Due to its higher degree of control and its scalability, catalytic chemical vapour deposition is now the prevailing synthesis method of carbon nanotubes. Catalytic chemical vapour deposition implies the catalytic conversion of a gaseous precursor into a solid material at the surface of reactive particles or of a continuous catalyst film acting as a template for the growing material. Significant progress has been made in the field of nanotube synthesis by this method although nanotube samples still generally suffer from a lack of structural control. This illustrates the fact that numerous aspects of the growth mechanism remain ill-understood. The first part of this review is dedicated to a summary of the general background useful for beginners in the field. This background relates to the carbon precursors, the catalyst nanoparticles, their interaction with carbonaceous compounds and their environment. The second part provides an updated review of the influence of the synthesis parameters on the features of nanotube samples: diameters, chirality, metal/semiconductor ratio, length, defect density and catalyst yield. The third part is devoted to important and still open questions, such as the mechanism of nanotube nucleation and the chiral selectivity, and to the hypotheses currently proposed to answer them.

Nano-objects would be of great interest for the development of new types of electronic circuits if one could combine their nanometer scale with original functionalities beyond the conventional transistor action. However, the associated circuit architectures will have to handle the increasing variability and defect rate intrinsic to the nanoscale. In this context, there is a very fast growing interest for memory devices, and in particular resistive memory devices, used as building blocks in reconfigurable circuits tolerant to defects and variability. It was recently shown that optically gated carbon nanotube field effect transistors (OG-CNTFETs) based on large assemblies of nanotubes covered by an organic photoconductive thin film can be operated as programmable resistors and thus used as artificial synapses in circuits with function-learning capabilities. Here, the potential of such approach is evaluated in terms of scalability by integrating and addressing several individually programmable resistances on a single carbon nanotube. In addition, the charge storage mechanism can be controlled at a length scale smaller than the device length allowing to also program the direction in which the current flows. It thus demonstrates that a single nanotube section can combine all-in-one the properties of an analog resistive memory and of a rectifying diode with tunable polarity.

In this paper, we compare the Raman responses obtained on individual suspended Single-Walled Carbon Nanotubes (SWNTs) and Double-Walled Carbon Nanotubes (DWNTs). We focus on the comparison of the frequencies, line widths, intensities and resonance conditions of the main Raman active modes measured on an index-identified DWNT with those measured on SWNTs having atomic structures close to the inner and outer tubes of the DWNT. By this way, we state that the relation between the radial breathing mode frequencies and the diameters established for SWNTs do not work in DWNTs. We found that resonance of only one tube can be sufficient to observe the response of the coupled layers in DWNTs. These results are understood in terms of mechanical coupling between the layers in DWNTs. We evidence that the spectral line widths of the Raman active modes are systematically narrower for DWNTs compared to the corresponding SWNTs. Finally, we present the measurements of the G modes of two different DWNTs which behave in a different way. For the first one, the frequencies of the G modes are not significantly affected by the interaction between the layers, while for the second one we evidence a downward shift of the LO and TO bands arising from the inner layer.

The atomic structure of ultra-long carbon nanotubes grown by catalytic chemical vapor deposition has been studied along the nanotube length via electron diffraction and high-resolution transmission electron microscopy. Contrary to other techniques, electron diffraction studies provide a direct determination of the chiral structure of nanotubes. These studies demonstrate that the chirality of the nanotubes remained constant all along their length. A tendency to double-walled nanotubes has been observed, as well as, a preferential distribution to armchair configuration. Furthermore, the studies yield a metallic:semiconducting ratio close to the one expected from a natural distribution of nanotubes (1:2).

The extraordinary electronic, thermal and mechanical properties of carbon nanotubes (CNTs) closely relate to their structure. They can be seen as rolled up graphene sheets with their electronic properties depending on how this rolling up is achieved. However this is not the way they actually grow. Various methods are used to produce carbon nanotubes. They all have in common three ingredients: i) a carbon source, ii) catalyst nanoparticles, iii) an energy input. In the case where the carbon source is provided in solid form, one speaks about "high temperature methods" because they involve the sublimation of graphite which does not occur below 3200°C. The first CNTs were synthesized by these techniques. For liquid or gaseous phases, the generic term of "medium or low temperature methods" is used. CNTs are now commonly produced by these latter techniques at temperatures ranging between 350 and 1000˚C, using metal nanoparticles that catalyze the decomposition of the gaseous carbon precursor and make the growth of nanotubes possible. The aim of this review article is to give a general overview of all these methods and an understanding of the CNT growth process.

It is frequently observed that as-grown single-walled carbon nanotubes (SWCNTs) contain defects. Controlling the defect density is a key issue for the control of nanotube properties. However, little is known about the influence of the growth conditions on the formation of nanotube defects. In addition, SWCNT samples frequently contain carbonaceous by-products which affect their ensemble properties. Raman spectroscopy is commonly used to characterize both features from the measurement of the defect-induced D band. However, the contribution of each carbonaceous species to the D band is usually not known making it difficult to separately extract the defect density and relative abundance of each. Here, we report on the correlated evolution of the D and G' bands of SWCNT samples with increasing growth temperature. In the general case, three to four Lorentzian components are required to fit them. Coupled with HRTEM characterization, the low frequency components of the D and G' can be attributed to the contribution of SWCNTs while high frequency components are associated with defective carbonaceous by-products. The nature of these defective by-products varies with the type of catalysts and with the growth conditions.

Ces travaux portent sur la croissance catalytique des nanotubes de carbone par la méthode dite de Catalytic Chemical Vapor Deposition. La première partie est consacrée à une revue de la compréhension actuelle de ce processus de croissance dans la littérature en particulier concernant les connaissances antérieures issues d'autres domaines de recherche, la relation synthèse-structure et les questions encore ouvertes. La deuxième partie est consacrée aux travaux du candidat pour répondre à ces questions et utilisant essentiellement la technique de spectroscopie Raman pour des mesures in situ et ex situ. Quatre aspects sont étudiés : l'activation des particules catalytiques, la densité de défauts des nanotubes, les cinétiques de croissance / désactivation et la distribution en diamètre des nanotubes.