Optical and structural characterization of a self-aligned single electron transitor structure by cathodoluminescence microscopy

We report about optical and structural investigations of a self-aligned single electron transistor (SET) structure using cathodoluminescence-(CL) and transmission electron microscopy (TEM). The SET structures were fabricated by MBE growth of GaAs/AlAs on different prepatterned GaAs (1 0 0) substrates. This technique for the in situ formation of nanoscopic semiconductor heterostructures is presently a widely used and promising approach for the fabrication of low-dimensional systems like quantum wires and quantum dots (QD). The active region of the SET structure consists of a GaAs/AlGaAs-QD formed by thickness modulation of a single quantum well (SQW) during the MBE growth. The position and the size of the QD is defined by the design of the substrate pattern. The thickness modulation of the GaAs-SQW is evidenced by TEM investigations. The lateral confinement potential given by the thickness modulation of GaAs-SQW is directly imaged by CL microscopy.     

Ab initio study of structural, electronic and optical properties of MnHg(SCN)4 and FeHg(SCN)4

 The structural, electronic and optical properties of MnHg(SCN)₄ and FeHg(SCN)₄ were studied by means of quantum-mechanical calculations based on the density-functional theory and pseudopotential method. The lattice constants can be compared with the experimental values when the effects of temperature are considered. The peaks of partial density of states of S, C, N and Hg of FeHg(SCN)₄ have a tendency of shifting to the higher energy levels relative to those of MnHg(SCN)₄. The distributions of the 3d electronic states in the transition metal atoms show quite large difference and decide different optical properties. We found that absorptional peaks of FeHg(SCN)₄ lag behind those of MnHg(SCN)₄ and the peak in the infrared range has a higher absorptional intensity, which are in accord with the experimental results. By analyzing the distributions and transitions of the 3d electronic states, we explained the different absorption phenomena.     

Investigation on crystalline structure and dielectric relaxation behaviors of hot pressed poly(vinylidene fluoride) film

The dielectric relaxation behaviors of hot pressed poly(vinylidene fluoride) (PVDF) film have been studied using dielectric spectroscopy in the frequency domain from 20 Hz to 5 MHz at temperatures between 20 °C and 200 °C. Crystalline/amorphous interphase is suggested with methods of FTIR, XRD, and DSC. Frequency and temperature dependence of dielectric spectroscopy reveals the relaxation behavior and structural dynamics of the samples, and three types of relaxation processes are suggested, α_Ac relaxation process contributed by the hopping transport process near the periphery of conduction band or valence zones at Fermi energy, α_c relaxation process related to the structure change of crystal lattice trapped dipoles in crystalline regions, and α_a relaxation process arising from segmental dipole rearrangement of interphases in amorphous regions. Cole-Cole and Havriliak-Negami experimental equations were utilized to analyze these relaxation processes, and differences of Arrhenius parameters for α_Ac and α_c relaxation processes obtained from Cole-Cole and Havriliak-Negami equations were discussed in detail. Activity energy of different relaxation processes obtained from Arrhenius equation and VFT equation indicates non-single thermal activation mechanism for hot pressed PVDF film.     

Optical limiting action of C60 doped poly(dimethylacetylendicarboxylate)

The optical limiting action of poly(dimethylacetylendicarboxylate) polymer doped with fullerene C₆₀ has been investigated under irradiation with 10 ns laser pulses at 532 nm. The optical limiting measurements were performed at four different dopant concentrations. The threshold limiting fluence at 0.3 J/cm² was observed at high doping concentrations, with transmission of about 55%. An explanation based on the combination of two-photon absorption and reverse saturable absorption was proposed for its nonlinear optical absorption behavior.     

Optical spectra and energy band structure of AgAsS2 crystals

Ground and excited states of three exciton series are observed in the region of fundamental absorption edge of AgAsS₂ crystals. The contours of exciton reflection spectra are calculated and the main parameters of excitons and energy bands are determined in the center of Brillouin zone. The optical reflection spectra are investigated at 30 K in E∥c and E⊥c polarizations in AgAsS₂ crystals in the region of 2-6 eV. The optical functions are calculated from the reflection spectra and a scheme of electronic transitions responsible for peculiarities of reflection spectra deep into the absorption band is proposed.     

Fabrication, study of optical properties and structure of most stable (CdP2)n nanoclusters

CdP₂ nanoclusters were fabricated by incorporation into pores of zeolite Na–X and by laser ablation. Absorption and photoluminescence (PL) spectra of CdP₂ nanoclusters in zeolite were measured at the temperatures of 4.2, 77 and 293 K. Both absorption and PL spectra consist of two bands blue shifted with respect to bulk crystal. We performed the calculations aimed to find the most stable clusters in the size region up to size of the zeolite Na–X supercage. The most stable clusters are (CdP₂)₆ and (CdP₂)₈ with binding energies of 9.30 and 10.10 eV per (CdP₂)₁ formula unit, respectively. Therefore, we attributed two bands observed in absorption and PL spectra to these stable clusters. The Raman spectrum of CdP₂ clusters in zeolite was explained to be originated from (CdP₂)₆ and (CdP₂)₈ clusters as well. The PL spectrum of CdP₂ clusters produced by laser ablation consists of the asymmetric band with low-energy tail that has been attributed to emission of both (CdP₂)₈ cluster and CdP₂ microcrystals.     

A theoretical study on the electronic structure of GaAs/AlAs and AlAs/GaAs core/shell nanoparticles

Results of theoretical investigation on the structural and electronic properties of GaAs/AlAs and AlAs/GaAs core/shell nanoparticles are presented. We have considered relaxed structures of essentially spherical parts of the zinc-blende crystal structure. The electronic properties and the total energy were calculated using density-functional tight-binding method. Our results include the charge distribution, density of states (DOSs), electronic energy levels (in particular HOMO and LUMO), HOMO-LUMO gap, excitation spectra and their variation with shell thickness for both GaAs/AlAs and AlAs/GaAs core/shell systems.     

同步测量大气湍流折射率结构常数和内尺度的光学方法

 基于不同波长的光闪烁,采用修正的大气湍流Hill谱模型,提出了一种同时反演大气湍流内尺度及折射率结构常数的方法。假定内尺度在某一个范围内取值,对于不同波长的闪烁指数,如果当内尺度取某一定值时,由光传输理论计算的C²_n(λ₁,…)和C²n (λ₂,…)相等,反演成功。根据此原理设计了三波长闪烁计并在某地进行了外场测量。近地面大气湍流的内尺度一般在2~10 mm之间,且随折射率结构常数（其量级为10^-16~10^-13）的变化而变化,两者之间存在一定的正相关;任意两波长组合进行反演得到的内尺度(或折射率结构常数)值具有自洽性,其相关系数的最小值为0.81,因此证明了该方法的可行性。     

Electronic structure and optical properties of crystalline strontium azide and barium azide by ab initio pseudopotential plane-wave calculations

Detailed ab initio studies on the electronic structure and optical properties of crystalline strontium azide and barium azide have been performed using density functional theory (DFT) within the generalized gradient approximation (GGA). Relaxed crystal structures compare well with experimental data. An analysis of electronic structure, charge transfer, and bond order shows that the two azides are mainly ionic compounds. Our calculated optical properties are found to be in good agreement with available experimental data. The absorption spectra of the two azides show a number of absorption peaks in the fundamental absorption region. The photoconductivity spectra display a broad photocurrent response in the fundamental absorption region. The density of states of the two azides reveal the effects of the metal states on the valence electron of the azide group, and so are correlated with their thermal decomposition.     

左旋尤利沙星电子结构及ECD谱的理论研究

采用DFT及TD-DFT方法在B3LYP/6-311++G**水平对左旋尤利沙星的电子结构及ECD谱进行了理论研究. 研究发现,环A、环B、环C及羰基之间共轭,成刚性平面结构. 电子密度拓扑分析发现,H(23)与O(19)之间存在分子内氢键;水溶液中,分子内氢键作用加强,键长缩短为0.1624 nm,键鞍点电荷密度增加为0.0581 a.u.. 理论研究获得的ECD谱与实验谱基本吻合. 水溶液中,左旋尤利沙星在244 nm处存在负性康登效应,在253、278、333 nm处存在正性康登效应. 轨道成份分析显示,电子跃迁所涉及的轨道均为π轨道;因此,所有的康登效应均由π→π*荷移跃迁引起. 这些结论对于深入理解尤利沙星的电子结构和手性光学性质具有一定的意义.     

左旋尤利沙星电子结构及ECD谱的理论研究

采用DFT及TD-DFT方法在B3LYP/6-311+-G**水平对左旋尤利沙星的电子结构及ECD谱进行了理论研究.研究发现,环A、环B、环C及羰基之间共轭,成刚性平面结构.电子密度拓扑分析发现,H(23)与O(19)之间存在分子内氢键;水溶液中,分子内氢键作用加强,键长缩短为0.1624 nm,键鞍点电荷密度增加为0.0581 a.u..理论研究获得的ECD谱与实验谱基本吻合.水溶液中,左旋尤利沙星在244nm处存在负性康登效应,在253、278、333 nm处存在正性康登效应.轨道成份分析显示,电子跃迁所涉及的轨道均为π轨道;因此,所有的康登效应均由π→π*荷移跃迁引起.这些结论对于深入理解尤利沙星的电子结构和手性光学性质具有一定的意义.     

Growth and crystalline structure of Co layers on Cu(0 0 1)

The crystalline structure of Co layers deposited on the Cu(0 0 1) surface was investigated with the use of the directional elastic peak electron spectroscopy (DEPES). For clean Cu(0 0 1) the experimental DEPES profiles obtained for different energies of the primary electron beam exhibit intensity maxima corresponding to the close packed rows of atoms. The Auger peak kinetics recorded during continuous Co deposition suggest the layer-by-layer growth mode. The DEPES profiles recorded for 10 monolayers (ML) of Co on Cu(0 0 1) reflect a short-range order in the adsorbate. Intensity maxima observed in the DEPES profiles for Co along [1 0 0], [0 1 0], and [1 1 0] azimuths of Cu(0 0 1) are characteristic of the face centered cubic (fcc) Co(0 0 1) layers. Low-intensity reflections and considerable background intensities were found in the low energy electron diffraction (LEED) patterns recorded from 10 ML of Co, which indicates a weak long-range order in the adsorbate. The adsorption of about 20 ML of Co results in considerable background contribution to DEPES. No reflections but a large background were observed with the use of LEED for this layer. The heating of the Co/Cu(0 0 1) system at T = 770 K leads to an increase of the short- and long-range order in the overlayer, observed in the DEPES profiles and LEED patterns, respectively. The theoretical DEPES profiles were obtained with the use of a multiple scattering approximation. A very good agreement between experimental and theoretical scans was found for the clean and covered copper substrate. The latter proves the epitaxial growth of Co layers on Cu(0 0 1).     

Electronic structure and optical properties of non-metallic modified graphene: a first-principles study

In this paper, the electronic structure and stability of the intrinsic, B-, N-, Si-, S-doped graphene are studied based on first-principles calculations of density functional theory. Firstly, the intrinsic, B-, N-, Si-, S-doped graphene structures are optimized, and then the forming energy, band structure, density of states, differential charge density are analyzed and calculated. The results show that B- and Si-doped systems are p-type doping, while N is n-type doping. By comparing the forming energy, it is found that N atoms are more easily doped in graphene. In addition, for B-, N-, Si-doped systems, it is found that the doping atoms will open the band gap, leading to a great change in the band structure of the doping system. Finally, we systematically study the optical properties of the different configurations. By comparison, it is found that the order of light sensitivity in the visible region is as follows: S-doped> Si-doped> pure > B-doped > N-doped. Our results will provide theoretical guidance for the stability and electronic structure of non-metallic doped graphene.     

GaN(0001)表面电子结构和光学性质的第一性原理研究

采用基于第一性原理的密度泛函理论平面波超软赝势方法计算了(2×2)GaN(0001)清洁表面的能带结构、态密度、表面能、功函数和光学性质.发现弛豫后GaN(0001)表面的能带结构发生较大变化,表面呈现金属导电特性,导带底附近存在明显的表面态,在偶极矩的作用下表面电荷发生转移,Ga端面为正极性表面;计算获得了GaN(0001)表面的表面能和功函数分别为2.1J.m^-2和4.2eV;比较分析了GaN(0001)表面和体相GaN的光学性质,发现两者存在较大差异.     

聚对苯撑及其烷氧基衍生物的能带研究

利用扩展Hückel分子轨道方法，运用BICON-CEDiT程序包计算了聚对苯撑及其系列烷氧基取代物的一维能带结构.计算结果表明：聚合物的能带结构在很大程度上受到杂原子、侧链等因素的影响，这与已知的实验结果相符；随着烷氧基侧链中C原子数的改变，聚合物的带隙呈现规律性变化.理论计算得到的带隙值与已有的实验观察值符合得相当好.     

Crystal chemical and dielectric study of niobochromates with the tungsten bronze structure

Abstract

A crystal chemical study has allowed us to identify new niobochromates crystallizing with the tungsten bronze structure: Ba₂LnNb₄CrO₁₅ (Ln = Bi, La), La₂ANb₄CrO₁₅ (A = Li, Na, K) and Ba₂Na_1-x La _x Nb_5-x Cr _x O₁₅ (0 ? x ? 1). A dielectric study has shown that the T _c (x) curve goes through a minimum at x ? 0.5 along the solid solution Ba₂Na_1-x La _x Nb_5-x Cr _x O₁₅, while the ferroelastic transition T_c changes very slightly in the same range of composition.     

近地面折射率结构常数的长期测量和统计分析

 统计分析了1997～2000年合肥地区一复杂地形处近地面折射率结构常数的测量数据。给出了不同下垫面、不同季节、不同高度上的统计结果。白天强弱依次为6月、5月、4月、9月、1月。白天水面上比草地上小，夜间比草地上大。不论白天还是夜晚，近地面结构常数都随高度递减，且3～10m高的结构常数递减较慢，10～15m高的结构常数递减较快。结构常数随月份的日变化与模式计算结果基本一致。     

高硼钢中B与Fe作用的超精细结构研究

采用真空感应熔炼的方法制备出含B量为0.15%—0.55%的低合金钢.通过X射线衍射技术和穆斯堡尔谱分析技术,研究了其中B与Fe元素作用的微结构.确定了穆斯堡尔谱的基本参量———化学位移(IS)、四极分裂(QS)、内磁场(Hhf)随高硼钢成分变化的规律.研究结果表明,B元素少部分固溶在αFe中,大部分与Fe形成Fe2B和FeB.分析了B和Fe原子核外电子结构的变化特征及超精细结构变化的原因 关键词： 高硼钢 相结构 超精细参量 核外电子     

聚合物和小分子叠层结构有机太阳电池研究

旋涂法和真空蒸发结合制备了MEH-PPV:PCBM体异质结和CuPc/C60有机小分子叠层有机太阳电池. 测试结果表明:MEH-PPV:PCBM有源层和Ag中间层分别为50 nm和0.5 nm时,与同等厚度有源层的MEH-PPV:PCBM体异质结器件和CuPc/C60小分子器件相比,叠层器件太阳能转换效率大大提高,达到了1.86%. 关键词： 聚(2-甲氧基,5-(2-乙基-乙氧基)-对苯乙炔) 铜酞菁 叠层结构 太阳电池     

拓扑相MoS2电子结构及光学性质的第一性原理研究

基于密度泛函理论的第一性原理对二维拓扑相1T′-MoS₂和2M-MoS₂的电子结构、有效质量和光学性质进行研究,并将其与二维H-MoS₂进行对比分析.研究表明,电子有效质量大小关系为：2M-MoS₂22,空穴有效质量大小关系为：T′-MoS₂<2M-MoS₂2,但2M-MoS₂的空穴有效质量和T′-MoS₂相差不大,二者均适用于高性能电子器件.由于拓扑相1T′-MoS₂和2M-MoS₂均存在能带反转,导致带间相关性以及导带和价带的波函数重叠增强,进而光电流响应增强,二者的光学性质均优于H-MoS₂. 2M-MoS₂具有较大的吸收系数和光电导率,2M-MoS₂对红外光和紫外光有着优...