4He adsorbed outside a single carbon nanotube

TL;DR

This study uses diffusion Monte Carlo simulations to explore how helium-4 adsorbs on the outside of single-walled carbon nanotubes, revealing different phases depending on nanotube radius.

Contribution

It provides the first detailed phase diagrams of helium-4 on nanotube surfaces, identifying stable solid and liquid phases based on nanotube size.

Findings

Narrow nanotubes favor incommensurate solid phases.

Wider nanotubes favor liquid layers.

Registered solid phases are unstable across all sizes.

Abstract

The phase diagrams of $^4$He adsorbed on the external surfaces of single armchair carbon nanotubes with radii in the range 3.42 -- 10.85 \AA \ are calculated using the diffusion Monte Carlo method. For nanotubes narrower than a (10,10) one, the ground state is an incommensurate solid similar to the one found for H$_2$ on the same substrates. For wider nanotubes, the phase with the minimum energy per particle is a liquid layer. Curved $\sqrt 3 \times \sqrt 3$ registered solids similar to the ones found on graphene and graphite were unstable for all the tubes considered.