Wetting-to-Nonwetting Transition in Metal-Coated ${\mathrm{C}}_{60}$

Based on ab initio and density-functional theory calculations, an empirical potential is proposed to model the interaction between a fullerene molecule and many sodium atoms. This model predicts homogeneous coverage of ${\mathrm{C}}_{60}$ below eight Na atoms and a progressive droplet formation above this size. The effects of ionization, temperature, and external electric field indicate that the various, and apparently contradictory, experimental results can indeed be put into agreement.

Figure 1

Some optimal structures of ${\mathrm{N}\mathrm{a}}_n{\mathrm{C}}_{60}$ clusters. (a) $n=4$; (b) $n=7$; (c) $n=8$; (d) $n=12$; (e) $n=20$. The lowest energy structure for ${\mathrm{N}\mathrm{a}}_2{\mathrm{C}}_{60}$ within an electric field $E=2.55\times {10}^8\mathrm{V}{\mathrm{m}}^{-1}$ is represented in (f).

Figure 2

Arrhenius plots of the diffusion constants of some ${\mathrm{N}\mathrm{a}}_n{\mathrm{C}}_{60}$ clusters, for $n=4$, 8, 12, 20 (no field), and 6 within an electric field.

Figure 3

Size of the largest fragment of sodium atoms in ${\mathrm{N}\mathrm{a}}_n{\mathrm{C}}_{60}$ clusters in various conditions and for neutral or charged molecules.

Figure 4

Electric susceptibilities at 300 K. Inset: electric dipole moment and comparison with DFT calculations.