Transmission electron microscopy lattice imaging techniques

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). 

The X-ray images of extended lattice imperfections within the crystal arise fi om variations in beam intensity caused by local distortions of the lattice. Dislocation densities of up to 10 mm can be resolved in transmission studies or ten times this by the reflection technique. This resolution is lower than that obtainable by transmission electron microscopy, but the sample used may be thicker and does not have to be examined under high vacuum. X-ray beams also produce less radiation damage in the sample. When decomposition proceeds beyond a > 0.01, distortion of the lattice is such that the X-ray image loses resolution and the exposures required become even longer. Reflection data obtained at several different diffraction angles may be required to characterize the imperfections present. 

Transmission electron microscopy using high resolution lattice imaging techniques allows polytype analysis within single grains in the microstructure of dense SiC bodies [27],... 

Controlled synthesis of platinum particles was made possible in the late sixties and seventies by significant advances in electron microscopy. Lazio L. Ban of the Cities Service Laboratories in nearby Rightstown was able to obtain lattice imaging with a resolution of 0.05 A while Joseph Wall at the Brookhaven National Laboratory constructed a scanning transmission electron microscope with a resolution of 2.5 A permitting visualization of individual platinum atoms. These techniques together with the use of the ultracentrifuge of Barbara... 

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