Fullerene-like models for microporous carbon

Microporous carbons are important in a wide variety of applications, ranging from pollution control to supercapacitors, yet their structure at the molecular level is poorly understood. Over the years, many structural models have been put forward, but none has been entirely satisfactory in explaining the properties of the carbons. The discovery of fullerenes and fullerene-related structures such as carbon nanotubes gave us a new perspective on the structure of solid carbon, and in 1997 it was suggested that microporous carbon may have a structure related to that of the fullerenes. Recently, evidence in support of such a structure has been obtained using aberration-corrected transmission electron microscopy, electron energy loss spectroscopy and other techniques. This article describes the development of ideas about the structure of microporous carbon, and reviews the experimental evidence for a fullerene-related structure. Theoretical models of the structural evolution of microporous carbon are summarised, and the use of fullerene-like models to predict the adsorptive properties of microporous carbons are reviewed.     

水热合成NiX(WYM01-Y)1-XS2纳米管

无机类富勒烯纳米粒子具有良好的润滑性能.宏量制备高纯度的样品以满足性能测试的要求,是目前面临的主要技术难题.本文采用剥离-掺杂-水热处理这一工艺流程制备了多元金属二硫化物纳米粒子,应用XRD、TEM、HRTEM和EDS等分析手段对其形貌、晶相组成、结构和化学组成进行了表征.实验结果表明,多元金属二硫化物纳米颗粒具有管状形貌,管壁为多层状结构,化学组成为NiX(WYMo1-Y)1-XS2,同时,样品中具有类富勒烯结构的纳米粒子大幅度提高;并依据实验结果对多元金属二硫化物纳米管的形成机理进行了探讨.     

水热合成NiX(WYMo1-Y)1-XS2纳米管

无机类富勒烯纳米粒子具有良好的润滑性能. 宏量制备高纯度的样品以满足性能测试的要求, 是目前面临的主要技术难题. 本文采用剥离-掺杂-水热处理这一工艺流程制备了多元金 属二硫化物纳米粒子, 应用XRD、TEM、HRTEM和EDS等分析手段对其形貌、晶相组成、结构和化学组成进行了表征. 实验结果表明, 多元金属二硫化物纳米颗粒具有管状形貌,管壁为 多层状结构, 化学组成为Ni_X(W_YMo_1-Y)_1-XS₂, 同时, 样品中具有类富勒烯结构的纳米粒子大幅度提高; 并依据实验结果对多元金属二硫化物纳米管的形成机理进行了探讨.     

Spray drying process to synthesize multiple fullerene-like MoS2 particles

Multiple inorganic fullerene-like (IF) molybdenum disulfide hollow spheres were synthesized through spray drying method. The molybdenum trisulfide precursor, which was prepared by the mixed solution of ammonium molybdate ((NH₄)₂MoO₄) and ammonium disulfide ((NH₄)₂S) with a spray drying method, was desulfurized at 850 °C in a mixture of hydrogen and argon, and subsequently multiple fullerene-like molybdenum disulfide hollow spheres were obtained. The samples were identified and characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM), and the mechanism of formation is also discussed based on the experimental result. The spray drying process would be an effective method to synthesize large-scale of inorganic fullerene-like materials.     

Extracting of fullerene-like nanoparticles from environmental soots

It is well known that burning graphite electrodes in electric arc is an efficient method for obtaining of fullerenes. However, fullerenes form in any sooting flames. Therefore, detection fullerene in natural burning fuel is of a great interest for understanding of mechanism of soot formation. This research extracted samples of environmental soots in toluene. Soots and products of extraction were characterized by UV-vis spectroscopy, sedimentation analysis, atomic force microscopy. Analysis of extracts found fullerene-like clusters. The concentration of particles decreased in the following sequence: charcoal – carbon black – gas soot.     

Opportunities and pitfalls in characterisation of nanoscale features

Abstract

Thermally assisted field emission gun TEM (FEGTEM), with associated electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI) is used to characterise nanoscale features in technologically important materials. The exceptionally high spatial and temporal coherence of the FEG source allows high resolution image information down to 0.1 nm to be routinely imaged, but the complexity of the atomic contrast makes interpretation of interface structure more difficult than with LaB₆ sources. A spatial resolution of 0.9 nm for through thickness features and 2 nm for embedded particles is demonstrated for ESI, illustrating the remarkable sensitivity of this technique. The energy resolution of the FEG source (0.65 eV) is sufficient to resolve the fine near edge structure in EELS spectra to allow bonding information to be obtained with a spatial resolution of 1 nm or possibly better. X-ray energy dispersive spectroscopy can be performed on a similar scale, sufficiently small to identify submonolayer segregates at interfaces. The limitations of each technique are discussed in relation to the critical microstructural information required for each material investigated.     

Electron holographic tomography

The exact knowledge about intrinsic electrostatic potentials and in particular their three-dimensional distribution at the nanometer scale is a key prerequisite for understanding the solid state properties. Electron holographic tomography (EHT), the combination of off-axis holography with tomography in the transmission electron microscope, provides a unique access to this information. We review the development and application of automated EHT to reconstruct 3D potentials in nanostructures such as the mean inner potential of a material or the diffusion potential across p–n junctions in semiconductors. We also discuss future challenges of the 3D reconstruction of electric crystal potentials at atomic resolution and magnetostatic fields as well as ways to overcome present limitations of the method.     

Nanostructural and chemical characterization of supported metal oxide catalysts by aberration corrected analytical electron microscopy

The performance of catalyst materials are usually governed by the precise atomic structure and composition of very specific catalytically active sites. Therefore, structural and chemical characterization at the atomic scale becomes a vital requirement in order to identify any structure-performance relationships existing in heterogeneous catalyst systems. Aberration-corrected scanning transmission electron microscopy (STEM) represents an ideal means to probe the atomic scale structural and chemical information via a combination of various imaging and spectroscopy techniques. In particular, high-angle annular dark-field (HAADF) imaging provides directly interpretable atomic number (Z) contrast information; while X-ray energy dispersive spectroscopy (XEDS) and electron energy-loss spectroscopy (EELS) spectrum imaging can be used to identify the chemical composition and oxidation state. Here we review some applications of aberration-corrected STEM to catalyst research, firstly in the context of supported metal catalysts, which serve as ideal material systems to illustrate the power of these techniques. Then we focus our attention on more recent progress relating to the characterization of supported metal oxide catalysts using aberration-corrected STEM. We demonstrate that it is now possible to directly image supported surface oxide species, study oxide wetting characteristics, identify the catalytic active sites and develop new insights into the structure-activity relationships for complex double supported oxide catalysts. Future possibilities for in situ and gentle low voltage electron microscopy studies of oxide-on-oxide materials are also discussed.     

Lubrication mechanisms of hollow-core inorganic fullerene-like nanoparticles: coupling experimental and computational works

Inorganic fullerene-like (IF) nanoparticles made of metal dichalcogenides have previously been recognized to be good friction modifiers and anti-wear additives under boundary lubrication conditions. The tribological performance of these particles appears to be a result of their size, structure and morphology, along with the test conditions. However, the very small scale of the IF nanoparticles makes distinguishing the properties which affect the lubrication mechanism exceedingly difficult. In this work, a high resolution transmission electron microscope equipped with a nanoindentation holder is used to manipulate individual hollow IF-WS(2) nanoparticles and to investigate their responses to compression. Additional atomistic molecular dynamics (MD) simulations of similarly structured, individual hollow IF-MoS(2) nanoparticles are performed for compression studies between molybdenum surfaces on their major and minor axis diameters. MD simulations of these structures allows for characterization of the influence of structural orientation on the mechanical behavior and nano-sheet exfoliation of hollow-core IF nanoparticles. The experimental and theoretical results for these similar nanoparticles are qualitatively compared.     

A stable LaB6 nanoneedle field-emission electron source for atomic resolution imaging with a transmission electron microscope

Field-induced electron emission offers the best performance point electron source for electron microscopes. Herewith we report a new cold field-emission point electron source utilizing a nanoneedle made of lanthanum hexaboride (LaB₆) and its implementation in a spherical aberration-corrected transmission electron microscope (TEM). A sub-ångstrom resolution of 0.96 Å has been obtained with the TEM operated at an acceleration voltage of 60 kV and a smaller energy spread was also observed compared with the contemporary W(310) electron source. In particular, the LaB₆ nanoneedle cold field-emission electron source required no thermal flashing for continuous operation of extended hours (>100 hours) while exhibiting and sustaining a high stability in emission current (<1%). We attribute the excellent performance of the LaB₆ nanoneedle electron source to (i) a low work function of LaB₆; (ii) excellent alignment of the nanoneedle emitter by the electron and ion dual-beam processing with nanoscale precision and (iii) robustness of the nanometric structure that suppressed mechanical vibrations of the LaB₆ emitter even in a high electric field. This new LaB₆ nanoneedle cold field-emission electron source enables stable high-resolution imaging in TEM and it will also benefit cryogenic electron microscopy, scanning electron microscopy, electron beam lithography, and other electron beam technologies.     

Local surface charges direct the deposition of carbon nanotubes and fullerenes into nanoscale patterns

This article reports on the directed deposition of carbon nanotubes (CNTs) and fullerenes onto solid surfaces using local electrostatic fields. Arbitrary patterns of local surface charges are created by charge writing with an atomic force microscope. During the subsequent development of the sample in an aqueous suspension containing surfactant-stabilized CNTs or fullerenes, Coulomb attraction guides the positioning and alignment of these particles onto the charge patterns. The surface potential of the charge patterns provides a direct control over the particle attachment. CNTs and fullerenes precisely reproduce the charge patterns, yielding structures with a lateral resolution down to the particle diameter.     

Achieve atomic resolution in in situ S/TEM experiments to examine complex interface structures in nanomaterials

Characterization methods utilizing Scanning / Transmission Electron Microscopes have become routine techniques to investigate interface structures in nanomaterials. High resolution imaging methods reveals atomic structure; while spectroscopy gives additional access to elemental distribution and chemical bonding. Focus behind these developments is the research on nanomaterial-based technologies.Current trends in S/TEM research focus on extending atomic scale characterization capabilities from static to dynamic studies to understand in more detail the link between structure and its evolution vs. unique properties directly on its characteristic length scale.Progress in recent research is briefly reviewed to highlight the potential when using latest S/TEM methodology optimized for atomic scale investigations and how this can be extended to in situ studies of interfacial effects, followed by comments on how to achieve and maintain highest possible resolution & sensitivity when keeping the effect of electron beam under control during these atomic-scale in situ experiments.     

Calibration of High-Resolution X-Ray Tomography With Atomic Force Microscopy

For two-dimensional x-ray imaging of thin films, the technique of scanning transmission x-ray microscopy (STXM) has achieved images with feature sizes as small as 40 nm in recent years. However, calibration of three-dimensional tomographic images that are produced with STXM data at this scale has not yet been described in the scientific literature, and the calibration procedure has novel problems that have not been encountered by x-ray tomography carried out at a larger scale. In x-ray microtomography, for example, one always has the option of using optical imaging on a section of the object to verify the x-ray projection measurements; with STXM, on the other hand, the sample features are too small to be resolved by light at optical wavelengths. This fact implies that one must rely on procedures with higher resolution, such as atomic force microscopy (AFM), for the calibration. Such procedures, however, generally depend on a highly destructive sectioning of the sample, and are difficult to interpret because they give surface information rather than depth information. In this article, a procedure for calibration is described that overcomes these limitations and achieves a calibration of an STXM tomography image with an AFM image and a scanning electron microscopy image of the same object.A Ge star-shaped pattern was imaged at a synchrotron with a scanning transmission x-ray microscope. Nineteen high-resolution projection images of 200 × 200 pixels were tomographically reconstructed into a three-dimensional image. Features in two-dimensional images as small as 40 nm and features as small as 80 nm in the three-dimensional reconstruction were resolved. Transverse length scales based on atomic force microscopy, scanning electron microscopy, x-ray transmission and tomographic reconstruction agreed to within 10 nm. Toward the center of the sample, the pattern thickness calculated from projection images was (51 ± 15) nm vs (80 ± 52) nm for tomographic reconstruction, where the uncertainties are evaluated at the level of two standard deviations.     

螺旋炭纤维的结构分析

分析了螺旋炭纤维的微观结构,发现其主要由纳米级石墨片层(nano graphite structurecell,NGSC,约为5 nm×5 nm)构成,其间夹杂着无定形碳和多层富勒烯等无序结构.由于螺旋炭纤维具有螺旋结构,其中的NGSC发生了一定的弯曲.在宏观尺度上,螺旋炭纤维表现出无序碳结构的特征.根据结构分析的结果提出了表征螺旋炭纤维的几何参数,并对不同螺旋炭纤维的螺旋角进行了比较分析.结果表明,虽然螺旋炭纤维的直径和螺距各不相同,但是其螺旋角具有一定的规律.在微观结构观察和几何构形分析的基础上提出了螺旋炭纤维的生长机理.     

Direct imaging of atomic-scale ripples in few-layer graphene

Graphene has been touted as the prototypical two-dimensional solid of extraordinary stability and strength. However, its very existence relies on out-of-plane ripples as predicted by theory and confirmed by experiments. Evidence of the intrinsic ripples has been reported in the form of broadened diffraction spots in reciprocal space, in which all spatial information is lost. Here we show direct real-space images of the ripples in a few-layer graphene (FLG) membrane resolved at the atomic scale using monochromated aberration-corrected transmission electron microscopy (TEM). The thickness of FLG amplifies the weak local effects of the ripples, resulting in spatially varying TEM contrast that is unique up to inversion symmetry. We compare the characteristic TEM contrast with simulated images based on accurate first-principles calculations of the scattering potential. Our results characterize the ripples in real space and suggest that such features are likely common in ultrathin materials, even in the nanometer-thickness range.     

Aberration-corrected transmission electron microscopy of the intergranular phase in magnetic recording media

In perpendicular hard disk memory media, nanometric magnetic Co-rich grains are separated by a ～1 nm thick nonmagnetic and preferably amorphous intergranular phase (IP). Attempts at observing the IP structure at high resolution using TEM have been obstructed by the superposition of lattice fringes from the crystalline grains extending into the IP region in images. Here we present the first images of a magnetic recording medium produced using a spherical aberration-corrected TEM showing the true amorphous IP structure in contrast to the crystalline grains, allowing the accurate determination of the grain-IP interface and the grain and IP dimensions. It is shown that these aberration-corrected TEM images are functionally superior for analyzing certain features of the ultrahigh capacity data recording media.     

Utilizing boron nitride sheets as thin supports for high resolution imaging of nanocrystals

We demonstrate the use of thin BN sheets as supports for imaging nanocrystals using low voltage (80 kV) aberration-corrected high resolution transmission electron microscopy. This provides an alternative to the previously utilized 2D crystal supports of graphene and graphene oxide. A simple chemical exfoliation method is applied to get few layer boron nitride (BN) sheets with micrometer-sized dimensions. This generic approach of using BN sheets as supports is shown by depositing Mn doped ZnSe nanocrystals directly onto the BN sheets and resolving the atomic structure from both the ZnSe nanocrystals and the BN support. Phase contrast images reveal moiré patterns of interference between the beams diffracted by the nanocrystals and the BN substrate that are used to determine the relative orientation of the nanocrystals with respect to the BN sheets and interference lattice planes. Double diffraction is observed and has been analyzed.     

Transmission electron microscope investigation of cadmium sulfide nanoparticles grown under Langmuir monolayer

Study of the lattice structure of nanoparticles templated by surfactant assemblies is of importance in the understanding of the templating mechanism and the properties of the particles. Here a transmission electron microscope (TEM) investigation on the lattice structure of cadmium sulfide nanoparticles grown under a stearic acid Langmuir monolayer is demonstrated. TEM study reveals that an isolated nanoparticle can only form a one-dimensional electron diffraction pattern. Therefore the atomic packing in the particles shows one-dimensional order.     

PyDDP表面修饰纳米硼钼剂的制备及极压性能研究

以二烷基二硫代磷酸吡啶（PyDDP）为表面修饰剂, 分别制备了PyDDP表面修饰纳米硼酸镧和PyDDP表面修饰纳米二硫化钼, 并将两者复配制备了PyDDP表面修饰纳米硼钼剂. 采用IR、XRD、TEM等分析方法对表面修饰纳米微粒进行了表征. 结果表明, 纳米硼钼剂由硼酸镧和二硫化钼微粒组成, 粒径在30～50nm之间. 通过四球试验研究了PyDDP表面修饰纳米硼钼剂的摩擦学性能, 并利用SEM、EDXA、XPS等方法对蚀球表面形貌和表面元素进行了分析. 结果表明, PyDDP表面修饰纳米硼钼剂具有较好的极压抗磨性能, 表面元素在摩擦副表面形成无机化学反应膜是具有良好的极压性能的主要原因.     

Developments of electron microscopy methods in the study of catalysts

Recent developments in electron microscopy methods for in-situ probing of catalysis at the atomic level, ultrahigh resolution surface tools, energy filtered imaging for elucidating the structure and chemistry of nanoparticles and electron tomography for three-dimensional visualization of nanocatalysts are transforming heterogeneous catalysis research. In this short review, recent experimental and theoretical developments of electron microscopy methods for the study of gas–solid catalyst reactions, liquid–catalyst reactions, polymerization in the solution and solid phase, oxides and nanocatalysts are presented. They demonstrate the powerful role of electron microscopy in the design and development of catalyst materials and technologies.