Dislocation generation

D.E. Mikkola and R.N. Wright, Dislocation Generation and its Relation to the Dynamic Plastic Response of Shock Loaded Metals, in Shock Waves in Condensed Matter—1983 (edited by J.R. Asay, R.A. Graham, and G.K. Straub), Elsevier Science, New York, 1984, 415 pp. 

G. Meir and R.J. Clifton, Effects of Dislocation Generation at Surfaces and Subgrain Boundaries in Precursor Decay in High-Purity LiF, J. Appl. Phys. 59, 124-148 (1986). 

Lehoczky, S. L., "Retardation of Dislocation Generation and Motion in Thin-Layered Metal Laminates, Phys. Rev. Lett., Vo1.41,No.26, 1978,pp. 1814-1818. 

In Fig. 6.5(b), it is seen that dislocations in the seed are inherited, and that only a small number of dislocations generate from the seed surface, whereas in Fig. 6.5(a) most of the dislocations are newly generated on the seed surface. These newly generated dislocations start from initial liquid inclusions trapped at etch pits. The dislocations originate due to the failure of matching of lattice planes when inclusions... 

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.. 

Lehoczky, S.L. (1978a), Retardation of dislocation generation and motion in thin-layered metal laminates , Physical Review Letters, 41, 1814-1818. 

When GBS is accommodated by the movement of dislocations, the strain rate can be deduced in a similar way as for recovery creep the dislocations generated at the grain boundaries move either along the grain boundaries or... 

The FWHMs of 00.2 reflection for GaN layers on sapphire 00.1 vary between 30 arc sec [17] and more than 1000 arc sec [18], Such a large scatter of the results is caused by different types and concentrations of threading dislocations generated by a large (about 16%) lattice mismatch between GaN layers and sapphire. 

FIGURE 1 shows a typical SIMS profile of Mg in GaN. The Mg concentration was uniformly distributed at a growth temperature of 750°C [8], The concentration of the Mg is 2 - 3 x 101 cm" near the surface and is the same at a depth of 0.4 pm towards the substrate. At the junction between the GaN Mg and undoped GaN buffer, the Mg concentration increases to 1 x 1019 cm 3 and is seen to diffuse into the buffer layer. This Mg peak is probably caused by enhanced diffusion of Mg, associated with defects and dislocations generated at the layer/substrate interface, towards the substrate. A wide chemical doping range in GaN Mg of 1 x 1017to 1 x 1019 cm 3 was obtained. 

Later on [87, 88] it was observed by STM that ion bombardment of the Pt25Ni7s(l 11) surface leads to the formation of a pattern of shallow ditches (some 0.2-0.5 A deep) that have been attributed to the dislocations generated by the lattice mismatch of the top layers and the bulk ones. The top layers are enriched in Pt by ion bombardment and hence have a different lattice constant. These dislocations in sputtered alloys may provide diffusion pipes for implanted atoms to reach the surface. Diffusion of metal atoms in the surface region at relatively low temperatures has however been proven to be related to the presence of defects, such as the pinholes observed by STM at the Co/Cu( 100) interface [89]... 

Perm RL, Banfield JF, Kerrick, DM (1999) TEM investigation of Lewiston, Idaho Fibrolite Implications for grain boundary energetics and A SiOs phase relations. Am Mineral 84 152-159 Perm RL, Banfield JF (1998a) Imperfect oriented attachment Dislocation generation in defect-free nanocrystals. Science 281 969-971... 

Penn RL, Banfield JF (1998) Imperfect oriented attachment Dislocation generation in defect-free nanocrystals. Science 281 969-971... 

In particular, regarding GBs, numerous observations and theoretical models of dislocation generation have been reported for metals and their... 

In the present analyses, prismatic dislocation loops distributed on different slip planes are used as agents for dislocation generation. For copper, sources length of about 0.60 p,m are used. It is worthy to mention that the boundary conditions of the computational cell sides are different in FE and DD parts of the code. In DD, periodic boundary condition for the representative volume element RVE is used to ensure both the continuity of the dislocation curves and the conservation of dislocation flux across the boundaries, by that we take into account the periodicity of single crystals in an infinite media. In FE analysis however, the sides are constrained to move only in the z direction so that a imiaxial strain consistent with the shock experiment is achieved. In order for the boundary conditions in FE and DD to be consistent, periodic FE bormdary condition is implemented as well. The result of this implementation is discussed in the next section. 

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