A methodology to optimize the quantification of sp2 carbon fraction from K edge EELS spectra

Bernier, Nicolas; Bocquet, François C.; Allouche, A.; Saikaly, W.; Brosset, C.; Thibault, J.; Charaı̈, A.

doi:10.1016/j.elspec.2008.04.006

Cited by 46 publications

(33 citation statements)

References 34 publications

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“…The method used in this work for the determination of R is illustrated in Fig. 1 and took inspiration from the work of Bernier et al [60] in which the π * peak is modeled by using a sum of Gaussian functions of equal standard deviation and separated by 0.5 eV. Only three unknown parameters are required for this fit, the amplitude of all the Gaussian functions being constrained to match the decrease of π * contribution in the density of states of graphite.…”

Section: Eels Acquisition and Data Treatmentmentioning

confidence: 99%

“…This method has also been applied successfully to amorphous carbon with various sp 2 ratios [60]. The fit was performed between 284 and 286 eV in order to reproduce precisely the shape of the π * peak and the modeled function was then extended toward lower and higher energies.…”

Section: Eels Acquisition and Data Treatmentmentioning

confidence: 99%

“…Titantah et al [63]: to reproduce the π * character of the graphite C-K edge which, as highlighted by ab-initio calculations [60,63], is asymmetric and go on several dozens of eV after the edge threshold and thus overlap with the σ * states. This method has also been applied successfully to amorphous carbon with various sp 2 ratios [60].…”

Section: Eels Acquisition and Data Treatmentmentioning

confidence: 99%

“…1) is observed in the graphite spectrum but not in the diamond spectrum, the transitions to σ * states appearing at higher energy (around 292 eV) [48,56]. Beyond this qualitative description, the sp 2 fraction can also be determined from thorough analysis of the C-K edge [57][58][59][60]. However, the determination of the sp 2 fraction of carbon-based materials from core-loss EELS is not an easy task and two main pitfalls should be avoided.…”

Section: Introductionmentioning

confidence: 99%

“…the determination of the R ratio) and the second one concerns the structural and electronic anisotropy of these sp 2 carbon materials. Regarding this first limitation, most of the models in the literature use an improper combination of Gaussian and/or Lorentzian functions [61,62], whereas ab-initio calculations have shown that the π * component is asymmetric and spreads out several dozens of eV after the edge threshold [60,63]. As a direct consequence, models using a combination of Gaussian and/or Lorentzian functions need to add another artificial component to compensate the real asymmetry of the π * character [61,62,64].…”

Section: Introductionmentioning

confidence: 99%

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Advanced spectroscopic analyses on a:C-H materials: Revisiting the EELS characterization and its coupling with multi-wavelength Raman spectroscopy

Lajaunie

Pardanaud

Martin

et al. 2017

Carbon

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Hydrogenated amorphous carbon thin films (a:C-H) are very promising materials for numerous applications. The growing of relevance of a:C-H is mainly due to the long-term stability of their outstanding properties. For improving their performances, a full understanding of their local chemistry is highly required. Fifteen years ago, electron energy-loss spectroscopy (EELS), developed in a transmission electron microscope (TEM), was the technique of choice to extract such kind of quantitative information on these materials. Other optical techniques, as Raman spectroscopy, are now clearly favored by the scientific community. However, they still lack of 2 the spatial resolution offered by TEM-EELS. In addition, nowadays, the complexity of the physics phenomena behind EELS is better known. Here, a:C-H thin films have been isothermally annealed and the evolution of their physical and chemical parameters have been monitored at the local and macroscopic scales. In particular, chemical in-depth inhomogeneities and their origins are highlighted. Furthermore, a novel procedure to extract properly and reliably quantitative chemical information from EEL spectra is presented. Finally, the pertinence of empirical models used by the Raman community is discussed. These works demonstrate the pertinence of the combination of local and macroscopic analyses for a proper study of such complex materials.

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Section: Eels Acquisition and Data Treatmentmentioning

confidence: 99%

Section: Eels Acquisition and Data Treatmentmentioning

confidence: 99%

Section: Eels Acquisition and Data Treatmentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Advanced spectroscopic analyses on a:C-H materials: Revisiting the EELS characterization and its coupling with multi-wavelength Raman spectroscopy

Lajaunie

Pardanaud

Martin

et al. 2017

Carbon

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Revisiting the EELS analyses and its coupling with multi‐wavelength Raman spectroscopy: the case of hydrogenated amorphous carbon thin films

Lajaunie

Pardanaud

Martin

et al. 2016

European Microscopy Congress 2016: Proceedings

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Thanks to the long‐term stability of their properties, hydrogenated amorphous carbon (a:C‐H) thin films are very promising materials for numerous applications including coatings for spatial applications. 1 In order to improve their performances, a full understanding of their local chemistry is highly required. Fifteen years ago, according to the seminal work of Ferrari et al. , 2 EELS was the most used technique to get such kind of quantitative information on these materials. Nowadays the complexity of the physics phenomena behind EELS is well known 3 and this technique is regarded as time‐consuming and difficult to interpret properly. Other optical techniques such as Raman spectroscopy are now clearly favored by the scientific community. However they still lack of the spatial resolution that EELS in a STEM offers for getting direct chemical information. a‐C:H thin films, with a thickness around 300 nm, were deposited on a Si wafer and submitted to isothermal annealing at 500°C with different annealing times up to 2500 minutes. The hydrogen content was monitored by multi‐wavelength (MW) Raman using a set of reference materials. To determine the sp 2 fraction (sp 2 %) from core‐loss EELS, the R ratio ( R = I π*(ΔE) /I( π*(ΔE) + σ*(ΔE) ) was determined first by taking into account the asymmetry of the π* character ( Fig. 1a ). 4,5 This value was then normalized by the maximum R value (R REF ) that could be obtained from a HOPG sample in the same experimental condition using relativistic calculations ( Fig. 1b ). 6 When needed, this method was also slightly modified to take into account the contribution of heterospecies. In addition, the mass density and the oxygen content was derived from low‐loss and core‐loss spectra, respectively. The EELS C‐K edge spectra ( Fig. 2a) present all a typical signature of amorphous carbons. However, the intensity of the massif above 292 eV differs from sample to sample and clearly highlights a slight variation of the sp 2 %. The samples annealed 2500 min also presents a supplementary peak (red arrow in Fig. 2a ), which is related to the oxidation of the thin film. As expected, the sp 2 % increases with the annealing time ( Fig. 2b ). This effect is related to the H desorption of the thin films as monitored by Raman spectroscopy. Two samples do not follow this trend: the as‐deposited sample and the sample annealed 2500 minutes. This latter presents a strong oxidation, leading to a decrease of the sp 2 %. On the other hand, the as‐deposited sample shows variation of the C‐K edge fine structures ( Fig. 3a ) highlighting chemical inhomogneities in the thin film. This sample presents a strong gradient of the sp 2 % induced by the deposition process ( Fig. 3b ) which is cured with the annealing time. All these results will be detailed together with the influence of the oxidation on the chemical and physical properties. In addition, the coupling of MW Raman, infrared and EELS spectroscopies to extract a wealth of chemical information will be discussed. Our results provide a complete combination of C‐hybridization, spatial elemental analyses and structural defects studies for shedding light on these complex materials. 7,8

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Ultrastiff, Strong, and Highly Thermally Conductive Crystalline Graphitic Films with Mixed Stacking Order

et al. 2019

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A macroscopic film (2.5 cm × 2.5 cm) made by layer‐by‐layer assembly of 100 single‐layer polycrystalline graphene films is reported. The graphene layers are transferred and stacked one by one using a wet process that leads to layer defects and interstitial contamination. Heat‐treatment of the sample up to 2800 °C results in the removal of interstitial contaminants and the healing of graphene layer defects. The resulting stacked graphene sample is a freestanding film with near‐perfect in‐plane crystallinity but a mixed stacking order through the thickness, which separates it from all existing carbon materials. Macroscale tensile tests yields maximum values of 62 GPa for the Young's modulus and 0.70 GPa for the fracture strength, significantly higher than has been reported for any other macroscale carbon films; microscale tensile tests yield maximum values of 290 GPa for the Young's modulus and 5.8 GPa for the fracture strength. The measured in‐plane thermal conductivity is exceptionally high, 2292 ± 159 W m−1 K−1 while in‐plane electrical conductivity is 2.2 × 105 S m−1. The high performance of these films is attributed to the combination of the high in‐plane crystalline order and unique stacking configuration through the thickness.

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A methodology to optimize the quantification of sp2 carbon fraction from K edge EELS spectra

Cited by 46 publications

References 34 publications

Advanced spectroscopic analyses on a:C-H materials: Revisiting the EELS characterization and its coupling with multi-wavelength Raman spectroscopy

Advanced spectroscopic analyses on a:C-H materials: Revisiting the EELS characterization and its coupling with multi-wavelength Raman spectroscopy

Revisiting the EELS analyses and its coupling with multi‐wavelength Raman spectroscopy: the case of hydrogenated amorphous carbon thin films

Ultrastiff, Strong, and Highly Thermally Conductive Crystalline Graphitic Films with Mixed Stacking Order

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