Hetero-interfaces

As a final example of interfaces we consider a planar interface between two different crystals. We will assume that the two solids on either side of the interface have the same crystalline structure, but different lattice constants. This situation, called a hetero-interface, is illustrated in Fig. 11.17. The similarity between the two crystal structures makes it possible to match smoothly the two solids along a crystal plane. 

The difference in lattice constants, however, will produce strain along the interface. There are two ways to relieve the strain. 

However, since the film is free to relax in the direchon perpendicular to the surface, (7 2 = 0, which, together with Eq. (11.37), leads to the following relation  

From this, we obtain the strain in the z direction, and the misht shess in the xy plane, cr = a x = Oyy, in terms of the misht strain 

Consequently, the critical thickness of the film at which the introduction of misfit dislocations becomes energetically favorable is determined by the condition 

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Heterogenous immunoassays, 14 151-152 Heteroglycans, 4 697, 702 23 64 Hetero-interface, 24 71 Heterojunction, 23 34 Heterojunction bipolar transistors (HBTs), 22 166-169... 

These results on physisorption-induced work function changes on metals are also interesting with regard to the common assumption on metal/molecule hetero-interfaces, namely that metals are the hard and molecules are the soft component. The theoretical results clearly demonstrate that with respect to the charge density the metal acts as soft and the molecule as the hard partner, since the - essentially undisturbed - organic molecule imprints its shape in the charge distribution on the metal surface. 

An important class of hetero-interface is that between metals and ceramics. This occurs in such areas as metal oxidation and catalyst support. It is also important in understanding such phenomena as wetting. Stoneham and Tasker (1985) argued for the importance of image terms in the adhesion of these interfaces. Simple image theory predicts that the adhesion energy of a... 

The interdiffiision of iso-electronic constituents across hetero-interfaces during the liquid-phase epitaxial growth of Hgj xCdxTe on Cdj.yZnyTe and CdTej.ySey... 

Han JW, Yildiz B (2012) Mechanism for enhanced oxygen reduction kinetics at the (La, Sr)Co03-delta/ (La, Sr)(2)Co04-l-delta hetero-interface. Energ Environ Sci 5 8598... 

Sase M, Yashiro K, Sato K, MizusaM J, Kawada T, Sakai N, Yamaji K, Horita T, Yokokawa H (2008) Enhancement of oxygen exchange at the hetero interface of (La, Sr)Co03/(La, Sr)2Co04 in composite ceramics. Solid State Ionics 178(35-36) 1843-1852... 

An interface is a plane which joins two semi-infinite solids. Interfaces between two crystals exhibit some of the characteristic features of surfaces, such as the broken bonds suffered by the atoms on either side of the interface plane, and the tendency of atoms to rearrange themselves to restore their bonding enviroiunent. We can classify interfaces in two categories those between two crystals of the same type, and those between two crystals of different types. The first type are referred to as grain boundaries, because they usually occur between two finite-size crystals (grains), in solids that are composed of many small crystallites. The second type are referred to as hetero-interfaces. We discuss some of the basic features of grain boundaries and hetero-interfaces next. 

The polarization-related effects in wurtzite heterostructures can be entirely avoided by growing devices on alternative orientations of GaN crystals, such as the 1100 m planes or the 1120 a planes, in which the polar c-axis is parallel to the free surface and any planar hetero-interfaces. Since polarization fields exist entirely within the plane of the device structure, heterostructures grown on these planes exhibit flat-band conditions under zero bias. 

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