透射电子显微技术在RIPP炼油催化剂表征中的应用

利用透射电子显微技术对加氢催化剂以及积炭催化裂化催化剂进行了表征。扫描透射电子结合X射线能谱技术确定了氧化态加氢催化剂中的微粒为活性金属组分的适度聚集；能量过滤透射显微技术获得了积炭催化裂化催化剂的Al、C的元素分布像。     

Effect of carbon nanotube structural parameters on field emission properties

Experimental studies were devoted to the effect of structural parameters, i.e., tube diameter and density, on the field electron emission characteristics of carbon nanotubes. Thermal chemical vapor deposition system was employed to synthesize carbon nanotubes. Nanotubes with different diameters and densities were obtained by adjusting the thickness of the iron (Fe) catalyst film. The morphologies of the Fe and carbon nanotube film were characterized by scanning electron microscopy respectively. Further field emission measurement confirmed that the tube diameter and density could significantly affect the electron emission properties of the carbon nanotube. Possible physical reasons for the effect are discussed.     

Mapping of ELNES on a nanometre scale by electron spectroscopic imaging

The amorphous interfacial layer between Si substrates and diamond films grown by plasma-assisted chemical vapour deposition has been studied by electron spectroscopic imaging. The amorphous layer consists mainly of carbon, which can only be distinguished from the diamond film by analysis of the near-edge structure (ELNES) of the carbon K edge. Series of electron spectroscopic images were acquired across the carbon K edge and were analysed in order to reveal the presence of the π*- and σ*-excitations. After background removal from the corresponding images, phase maps for the distribution of sp² and sp³ hybridized carbon can be obtained. From the whole series of images, electron energy-loss spectra can be extracted for any given area in the images. The results show that the amorphous layer covers large areas along the interface and that regions with only 1–2 nm layer thickness can clearly be analysed. The results obtained with the electron spectroscopic imaging technique will be compared with results obtained on a field emission gun scanning transmission electron microscope.     

Parameters affecting specimen flatness of two-dimensional crystals for electron crystallography

The flatness of two-dimensional (2D) crystals on the support film is a critical factor in protein electron crystallography. The influence of the carbon support film and of different grid makes and materials on flatness was investigated, using as a criterion the sharpness of diffraction spots perpendicular to the tilt axis of electron diffraction patterns of purple membrane tilted in the microscope at 45 degrees. In a quantitative test, carbon film that had been evaporated without sparks forming gave a much larger proportion of flat crystals than "sparked" carbon. Titanium grids were superior to copper, probably because they introduce less cryo-crinkling of the carbon film when the sample is cooled to liquid nitrogen temperature, as their thermal expansion coefficient is closer to that of carbon. While the molybdenum grids from Plano were unsuitable for data collection because of their tendency of break the carbon, molybdenum grids from Pacific GridTech gave a much larger yield of flat crystals than the titanium grids. Scanning electron microscope images of the grids as supplied by the manufacturer showed that the Plano grids had very narrow and irregular grid bars, while the Pacific GridTech grids were very smooth with a large surface-to-hole ratio.     

Damages of screen-printed carbon nanotube cold cathode during the field emission process

The field emission properties of the screen-printed carbon nanotube (CNT) composite cathode have close relationship with its microstructure. In this study, carbon nanotube composite cold cathode with ZnO nano-particles as binding material was prepared using screen-printing method. Electric field cycles were used to post-treat the carbon nanotube composite cold cathode. During the process of electric field cycle treatment, obvious heat-induced damages were observed from the cathode. Scanning electron microscope and transmission electron microscope were employed to analyze the morphology and microstructure of the cathode. The possible mechanisms responsible for damages were discussed.     

A porous carbon film for the collection of atmospheric aerosol for transmission electron microscopy

This paper describes a method of direct sampling of fine urban aerosol using porous carbon films, to increase collection efficiency and retain the structural integrity of the aerosol. A nuclepore membrane filter was coated with carbon and washed with chloroform to leave a clean porous carbon film on a 200-mesh transmission electron microscope copper grid. The grid was attached to a clean nuclepore filter using carbon cement. Sampling was conducted for 1 h at 1.9 L min⁻¹ flow rate. The porous carbon grid with sample was then assayed using transmission electron microscopy, and negatives were suitable for image analysis. The collection of fine airborne particles using this method is appropriate for electron microscopy, with a minimum of interference to the structure of collected particles.     

A series of tufted carbon fiber cathodes designed for different high power microwave sources

We report the fabrication technique of tufted carbon fiber cathodes for different microwave sources. Three carbon fiber cathodes were constructed, including a planar cathode, an annular cathode, and a cylindrical cathode for radial emission. Experimental investigations on these cathodes were performed in a reflex triode virtual cathode oscillator (vircator), a backward wave oscillator (BWO), and a magnetically insulated transmission line oscillator (MILO), respectively. The pulse duration of microwave emission from the reflex triode vircator was lengthened by using the planar carbon fiber cathode. In the BWO with the annular carbon fiber cathode, the uniform electron beam with a kA/cm(2) current density was observed. In addition, carbon fiber has great promise as field emitter for MILOs. These results show that the carbon fiber cathodes can be utilized for electron emission in high power diodes with different structures.     

Effects of the composition and fibrous texture of lithium soap grease on wear and friction

The effects of anions and fibrous texture of soap on the wear and friction properties of lubricating grease were investigated with the aid of four-ball machine testing and scanning electron microscopy. The results indicated that the carbon chain length and the odd or even carbon number in the chains had significant influences on the wear and friction properties of lubricating grease. With the aid of a scanning electron microscope, certain relationships were found to exist between wear and friction properties and fibrous texture of lithium soap.     

Crater wear mechanism of wc-co tools at high cutting speeds

To clarify the mechanism of crater wear when carbon steel is turned by a WC-Co at high speed, the crater surface, chip underside and wear debris were examined with a scanning electron microscope, an electron probe microanalyser, an ion microprobe analyser and an X-ray diffractometer. Crater wear is not due to carbon diffusion from the tool carbides into the chips to form complex carbides; it arises because tungsten, titanium, tantalum and carbon from the carbides diffuse atomically directly into the chips and because the carbides are abraded by hard inclusions in the carbon steel.     

Anti-wear and Friction Reducing Mechanisms of Carbon Nano-onions as Lubricant Additives

Carbon nano-onions have better tribological properties than graphite powder when used as additives dispersed in a poly-alpha-olefin base oil. Carbon nano-onions give a better dispersion in the liquid base oil due to their nanometre-scale size. In particular, the anti-wear efficiency of carbon onions under boundary lubrication and mild wear regime is much better than that of graphite powder. This effect can be attributed to the different structure of the carbon layers in the two species. High-resolution transmission electron microscopy and electron energy-loss spectroscopy were used to characterize the carbon samples, and significant differences in the carbon layer spacing and the density were shown. Wear debris were also observed by the same techniques. In the tribofilm material we depicted new chemical and crystal nano-structures species similar to some microstructures observed in chondrite meteorites, the most interesting one being maghemite iron oxide. The origin of the low friction and wear is still largely unknown.     

The application of convergent beam electron diffraction (CBED) analysis on transformation‐induced plasticity (TRIP) steels

Convergent beam electron diffraction (CBED) in transmission electron microscopy (TEM) was applied to determine local carbon concentrations in low‐carbon transformation‐induced plasticity (TRIP) steels. High‐order Laue‐zone (HOLZ) lines were experimentally obtained for comparison with simulation results. A new procedure for calculating carbon content is thus proposed. Retained austenite (RA) is classified into three types by morphology; the relationship between the carbon content and the corresponding RA morphology is discussed based on CBED results. Furthermore, results of X‐Ray diffractometry measurements are also used for comparison.     

碳纤维表面化学镀铜工艺优化及摩擦性能研究

研究了碳纤维表面预处理和化学镀铜工艺,采用正交设计方法对碳纤维镀铜工艺进行优化,并对制备的镀铜碳纤维进行SEM和XRD微观表征.在镀铜碳纤维中加入PTFE制备固体润滑复合材料,并进行摩擦磨损实验.实验结果表明:碳纤维表面有C= =O及C-O-C等极性基团,能与铜产生较好的机械结合力;经过解胶、还原等表面处理后,碳纤维表面形成凹槽和微孔,便于化学镀时铜附着在其表面;化学镀后铜与碳纤维结合紧密,碳纤维表面镀层光亮、均匀致密、具有较好的结合力;采用化学镀原料配比CuSO4·5H2O 15 g/L,EDTA 25 g/L,NaOH 16 g/L制得的镀铜碳纤维,其镀铜量居中,加入PTFE所制得的固体润滑材料摩擦因数和磨损量较低,且摩擦因数有下降的趋势.     

Observation of human dentine by focused ion beam and energy-filtering transmission electron microscopy

Molar dentine was sliced into 100 nm ultrathin sections, by means of a focused ion beam, for observation by energy-filtering transmission electron microscopy (EFTEM). Within the matrix, crystals approximately 10 nm wide and 50–100 nm long were clearly observed. When carbon and calcium were mapped in electron spectroscopic images by EFTEM, carbon failed to localize in crystals. However, it was found in other regions, especially those adjacent to crystals. Because carbon localizations were thought to reflect the presence of organic components, carbon concentration in regions near crystals suggested the interaction of crystals and organics, leading to organic control of apatite formation and growth. Ca was present in almost all regions. The majority of Ca localizing in regions other than crystals may be bound to organic substances present in dentine matrix. These substances are thought to both accumulate Ca and act as reservoirs for crystallization of apatite in dentine.     

In situ measurements and transmission electron microscopy of carbon nanotube field-effect transistors

We present the design and operation of a transmission electron microscopy (TEM)-compatible carbon nanotube (CNT) field-effect transistor (FET). The device is configured with microfabricated slits, which allows direct observation of CNTs in a FET using TEM and measurement of electrical transport while inside the TEM. As demonstrations of the device architecture, two examples are presented. The first example is an in situ electrical transport measurement of a bundle of carbon nanotubes. The second example is a study of electron beam radiation effect on CNT bundles using a 200 keV electron beam. In situ electrical transport measurement during the beam irradiation shows a signature of wall- or tube-breakdown. Stepwise current drops were observed when a high intensity electron beam was used to cut individual CNT bundles in a device with multiple bundles.     

Revealing the 1 nm/s extensibility of nanoscale amorphous carbon in a scanning electron microscope

In an ultra‐high vacuum scanning electron microscope, the edged branches of amorphous carbon film (～10 nm thickness) can be continuously extended with an eye‐identifying speed (on the order of ～1 nm/s) under electron beam. Such unusual mobility of amorphous carbon may be associated with deformation promoted by the electric field, which resulted from an inner secondary electron potential difference from the main trunk of carbon film to the tip end of branches under electron beam. This result demonstrates importance of applying electrical effects to modify properties of carbon materials. It may have positive implications to explore some amorphous carbon as electron field emission device. SCANNING 35: 261‐264, 2013. © 2012 Wiley Periodicals, Inc.     

气相沉积制备C/C复合材料微观组织分析

详细分析了等温 CVI法制备的 C/ C复合材料中基体碳的组织形貌 ,主要对光滑层、粗糙层及各向同性组织的特征作了详细描述 ,并且分析了各种工艺条件对组织形成的影响 ,首次指出沉积空间的大小影响热解碳的成核和生长并最终导致形成不同的组织。用偏光显微照片中的热解碳组织与断口 SEM形貌作对比 ,证明在层状热解碳的层间存在内应力。     

Analysis of bonding state in pure and gold-implanted amorphous SiC by a combination of UHVEM and AES

Single crystalline α-SiC films and Au(target metal)/α-SiC(substrate) bilayer films were irradiated with 2-MeV electrons in an ultrahigh-voltage electron microscope (UHVEM) to form, in situ, pure amorphous SiC (a-SiC) and gold-implanted a-SiC. respectively. In the latter case, sample films were set so that the electron beam was incident on the gold layer. Differences in the bonding state between pure a-SiC and gold-implanted a-SiC were studied by Auger valence electron spectroscopy (AES). In pure a-SiC. the carbon valence state was markedly different from that of α-SiC but the silicon valence state was similar to that of α-SiC. In gold-implanted α-SiC. both the carbon and the silicon valence states were different from those of α-SiC. It is suggested that a high density of molecularized carbon clusters are formed in the amorphous matrix in gold-enriched a-SiC.     

Direct preparation of particles from liquid suspension for ESEM or SEM analysis

A simplified method for the preparation of particles from liquid suspensions has been developed. Particles are deposited directly on carbon planchets for rapid analysis by environmental scanning electron microscopy or by conventional scanning electron microscopy after an additional drying step. This is accomplished by filtering the liquid through thin carbon planchets. Three different grades of graphite were investigated for their suitability as the source material for these planchets. The high quality isomolded graphite is recommended for the filtration and direct observation of particles by electron microscopy. This technique is demonstrated for particles in hydraulic fluid and aquatic suspended particulate material from a natural water source.     

A method for the characterization of surface-modified asbestos fibres by electron energy-loss spectroscopy and electron spectroscopic imaging

A method for the characterization of surface-treated asbestos fibres with electron microscopy is presented. Electron spectroscopic imaging (ESI) of organosilane-treated chrysotile asbestos fibres has been carried out. Initially, the region below the carbon edge was inspected in ESI mode for its effectiveness as a background correction. Elemental mapping was performed on standard untreated fibres to take into account non-characteristic signals from extrapolation errors and camera artefacts. The highest resulting pixel value that results from non-characteristic signals was used as a threshold for further background correction in the net images. Samples for electron energy-loss spectroscopy were prepared in two different ways, either by gluing on grids, or by using perforated carbon foils. The results show that the use of a conducting carbon film is necessary for the analysis of such electrically insulating asbestos fibres. Focusing of the electron beam on the individual fibres results in a thermal effect promoting the evaporation of the organosilane reaction products.     

Tribological Thermostability of Carbon Film with Vertically Aligned Graphene Sheets

Tribological thermostability of carbon film with vertically aligned graphene sheets was studied with annealing temperatures up to 1,750 °C. The carbon film was deposited on silicon carbide substrate by electron cyclotron resonance plasma sputtering. Tribological thermostabilities of the carbon film in terms of friction coefficient, wear life, and nanoscratch depth were investigated by Pin-on-Disk tribometer and atomic force microscopy. The evolution of nanostructure of vertically aligned graphene sheets in the carbon film as a function of annealing temperature was examined by Raman spectroscopy and transmission electron microscopy. The results showed that the friction coefficient, wear life, and nanoscratch depth of the carbon film were thermally stable up to 1,250 °C. When the annealing temperature was 1,500 °C, the friction coefficient and the nanoscratch depth increased, the wear life decreased, but still all were of considerable values. These variations were attributed to the initiation of tubular-like structure originated from graphene sheets stacks. After annealing at 1,750 °C, tribological performances degraded catastrophically due to the abundant formation of tubular-like structures and the appearance of a graphitic interlayer between the film and the substrate.