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Synthèse CVD assistée par radicaux basse pression de SWCNT pourmise en œuvre potentielle technique d'analyse in-situ et en temps réel (ETEM)

by Thi thanh loan Truong

Thesis project in Physique

Under the supervision of Costel-Sorin Cojocaru.

Ongoing thesis at Institut polytechnique de Paris , under the authority of École doctorale de l'Institut polytechnique de Paris , in a partnership with LPICM - Laboratoire des Interfaces et des Couches Minces (laboratoire) and Couches minces et nanomatériaux pour le photovoltaïque (equipe de recherche) since 01-01-2019 .

  • Alternative Title

    Low-pressure, radicals assisted CVD synthesis of SWCNTs for thepotential implementation in-situ and real-time analysis technique (ETEM)


  • Abstract

    Materials science of carbon nanotubes (CNT) lies at the intersection of various paradigms from fundamental to applied physics and chemistry. Recognizing how the different concepts can be combined together to understand CNT formation still remains a challenge. The synthesis of CNTs with desired chirality and diameter is one of the most important challenges in nanotubes science and achieving such selectivity requires understanding of their growth mechanism. There is an overwhelming body of evidence that catalytic growth is the most promising method for the CNTs synthesis, including the potential for chiral selectivity.[ , ] Although knowledge of the different stages of growth has advanced considerably[ ] a full picture is still elusive. Recent advances have made possible a better control of the diameter of the obtained carbon nanotubes. Mastering chirality control however, requires a deeper understanding of the very early stage of CNT nucleation, when the symmetry type is set. A well-controlled synthesis of catalyst nanoparticles (composition, morphology, size) appears to be a mandatory condition for controlling the characteristics of the as-synthetized nanotubes.[ ] Recent researches focused especially on growth of multiwalled CNT[ , ] have shown that the catalyst (re)shaping is correlated with surface energy modification due to C adsorption. To our knowledge studies of the relationship between changes in catalyst particle morphology and CNT nucleation are narrowly studied [ , , ] and a quantitative description is greatly needed for the elaboration of nanotubes with targeted electronic properties (either metallic or semiconductor). The aim of the thesis project is to complement the well-established ex situ observation of SWCNTs growth [ ] with direct and real-time, in-situ TEM observations as close as possible to the real CVD growth reactions and this without a significant resolution loosen. The actual trend is to develop in-situ techniques and in the field of electron microscopy, the TEM community has witnessed lately the development of first environmental microscopes with pressures range up to 25 mbar and closed environmental cells that can operate in more “extreme” conditions. The fundaments of the actual project refer to the use of a very promising and unique approach that combines the HRTEM technique, with the implementation of the CVD gas sources in a modified environmental transmission electron microscope (ETEM) equipped with a Cs image aberration-corrector, for carrying out real-time in-situ observation on the catalyst reshaping and its morphology dynamics during CNT nucleation and growth under controlled conditions. This original approach aims mainly at the assessment of the kinetics of surface and/or volume transformations within catalyst nanoparticles as identified at atomic level under controlled conditions. As applied to different types of catalysts nanoparticles, the emphasis is to put forward a nucleation mechanism based on the catalyst (re)shaping that will determine the growth of SWCNTs with specific and targeted electronic properties. By “predicting” the most stable configurations, such valuable information will constitute strong basis for further investigations by molecular dynamics simulations.


  • Abstract

    Le projet de thèse a pour but de compléter l'observation ex situ bien établie de la croissance des SWCNT par des observations TEM in-situ directes et en temps réel aussi proches que possible des réactions de croissance réelles des CVD, et ce sans perte de résolution significative. . La tendance actuelle est de développer des techniques in situ et dans le domaine de la microscopie électronique, la communauté TEM a récemment assisté au développement de premiers microscopes environnementaux avec des pressions allant jusqu'à 25 mbar et des cellules environnementales fermées pouvant fonctionner dans des conditions plus «extrêmes». . Les fondements du projet actuel reposent sur l'utilisation d'une approche très prometteuse et unique combinant la technique HRTEM et la mise en œuvre des sources de gaz CVD dans un microscope électronique à transmission environnementale modifié (ETEM) équipé d'un correcteur d'aberration d'image Cs, pour effectuer une observation in situ en temps réel du remodelage du catalyseur et de sa dynamique morphologique au cours de la nucléation et de la croissance des CNT dans des conditions contrôlées. Cette approche originale vise principalement à évaluer la cinétique de transformations de surface et / ou de volume au sein de nanoparticules de catalyseur, identifiées au niveau atomique dans des conditions contrôlées. Appliqué à différents types de nanoparticules de catalyseurs, l'accent est mis sur la mise en avant d'un mécanisme de nucléation basé sur la (re) mise en forme du catalyseur qui déterminera la croissance des SWCNT dotés de propriétés électroniques spécifiques et ciblées. En "prédisant" les configurations les plus stables, ces informations précieuses constitueront une base solide pour des investigations ultérieures par des simulations de dynamique moléculaire.