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The Optical Floating
Zone Unit uses ellipsoidal mirrors to focus the radiation to generate
the temperatures necessary to melt the various materials of the
feed and seed rods. The shells are gold plated, and they are elliptical
in shape so that light rays generated from the halogen lamps on
the ends of the shells are reflected to a focal point, which is
then referred to as the "hot zone" which is ~1 cm in diameter.
The stainless steel rods
that support the feed and seed rods rotate opposite each other thereby
causing a shearing action to occur as the feed and the seed rods
are joined and also during the duration of the growth. This counter-rotation
generates convective flow to transport heat throughout the molten
zone.
During the growth, the
stainless steel rods both move down through the stationary hot-zone
at a rate specified by the operator. The rate is usually very slow
and is measured in millimeters per hour. This process melts the
material from the feed-rod and solidifies it on the growing seed
crystal.
The Optical Floating
Zone units have lamps ranging in power from .75 kW to 4.0 kW. The
principles are the same for the Xenon Optical Floating Zone Unit,
but the unit itself consists of only one "shell," and the light
is generated by Xenon Lamp which is usually higher in power (6.5
kW).
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