A STUDY OF C-13-ENRICHED CHEMICAL-VAPOR-DEPOSITED DIAMOND FILM BY MEANS OF C-13 NUCLEAR-MAGNETIC-RESONANCE, ELECTRON-PARAMAGNETIC-RESONANCE, AND DYNAMIC NUCLEAR-POLARIZATION

C-13 nuclear magnetic resonance (NMR), with and without dynamic nuclear polarization (DNP), and electron paramagnetic resonance (EPR) measurements are presented on two C-13-enriched chemical vapor deposited (CVD) diamond films. The samples were prepared by the decomposition in a microwave discharge of a gas mixture of CH4 and H-2, with and without O2. C-13 NMR spectra, obtained with or without magic-angle spinning (MAS) both at a field of 14 T using direct polarization (DP) and at 3.5 T via cross polarization (CP), are presented. Because the samples contain both nuclear and (unpaired) electron spins, irradiation of the sample with microwaves with a frequency at or near the electron Larmor frequency leads to an enhancement of the nuclear spin polarization via the effect referred to as dynamic nuclear polarization (DNP). This enhancement (at a field of 1.4 T), combined with the effects of isotopic enrichment (14% C-13), makes it possible to measure C-13 DNP-CP-MAS spectra within a couple of hours, compared to almost 20 h for the CP-MAS spectra taken at high field without DNP. Data based on DNP-CP-MAS experiments with variable CP-match time or dipolar-dephasing time are shown and discussed in terms of structural models. The cross-polarization signals are rationalized in terms of estimates of the chemical shifts of hydrogenated diamond surfaces; this approach indicates that most of the hydrogens in the polycrystalline sample are at the intergrain boundaries.