CNT arrays grown upon catalytic nickel particles as applied in the nanoelectronic devices: Ab initio simulation of growth mechanism

Carbon nanotubes, due to their exceptional and unique properties, have aroused a lot of research interest making them promising candidates as interconnects for future high-speed nanoelectronics. To predict a growth mechanism for carbon nanotubes (CNTs) upon a metal particle as synthesized in the porous membrane block then incorporated in the nanoelectronic device, we have performed a series of large-scale DFT-LCAO calculations using the CRYSTAL-06 code. Carbon adatoms can appear upon the densely-packed Ni(111) catalyst surface due to dissociation of hydrocarbon molecules (e.g., CH ₄) when applying the CVD method for the nanotube growth. We have started with adsorption properties of carbon atoms. Then, we have simulated the regular C/Ni(111) interface, where adatoms initially form a monolayer which can be disintegrated to nanoflakes gradually transforming into CNT embryos (in the form of semi-fullerenes) and, finally, into the capped CNTs (d _C-C ≈ 1.42 Å) with either armchair or zigzag chirality. Periodicity of this system results in models of infinite arrays (bundles) of single-walled (SW) CNTs with a diameter 8.0-8.2 Å and the inter-tube distance 4.2-4.6 Å (depending on chirality). Analyzing the results of calculations on the CNT/Ni interconnect, we have observed a considerable transfer of the electronic charge from the metallic catalyst towards the nanotube (up to ∼1.4 e per contacting C atom) accompanying by substantial redistribution of the electronic density, especially in the case of nanostructured Ni(111) containing nickel nanoclusters. The nanostructured morphology of metal substrate has been found to be the most effective for the growth of CNT bundles.