Melt Technique Verneuil Flame-Fusion

For growing sapphire crystals, high-purity aluminum oxide powder of a uniform particle size is fed at a 

Vapor-phase techniques are not as widely used as growth from the melt or solution because the growth rate is generally slow or only small crystals can be grown. However, two vapor-phase techniques have commercial application the growth of whiskers or small islands (e.g., SiC and GaN) by the VLS process and the growth of SiC and nanotubes by sublimation processes. 

A large single crystal in the as-grown form is often referred to as a boule, from the French word for ball, or as an ingot (which may also be used to describe a polycrystal). 

When a boule is cut into fiat sections, the singlecrystal slices are typically referred to as wafers. 

When the wafers are cut into small units (usually either square, rectangular, or circular) they are referred to as substrates or windows. 

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The Verneuil, or flame-fusion, method is illustrated in Figure 29.1. It is a well-established technique for growing single crystals of oxides that have high melting temperatures. The largest application of the Verneuil method is for the growth of sapphire and ruby. 

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