Epitaxial coherency

Once one layer has formed (the primary nanotube core), further secondary layers appear to deposit with various degrees of epitaxial coherence. When inhomogeneous deposition occurs in PCNTs, the thickening has a characteristic spindle shape, which may be a consequence of non-carbon impurities which impede graphitization (see below) —this is not the case for ACNTs were growth takes place in an essentially allcarbon atmosphere, except, of course, for the rare gas. These spindles probably include the appropriate num-... 

Epitaxial coherency maintained for the three low-index orientations of the fee copper lattice substrate to various degrees. 

If there is no epitaxial (coherent) relation between the substrate and the growing crystals, and the nuclei formed initially have completely random orientation, and the growth rate is more or less isotropic, geometrical selection operates in one direction only perpendicular to the substrate surface. When there is an epitaxial and coherent relation between the substrate and the crystals, and the growth rate... 

The physical stmcture of mixed-layer minerals is open to question. In the traditional view, the MacEwan crystallite is a combination of 1.0 nm (10 E) non-expandable units (iUite) that forms as an epitaxial growth on 1.7 nm expandable units (smectite) that yield a coherent diffraction pattern (37). This view is challenged by the fundamental particle hypothesis which is based on the existence of fundamental particles of different thickness (160—162). 

The interface between the substrate and the fully developed film will be coherent if the conditions of epitaxy are met. If there is a small difference between the lattice parameter of the film material and the substrate, die interface is found to contain a number of equally spaced edge dislocations which tend to eliminate the stress effects arising from the difference in the atomic spacings (Figure 1.13). 

The fundamental issue of epitaxial growth on polycrystalline substrates has been addressed in a more refined manner in relation to the electrodeposition of CdSe on metals. Polycrystalline, lll -textured Au surfaces were shown [17] to promote the electrodeposition of coherent, epitaxial CdSe quantum dot films over areas micrometers in size, i.e., much larger than the polycrystalline Au grains, despite the numerous grain boundaries present in the substrate. The Au films (considered as... 

Magnesium chloride has a crystal structure very similar to violet titanium trichloride. This dictates the possibility of an epitaxial coordination of TiCU units (or TiCl3 units, after reduction) on the lateral coordinatively unsatured faces of MgCl2 crystals, giving rise to relieves crystallographically coherent with the matrix.150... 

Calculate the strains and that would be applied if the lattice parameters in the interface plane of the layer were forced to conform to the substrate (full coherent epitaxy). Multiply these by (1-i ) where R is the (fractional) relaxation of the layer. (See the discussion of measurement of relaxation in Chapters.)... 

Three-dimensional epitaxial crystallites (TECs) were observed in the first stages of electrodeposition of copper (51) and nickel (58) on copper substrates. TECs of nickel formed on copper-film substrate from nickel sulfate solutions in low concentration are shaped rectangularly with edges averaging 1300 A in length. The coherent... 

Borysiuk J, Bozek R, Strupinski W et al (2010) Graphene growth on C and Si-face of 4 H-SiC - TEM and AFM studies. Mater Sci Forum 645-648 577-580 Berger C, Song Z, Li X et al (2006) Electronic confinement and coherence in patterned epitaxial graphene. Science 312 1191-1196... 

When reading the literature, in many (probably most) cases it is not clear whether the deposition proceeds by an ion-by-ion process. The reason is that, unless another mechanism is specifically discussed, it is often assumed that the deposition proceeds via the ion-by-ion mechanism. If the exact deposition parameters are known, which mechanism is operative can, in most cases, be calculated. Two criteria have often been cited in the literature as proof of deposition via the ion-by-ion mechanism. One is epitaxial deposition of the CD film. (Epitaxy refers to growth of one material on another in such a way as to result in coherence between the lattice of the substrate and the deposit. Often—although not necessarily—the lattice of the deposit is aligned in the same direction as that of the substrate.) This is based on the expectation that a cluster mechanism will not result in an epitaxial film for this to occur, clusters of maybe thousands of atoms would need to be able to rearrange themselves on the substrate. Some examples of epitaxial growth are given in Sections 3.4.2 and 4.I.5.2. 

A primary focus of our work has been to understand the ferroelectric phase transition in thin epitaxial films of PbTiOs. It is expected that epitaxial strain effects are important in such films because of the large, anisotropic strain associated with the phase transition. Figure 8.3 shows the phase diagram for PbTiOs as a function of epitaxial strain and temperature calculated using Landau-Ginzburg-Devonshire (lgd) theory [9], Here epitaxial strain is defined as the in-plane strain imposed by the substrate, experienced by the cubic (paraelectric) phase of PbTiOs. The dashed line shows that a coherent PbTiOs film on a SrTiOs substrate experiences somewhat more than 1 % compressive epitaxial strain. Such compressive strain favors the ferroelectric PbTiOs phase having the c domain orientation, i.e. with the c (polar) axis normal to the film. From Figure 8.3 one can see that the paraelectric-ferroelectric transition temperature Tc for coherently-strained PbTiOs films on SrTiOs is predicted to be elevated by 260°C above that of... 

The literature in this field is almost unduly preoccupied with lattice mismatch, so it seems appropriate to make a comment before proceeding. In this Datareview, I use the Matthew s convention [1] to compute the misfit. This convention gives a misfit which is simply related to the number of dislocations the film needs to accommodate the misfit. In practice, coherent epitaxy is never achieved for misfits larger than about 2%, so computation of a misfit may not be terribly meaningful. Lattice misfits to the nitride semiconductors for the materials discussed in this paper are given in TABLE 1. 

The terms incommensurate and semi-commensurate are analogous to incoherent and semi-coherent for interfaces - in grain boundaries, heterophase interfaces and epitaxial layers (cf. also Nabarro - with which layered misfit structures have much in common. In extreme cases noncommensurability may arise by mutual rotation (to varying degrees) of component layers with identical component lattices... 

Pure bulk iron in the fee crystal structure (7-Fe) only exists at very high temperatures (between 1183 and 1667K). However, 7-Fe may be stabilized at low temperatures as small coherent precipitates in copper or copper-alloy matrices or as thin epitaxial films on a Cu or Cu-based alloy substrate [113], (114). Recently the interest in 7-Fe has been revived due to the existence of multiple magnetic states revealed by band-structure calculations [115], which is believed to be related to INVAR phenomena in 7-Fe-based alloys [116]. 

---