Neutron Scattering Group
Crystal Growth
The expertise of our crystal growth lab is to synthesize large single
crystals for neutron scattering experiments. The technique we are using is
the so called Traveling-Solvent Floating-Zone (TSFZ) method. The major
advantage of this technique is that crystals can be grown without getting
into touch with other materials, such as crucibles, which eliminates a major
source for contaminations. Currently our lab is operating two image furnaces
from NEC. With our latest model crystals with high melting point as well as
a large length can be grown. The latter is particularly important in the
case of incongruent melting systems, where large deviations between the
nominal composition and that of the grown crystal are observed in the
beginning of the growth experiment.
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| Genda growing a crystal |
Optical elements |
Schematic of optics |
Both image furnaces are equipped with two elliptic mirrors (see figure). As
a heat source halogen lamps are installed in the mirrors outer focus. Their
light is reflected into the inner focus, which for both mirrors coincides
with the location of the melt. The melt is situated between the
polycrystalline feed rod (upper shaft) and the grown material (lower shaft),
and hold in place by surface tension, only. Feed rod and grown crystal spin
in opposite directions to guarantee a homogenous melt as well as a
homogenous temperature distribution in the melt. Crystal growth is initiated
by a slow downward translation of the feed rod and the lower shaft, which
effectively corresponds to a melt traveling along the feed rod. The
optimum/maximum growth speed depends on the material and varies between a
few tenth of a millimeter and several centimeters per hour. The diameter of
the crystal is controlled by the ratio of the translation velocity for the
feed rod and the lower shaft. Feed rod, melt and crystal are located within
a sealed quartz tube, which allows performing crystal growth in different
atmospheres.
Watch a movie of a crystal growth. (.wmv
format ~1Mb) or (.mpg
format ~5Mb)
Last Modified: Wednesday, 24-Nov-2004 16:26:00 EST
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