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Theoretical Investigation of X-Ray Absorption near Edge Spectroscopy (XANES) Angular Dependence of Aligned Carbon Nanotubes Grown by DC HF CVD Process 认领 引用 被引量：1
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作者 Bridinette Thiodjio Sendja Rolant Eba Medjo +2 位作者 Jeannot Mane Mane Germain Hubert Ben-Bolie Pierre Owono Ateba 《Materials Sciences and Applications》 2015年第5期373-390,共18页
Carbon nanotubes (CNTs) grown on plain substrates SiO2/Si(100) by a direct current and hot filaments catalytic chemical vapor deposition process have been studied by synchrotron X-ray absorption near edge spectroscopy... Carbon nanotubes (CNTs) grown on plain substrates SiO2/Si(100) by a direct current and hot filaments catalytic chemical vapor deposition process have been studied by synchrotron X-ray absorption near edge spectroscopy (XANES) technique to theoretically investigate the angular-dependence of carbone (C) K-edge π* and σ* transitions. Experimental XANES spectra show that π* resonance increases with the incidence angle from normal to grazing incidence angle while σ* resonance decreases. This has been explained by the sine-square and cosine-square dependencies of π* and σ* intensities, respectively. These results were confirmed by theoretical XANES curves of highly oriented pyrolytic graphite (HOPG) and CNTs plotted versus incidence angle. It has been shown that π* and σ* transitions strongly depend on the nature of polarized light (linearly or circularly). At the linear polarized light, π* resonance is a preference as well as at right-circular polarized. At the left-circular polarized light, σ* resonance is a preference. The π* intensities are high at parallel orientation and the σ* intensities are low at normal orientation. The smallest π* intensity is noticed at normal orientation, where the π* orbitals are supposed to be lying parallel to the surface plane for perfectly aligned HOPG or CNTs. This explains the incomplete extinction of π* intensity. We noticed at parallel orientation a region where any π* and σ* transitions did not expect because of the lack of polarization light. 展开更多
关键词 Angular Dependence XANES Normal Incidence Grazing Incidence Carbon Nanotubes Intensity
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Alignment of Vertically Grown Carbon Nanostructures Studied by X-Ray Absorption Spectroscopy 认领 引用 被引量：1
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作者 Jeannot Mane Mane Francois Le Normand +9 位作者 Rolant Eba Medjo Costel Sorin Cojocaru Ovidiu Ersen Antoine Senger Carine Laffon Bridinette Thiodjio Sendja César Mbane Biouele Germain Hubert Ben-Bolie Pierre Owono Ateba Philippe Parent 《Materials Sciences and Applications》 2014年第13期966-983,共18页
X-Ray Absorption Spectroscopy (XAS) on the carbon K edge of carbon nanostructures (nanotubes, nanofibers, nanowalls) is reported here. They are grown on plain SiO2 (8 nm thick)/Si(100) substrates by a Plasma and Hot F... X-Ray Absorption Spectroscopy (XAS) on the carbon K edge of carbon nanostructures (nanotubes, nanofibers, nanowalls) is reported here. They are grown on plain SiO2 (8 nm thick)/Si(100) substrates by a Plasma and Hot Filaments-enhanced Catalytic Chemical Vapor Deposition (PE HF CCVD) process. The morphology and the nature of these carbon nanostructures are characterized by SEM, TEM and Raman spectroscopy. According to conditions of catalyst preparation and DC HF CCVD process, carbon nanotubes (CNTs), carbon nanofibers (CNFs), carbon nanowalls (CNWs), carbon nanoparticles (CNPs) with different orientation of the graphene plans or shells can be prepared. From the angular dependence of the incident light and geometrical morphology of the nanostructures, wide variations of the C K-edge intensity of the transitions to the empty π* and σ* states occur. A full lineshape analysis of the XAS spectra has been carried out using a home-made software, allowing estimating the relative proportion of π* and σ* transitions. A geometrical model of the angular dependence with the incidence angle of the light and the morphology of the carbon nanostructures is derived. With normalization to the HOPG (Highly Oriented Pyrolytic Graphite graphite) reference case, a degree of alignment can be extracted which is representative of the localized orientation of the graphitic carbon π bonds, accounting not only for the overall orientation, but also for local defects like impurities incorporation, structural defects ... This degree of alignment shows good agreement with SEM observations. Thus CNTs films display degrees of alignment around 50%, depending on the occurrence of defects in the course of the growth, whereas no special alignment can be detected with CNFs and CNPs, and a weak one (about 20%) is detected on CNWs. 展开更多
关键词 X-Ray Absorption Spectroscopy Carbon Nanostructures(CNTs,CNFs,CNWs,CNPs) Plasma-and Hot Filaments-Enhanced Catalytic Chemical Vapor Deposition Geometrical Model Angular Dependence
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Adsorption and desorption phenomena on thermally annealed multi-walled carbon nanotubes by XANES study 认领 引用
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作者 Camile Rodolphe Tchenguem Kamto Bridinette Thiodjio Sendja Jeannot Mane Mane 《Chinese Physics B》 SCIE EI CAS CSCD 2019年第9期145-149,共5页
The multi-walled carbon nanotubes(MWCNTs) studied in this work were synthesized by the catalytic chemical vapor deposition(CCVD) process, and were thermally annealed by the hot filament plasma enhanced(HF PE) method a... The multi-walled carbon nanotubes(MWCNTs) studied in this work were synthesized by the catalytic chemical vapor deposition(CCVD) process, and were thermally annealed by the hot filament plasma enhanced(HF PE) method at 550℃ for two hours.The x-ray absorption near edge structure(XANES) technique was used to investigate the adsorption and desorption phenomena of the MWCNTs at normal and grazing incidence angles.The adsorbates were found to have different sensitivities to the thermal annealing.The geometry of the incident beam consistently gave information about the adsorption and desorption phenomena.In addition, the adsorption of non-intrinsic potassium quantitatively affected the intrinsic adsorbates and contributed to increase the conductivity of the MWCNTs.The desorption of potassium was almost 70% greater after the thermal annealing.The potassium non-intrinsic adsorbates are from a physisorption mechanism whereas the intrinsic adsorbates result from chemisorption. 展开更多
关键词 multi-walled carbon nanotubes thermal annealing adsorption desorption
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Numerical Simulation of Water Waves’ Modulational Instability under the Effects of Wind’s Stress and Gravity Force Relaxation 认领 引用 被引量：1
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作者 Théodule Nkoa Nkomom César Mbane Biouele Jeannot Mane Mane 《Open Journal of Marine Science》 2016年第1期93-102,共10页
The waves driven by the wind do not move on the water as ordinarily done by sailboats. Indeed, the movement of the waves driven by the wind is more complex than the sailboats’ translation movement that we know. The m... The waves driven by the wind do not move on the water as ordinarily done by sailboats. Indeed, the movement of the waves driven by the wind is more complex than the sailboats’ translation movement that we know. The movement of the wave in our particular case results from the chain-job done by wind’s stress and gravity forces: material is collected upstream (erosion phenomenon) and then deposited on the wave’s summit by the wind. This material deposited on the summit of the wave by the wind is then removed and dispatched on the downstream side of the wave by gravity forces. As always happens in any chain-job: if the wind works faster than gravity forces, great accumulation of material will occur at the summit of the wave that will lead to an increase in its (the wave in this case) height. If conversely the wind works more slowly, a deficit in material delivery will occur and gravity force goes directly to remove material on the wave’s summit and lead to a decrease in its height. In terms of Mechanics, we know that the main obstacle that can seriously disturb the work of the wind is the unavailability of water or so its viscosity. Given the complexity of the process to be studied, it seemed necessary for us to make a use of modulational instability theories such as the standard NLSE in order to better understand the contribution of wind and water viscosity to modulations of driven waves’ amplitudes (or phases): modulations which sometimes can accidentally trigger unpredictable rogue waves. 展开更多
关键词 Waves Driven by the Wind Standard Nonlinear Schrödinger Equation Modulations of Driven Waves’ Amplitudes or Phases Unpredictable Rogue Waves
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Curvature, Hybridization and Contamination of Carbon Nanostructures Analysis Using Electron Microscopy and XANES Spectroscopy 认领 引用
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作者 Rolant Eba Medjo Bridinette Thiodjio Sendja Jeannot Mane Mane 《Materials Sciences and Applications》 2014年第2期95-103,共9页
The ability to control the nanoscale shape of carbon nanostructures during wide-scale synthesis process is an essential goal in research for Nanotechnology applications. This paper reports a significant progress towar... The ability to control the nanoscale shape of carbon nanostructures during wide-scale synthesis process is an essential goal in research for Nanotechnology applications. This paper reports a significant progress toward that goal. Variant CVD has been used for the synthesis of the samples studied. Curvature, hybridization and contamination are analyzed using Electron Microscopies and XANES spectroscopy. The investigations of the results show that four types of samples are obtained. They are carbon nanotubes (CNTs), carbon nanofibers (CNFs), carbon nanowalls (CNWs) and carbon nanoparticles (CNPs). Almost all of them have catalyst nanoparticles (metal) on top in top growth model or on base in base growth model and encapsulated or adsorbed in sidewalls. The orientation of tubular carbon nanomaterials depends on operating parameters. They are classified in three groups: the poorly oriented, the medium oriented and the highly oriented. Their contamination (radicals, atoms and molecules) and hybridization are intrinsically related to the curvature of their graphene layers. XANES spectroscopy allows quantitative characterization of nanomaterials. 展开更多
关键词 Carbon Nanostructures XANES Spectroscopy Electron Microscopy Characterization Contamination
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