Selected-area electron diffraction SAED

Asbestos fiber identification can also be achieved through transmission or scanning electron microscopy (tern, sem) techniques which are especially usefiil with very short fibers, or with extremely small samples (see Microscopy). With appropriate peripheral instmmentation, these techniques can yield the elemental composition of the fibers using energy dispersive x-ray fluorescence, or the crystal stmcture from electron diffraction, selected area electron diffraction (saed). 

Linear absorption measurements can therefore give the first indication of possible alloy formation. Nevertheless, in systems containing transition metals (Pd-Ag, Co-Ni,. ..) such a simple technique is no longer effective as interband transitions completely mask the SPR peak, resulting in a structurless absorption, which hinders any unambiguous identification of the alloy. In such cases, one has to rely on structural techniques like TEM (selected-area electron diffraction, SAED and energy-dispersive X-ray spectroscopy, EDS) or EXAFS (extended X-ray absorption fine structure) to establish alloy formation. 

Figure 57.12. The HRTEM selected area electron diffraction (SAED) of the CA53 leached for 45 min at rt showing the presence of the Ni/Al bee phase (A) and the coexistence of both the Ni-Al bee phase with the original Ni2Al3 alloy (B).

The transmission electron microscopy (TEM) and correlated electron diffraction patterns of quenched QAB2-4 alloy is shown in Figure 2. When annealed at 773K, by selected-area electron diffraction (SAED) patterns at transmission electron microscopy appears as a bright continuous ring, indicating an amorphous phase. 

For a long time, Selected-Area Electron Diffraction (SAED) performed with a parallel incident beam and a selected-area aperture was the only experimental method available. During the three last decades, new diffraction techniques based on a convergent electron incident beam (CBED Convergent-Beam Electron Diffraction, LACBED Large-Angle... 

Various electron diffraction techniques are available on modem transmission electron microscopes. Selected-Area Electron Diffraction (SAED) and Microdiffraction are performed with a parallel or nearly parallel incident beam and give spot patterns. Convergent-Beam Electron Diffraction (CBED) and Large-Angle Convergent-Beam Electron Diffraction (LACBED) are performed with a focused and defocused convergent beam... 

HREM), TEM results of aerinite are compared with X-ray and synchrotron powder diffraction data. Six selected area electron diffraction (SAED) patterns and two HREM images from Pb5MoOg single crystals are used to solve their structure. The unit cell parameters of these crystals confirm the known powder diffraction data. 

Fig. 11 a TEM image of single InN whisker with an In metal droplet at the tip of the whisker grown at 500 °C. Selected area electron diffraction (SAED) patterns of InN whiskers grown from N3ln[(CH2)3NMe2]2 taken along b [1120] and c [0001] zone axis... 

The combination of SEM with EDS has also been applied to atmospheric particles (e.g., Posfai et al., 1995 Anderson et al., 1996 McMurry et al., 1996 Ganor et al., 1998). For example, individual sea salt particles were analyzed using TEM combined with EDS as well as selected-area electron diffraction (SAED) by Posfai et al. (1995) and Anderson et al. (1996). The crystal shapes correlated well with the chemical composition determined using EDS and SAED. For example, cubic crystals of NaCl were observed. Sulfate occurred in either rod-shaped crystals, which had significant concentrations of (Mg + K + Ca) compared to Na, or tubular crystals, with much smaller concentrations of these three metals. In the latter case, the EDS showed... 

Transmission electron micrographs (TEM) of submicrometer-size particles show faceted particles, and selected area electron diffraction (SAED) patterns of isolated particles show that they are formed by a small number of crystallites (Fig. 9.2.14a), This result is consistent with the mean size of the crystallites, which can be inferred from the x-ray diffraction lines broadening analysis using a William-son-Hall plot (35) in order to take into account the contribution of microstrains to the line broadening. Over the whole composition range, the mean crystallite size is in the range 40-60 nm for particles with a mean diameter in the range 200-300 nm (Table 9.2.5) (33). 

Fig. 9.2.14 TEM image and selected area electron diffraction (SAED) pattern of (A) a single Co2oNigo particle, and (B) a single Fe25Ni75 particle. (From Ref. 8.)...

FIGURE 11. (a, b) TEM images of the iron nanorods encapsulated inside the carbon nanotubes from aligned nanotube bundles, (c) HREM image of a single-crystal iron nanorod encapsulated inside a carbon nanotube. The inset in (c) represents the selected area electron diffraction (SAED) pattern of a iron nanorod.11239... 

The nanotube shown in Fig. la was examined by normal-incidence selected area electron diffraction (SAED) with the electron beam perpendicular to the junction. The diffraction pattern of one of the arms close to the junction (Fig. 2a), shows a set of arcs corresponding to four (002) maxima. Similar diffraction patterns were obtained from the other two arms next to the junction,... 

Fig. 2. Selected area electron diffraction (SAED) patterns of the Y-junction carbon nanotubes (a) of the arms and (b) of the junction region, (c) and (d) Schematic drawings showing different ways of stacking of the graphene sheets in the Y-junction carbon nanotubes.

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