The influence of 1D, meso- and crystal structures on charge transport and recombination in solid-state dye-sensitized solar cells

We have prepared single crystalline SnO2 and ZnO nanowires and polycrystalline TiO2 nanotubes (1D networks) as well as nanoparticle-based films (3D networks) from the same materials to be used as photoanodes for solid-state dye-sensitized solar cells. In general, superior photovoltaic performance can be achieved from devices based on 3-dimensional networks, mostly due to their higher short circuit currents. To further characterize the fabricated devices, the electronic properties of the different networks were measured via the transient photocurrent and photovoltage decay techniques. Nanowire-based devices exhibit extremely high, light independent electron transport rates while recombination dynamics remain unchanged. This indicates, contrary to expectations, a decoupling of transport and recombination dynamics. For typical nanoparticle-based photoanodes, the devices are usually considered electron-limited due to the poor electron transport through nanocrystalline titania networks. In the case of the nanowire-based devices, the system becomes limited by the organic hole transporter used. In the case of polycrystalline TiO2 nanotube-based devices, we observe lower transport rates and higher recombination dynamics than their nanoparticle-based counterparts, suggesting that in order to improve the electron transport properties of solid-state dye-sensitized solar cells, single crystalline structures should be used. These findings should aid future design of photoanodes based on nanowires or porous semiconductors with extended crystallinity to be used in dye-sensitized solar cells. © 2013 The Royal Society of Chemistry.

Passively modelocked VECSEL using a single-layer graphene saturable absorber mirror

Optically pumped ultrafast vertical external cavity surface emitting lasers (VECSELs), also referred to as semiconductor disk lasers (SDLs), are very attractive sources for ps- and fs-pulses in the near infrared [1]. So far VECSELs have been passively modelocked with semiconductor saturable absorber mirrors (SESAMs, [2]). Graphene has emerged as a promising saturable absorber (SA) for a variety of applications [3-5], since it offers an almost unlimited bandwidth and a fast recovery time [3-5]. A number of different laser types and gain materials have been modelocked with graphene SAs [3-4], including fiber [5] and solid-state bulk lasers [6-7]. Ultrafast VECSELs are based on a high-Q cavity, which requires very low-loss SAs compared to other lasers (e.g., fiber lasers). Here we develop a single-layer graphene saturable absorber mirror (GSAM) and use it to passively modelock a VECSEL. © 2013 IEEE.

Photoluminescence and lasing properties of InAs/GaAs quantum dots grown by metal-organic chemical vapour deposition

Photoluminescence (PL) and lasing properties of InAs/GaAs quantum dots (QDs) with direrent growth procedures prepared by metalorganic chemical vapour deposition are studied. PL measurements show that the low growth rate QD sample has a larger PL intensity and a narrower PL line width than the high growth rate sample. During rapid thermal annealing, however, the lowgrowth rate sample shows a greater blue shift of PL peak wave length. This is caused by the larger InAs layer thickness which results from the larger 2-3 dimensional transition critical layer thickness for the QDs in the low-growth-rate sample. A growth technique including growth interruption and in-situ annealing, named indium flush method, is used during the growth of GaAs cap layer, which can flatten the GaAs surface effectively. Though the method results in a blue shift of PL peak wavelength and a broadening of PL line width, it is essential for the fabrication of room temperature working QD lasers.

Binding Energy and Spin-Orbit Splitting of a Hydrogenic Donor Impurity in AlGaN/GaN Triangle-Shaped Potential Quantum Well

In the framework of effective-mass envelope function theory, including the effect of Rashba spin-orbit coupling, the binding energy E-b and spin-orbit split energy Gamma of the ground state of a hydrogenic donor impurity in AlGaN/GaN triangle-shaped potential heterointerface are calculated. We find that with the electric field of the heterojunction increasing, (1) the effective width of quantum well (W) over bar decreases and (2) the binding energy increases monotonously, and in the mean time, (3) the spin-orbit split energy Gamma decreases drastically. (4) The maximum of Gamma is 1.22 meV when the electric field of heterointerface is 1 MV/cm.

Electronic structure and optical property of semiconductor nanocrystallites

Semiconductor nanostructures show many special physical properties associated with quantum confinement effects, and have many applications in the opto-electronic and microelectronic fields. However, it is difficult to calculate their electronic states by the ordinary plane wave or linear combination of atomic orbital methods. In this paper, we review some of our works in this field, including semiconductor clusters, self-assembled quantum dots, and diluted magnetic semiconductor quantum dots. In semiconductor clusters we introduce energy bands and effective-mass Hamiltonian of wurtzite structure semiconductors, electronic structures and optical properties of spherical clusters, ellipsoidal clusters, and nanowires. In self-assembled quantum dots we introduce electronic structures and transport properties of quantum rings and quantum dots, and resonant tunneling of 3-dimensional quantum dots. In diluted magnetic semiconductor quantum dots we introduce magnetic-optical properties, and magnetic field tuning of the effective g factor in a diluted magnetic semiconductor quantum dot. (C) 2004 Elsevier B.V. All rights reserved.

Photoluminescence study of InAlAs quantum dots grown on differently oriented surfaces

We reported the optical properties of self-assembled In0.55Al0.45As quantum dots grown by molecular beam epitaxy on (001) and (n11)A/B(n = 3,5)GaAs substrates. Two peaks were observed in the photoluminescence (PL) spectra from quantum dots in the (001) substrate and this suggested two sets of quantum dots different in size. For quantum dots in the high-index substrates, the PL spectra were related to the atomic-terminated surface (A or B substrate). The peaks for the B substrate surfaces were in the lower energy position than that for the (001) and A type. In addition, quantum dots in the B substrate have comparatively high quantum efficiency. These results suggested that high-index B-type substrate is more suitable for the fabrication of quantum dots than (001) and A-type substrates at the same growth condition. (C) 2000 American Vacuum Society. [S0734-211X(00)04701-6].

Analytical study of the antiferromagnetic Heisenberg films

With the variational cumulant expansion (VCE) method, the thermodynamic behaviors of S = 1/2 antiferromagnetic Heisenberg films in simple cubic lattices are studied analytically. From the analytic properties of the free energy, in principle we are able to calculate analytically the critical temperatures T-c(L) and the thermodynamic functions, to any order cumulant as the functions of the number of L (the hyperlayers in the hyperfilm). Explicit expressions for T-c(L) up to the fourth order are given. A comparison with the existing results for 3-dimensional system is given. The effective range of the interaction is obtained from numerical results.

Substrate surface atomic structure influence on the growth of InAlAs quantum dots

We have examined the influence of substrate surface orientation on self-assembled InAlAs/AlGaAs quantum dots grown on (0 0 1) and (n 1 1) A/B (n = 3, 5) GaAs substrates by molecular beam epitaxy (MBE). Preliminary characterizations have been performed using photoluminescence (PL) and transmission electron microscopy (TEM). The PL emission energies of quantum dots on high Miller index surface are found to be strongly dependent on the atomic-terminated surface (A or B surface) of the substrate. We observed that there were planar ordering larger islands on (3 1 1)B surface compared to (0 0 1) surface, in contrast, a rough interface and smaller "grains" on (3 1 1)A surface, this result is identical with PL emission energy from these islands. We propose that the rapid strain-induced surface "roughening" impedes the formation of 3D islands on A surface, and indicating that this is a promising approach of the realization of ordering distribution on (3 1 1)B plane for devices such as red-emitting semiconductor quantum dots lasers. (C) 1999 Elsevier Science B.V. All rights reserved.

Double crystal X-ray diffraction study of MBE self-organized InAs quantum dots

A series of GaAs/InAs/GaAs samples were studied by double crystal X-ray diffraction and the X-ray dynamic theory was used to analyze the X-ray diffraction results. As the thickness of InAs layer exceeds 1.7 monolayer, 3-dimensional InAs islands appear. Pendellosung fringes shifted. A multilayer structure model is proposed to describe the strain status in the InAs islands of the sample and a good agreement is obtained between the experimental and theoretical curves.

软件项目资源优化调度研究

信息技术的不断进步使得软件产品的应用领域不断扩大，同时软件产品的规模也在迅速膨胀。软件产品的开发模式已由最初的手工作坊式开发逐渐转变为大规模的工程化软件开发。这使得资源调度问题逐渐成为软件项目管理的核心研究内容之一。 软件项目与传统工业项目相比具有如下两个显著特点：其一是软件项目对人力资源能力的依赖性非常高；其二是软件项目在开发过程中具有的不确定性因素较多，也就是风险较高。这两个特点决定了传统工业调度方法不能很好地适用于软件项目管理，同时也为软件项目资源优化调度问题研究提出了新的挑战。需要根据软件项目的特点研究适合的资源调度方法为软件项目管理工作提供支持。 本文的研究工作旨在通过对软件项目的结构进行分析和描述，在建立软件项目核心要素模型的基础上，考虑软件项目高人力资源能力依赖性和高风险性两大特征，由人力资源能力和风险作为驱动因素，对软件项目中人力资源和项目缓冲两大核心资源进行优化分配和调度，以提高软件项目的资源利用效率和软件项目执行的稳定性。本文的主要贡献有： （1）建立了软件项目资源优化调度研究框架QMMT和项目核心要素模型PTHR。 QMMT研究框架由问题驱动(Question Driven)，模型描述(Model Description)，方法研究(Method Research)和工具验证(Tool Validation)四个模块构成。四个模块之间既存在顺序关系也存在信息反馈机制，框架具有良好的适应性和可扩展性。实践表明，QMMT研究框架对研究软件项目资源优化调度问题具有良好的指导作用。本文中涉及软件项目资源优化调度的多个研究问题均遵循QMMT研究框架。 通过对软件项目所包含的各个要素及要素之间的关系进行定义和描述，我们建立了软件项目核心要素模型PTHR。模型对软件项目的四个要素：项目（Project）、任务（Task）、人力资源（Human Resource）、风险（Risk）以及四个要素之间的关系进行了形式化定义和描述。PTHR模型涵盖了软件项目的核心要素并具有良好的可扩展性，可以为资源优化调度中具体问题的分析、算法的设计、流程的安排以及工具开发提供底层支持。PTHR模型是本文后续方法中相关系列子模型的基础模型。 （2） 提出了软件项目中任务-人员匹配的三维匹配模型3D-THM和基于3D-THM模型的任务人员优化分配方法。 任务人员匹配是人力资源调度的基础。3D-THM（3 Dimensional model for Task Human Matching）模型通过对人力资源的技术能力、性格能力和职业规划进行描述，以及对任务的技术能力需求、性格能力需求和职业规划需求进行描述，设定相应的多因素匹配算法，为任务-人员的全面优化匹配提供支持。实验表明，3D-THM模型较好的描绘了软件项目中任务-人员优化匹配问题，能够体现软件项目的高人力资源能力依赖性。模型实例化后所得到的匹配方法和相应的原型工具可为软件项目资源优化调度以及软件过程建模提供人员优化匹配支持，能够提高项目管理人员的工作效率，提升项目人员对任务分配的满意度。 （3） 提出了基于人员可用性的人力资源调度方法。 在对任务人员进行优化匹配的基础上，通过综合考虑人力资源能力和工作时间实现了基于人员可用性的人力资源调度方法。方法结合软件项目的结构特征，建立了任务人员可用性约束模型THACM（Task Human resources Availability Constraints Model）。基于THACM模型实现了在给定资源集合、任务集合下的人力资源自动分配和项目进度的自动安排。方法可有效解决采用矩阵组织结构的企业所面临的低资源可见性问题，协助其提高人力资源的利用效率。 （4）提出了基于任务优先级的抢占式人力资源调度方法PP-HAS。 在对人力资源可用性进行考虑的基础上，为了解决多项目环境下常见的资源冲突问题，我们提出了基于任务优先级的抢占式人力资源调度方法PP-HAS（Task Priority Based Preemptive Human Resource Scheduling Method）。方法首先建立了综合考虑进度、成本、质量三方面因素的基于价值的任务优先级模型VBTPM（Value Based Task Priority Model），将该任务优先级模型与过程Agent技术结合，通过设计支持抢占的人力资源调度流程，实现了多过程Agent协商下的人力资源优化调度。方法通过抢占和再计划实现了人力资源的动态高效利用，能够为资源冲突的解决以及项目的再计划工作提供决策支持。 （5）提出了风险驱动的软件项目缓冲资源分配方法。 项目缓冲的合理分配是降低风险对项目进度造成影响的重要手段。我们在软件项目资源调度方法中加入对风险因素的考量，基于软件项目中风险的特征，建立了简化的风险模型RRM（Reduced Risk Model）。基于RRM模型提出了风险驱动的项目缓冲分配方法，旨在软件项目的执行效率和稳定性二者之间进行权衡。模拟实验的结果表明，相对于传统关键链项目管理理论中尾部集中的项目缓冲分配方法，风险驱动的项目缓冲分配方法能够在确保对项目平均执行工期产生较小影响的同时，显著降低项目执行时计划变更的发生频率。该缓冲分配方法与项目模拟工具可以帮助项目经理确定合适的项目缓冲时间长度以及缓冲分配方案，进而提高软件项目计划的可信性和执行的稳定性。

Electronic structure and optical property of semiconductor nanocrystallites

Semiconductor nanostructures show many special physical properties associated with quantum confinement effects, and have many applications in the opto-electronic and microelectronic fields. However, it is difficult to calculate their electronic states by the ordinary plane wave or linear combination of atomic orbital methods. In this paper, we review some of our works in this field, including semiconductor clusters, self-assembled quantum dots, and diluted magnetic semiconductor quantum dots. In semiconductor clusters we introduce energy bands and effective-mass Hamiltonian of wurtzite structure semiconductors, electronic structures and optical properties of spherical clusters, ellipsoidal clusters, and nanowires. In self-assembled quantum dots we introduce electronic structures and transport properties of quantum rings and quantum dots, and resonant tunneling of 3-dimensional quantum dots. In diluted magnetic semiconductor quantum dots we introduce magnetic-optical properties, and magnetic field tuning of the effective g factor in a diluted magnetic semiconductor quantum dot. (C) 2004 Elsevier B.V. All rights reserved.

Non-commutative oscillator with Kepler-type dynamical symmetry

A 3-dimensional non-commutative oscillator with no mass term but with an appropriate momentum-dependent potential admits a conserved Runge-Lenz vector, derived from the dual description in momentum space. The trajectories lie on ellipses. The dynamical symmetry allows for an algebraic determination of the bound-state spectrum and extends to o(4,2). (c) 2010 Elsevier B.V. All rights reserved.

Synthesis and assembly of Au-Pt bimetallic nanoparticles

Au-Pt bimetallic nanoparticles (NPs) were synthesized by reducing the mixture of HAuCl4 and K2PtCl6 with ethanol in the presence of cinnamic acid (C6H5CHCHCO2H, CA) through a thermal process. It was found that the isolated NPs could gradually self-assemble into chain-like structures, ultimately to 3-dimensional network nanostructures by adjusting the molar ratio of CA to K2PtCl6. Energy-dispersive Spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction was used to confirm the formation of Au-Pt bimetallic nanostructures.

Reducing HAuCl4 by the C-60 dianion: C-60-directed self-assembly of gold nanoparticles into novel fullerene bound gold nanoassemblies

The C-60 dianion is used to reduce tetrachloroauric acid (HAuCl4) for the first time; three-dimensional C-60 bound gold (Au-C-60) nanoclusters are obtained from C-60-directed self-assembly of gold nanoparticles due to the strong affinities of Au-C-60 and C-60-C-60. The process was monitored in situ by UV-vis-NIR spectroscopy. The resulting Au-C-60 nanoclusters were characterized using transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy-dispersive spectroscopy (EDS), x-ray powder diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and FT-IR and Raman spectroscopies.

Entangled metal-organic frameworks modulated by N-donor ligands of different conformations

Based on the aromatic dicarboxylic acid and N-donor ligands with different conformations, four Zn(II) metal-organic frameworks, namely [Zn(mfda)(L-1)](1), [Zn-2(mfda)(2)(L-2)]center dot DMF center dot H2O (2), [Zn-2(mfda)(2)(L-3)(H2O)]center dot DMF (3) and [Zn-2(mfda)(2)(L-4)] (4) have been synthesized (mfda = 9,9-dimethylfluorene-2,7-dicarboxylate anion, L-1 = 1,10-phenanthroline, L-2 = 4,4 '-bipyridine, L-3 = 2,5-bis(4-pyridyl)-1,3,4-ocadiazole and L-4 = 1,4-bis(imidazol-1-ylmethyl)benzene). Single-crystal X-ray diffraction has revealed that all compounds exhibit entangled structures. Compound 1 is composed of 1D zigzag chains that are entangled through the pi-pi stacking interactions to generate a three-fold interpenetrating diamond-like networks.