th  - 1988 - 51st ENC Conference

I THU 11 : 05 I
DYNAMIC NUCLEAR POLARIZATION: A METHOD FOR SURFACE-SELECTIVE NMR
G. G. Maresch, R. D. Kendrick, and C. S. Yannoni*
IBM Research Division, Almaden Research Center, San Jose, California
and
M. E. Galvin
AT&T Bell Laboratories, Murray Hill, New Jersey
Dynamic Nuclear Polarization (DNP) holds promise as a method for the study of molecules
at the surface of materials which contain unpaired electrons. The idea in the kind of
experiments that will be described here is to use bulk samples, but to selectively polarize
nuclei in molecules that sit on the Internal surfaces of "islands" of electron-rich material
that has been dispersed in the bulk. Selectivity is achieved via the short range of the
electron-nuclear coupling. The bulk material may be an organic or inorganic solid or
polymer (e.g. polyethylene), while the electrons may be localized in metal clusters or
small islands of a semiconductor like polyacetylene. The requirement of confining the
dynamic polarization of even rare nuclei like 13C to the surface of the electron-rich islands
poses a challenge and our efforts to do this have resulted in the confirmation of a
"three-spin" effect. Although related observations have been made in DNP studies of
dilute solutions of free radicals 1, the three-spin effect discussed here arises from a
number of dynamical processes peculiar to the static configuration of the three spins
(electron, proton and carbon in this case) in solids.
. R. E. Richards and J. W. White, Disc. Faraday Soc. 3._44, 96 (1962);
K. H. Hausser and F. Reinbold, Phys. Lett. 2 , 53 (1962).
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