Structural and Chemical Analysis of Materials with High Spatial Resolution

 An understanding of the correlation between microstructures and properties of materials require the characterization of the material on many different length scales. Often the properties depend primarily on the atomistics of defects, such as dislocations and interfaces. The different techniques of transmission electron microscopy allow the characterization of the structure and of the chemical composition of materials with high spatial resolution to the atomic level: high resolution transmission electron microscopy allows the determination of the position of the columns of atoms (ions) with high accuracy. The accuracy which can be achieved in these measurements depends not only on the instrumentation but also on the quality of the transmitted specimen and on the scattering power of the atoms (ions) present in the analyzed column. The chemical composition can be revealed from investigations by analytical microscopy which includes energy dispersive X-ray spectroscopy, mainly quantitatively applied for heavy elements, and electron energy-loss spectroscopy. Furthermore, the energy-loss near-edge structure of EELS data results in information on the local band structure of unoccupied states of the excited atoms and, therefore, on bonding. A quantitative evaluation of convergent beam electron diffraction results in information on the electron charge density distribution of the bulk (defect-free) material. The different techniques are described and applied to different problems in materials science. It will be shown that nearly atomic resolution can be achieved in high resolution electron microscopy and in analytical electron microscopy. Recent developments in electron microscopy instrumentation will result in atomic resolution in the foreseeable future.     

Bismuth nanowires for potential applications in nanoscale electronics technology.

Nanowires of bismuth with diameters ranging from 10 to 200 nm and lengths of 50 microm have been synthesized by a pressure injection method. Nanostructural and chemical compositional studies using environmental and high resolution transmission electron microscopy with electron stimulated energy dispersive X-ray spectroscopy have revealed essentially single crystal nanowires. The high resolution studies have shown that the nanowires contain amorphous Bi-oxide layers of a few nanometers on the surface. In situ environmental high resolution transmission electron microscopy (environmental-HRTEM) studies at the atomic level, in controlled hydrogen and other reducing gas environments at high temperatures demonstrate that gas reduction can be successfully applied to remove th oxide nanolayers and to maintain the dimensional and structural uniformity of the nanowires, which is key to attaining low electrical contact resistance.     

Nanotube composites: novel SiO2 coated carbon nanotubes

A novel route to nanocomposites consisting of multi-walled carbon nanotubes (MWNTs) embedded in amorphous SiOx is reported; the material has been characterised by high resolution transmission electron microscopy (HRTEM) and high resolution electron energy loss spectroscopy (HREELS); for the first time, and based on our observations, we propose theoretical models accounting for stable SiOx/tube interfaces using density functional based tight binding (DFTB).     

Synthesis and Characterization of ZnO Ellipsoid-like Nanostructures

"ZnO ellipsoid-like structures assembled by ZnO nanrods were fabricated from common ZnO whiskers by autoclave tests and pyrolysis integrated method. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and high resolution transmission electron microscopy studies reveal ZnO ellipsoidal structures are single-crystals and formed from direct oriented attachment of nanorods. Raman and room temperature photoluminescence spectra are also discussed."     

Using fluctuation microscopy to characterize structural order in metallic glasses.

We have used fluctuation microscopy to reveal the presence of structural order on length scales of 1-2 nm in metallic glasses. We compare results of fluctuation microscopy measurements with high resolution transmission electron microscopy and electron diffraction observations on a series of metallic glass samples with differing degrees of structural order. The agreement between the fluctuation microscopy results and those of the other techniques is good. In particular, we show that the technique used to make thin specimens for electron microscopy affects the structure of the metallic glass, with ion thinning inducing more structural order than electro-polishing. We also show that relatively minor changes in the composition of the alloy can have a significant effect on the medium-range order; this increased order is correlated with changes in mechanical behavior.     

碳纳米管向金刚石纳米晶粒的转变

在碳60（C60）[1]和碳纳米管(CNTs)[2]发现之前,人们知道碳通常显示石墨和金刚石两种晶体结构.自从C60和碳纳米管发现后,由于其独特的纳米结构而具有广泛的应用前景,国内外许多学者致力于研究它们的物理和化学特性,而C60、巴基葱（多层碳纳米球）、碳纳米管和金刚石之间的转变是所研究的焦点之一.目前,由碳的其他形式向金刚石转变的主要方法有：Meilunas等人[3]以C60和C70薄膜为基底气相生长多晶金刚石,C60和C70的稳定性和微平面结构在外界条件下,有利于金刚石成核和外延生长;Banhart[4]小组研究了在电子束辐射作用下巴基葱转变…     

Synthesis and Characterization of SnO2 One-dimensional Nanostructures

Single-crystalline SnO2 nanowires have been successfully prepared in large scale on Au-coated silicon substrate by heating the mixture of self-made high-purity SnO2 powders and graphite powders at 900℃. Besides the line type nanowires some more features were observed. The products were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and Raman spectrum techniques. The results indicate that the tin dioxide nanowires have a rutile structure with diameters ranging from 30 to 120 nm and lengths up to several tens of micrometers. The possible mechanism of the growth and reaction for the nanowires was also discussed.     

熔体结晶聚乙烯晶体的高分辨电子显微学研究

聚乙烯在一定的不良溶剂中或在熔融结晶的条件下可以得到具有弧形生长边缘的单晶,对于具有弧形边的（200）晶面的形成机理,已有一些研究报道,但由于高分子链具有成千上万个结构单元,使其结晶过程很复杂,可能会导致弧形边的成因有所不同,因此对于弧形边的形成机理有不同的解释。     

Recent progress in quantitative and high spatial resolution AES

Progress in high resolution Auger electron spectroscopy (HR-AES or scanning Auger microscopy, SAM) during the past few years is characterized by the use of efficient field emission electron sources, parallel detection capabilities and improved data acquisition, storage and processing, thus enhancing spatial resolution (to about 10 nm), signal to noise figure and quantification of elements in different chemical bonding states, e.g. by routinely using factor analysis. Optimized ion sputtering facilities, particularly sample rotation, enable depth profiling with high, depth independent resolution. The basic features of SAM are discussed with respect to EPMA (electron probe micro-analysis), emphasizing fundamental limitations and future developments.     

A kind of carbon whiskers in new structure and morphology

Carbon whiskers with new structure and morphology were observed when heating the milled graphite. Transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) show that carbon layers are almost perpendicular to the growth axes of carbon whiskers. Field emission scanning electron microscopy (FESEM) indicates that there are spirals appearing on the surface of the whiskers. The structure analysis shows that the growth mechanism of carbon whiskers is related to the trace amount of ZrC in the heated samples.     

钛酸钡纳米颗粒聚集球的形成机理

采用水热法合成了具有新颖结构的钛酸钡纳米颗粒聚集球.X射线衍射(XRD)结果显示该聚集球为立方相,随着时间的延长其结晶性增强.利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、高分辨透射电子显微镜(HRTEM)和电子衍射(ED)谱研究了该纳米颗粒聚集球的生长特点.结果表明该聚集球是由5-8nm的纳米颗粒定向连接生长而成,整个聚集球对外显示类单晶的现象.聚集球的大小约为60nm,随着时间的延长有长大的趋势.X射线能谱(EDX)分析结果和Johnson-Mehl-Avrami(JMA)方程动力学模拟结果表明,在颗粒球形成初始阶段主要是Ba2+离子的扩散成核作用占主导地位.这种"扩散成核-定向生长"的形成过程揭示了钛酸钡纳米颗粒聚集球的生长机理.     

Mn3O4 nanoplates and nanoparticles: Synthesis, characterization, electrochemical and catalytic properties

Mn₃O₄ hexagonal nanoplates and nanoparticles were synthesized via a solvent-assisted hydrothermal oxidation process at low temperature and a solvothermal oxidation method, respectively. The synthesized product was characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), electron diffraction (ED), Fourier transform infrared (FT-IR) spectroscopy. Their capability of catalytic oxidation of formaldehyde to formic acid at room temperature and atmospheric pressure and electrochemical properties by cyclic voltammogram (CV) were compared. The results showed that Mn₃O₄ hexagonal nanoplate is a better catalyst, and the hexagonal nanoplates and nanoparticles modified electrodes blended with carbon black have a higher specific capacitance.     

Epitaxial Growth and Thermoelectric Measurement of Bi2Te3/Sb Superlattice Nanowires

Superlattice nanowires are expected to show further enhanced thermoelectric performance compared with conventional nanowires or superlattice thin films. We report the epitaxial growth of high density Bi₂Te₃/Sb superlattice nanowire arrays with a very small bilayer thickness by pulse electrodeposition. Transmission electron microscopy, selected area electron diffraction and high resolution transmission electron microscopy were used to characterize the superlattice nanowires, and Harman technique was employed to measure the figure of merit (ZT) of the superlattice nanowire array in high vacuum condition. The superlattice nanowire arrays exhibit a ZT of 0.15 at 330 K, and a temperature difference of about 6.6 K can be realized across the nanowire arrays.     

Superconductivity in a Copper(II)‐Based Coordination Polymer with Perfect Kagome Structure

A highly crystalline copper(II) benzenehexathiolate coordination polymer (Cu‐BHT) has been prepared. The two‐dimensional kagome structure has been confirmed by powder X‐ray diffraction, high‐resolution transmission electron microscopy, and high‐resolution scanning transmission electron microscopy. The as‐prepared sample exhibits bulk superconductivity at about 0.25 K, which is confirmed by the zero resistivity, AC magnetic susceptibility, and specific heat measurements. Another diamagnetic transition at about 3 K suggests that there is a second superconducting phase that may be associated with a single layer or few layers of Cu‐BHT. It is the first time that superconductivity has been observed in a coordination polymer.     

A new cellular carbon support for catalysts: preparation and study of structure

Cellular carbon has been prepared by pyrolysis of a propane—butane mixture in a flow reactor at 700–1250 K. Its structural characteristics were studied by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction and adsorption methods. It was shown that cell-type carbon possesses a unique structure in contrast to carbon composite “Sibunnit” and filamentous carbons and it may be a promising support for catalyst preparation.     

铂纳米空球的制备及其对甲醇氧化的电催化性能

以粒径为100nm的硒球作模板,在室温下批量合成了粒径约110nm、壳厚约5 nm的铂空球.采用扫描电子显微镜（SEM）、透射电子显微镜（TEM）、高分辨透射电子显微镜（HR-TEM）、选区电子衍射（SAED）、X射线衍射（XRD）、能量色散X射线谱（EDX）等检测技术表征了其形貌与结构;以甲醇为探针分子研究了铂纳米空球修饰玻碳电极对甲醇电氧化的催化性能.结果表明,由铂原子簇团构筑的多孔铂空球粒径均匀、分散性好、结构稳定、比表面积大、传质性能好,是甲醇氧化的理想催化材料.循环伏安（CV）结果表明:当甲醇氧化的电流密度0.10 mA·cm^-2,正扫时,铂纳米空球的氧化电位与实心铂纳米粒子及铂黑相比,分别负移了约110和64mV;负扫时,前者比后两者分别负移了约51与13 mV.经800圈循环伏安扫描后,正扫时,甲醇在铂纳米空球上氧化峰的电流密度为实心铂纳米粒子及铂黑上的13和15倍;负扫时,前者为后两者的19和38倍.表明铂纳米空球对甲醇氧化具有较好的催化活性和稳定性.     

Single‐Crystalline ZnO Nanowire Bundles: Synthesis,Mechanism and Their Application in Dielectric Composites

Single‐crystalline ZnO nanowire bundles have been synthesized in large‐scale by an improved microemulsion method in the presence of excessive hydrate hydrazine and dodecyl benzene sulfonic acid sodium salt (DBS) in xylene. The product is characterized using X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high‐resolution transmission electron microscopy (HRTEM). The result shows that the bundle is composed by many oriented single‐crystalline ZnO nanowires with a length of about 1 μm and a diameter of about 20–30 nm. The influence of DBS, hydrazine and the reaction time on the morphology of final product and the formation mechanism of such nanostructures were discussed; the application in the dielectric composites is also studied.     

Analytical electron microscopy of materials

Analytical electron microscopy enables combined crystallographic and chemical information with a high spatial resolution to be gained from microregions of electron-transparent specimens. This is reached by the combined application of imaging, diffraction and spectroscopic methods, using either a dedicated scanning transmission electron microscope or a conventional high-resolution electron microscope (having a strong objective lens) equipped with suitable X-ray or electron spectrometers. Of the diffraction methods especially the technique of convergent beam diffraction is used, yielding valuable information on crystal structures, lattice parameter changes, symmetry variations and crystal perfection, respectively. For chemical analysis, either energy-dispersive X-ray spectroscopy (EDX) is used or electron energy loss spectroscopy (EELS). Finally, high-resolution electron microscopy in the lateral resolution range of some 0.1 nm allows the reliable geometrical inspection of extreme microregions.     

Synthesis and Characterization of Magnetic TiO2/SiO2/NiFe2O4 Composite Photocatalysts

Magnetic TiO2/SiO2/NiFe2O4 composite photocatalytic particles with high crystalline TiO2 shell were synthesized via a mild solution route.The prepared composite particles were characterized with X-ray diffraction(XRD),transmission electron microscopy(TEM),high resolution transmission electron microscopy(HRTEM),scanning electron microscopy(SEM),ultraviolet-visible(UV-Vis) spectroscopy and vibrating sample magnetometer(VSM).The results show that the obtained TiO2/SiO2/NiFe2O4 composite particles were composed...     

Synthesis,Characterization, and Photocatalytic Activity of N‐Doped TiO2 Nanotubes

N‐doped TiO₂ nanotubes with high photocatalytic activity were prepared by the combination of sol‐gel process with hydrothermal treatment. The prepared materials are characterized with transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), x‐ray diffraction (XRD), x‐ray photoelectron spectra (XPS), and UV‐vis spectra. Photocatalytic performance of the N‐doped TiO₂ nanotubes is studied by testing the degradation rate of methyl orange under UV irradiation. Obtained results indicate that N‐doped TiO₂ nanotubes have high catalytic activity for photocatalytic oxidation.