Lattices electron microscopy

A progressive etching technique (39,40), combined with x-ray diffraction analysis, revealed the presence of a number of a polytypes within a single crystal of sihcon carbide. Work using lattice imaging techniques via transmission electron microscopy has shown that a-siUcon carbide formed by transformation from the P-phase (cubic) can consist of a number of the a polytypes in a syntactic array (41). 

To ensure quality control material suppliers and developers routinely measure such complex properties as molecular weight and its distribution, crystallinity and crystalline lattice geometry, and detailed fracture characteristics (Chapter 6). They use complex, specialized tests such as gel permeation chromatography (2, 3), wide- and narrow-angle X-ray diffraction, scanning electron microscopy, and high-temperature pressurized solvent reaction tests to develop new polymers and plastics applications. 

Regnlar arrays of platinnm were achieved by chemical reduction of a platinnm salt that had been deposited onto the S-layer of Sporosarcina ureae [132]. This S-layer exhibits sqnare lattice symmetry with a lattice constant of 13.2 nm. Transmission electron microscopy revealed the formation of well-separated metal clusters with an average diameter of 1.9 nm. Seven clnster sites per nnit cell were observed. UV-VIS spectrometry was nsed to study the growth kinetics of the clnsters. 

Peculiar DNA architecture was demonstrated in 25% aqueous ethanol when DNA was complexed with series of cationic detergents in the presence of poly(glutamic acid) [124]. Electron microscopy and x-ray scattering demonstrated that DNA can pack cetyltrimethylammonium bromide molecules into rodlike micelles, which form a hexagonal lattice. Interestingly, circular dichroism spectroscopy revealed that in these complexes DNA adopts left-handed conformation. 

High Resolution Transmission Electron Microscopy (HRTEM, Philips CM20, 200 kV) was applied to get structural and nanotextural information on the fibers, by imaging the profile of the aromatic carbon layers in the 002-lattice fringe mode. A carbon fiber coated with pyrolytic carbon was incorporated in epoxy resin and a transverse section obtained by ultramicrotomy was deposited on a holey carbon film. An in-house made image analysis procedure was used to get quantitative data on the composite. 

The mean sizes of windows, dw, and contacting cross sections, Dpc can be measured during analysis of the electron microscopy images as the relation of the first statistical moment to the zero one the sizes of dw can also be measured by adsorption methods (see Section 9.3). The direct interrelation between dw and, for example, Z)pc, is determined in view of a used model (e.g., in the framework of a model of isotropic deforming lattice of particles). Besides, also possible are correlations type of dwi dCi that relate the possible size of a cavity dCj to corresponding sizes of windows dWi from the cavity to the neighboring cavities. 

Some examples of direct measurement of the crystal distortion during the reaction by optical and electron microscopy, IR absorption, and x-ray diffraction have been reported (see references in Ref. 311). The observed (anisotropic) changes in lattice parameters have been used for calculating the kinetic parameters of the transformations. For some reactions, it was possible to follow by x-ray diffraction the change in lattice parameters and also in atomic coordinates, so the relaxation could be observed at atomic level. 

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