双壁碳纳米管的电子显微学研究

本文分析研究了甲酸镍二水合物作为催化剂前驱体,多壁管为原料,采用氢电弧放电法制得的双壁碳纳米管样品中不同管壁数目碳纳米管的分布及双壁碳管直径分布,发现样品中单壁和双壁碳管占主要地位,双壁管的内径主要分布在1.67 nm～3.67 nm之间,外径主要分布在2.33 nm～4.33 nm之间.此外,精确测定了三个双壁碳纳米管的螺旋指数,分别为[(28,3)(29,17)],[(19,8)(29,6)]及[(23,15)(28,22)],其电学性能分别为[半导体性,金属性],[半导体性,半导体性]及[半导体性,金属性].同时,观察了在不同条件下的电子辐照效应.结果表明,经辐照碳管的最内层管壁先发生断裂,其形变速度逐渐变慢,单根碳管易依附于大块物质.在相同的辐照条件下,管壁数目越多碳管越稳定.当管壁数目相同时,直径小的管比直径大的管稳定.高加速电压能够加速碳管的变形.     

碳纳米管精细结构的HRTEM研究

碳纳米管是近年来引起高度兴趣的一类新奇碳素材料 ,鉴于其在氢气及其它某些气体的储存 ,复合材料 ,电子器件 ,场发射 ,催化剂载体材料与吸附分离介质等科技领域有许多现实或潜在的重要用途 ,自 1991年Ｉｉｊｉｍａ[1] 首次发现碳纳米管以来 ,有关碳纳米管的研究在国际上迅速形成热潮。其中对碳纳米管结构的研究一直是人们普遍关心的问题 ,研究碳纳米管的精细结构对于澄清碳纳米管生长机制以及对碳纳米管生产工艺和性质的了解具有十分重要的意义。本文利用高分辨电子显微镜 (ＨＲＴＥＭ )对ＣＯ催化歧化法获得的碳纳米管的精细结构进行了观…     

碳纳米管材料和碳纳米管基器件的扫描电镜成像

本文探讨了在扫描电镜中单壁碳纳米管的成像问题.一般情况下碳纳米管的像衬度随入射电子能量,扫描速度,样品基底和环境而变,情况非常复杂.但在一定厚度的SiO2绝缘基底上且与金属电极相连的单壁碳纳米管的成像机理则相对简单.单壁碳纳米管像衬度的贡献主要来源于二次电子而不是背散射电子.像衬度产生的机理主要为SiO2绝缘基底在成像过程中的电荷积累导致的表面电势的变化对于碳纳米管以及周围SiO2基底二次电子发射效率的影响.     

Growth of multi-wall carbon nanotubes with three-dimensional network microstructure

Multi-wall carbon nanotubes (MWCNTs) were grown by spray pyrolysis of acetylene as the carbon source in the presence of Au-Co as catalyst precursors. A high yield of network-shaped carbon nanotubes (CNTs) with further purification has been obtained in the optimal conditions. The optimum synthesis parameters included a synthesis temperature of 700degC, growth time of 30 min, and a flow rate of acetylene and hydrogen of 40 and 300 sccm, respectively. The morphology and structure features of the MWCNTs are characterised using scanning electron microscopy, transmission electron microscopy, energy dispersive spectra, Raman spectroscopy and thermogravimetry analyses.     

用电镜照片定量描述多壁碳纳米管的曲折状态

碳纳米管的形貌受制备方法以及各种后处理过程的影响.为了清楚地描述碳纳米管的形貌特征,本文建立了一种用电镜照片对碳纳米管曲折状态进行定量表征的方法.将一定数量多壁碳纳米管的高分辨透射电镜或扫描电镜照片进行观察和统计分析后,通过引入曲折因子（tortuosity factor TF）和计算标尺（calculating scale CS）两个参数,可以定量表征多壁碳纳米管的曲折程度.本文用该方法对三种不同的多壁碳纳米管进行了表征：纳米聚团流化床反应器制备的多壁碳纳米管、浮游法制备的超长阵列多壁碳纳米管以及静电纺聚环氧乙烷纳米纤维中的多壁碳纳米管.结果显示在所统计的计算标尺范围内,不同多壁碳纳米管的曲折因子有着显著的差异,进而根据多壁碳纳米管曲折因子的差异深入分析了制备方法以及处理过程对其形貌的影响.     

Acidified multi-wall carbon nanotubes/polyaniline composites with high negative permittivity

Acidified multi-wall carbon nanotubes (MWCNTs-COOH) have been synthesized using mixed acid acidification, and then acidified multi-wall carbon nanotubes (MWCNTs-COOH)/polyaniline (PANI) composites with negative permittivity have been successfully synthesized by in situ polymerization. At the same time, the effects of composition and structure on the permittivity of MWCNTs-COOH/PANI composites have been systematically studied. The effects of MWCNTs-COOH content on the generation and variation of negative permittivity are illuminated by the structure model of “nano wires”. XRD analysis indicates that MWCNTs-COOH becomes the crystal nucleus and affects the crystallinity of the MWCNTs-COOH/PANI composites. SEM results indicate that different contents of MWCNTs-COOH cause various dispersion states of MWCNTs-COOH, thus lead to different morphologies of MWCNTs-COOH/PANI composites and variation of permittivity.     

High-resolution transmission electron microscopy on aged InP HBTs

We have used high-resolution transmission electron microscopy (HRTEM), with focused-ion-beam preparation of foils, to study InP HBT devices, both as-fabricated and after aging in life tests. The technology is HRL's G1 process. We found that even after aging for the equivalent of 2 × 10⁷ h under normal operating conditions, the visible damage is extremely benign: the base and emitter contacts are completely intact, there is no evidence of significant Au or Pt migration into the semiconductor, and minor crystal disorder that develops does not extend more than 100 nm below the metal–semiconductor interfaces. Except for these regions, the intrinsic devices are completely devoid of any anomalous features, to within the 0.3 nm resolution limit of the measurements. These observations provide strong evidence that failure mechanisms involving migration of metal from the ohmic contacts, or extended crystal defects, do not limit the reliability of this technology. The small disorder under the base contacts can probably explain the increases of gain (β) observed early in our life tests, and small increases in the base-collector leakage occurring later in the life tests. The minor disorder under the emitter contacts can probably explain the moderate increase of emitter resistance observed late in our life tests. But the mechanism for the eventual decline in β, observed after a long period of stress, for the equivalent of 10⁷ h of normal operation, is not apparent from the HRTEM images.     

CdGd2（WO2）4晶体的高分辨电子显微研究

闪烁晶体材料用上探测了X射线的能量和强度，在它全检测，各种射线检测装置的运行中起有关键性的作用。例如GdWO4是良好的闪烁晶体，对X射线吸收系数大，辐射长度短，可使高能物理探测器做得十分密集，从而降低整个谱仪的造价。近年来，由于CdWO4晶体具有优越的光学性能，使它成为了应用在XCT探测器上的首选闪烁体材料。     

High-resolution electron microscopy of enamel-crystal demineralization and remineralization in carious lesions

Although dental caries destroys dental hard tissues, both demineralization as a destructive process and remineralization as a restorative process take place in carious lesions. These conflicting processes occur constantly either simultaneously or alternately. In crystallographic terms, demineralization is crystal dissolution, and remineralization is restoration of partially dissolved crystals, new crystal formation and growth of surviving crystals. In this review, we employ high-resolution transmission electron microscopy to demonstrate demineralization and remineralization of enamel crystals obtained from cross-cut sections of the c-axes of crystals from carious lesions.     

High-resolution electron microscopy of crystal defects in C70-toluene solvate

Defects in C70 x C6H5CH3 were examined using transmission electron microscopy. Two types of defects with respect to (001) and [011] were observed. The former is an inter-grain of BCT phase in Amm2 orthorhombic matrix, whereas the latter is a twin. Origins of the observed defects were determined to be of a shearing nature in the directions of [010] and <011>. In addition, an attempt is made to explain the decagonal symmetry of the compound, as reported by several authors, with respect to strain relaxation by observing defects as well as a multiple-twinning model described by Fleming et al. (Phys. Rev. B44: 888 (1991)). The conversion of C70-toluene solvate into C70 pure phases is discussed in terms of the defects.     

精确测定碳纳米管螺旋度的电子衍射方法

本文介绍精确测定碳纳米管原子结构的电子衍射方法.电子衍射方法利用碳纳米管的电子衍射图与碳纳米管螺旋指数(u,v)间的内在关系,可以从(a)衍射层线上的电子散射强度分布或(b)衍射层线间距的比例测定碳纳米管的螺旋指数.电子衍射方法是迄今为止测定碳纳米管的螺旋指数的最有效方法.电子衍射方法除具有结果精度高外,亦可用于测定多层碳纳米管的每层的螺旋指数.     

用场发射显微镜测量单壁碳纳米管的逸出功

该文利用场发射显微镜对单壁碳纳米管的逸出功进行了研究和测量。未进行加热除气的单壁碳纳米管的表面吸附大量气体,此时测量的逸出功不是清洁表面单壁碳纳米管的逸出功。实验首先加热除气得到单壁碳纳米管的场发射清洁像,然后利用场发射显微镜测量I-V曲线,得到Fowler-Nordheim直线斜率;再利用透射电镜观测单壁碳纳米管微束形貌像,测量管束半径,通过三种公式估算比例因子,最后计算得到单壁碳纳米管的逸出功。     

High-resolution transmission electron microscopy calibration ofcritical dimension (CD) reference materials

The National Institute of Standards and Technology and Sandia National Laboratories have developed a procedure for producing and calibrating critical dimension (CD), or linewidth, reference materials. These reference materials will be used to calibrate metrology instruments used in semiconductor manufacturing. The reference features, with widths down to 100 nm, are produced in monocrystalline silicon with all feature edges aligned to specific crystal planes. A two-part calibration of these linewidths is used: the primary calibration, with accuracy to within a few lattice plane thicknesses, is accomplished by counting the lattice planes across the sample as-imaged through use of high-resolution transmission electron microscopy. The secondary calibration is the high-precision electrical CD technique. In this paper, we describe the calibration procedure for these reference materials and estimate the related uncertainties     

High-resolution ultrahigh-vacuum electron microscopy of helical gold nanowires: junction and thinning process

Helical multishell (HMS) gold nanowires were observed in situ by ultra-high-vacuum electron microscopy. During thinning of the helical nanowire, a junction was formed between two nanowires of different diameter. The structure of the gold junction is proposed in comparison with the multiwall carbon nanotube. The gold junction has a dislocation-like core to accommodate the number difference of the atomic rows that compose the HMS nanowires, while the carbon junction has a pair of five- and seven-membered rings. Thinning of the helical gold nanowire by electron-beam radiation can be caused by the climbing motion of the dislocation-like core along the nanowire.     

碳纳米管团聚结构的电镜研究

纳米聚团床催化裂解法制得的碳纳米管均以团聚体形式存在，本文利用电子显微镜观察了两种碳纳米管团聚体的团聚结构，分散形态及微观结构，研究表明，纳米聚团床催化裂解法制备的碳纳米管具有多级团聚结构，范德华力及缠绕作用共同造成了多级团聚体的形成，细长的碳纳米管分散困难，易絮凝；短小弯曲的碳纳米管易于分散。     

Histochemistry of food tissue by colour scanning electron microscopy

A low-vacuum scanning electron microscope (SEM) allows microscopy of insulating specimens without metal coating, and so preserves the intact colour information on the specimen surface. We have attempted a new approach to characterize constituent distribution of food tissues by a histochemical method utilizing a colour SEM with an optical microscope and the low-vacuum SEM through digital image processing. To observe food tissues such as brown rice and adzuki bean, a colour SEM image of the specimen that has been stained by a modified method used in optical microscope histochemistry has proved to provide information of both the microscopic structure and constituent distribution on the specimen surface.     

Field electron emission of multiwalled carbon nanotubes and carbon nanofibers grown from Camphor

Vertically aligned carbon nanofibers (CNF) and multiwalled carbon nanotubes (MWCN) were synthesized from camphor by catalytic thermal chemical vapor deposition on Co and Co/Fe thin films (for CNF) and on silicon substrates using a mixture of camphor and ferrocene (for MWCN). CNF and MWCN were studied by scanning and transmission electron microscopy, visible Raman spectroscopy, X-ray diffraction in order to get insight into the microstructure and morphology of these materials. Field electron emission study indicates turn-on field of about 1.52, 2.3 and 4.3 V/μm for MWCN, Co/CNF and Co/Fe/CNF films, respectively; and threshold field of about 2.48, 3.1 and 6 V/μm, respectively. Our study indicates a better performance for field electron emission compared with some of the earlier published reports which might be due to higher aspect ratio, good graphitization and suitable density.     

Sr2CuO3+x无公度调制结构的高分辨电子显微学研究

锶铜氧超导化合物Sr2CuO3+x有无公度调制结构,Zhang H等人把它当作52a×52a的超结构,对高分辨电子显微像作了平均处理,建立了公度调制近似下的结构模型。本文用高分辨电子显微像解卷处理方法研究了Sr2CuO3+x的无公度调制结构。图1a、b分别为Sr2CuO3+x[001]和[010]电子衍射花样,强衍射斑为主衍射,每个主衍射的周围有卫星衍射,呈二维分布,反映出二维无公度调制结构。根据主衍射测得基本结构属四方晶系,空间群I/4mmm,晶胞参数a0=3·79和c0=12·45。两个调制波矢分别为q1≈0·1966a*+0·1924b*,q2≈-0·1962a*+0·1898b*,调制波矢的方向略…     

CoSi2薄膜与Si(001)界面的高分辨电子显微镜观察

利用高分辨透射电镜研究了经过550℃退火处理的共溅射CoSi2非晶结构薄膜与Si基体的界面.结果表明,550℃退火后薄膜已经发生晶化转变;同时CoSi2薄膜与Si基体发生反应扩散,在界面上生成了形状规则的CoSi2化合物,并与Si基体保持着相同的位向关系或孪晶位向关系.结合以上电镜观察,对这些界面化合物的生长机制进行了讨论.