Other Research Interests
Introduction:
There is other ongoing work in the laboratory besides that listed as separate
headings.
One project is designed to examine the question of how much 4He might be take up by the C60 matrix. Earlier work with third sound and quartz crystal microbalances here concluded that the data was consistent with no 4He entering the C60 matrix for 4He added to a film of C60 at low temperatures [1,2]. The Kosterlitz-Thouless transition was observed to behave normally for 4He on the C60 surface, and third sound propagated normally on the C60 with the surface appearing to have an index of refraction for third sound about the same as smooth glass microscope slides. Work with quartz crystal microbalances is consistent with our earlier work and concludes that no more than 0.06 4He atom per C60 molecule enters the C60 matrix for dosing done at T = 1.68 K. Recent investigations have involved single-wall carbon nanotubes arranged in bundles, and have been directed at the adsorption behavior of helium in such bundles. For nanotubes that have not had their caps removed, it appears that the adsorption talks place in the interstitials between the tubes and does so with a rather high binding energy[3].
Another project (which has recently concluded) involved non-linear IV measurements of polycrystalline YBCO high temperature superconductors [4-10]. Studies were concerned with the effect of grain size on the exponents. Measurements were taken at selected fixed temperatures, as a function of current in various values of the magnetic field.
References:
1. K.S. Ketola, S. Wang, A.F. Hebard, and R.B. Hallock, J. Low Temp. Phys. 89, 609 (1992).
2. K.S. Ketola, S. Wang, A.F. Hebard, and R.B. Hallock, Physica B 194-196, 651 (1994).
3. W. Teizer, R.B. Hallock, E. Dujardin and T. W. Ebbesen), Phys. Rev. Letters 82, 5305 (1999); Erratum: 84, 1844 (2000).
4. W.M. Tiernan, J.M. Madsen, J.C.W. Chien, B.M. Gong, Y.S. Yang and R.B. Hallock, Physica C 165, 279 (1990).
5. W.M. Tiernan and R.B. Hallock, Phys. Rev. B 43, 10508 (1991).
6. W.M. Tiernan and R.B. Hallock, Phys. Rev. B 44, 4661 (1991).
7. W.M. Tiernan and R.B. Hallock, Phys. Rev. B 46 3688 (1992).
8. W.M. Tiernan, R. Joshi and R.B. Hallock, Phys. Rev. B 48, 3423 (1993).
9. W.M. Tiernan and R.B. Hallock, Phys. Rev. B 49, 9168 (1994).
10. R.J. Joshi, R.B. Hallock, and J.A. Taylor, Phys. Rev. B 55, 9107 (1997).