Transmission electron microscopy dispersion techniques

Dispersious of IF-WS2 can also be smdied by the wet scaiming transmission electron microscopy (STEM) technique, which allows the observatiou of nano-objects dispersed in a... 

Transmission electron microscopy is one of the techniques most often used for the characterization of catalysts. In general, detection of supported particles is possible, provided that there is sufficient contrast between particles and support - a limitation that may impede applications of TEM on well-dispersed supported oxides. The determination of particle sizes or of distributions therein is now a routine matter, although it rests on the assumption that the size of the imaged particle is truly proportional to the size of the actual particle and that the detection probability is the same for all particles, independent of their dimensions. 

Transmission electron microscopy (TEM) can provide valuable information on particle size, shape, and structure, as well as on the presence of different types of colloidal structures within the dispersion. As a complication, however, all electron microscopic techniques applicable for solid lipid nanoparticles require more or less sophisticated specimen preparation procedures that may lead to artifacts. Considerable experience is often necessary to distinguish these artifacts from real structures and to decide whether the structures observed are representative of the sample. Moreover, most TEM techniques can give only a two-dimensional projection of the three-dimensional objects under investigation. Because it may be difficult to conclude the shape of the original object from electron micrographs, additional information derived from complementary characterization methods is often very helpful for the interpretation of electron microscopic data. 

Because of the instrumental requirements, these are usually not routine monitoring techniques. However, unlike other methods, they give detailed information on particle shapes. In addition, chemical composition information can be obtained using transmission electron microscopy (TEM) or scanning electron microscopy (SEM) combined with energy-dispersive spectrometry (EDS). The electron beam causes the sample to emit fluorescent X-rays that have energies characteristic of the elements in the sample. Thus a map showing the distribution of elements in the sample can be produced as the electron beam scans the sample. 

Although a number of secondary minerals have been predicted to form in weathered CCB materials, few have been positively identified by physical characterization methods. Secondary phases in CCB materials may be difficult or impossible to characterize due to their low abundance and small particle size. Conventional mineral identification methods such as X-ray diffraction (XRD) analysis fail to identify secondary phases that are less than 1-5% by weight of the CCB or are X-ray amorphous. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM), coupled with energy dispersive spectroscopy (EDS), can often identify phases not seen by XRD. Additional analytical methods used to characterize trace secondary phases include infrared (IR) spectroscopy, electron microprobe (EMP) analysis, differential thermal analysis (DTA), and various synchrotron radiation techniques (e.g., micro-XRD, X-ray absorption near-eidge spectroscopy [XANES], X-ray absorption fine-structure [XAFSJ). 

Techniques of transmission electron microscopy have proved valuable in many areas of solid state science. Use of electron diffraction permits identification of crystal types, determination of unit cell sizes and characterization of crystal defects in the phases. Measurement of Energy Dispersive X-ray (EDS) line intensity allows calculation of the elemental composition of the phases. It is difficult to overestimate the value of such applications to metallic alloys, ceramic materials and electron-device alloys (T-4V Applications to coal and other fuels are far fewer, but the studies also show promise, both in characterization of mineral phases and in determination of organic constituents (5-9. This paper reports measurements on a particular feature of coal, the spatial variation of the organic sulfur concentration. 

Samples of catalysts B and C were investigated using Transmission Electron Microscopy coupled with Energy Dispersive X-ray Analysis (TEM/EDX). This technique makes it possible to gather elemental data from discreet areas of the catalyst and allows comparison between the nickel areas and the support. The catalyst samples examined had been exposed to the molten carbonate atmosphere for 0, 50,100, 1000 and 2500 hours. 

Despite the results presented above, near-field microscopy has not been extensively used to characterize polymer/nanotube composites However, it can be noticed that AFM is a useful technique to locally probe the mechanical properties of the composites (at the polymer-nanotube interface for example). One possible reason for the small amount of studies by AFM and STM could be that observing the surface only does not permit to obtain much information on the nanotube dispersion state. For that kind of characterization, transmission electron microscopy is a key technique owing to the small nanotube diameter. 

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