Interaction of ${\mathrm{C}}_{60}$ with Carbon Nanotubes and Graphite

The interaction of ${\mathrm{C}}_{60}$ with single-wall carbon nanotubes (SWNTs) and graphite is studied experimentally by thermal desorption spectroscopy and theoretically by molecular-mechanics and molecular-dynamics calculations. The van der Waals parameters and force field for ${\mathrm{C}}_{60}$-graphene and ${\mathrm{C}}_{60}$-SWNT interactions are derived from the low-coverage ${\mathrm{C}}_{60}$ binding energy to the graphite surface. We use these to compare the efficiency of different mechanisms by which ${\mathrm{C}}_{60}$ can be encapsulated into SWNTs.

Figure 1

Thermal desorption spectra from HOPG and SWNT samples. (a) Series of TD spectra after adsorption of 0.06–3.3 ML of ${\mathrm{C}}_{60}$ on HOPG. (b) Arrhenius plot of the desorption rate at low coverage. (c) Calculated spectra using a multilayer desorption scenario. (d) Spectra from SWNT samples after exposure to similar amounts of ${\mathrm{C}}_{60}$ are broadened and shifted to higher temperatures as are the calculated traces indicating a small increase of the activation energy for desorption from SWNT bundles. (e) Conceivable adsorbate layer arrangements on an idealized SWNT substrate. $\alpha$ and $\beta$ phases exhibit the largest number of highly coordinated sites within an almost close-packed layer. Unit cells are marked by red lines.

Figure 2

(a) van der Waals parameters and the resulting material properties for different systems. (${\mathrm{C}}_6,{\mathrm{C}}_{12}$ parameters on the long-dashed line, for example, yield the measured activation energy for ${\mathrm{C}}_{60}$ desorption from graphite. To simultaneously account for properties of graphite such as lattice constant or $c$-axis compressibility we chose a set of (${\mathrm{C}}_6,{\mathrm{C}}_{12}$) parameters in the lower part of the graph, marked by a star. The VDW parameters used by Lu et al. [10] and Girifalco et al. [12, 13] are given by open squares and circles, respectively. (b) The corresponding Lennard-Jones potentials.

Figure 3

Cut through three-dimensional potential energy surface of a small (10,10) tube bundle. Spontaneous encapsulation along all relevant reactions paths is prevented by lip barriers (LBs) due to the lower ${\mathrm{C}}_{60}$ coordination at the rim of SWNTs. Calculations show that encapsulation is most efficient via the head-on approach along the reaction path labeled (c).Transition states are marked by a double dagger (‡).