(92a) Evolution of the Catalyst Nanoparticle Structure and Composition during Single Walled Carbon Nanotube Nucleation and Growth
The incorporation of single-walled carbon nanotubes (SWCNTs) into commercial technologies that exploit their remarkable properties is to a great extent dependent on the ability to synthesize them with specific structures and chiralities. The structural features of the metal catalyst nanoparticle during synthesis conditions by catalytic chemical vapor deposition (CCVD) are believed to play a fundamental role in determining the structure of the nascent nanotube cap throughout nucleation and subsequent growth. With the aid of computational tools such as reactive and ab initio molecular dynamics, and density functional theory together with real-time atomic-resolution transmission electron microscope observation of SWCNT growth on supported Co nanoparticles, we are able to look at the structure of the nanoparticle at different stages of the process. The evolution of the nanoparticle in terms of structural parameters and distribution of C atoms in the nanoparticle is monitored during the C dissolution, nanotube nucleation and growth stages. The interactions of the nanoparticle with the substrate and with the nucleating nanotube are found to play an important role in determining the nanoparticle shape and the distribution of C atoms inside the nanoparticle. Moreover, the observation of a C gradient and identification of pure metal and carbide-like size-fluctuating regions inside the nanoparticle and the correlation observed between such phenomena with the rates of incorporation of C atoms to the nanotube shed some light into the transport and reaction mechanisms.