Fault twinning

The lattice defects are classified as (i) point defects, such as vacancies, interstitial atoms, substitutional impurity atoms, and interstitial impurity atoms, (ii) line defects, such as edge, screw, and mixed dislocations, and (iii) planar defects, such as stacking faults, twin planes, and grain boundaries. 

Planar stacking faults, twins, and grain boundaries ... 

These defects are generally detrimental to electronic, thermal and mechanical properties of diamond films, although in some cases they may be neutral or beneficial. The frequently occurring defects appear to be stacking faults (twinned clusters with many re-entrant surfaces/comers), which are deemed to play a major role in enhancing diamond growth rates.t ... 

The knowledge of chemically deposited films, from a morphological and structural point of view, requires determination of different characteristics roughness at different scales, nature of the crystallographic structure, existence of textures, nature and density of crystallographic defects like dislocations, stacking faults, twins, etc. such characteristics depend on numerous parameters and are the consequence of the nucleation and growth mechanism. 

Second-stage phases have been prepared for NH3 or simple organic molecules. Detailed structural knowledge is lacking. It seems that stacking faults, twinning and... 

Hashimoto H et ai 980 Direot observations of the arrangement of atoms around staoking faults and twins in gols orystals and the movement of atoms aooompanying their formation and disappearanoe Japan. J. Appi. Phys. 19 LI... 

However, it is not yet clear why the ener es of the SISF and the twin boundary increase with increasing A1 concentration. To find a clue to the problem, it would be needed to make out the effects of the short-range ordering of A1 atoms in excess of the stoichiometric composition of the HAl phase on the energies of planar faults and the stmcture of dislocation cores in the Al-rich HAl phase. 

The core structure of the 1/2 [112] dislocation is shown in Fig. 4. This core is spread into two adjacent (111) plames amd the superlattice extrinsic stacking fault (SESF) is formed within the core. Such faults have, indeed, been observed earlier by electron microscopy (Hug, et al. 1986) and the recent HREM observation by Inkson amd Humphreys (1995) can be interpreted as the dissociation shown in Fig. 4. This fault represents a microtwin, two atomic layers wide, amd it may serve as a nucleus for twinning. Application of the corresponding external shear stress, indeed, led at high enough stresses to the growth of the twin in the [111] direction. 

While the c/a ratio deviates only by about 2% from one, it is not ideal and this has significant consequences for the pseudotwin and 120° rotational fault. It results in a misfit at these interface which is compensated by a network of misfit dislocations (Kad and H2izzledine 1992). In contrast, the non-ideal c/a ratio does not invoke any misfit at ordered twins. However, the misfit dislocations present at interfaces are about fifty lattice spacings apart and thus there are large areas between them where the matching of the lamellae is coherent. The structures and... 

It is well known that in rutile-like structures the planes [Oil] and [0 3 1] are twinning planes. Hence, Chabre and Pannetier concluded that twinning faults in the planes [0 2 1] and [0 6 1] (the equivalent planes in the ramsdel-lite doubled unit cell) are the explanation for some features in the diffraction patterns of y — Mn02 e.g., the lineshift of the (1 1 0) reflection toward lower angles or the merging of the reflection groups (h 2 1 )/(h 4 0) and (h 6 1 )/(h 0 2). 

Similarly, the (111) GaAs substrate could be used to achieve epitaxial growth of zinc blende CdSe by electrodeposition from the standard acidic aqueous solution [7]. It was shown that the large lattice mismatch between CdSe and GaAs (7.4%) is accommodated mainly by interfacial dislocations and results in the formation of a high density of twins or stacking faults in the CdSe structure. Epitaxy declined rapidly on increasing the layer thickness or when the experimental parameters were not optimal. 

SO that any structural features such as twin or faults can be revealed. For larger particles, In the 20-50% size range, the diffraction pattern may be seen to change as the beam Is moved across the particle. 

For the smaller particles which Include only a few tens or hundreds of atoms, any twinning or faulting reduces the range of ordering to the extent that the pattern can not be Interpreted In the same way as a pattern from an extended crystal. The Individual single-crystal regions may contain only two or three atomic planes. Interpretation can be made only by calculation of patterns from postulated models for the configurations of atoms (22). 

In a series of studies of carefully prepared catalysts of Pt on silica gel (7,10-12) we have shown that the Pt particles are equi-axed, (and de-finitely not cuboidal as is often assumed) that the size (or percent metal exposed) agrees with results from hydrogen chemisorption, and that the particles are free of microstrain faults or twins, except when the average size is similar to the pore size of the support. In this latter case, the particles are elongated, and there is microstrain, probably due to differ-... 

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