On the Structure of Thin diamond Films: A 1H and 13C Nuclear Magnetic Resonance Study

ABSTRACTThe 1H and 13C nuclear magnetic resonance (NMR) of thin diamond films deposited from naturally abundant (1.1 at.%) as well as 50% and 100% 13C-enriched CH4 heavily diluted in H2is described and discussed. Less than 0.6 at.% of hydrogen is found in the films which contain crystallites up to ∼15 μm across. The 1H 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 found not to be intrinsic to the diamonds. The 13C NMR demonstrates that >99.5% of the C atoms reside in a quaternary diamond-like configuration. The 13C spin-lattice relaxation times T1 are four orders of magnitude shorter than in natural diamond and believed to be due to 13C spin diffusion to paramagnetic centers, presumably carbon dangling bonds. Analysis of T1 indicates that within the 13C spin diffusion length of ∼0.05 μm these centers are uniformly distributed in the diamond crystallites, possibly concentrated on the internal surfaces of a relatively dense system of nanovoids.