Selected area electron diffraction patterns

Figure C2.17.7. Selected area electron diffraction pattern from TiC nanocrystals. Electron diffraction from fields of nanocrystals is used to detennine tire crystal stmcture of an ensemble of nanocrystals [119]. In tliis case, tliis infonnation was used to evaluate the phase of titanium carbide nanocrystals [217].

Figure 5a. Mineral aurichalcite calcined at 350°C for 4 hours. Selected area electron diffraction pattern showing ZnO orientations with zone axes of [lOTo] and [3031]. See text for other ZnO orientations. An aurichalcite pattern close to a [101] zone axis is also present.

Bismuth Molybdates. Bismuth molybdates are used as selective oxidation catalysts. Several phases containing Bi and/or Mo may be mixed together to obtain desired catalytic properties. While selected area electron diffraction patterns can identify individual crystalline particles, diffraction techniques usually require considerable time for developing film and analyzing patterns. X-ray emission spectroscopy in the AEM can identify individual phases containing two detectable elements within a few minutes while the operator is at the microscope. 

Structure refinement based on kinematical scattering was already applied by the Russian scientist 60 years ago. Weirich et al. (1996) first solved the structure of an unknown TinSe4by HREM combined with crystallographic image processing. Then they used intensities extracted from selected area electron diffraction patterns of a very thin crystal and refined the structure to a precision of 0.02 A for all the atoms. Wagner and Terasaki et al. (1999) determined the 3D structure of a new zeolite from selected area electron diffraction, based on kinematical approach. 

Figure 15. Crystal structure of a-Tl2Se solved in projeetion via direct methods using quantified intensities from the selected area electron diffraction pattern shown in (a) [film data]. The potential map (E-map) in (b) was used to eonstruet an initial structural model which was later improved by kinematical least-squares (LS) refinement (c). Note that the potential of the selenium atoms in (c) appear after LS-refinement somewhat stronger than the surrounding titanium atoms (see the structural model in figure lOd). The average effective thiekness of the investigated thiekness of the crystal is about 230 A [22].

Fig. 2. Selected area electron diffraction patterns of the murataite varieties with (A) eight-, (B) seven-, (C) five-, and (D) threefold elementary fluorite unit cells.

Fig. 6.4 CdS deposits obtained on a Mo mesh after electrolyses at-0.65 V (vs. SCE) for 3 h in a 0.05 M CdCl2 + 0.1 M TAA aqueous mixed solution (initial pH = 2.0) maintained at 70°C TEM photographs observing the hexagonal particle from its side (a), high magnification image of the same particle (b), and complementary selected area electron diffraction pattern (c). (From K. Yamaguchi et al., J. Phys. Chem. B, 102, 9682 (1998))...

Professor Tadakoro s recent book(l ) illustrates the considerable advantages and benefits to be gained by coupling infra-red spectroscopy with fibre x-ray diffraction. The increasing availability of Fourier transform infra-red spectrometers allows the same thick samples, suitable for x-ray work, to be used in the spectrometer thus ensuring that both sets of information emanate from the same structure. The delightful selected area electron diffraction patterns obtained from polysaccharides by Dr. Chanzy (2), which exhibit such remarkable resolution and definition, indicate the importance and value of the modern application of electron micro-... 

SAED selected area electron diffraction (patterns)... 

Figure 8. High-resolution electron micrographs showing cross-section of FePt/Pt/MgO sample (a) [001] projection. Note surface flatness (b) [110] projection showing FePt/Pt/MgO interface region. Insets show corresponding selected-area electron diffraction patterns [13].

Figure 4. The HREM image and the selected area electron diffraction patterns of a typical example42 of autoepitaxy, where one substoichiometric perovskite CaMn0275 grows in coherent contact with its less fully reduced parent, CaMnO,s.

Fig. 2.3 (a) Star-shape PbSe nanocrystals and tb e) radially branched nanowires, (d) TEM image of the (100) view of the branched nanowire and the corresponding selected area electron diffraction pattern, (e) TEM image of the (110) view of the branched nanowire and the corresponding selected area electron difl raction pattern. Reprinted with permission from K.-S. Cho, D. V, Talapin, W Gaschler and C. B. Murray, J. Am. Chem. Soc., 2005,127, 7140. 2005 American Chemical Society. 

Selected area electron diffraction patterns of ZSM-5 from circular region of diameter 3,500ft... 

FIGURE 11.11 (a) TEM image, (b) selective-area electron diffraction pattern, and (c) EDS spectra for synthetic Al-substituted goethite. 

Fig. 5.6 shows the XRD powder pattern of a 23-year-old paste of (f-CjS. Patterns of fully reacted CjS pastes are similar, except that the CH peaks are relatively more intense. The only effects definitely attributable to C-S-H are the diffuse peak at 0.27-0.31 nm and the somewhat sharper one at 0.182 nm. Attempts to obtain selected area electron diffraction patterns from the C-S- H of calcium silicate or cement pastes have usually failed, but, occasionally,. particles present in ground and redispersed samples have yielded poorly defined patterns (G41,C25) (Section 5.4.6). A later study by this method (M48) has been severely, and in the writer s opinion justifiably, criticized (G45).. 1... 

Several other lines of evidence were cited in support of this hypothesis. The TG curve of C-S-H gel (Fig. 5.3), expressed in terms of H20/Ca ratio, was shown to be intermediate between those of 1.4-nm tobermorite and jennite. The densities and H20/Ca ratios of C-S-H gel are similar to those of 1.4-nm tobermorite, jennite and structurally related minerals of comparable H20/Ca ratios (Table 5.5). The XRD evidence has already been noted of the few selected area electron diffraction patterns that have been obtained from particles of C-S H gel, some were shown to resemble ones of tobermorite minerals, and others that of C-S-H(II). Finally, the occurrence of two types of structure, with differing compositions, could explain the local variability in composition observed in electron optical analyses. 

Specimens of wollastonite from a number of localities have been examined by TEM by Jefferson and Thomas (1975), Wenk et al. (1976), Hutchison and McLaren (1976, 1977), and others. A typical selected-area electron diffraction pattern from a foil oriented with [001] parallel to the electron beam is shown in Figure 8.8. It can be seen that the diffraction maxima MO with k = 2n + (/i = 0,1,2,...) are streaked parallel to a. DF images with g = (6,2/i- -l,0) reveal a high density of planar defects parallel to (100). These are usually randomly distributed, as in Figure 8.9(a). However, as in Figure 8.9(b), these defects are completely out-ofcontrast when k = 2n. This behavior is consistent with the planar defects being stacking faults with R = 4[010], because... 

Fig. 12. a Wide angle selected area electron diffraction pattern from the white region of the air craze in PS shown in b, From Ref courtesy of Dr. B. D. Lauterwasser... 

Figure 1. Transmission electron microscopy (TEM) images and selected area electron diffraction pattern (SAED) of preformed gold nanopaiticles before and after ultrasonic treatment A), C) and E) TEM images of gold nanopaiticles bef e soiication, after 20 rain and 45 min of ultrasonic treatment, respectively. B), D) and F) SAED patterns (camera length 360 nm) of gold nanopaiticles before ultrasonic treatment and after sonication for 20 min and 45 min respectively.

Fig. 10.21. ATEM image of Ge nanowires and a selected-area electron-diffraction pattern (inset) [35].

Fig. 4. Crystallized ZnTTBPc films after methanol annealing a) a bright field TEM image and b) a selected area electron diffraction pattern.

A transmission electron microscope (PHILIPS EM 420) equipped with an X-ray spectral analyzer (EDAX) was used to obtain the selected area electron diffraction pattern and for microanalysis of the catalyst. Speciments for microanalysis were prepared by dispersing the powders in ethanol, placing a drop of this suspension on a thin carbon support net and allowing the solvent evaporate. 

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