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experimental opening of single walled carbon nanotubes, few studies have been reported [5,6.7.8]. In these later methods, reactive reagents are introduced and the nanotubes appear severely damaged. Consequently, a mechanical method that involves soft conditions has been investigated. It prevents the chemical modification of the specimen surface and the nanotube inner core remains unfilled after the opening. The treated material has been studied by high resolution transmission electron microscopy (HRTEM) to make sure that the nanotube bundles have been cut, that the tube ends are opened and likely, to propose a mechanism of cutting. In order to check that the bundle organisation is always well organised, X-ray diffraction pattern has been carried out. Finally, adsorption measurements have been performed to confirm the opening of the nanotubes. EXPERIMENTAL The single walled carbon nanotubes (SWNTs) are produced by the classical electric arc discharge under helium atmosphere with a graphite anode doped with metallic catalysts (Ni:Y:C ; 4.2:1:94.8 at%) [9]. We choose as pristine material the collaret part of the synthesis product in which the estimated yield of SWNTs is about 70 vol%. Typically, SWNTs are close-packed into bundles with diameter ranging from 5 to 20 nm where nanotubes are well aligned in a two-dimensional periodic triangular lattice bonded by Van der Waals interactions. The average tube diameter is around 1.3 nm and the triangular lattice parameter is 1.7 nm. The raw material is preliminary dispersed in ethanol at ambient temperature in 119 Mat. Res. Soc. Symp. Proc. Vol. 593 © 2000 Materials Research Society

order to obtain a homogeneous suspension. Both ultrasounds and magnetic stir assist the dispersion. Secondly, the solution is disposed between two diamond lapping film discs (with 0. 1-pm granulometry) and it is rubbed until the complete evaporation of ethanol. Finally, we obtain a fine powder on the surface of the discs, which is removed by addition of ethanol. After evaporation of the solvent, the as-obtained material is ready to further characterisations. Morphologies and structures of the treated SWNTs are studied by HRTEM using a CM20 Philips instrument. The sample is dispersed in ethanol by means of a sonicator and scooped up with a holey amorphous carbon grid. The nitrogen adsorption experiments are performed using a SORPTOMATIC 1900 apparatus (Milestones) at 77K and ambient pressure. The raw and the mechanically treated material have first been outgassed over one night at 150'C under vacuum in order to eliminate the foreign adsorbed molecules (H20...). Then, the collected adsorption data are treated by the Horvath-Kawazoe method [9] to evaluate the pore size distribution of each sample. RESULTS AND DISCUSSION HRTEM picture 1 reveals that the as-obtained material is highly distorted. Many ropes are bent or strongly curved to form kinks. These curvatures result from the successive rubbings. But, the degree of curvature depends on the radial mechanical stress exerted by the diamond particle