Silica nanotube multi-terminal junctions as a coating for carbon nanotube junctions

The possibility of coating carbon nanotube junctions with single-walled, square-lattice silica nanotubes is considered. We describe the topology of junctions of such tubes, based on the generalized Euler formula for a tetragonal lattice with trigonal, pentagonal, and hexagonal topological defects. The types of silica nanotubes best fitting the considered carbon nanotube types are determined using a classical interatomic force field. The influence of the silica coating on the electronic properties of the carbon nanotube is evaluated using semiempirical Paramagnetic Model 3 (PM3) method calculations. It is found that the electronic properties of the carbon nanotube near the Fermi level are not changed considerably. Finally, we propose some examples of $\mathrm{Si}{\mathrm{O}}_2\text{−}\mathrm{C}$ composite T-, Y-, and X-junction structures.

Figure 1

(Color online) The cluster structure that was used to determine the types of silica nanotubes best fitting various carbon nanotubes. The structure shown is a (14, 0) carbon nanotube inside a (20, 0) silica nanotube. (a) side view, (b) axial view.

Figure 2

(Color online) The energies of interaction between carbon and silica nanotubes with respect to the difference of their radii. The types of carbon nanotubes are $(n,0)$, where $n$ equals 6 (circles), 7 (squares), 8 (up triangles), 12 (down triangles), and 14 (diamonds). The types of silica nanotubes are given next to the data points.

Figure 3

(Color online) The PM3 density of states for a (6, 0) carbon nanotube inside a (10, 0) silica nanotube: blue/dark line, isolated carbon cluster; green/light line, isolated silica cluster; and red/dashed line, the composite system. The Fermi level energy is taken as zero.

Figure 4

(Color online) A (6, 0)–(8, 0) carbon nanotube junction coated with a (12, 0)–(14, 0) silica nanotube junction. The topological defects (a pentagon and a heptagon in the carbon tube, three- and five-member rings in the silica tube) are highlighted.

Figure 5

(Color online) Multi-terminal carbon nanotube junctions coated with silica nanotube junctions: (a) and (b) T-junctions; (c) and (d) Y-junctions; and (e) and (f) X-junctions. The topological defects in silica nanotube junctions are designated as $P$ (pentagons) and $H$ (hexagons).