NATURAL-ABUNDANCE C-13 DYNAMIC NUCLEAR-POLARIZATION EXPERIMENTS ON CHEMICAL VAPOR-DEPOSITED DIAMOND FILM

C-13 cross-polarization (CP) and direct-polarization (DP) spectra of an 83 mg sample of a chemical vapor deposited (CVD) diamond film (combined from 12 separate depositions) have been obtained via dynamic nuclear polarization (DNP) combined with magic-angle spinning (MAS). With DNP, the presence of unpaired electron spins in the sample, measured to be 2 X 10(18) spins/g, provides a way to enhance the C-13 or the "residual" H-1 signal by irradiating the sample with microwaves at or near the electron spin resonance (ESR) Larmor frequency; the interactions between the unpaired electrons and protons or C-13 spins lead to a transfer of polarization from the electron spin system to the H-1 and/or C-13 spin systems. No signal for sp2 hybridized carbons could be observed. The DNP-CP-MAS spectrum, obtained in an experiment in which the DNP-enhanced proton polarization is in tum transferred via CP to the C-13 spin system, differs significantly from the DNP-DP-MAS spectrum, in which the C-13 spins are directly enhanced.