Interfacial dislocation

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. 

Crystal/crystal interfaces possess more degrees of freedom than vapor/crystal or liquid/crystal interfaces. They may also contain line defects in the form of interfacial dislocations, dislocation-ledges, and pure ledges. Therefore, the structures and motions of crystal/crystal interfaces are potentially more complex than those of vapor/crystal and liquid/crystal interfaces. Crystal/crystal interfaces experience many different types of pressures and move by a wide variety of atomic mechanisms, ranging from rapid glissile motion to slower thermally activated motion. An overview of crystal/crystal interface structure is given in Appendix B. 

Glissile Motion of Sharp Interfaces by Interfacial Dislocation Glide... 

Sharp boundaries of several different types can move conservatively by the glide of interfacial dislocations. In many cases, this type of motion occurs over wide ranges of temperature, including low temperatures where little thermal activation is available. 

Heterophase Interfaces. In certain cases, sharp heterophase interfaces are able to move in military fashion by the glissile motion of line defects possessing dislocation character. Interfaces of this type occur in martensitic displacive transformations, which are described in Chapter 24. The interface between the parent phase and the newly formed martensitic phase is a semicoherent interface that has no long-range stress field. The array of interfacial dislocations can move in glissile fashion and shuffle atoms across the interface. This advancing interface will transform... 

The motion of many interfaces requires the combined glide and climb of interfacial dislocations. However, this can take place only at elevated temperatures where sufficient thermal activation for climb is available. 

The example in Fig. 13.4 is an extension of the model for the motion of a small-angle boundary by the glide and climb of interfacial dislocations (Fig. 13.3). Figure 13.4 presents an expanded view of the internal surfaces of the two crystals that face each other across a large-angle grain boundary. Crystal dislocations have... 

See Section B.7 for a discussion of extrinsic vs. intrinsic interfacial dislocations. 

In crystalline solids, only coherent spinodal decomposition is observed. The process of forming incoherent interfaces involves the generation of anticoherency dislocation structures and is incompatible with the continuous evolution of the phase-separated microstructure characteristic of spinodal decomposition. Systems with elastic misfit may first transform by coherent spinodal decomposition and then, during the later stages of the process, lose coherency through the nucleation and capture of anticoherency interfacial dislocations [18]. 

Reproducible junction characteristics depend on the ability to control the structure and the thickness of the barrier layers. In addition, the interfaces between the YBCO and the barrier layer may have a much stronger influence on the junction properties than the barrier layer itself [14.82]. Interfacial dislocations and oxygen depletion of the YBCO adjacent to the barrier layer are structural details that need to be considered. 

Fig. 8.5 Scanning Eiectron Microscope image of a perovskite-paliadium cermet (ceramic-mettii) made by sintering together LaFeo.wCro.ioOs-x and Pd powder to form dense continuous matrices of both metal and ceramic. The palladium and ceramic were lattice matched to minimize stiain and interfacial dislocations. (S. Rolfe, Eltron Research) (Copyright Elsevier, 2005. Adapted with permission from [11], Ctubon Dioxide Capture and Storage in Deep Geological Formations.)...

The facets often meet at 60° or 120° angles. The three orientation variants are shown as A-C. Two TJs between all three variants can be seen in the image. Variant A contains irregular contrast associated with the interfacial dislocation network variants B and C show moire fringes. 

If the corresponding planes [e.g., in the (OOl)Nio/ (OOl)Mgo interface] are rotated about an axis that lies in the plane, then the interfacial dislocations must have a component that is normal to the plane of the interface. Again, this situation has been demonstrated for both semiconductors and oxides. The presence and distribution of... 

This behavior may be modeled by the structure shown in Fig. 16.19, which is seen to be formed out of lap joint sub-units in the same way as the model used in Fig. 16.17. When such a stracture is stretched, it is evident that the joints between the ends of the nacre crystals could open up and cause interfacial dislocations to propagate along the flat crystal interfaces. The weakest joint opens first, then heals to form the dislocation. It cannot open further because the... 

The criterion for interfacial dislocations is that aacks start to move along the intaface, but the aack opening is constrained to cause healing. Thus the condition for dislocation formation is the same as that for interface cracking in the lap joint (Chapter 15). Dislocations will form at a stress... 

For fine fibers with very smooth snrfaces, healing can also occur after debond, so that interfacial dislocations are produced. For fat fibers with rough surfaces, molecular contact cannot be reformed easily. Consequently frictional pull-out is then observed, with damage at the interface. 

An understanding of strain effects in films is of critical importance for our subsequent discussion of superlattices in sect. 5. The topic of strain relief through interfacial accommodation began with Van der Merwe s treatment of critical thickness for the formation of interfacial dislocations (Van der Merwe 1950,1962) and has been the subject of reviews (Matthews 1979, Freund 1993). In the interest of brevity we present only a sketch of strain relief phenomena in what follows, and illustrate the substance of the discussion by relevant examples of magnetic behavior in thin rare-earth films. 

Figure 7.7 Dislocation array at an asymmetric low-angle boundary in Zr02- The individual lattice planes are distinguished in this high-resolution transmission electron micrograph. Each arrow indicates the termination of a lattice plane in an interfacial dislocation. 

Dehm, G., Wagner, T., Balk, T.J. and Arzt, E. (2002a), Plasticity and interfacial dislocation mechanisms in epitaxial and polycrystalline A1 films constrained by substrates. Journal of Materials Science and Technology 18, 113-117. 

FIGURE 3.19 (a) Schematic model of a nanotube cross section. Interfacial dislocations (bold lines) are... 

The microstructure influences not only the composition but also the initial growth of the passive film, which determines the compact properties. The initial oxide layer formation is accompanied by the gradual growth of the oxide film. Oxide growth by cation diffusion over vacancies requires the annihilation of the vacancies by the increase of either misfit or misorientation interfacial dislocations. ... 

The final microstructure of the two composites is characterized by the formation of Ta-containing solid solutions, which grew epitaxially on the matrix grain. The misfit between the core and the shell was accommodated by a interfacial dislocation loop. These features evidence a discrete solubility of Ta in both ZrB2 and HfB lattices. 

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