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Curvature, Hybridization and Contamination of Carbon Nanostructures Analysis Using electron Microscopy and XANeS Spectroscopy

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ma.erials Sciences and Applications 2014年第2期5卷 95-103页

作者： Rolant eba Medjo bridinette thiodjio sendja.jea.not ma.e ma.e Department of mathematics and Physical Sciences Ecole Nationale Supérieure Polytechnique (National Advanced School of Engineering) University of Yaoundé I Yaoundé Cameroon Department of mathematics and Physical Sciences Ecole Nationale Supérieure Polytechnique (National Advanced School of Engineering) University of Yaoundé I Yaoundé Cameroon Basical Scientist Teaching (eSB) Department Training School of Secondary Technical School Teachers (ENSET) University of Douala Douala Cameroon Physics Department Faculty of Science University of Douala I Douala Cameroon

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 nanoma.erials 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 nanoma.erials.

关键词： Carbon Nanostructures XANeS Spectroscopy electron Microscopy Characterization Contamination

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Adsorption and desorption phenomena on thermally annealed multi-walled carbon nanotubes by XANeS study

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Chinese Physics B 2019年第9期28卷 145-149页

作者： Camile Rodolphe Tchenguem Kamto bridinette thiodjio sendja.jea.not ma.e ma.e University of Yaounde Ⅰ Faculty of ScienceDepartment of PhysicsYaoundeCameroon University of Yaounde Ⅰ National Advanced School of EngineeringDepartment of Mathematic and Physical ScienceYaoundeCameroon University of Dschang DschangCameroon

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 *** 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 *** adsorbates were found to have different sensitivities to the thermal *** geometry of the incident beam consistently gave information about the adsorption and desorption *** addition, the adsorption of non-intrinsic potassium quantitatively affected the intrinsic adsorbates and contributed to increase the conductivity of the *** desorption of potassium was almost 70% greater after the thermal *** potassium non-intrinsic adsorbates are from a physisorption mechanism whereas the intrinsic adsorbates result from chemisorption.

关键词： multi-walled carbon nanotubes thermal annealing adsorption desorption

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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

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ma.erials Sciences and Applications 2015年第5期6卷 373-390页

作者： bridinette thiodjio sendja Rolant eba Medjo jeannot ma.e ma.e Germain Hubert Ben-Bolie Pierre Owono Ateba ecole Nationale Supérieure Polytechnique (National Advanced School of engineering) Department of Mathematics and Physical Sciences University of Yaoundé I Yaounde Cameroon Physics Department Faculty of Science University of Douala Douala Cameroon Physics Department Faculty of Science University of Yaoundé I Yaounde Cameroon

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.

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

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ma.erials Sciences and Applications 2014年第13期5卷 966-983页

作者： jeannot ma.e ma.e Francois Le Normand 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 IPCMS UMR 7504 CNRSStrasbourgFrance ecole Nationale Supérieure Polytechnique(National Advanced School of engineering) Department of Mathematics and Physical SciencesThe University of YaoundéIYaoundeCameroon Physics Department Faculty of ScienceUniversity of YaoundéIYaoundeCameroon Physics Department Faculty of ScienceUniversity of DoualaDoualaCameroon LURe UMR CNRSCentre Universitaire Paris SudOrsayFrance

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-ma.e 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.

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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