P.Bernier suggested that exact limits for the diameter should be given, e. g. up to 10 nm for nanotubes and ca. 100 m for filaments. Nanoubes show an unuslal conductivity (quantum behavior), which can be metallic or semiconducting and differs from the classical conductivity of macoscopic carbon systems. L. P.Biro added that the STS spectrum of thick carbon nanotubes (ca. 30 nm) is similar, if not identical, to that of graphite and does not reveal the characteristic features of nanotubes with diameters smaller than 30 mm. According to theory, the electronic band gap of a nanotube shrinks with increasing diameter and therfore this gap could be used to indirectly determine tube diameters.
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