A Technique for Growing Helium Crystals in Preferred Orientations

An apparatus has been developed in which hcp 4He single crystals of high quality are grown with a 0.3 probability of obtaining c-axis orientations of 0 or 90 deg with respect to the direction of growth. Methods of influencing the relative distribution of crystals between these two angles have been o...

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Bibliographic Details
Main Author: Lawson,D. T
Format: Report
Language:English
Subjects:
CRYOGENICS
CRYSTAL GROWTH
Crystallography
FREEZING
HELIUM
HELIUM 4
HEXAGONAL CLOSE PACKED CRYSTAL LATTICES
NUCLEATION
SINGLE CRYSTALS
Solid State Physics
SOLIDIFIED GASES
THERMAL CONDUCTIVITY
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Summary:An apparatus has been developed in which hcp 4He single crystals of high quality are grown with a 0.3 probability of obtaining c-axis orientations of 0 or 90 deg with respect to the direction of growth. Methods of influencing the relative distribution of crystals between these two angles have been observed and are believed to depend on the anisotropy in the thermal conductivity of hcp 4He. A simple computer simulation of the nucleation process supports our identification of the orientation angles and our explanation of the observed orientation preferences. Some possible applications of similar techniques were surveyed. (Author)