Investigation of the structure and physical properties of pure and doped systems based on carbon nanotubes

Información del proyecto

Identificador del acuerdo de subvención: INTAS-94-0157

Proyecto cerrado

Fecha de inicio 1 Marzo 1995

Fecha de finalización 28 Febrero 1997

Financiado con arreglo a

• International Association for the promotion of cooperation with scientists from the independent states of the former Soviet Union (INTAS), 1993-

Coste total € 0,00

Aportación de la UE € 55 000,00

Coordinado por

Centre National de la Recherche Scientifique
France

Exploitable results

Investigation of the structure and physical properties of pure and doped systems based on carbon nanotubes

A technology of production of purified multi-shell carbon nanotube "wool" was optimised. It includes a nanotube bundles synthesis in highly stable arc discharge, an ultrasonic treatment of carbon deposit in ethanol with addition of surface active polianline based substance, and a thermal oxidation at 680 C to crack the bundles and to remove small carbon particles. The process of "wet" doping of nanotubes with metals was developed, it resulted in the appearance of a small metal particles inside the nanotubes. We have found that the nanotube containing powder is a good raw material for the synthesis of diamond powder. Afer 1 hour of treatment at 1180 C and a pressure of 100 kbar the sample was completely transformed into diamond powder with a grain size less or about 100 µ. It was shown that characteristic features of nanotubes in Raman spectra are the softening of the Raman active E2g graphite hexagon vibration mode and appearance of a new 120 cm-l Raman band. The 120 cm-1 Raman mode is a specific feature of nanotubes and can be assigned to vibrations of their cylindrical walls. A fine structure of IR absorption spectra was found in a spectral range 0.05-0.3 eV consisting of a periodic set of narrow lines with a period of 15 meV ( 120 cm-1). The observed "oscillations" of absorption correspond to the phonon - assistant electronic transitions. In addition, the broad peculiarities at 0.16, 0.3 and 0.5 eV were found in absorption spectra. Their exact nature is not very clear, but these energies are surpassingly close to the rough estimation of electronic energy split due to periodicity of electron wave function in a circular tube cross-section (so that nλ/2=2πr). In addition to known EPR lines in the vicinity of g=2 that correspond to paramagnetic defects and free electrons. a new EPR line with g=4.26 was found in nanotube samples. It was found that the high frequency conductance of nanotubes is proportional to log(T) in a temperature range from 1.5 to 70K. In a temperature below 15-20K a negative magnetoresistance of nanotubes was observed in microwave conductivity. These results agree with the idea of importance of weak localisation effects in nanotube conductance.