STRUCTURE OF THIN DIAMOND FILMS - A H-1 AND C-13 NMR-STUDY

The H-1 and C-13 nuclear magnetic resonance (NMR) of thin diamond films deposited from naturally abundant (1.1 at. %) as well as 50% and 100% C-13-enriched CH4 heavily diluted in H-2 is described and discussed. Less than 0.6 at. % of hydrogen is found in the films which contain crystallites up to approximately 15 mum across. The H-1 NMR consists of a broad 50-65-kHz-wide Gaussian line attributed to H atoms bonded to carbon and covering the crystallite surfaces. A narrow Lorentzian line was only occasionally observed and is found not to be intrinsic to the diamond structure. The C-13 NMR demonstrates that >99.5% of the C atoms reside in a quaternary diamondlike configuration. H-1-C-13 cross-polarization measurement indicates that, at the very least, the majority of C-13 nuclei cross polarized by H-1, i.e., within three bond distances from a H-1 at a crystallite surface, reside in sp3 diamondlike coordinated sites. The C-13 relaxation rates of the films are four orders of magnitude faster than that of natural diamond and believed to be due to C-13 spin diffusion to paramagnetic centers, presumably carbon dangling bonds. Analysis of the measured relaxation rates indicates that within the C-13 spin-diffusion length of square-root/DT1c approximately 0.05 mum, these centers are uniformly distributed in the diamond crystallites. The possibility that the dangling bonds are located at internal nanovoid surfaces is discussed.