In:
ECS Transactions, The Electrochemical Society, Vol. 16, No. 6 ( 2008-10-03), p. 351-356
Abstract:
The naturally based redefinition of the kg unit being aimed by the Avogadro project ultimately requires a precise 1kg-sphere of mono isotopic silicon with practically perfect crystallinity. Silicon isotopes (28, 29, 30) can be effectively separated by the ultra-centrifugation technique. A large amount (ca.10kg) of gaseous 28SiF4 was extraordinarily highly enriched up to 99.996% using ca. 240 specially interconnected centrifuges over 6 months. Then, 28SiF4 was transformed to 28SiH4 and purified by cryo distillation. Polycrystalline 28Si was pyrolytically deposited to a cylindrical 6kg rod. After multiple FZ-purification, a dislocation-free 28Si FZ crystal of 4,5 kg mass was grown, just enough for two 1kg spheres and auxiliary samples. The enrichment was still 99,994%. Similarly, small (10-20g) 29Si and 30Si crystals were prepared for basic research needs. Si28 enables dramatic line narrowing improving deep and shallow defect spectroscopy. Under magnetic field, electronic and nuclear spins embedded in a zero-spin 28Si matrix could be individually determined.
Type of Medium:
Online Resource
ISSN:
1938-5862
,
1938-6737
Language:
Unknown
Publisher:
The Electrochemical Society
Publication Date:
2008
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