AVS 50th International Symposium
    Nanotubes Thursday Sessions
       Session NT-ThM

Paper NT-ThM2
Iron-carbide Cluster Thermal Dynamics for Catalysed Carbon Nanotube Growth

Thursday, November 6, 2003, 8:40 am, Room 317

Session: Nanotube Growth and Processing
Presenter: A. Rosen, Goteborg/Chalmers University, Sweden
Authors: F. Ding, Goteborg/Chalmers University, Sweden
K. Bolton, Goteborg/Chalmers University, Sweden
A. Rosen, Goteborg/Chalmers University, Sweden
Correspondent: Click to Email
The mechanism of the growth of carbon nanotubes by chemical vapor deposition (CVD) method is still not well understood. It seems that the catalyst particles play a key role in controlling the size, defects, number of walls and chirality of the nanotubes. Knowledge about thermal properties of the catalyst particles in the temperature range (500-1200)@super o@C used in the CVD growth would be beneficial to the understanding of the growth mechanism. We have used molecular dynamics (MD) simulations for studies of the thermal behavior of C@sub m@Fe@sub N-m@ clusters with N up to 2400. Comparison of the computed results with experimental data shows that the simulations yield the correct trends for the liquid-solid region of the iron-carbide phase diagram as well as the correct dependence of cluster melting point as a function of cluster size. The calculations also show that the melting points of both pure Fe clusters (m=0) with diameter larger than 3 nm (about N>1000) and clusters composed of 10% C with diameter larger than 4 nm (about N>2400) are higher than 1000@super o@C. This indicates that, when nanotubes are grown on large catalyst particles at these lower temperatures, the catalyst particles are primarily in the solid - and not the liquid - state. The simulations indicate that nanotube growth may depend only on the surface melting of these clusters. This surface melting behavior and the coalescence of C@sub m@Fe@sub N-m@ clusters at temperatures lower than the melting point is also studied. At these low temperatures surface melting results in the coalescence of two clusters, where the final structure is similar to the minimum energy geometry.