The
interest in carbon nanotubes (CNTs) and
graphene originates
from their unique properties such as electronic and thermal transport and the
fact that they are strong and light weight.
Depending on the structure (chirality) of CNTs and the width of the
graphene ribbons, they can be either metallic
or semiconducting. This, together
with their nanometer sizes, makes them ideal for producing nanoscale
electronic devices. Since they are light
and strong they are also used to reinforce and modify materials such as plastics
(polymers) and textiles.
Two
of the challenges that remain in carbon nanotechnology are:
1) Development of methods to produce CNTs and graphene having a desired property.
2) Controlled processing of polymer nanocomposites to produce products with desired properties (such as strong textiles that conduct electricity and heat).
A deep understanding of the carbon nanotube growth mechanisms may allow us to grow the desired nanotube (i.e., having the desired structure) in the absence of other nanotubes. The figure below shows results of our simulated growth of carbon nanotubes from an iron-carbide particle. These simulations allow us to understand many details of the growth procedure, such as the role of the particle in maintaining an open end of the carbon nanotube (which is critical for continued nanotube growth), the fact that only one CNT can grow from each metal particle of this size and that the diameter of the CNT increases with the diameter of the metal particle.
We have used a semiempirical tight binding method to study the growth of graphene. The figures below shows that we can simulate the growth of a perfect graphene structure (where all of the defects are at the edges of the graphene and they are healed before they enter the hexagonal network). Comparison of the growth in vacuum and on a nickel surface shows that the metal surface i) allows C atoms to be dissolved in subsurface sites, ii) allows the growth of long carbon chains and iii) stabilises the carbon islands that are the nucleation sites for the growth of large graphene layers.
Collisions between ambient gas molecules and nanotubes
are important during nanotube growth and are important when using CNTs as sensor devices. It is thus important to understand scattering dynamics between gas molecules and nanotubes. The movies below (click on the figures) show collisions between a Xe atom (in red) and a carbon nanotube. In the first movie the nanotube is at 0 K so that the impact induced indentation of the nanotube by the Xe is clearly seen. The second movie shows a single-encounter collision with a tube at 1300 K. The frames are more frequent in this movie (one frame per 10 fs) so that the large amplitude thermal motion of the tube atoms are clearly seen. Two encounters of a multiple-encounter collision are shown in the third movie. Experimental results have also ahown that these large amplitude collisions change the electrical (scattering) properties of the CNTs, hence making them very accurate sensors of inert gases.
More information can be found in our publications.
This research, which is done in collaboration with experimental groups, has been or is funded by the Swedish Foundation for Strategic Research, Honda Research Institute Inc, and The Swedish Research Council.