No abstract

No abstract

No abstract

We investigated the influence of catalyst preparation on the growth of coil-shaped nanotubes by varying the pH of the solution during catalyst impregnation, to elucidate their formation process. The spirals were observed by transmission electron microscopy, and we determined the dimensions of these coils for a large number of them, to compare them to straight nanotubes, and also to establish correlations between these dimensions and catalyst preparation. We also looked for the nature of curling at the nanometer scale. A growth mechanism for these spirals is finally suggested.

Through 13C NMR spin lattice relaxation ( T1) measurements in cubic Na2C60, we detect a gap in its electronic excitations, similar to that observed in tetragonal A4C60. This establishes that Jahn-Teller distortions (JTD) and strong electronic correlations must be considered to understand the behavior of even electron systems, regardless of the structure. Furthermore, in metallic Na2CsC60, a similar contribution to T1 is also detected for 13C and 133Cs NMR, implying the occurrence of excitations typical of JT distorted C( 2-)60 (or equivalently C( 4-)60). This supports the idea that dynamic JTD can induce attractive electronic interactions in odd electron systems.