Multifrequency EPR,1HENDOR, and saturation recovery of paramagnetic defects in diamond films grown by chemical vapor deposition

Paramagnetic defects in free-standing polycrystalline chemical vapor deposition (CVD) diamond films have been studied using multifrequency electron paramagnetic resonance (EPR) (1–35 GHz), electron-nuclear double resonance (ENDOR), saturation recovery, and infrared absorption. The results confirm the ${}^1$H hyperfine parameters for the recently identified H1 defect [Zhou et al., Phys. Rev. B 54, 7881 (1996)]. However, in the CVD diamond samples studied here, H1 is always accompanied by another defect at $g=2.0028\mathrm{}\left(1\right)\mathrm{}$. Saturation recovery measurements are consistent with two defects centered on $g=2.0028\mathrm{}$. At temperatures below 100 K the spin-lattice relaxation rate of H1 is determined by the direct process and is a factor of 10–100 times more rapid than the single substitutional nitrogen center, which is known to be incorporated into the bulk diamond. ${}^1$H matrix ENDOR measurements indicate that the H1 center is in an environment with hydrogen atoms 0.2–1.0 nm from the center. The near-neighbor hydrogen identified by multifrequency EPR was not detected in the ENDOR experiments. The concentration of H1 correlates with the total integrated CH stretch infrared absorption in the samples studied here. All the evidence is consistent with H1 being located at hydrogen decorated grain boundaries (or in intergranular material) rather than in the bulk diamond. A third EPR resonance at $g=2.0028\mathrm{}\left(1\right)\mathrm{}$ has been observed in some of the CVD diamond samples studied. The resonance is distinguished by its temperature-dependent linewidth: above 50 K the line is exchange narrowed, but below 50 K it broadens rapidly with decreasing temperature.