Stacking-faults-free zinc blende GaAs/AlGaAs axial heterostructure nanowires during vapor-liquid-solid growth

Pure zinc blende structure GaAs/AlGaAs axial heterostructure nanowires (NWs) are grown by metal organic chemical vapor deposition on GaAs(111) B substrates using Au-catalyzed vapor-liquid-solid mechanism.Al adatom enhances the influence of diameters on NWs growth rate.NWs are grown mainly through the contributions from the direct impingement of the precursors onto the alloy droplets and not so much from adatom diffusion.The results indicate that the droplet acts as a catalyst rather than an adatom collector.     

Guided modes in asymmetric metal-cladding left-handed material waveguides

We investigate guided modes in the asymmetric waveguide structure with a left-handed material (LHM) layer surrounded by air and metal. A graphical method is proposed to determine the guided modes. New properties of the oscillating and surface guided modes, such as absence of the fundamental mode, coexistence of the oscillating and surface guided modes, fast attenuation of the surface guided modes, and mode degeneracy, are analyzed in detail. We also investigate dispersive characteristics of the metal-LHM- air optical waveguide. The propagation constant increases with decreasing slab thickness for the first-order oscillating mode, which is different from that in traditional metal-cladding waveguides.     

Photon tunneling and transmittance resonance through a multi-layer structure with a left-handed materialvspace2pt

This paper investigates the photon tunneling and transmittance resonance through a multi-layer structure including a left-handed material(LHM). An analytical expression for the transmittance in a five-layer structure is given by the analytical transfer matrix method. The transmittance is studied as a function of the refractive index and the width of the LHM layer. The perfect photon tunneling results from the multi-layer structure, especially from the relation between the magnitude of the refractive index and the width of the LHM layer and those of the adjoining layers. Photons may tunnel through a much greater distance in this structure. Transmittance resonance happens, the peaks and valleys appear periodically at the resonance thickness. For an LHM with inherent losses, the perfect transmittance is suppressed.     

固体超强酸SO_4~(2-)/TiO_2对萘齐聚反应的催化作用

报道了使用固体超强酸催化剂ＳＯ２４／ＴｉＯ２对萘进行的齐聚反应。考察了不同制备条件如焙烧温度、硫酸浓度与催化活性之间的关系，同时研究了反应因素对收率的影响。实验表明，当硫酸浓度为０．５ｍｏｌ／Ｌ、焙烧温度在４５０～５００℃之间，催化剂的反应活性最高；延长反应时间、提高反应温度将有利于齐聚反应的进行；改变催化剂剂量也会影响齐聚反应。此外采用质谱分析方法对萘齐聚产物进行了分析，结果表明萘在ＳＯ２４／ＴｉＯ２的作用下生成的齐聚产物以二聚体为主，其分子量分布主要集中在二聚体到四聚体之间。     

固体超经酸SO^2—4／TiO2对萘齐聚反应的催化作用

报道了使用固体超强酸催化剂ＳＯ＾２－４／ＴｉＯ２对萘进行的齐聚反应。考察了不同制备条件如焙烧温度，硫酸浓度与催化活性之间的关系，同是研究了反应因素对收率的影响。实验表明，当硫酸浓度为０．５ｍｏｌ／Ｌ，焙烧温度在４５０－５００℃之间，经剂的反应活性最高。     

知识、能力、素养融合的现代表征方法与技术研究生课程建设

主要介绍本校研究生课程现代表征方法与技术的改革和实践,包括科学设计课程知识体系的架构,将多种现代表征技术基于研究目的分类介绍其原理和应用;融合PBL教学模式开发讨论式课堂,让学生掌握现代表征技术的实际应用,为科学研究服务的同时,提升研究生发现问题、解决问题的能力;深入挖掘课程思政元素,从文化自信、民族自豪感、工匠素养的培养视角,将素质教育融入专业知识的传授过程,充分发挥课程教学的育人功能。     

关于《集值优化问题Henig真有效解的最优性条件》一文的注记北大核心CSCD

本文指出《集值优化问题Henig真有效解的最优性条件》一文的主要结论是《近似锥-次类凸集值优化的严有效性》一文相应结论的特例.     

Growth and characterization of GaAs/InxGa1-xAs/GaAs axial nanowire heterostructures with symmetrical heterointerfaces

We report on the Au-assisted vapour-liquid-solid （VLS） growth of GaAs/InxGal xAs/GaAs （0.2 ≤ x ≤1） axial double-heterostructure nanowires on GaAs （ 111 ） B substrates via the metal-organic chemical vapor deposition （MOCVD） technique. The influence of the indium （In） content in an Au particle on the morphology of nanowires is investigated systematically. A short period of pre-introduced In precursor before the growth of InxGal xAs segment, coupled with a group III precursor interruption, is conducive to obtaining symmetrical heterointerfaces as well as the desired In/Ga ratio in the InxGa1-xAs section. The nanowire morphology, such as kinking and tapering, are thought to be related to the In composition in the catalyst alloy as well as the VLS growth mechanism.     

Y3Al5O12:Ce3+,Cr3+和Y3Al5O12:Ce3+,pr3+,Cr3+荧光粉体系中的能量传递

通过在YAG:Ce3+和YAG:Ce3+,pr3+荧光粉体系中分别掺入Cr3+离子来提高蓝光管芯白光LED的显色指数.Cr3+离子的加入,增加了红光发射,这归因于Cr3+的2E-4 A2跃迁的零声子线和声子边带发光.Ce3+→Cr3+的能量传递是增强红光发射的重要方式,在YAG:Ce3+,Cr3+体系中,由发射光谱得到...