R. Aznar

Purification procedure of carbon nanotubes

We report results on purification and characterization of single wall carbon nanotubes prepared by the electric arc method. The process consists of a chemical treatment based on a reflux with nitric acid followed by successive filtration steps (tangential flow and frontal filtration) of a suspension of the raw material. The effects of each step are analysed by SEM and TEM.

High resolution 13C NMR of K6C60

We report on a 13C NMR investigation of K6C60. The previously reported 13C NMR measurements of the fully doped alkali fullerides suffered from limited resolution and show very broad spectra which were dominated by chemical shift anisotropy. By applying magic angle spinning (MAS) to K6C60 we obtained a highly resolved 13C NMR spectrum which shows one isotropic line at 156 ppm at ambient temperature. Careful analysis of this line enabled us to distinguish three separated narrow lines. This result is consistent with orientationally ordered C60 moieties leading to three non-equivalent carbon sites in the saturated compound.

Purification of C60 by a simple crystallization procedure

C60(98% pure) crystallizes during toluene Soxhlet extraction of fullerenes from soot—recrystallization of this enriched material gives 99.5% pure C60.

Inelastic neutron scattering investigation of CsC60 in its polymer and dimer phases

Abstract We present an inelastic neutron scattering study of the low frequency vibrational dynamics of CsC 60 . In its polymeric phase, two main excitations are observed at 0.65 and 1.15 THz. The Q-dependence of their structure factor allows to confirm their assignment to twisting modes. For quenching-prepared samples, the modes shift at lower frequencies in agreement with the formation of dimers. We compare our results to previous Raman data and time of flight measurements of Renker et al. on RbC 60 and derive a general description of the vibrational dynamics of alkali-doped C 60 phases.

Molecular motion in solid C70 by 13C high resolution NMR

Abstract A 13 C NMR approach of molecular dynamics of solid C 70 is presented. A strong correlation between the measured spin-lattice relaxation times T 1 , their temperature dependence and sample purity is described and compared to the solid C 60 behaviour. An axial rotation of C 70 molecules and their random orientation at room temperature is demonstrated by chemical shift anisotropy analysis.

Influence of impurities on 13C high resolution NMR of solid fullerite C60

Abstract The influence of two types of impurities, toluence and C 70 on high resolution 13 C NMR parameters of solid C 60 is reported. The evolution of the spectrum upon thermal treatment of the sample is described and the solvent free material is characterized. A strong dependence of the measured spin-lattice relaxation time T 1 on the thermal history of the sample and on the C 70 presence is analysed.

Low-temperature anomalies in photoluminescence of (C60)1−x-(C70)x solid solutions

In this communication, is reported a detailed analysis of the temperature dependence of the photoluminescence measured on (C60)1−x-(C70)x thin films (x in the range: 0, 0). The intensity of this peak is closely related to the amount of C70 (the x value) in the (C60)1−x-(C70)x films (at least in the [0<x <7%] range). In the [10 K-90 K] temperature range, its intensity significantly increases when the temperature decreases. Nevertheless the origin of this peak is unclear and the assignment of the enhancement of the 1.77 eV emission peak intensity below 90 K to the photoluminescence signature of the “glass phase transition” in the (C60)1−x-(C70)x mixed compounds is discussed.

Supramolecular organization of pi-conjugated molecules monitored by single-walled carbon nanotubes

Abstract. Photoactive pi-conjugated molecules (quaterthiophene and phthalocyanine) are either encapsulated into the hollow core of single-walled carbon nanotubes or noncovalently stacked at their outer surface in order to elaborate hybrid nanosystems with new physical properties, providing practical routes to fit different requirements for potential applications. We are interested in the relationship between the structure and the optoelectronic properties. The structural properties are investigated mainly by x-ray diffraction and/or transmission electron microscopy and Raman spectroscopy. We show that the supramolecular organizations of confined quaterthiophenes depend on the nanocontainer size, whereas phthalocyanine encapsulation leads to the formation of a one-dimensional phase for which the angle between the molecule ring and the nanotube axis is close to 32 deg. Confined phthalocyanine molecules display Raman spectra hardly altered with respect to the bulk phase, suggesting a rather weak interaction with the tubes. In contrast, the vibrational properties of the molecules stacked at the outer surface of tubes display important modifications. We assume a significant curvature of the phthalocyanine induced by the interaction with the tube walls and a change of the central atom position within the molecular ring, in good agreement with our density functional theory calculations.

Inelastic neutron scattering investigation of quenched CsC60 phases

Abstract We present an inelastic neutron scattering investigation of the low-frequency vibrational dynamics of liquid nitrogen-quenched CsC 60 . The low-frequency vibrational signatures of the different phases are discussed on the basis of the sequence of phases transitions stated by Kosaka et al . The librational modes of C 60 − monomer and (C 60 ) 2 2− dimer are observed below 150 K (monomer ordered phase) and around 210 K (dimer phase) respectively. Above 240 K the appearance of a quasi-elastic component agrees with the existence of an orientationally disordered phase.

A new type of p-doping for polyacetylene

Summary form only given. We report here a new p-doping for polyacetylene which seems to be very promizing. The new dopant is the ion: (CF/sub 3/SO/sub 2/)/sub 2/N/sub -/ (TFSI). It is possible to use various counter-ions in the salt and make so to performe electrochemical or chemical doping. For chemical doping we used the copper salt in a CH/sub 3/CN solution and observed a swelling and a color change of the sample. For electrochemical doping we used the lead or the lithium salt in various solvents such as CH/sub 3/CN or (C/sub 2/H/sub 5/)/sub 2/NSO/sub 2/N(C/sub 2/H/sub 5/)/sub 2/. With electrochemical doping we reached a maximum doping level close to 8% and the conducdvity increased up to 20 S/cm. A spontaneous slow dedoping process occured. We performed Raman measurements with various wawelenghts and we observed the characteristic peaks of cis and trans polyacetylene simultaneously. This behaviour can be interpreted as the result of an inhomogenous, doping of the sample. More surprising is the photoluminescence of the systems which does not depends on the way the samples were doped (electrochemically or chemicaly). This photoluminescence is also independent on the wawelenght: we observed this behaviour with an energy between 1,7 eV for a 6471 /spl Aring/ exciting line and 1,975 eV for a 4880 /spl Aring/ exciting line. We have also performed EPR and Infra-Red Spectroscopy experiments to complete our study of these new p-doped samples.