A Molecular Dynamics Study Of Metal Nanoparticle-carbon Nanotube Composites

Metal nanoparticle-carbon nanotube composites are new emerging nanometerials with a variety of potential technological applications. Significant experimental efforts have been devoted to this subject in recent years, but fabrication of these nanocompisite materials is still under guess and trial due to lack of understanding of their fundamental growth mechanism which should be different from the description of the traditional materials growth theory for flat surfaces due to the large curvature of nanotubes. It is difficulty to obtain the real-time information about the formation process of these materials by experimental techniques. Because the composite contains a large number of atoms, it is not possible to use the first principles methods to investigate the growth process. Molecular dynamics (MD) simulation becomes the best approach to study the problem at the atomistic level.In the paper, we have simulated the formation process of gold nanoparticles on surfaces of single-wall carbon nanotubes with molecular dynamics method. We have analyzed the structures, energy of gold nanoparticles and the interaction between gold nanoparticles( Au1 5- Au 200) and carbon nanotubes. The motion and coalescence of nanoparticles on carbon nanotubes are also studied. We found that, at room temperature (298K), small gold nano- particles sitting on a carbon nanotube have different structures compared with isolated gold nanoparticles. Because of the interaction of between the nanoparticle and carbon nanotube, the melting point of a small Au nanoparticle on the surface of a nanotube is lower than room temperature. As a result, the nanoparticles in the range of ( Au1 5- Au1 30) have amorphous structures. We also found that the larger the nanoparticle the higher the melting temperature. Nanoparticles larger than Au1 40have melting temperatures higher than room temperature and remain their FCC structures. They exhibit bending deformation following the direction of the nanotube curvature. At room temperature, a nanoparticle smaller than Au 70 often escapes from the carbon nanotube surface and can be captured again by the nanotube or coalesces with other nanoparticles to form a larger nanoparticle. The larger nanoparticle then only moves along the nanotube direction and coalesce other nanoparticles on the nantube surface. Eventually, the nanoparticle becomes very large which only oscillates on the carbon nanotube locally and captures some small nanoparticles around it.