Seed crystals growth onto

Figure 4.1-5 Modified Bridgeman seal autoclave showing the temperature gradient crystal growth onto seed crystals [17]. The nutrient is held at a higher temperature than the seed crystals, thus leading to supersaturation conditions in the seed region. The transport is ill a...

In the flux-growth method, crystals of the desired ceramic are precipitated from a melt containing the components of the product phase, often in addition to additives used to suppress the melting point of the flux. These additives remain in solution after crystal growth is complete. Crystals are precipitated onto seeds by slowly cooling the melt or the seed, or occasionally by evaporating volatile components of the melt such as alkaH haHdes, depressing the solubiHty of the product phase. 

One of the methods of growing bulk GaN is a sublimation method [1-3], In this method, the source GaN powder and a seed crystal or a substrate facing the source are loaded in a crucible. Upon heating the crucible, the source powder sublimates and recrystallises onto the seed crystal or on the substrate. When a system needs a reaction gas such as NH3 for growth, the system is not a sublimation but a VPE system. Now, a 4-inch SiC wafer grown by a sublimation method is commercially available [4],... 

Extensive seeded calclte growth experiments in the presence of phosphate ion indicate that the phosphate ion adsorbs onto the crystal surface as a monolayer. At a concentration of 10" M, phosphate ion can strongly inhibit calcite formation however, short term experiments show that this monolayer adsorption removes insignificant amounts of phosphorus from solution. In experiments lasting several days a further decrease in solution phosphate concentration occurs, presumably caused by nucleation of a surface calcium phosphate phase on the calcite seed. 

Homoelement materials can be made a number of ways. In the semiconductor industry, silicon chips are made by evaporating silicon compounds down onto a crystal template that helps seed the crystal growth. 

The most successful approach to control membrane formation involves segregation of the processes of crystal nucleation and growth [40]. The so-called ex situ or secondary (seeded) growth methods, unlike the direct synthesis procedures just discussed, includes a first step in which a closely packed layer of colloidal zeolite crystals, synthesized homogenously, is deposited onto the surface of a support. These seeds act as nuclei for further crystal growth with a secondary gel under hydrothermal synthesis conditions in a second stage. 

The growth of one crystal onto the surface of another is called epitaxy (or epitaxis)—that is, the surface of one crystal seeds the growth of the other form. When the two substances have the same structure, we refer to it as homoepitaxy and when they are different the phenomenon is called heteroepitaxy. 

Fig. 16.3 Stages ofVerneuil growth of ruby without seed crystal, schematic (a) formation of sinter cone and central melt droplet onto alumina rod, (b) growth of the neck for nucleation...

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