激光直接快速成形金属零件过程中多道搭接的理论及实验研究

对激光直接快速成形金属零件过程中多道搭接进行了理论及实验研究,包括搭接率的确定,多道搭接的工艺研究以及搭接烧结层的组织形貌分析等.     

Influence of N2 and O2 annealing treatment on the optical bandgap of polycrystalline Ga2O3:Cu films

Cu-doped Ga₂O₃ thin films were deposited by electron beam evaporation with subsequent annealing at 1000 °C in N₂ and O₂ for 1 h. The influence of the annealing atmosphere on the crystal structure, surface morphology and optical properties of Ga₂O₃:Cu films was investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and transmittance and photoluminescence (PL) spectroscopy. The optical bandgap deduced from the absorption spectrum was greater for the O₂ annealed than for N₂ annealed samples. In both cases the bandgap was wider than for bulk β-Ga₂O₃. The grain size and surface roughness were sensitive to the annealing atmosphere. Results confirmed that the annealed samples were polycrystalline β-Ga₂O₃ with some amorphous phase. We hypothesize that annealing in oxygen led to recrystallization of the Ga₂O₃:Cu film. Annealing treatment improved the crystal quality of Ga₂O₃:Cu films and the PL intensity of the samples increased.     

小波变换和数学形态学在红外图像检测中的应用

红外图像的检测、识别和跟踪技术是当前精确制导领域研究的关键技术之一。文章从处理技术的角度，将适合于红外图像的目标检测技术以分割为基础分为基于数学形态学、小波变换、神经网络和模糊数学几类，重点综述了基于数学形态学和基于小波变换的目标检测技术的研究现状和发展趋势。     

Shape‐Controlled Synthesis of Polyhedral Nanocrystals and Their Facet‐Dependent Properties

Growth of inorganic polyhedral nanocrystals with excellent morphology control presents significant synthetic challenges, especially when the development of synthetic schemes to make nanocrystals with systematic shape evolution is desired. Nanocrystals with fine size and shape control facilitate formation of their self‐assembled packing structures and offer opportunities for examination of their facet‐dependent physical and chemical properties. In this Feature Article, recent advances in the synthesis of nanocrystals with systematic shape evolution are highlighted. The reaction conditions used to achieve this morphology change offer insights into the growth mechanisms of nanocrystals. A novel class of polyhedral core–shell heterostructures fabricated using structurally well‐defined nanocrystal cores is also presented. Facet‐dependent photocatalytic activity, molecular adsorption, and catalytic and electrical properties of nanocrystals have been examined and are discussed. Nanomaterials with enhanced properties and functionality may be obtained through continuous efforts in the synthesis of nanocrystals with well‐defined structures and investigation of their plane‐selective properties.     

Tuning the Intermolecular Electrostatic Interaction toward High-Efficiency and Low-Cost Organic Solar Cells

Organic solar cells (OSCs) have achieved much progress with rapidly increasing power conversion efficiencies (PCEs). It should be noted that the top-performance OSCs are generally consisted of active materials with complex chemical structures, resulting in high costs. Here, combining the material design and morphology control, high-efficiency OSCs are fabricated by a low-cost donor: acceptor blend. A completely non-fused electron acceptor named Tz is designed and synthesized via introducing thiazole units on both sides of a bithiophene core, which shows an outstanding PCE of 13.3% with a typical polythiophene donor. More importantly, optimization guidelines are presented to get excellent morphology for low-cost donor:acceptor systems. Three polythiophenes are selected, poly(3-hexylthiophene) and its two derivatives with electron-withdrawing substitutions (PDCBT and PDCBT-2F), as donors to fabricate the cell devices. The computational and experimental data reveal that decreasing the electrostatic interaction between polythiophene and Tz is the key to getting a suppressed miscibility and thus a high phase purity. This study provides insight into the molecular design and donor:acceptor matching requirements for high-efficiency and low-cost OSCs.     

Distributions of substitutional and interstitial impurities in silicon ingot with different grain morphologies

A multicrystalline silicon ingot with columnar and irregular grains was obtained from metallurgical-grade silicon (MG-Si) by directional solidification. The segregation behaviors of substitutional and interstitial impurities in different grain morphologies have been studied. The concentration distribution of substitutional impurities (B and Al) in the silicon ingot was accord with the Scheil's equation, which depended on the grain morphology. However, the concentration distribution of interstitial impurities (Fe, Ti, Cu, and Ni) was only accord with the Scheil's equation under the columnar grains growth condition. The difference lattice sites of the impurities will result in the disparate segregation behavior of impurities for columnar and irregular grains growth, which leads to the diverse concentration distribution of substitutional and interstitial impurities in the silicon ingot. Furthermore, the transport mechanism of interstitial and substitutional impurities in front of the solid-liquid interface boundary has been revealed.     

Influence of ammonia concentration on the microstructure,electrical and raman properties of low temperature chemical bath deposited ZnO nanorods

Nanostructured zinc oxide synthesized using an easy and low temperature chemical bath deposition method are among the most promising low cost semiconducting nanostructures investigated for a variety of applications. We successfully report the effects of ammonia solution in the growth of ZnO nanorods at a temperature of 60 °C. Successive addition of ammonia altered the degree of supersaturation of the growth solution, causing a significant deviation in the morphology and crystal orientation of ZnO nanorods. Field emission scanning Electron Microscopy images revealed changes in surface morphology of ZnO nanorods with respect to addition of specific amounts of ammonia. X-ray diffraction analysis revealed wurtzite crystal structure of ZnO which was further supported by X-ray photoelectron studies, optical absorbance and Raman spectra that also revealed the existence of wurtzite ZnO. The current-voltage measurement showed the electrical properties of the synthesized ZnO nanorods. The vertically grown nanorods with flat tops, effect more rectifying Schottky contacts to be realized on comparison to needle like structures.     

氮掺杂对a-C:F薄膜表面形貌和键结构的影响

用射频等离子体增强化学气相沉积设备制备了氮掺杂a-C:F(氟化非晶碳)薄膜,研究了不同氮源流量比对薄膜表面形貌和键结构的影响。AFM观察结果发现:随氮流量的增加,薄膜表面粗糙度降低,颗粒粒径变小,薄膜更加均匀致密。Raman光谱分析表明:氮源流量的增加会引起薄膜内sp2键态含量增加,即芳香环式结构比例上升,当r(N2/(CF4+CH4+N2))为68%时,ID/IG由未掺N2时的1.591增至4.847,薄膜的热稳定性增强。     

退火温度对纳米TiO2薄膜微结构的影响

利用XRD、IR、UV-VIS、AFM、XPS等手段,研究了退火温度对溶胶–凝胶法制备的纳米TiO2薄膜微结构和表面形貌的影响。450~600℃退火处理的薄膜呈锐钛矿和金红石型混晶结构,700℃退火后为纯金红石相;水峰的吸收峰消失在300~500℃之间,至500℃有机基团完全消失,薄膜表面主要有C,Ti,O三种元素;改变退火温度,可以使薄膜的禁带宽度在3.26~3.58eV之间变化,可以在一定范围内,获得不同折射率的TiO2纳米薄膜;薄膜的表面粗糙度(RMS)为2~3nm。     

基于能量增强和形态学滤波的车标定位方法

根据车标在垂直方向上能量高且集中的特点,提出了一种新的快速且鲁棒性较高的车标定位方法。先通过能量增强和自适应形态学滤波进行图像过滤,进而通过自适应阈值分割出车标候选区域,然后根据车标特征及其与车辆的相互关系进行了车标精确定位。大量实验表明,晴朗天气下,定位准确率在94．5％左右,天气较差时定位准确率在89．2％左右,定位时间为120～150ms。