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First measurements of the structure of 4He adsorbed on carbon nanotubes

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As helium is added, it is adsorbed first in 1D lines in groves on the outer ... As more is added, it is adsorbed around the grooves (middle figure) and then ... – PowerPoint PPT presentation

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Title: First measurements of the structure of 4He adsorbed on carbon nanotubes


1
First measurements of the structure of 4He
adsorbed on carbon nanotubes J.V. Pearce, M.A.
Adams, O.E. Vilches, M. Johnson, and H.R. Glyde
Carbon nanotubes are sheets of carbon atoms
rolled into seamless cylinders of 1-2 nanometers
diameter and thousands of nanometers long. They
combine into long bundles or ropes containing
many tubes, as shown opposite. Nanotubes are of
great interest for their unique, nearly one
dimensional (1D) character, their rigidity and
potential to adsorb large amounts of gas by
percentage weight. Widely varying amounts of
hydrogen absorption have been reported and
results still remain difficult to interpret
microscopically. We report the first
measurements of the structure of helium absorbed
on nanotubes using neutron scattering. The aim is
to test many remarkable predictions and to
explore a simpler quantum system than hydrogen
that is easier to interpret. As helium is added,
it is adsorbed first in 1D lines in groves on the
outer surface of the bundles (upper figure). As
more is added, it is adsorbed around the grooves
(middle figure) and then over the whole outer
surface of the bundles (lower figures). This
shows that a genuine 1D system can be created in
which 1D transport models can be tested and that
there is a 1D to 2D crossover as filling
increases. Higher fillings with open-ended
nanotubes remain to be explored.

Figure Helium on closed end nanotube bundles
green spheres are 4He atoms, grey spheres are
carbon atoms. The configurations, generated using
molecular dynamics simulations, reproduce neutron
measurements. Top 1D lines of 4He atoms, middle
3-line phase, bottom 1 monolayer coverage (2D
system).
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