Fig. 4.
Summary of DFT results. (A) DFT-optimized structure for a (9, 0) single-walled carbon nanotube/Co periodic heterojunction (see Fig. 1). The bonds between the Co atoms and the carbon atoms are highlighted in orange and have been drawn by using a cutoff of 2.1 Å. (B–D) Isocontour plots of the charge density for 3 different longitudinal planes cut parallel to the system's axis. Metallic binding is apparent in the Co section, whereas covalent (directional) binding can be seen both in the nanotube section and at the interface between the tube and the metallic particle. The atomic positions in the ball-and-stick representation are drawn in correspondence to the 3 isocontour plots. The units of the color bar are in electrons/Å3. (E) Isosurface plots (q = 10−6 electrons per Å3) of the charge density in a periodic multijunction system at the Fermi level (red, density integrated in a small window of 0.2 eV below the Fermi level; blue, in a 0.2 eV window above the Fermi level).