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Low temperature annealing in tetrahedral amorphous carbon thin films observed by 13 C NMR spectroscopy

2003; American Physical Society; Volume: 67; Issue: 24 Linguagem: Inglês

10.1103/physrevb.67.245309

1095-3795

Todd M. Alam, T. A. Friedmann, Peter A. Schultz, Daniel Sebastiani,

Advanced NMR Techniques and Applications

For the first time to our knowledge, the ${}^{13}\mathrm{C}$ solid-state magic angle spinning (MAS) NMR spectrum of a 99% ${}^{13}\mathrm{C}$ enriched tetrahedral amorphous-carbon (ta-C) thin film containing a high concentration of fourfold coordinated carbon species (82%) is reported along with measured NMR spectra for the ta-C film after low temperature annealing (650 \ifmmode^\circ\else\textdegree\fi{}C). Differential changes are observed for the ${}^{13}\mathrm{C}$ MAS NMR chemical shifts and linewidths of both the fourfold (diamondlike) and threefold (graphitelike) coordinated carbon species within the thin films with increasing annealing time; however, there was no change (\ifmmode\pm\else\textpm\fi{}2%) in the relative fourfold content. These spectral changes are associated with the large compressive stress reduction (6--8 GPa) in the carbon film. Ab initio calculations of the ${}^{13}\mathrm{C}$ NMR chemical shift, along with shift variations as a function of atomic volume are reported for amorphous carbon and crystalline diamond. Using the observed spectral variations in the solid-state ${}^{13}\mathrm{C}$ MAS NMR, along with the ab initio chemical shift calculations, the effect of annealing on the ta-C films is discussed and related to current models of thermal stress relaxation in ta-C thin films.