Dislocation propagation

Draw a Burger s circuit and identify the direction of dislocation propagation. 

Figure 8.10 Schematic of an interlayer blocking threading dislocations from the template. Dislocations propagating through a window bend sideways as the GaN island grows laterally...

Figure 8.14 Transmission electron micrograph of GaN grown on a SiN interlayer. Some dislocations were blocked by the interlayer, and those dislocations propagating through the openings in the interlayer were observed to bend sideways...

A. Sakai, H. Sunakawa, A. Kimur, and A. Usui, Dislocation propagation in GaN films formed by epitaxial lateral overgrowth,/. Electron Microsc. 49, 323-330 (2000). 

The critical stress needed for homogenous nucleation of dislocations is considerable larger than that for dislocation propagation or multiplication. In order to tolerate fairly high stress levels during processing, the heterogenous nucleation of dislocations has to be avoided /13/ (fig.8). 

Plastic deformation can be studied and the dislocation propagation observed in real time in a straining stage. 

Hull, R., Bean, J. C., Bahnck, D., Peticolas, L. J., Short, K. T. and Unterwald, F. C. (1991), Interpretation of dislocation propagation velocities in strained Gea Sii a /Si(100) heterostructures by the diffusive kink pair model, Journal of Applied Physics 70, 2052-2065. 

Intrinsic defects (or native or simply defects ) are imperfections in tire crystal itself, such as a vacancy (a missing host atom), a self-interstitial (an extra host atom in an otherwise perfect crystalline environment), an anti-site defect (in an AB compound, tliis means an atom of type A at a B site or vice versa) or any combination of such defects. Extrinsic defects (or impurities) are atoms different from host atoms, trapped in tire crystal. Some impurities are intentionally introduced because tliey provide charge carriers, reduce tlieir lifetime, prevent tire propagation of dislocations or are otlierwise needed or useful, but most impurities and defects are not desired and must be eliminated or at least controlled. 

J.N. Johnson, O.E. Jones, and T.E. Michaels, Dislocation Dynamics and Single-Crystal Constitutive Relations Shock-Wave Propagation and Precursor Decay, J. Appl. Phys. 41, 2330-2339 (1970). 

A pecuhar sohd phase, which has been discovered not too long ago [172], is the quasi-crystalline phase. Quasi-crystals are characterized by a fivefold or icosahedral symmetry which is not of crystallographic type and therefore was assumed to be forbidden. In addition to dislocations which also exist in normal crystals, quasi-crystals show new types of defects called phasons. Computer simulations of the growth of quasicrystals [173] are still somewhat scarce, but an increasing number of quasi-crystalline details are studied by simulations, including dislocations and phasons, anomalous self-diffusion, and crack propagation [174,175]. 

R. Mikulla, F. ICrul, P. Gumbsch, H.-R. Trebin. Numerical simulations of dislocation motion and crack propagation in quasicrystals. In A. Goldmann,... 

In the case of TiCl2 the number of propagation centers do not exceed 0.5% of the number of surface titanium ions this shows that the formation of the propagation centers proceeds at specific points on the surface of the crystalline catalyst (e.g. lateral faces, outlets of the spiral dislocations). 

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