Electron diffraction plate

Electron diffraction investigations showed that epitaxy did indeed exist when one metal was electrodeposited on another, but that it persisted for only tens or hundreds of atomic layers beyond the interface. Thereafter the atomic structure (or lattice) of the deposit altered to one characteristic of the plating conditions. Epitaxy ceased before an electrodeposit is thick enough to see with an optic microscope, and at thicknesses well below those at which pseudomorphism is observed. 

The best formed plate textures are found in crystals with a layer lattice, and generally in all crystals having the form of thin plates. Diffraction pattern (Fig.7) indicates a texture of this type, and was obtained from crystals in the shape of thin hexagonal plates. The specific role of the oblique-texture type electron diffraction patterns have in the study of clay minerals having layer structures (B.B.Zviagin, 1964, 1967). 

Thus, mosaic single crystal, polycristal, texture electron diffraction patterns provide valuable material for complete structural investigations. A complete determination of the unit cell of any crystal can be made from electron diffraction patterns, particularly of plate textures. 

The electron diffraction texture pattern was obtained using a tilt angle of -60° and recorded on image plates scanned with a resolution of 17.5 pm/pixel (at 250 kV). 

If a photographic plate is used for registration, first the optical density distribution of the electron diffraction pattern is determined, followed by... 

Figure 20 (a) SEM of T 2.xCdxCu06+f plates, (b) HREM with the corresponding electron diffraction pattern inset. 

FIG. 9.15 Path of a diffracted electron beam in low-energy electron diffraction (LEED), and indexing of points in reciprocal space, (a) interaction of a diffracted beam with a photographic plate for small angles of incidence and (b) illustration of the indexing of points in reciprocal space relative to the primary beam, labeled 00. 

An alternative hypothesis, developed from studies of the synthesis of Linde A zeolite carried out by Kerr (5) and Ciric (6), pointed to growth occurring from solution. The gel was believed to be at least partially dissolved in solution, forming active aluminosilicate species as well as silicate and aluminate ions. These species linked to form the basic building blocks of the zeolite structure and returned to the solid phase. Aiello et al. (7) followed the synthesis from a highly alkaline clear aluminosilicate solution by electron microscopy, electron diffraction, and x-ray diffraction. These authors observed the formation of thin plates (lamellae) of amorphous aluminosilicates prior to actual crystal formation. 

Three diffraction patterns and one micrograph are thus recorded on the same plate or film. In some cases, we tried to evaluate the degradation of the crystalline patterns during one exposure this is analogous to an idea of a previous work of Dobb (9) who has studied the kinetics of the disappearance of the main interferences in the electron diffraction pattern of cellulose under constant irradiation rate by a method of "time-lapse series". Our aim was to try to determine a "true" crystallinity by an extrapolation to zero dose. In such a mode, the "crystalline" pattern of the same selected area is recorded three times (on the same emulsion) the irradiation rate corresponding to an exposure being set only during the exposure time. 

The electrolysis of the studied systems was carried out in the same cell as voltammetry measurements under the mode of either constant current or voltage. In the constant current mode, the applied current density was in the range of 0.01 0.2 A/ sm2 with reference to the surface area of the cathode before starting the electrolysis. Semi-immersed glassy carbon plate electrodes (cathode area - 5 sm2, anode area - 10 sm2) were used while electrolysis experiments. A powder product was either settled down onto the crucible bottom or assembled on the cathode in the view of electrolytic pear . The deposit was separated from salts by successive leaching with hot water. Thereafter, the precipitate was washed with distilled water by decantation method several times and dried to a constant mass at 100 - 150 °C. The electrolysis products were analyzed by chemical and X-ray phase analyses, methods of electron diffraction and electronic microscopy (transmission and scanning). 

FIGURE 5 Convergent beam electron diffraction patterns obtained for the same sample thickness (130 nm) in the transparent (a) and yellow (b) parts of the plate crystal. 

This interpretation is not universally accepted. We find it convincing. We see no more feasible way to reconcile the observed nonstoichiometry, the x-ray and electron diffraction spots which appear to indicate non-whole-numbers of atoms aligned to give a non-whole-number plate thickness, and the impossibility... 

Figure 5. TEM images and selected-area electron diffraction (SAED) patterns from the c axis direction (perpendicular to the basis plane of the plate-like crystal particle) for NMO-6 (A, B), NMO-5 (C, D), and NMO-3 (E, F), respectively.

To confirm the structure of NMO, TEM observation and selected-area electron diffraction (SAED) studies were carried out on NMO samples. NMO-6 has a plate-like particle morphology (Figure 5(A)). When the electron beam is perpendicular to the basis plane, the SAED pattern contains two incommensurate hexagonal networks of (h k 0)... 

In addition to those minerals associated with the granular constituent, there are numerous submicron-sized minerals that are intimately mixed with other coal macerals. A typical example can be seen in Figure 11, which is a TEM micrograph of vitrinite, where the circular aperture identifies the region from which the electron diffraction pattern, shown in the inset, was obtained. The mineral, which was identified as kaolinite, appears to have been deposited as plates parallel with the coal bedding, based upon an analysis of the diffraction pattern. Also present in these coals is the clay mineral illite, which can be distinguished from kaolinite by both EDX and SAD analyses, lllites contain potassium (K)... 

Electron diffraction patterns recorded from isolated upper elements showed that these complex units were well-defined single crystals. The c axis was oriented parallel to the long axis of the upper element and the hammerhead extension at 90° to the stem corresponded to the [100] direction. The alignments of the crystallographic axes were coincident with those determined on the base plate, indicating that the whole segment was a continuous single crystal. 

With electron diffraction, the sequential nature of data-point acquisition in STEM also results in an unfavourable comparison with CTEM. Since S/N and the sharpness of reflections are both of prime importance in the determination of the clarity of a diffraction pattern, it must again be noted that the collection angle in STEM affects these two parameters inversely, and a compromise must inevitably be struck. Furthermore, the dynamic range of the electronically detected STEM signal, once amplified, may not match that of the photographic plate in STEM. It seems unlikely, therefore, that STEM will ever replace TEM for those microscopists with purely structural interests. STEM does, however, allow the user full scope to display diffraction effects, in an often unusual manner, and to vary freely the method of formation of diffraction patterns. 

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