One-Dimensional and Two-Dimensional Quantum Systems on Carbon Nanotube Bundles

We report the first measurement of the structure of ⁴He atoms adsorbed on bundles of single-walled carbon nanotubes. Neutron diffraction techniques and nanotube samples closed at the end were used. At low coverage, ⁴He forms a 1D, single line lattice along the grooves between two nanotubes on the surface of the nanotube bundles. As coverage is increased, additional lines of 1D lattices form along the grooves. This is followed by an incommensurate, 2D monolayer covering the whole nanotube bundle surface. The lattice constants of these 1D and 2D systems are largely independent of filling once a single 1D line is formed. No occupation of the interstitial channels between nanotubes is observed in the present sample.