Electron microscopy phase identification

Electron diffraction performed with a parallel incident beam, i.e. Selected-Area Electron Diffraction is used to obtain good electron micrographs. The two-beam condition allows the observation of defects. SAED is also used in High-Resolution Electron Microscopy (HREM) to set a crystal to a zone axis so that the atomic columns are vertical in the microscope. SAED is very useful for the identification of phases and the... 

The chemical analyses were done by a combination of wet chemical, atomic absorption (Hitachi Z-800) and ICP (JY-38 VHR) methods. The crystalline phase identification was carried out by XRD (Philips PW-1710 Cu K scanning electron microscopy (Cambridge, Stereoscan 400), thermal analysis (Netsch, Model STA 490), ESR... 

The identification of the superconducting phase YBagCug-O7 g provides an example in which knowledge of thermodynamics, i.e. the Gibbs phase rule and the theory of equilibrium phase diagrams coupled with X-ray diffraction techniques led to success. Further, the use of databases that can now be easily accessed and searched on-line provided leads to a preliminary structure determination. The procedures outlined here are among the basic approaches used in solid state chemistry research, but by no means are they the only ones. Clearly the results from other analytical techniques such as electron microscopy and diffraction, thermal... 

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). 

Analysts. Analytical investigations may be undertaken ro identify the presence of an ABS polymer, characterize the polymer, or identify nonpolymenc ingredients. Fourier transfrom infrared (fhr) spectroscopy is the method of choice to identify the presence of an ABS polymer and determine the acrylonitrile-butadiene-styrene ratio of the composite polymer. Confirmation of the presence of rubber domains is achieved by electron microscopy. Comparison with available physical properly data serves to increase confidence in the identification or indicate the presence of unexpected structural features. Phase-seperalion techniques can be used to provide detailed compositional analyses. 

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. 

In electron microscopy as in any field of optics the overall contrast is due to differential absorption of photons or particles (amplitude contrast) or diffraction phenomena (phase contrast). The method provides identification of phases and structural information on crystals, direct images of surfaces and elemental composition and distribution (see Section H below). Routine applications, however, may be hampered by complexities of image interpretation and by constraints on the type and preparation of specimens and on the environment within the microscope. 

Because Raman spectmm stems from the bonds vibrations, it provides an intrinsic nano-probing and offers a bottom-up approach of nanostmctured materials that comes as a good complement to other techniques such as transmission electron microscopy. X-ray diffraction, and infrared, and Mossbauer spectroscopy. Since almost no sample preparation is needed, Raman technique [12, 13] is commonly used to investigate nanomaterials. This could provide the phase identification and, possibly, size estimation [14]. 

To reveal dendritic and interdendritic ferrite, carbides, phosphides and intermetallic phases, appropriate etchants for the steels in question were used [15]. In some cases the visual observations were supported by identification of the phases using microprobe analysis. X-ray diffraction and transmission electron microscopy. 

The further progress can be related to the development of alloys of Ti-B-Si-X system. Preliminary study of these alloys has shown an availability of some additional early unknown phase. In addition to typical lamellar borides visible in structure of the alloys is extremely disperse phase having boron and silicon in its composition. Electron microscopy image of this phase is shown in Figure 4. Structural identification of this silicoboride is not completed yet, however it is already possible to note appreciable increase of stiffness of the alloys at simultaneous presence of boron and silicon (Table ) ... 

Lipid samples that exhibit well-ordered phases are optimally suited for TRXRD measurements. Lack of order suggests that other techniques such as electron or scanning tunneling microscopy may prove more useful for phase identification and characterization. Alternatively, the sample may be rendered more ordered by partial desiccation and/or preferential orientation [33]. 

It is clear that electron microscopy is not the most favourable technique for structure determination of new (superconducting) phases X-ray diffraction and particularly neutron diffraction do a far better job in the ab initio structure determination. Electron microscopy and electron diffraction are extremely powerful however to determine the local structure i.e. to detect deviations from the average structure, as determined by X-rays or neutrons. In this way several new phases have been first identified by electron microscopy some of them have been later made into bulk superconductors. In other cases the identification of isolated defects in an existing material have inspired chemists to produce new superconducting materials this was, for example, the case for the occurrence of double HgO layers in a one-layer Hg-1223 superconductor. 

Microstructure was studied by electron microscopy. Figure 1 shows typical images of C-3 sample. A worm-like porous structure is observed (Fig. la) and HREM of the nanometric crystals allowed the identification of the cerianite phase. 

XRD and TEM investigations at different length scales can deliver information on crystal stmcture, symmetry, periodic lattice spacings, phase purity, arrangement of pores, and other types of nanoscopic organization. These two techniques are thus essential for proper identification and characterization of ordered microporous and mesoporous materials. In addition, scanning electron microscopy (SEM) is most often used to examine the morphology, size, and size distribution of nanoporous particles or crystals. 

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