Oriented overgrowths

The oriented overgrowth of a crystalline phase on the surface of a substrate that is also crystalline is called epitaxial growth [104]. Usually it is required that the lattices of the two crystalline phases match, and it can be a rather complicated process [105]. Some new applications enlist amorphous substrates or grow new phases on a surface with a rather poor lattice match. 

Oriented overgrowth (epitaxial growth) rutile (too) on hematite (0001) chalcopyrite (112) on enargite (001) many other examples... 

Oriented overgrowth. Isomorphous substances which do not form mixed crystals may do the next best thing one crystal may grow on the other in parallel orientation. Sodium nitrate grows on calcite this way. Isomorphism is not, however, a necessary condition for oriented overgrowth it is sufficient if the arrangement of atoms on a particular plane of one crystal is similar, in type and dimensions, to the arrangement on one of the planes of the other crystal the two structures may be in other respects completely different from each other (Royer, 1926,... 

Orientation overgrowth of condensed polycyclic aromatic compounds vacuum-evaporated onto cleaved face of mica. Journal of Applied Physics, 36,1453-60. 

Ashida, M. (1966) The orientation overgrowth of metal-phthalocyanines on the surface of single crystals. I. vacuum condensed films on muscovite. Bulletin of the Chemical Society of Japan, 39,... 

Another consequence of these films of grease is the prevention of oriented overgrowths .4 It is often found that if a crystal with a clean, freshly cleaved surface, is moistened with a solution of an isomorphous, soluble salt, which is then allowed to evaporate, the crystals deposited from the soluble salt are oriented with their edges parallel to those of the original crystal. Such overgrowths are well shown by sodium nitrate deposited on calcite. They are only obtained in perfection, however, if the surface of the first crystal is free from contamination the power of orienting deposited isomorphous crystals is much diminished if the freshly cleaved surface is left in the air. 

Alexander McPherson and Paul J. Shlichta have suggested using insoluble minerals as heterogeneous nuclei for the crystallization of macromolecules. They obtained excellent protein crystals, which could be cleaved from the mineral nucleus and used for X-ray diffraction studies. The mineral is introduced into a supersaturated solution of the material to be crystallized. As supersaturation increases, nucleation occurs on a specific face of the mineral nucleus, and a crystal begins to grow. The orientation and periodicity of the molecules on the nucleus surface promote an oriented overgrowth that has a similar periodicity. 

Epitaxy The oriented overgrowth of one crystalline material on the surface of another. Generally there is some match of periodicity between the two. 

Bunn, C. W. Absorption, oriented overgrowth and mixed crystal formation. Proc. Roy. Soc. (London) A141, 567-593 (1933). 

Owing to the close relationship of cell dimensions, polymeric iso-morphs often form orientated overgrowths. Solid solution between them, however, appears to be rare. 

F.C. Frank and J.H. van der Merwe. One Dimensional Dislocations. II. Misfitting Monolayers and Oriented Overgrowth. Proc. R. Soc. London A198 216 (1949). 

Table 4.3. Oriented overgrowth of inorganic crystals on insoluble substrates with large lattice misfits ...

There are, however, some a priori arguments which favour non-epitaxial processes as the major mechanism of oriented overgrowth of biominerals from ion precipitation at organic surfaces. Firstly, epitaxis requires a rigid two-dimensional atomic net whereas non-epitaxial deposition can be achieved from a more flexible surface on which there are specific molecular configiirations of polypeptide side chains. For example, it has been suggested that the deposition of apatite within the 640 A ( hole ) zones between colla-... 

---