Concepedia

Ordered phases of fullerene molecules formed inside carbon nanotubes

Physical review. B, Condensed matter · 2003 · 124 citations · 27 references

TL;DR

The phase structure of C60 inside carbon nanotubes is highly sensitive to tube radius and differs from hard‑sphere packing. The authors employed simulated annealing to identify minimum‑energy configurations, revealing achiral phases composed of stacked polygon layers rotated by 360/(2k) degrees. Simulations of over 50 nanotubes (6.27–13.57 Å) uncovered ten distinct phases, including chiral multistranded helices and achiral polygonal layers; larger (n,n) tubes also show helical and layered phases, tubes larger than (24,24) allow C60 at the center as well as the wall, and multi‑walled versus single‑walled tubes have only minor effects.

Abstract

A simulated annealing method was used to study the minimum energy configurations of ${\mathrm{C}}_{60}$ molecules inside carbon nanotubes. Simulations for over 50 nanotubes with radii from 6.27 \AA{} to 13.57 \AA{} showed that ten different phases exist in this size range. Both chiral and achiral phases were found. The achiral phases consist of layers of stacked polygons rotated by an angle of $360/(2k)$ relative to each other, where k is an integer. The chiral phases consist of multistranded helices. Tubes of larger radii, each of the $(n,n)$ type, were also studied; these also exhibited helical and polygonal-layered phases. For tubes larger than (24,24), ${\mathrm{C}}_{60}$ molecules can be at the tube center as well as at the wall. The effects of multiwalled versus single-walled tubes were shown to be small. The phase structure is very sensitive to the tube radius and is different from that for the packing of hard spheres.