Crystal defect formation dislocations

The destruction of monocrystalline epitaxial growth occurs by accumulation of crystal defects as dislocations and than twin formation (Fig.6). 

Dislocation theory as a portion of the subject of solid-state physics is somewhat beyond the scope of this book, but it is desirable to examine the subject briefly in terms of its implications in surface chemistry. Perhaps the most elementary type of defect is that of an extra or interstitial atom—Frenkel defect [110]—or a missing atom or vacancy—Schottky defect [111]. Such point defects play an important role in the treatment of diffusion and electrical conductivities in solids and the solubility of a salt in the host lattice of another or different valence type [112]. Point defects have a thermodynamic basis for their existence in terms of the energy and entropy of their formation, the situation is similar to the formation of isolated holes and erratic atoms on a surface. Dislocations, on the other hand, may be viewed as an organized concentration of point defects they are lattice defects and play an important role in the mechanism of the plastic deformation of solids. Lattice defects or dislocations are not thermodynamic in the sense of the point defects their formation is intimately connected with the mechanism of nucleation and crystal growth (see Section IX-4), and they constitute an important source of surface imperfection. 

The connection between processing conditions and crystalline perfection is incomplete, because the link is missing between microscopic variations in the structure of the crystal and macroscopic processing variables. For example, studies that attempt to link the temperature field with dislocation generation in the crystal assume that defects are created when the stresses due to linear thermoelastic expansion exceed the critically resolved shear stress for a perfect crystal. The status of these analyses and the unanswered questions that must be resolved for the precise coupling of processing and crystal properties are described in a later subsection on the connection between transport processes and defect formation in the crystal.. 

Many industrial crystallization processes, by necessity, push crystal growth rates into a regime where defect formation becomes unavoidable and the routes for impurity incorporation are numerous. Since dislocations, inclusions, and other crystal lattice imperfections enhance the uptake of impurities during crystallization, achieving high purity crystals requires elimination of impurity incorporation and carry-over by both thermodynamic and non-thermodynamic mechanisms. Very generally, the impurity content in crystals can be considered as the sum of all of these contributions... 

Nanoscale clusters of metals or voids, which may be formed with irradiation (cf. Bjo as, 2012 Dubinko, 2012), interacts with dislocations at their boundaries in addition to DLs and branches inside the crystal. The formation of such permanent dislocation inside the material may give it superior hardness and yield strength, because it is not easy to move such dislocations (Kittle, 1996). That is why irradiated material is hardened (cf. Dubinko et al., 2009). Interaction of the radiation-induced electron cloud with nearby defect site may occur under certain conditions, while synthesis of new chemical compounds is dependent on the TDs of the inorganic material. Such effect may help in development of new materials or deterioration of an efQdent material. 

As mentioned earlier the defect formation processes in a semiconductor crystal, in general, and in silicon, in particular, have been described using the model of point defect dynamics in this case, the crystal has been considered a dynamic system and real boundary conditions have been specified. However, the model of point defect dynamics has not been used for calculating the formation of interstitial dislocation loops and microvoids under the... 

Talanin, V.I. Talanin, I.E. (2010c). Modeling of defect formation processes in dislocation-free silicon single crystals. Crystallography Reports, Vol. 55, No. 4, pp. 675-681, ISSN 1063-7745. 

Physically, the onset of instabihty at the point is interpreted as the formation of crystal defect there. It should be noted that local instability does not imply global instability of the configuration. If angle between the vectors k and w established in this way is larger than 60°, then the nucleated defect is expected to be a dislocation with slip plane normal k and Burgers vector approximately along w. On the other hand, if the angle between k and w and instability is less than 30°, the nucleated defect would likely be a microcrack or a void. 

In Sec. 2 the overall surface dissolution was considered. Except in the case of surface diffusion, we assumed that a dissolving surface is free from defects. Since real crystals usually contain dislocations and other defects, it Is necessary to know their effect on dissolution rates and the mechanism of formation of etch pits at their emergence points. 

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