Page 254 - Chalcogenide Glasses for Infrared Optics

AMI Infrar ed Crystalline Materials 229

Single-crystal fibers had been drawn from sapphire using a carbon
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dioxide laser as a heat source. The results were encouraging. At
about the same time, AMI had been working to produce flexible
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single-crystal silicon fibers using the float zone technology. The
feed crystal was reduced to an 8-mm diameter, the seed diameter
was reduced to 2 to 4 mm, and the RF coil reduced to a single turn
with a 1.5-cm ID. Linear growth rate was increased and top or bottom
spin reduced or eliminated. Single-crystal rods were grown 1 to
2 mm in diameter and 30 to 40 cm long. The sides were irregular due
to spin or facet formation. Figure 9.13 shows, in the top photograph,
typical small-diameter single-crystal silicon rods. A pencil is included
in the photo for comparison. The lower photograph shows a rod
being grown from the top of a feed crystal.
Besides being grown with the seed in the <111>, the <100> and
<110> orientations were tried in hopes of eliminating the facet effect
so the surfaces would be smooth. None seemed better than the other.

FIGURE 9.13 Small-diameter single-crystal silicon rods and rod growth in
process.