Formation of Stone–Wales edge: Multistep reconstruction and growth mechanisms of zigzag nanographene

Although the existence of Stone–Wales (5‐7) defect at graphene edge has been clarified experimentally, theoretical study on the formation mechanism is still imperfect. In particular, the regioselectivity of multistep reactions at edge (self‐reconstruction and growth with foreign carbon feedstock) is essential to understand the kinetic behavior of reactive boundaries but investigations are still lacking. Herein, by using finite‐sized models, multistep reconstructions and carbon dimer additions of a bared zigzag edge are introduced using density functional theory calculations. The zigzag to 5‐7 transformation is proved as a site‐selective process to generate alternating 5‐7 pairs sequentially and the first step with largest barrier is suggested as the rate‐determining step. Conversely, successive C₂ insertions on the active edge are calculated to elucidate the formation of 5‐7 edge during graphene growth. A metastable intermediate with a triple sequentially fused pentagon fragment is proved as the key structure for 5‐7 edge formation. © 2017 Wiley Periodicals, Inc.     

基于光子晶体带边效应的表面增强拉曼基底

将光子晶体的带边效应与金纳米粒子的拉曼散射增强作用相结合,制备了一种新型光子晶体表面增强拉曼散射基底(PC-AuNPs),利用罗丹明B(RhB)作为报告分子,对所得基底性能进行检测.PC-AuNPs基底的制备包括3个步骤:在SiO2微球表面修饰氨基,再通过垂直沉降自组装得到蛋白石结构光子晶体(PC), 最后, 在光子晶体表面负载金纳米粒子(AuNPs).结果表明,光子晶体的带隙范围及AuNPs的负载量直接影响了PC-AuNPs基底的检测效果;以所得的PC-AuNPs基底测定RhB分子,其拉曼散射特征峰强度与浓度对数值呈现良好的线性关系,线性方程为I=1711lg[RhB(mol/L)]+15244,线性相关系数R2=0.9994,检出限为1×10-8 mol/L,表明此PC-AuNPs基底可用于目标物的定性及定量检测.本方法提高了传统拉曼散射光谱检测灵敏度,操作简单,具有良好的重现性,可为其它新型检测基底的制备提供.     

刃型位错和圆弧形刚性线夹杂的干涉效应

位错和夹杂的干涉效应对于理解材料的强化和韧化机理具有十分重要的意义。文中研究了晶体材料中刃型位错和多条共圆弧刚性线夹杂的干涉作用。利用Riemann—Schwarz反照原理和复势函数的奇性主部分析技术，得到了问题的一般解答；对于只含一条刚性线夹杂的情况，给出了复势函数的封闭形式解。由Peach-Koehler公式求出了作用在刃型位错上的位错力，并讨论了圆弧形刚性线夹杂对位错力的影响规律，发现弧形刚性线对刃型位错有很强的排斥作用。本文解答不但可作为格林函数获得任意分布位错的相应解答，而且可以用于研究刚性线夹杂和任意形状裂纹的干涉效应问题。     

交叉分子束研究氯原子与硅烷的反应动力学

利用通用型交叉分子束研究了氯原子与硅烷的反应,观测到SiH₃Cl+H通道. 测量到产物SiH₃Cl在实验坐标下的角度分辨的飞行时间谱,获得了这个通道质心坐标下的产物角分布和动能分布. 结果表明,相对于氯原子束方向,产物SiH₃Cl主要是后向散射,说明这个通道主要是通过典型的双分子亲核取代反应(S_N2)机理进行的.     

Capped semiconductor nanocrystals for device applications

For device purpose, our main aim is to synthesise material which is chemically and thermally stable, as well as enhancement in luminescence properties followed with matching lattice parameters. This can be achieved by precisely controlling the size of semiconductor nanocrystals which can create an opportunity for producing functional materials with new properties. Here we showed advantages of using both organic and inorganic capping agents. We reported two synthesis routes, one will lead to nanocomposites and other to Core/Shell nanostructures. Our mechanism consists of two stages: core nanoparticle formation and shell growth. Gibbs free energy of hydration of Zn+2 gives more clarity for shell growth over core rather than ion displacement from core. Colloidal films comprising of nanocrystalline CdS/ZnS were fabricated by the dip coating method. A blue shift in energy level at the nanoscale is demonstrated by optical absorption. Electron microscopy studies with an SEM and TEM show a particle size of 10 nm and diffraction patterns show a crystalline nature. Absence of lattice mismatching is one of the important parameter for device fabrication, which is confirmed by Raman spectroscopy. Overall reduction in optical absorption due to blue shift is expected to result in higher performance, especially in short-circuit currents in CdS/CdTe solar cells.     

聚酰亚胺薄膜的电致发光和光致发光

测量了氙灯辐照后聚酰亚胺(PI)薄膜的光致发光(PL)强度、PL谱和氙灯辐照后直流高电场下PI薄膜的电致发光(EL)强度、EL谱、XRD谱和吸收光谱,研究了其EL、PL特性与微观结构的关系.结果表明:PI薄膜的PL强度随测量时间呈指数衰减,EL强度随场强呈指数增长;辐照39 h后,PI的预击穿场强为2.56MV/cm,...     

一种短程无衍射激光图像定中算法

针对短程无衍射激光图像特点,提出了一种由亮度梯度确定图像中心的方法。利用光斑图像边缘的亮度梯度,设定图像二值化阂值范围,根据二值化结果确定光斑图像边缘点,对于各边缘点,利用圆上两点直径最长的原理,通过直径的中点确定圆心,求出均值,作为光斑图像的中心。本方法速度快、精度高,适合于实时性要求较强的应用场合,已经在实际应用中...     

叶片锯齿尾缘对降低空调室外机气动噪声影响的试验研究

依据现有的叶片尾迹宽度计算公式,计算了一空调室外机风机叶片的尾迹宽度,然后,以此尾迹宽度为参考基准,设计了两组不同形状和大小的锯齿形叶片尾缘,制作并试验研究了锯齿形尾缘对风机气动噪声的影响规律。结果表明,锯齿尾缘有明显降噪效果,正弦形锯齿较正三角形更好。锯齿尾缘通过降低宽频噪声降噪,而对离散噪声影响很小。采用与叶片尾迹...     

Approximation in weighted p-mean by RBF networks of Delsarte translates

We give conditions on the kernel function (or activation function) for the family of radial basis function (RBF) neural networks obtained upon replacing the usual translation by the Delsarte one, with not necessarily the same smoothing factor in all kernel nodes, to have the universal approximation property in suitable weighted L^p$L^p$-spaces (1?p<∞)$(1?p<\infty )$. A complete characterization of such kernels for p=1$p=1$ and p=2$p=2$ is provided.     

On the tangent space to the BMO-Teichmüller space

In a previous paper [31] we established the complex analytic manifold theory of the BMO-Teichmüller space. In this paper we identify the function space which is the tangent space to the BMO-Teichmüller space.