Confined crystal growth

Batte, H.D., and Marangoni, A.G. (2005). Fractal growth of milk fat crystals is unaffected by microstructural confinement. Crystal Growth Des. 5, 1703-1705. 

Epitaxial crystal growth methods such as molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) have advanced to the point that active regions of essentially arbitrary thicknesses can be prepared (see Thin films, film deposition techniques). Most semiconductors used for lasers are cubic crystals where the lattice constant, the dimension of the cube, is equal to two atomic plane distances. When the thickness of this layer is reduced to dimensions on the order of 0.01 )J.m, between 20 and 30 atomic plane distances, quantum mechanics is needed for an accurate description of the confined carrier energies (11). Such layers are called quantum wells and the lasers containing such layers in their active regions are known as quantum well lasers (12). 

Secondly, I wish to counteract anticipated despondency which some of the complexities on the present theoretical scene may perhaps provoke. For this purpose, I wish to invoke the decisive simplicity and definiteness of some of the experimental effects observed within the confines of the above, near ideal systems. This, as I often pointed out elsewhere, is unmatched in the field of crystal growth of simple substances. Complicated as polymers may seem, and subtle as some of the currently relevant theoretical issues, this should not obscure the essential simplicity and reproducibility of the core material. To be specific, the appropriate chains seem to want to fold and know when and how, and it is hardly possible to deflect them from it. Clearly, such purposeful drive towards a predetermined end state should continue to give encouragement to theorists for finding out why Those who are resolved to persevere or those who are newly setting out should find the present review a most welcome source and companion. 

For the ion-by-ion reaction, nucleation is generally slower and the density of nuclei smaller. Additionally, growth occurs (ideally) only at a solid surface therefore nucleation is confined to two dimensions, in contrast to three dimensions for the cluster mechanism. The crystal growth may terminate when adjacent crystals touch each other or by some other termination mechanism, e.g., adsorption of a surface-active species. These factors should be valid regardless of whether the mechanism proceeds via free chalcogenide ions or by a complex-decomposition mechanism. 

The many technological innovations in melt crystal growth of semiconductor materials all build on the two basic concepts of confined and meniscus-defined crystal growth. Examples of these two systems are shown schematically in Figure 1. Typical semiconductor materials grown by these and other methods are listed in Table I. The discussion in this section focuses on some of the design variables for each of these methods that affect the quality of the product crystal. The remainder of the chapter addresses the relationship between these issues and the transport processes in crystal growth systems. 

The lipidic cubic phase has recently been demonstrated as a new system in which to crystallize membrane proteins [143, 144], and several examples [143, 145, 146] have been reported. The molecular mechanism for such crystallization is not yet clear, but the interfacial water and transport are believed to play an important role in nucleation and crystal growth [146, 147], Using a related model system of reverse micelles, drastic differences in water behavior were observed both experimentally [112, 127, 128, 133-135] and theoretically [117, 148, 149]. In contrast to the ultrafast motions of bulk water that occurs in less than several picoseconds, significantly slower water dynamics were observed in hundreds of picoseconds, which indicates a well-ordered water structure in these confinements. 

Metallic carbides, nitrides, and oxides are used industrially in many applications their physical properties are also of intrinsic interest. This section pinpoints various preparative techniques and reviews methods of crystal growth for this group of compounds. More detailed discussion is found in the reviews cited and in the references therein. The discussion is confined to binary compounds, M Xi, (M is a cation X = C, N, or O a and b are simple integers) that display metallic properties the very numerous ternaries MoMcXj, (M, M being different cations) cannot be described in this brief presentation. 

At some stage, oxidation by the protein would cease to be important with essentially aU of the oxidation taking place on the surface of the mineral. The role of the protein is to maintain the growing ferrihydrite core within the confines of the protein shell, thus maintaining the insoluble ferric oxyhydroxide in a water-soluble form, while the crystal growth phase of biomineralisation takes place exclusively on the surface of the growing iron mineral crystallite. 

Advances in epitaxial crystal growth methods make it possible to prepare heterostructures with essentially arbitrary thiekness of the small-gap layer. When the thickness of this layer is reduced to dimensions of the order of 10 nm (between 20 and 30 atomic planes) a quantum mechanical description of the confined carriers is needed. Such heterostructures are called quantum wells [41. 42]. 

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