Floating zone

Silicon is prepared commercially by heating silica and carbon in an electric furnace, using carbon electrodes. Several other methods can be used for preparing the element. Amorphous silicon can be prepared as a brown powder, which can be easily melted or vaporized. The Gzochralski process is commonly used to produce single crystals of silicon used for solid-state or semiconductor devices. Hyperpure silicon can be prepared by the thermal decomposition of ultra-pure trichlorosilane in a hydrogen atmosphere, and by a vacuum float zone process. 

Molten zones are also formed by radiant heating (71). The light source may be focused carbon arcs, xenon lamps, sunlight, or lasers. Very high temperatures have been achieved with all of these. For example, sapphire has been float-zoned in this manner, at over 2000°C. 

Fig. 8. Geometry for float-zoning large-diameter conducting materials.

The primary application for floating-zone melting is crystal growth rather than purification. Semiconductor-grade siUcon is not purified by zone refining siUcon chlorides are distilled and then reduced with hydrogen. 

W. KeUer and A. Mbhlhauer, Floating-Zone Silicon Marcel Dekker, Inc., New York, 1981. 

Some materials are so reactive that they cannot be zone-melted to a high degree of purity in a container. Floating-zone techniques in which the molten zone is held in place by its own surface tension have been developed by Keck et al. [Phys. Rev., 89, 1297 (1953)]. 

E. Chenier, C. Delcarte, G. Labrosse. Multiple thermocapillary solutions in floating zone at zero gravity. Eur Phys J Appl Phys 2 93, 1998. 

T. Kaiser, K. W. Benz. Floating-zone growth of silicon in magnetic fields. III. Numerical simulation. J Cryst Growth 183 56A, 1998. 

A. Muehlbauer, A. Muiznieks, J. Virbulis. Analysis of the dopant segregation effects at the floating zone growth of large silicon crystals. J Cryst Growth 750 372, 1997. 

Elements dissolved in boron influence its crystal structure. Dissolved impurities also influenee the physical and chemical properties of boron, especially the electrical properties, because boron is a semiconductor. Preparation of solid solutions in jS-rh boron requires a careful choice of crucible material. To avoid contamination, boron nitride or a cold, coinage-metal crucible should be used or the levitation or floating-zone melting techniques applied. 

Crystal Growth of Borides 6.7.4.2. Liquid-Phase Methods B.7.4.2.2. Floating-Zone Technique. 

The vertical method shown above has sometimes been called the "floating zone" method. The thickness of polycrystalline rod determines the... 

The nature of the nucleation site as well as the kinetics of formation and dissociation of the H-induced and stabilized platelets have yet to be experimentally studied in detail. However, their generation in float-zone (Johnson and Herring, 1988b) as well as Czochralski-grown (Fig. 8) silicon argues against the involvement of oxygen or carbon in platelet nucleation. 

Floating, coating film defect, 7 122-123 Floating-roof tanks, 24 289-292 Floating solids, entrainment of, 16 694-696 Floating zone technique, fabrication... 

Float zone crystal growth, silicon purification via, 22 496 Float zone refining, of silicon, 22 492-493 Flocculant addition point, 11 639 Flocculant chemistry, selection of, 11 638 Flocculants, 8 709-710 16 659. See also Flocculating agents dispersants contrasted, 8 687 organic, 11 627-631... 

Melting properties, of fats, 10 827 Melting (floating zone) technique, fabrication method for inorganic materials, 7 415t... 

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