Thermal stability and rehybridization of carbon bonding in tetrahedral amorphous carbon

Abstract

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 bonding 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 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.

Influence of surface passivation on the friction and wear behavior of ultrananocrystalline diamond and tetrahedral amorphous carbon thin films

“…13,33,43 This shift is well within the energy resolution of our NEXAFS spectroscopy. None of the spectra from any of the wear tracks show a shift in the C 1s π* transition, indicating there is no detectible graphite.…”

“…32 The annealing causes a restructuring of the film that relieves stress without significantly changing the bonding hybridization. 33 UNCD was deposited at Argonne National Laboratory using a 2. 34 These films were 1-2 μm thick.…”

Repressing oxidative wear within Si doped DLCs

“…This observed change in the mechanical properties could be, perhaps, mediated by a localised change in the sp 2 /sp 3 ratio within the coating. This has been noted in other DLCs but typically with thermal annealing in place of mechanical agitation (34). It is also possible and has been shown previously that the nano hardness values of DLC coatings (as measured by nano indentation) can and do vary with the indentation depth employed.…”

Quantitative Evaluation of the Carbon Hybridization State by Near Edge X-ray Absorption Fine Structure Spectroscopy

“…hybridization state of carbon atoms in the near-surface region of carbon-based materials, such as diamond [45][46][47][48][49] , amorphous carbon 14,29,[50][51][52] , graphene 53,54 , and polymers [55][56][57] . The dependence of the intensity of the detected spectral features on the orientation of the final state orbital with respect to the electric field vector of the incident photon beam 58 also allows the surface molecular orientation of nanomaterials [59][60][61] and adsorbates 62 to be investigated.…”