HCOOH在Pd-Fe(111)(nPd∶nFe=1∶1)表面吸附的密度泛函理论研究简

采用密度泛函理论与周期性平板模型相结合的方法,对HCOOH在Pd(111)表面top,fcc,hcp,bridge四个吸附位和Pd-Fe(111)表面Pd-top,Fe-top,PdPd-bridge,PdFe-bridge,FeFe-bridge,Pd2Fehcp,PdFe2-hcp,Pd2Fe-fcc,PdFe2-fcc等9个吸附位的13种吸附模型进行了能量计算、构型优化,得到了HCOOH较有利的吸附位;并对清洁表面进行能带分析.结果表明:掺杂Fe后,Pd催化剂对HCOOH催化活性增强;HCOOH在Pd(111)表面的最稳定吸附位fcc的吸附能是-41.8kJ·mol-1,在Pd-Fe(111)表面的最稳定吸附位Pd2Fe-hcp的吸附能是-126.5kJ·mol-1,而且HCOOH在金属表面属于化学吸附.     

HCOOH在Pd-Fe(111)(nPd:nFe=1:1)表面吸附的密度泛函理论研究

采用密度泛函理论与周期性平板模型相结合的方法,对HCOOH在Pd(111)表面top, fcc, hcp, bridge 四个吸附位和Pd-Fe(111)表面Pd-top, Fe-top, PdPd-bridge, PdFe-bridge, FeFe-bridge, Pd2Fe-hcp, PdFe2-hcp, Pd2Fe –fcc, PdFe2-fcc等9个吸附位的13种吸附模型进行了能量计算、构型优化,得到了HCOOH较有利的吸附位;并对清洁表面进行能带分析。结果表明：掺杂Fe后,Pd催化剂对HCOOH催化活性增强;HCOOH在Pd(111)表面的最稳定吸附位fcc的吸附能是-41.8kJ•mol-1,在Pd-Fe(111)表面的最稳定吸附位Pd2Fe-hcp的吸附能是-126.5 kJ•mol-1,而且HCOOH在金属表面属于化学吸附。     

钴原子及其团簇在Rh(111)和Pd(111)表面的扫描隧道显微学研究

利用扫描隧道显微镜和扫描隧道谱(STM/STS)及单原子操纵,系统研究了单个钴原子(Co) 及其团簇在Rh (111)和Pd (111)两种表面的吸附和自旋电子输运性质. 发现单个Co原子在Rh (111)上有两种不同的稳定吸附位,分别对应于hcp和fcc空位, 他们的高度明显不同,在针尖的操纵下单个Co原子可以在两种吸附位之间相互转化. 在这两种吸附位的单个Co原子的STS谱的费米面附近都存在很显著的峰形结构, 经分析认为Rh (111)表面单个Co原子处于混价区,因此这一峰结构是d轨道共振 和近藤共振共同作用的结果.对于Rh (111)表面上的Co原子二聚体和三聚体, 其费米面附近没有观测到显著的峰,这可能是由于原子间磁交换相互作用 和原子间轨道杂化引起的体系态密度改变所共同导致.与Rh (111)表面不同, 在Pd (111)表面吸附的单个Co原子则表现出均一的高度.并且对于Pd (111)表面所有 单个Co原子及其二聚体和三聚体,在其STS谱的费米面附近均未探测到显著的电子结构, 表明Co原子吸附于Pd (111)表面具有与Rh (111)表面上不同的原子-衬底相互作用与自旋电子输运性质.     

Rh在CeO_2(111)表面吸附的第一性原理研究

采用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,用第一原理计算方法,计算并分析了Rh在CeO_2(111)表面吸附所形成的Rh/CeO_2(111)界面体系的吸附能,价键结构和局域电子结构.考虑了Rh在不同吸附位置的吸附情况.结果表明:1)Rh在CeO_2(111)面有较大的吸附能,表明Rh与CeO_2(111)面有较强的相互作用,而且Rh在位于表面O的三度位,且位于次层氧的顶位的吸附最强;2)Rh的4d态同衬底O的2p态有明显的杂化作用,这是Rh同CeO_2较强作用的主要原因;3)Rh被CeO_2(主要是Rh的次近邻的Ce)氧化为Rh~(3+),并伴随着Ce~(4+)→Ce~(3+)反应的发生.     

C_2H_x(x=4～6)在Ni(111)表面吸附的DFT研究

采用密度泛函理论与周期平板模型相结合的方法,对物种C_2H_x(x=4～6)在Ni(111)表面的top,fcc,hcp和bridge位的吸附模型进行了结构优化、能量计算,得到了各物种较有利的吸附位;并对最佳吸附位进行密立根电荷和总态密度分析.结果表明:C_2H_6和C_2H_4在Ni(111)表面的最稳定吸附位都是top位,吸附能分别是-36.41和-48.62 kJ·mol~(-1),物种与金属表面吸附较弱;而C_2H_5在Ni(111)表面的最稳定吸附位hcp的吸附能是-100.21 kJ·mol~(-1),物种与金属表面较强;三物种与金属表面之间都有电荷转移,属于化学吸附.     

分子取向对CO在Pd(111)面吸附的影响

 用基于密度泛函理论广义梯度近似下的平面波赝势方法计算了在Pd(111)晶面两种不同CO分子取向的吸附结构。计算结果表明，CO分子碳端和氧端靠近Pd(111)面的吸附能分别为-1.75，-0.28 eV，碳端吸附的结构比氧端吸附能力强。因此，分子取向影响CO在Pd(111)面上的吸附，通过控制CO的取向可能减小Pd(111)的吸附进而减弱Pd(111)面CO分子的中毒。     

外吸附CO过渡金属团簇Pd5(CO)n(n=1～6)的几何结构、电子性质、前线轨道和磁性的密度泛函计算研究

本文采用密度泛函理论中的广义梯度近似对过渡金属团簇Pd5(CO)n(n=1～6)的几何结构、电子性质、前线轨道和磁性进行计算研究,由结构优化可知:当CO分子的C原子吸附在面桥位时形成的单重态Pd5 CO结构热力学最稳定,和Zanti等人(Eur.J.Inorg.Chem.2009,3904)得到的结论一致.Pd5(CO)2和Pd5 (CO)2最稳定结构中,第二个和第三个CO分子都吸附在边桥位,而第一个CO分子吸附在面桥位.但是对于最稳定的Pd5 (CO)n(n=4,5,6),所有的CO分子都位于边桥位,从吸附能的角度看,Pd5(CO)2应该是最容易得到的吸附产物.由能隙可知:Pd5 (CO)n(n=1～6)的动力学稳定性相比较Pd5有所增加,但是并不会随着CO分子数目的增加而呈现递增或者递减的规律,其中Pd5 (CO)3具有最好的动力学稳定性.CO在Pd5上发生非解离性化学吸附,CO健的强度变化逐渐变小.CO对HOMO和LUMO贡献很小,使得HOMO和LOMO的成分发生一定的改变.由VIP和VEA计算可知:随着CO数目的增加,Pd5(CO)n(n=1～6)的失电子能力逐渐降低,而得电子能力逐渐增强.Pd5具有2μB的磁矩,但是Pd5 (CO)n(n=1～6)的磁性完全淬灭.     

NO_x在Pt及其合金表面吸附的第一性原理模拟研究

本研究通过密度泛函理论(DFT)模拟氮氧化物(NO_X)在Pt及Pt/(Au,Rh)合金slab模型(111)表面的吸附行为,计算其吸附能与结合能.对比NO和NO_2的实验结果,表明合金元素的添加,可能使Pt(111)对NO_X的吸附能力和选择性发生变化,其中Au元素表面置换使得总吸附能力下降,但更容易吸附NO_2; Rh元素表面置换则使得总吸附能力提高,且更容易吸附NO.     

Pd与CeO2(111)面的相互作用的第一性原理研究

采用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，用第一性原理计算方法，计算并分析了Pd在CeO₂(111)面上不同覆盖度时的吸附能，价键结构和局域电子结构. 考虑了单层Pd和1/4单层Pd两种覆盖度吸附的情况. 结果表明：1)在单层吸附时，Pd的最佳吸附位置是O的顶位偏向Ce的桥位；在1/4单层吸附时，Pd最易在O的桥位偏向次层O的顶位吸附.2) 单层覆盖度吸附时，吸附原子Pd之间的作用较强；1/4单 关键词： 三元催化剂 Pd 2')" href="#">CeO₂ 吸附 密度泛函理论     

Al吸附在Pt,Ir和Au的(111)面的低覆盖度研究

应用密度泛函理论,系统研究了Al原子在Pt(111),Ir(111)和Au(111)表面的桥位、顶位、三重面心立方(fcc)洞位和六角密排(hcp)洞位这四个典型位置的吸附情况. 主要计算了三吸附体系的几何结构、平均结合能和差分电荷密度,并系统讨论了相关原子的密立根电荷布居数和投影态密度.研究发现,对于Pt(111)和Ir(111)表面,Al原子在hcp洞位最稳定,但是对于Au(111)表面,Al原子在fcc洞位最稳定. 关键词： 吸附 密度泛函理论 结合能 电子结构     

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.     

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.     

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.