实用Nb_3Sn超导线电镜样品制备的新技术

本文报导了一种制备“Nb管富Sn法”实用Nb_3Sn超导线TEM样品的新技术用JEM—200CX电镜观察了Nb_3Sn/Nb、Nb_3Sn/CuSn以及Nb_3Sn晶粒和晶界形貌,在晶粒尺寸较大的区域中观察到大量叠栅(Moire)条纹并有许多位错存在。在添加合金元素Mg后的Nb_3Sn晶粒中发现了Mg—Nb—O化合物沉淀相。这些观察结果有助于我们深入认识Nb_3Sn材料中的磁通钉札机理以及合金元素的作用机理。     

互不溶Sn-Al合金中自发生长Sn纳米线及其作为锂离子电池负极的电化学性能

本文介绍互不溶Sn-Al合金表面上Sn纳米线(直径为100 ～ 500 nm)自发生长的两种情况,它们都不需要模板和催化剂.通过SEM、TEM分析和对Al、Sn相的相互作用机理研究表明,这些Sn纳米线具有[200]生长方向,它们的生长与Sn熔点和Al-Sn共晶点的差异,以及Sn-Al合金(块体、薄膜)中存在的残余压应力...     

互不溶Sn-Al合金中自发生长Sn纳米线及其作为锂离子电池负极的电化学性能

本文介绍互不溶Sn-Al合金表面上Sn纳米线(直径为100 ～ 500 nm)自发生长的两种情况,它们都不需要模板和催化剂.通过SEM、TEM分析和对Al、Sn相的相互作用机理研究表明,这些Sn纳米线具有[200]生长方向,它们的生长与Sn熔点和Al-Sn共晶点的差异,以及Sn-Al合金(块体、薄膜)中存在的残余压应力有关.将含有Sn纳米线的Sn-Al薄膜作为锂离子电池负极材料进行电化学测试,在0.3～1.5 V vs.Li/Li+(Li/Li+为对电极和参比电极)电压范围循环时,它的稳定可逆容量为300 mAh/g.通过与纯Sn薄膜负极比较研究可知,Sn纳米线的一维特征有利于改善Li+的扩散动力学,从而提高Sn-Al薄膜电极的电化学性能.     

升温速率对AgSn合金结构和性能的影响研究

采用冷压工艺将Ag Sn合金粉压制成Ag Sn合金素坯。研究了升温速率对Ag Sn合金素坯微观结构的影响。采用扫描电子显微镜(SEM)和能量色散光谱仪(EDS)对Ag Sn合金粉末及其片材的形貌进行了表征。同时对Ag Sn合金素坯的硬度、质量及其密度进行了分析。结果表明:当升温速率减小时,截面中的Sn、O含量增加,从而使Ag Sn合金素坯质量增加,密度和硬度反而下降。通过对Ag Sn合金素坯截面进行SEM、EDS分析,发现截面处有细小的氧化锡颗粒析出。Ag Sn合金素坯在30℃/min的升温速率下升至700℃,可获得粒径为70~150 nm的氧化锡颗粒,并维持较高的硬度和密度。     

添加SAC微粒对SnBi锡膏焊后性能的影响

采用机械混合的方法,向Sn58Bi(Sn Bi)共晶锡膏中添加不等量的Sn-3.0Ag-0.5Cu(SAC)微粒,制备Sn Bi-SAC复合锡膏。在不改变Sn Bi锡膏低温焊接工艺的前提下,改善Sn Bi锡膏焊后合金硬脆缺陷。实验结果表明:Sn Bi-SAC复合锡膏中SAC微粒含量分别为质量分数0,3%,5%,8%时,采用180℃低温焊接均可获得良好的钎焊效果。与Sn Bi共晶锡膏焊后合金相比较,Sn Bi-SAC复合锡膏中SAC微粒含量的增加促使焊后合金微观组织中的β-Sn相含量与晶粒尺寸增大,改善了Sn Bi焊后合金中富Bi相的致密网状结构。当锡膏中SAC微粒含量由0增大至质量分数8%时,合金硬度从213.9 m Pa下降到117 m Pa,对Sn Bi锡膏焊后合金硬脆缺陷起到改善效果。     

烧结温度对AuSn焊料薄膜及封装激光器性能的影响

采用不同温度对Au80Sn20共晶合金焊料进行烧结实验,研究了AuSn焊料薄膜在烧结后的形貌、物相组成以及对封装激光器的性能影响等.焊料在烧结后形成ξ相Au5Sn和δ相AuSn两种金属间化合物,随着烧结温度的上升,两相晶粒均明显长大,而ξ相Au5Sn趋向于形成枝晶.较低温度下烧结的焊料表面粗糙度较高,不利于激光器管芯的贴装.高温过烧焊料薄膜的导电导热性能有少许提升,对封装激光器管芯的功率没有明显影响,但焊料薄膜中残余应力较高,使激射波长有所蓝移.该结果将为AuSn焊料的烧结参数优化和硬焊料封装激光器的性能分析提供参考和指导.     

时效处理快速凝固Mg-5 wt.％Sn合金微观结构的电子显微分析

用显微维氏硬度仪、X射线衍射仪（ XRD）、扫描电子显微镜（ SEM）和透射电子显微镜（ TEM）研究分析了快速凝固Mg?5 wt?％Sn合金条带的时效硬化规律。实验结果表明,快速凝固Mg?5 wt?％Sn合金在593 K温度下时效3 h后达到峰值硬度。时效后峰值硬度下的快速凝固Mg?5 wt?％Sn合金中有β?Mg2 Sn相颗粒析出,大多数的析出相β?Mg2 Sn颗粒分布在晶界,少部分析出相β?Mg2 Sn颗粒分布在晶粒内部。在593 K温度下时效3 h后的合金中观察到析出相β?Mg2Sn 颗粒与基体α?Mg 的一种新取向关系：（202261）β／／（0110）α,（7236）β／／（0001）α,[512]β／／[2110]α。     

Zn_(0.7)Co_(0.3)(Ti_(1-x)Sn_x)Nb_2O_8陶瓷微波介电性能研究

采用传统固相法制备Zn0.7Co0.3(Ti1-xSnx)Nb2O8(x=0.1,0.15,0.2,0.25,0.3,0.35)微波陶瓷。研究了Sn取代Ti对Zn0.7Co0.3(Ti1-xSnx)Nb2O8微波介质陶瓷的物相结构与介电性能的影响。XRD研究表明,Zn0.7Co0.3(Ti1-xSnx)Nb2O8陶瓷主晶相为ZnTiNb2O8,有极少杂相Zn0.17Ti0.5Nb0.33O2存在;随着Sn含量的增加,陶瓷晶格常数增大,晶胞体积变大,陶瓷密度增大;电子扫描显微镜(SEM)显示随着Sn含量增加陶瓷结构致密;相对介电常数εr逐渐变小,温度系数τf逐渐变小,Q×f值逐渐增大;当Sn含量为0.35时,烧结温度为1 080℃,εr=30.5,Q×f=46 973GHz,τf=-45.4×10-6/℃。     

Zr添加对V_(2.1)TiNi_(0.3)贮氢合金结构和电化学性能的影响

利用电弧熔炼法制备了V_(2.1)TiNi_(0.3)Zr_x(x=0~0.12)贮氢合金,系统研究了该系列合金的相结构和电化学性能。显微组织及X射线衍射(XRD)分析表明:无Zr合金由体心立方结构的V基固溶体主相和Ti Ni基第二相组成,当加入Zr后,合金第二相变为具有六方结构的C14型Laves相而主相不变,所有第二相均呈网状分布于主相晶界附近。随着Zr添加量的增加,合金主相的晶胞参数和晶胞体积呈增大趋势。电化学测试表明:添加一定量的Zr既能提高其活化性能,又能提高其最大放电比容量;同时,随着Zr添加量的增加,合金电极的高倍率放电能力及交换电流密度均有所提高。通过比较发现,V_(2.1)TiNi_(0.3)Zr_(0.06)合金电极具有较好的综合性能。     

FeSiAlCr片状合金微粉超精细结构对材料饱和磁化强度的影响

为了研究FeSiAlCr片状合金微粉的超精细结构和材料饱和磁化强度的影响关系,本文对合金微粉进行了不同温度的退火处理,并对合金微粉进行XRD、穆斯堡尔谱测试。研究发现通过球磨法获得的片状合金微粉的晶体结构为A2结构(即α-Fe结构),经过高于500℃的氮气保护退火后转变为A2结构和D03超晶格结构。穆斯堡尔谱测试结果显示,使用湿法球磨方法得到的原始合金微粉具有连续分布的超精细磁场,经过高于500℃退火的合金微粉具有分立的超精细磁场,可以使用四种原子占位来进行拟合,显示出更高的有序度。同时,合金微粉的饱和磁化强度和平均超精细磁场有接近线性的关系,均随着退火温度的升高有明显提升。研究中还发现,在退火温度为600℃时,存在超精细磁场和饱和磁化强度的拐点,分析是由于在该温度点退火过程中产生了非磁性的B2相。     

From Smart Denpols to Remote‐Controllable Actuators: Hierarchical Superstructures of Azobenzene‐Based Polynorbornenes

For the demonstration of remote‐controllable actuators, a dendronized polymer (denpol) is newly designed and successfully synthesized by ring‐opening metathesis polymerization of azobenzene‐based macromonomers. The incorporation of azobenzene mesogens into the denpols helps to construct finely tuned hierarchical superstructures with anisotropic physical properties and reversible photoisomerization. The polynorbornene backbones and azobenzene side chains in the uniaxially oriented films are aligned perpendicularly and parallel to the layer normal, respectively. Based on photoreversible actuation experiments combined with diffraction results, direct relationships between the chemical structures, hierarchical superstructures, and their corresponding photomechanical behaviors are proposed. Smart denpols possess great potential for practical applications in photoresponsive switches.     

Novel two-dimensional lead sulfide quadrangular pyramid-aggregated arrays with self-supporting structure prepared at room temperature

Two dimensional (2D) self-supporting lead sulfide (PbS) arrays composed of ordered quadrangular nanopyramids were successfully fabricated through a convenient wet-chemical route at room temperature. The as-synthesized products were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, UV–vis–NIR absorption and photoluminescence spectroscopy. The as-prepared highly ordered self-supporting superstructures are stable under ultrasonic conditions. A “template-mediated in situ growth” mechanism is proposed for the formation of 2D PbS superstructures. With the prolongation of reaction time, the morphology evolution of PbS is clearly observed, which could be changed from nanopyramid-aggregated arrays into nanocube-aggregated arrays at original position. The optical properties of PbS self-supporting superstructures are investigated in detail.     

Enzyme‐Driven Hasselback‐Like DNA‐Based Inorganic Superstructures

DNA structures have gained much attention due to its ease of self‐assembly and precise controllability. Although DNA technology has been successfully applied to generate a variety of DNA structures, there are only few attempts to apply DNA technology to generate inorganic materials due to lack of controllability of interactions between DNA and inorganic materials. In addition, the synthesis of a predictable structure of hybrid materials still remains a significant challenge. To address the challenge, here a novel strategy for the synthesis of DNA‐based inorganic superstructures using DNA polymerase is reported. In particular, strategic feeding of metal ions for generating DNA‐inorganic hybrid superstructures during DNA polymerization is established. This approach can produce a variety of structures with varying metal ions and can easily add functionality to the product. The structural features are also easily studied by first‐principles calculations. With these advantages, DNA‐Mn particles show the potential as a cell tracking agent, a contrast agent for MRI, and an electrode material for supercapacitors. The enzyme‐driven synthesis in this study will provide a novel route for the generation of a range of organic–inorganic hybrid superstructures for biomedical and energy applications.     

Model of the epitaxial growth of SiC-polytypes under surface-stabilized conditons

Molecular beam epitaxial (MBE) experiments demonstrate that it is possible to achieve a controlled layer-by-layer growth of SiC polytypes at temperatures below 1000°C under surface-stabilized conditions. It is of substantial importance to stabilize characteristic Si-rich superstructures by an alternate supply of Si and C, switching periodically between more Si-rich and less Si-rich surface superstructures. The MBE growth of SiC happens in two basic steps: Firstly, Si overlayers are grown on SiC. Secondly, the Si overlayers are carbonized under supply of C, leading to growth of SiC. On the basis of first principles calculations within the framework of density functional theory in the local density approximation, we derive an equilibrium phase diagram for various structural models which provide a theoretical framework to rationalize some of the experimental findings qualitatively.     

Hierarchical Superstructures with Helical Sense in Self‐Assembled Achiral Banana‐Shaped Liquid Crystalline Molecules

The self‐assembly of 1,3‐phenylene bis[4‐(4‐n‐heptyloxybenzoyloxy)‐benzoates] (BC7) is studied to examine the formation of helical morphologies from achiral banana‐shaped liquid crystal molecules at different self‐assembling levels. Various hierarchical superstructures including flat‐elongated lamellar crystal, left‐ and right‐handed helical ribbons, and tubular texture are observed while the BC7 molecules self‐assemble in THF/H₂O solution. By contrast, only plate‐like morphology is observed in the self‐assembly of achiral linear shaped 1,4‐phenylene bis[4‐(4‐n‐heptyloxybenzoyloxy)‐benzoates] (LC7) molecules, indicating that the chirality of the self‐assembled texture is strongly dependent upon the molecular geometry of the achiral molecules. The formation of the helical superstructures, namely hierarchical chirality, is attributed to the conformational chirality from the achiral banana‐shaped liquid crystalline molecules, as evidenced by significant optical activity in time‐resolved circular dichroism experiments. Selective area electron diffraction is performed to examine the structural packing of the hierarchical superstructures. As observed, the molecular disposition of the lamellar crystal is identical to that of the helical superstructure. Also, the diffraction patterns of the helical superstructures appeared arc‐like patterns consisting of a series of reflections, suggesting that the helical morphology resulted from the curving of the lamellar crystals through a twisting and bending mechanism. Consequently, the model of molecular disposition in the self‐assembled helical superstructures from the achiral banana‐shaped molecules is proposed. The morphological evolution in this study may provide further understanding with respect to the chiral information transfer mechanism from specific molecular geometry to hierarchical chirality in the achiral banana‐shaped molecules.     

Synthesis of Cu2PO4OH Hierarchical Superstructures with Photocatalytic Activity in Visible Light

Using a wet‐chemical method and without any surfactants or templates, various 3D hierarchical superstructures of Cu₂PO₄OH were synthesized by simply adjusting the pH. The resulting hierarchical superstructures were characterized using X‐ray diffraction (XRD), field‐emission scanning electron microscopy (FESEM), high resolution‐TEM (HRTEM), Fourier transform infrared spectroscopy (FTIR), Raman, and UV–Vis spectroscopy. With an increase in pH from 2.5 to 7.0, the morphology of Cu₂PO₄OH varied from microrods to walnut‐shaped microspheres of self‐assembled nanoparticles. A possible mechanism for the formation of the Cu₂PO₄OH hierarchical superstructures was also proposed. The optical properties of the Cu₂PO₄OH hierarchical superstructures were strongly related to their morphologies and the size of the assembled crystallites. We further demonstrated the useful photocatalytic activity of these complex structures in the degradation of methylene blue (MB) dye under visible light irradiation (λ > 410 nm). The best photocatalytic performance was achieved by Cu₂PO₄OH with a walnut‐shaped morphology due to the excellent absorption of visible light as well as a high BET surface area.     

LiNbO3晶体中光折变光栅各向异性衍射的定量研究

对LiNbO3晶体中光折变光栅的各向异性衍射进行了定量研究。基于有效电光系数非零和布拉格相位匹配条件,对在LiNbO3晶体中各向异性衍射的衍射效率与光束偏振态和写入几何的关系进行了较为详细的理论计算和分析,根据建立的数学模型进行了数值计算,发现光轴垂直于写入平面时,写入的光栅可发生显著的各向异性衍射。实验测量与理论计算结果基本符合。     

Assembly and Biomineralization of Polymorphic Gold–Peptide Superstructures Using Tyrosine-Rich Short Peptides

Peptides show tremendous promise in synthesizing metal–peptide superstructures with tailored shapes and functions. However, bottom-up control of the polymorphs of these superstructures using a single short peptide without molecular modification has not been mechanistically clarified. Therefore, an approach to constructing gold–peptide superstructures with unprecedented structural diversity using a tyrosine-rich short peptide is developed, based on the assembling and mineralizing attributes of tyrosine. One-step UV irradiation of peptide/gold-salt systems enables on-site mineralization of gold ions, permitting controlled solvent-dependent fabrication of various superstructures. 0D colloids, 2D sheets, 3D superspheres, and 3D hollow capsules are produced via one-pot reactions in a pH-10 buffer, at the interface of a toluene–water biphasic system, in water, and in toluene-in-water emulsions, respectively, whereas 1D rod/fibril structures are produced using rapidly assembling peptides (A, F, I, L, N, V, Y, and D as X in YY-X-YY) in a two-step process. Several peptide derivatives, which also exhibit assembling and biomineralizing abilities and form various superstructures, validate the functionality of the tyrosine-rich peptide. This study sheds light on the design and development of diverse gold-peptide superstructures for applications including catalysis, sensing, imaging, and photothermal therapy.     

Microwave scattering from dielectric wedges with planar surfaces: adiffraction coefficient based on a physical optics version of GTD

The development is presented here, derived from a physical optics version of the geometrical theory of diffraction (POGTD) of a simple edge coefficient for external and internal diffraction at planar dielectric edges. This is required in connection with a simulator for synthetic aperture radar (SAR) images. The diffraction coefficient is assessed by comparison of calculations using POGTD, excluding multiple scattering processes, with an extensive set of experimental microwave scattering data on dielectric wedges and some corresponding calculations by the finite-difference time-domain method (FDTD) of solving Maxwell's equations. The experimental results were gained from dielectric wedges of four wedge angles, each for a wide range of angles of incidence, separately for TE and TM plane polarized components, and for two sets of wedges with different dielectric constants. The intensity distribution found by using the diffraction coefficient for external diffraction is found to be in good agreement with both experiment and calculations using FDTD. For internal wedge diffraction, POGTD predicts an intensity distribution of similar angular shape to the experimental one but, due to the neglect of absorption, the intensity level is too high     

Architectural Control of Hierarchical Nanobelt Superstructures in Catanionic Reverse Micelles

BaXO₄ (X = Mo, W) nanobelts and a variety of hierarchical superstructures assembled from the nanobelts have been synthesized in a catanionic reverse‐micelle system. The effects of various factors, such as the mixing ratio (r) between the anionic and cationic surfactants, the temperature, and the presence of polymeric additives, on the formation of the nanobelts and their hierarchical assembly have been examined in detail. In particular, r has been shown to be powerful in modulating the formation and assembly of the BaMoO₄ and BaWO₄ nanobelts. Architectural control of the penniform nanobelt superstructures has been readily achieved by changing the experimental parameters. A plausible two‐stage growth mechanism has been proposed for the formation of penniform BaXO₄ nanobelt superstructures in catanionic reverse micelles.