Reassembly of single-walled carbon nanotubes into hybrid multilayered nanostructures inside nanotube extruders

High-pressure induced structural reassembly of single-walled carbon nanotubes (SWNTs) inside carbon nanotube extruders is investigated by reactive molecular dynamics simulations. It is found that the encapsulated SWNTs undergo a series of structural transformations depending on tube diameters with increasing internal pressure, and finally reassemble into hybrid $s{p}^2\text{−}s{p}^3$ cross-linked multilayered tubular nanostructures inside the nanotube extruders. Density-functional calculations show that strong compression causes a semiconducting-to-metallic transition in the encapsulated tubes. The metallic properties of the formed nanostructures are mainly attributed to the shortening of carbon bonds and strong interlayer correlation.

Figure 1

(Color online) Systematic display of a (16,0) SWNT encapsulated into a (16,0) nanotube extruder. (a) The cross section and (b) sidewall display of the encapsulated tube (blue) and the outer nanotube extruder (red). The dash line in (b) represents the tube axis. The radius $R_o$ of the outer nanotube extruder is adjusted artificially by elongation or reduction of the carbon bonds on the wall which have initial angles of about 60° with respect to the axis of the tube. The pressure $P_o$ is exerted on the inner tube by reducing the radius of the outer nanotube extruder.

Figure 2

(Color online) (a) Average inner (16,0) tube radius $R_i$ after $100\mathrm{ps}$ MD relaxation and (b) corresponding average pressure $P_o$ buildup on the inner tube with decreasing the radius $R_o$ of the outer nanotube extruder after the whole system is stable. The arrows denote the critical values of damaging the inner tube.

Figure 3

(Color online) The cross section snapshots after $100\mathrm{ps}$ MD relaxation of the encapsulated (16, 0) SWNT under different internal pressures $P_o$ within the fixed (16, 0) nanotube extruder. The outmost layer is the nanotube extruder. The red lines in (b) represent the $s{p}^3$ carbon bonds.

Figure 4

(a) Potential energy of the CNTs, (b) average interlayer distance between the encapsulated nanotube and the outmost nanotube extruder, and (c) interlayer van der Waals energy with the radius $R_o$ of the CNT extruder.

Figure 5

The electronic properties of the encapsulated (16,0) SWNT under $P_o=35.6$ and $41.9\mathrm{GPa}$ and the isolated carbon nanostructures formed inside the nanotube extruder under $P_o=18.3$ and $35.2\mathrm{GPa}$ after the inner SWNT is collapsed. (a) Band structures. (b) Corresponding density of states.

Figure 6

(Color online) [(a) and (b)] Total charge density contour plots for the formed carbon nanostructures under 18.3 and $35.2\mathrm{GPa}$. [(c) and (d)] Corresponding charge density of the bands($-0.1–0.1\mathrm{eV}$ around the Fermi energy) closest to the Fermi level.

Figure 7

(Color online) (a) The tubular nanostructure formed under $35.2\mathrm{GPa}$ within the extruder and (b) the corresponding relaxed structure. (c) The tubular nanostructure formed under $51.7\mathrm{GPa}$ within the extruder and (d) the corresponding relaxed structure. Here, the red lines represent the $s{p}^3$ carbon bonds.

Figure 8

(Color online) The variations of the radius $R_i$ of 0.85 and $4.3\mathrm{nm}$ inner tubes with average pressure $P_o$ buildup on the inner tubes. The arrows denote the critical values of damaging the inner tube. The inset shows the cross sections of damaged inner tubes under the compression of the outer nanotube extruder slightly larger than the critical value.

Figure 9

(Color online) The cross section snapshots after $100\mathrm{ps}$ MD relaxation of the encapsulated (16, 0) SWNT with a finite length of $4.3\mathrm{nm}$ under (a) $P_o=49.9\mathrm{GPa}$ and $R_o=0.756\mathrm{nm}$ (here, the interlayer carbon bonds of the tube ends are denoted by the red color), (b) $P_o=44.9\mathrm{GPa}$ and $R_o=0.746\mathrm{nm}$, and (c) $P_o=35.9\mathrm{GPa}$ and $R_o=0.736\mathrm{nm}$. In (b) and (c), the inner tubes are denoted by the red color.

Figure 10

(Color online) The cross section snapshots after $100\mathrm{ps}$ MD relaxation of the encapsulated (26, 0) SWNT under different internal pressures $P_o$ within the fixed (26, 0) nanotube extruder. The outmost layer is the nanotube extruder and the $s{p}^3$ carbon bonds are denoted by the red color.