cm²电流密度对应电势达260 mV vs. RHE(可逆氢电极), 塔菲尔斜率达68 mV/dec), 其粗糙表面以及多孔结构可获得更大的电化学接触面积以促进析氢反应. 进一步将其作为光阴极应用于串联制氢器件, 可有效降低过电势损失和提高光生电流密度输出, 与光阳极结合有望提高制氢效率.     

氢分子在Mg2Ni(010)面的吸附与分解

本文采用基于密度泛函理论(DFT)的第一原理赝势平面波(PW-PP)方法,对氢分子在Mg2Ni(010)面的吸附与分解进行了研究,发现氢分子以Horl的方式吸附在表面层Ni原子的顶位时吸附能最高,为0.6769 eV,这表明氢分子最可能以Horl的方式吸附在表面层Ni原子的顶位,此时氢分子跟表面的距离(rd)和氢分子的键长(rH)分别为1.6286 A和0.9174 (A).在分子吸附的基础上计算了氢分子沿着选取的反应路径分解时的反应势垒,发现要使氢分子分解需要0.2778 eV的活化能,而氢分子分解时的吸附能为0.8390 eV,分解后两个氢原子的距离为3.1712(A).在分子吸附和分解吸附时氢原子跟正下方的Ni原子都有较强的相互作用,氢原子所得到的电子主要来自氢分子正下方的Ni原子.     

2D SnP_3:具有高载流子迁移率和光吸收率的范德瓦尔斯晶体（英文）

本文基于第一性原理计算,预测了二维SnP_3层作为新型半导体材料,具有0.71 eV(单层)和1.03 eV(双层)的间接带隙,这与体结构的金属特性不同.值得注意的是,2D SnP_3具有9.171×10~4 cm~2·V~(-1)·s~(-1)的高空穴迁移率和对于整个可见光谱的高光吸收(～10~6 cm~(-1)),这预示2D SnP3层有望成为纳米电子学和光电子学的候选材料.有趣的是,本文发现2D SnP_3双层具有与硅类似的电子和光学特性.考虑到硅基微电子和光伏技术的巨大成功,本文的研究结果将有助于纳米领域的相关研究.     

MgH_2(110)表面Pd单原子催化氢脱附反应的第一性原理研究（英文）

本文采用第一性原理密度泛函理论计算研究了MgH_2(110)表面吸附单原子Pd后的氢脱附反应.计算发现,在吸附一个Pd单原子后,MgH_2(110)表面氢脱附反应的能垒可以从1.802 eV显著地降低到1.154 eV,表明Pd单原子对于氢脱附具有很强的催化效应.并且,Pd单原子催化还可以将氢脱附的温度从573 K显著地降低到了367 K,从而使MgH_2(110)表面的氢脱附反应更加容易和快速地发生.此外,通过MgH_2(110)表面氢溢出机制的反向过程来讨论了氢脱附反应的微观过程.该研究表明Pd/MgH_2薄膜在未来的实验中可作为良好的储氢材料.     

Ni(111)表面一氧化碳和氢共吸附的密度泛函理论研究

本文用密度泛函理论(DFT)的总能计算研究了一氧化碳和氢原子在Ni(111)表面上p(2×2)共吸附系统的原子结构和电子态，结果表明CO和H原子分别被吸附于两个对角p(1×1)元胞的hcp和fcc位置.以氢分子和CO分子作为能量参考点，总吸附能为2.81 eV，相应的共吸附表面功函数φ为6.28 eV.计算得到的C—O，C—Ni和H—Ni的键长分别是1.19?, 1.96?和 1.71?，并且CO分子以C原子处于hcp的谷位与金属衬底原子结合.衬底Ni(111)的最外两层的晶面间距在吸附后的相对变化分别是 关键词： Fisher-Tropsch反应 催化作用 Ni(111) p(2×2)/(CO+H) 共吸附     

单个钛原子储氢能力和储氢机制的第一性原理研究

采用基于密度泛函理论的第一性原理方法研究了单个过渡金属钛原子吸附氢分子的物理机制. 研究表明,单个钛原子最多能吸附8对氢分子,吸附结构为对称的两个类金字塔型结构, 其平均吸附能为- 0.28 eV.通过计算轨道能级和差分电荷密度分布,分析决定吸附结构、 吸附能大小以及吸附氢分子数目的内在物理机制.研究表明,钛原子的4s电子转移到3d轨道上, 从而产生较强的极化电场,导致氢分子极化,钛原子通过静电极化作用吸附氢分子. 本文的研究将对设计高密度储氢材料有一定的指导作用.     

Al2O3X2（X=H,D,T）的电子振动近似方法

用密度泛函理论在B3LYP/6-311++g（d,p）基组水平上对Al₂O₃X₂（X=H,D,T）分子的可能较低能量构型进行了几何优化.结果表明该分子的基态电子态和对称性为Al₂O₃X₂（X=H,D,T）（¹A′）C_s,计算了氢同位素分子及Al₂O₃X₂（X=H,D,T）的电子能量E、定容热容C_V和熵S.用电子振动近似方法计算了固体Al₂O₃的氢化热力学函数△H⁰,△S⁰,△G⁰,以及平衡压力与温度的关系.当Al₂O₃吸附氢（氘,氚）形成固体时,反应的氢氘氚排代效应的顺序为氚排代氘,氘排代氢,与钛等金属与氢及其同位素反应的氢氘氚排代效应的顺序相反.总体来说,这种排代效应都非常弱.随着温度的增加,这系列反应的氢氘氚排代效应趋于消失.     

MgH2(110)表面Pd单原子催化氢脱附反应的第一性原理研究

本文采用第一性原理密度泛函理论计算研究了MgH₂(110)表面吸附单原子Pd后的氢脱附反应. 计算发现,在吸附一个Pd单原子后,MgH₂(110)表面氢脱附反应的能垒可以从1.802 eV显著地降低到1.154 eV,表明Pd单原子对于氢脱附具有很强的催化效应. 并且,Pd单原子催化还可以将氢脱附的温度从573 K显著地降低到了367 K,从而使MgH₂(110)表面的氢脱附反应更加容易和快速地发生. 此外,通过MgH₂(110)表面氢溢出机制的反向过程来讨论了氢脱附反应的微观过程. 该研究表明Pd/MgH₂薄膜在未来的实验中可作为良好的储氢材料.     

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.     

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.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

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.     

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.