Structural studies of argon-sputtered amorphous carbon films by means of extended x-ray-absorption fine structure

Comelli, Giovanni; Stöhr, J.; Robinson, C. Jane; Jark, W.

doi:10.1103/physrevb.38.7511

Cited by 197 publications

(148 citation statements)

References 29 publications

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“…These are all typical features of amorphous carbon films. 23 For the annealed films, there is little change in the spectra until the annealing temperature exceeds 600°C, above which the C 1s → ‫ء‬ peak grows in both intensity and width, and shifts to a higher energy. At 800°C the increase in the C 1s→ ‫ء‬ peak is accompanied by a lowering of the intensity of the broader C 1s → ‫ء‬ hump at the lower energies ͑ϳ290 eV͒.…”

Section: Resultsmentioning

confidence: 99%

Thermal stability and rehybridization of carbon bonding in tetrahedral amorphous carbon

Grierson¹,

Sumant²,

Konicek

et al. 2010

Journal of Applied Physics

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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.

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Section: Resultsmentioning

confidence: 99%

Thermal stability and rehybridization of carbon bonding in tetrahedral amorphous carbon

Grierson¹,

Sumant²,

Konicek

et al. 2010

Journal of Applied Physics

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“…The intensity of this peak directly correlates with the fraction of sp 2 -bonded carbon in the near surface region. For a-C:H films, the NEXAFS spectra are characterized by a broad hump between 288 and 305 eV (which is due to the C1s→σ * transition for disordered carbon-carbon bonds 1,42,76 ), whereas the spectrum of UNCD exhibits sharper C1s→σ * transitions that are characteristic of ordered sp 3 -hybridized carbon-carbon bonds, namely the edge jump at ~289 eV, the exciton peak at ~289.3 eV, and the second band gap at 303 eV 13 . The presence of significant amounts of hydrogen in a-C:H films and the hydrogen-termination of UNCD also resulted in the detection of a shoulder at ~287.0 eV (for a-C:H) and ~287.5 eV (for UNCD), which can be assigned to the C1s→σ * transition for C-H bonds 1 .…”

Section: Resultsmentioning

confidence: 99%

Accounting for Nanometer-Thick Adventitious Carbon Contamination in X-ray Absorption Spectra of Carbon-Based Materials

et al. 2014

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Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy is a powerful technique for characterizing the composition and bonding state of nanoscale materials and the top few nanometers of bulk and thin film specimens. When coupled with imaging methods like photoemission electron microscopy, it enables chemical imaging of materials with nanometerscale lateral spatial resolution. However, analysis of NEXAFS spectra is often performed under the assumption of structural and compositional homogeneity within the nanometer-scale depth probed by this technique. This assumption can introduce large errors when analyzing the vast majority of solid surfaces due to the presence of complex surface and near-surface structures such as oxides and contamination layers. An analytical methodology is presented for removing the contribution of these nanoscale overlayers from NEXAFS spectra of two-layered systems to provide a corrected photo-absorption spectrum of the substrate. This method relies on the subtraction of the NEXAFS spectrum of the overlayer adsorbed on a reference surface from the spectrum of the two-layer system under investigation, where the thickness of the overlayer is independently determined by X-ray photoelectron spectroscopy (XPS). This approach is applied to NEXAFS data acquired for one of the most challenging cases: air-exposed hard carbon-based materials with adventitious carbon contamination from ambient exposure. The contribution of the adventitious carbon was removed from the as-acquired spectra of ultrananocrystalline diamond (UNCD) and hydrogenated amorphous carbon (a-C:H) to determine the intrinsic photoabsorption NEXAFS spectra of these materials. The method alters the calculated fraction of sp 2 -hybridized carbon from 5 to 20%, and reveals that the adventitious contamination can be

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“…When recorded as a function of the photon excitation energy, exciting from the C͑1s͒ core level, it has been shown to be a powerful probe of the diamond electronic structure. [43][44][45][46] Unlike Raman spectroscopy, NEXAFS has a similar cross section for different carbon allotropes and it is sensitive to local chemical bonding, which enables analysis of nanosized carbon materials. 47,48 …”

Section: Introductionmentioning

confidence: 99%

Bulk and surface thermal stability of ultra nanocrystalline diamond films with 10–30 nm grain size prepared by chemical vapor deposition

Michaelson

Stacey

Orwa

et al. 2010

Journal of Applied Physics

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The thermal stability of nanocrystalline diamond films with 10–30 nm grain size deposited by microwave enhanced chemical vapor deposition on silicon substrate was investigated as a function of annealing temperature up to 1200 °C. The thermal stability of the surface-upper atomic layers was studied with near edge x-ray absorption fine structure (NEXAFS) spectroscopy recorded in the partial electron yield mode. This technique indicated substantial thermally induced graphitization of the film within a close proximity to the surface. While in the bulk region of the film no graphitization was observed with either Raman spectroscopy or NEXAFS spectroscopy recorded in total electron yield mode, even after annealing to 1200 °C. Raman spectroscopy did detect the complete disappearance of transpolyacetylene (t-PA)-like ν1 and ν3 modes following annealing at 1000 °C. Secondary ion mass spectroscopy, applied to investigate this relative decrease in hydrogen atom concentration detected only a ∼30% decrease in the bulk content of hydrogen atoms. This enhanced stability of sp3 hybridized atoms within the bulk region with respect to graphitization is discussed in terms of carbon bond rearrangement due to the thermal decomposition of t-PA-like fragments.

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Structural studies of argon-sputtered amorphous carbon films by means of extended x-ray-absorption fine structure

Cited by 197 publications

References 29 publications

Thermal stability and rehybridization of carbon bonding in tetrahedral amorphous carbon

Thermal stability and rehybridization of carbon bonding in tetrahedral amorphous carbon

Accounting for Nanometer-Thick Adventitious Carbon Contamination in X-ray Absorption Spectra of Carbon-Based Materials

Bulk and surface thermal stability of ultra nanocrystalline diamond films with 10–30 nm grain size prepared by chemical vapor deposition

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