Selected Area Diffraction SAD

Selected area diffraction (SAD) combined with microscopy is an important supplementary tool to X-ray diffraction in crystal structure analysis. SAD has the additional advantage of giving the correlation between morphology and crystal structure whenever single crystals are too small for single-crystal X-ray analysis. 

Transmission electron microscopy ( ) analysis reveals that these materials crystallize as hexagonal planar particles with marked anisotropic shape,8,37 as shown in Figure 6. When appropriate preparation methods are used, plate-like crystals are obtained with small thickness of about 20-30 nm and an aspect ratio D/h=5-10. Selected area diffraction (SAD) patterns of incident beams perpendicular and parallel to the large hexagonal facet show that they correspond to the crystallographic planes perpendicular to the c axis. The anisotropic shape of the... 

Looking at the microstructure for samples above and below the maximum in coercivity, Fig. 21 shows that the FePt islands become interconnected above the coercivity maximum while below the maximum the islands are well separated. In the insets of Fig. 21(a) and (b) are the selected area diffraction (SAD) patterns for the samples. These indicate a single crystal FCT pattern with (001) orientation. Adjacent to the FePt diffraction spots are the (001) MgO single crystal spots indicating a slight mismatch in the lattice spacing of the two materials and a good epitaxial relationship between the two. 

Figure 1. Test micrograph showing the displacement of the unscattered beam (small dots) in the selected area diffraction (SAD) pattern when it occurs in polar coordinates (Philips EM 300). The tilt has been fixed at the 002 Bragg angle for carbon ( 0.3°) and the azimuth changed by small increments. The 000 spot displaces along a practically perfect circle which corresponds to the 002 Debye Scherrer ring. Such a device allows exploration of any position in the SAD pattern, even when neither sharp nor intense hkl reflections are visible. The SAD pattern of an asphaltene heat-treated at 500°C has been superimposed to the test micrograph. Various positions of a 0.13 A aperture are shown.

Crystallinity, Bulk Crystallinity, Local X-ray diffraction TEM/-selected area diffraction (SAD) Differential scanning calorimetry (DSC)... 

The size and distribution of pores and the size, distribution, and identity of minerals in coal specimens from an eastern Kentucky splint coal and the Illinois No. 6 coal seam were determined by means of transmission electron microscopy (TEM) and analytical electron microscopy (AEM). The observed porosity varies with the macerals such that the finest pores (<2-5 nm) are located in vitrinite, with a broad range of coarser porosity (40-500 nm) associated with the macerals exinite and inertinite. Elemental analyses, for elements of atomic number 11 or greater, in conjunction with selected area diffraction (SAD) experiments served to identify the source of the titanium observed in the granular material as the mineral rutile. Only sulfur could be de-tected in the other coal macerals. Dark-field microscopy is introduced as a means for determining the domain size of the coal macerals. This method should prove useful in the determination of the molecular structure of coal. 

Figure 10. (a) TEM bright-field image, (b) selected area diffraction (SAD) pattern, and (c) convergent beam electron diffraction (CBED) pattern of the optimally reannealed (r, 83 K) Tl-2201 thin film. 

A diffraction pattern is formed on the back-focal plane of the objective lens when an electron beam passes through a crystalline specimen in a TEM. In the diffraction mode, a pattern of selected area diffraction (SAD) can be further enlarged on the screen or recorded by a camera as illustrated in Figure 3.16. Electron diffraction is not only useful to generate images of diffraction contrast, but also for crystal structure analysis, similar to X-ray diffraction methods. SAD in a TEM, however, shows its special characteristics compared with X-ray diffraction, as summarized in Table 3.4. More detailed SAD characteristics are introduced in the following section. 

Note that both the mass-density and the diffraction contrast require only a transmitted beam to pass through the objective aperture. How can you know you have diffraction contrast without checking selected area diffraction (SAD) ... 

This in situ formed TiN layer on GaN is of the form of textured polycrystals with their (111) planes parallel to the GaN (0001) plane [23]. The crystalline nature of the porous TiN is also confirmed by the selective area diffraction (SAD) pattern in our TEM analysis. 

Figure 8.23. Transmission electron micrographs and selected area diffraction (SAD) pattern for Zr02 + 3 mol% Y2O3 (a) in the as-received condiition showing equiaxed grains with average size d = 0.4 to 0.5 /rm (b) near the fracture surface of a specimen tested in water at 22° C and (c) SAD pattern from (b) identifying the new twinned martensite phase near the fracture surface and its orientation relationship with the t-matrix [4].

Ramesh et al. (1987) addressed furthermore the problems associated with the observation of the bcc phase mentioned above. They note that the bcc phase, in all reported cases, was observed by the selected area diffraction (SAD) technique, using argon ion-milled specimens. SAD using a 0.5 j.m aperture has been carried out by Ramesh et al. on argon ion-milled specimens. When the SAD aperture is placed over the matrix only, Ramesh et al. observed a bcc ring pattern with a lattice parameter of 0.29 nm. However, when the SAD aperture was placed over the... 

The preparations were observed by transmission electron microscopy, with a Jeol 2000 FX for selected area diffraction (SAD) and convergent beam (CBED), a Jeol FEG 2010 and a Jeol 4000 EX instrument for high-resolution imaging. 

Raman and Fourier transform infrared (FTIR) are well-known techniques for the chemist and are increasingly important in ceramics Selected-area diffraction (SAD) in the TEM... 

Hacl] Induction melting, annealing, rapid water quenching, chemical analysis, etching (nital), optical microscopy, TEM, selected-area diffraction (SAD), field-emission gun-transmission electron microscopy (FEG-TEM), energy-dispersive X-ray spectroscopy (EDS)... 

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