Thermal stability and rehybridization of carbon bonding in tetrahedral amorphous carbon

D. S. Grierson, A. V. Sumant, A. R. Konicek, T. A. Friedmann, J. P. Sullivan, R. W. Carpick
2010 Journal of Applied Physics  
We preform a quantitative investigation of the energetics of thermally induced sp 3 → sp 2 conversion of carboncarbon bonds in tetrahedral amorphous carbon (ta-C) films by using near edge x-ray absorption fine structure (NEXAFS) and Raman spectroscopy. We investigate the evolution of the bonding configuration in ta-C thin films subjected to high temperature annealing in flowing Argon gas using a rapid thermal annealing furnace over the range of 200-1000 ºC. We observe no substantial change in
more » ... nding structure below 600 ºC, and by 1000 ºC a significant increase in the sp 2 bonding in the film is observed. No oxygen bonding is detected in the NEXAFS spectra, but we do observe an isosbestic point, demonstrating that the thermally driven sp 3 → sp 2 conversion reaction occurs without passing through an intermediate transition state. This allows us to use NEAFS spectra of thermally annealed ta-C films to quantitatively determine that the activation energy for directly converting the sp 3 -bonded carbon to the sp Disciplines Engineering | Mechanical Engineering Comments Suggested Citation: We perform a quantitative investigation of the energetics of thermally induced sp 3 → sp 2 conversion of carbon-carbon bonds in tetrahedral amorphous carbon ͑ta-C͒ films by using near-edge x-ray absorption fine structure ͑NEXAFS͒ and Raman spectroscopy. We investigate the evolution of the bonding configuration in ta-C thin films subjected to high temperature annealing in flowing Argon gas using a rapid thermal annealing furnace over the range of 200-1000°C. We observe no substantial change in bonding structure below 600°C. Changes in the NEXAFS and Raman spectra start to appear above 600°C, and by 1000°C a significant increase in the sp 2 bonding in the film is observed. No oxygen bonding is detected in the NEXAFS spectra, but we do observe an isosbestic point, demonstrating that the thermally driven sp 3 → sp 2 conversion reaction occurs without passing through an intermediate transition state. This allows us to use NEXAFS spectra of thermally annealed ta-C films to quantitatively determine that the activation energy for directly converting the sp 3 -bonded carbon to the sp 2 -bonded configuration is 3.5Ϯ 0.9 eV. Downloaded 13 Oct 2010 to 130.91.117.41. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 033523-2 Grierson et al. J. Appl. Phys. 107, 033523 ͑2010͒ Downloaded 13 Oct 2010 to 130.91.117.41. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions
doi:10.1063/1.3284087 fatcat:xnewhib4pfcitgevb5xnvrzrxm