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5765.
Multiple Quantum Nuclear Magnetic Resonance as a Probe for the Dlmensionality of Hydrogen in Polycrystalline Powders and Diamond Films
'I;
D.H.Levy and K. K.Gleason* Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (Received: March 31, 1992; In Final Form: June 9, 1992)
Hydrogen distributions in various solid systems were studied by multiple quantum (MQ) nuclear magnetic resonance (NMR). The rate of growth of MQ coherences for bulk, infinite, three-dimensional hydrogen lattice found in materials such as calcium hydride, sodium bicarbonate, and adamantane followed a universal growth curve when the time axis was scaled by a the square root of the second moment (M2'/*), while three chemically vapor deposited diamond films and a natural diamond powder sample showed a noted departure from this universal growth curve. The natural diamond powder shows MQ growth consistent with an infinite spin system yet at a slower growth rate than that observed for the bulk systems. This phenomenon is interpreted with a model for MQ coherence growth which takes into account differences arising from surface versus bulk hydrogen distributions. Strong similarities in the NMR line shape, spin-lattice relaxation, and the MQ dynamics between the diamond powder and the diamond films were also observed. These indicate a nonbulk distribution of hydrogen in the polycrystalline films, possibly indicating that hydrogen exists at surfaces between individual crystallites.
Introduction Multiple quantum (MQ) nuclear magnetic resonance (NMR) has been used to study proton distributions in liquid crystals,' simple organic systems: amorphous hydrogenated silicon3and silicon carbide? and fluorine distributions in salts5 and photosensitive polymer mixtures.6 The growth of MQ coherences in solids has recently been reviewed.' While MQ NMR has been used to determine the size of small (
