Growth of Single Crystals From

Growth of Single Crystals From a Molten Flux 

The apparatus is simple and consists of a furnace whose temperature can be accurately controlled, a crucible to hold the molten flux, and a method of rotating the crucible to stir the flux containing the dissolved material. Single crystals can be induced to grow along the sides of the crucible by controlling the temperature and supercooling of the molten flux. 

The steps involved in using this method are as follows  

A flux such as lead borate is melted. PbB204 is useful in this method because it will undergo supercooling rather easily. 

The material which is to form single crsrstals is dissolved in the molten flux to near saturation (Note that this requires prior knowledge regarding solubility of compound in molten flux). 

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In a paper by Fisk and Remeika (1989) several points concerning the growth of single crystals from metal fluxes have been discussed. Attention has been dedicated to various aspects of the problem of separating crystal and flux, for which two main approaches, chemical and mechanical, may be considered. The following examples drawn from the preparative chemistry of the rare earth alloys were described. 

Fisk, Z. and Remeika, J.P. (1989) Growth of single crystals from molten metal fluxes. In Handbook on the Physics and Chemistry of Rare Earths, eds. Gschneidner Jr., K.A. and Eyring, L.R. (North Holland, Amsterdam), Vol. 12, p. 53. 

Considerable effort has been expended in growing single crystals of compositions in the solid solution, with particular emphasis on the superconducting composition. A variety of methods have been employed, all flux type, as the solid solution members are not congruently melting. There have been a few detailed reports on growth of single crystals from melts in the... 

Z. Fisk and J.P. Remeika, Growth of single crystals from molten metal fluxes 53... 

Potentials or gradients in concentration or other driving forces determine the direction of the reactions. If the potentials are low and the mobility of the atoms is high enough, potentials affect rates. These effects have been well studied and dominate the formation of solids if it takes place under conditions not far removed from thermodynamic equilibrium, e.g., the growth of single crystals from a melt or from solution. 

Another concept in synthesis is epitaxy. Epitaxy is the continuation of the crystal orientation of the monocrystalline substrate in the deposited crystalline product, which may be the same compound as the substrate or a different solid that has the same crystal orientation as the monocrystalline solid. Epitaxial layers are essential for microlithography in the electronic industry carefully formed epitaxial layers do not have localized electronic interface states, which are deleterious for the functioning of the device. The process conditions for epitaxy by molecular beam epitaxy (MBE) are very low process pressure, comparatively high temperatures, and a low growth rate. MBE is a form of CVD, which was described in Chapter 6. Liquid phase epitaxy (LPE) is a form of growth of single crystals from a melt. 

Table 8.4. Process Conditions for Growth of Single Crystals from Solutions"... 

GROWTH OF SINGLE CRYSTALS FROM MOLTEN METAL FLUXES... 

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