Diffraction patterns electron

The otiier type of noncrystalline solid was discovered in the 1980s in certain rapidly cooled alloy systems. D Shechtman and coworkers [15] observed electron diffraction patterns with sharp spots with fivefold rotational synnnetry, a syimnetry that had been, until that time, assumed to be impossible. It is easy to show that it is impossible to fill two- or tliree-dimensional space with identical objects that have rotational symmetries of orders other than two, tliree, four or six, and it had been assumed that the long-range periodicity necessary to produce a diffraction pattern with sharp spots could only exist in materials made by the stacking of identical unit cells. The materials that produced these diffraction patterns, but clearly could not be crystals, became known as quasicrystals. 

Figure Bl.8.6. An electron diffraction pattern looking down the fivefold synnnetry axis of a quasicrystal. Because Friedel s law introduces a centre of synnnetry, the synnnetry of the pattern is tenfold. (Courtesy of L Bendersky.)...

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].

As suggested by electron diffraction patterns, it, and Raman spectra. 

Treatment of the algal cellulose (mixture of la—IP) from Valonia in ethylenediamine to give Cellulose IIIj simultaneously induced sub fibrillation in the initial microfihril (75). Thus crystallites 20 nm wide were spHt into subunits only 3—5 nm wide, even though the length was retained. Conversion of this IIIj back to I gave a material with an electron diffraction pattern and nmr spectmm similar to that of cotton Cellulose ip. 

TEM offers two methods of specimen observation, diffraction mode and image mode. In diffraction mode, an electron diffraction pattern is obtained on the fluorescent screen, originating from the sample area illuminated by the electron beam. The diffraction pattern is entirely equivalent to an X-ray diffraction pattern a single crystal will produce a spot pattern on the screen, a polycrystal will produce a powder or ring pattern (assuming the illuminated area includes a sufficient quantity of crystallites), and a glassy or amorphous material will produce a series of diffuse halos. 

Films produced in oxalic acid contain smaller amounts (about 3%) of the electrolyte and only traces of chromium are found in chromic acid films. Sealed films show the electron diffraction pattern of the monohydrate, bohmite. 

Figure 9-7. Elastic electron-diffraction pattern of a highly textured hcxaphenyl film. The Miller indices arc assigned using the intcrplauar spacings calculated in Kef. 11371. Inset Intensity of the f020) peak as a function of the angle between momentum transfer and the Teflon rubbing direction (see text) - taken from Ref. 138. ...

Figure 16-17. Left transmission electron micrograph of small single crystals of Ooct-OPV5 scale bar 5 pnt. The arrows indicate the 6-axis direction. Right electron diffraction pattern of the same single crystals. The arrow indicates the 613 relteclion spot (crysial dimensions 5x40 pm2 Philips STiiM CM 12 operated at 120 kV. lnslilul Charles Sudron, Strasbourg).

Since the first structure determination by Wadsley [56] in 1952 there has been confusion about the correct cell dimensions and symmetry of natural as well of synthetic lithiophorite. Wadsley determined a monoclinic cell (for details see Table 3) with a disordered distribution of the lithium and aluminium atoms at their respective sites. Giovanoli et al. [75] found, in a sample of synthetic lithiophorite, that the unique monoclinic b-axis of Wadsley s cell setting has to tripled for correct indexing of the electron diffraction patterns. Additionally, they concluded that the lithium and aluminum atoms occupy different sites and show an ordered arrangement within the layers. Thus, the resulting formula given by Giovanelli et al. 

H. Ohtani, C.-T. Kao, M.A.V. Hove, and G. Somorjai, A tabulation and classification of the stmctures of clean solid surfaces and of adsorbed atomic and molecular monolayes as determined from low energy electron diffraction patterns, Progress in Surface Science 23(2,3), 155-316 (1986) and reference therein. 

Fig. 11—Observation of subsurface damage, (a) Cross section HTEM images of surface undergoing collision for ten minutes, (b) Electron diffraction pattern from an amorphous area.

Fig.l. Scanning electron micrography (a) and electron diffraction pattern (b) of Sn02 film on PET substrate prepared by ECR-MOCVD. 

Combined analyses by XRD and TEM showed that the aurichalcite mineral was sufficiently similar to the synthetic aurichalcite to be used as a model compound, to study the microstructural changes occurring during the catalyst preparation procedures. Calcination of the mineral and synthetic samples led to highly preferred orientations of ZnO. ZnO electron diffraction patterns with [lOlO] and [3031] zone... 

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.

FIG. 20-24 High -resolution TEM image of Si nanowires produced at 500 C and 24.1 MPa in supercritical hexane from gold seed crystals. Inset Electron diffraction pattern indexed for the <111> zone axis of Si indicates <110> growth direction. [Reprinted with permission from Lu et al. Nano Lett., 3(1), 93-99 (2003). Copyright 2003 American Chemical Society. ]... 

Bird, D.M. and Saunders, M. (1992) Inversion of convergent-beam electron diffraction patterns, Acta Cryst. A, 48, 555-562. 

Although conventional electron-probe microanalysis appears to be unsuitable for analysis of the exposed surface layer of atoms in an alloy catalyst, recent developments have shown that X-ray emission analysis can still be used for this purpose (89, 90). By bombarding the surface with high energy electrons at grazing incidence, characteristic Ka radiation from monolayer quantities of both carbon and oxygen on an iron surface was observed. Simultaneously, information about the structure of the surface layer was obtained from the electron diffraction pattern. 

Fig. 5.16 (A) Bright-field TEM image and (B) element mapping carbon (brighter contrast corresponds to higher concentration of carbon) of ZnO synthesized in aqueous solution at 37 °C in pH 8 buffer for 4 h in the presence of 1.2 mgmL-1 of gelatin. The inset shows the electron diffraction pattern taken parallel to the platelet normal. (Reprinted with permission from [77], Copyright (2006) American Chemical Society).

Fig. 29. Icosahedral phase in electrodeposited Mn-Al alloys (a) bright field image (b) electron diffraction pattern showing 5-fold symmetry. Reproduced from Grushko et al. [126] by permission of Elsevier.

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