Synthesis and characterization of carbon-based materials

Carbon is a fascinating element which can be observed in a large variety of morphologies and atomic structures due to its chemical ability to form different hybridizations. The present PhD thesis proposes the synthesis of several carbon-based materials using a unique and quite simple technique: the oxy-acetylene combustion flame method. From crystalline sp3- diamond to planar sp2- graphite, from the unidirectional nanotubes, needles and rods to bidimensional petals, a large variety of carbon materials are synthesized under the atmospheric pressure. These various carbon forms have been produced using a set of different experimental parameters. Both the input gas ratio and the substrate temperature are found to play a key role in the synthesis of these new carbon materials. The high quality of the graphitic phases can be correlated to the large acetylene content in the gas and to the high temperature of the substrate. Some specific morphologies such as petal-like single graphite crystals have been synthesized. Their sizes reach up to 20 mm. These bidimensional carbon materials are of particular importance to investigate fundamental physics in ideal low-dimensional systems. Polyhedral graphite crystals, which exhibit a unidirectional morphology, have also been produced. Their crystal structure is found to be highly graphitic although they display a cylindrical/polyhedral shape. Preliminary measurements of their field emission properties reveal a huge emission current, which is higher than the emission current obtained for multi-wall carbon nanotubes. The latter have also been synthesized in large amount and high quality using our oxy-acetylene combustion flame technique. At last, using again the same experimental set-up, a crystalline carbon nitride phase has been synthesized for the first time using a specific molecule called "melamine" as an organic precursor. Several experimental techniques, such as Energy Dispersive X-ray (EDX), X-ray Photoelectron Spectroscopy (XPS), Electron Energy Loss Spectroscopy (EELS), X-ray diffraction and Raman and infra-red spectroscopies have been used to analyze both the chemical composition and the crystalline structure of this new material, revealing a graphitic-C3N4 phase.(FSA 3)--UCL, 200