Chemical and physical characterization of nanomaterials is essential to improve synthesis processes, for new technological and commercial applications, and to assess their toxicity through in vitro and in vivo studies. New nanomaterials and new synthesis processes are continuously tested and updated to exploit their innovative properties. In this paper, low-dimensional carbon nanostructure characterization was performed using analytical transmission electron microscopy. Conventional and advanced microscopy techniques, such as acquisition of high resolution images, nanobeam electron diffraction patterns, X-ray energy dispersion, and electron energy loss spectra, were used to determine the main physical and chemical properties of single wall and multiwall carbon nanotubes, graphene flakes, and amorphous carbon films. Through the resulting micrographs, diffraction patterns, and spectra, the main low-dimensional carbon nanostructures properties were determined in terms of structural defects and/or the presence of metallic or heavy elements, such as those used as catalyst or to decorate nanotubes. The obtained information is of crucial importance to investigate low-dimension nanomaterial biological activity. 1. Introduction Among low-dimensional carbon nanostructures, nanotubes play the main role up to now. They were discovered by chance in 1991 by the physicist Sumio Iijima (NEC Corporation, Tsukuba, Ibaraki, Japan), in the analysis of the products obtained in the growth of fullerenes, the third allotropic species of carbon [1]. Actually, in the late 1950s, researchers, Roger Bacon (Union Carbide Corporation, Cleveland, OH, USA) and then in the 1970s and 1980s (Morinobu Endo), had unknowingly observed nanotubes but had not recognized them as such [2, 3]. As for all materials of nanometric dimension, nanotubes have technical characteristics making them especially attractive in a wide range of applications [4–16]. There are numerous sectors in which the specific properties of carbon nanotubes can be used, and there are many other potential sectors where applied research is investing considerable resources. For example, these materials are very resistant to traction. Indeed, it can be said that carbon nanotubes, without structural defects, are the most resistant organic material. Nanotubes are likewise very light and highly flexible and can be folded repeatedly up to 90° without being damaged. All these properties make them the best materials available today for reinforcing fibres in high performance composite materials, replacing and having definitely
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