Showing papers by "Rodney S. Ruoff published in 1994"

Structural properties of a carbon-nanotube crystal.

Abstract: Carbon nanotubes of uniform size may soon be available in macroscopic quantities. Here we examine the ordered condensed phase of these tubes. As the tube diameter varies, the structural properties show a clear transition between two regimes with qualitatively different behavior. Tubes 10 \AA{} and less in diameter behave as rigid cylinders. For diameters over 25 \AA{}, the tubes flatten against each other under the van der Waals attraction, forming a honeycomb structure. This structure exhibits an anomalous rigidity, which does not decrease as expected with increasing tube diameter. Based on reported tube sizes, both regimes should be experimentally accessible.

Susceptibility discontinuity in single crystal C60

Abstract: Magnetization of a large single ${\mathrm{C}}_{60}$ crystal was measured as functions of applied field and temperature. At $T=260$ K, a discontinuity in susceptibility was observed. The relative change in total moment is 1.2%, independent of applied field to within experimental accuracy. This discontinuity is attributed to the change in the intramolecular geometry at the orientational order-disorder transition. This is the first experimental demonstration that the cooperative phase transition affects the magnetic susceptibility of a single molecule.

ESR Characterization of Singly-, Doubly-, and Triply-Reduced C84 Isomers.

Abstract: Initial electrochemical studies of C[sub 84] in benzonitrile (PhCN) and o-dichlorobenzene (ODCB) have been reported but did not clearly distinguish between these two isomers. We have reproduced these electrochemical results in benzonitrile (PhCN) as well as carried out new experiments in pyridine and a 15/85 dimethylformamide (DMF)/toluene mixture and have observed that two distinct sets of multiple redox processes can be resolved in the latter solvents, each of which can be associated with reduction of a different isomer. Combined electrochemical and electron spin resonance (ESR) measurements are now reported in these two new solvents which allow us to assign, for the first time, both half-wave potentials and ESR parameters to a given D[sub 2] or D[sub 2d] C[sub 84][sup n[minus]] isomer, where n = 1, 2, or 3. 21 refs., 2 figs., 1 tab.

Charge transfer in collisions involving multiply charged C60 molecules

Abstract: Electron capture in collisions of C602+ and C603+ molecular ions with atomic and molecular gases has been studied at impact energies around 100 keV. The cross-section dependence on the target-ionization potentials is discussed, and a simple over-barrier model is evoked to explain the energy dependences. The cross sections for endothermic processes are discussed in the light of a simple two-state model, and a general understanding of their behaviour is obtained.

Scanning tunneling microscopy and spectroscopy of carbon nanotubes

Abstract: Scanning tunneling microscopy (STM) and spectroscopy have been used to obtain images and current-voltage (I–V) curves of carbon nanotubes. The nanotubes are 5–7 nm in diameter and up to 1 in length. The I–V curves indicate that carbon nanotubes with diameters of approximately 5.0 nm are metallic. This observation is consistent with recent theoretical predictions concerning the electronic structure of carbon nanotubes in relation to their diameter and helicity. Using STM, we also observe graphene sheets in the carbon soot that is produced during the arc discharge. The STM images of nanotubes are in good agreement with transmission electron microscopy images. Potential applications of carbon nanotubes include novel nanometer-size electronic devices and fiber-reinforced materials.