Topochemical polymerization of C70 controlled by monomer crystal packing.

Polymeric forms of C60 are now well known, but numerous attempts to obtain C70 in a polymeric state have yielded only dimers. Polymeric C70 has now been synthesized by treatment of hexagonally packed C70 single crystals under moderate hydrostatic pressure (2 gigapascals) at elevated temperature (300 degrees C), which confirms predictions from our modeling of polymeric structures of C70. Single-crystal x-ray diffraction shows that the molecules are bridged into polymeric zigzag chains that extend along the c axis of the parent structure. Solid-state nuclear magnetic resonance and Raman data provide evidence for covalent chemical bonding between the C70 cages.

Reversible hole engineering for single-wall carbon nanotubes.

Experimental results are provided for reversible generation of holes on single-wall carbon nanotubes and their closing by temperature treatment. The generation of the holes was analyzed by checking the amount of C60 fullerenes that can be filled into the tubes and subsequently transformed to an inner-shell tube. The concentration of the latter was determined from the Raman response of the radial breathing mode. The tube opening process was performed by exposure of the tubes to air at elevated temperatures. This process was found to be independent from the tube diameters. In contrast, the tube closing process was found to depend strongly of the tube diameter. For large diameter tubes (d = 1.8 nm) the activation energy was 1.7 eV whereas for the small diameter tubes this energy was only 0.33 eV. Optimum conditions for tube closing were found to be one hour at 800 degrees C or 10 minutes at 1000 degrees C. From the almost identical Raman spectra for the tubes before and after engineering, a predominant generation of the holes at the tube ends is concluded.

Determination of the diameter distribution of single-wall carbon nanotubes from the Raman G-band using an artificial neural network.

A novel, artificial neural network-based method is now available for obtaining the mean diameter of single wall carbon nanotube (SWCNT) samples from the diameter dispersive features of their Raman G-band. The method is demonstrated here for six different diameter SWCNT samples and 14 different excitation wavelengths. With an adequately large pool of standard nanotube samples, the suggested method is a useful complementary technique for SWCNT diameter analysis as it is capable of rapid diameter evaluation without prior knowledge of the relevant phonon dispersion relations.

Periodic resonance excitation and intertube interaction from quasicontinuous distributed helicities in single-wall carbon nanotubes

Photoselective resonance Raman scattering from laser ablation grown single-wall carbon nanotubes is demonstrated to be consistent with a response from tubes with all geometrically allowed helicities. This information is drawn from an analysis of the resonance scattering by combining ab initio calculations for the mode frequencies with evaluations of the resonance cross sections for isolated tubes. The resonance excitation was found to exhibit an oscillatory behavior. To match the experiments and the calculations, the frequencies obtained from the latter must be up-shifted by 8.5% on the average. This stiffening is ascribed to the tube-tube interaction in the carbon nanotube bundles.

Diameter selective charge transfer in p- and n-doped single wall carbon nanotubes synthesized by the HiPCO method.

The unusually broad diameter distribution of single wall carbon nanotubes (SWCNTs) in a HiPCO derived sample made it possible to observe for the first time a selective loss of Raman resonances corresponding to large diameter tubes upon both p- (FeCl3) and n-type (K) doping.