Microtwin defects

Similar to PbSe, the controlled growth of lead telluride, PbTe, on (111) InP was demonstrated from aqueous, acidic solutions of Pb(II) and Cd(II) nitrate salts and tellurite, at room temperature [13]. The poor epitaxy observed, due to the presence of polycrystalline material, was attributed to the existence of a large lattice mismatch between PbTe and InP (9%) compared to the PbSe/InP system (4.4%). The characterization techniques revealed the absence of planar defects in the PbTe structure, like stacking faults or microtwins, in contrast to II-VI chalcogenides like CdSe. This was related to electronic and structural anomalies. 

The investigation by Fitz Gerald (1980) of microtwins in plagioclase feldspars is probably the most detailed yet undertaken of this type of defect in important rock-forming minerals and provides an excellent example of the theoretical and experimental procedures involved in characterizing these defects from their TEM contrast. 

Crystals deformed at a constant strain-rate (e = 10 s ) with a confining pressure of 300 MPa and 400 C in an orientation expected to activate the (100) [010] slip system, developed numerous microtwins in (100) and some dislocations that were not fully characterized. However, interesting dislocations and associated faults were observed in specimens scratched on a (110) surface. Figure 9.32 is typical of the dislocation microstructures observed in these specimens and shows segments of dislocation loops bounding planar defects on (100). 

Figure 7.7 (a) is the (100) interface between the basal single crystal diamond and the CVD diamond layer. There exist many defects of 5-20 nm in diameter along the interface. Also, there were many stacking faults and microtwins at the iTl corner of the diamond specimen. Similarly, stacking faults and microtwins were present on the iTO corner, and dislocations were dominant in the near surface region. 

The mechanism of this transformation has been elucidated by Bursill, Netherway, and Grey. They have found that in the progression from 121 and 132 CS planes to 020 CS planes, wave-like CS boundaries form. They are often very well ordered and show a remarkable sinusoidal variation illustrated in Fig. 2. The wave vectors found are k(lOI), k(lOO), and k(OOI), and the wavelengths are large, of the order of 10—50 nm. Possible reaction paths which allow for the reorientation can be by way of a microtwinning of the 121 rutile CS structure, a type of defect which is commonly observed in high-temperature preparations of these oxides. The nature... 

B-TEM sanple corresponding to the above specimen. From the B-ThM saitples, it was possible to conduct detailed TEM analysis which gave the follcwing information on the above defects. Dislocation loops at depth level I were dominantly a/3 <111> type and extrinsic (extra layers) in nature. The tips of the hair-pin dislocations were of the same character as at I, however, the arms of the hair-pins lay along all six <110> directions. The defects in layer III were found to be stacking fault bundles and microtwins by atomic resolution transmission electron microscopy (17). 

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