Epitaxial twins

Epitaxial twins (Fig. 4.11) consist of a hematite centre with outgrowths of acicular goethite. As the structures of both goethite and hematite are based on an hep anion array, some of the interplanar spacings in the two compounds are similar and this fa-... 

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. 

Twinning and epitaxial growth are also methods of controlled growth, and therefore crystals grown by these methods often exhibit a very different characteristic morphology from that of coexisting single crystals. 

P. Hartman, Epitaxial aspects of the atacamite twin, Cursillosy Conferencias, C.S.I.C. 

In order to obtain reliable results, magnetostriction should be measured in epitaxial films, free of twins, which are typical for materials of perovskite structure. In the case of films it is not easy, because usually the films are deposited on perovskite substrates, thus presenting difficulties in eliminating twin structures. 

It was shown that orientations of metal particles, located inside carbon nanotubes (nanofibers), along the longitudinal axis for fee and bcc crystal lattices can be characterized by the same directions [100], [110], [111] and [112]. It was found that fcc-particles of all three metals often contain twins. The obtained results are discussed in the framework of the epitaxial growth model and deformation processes inside nanotubes. 

Cubic boron nitride (cBN) has a zinc blende-type crystal structure with a lattice constant of 3.615 A, which is very close to that of diamond (3.567 A). The difference is only about 1.3%. According to RHEED measurements with the electron beam parallel to the 111 layer of cBN, a growth of diamond by DC plasma CVD on cBN(lll) [150] using c = 0.5%CH4/H2, T = 900°C, and F=180Torr led to a result that a smooth (111) layer of diamond was epitaxially deposited in such a way that the [110] direction of diamond was parallel to that of cBN. Namely, D 111 //cBN(lll and D[110]//cBN[110]. In the RHEED pattern, however, extra spots were observed, which were presumably due to the twinnings of (111 diamond layers. In the Raman spectra, there were two lines due to cBN at 1054.5 and... 

Many different etchants have been developed for the evaluation of different types of crystal defects such as flow-pattern defects [115], stacking faults [74, 192, 193], dislocations [69, 72-74, 194], dislocation network [72, 193, 195], oxide precipitates [196], swirl patterns [74, 75, 148], striations [74, 197], hillock defects [198], epitaxial defects [192], epitaxial alignment [199], grain boundary [69, 72, 200], twin band [69], diamond saw damage [201], pn junction [202-204], metallic precipitates [205], and damaged layer of mechanically polished surface [206],... 

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