(a) 15-atom nanoparticles of copper (orange) and cobalt (blue) interacting with nanotube caps of (n,m) chiralities (carbon atoms shown as gray spheres). The angle defined by the highlighted atomic plane (red line) in the nanoparticle and the perpendicular to the nanotube axis correlates with the chiral angle of the nascent nanotube (cap). The nanotube schematic at the right is introduced to facilitate interpretation. (b) Top view (top) and side view (bottom) of the epitaxial matching between a cobalt nanoparticle (blue atoms) and a molybdenum-carbide support (Mo atoms gray, C atoms yellow). (c) Structure of a Co nanoparticle (blue) during nanotube growth for strong nanoparticle/substrate interaction E adh (left) and for a weaker interaction (right). E adh is related to the potential well of the metal-substrate potential (see methods).
Time-evolution of metal density profile in the z direction perpendicular to the substrate, for different metal/substrate interaction strengths (E adh), along with corresponding structures taken at approximately the same stage of nanotube growth. The bar diagrams show the different types of growth through the 6.0 ns of simulation: (D) dissolution (yellow), (N) cap nucleation (red), (L) cap lift-off, and (G) growth (blue). Statistical data for the density profiles are gathered for four time intervals: 0–1.5 ns (blue), 1.5–3.0 ns (red), 3.0–4.5 ns (green), and 4.5–6.0 ns (purple).
The surfaces modeling a step defect in the catalytic nanoparticle. Top: schematic images represent the nanoparticles being modeled. (a) The step/terrace structure of the Co(321) surface (middle left image) and the most stable chain structure around the step (bottom, left). (b) The step/terrace structure of the Co(211) surface (middle right) and the most stable structure around the step (bottom, right). Co atoms in light blue, C atoms in yellow, step Co atoms in dark blue, and the (100) step is highlighted with the yellow straight line.
(a) Carbon dimers on the Co(211) surface initially located to bias the formation of an armchair chain (top), and the final configuration after optimization (bottom). (b) Carbon dimers on the Co(321) surface initially located to bias the formation of a zigzag chain (top), and the final configuration after optimization (bottom). Addition of carbon in positions denoted with an “x” completes a continuous armchair structure. (c) Schematic of armchair (ac) and zigzag (zz) orientations of a hexagonal ring respect to the step in Co(211) (red line), and Co(321) (green line). (d) Hexagonal rings at different orientations on a Co(211) surface. An “o” denotes a metallic atom halting a carbon–carbon bond (top). Addition of carbon in the positions denoted with an “x” completes a new ring (bottom). (e) Hexagonal rings at different orientations on a Co(321) surface. Color code for the atoms as in Fig. 3.
(a) Carbon nucleation by sequential addition of single C atoms on the step of Co(211). (b) Successful armchair carbon chain nucleation sequence on the step of Co(321). (c) Carbon adsorption energy diagram during the nucleation steps in (a) and (b).
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