| AVS 55th International Symposium & Exhibition | |
| In Situ Microscopy and Spectroscopy: Interfacial and Nanoscale Science Topical Conference | Thursday Sessions |
| Session IS+NS+TR+NC-ThM |
| Session: | In Situ Spectroscopy – Dynamic Nanoscale Processes |
| Presenter: | E.A. Stach, Purdue University |
| Authors: | E.A. Stach, Purdue University S.M. Kim, Purdue University D.N. Zakharov, Purdue University P. Amama, Purdue University C. Pint, Purdue University R.H. Hauge, Purdue University B. Maruyama, Purdue University |
| Correspondent: | Click to Email |
In order to understand how carbon nanotubes form, one must have a detailed understanding of the size, shape and evolution of the catalysts responsible for their nucleation and growth. In this presentation, we describe our recent studies in understanding the evolution of Fe catalysts deposited on alumina during the so-called supergrowth of carbon nanotubes. These studies rely heavily on the exploitation of the unique capabilities of environmental transmission electron microscopy to observe at the atomistic scale how catalyst nanoparticles transform under varying regimes of temperature and pressure. We will show that modifications of the substrate treatment and carrier gas atmosphere have a strong effect on catalyst coarsening. In particular, we find the presence of H2O – the key ingredient in supergrowth – leads to a reduction in the Ostwald ripening of the Fe catalysts, thereby leading to denser nanotube carpets. Additionally, under conditions identical to those used in supergrowth, we confirm the diffusion of Fe into the Al2O3 supporting layer. This effect could play a significant role in the catalyst surface density during supergrowth, as well as provide another route in which carpet growth may terminate. These studies are correlated with real time TEM observations of the Ostwald ripening rate of Fe nanoparticles on different supports in H2 and H2 + H2O atmospheres, and on the nucleation and growth of the tubes themselves.