Études optiques in situ de l'influence de la vapeur d'eau sur la cinétique de croissance des nanotubes de carbone

Carbon nanotubes (CNTs) have exceptional electrical and optoelectronic properties, determined by their structure or chirality, defined by (n,m) indices, which relate to their diameter and chiral angle. This chirality dictates whether a CNT is metallic or semiconducting, crucial for applications like electronics that require high chiral purity. However, achieving chirality-selective synthesis of single-walled CNTs (SWCNTs) remains challenging. While various experimental factors affecting SWCNT chirality have been studied extensively, there is limited focus on understanding the correlation between chiral selectivity and growth kinetics.The objective of this thesis is to deepen our understanding of the influence of the partial pressure of water vapor on the kinetics of horizontally-aligned SWCNTs grown on ST-cut quartz by chemical vapor deposition (CVD) using ethanol as the carbon precursor. By investigating the influence of both constant and dynamic changes in water vapor concentration during growth, this work seeks to explore how these conditions affect the growth and etching kinetics, chirality, and structural characteristics of SWCNTs.We employed a custom setup that combines in situ homodyne polarization microscopy with a miniature CVD cell. This setup enables real-time observation of individual SWCNTs during their growth. In this work, in situ imaging was employed to monitor the growth rate, to observe the correlation between applied stimuli and chirality changes, and the iterative cycles of growth, etching, and mutation.As previously reported, spontaneous switches from growth to shrinkage (etching) are frequently observed during SWCNT growth. Our results indicate that, in line with water's etchant role, the proportion of etching events and the etching rate of individual SWCNTs increase with increasing water vapor pressure, ranging from 50 ppm to 1220 ppm. Surprisingly, we observed that the mean growth rate of SWCNTs increases with higher water concentration, in contradiction with existing theories. This is accompanied by a decrease in the mean lifetime of the SWCNTs.Experiments with dynamic changes of water concentrations revealed that reversible switches between growth and shrinkage can be induced by modulating the carbon supply and etchant concentration, offering insights into how these processes influence chiral selectivity.The study proposes hypotheses to explain how water vapor influences growth kinetics and their relationship to the structural characteristics of as-grown SWCNTs, as determined by Raman spectroscopy analysis.The thesis is organized into three main chapters of experimental results. Chapter 3 presents the results of growth kinetics experiments under constant water vapor concentration conditions. Chapter 4 details the experiments where dynamic changes in water vapor and ethanol concentrations were applied during synthesis. Chapter 5 focuses on the structural characterization of SWCNTs, particularly their diameter and metallicity, through Raman spectroscopy, under constant water vapor concentration conditions.