(615e) Chiral-Selective Growth of Single-Walled Carbon Nanotubes by Lattice Matching Criterion

The synthesis of CNTs with predefined chirality and, therefore, functionality, remains one of the ultimate goals of nanoscience because of its potential impact on a wide-range of emerging technologies including nanoelectronics, renewable energy, nanocomposites, sensor and medical.  Recently, we showed that changing the composition of Ni_xFe_1-x bimetallic nanoparticles via a novel microplasma synthesis route resulted in chiral-selective growth of specific nanotube chiralities.  In this work, we used density functional theory calculations to explain and predict how the catalyst structure determines the chirality of as-synthesized SWCNTs.  Tuning composition will perturb the crystal structure, and affect the lattice matching of the nanoparticle with certain chiralities of the SWCNT, promoting chiral-selective growth.  To understand the effect of compositional tuning and perturbation to the crystal structure of a bimetallic catalyst on SWCNT chirality, we studied the energetics of representative chiralities such as the (8,4), (6,5), (9,4), (8,6), (7,5) and (10,3) nanotubes, which are predominantly seen in our experimental results.  We observe that a small increase in the average Ni-Ni bond length resulted in the increased stability of the (8,4) and (6,5) nanotube caps adsorbed on the Ni (111) surface whereas the (9,4) and (8,6) caps were destabilized. Remarkably, the (8,4) and (6,5) nanotubes are predominatly observed when the CVD growth took place on the Ni_0.27Fe_0.73 bimetallic nanoparticle which have a distorted fcc structure with a slightly increased Ni bond length. The findings strengthen our belief that chiral-selective growth of SWCNTs can be obtained by controlling the constituent atoms and their composition that results in a change in the lattice parameter of the bimetallic nanoparticle.