Multiterminal junctions formed by heating ultrathin single-walled carbon nanotubes

Ultra-thin single-walled carbon nanotubes can be welded by heating to form molecular multi-terminal junctions at elevated temperatures without initially introducing structural defects such as vacancies and interstitials. This was demonstrated by classical molecular dynamics simulations with an empirical Brenner II potential and quantum mechanics calculation with PM3. The dynamic formation pathway of the junctions between crossed nanotube pairs was simulated. Junctions were established by forming intertube ${\mathrm{sp}}^3$-related covalent bonds and breaking of bonds in original nanotubes. The final configuration of junctions depends on the chirality of the crossed tube pairs and reaction temperature. Junction formation from nanotubes with larger diameters requires higher temperature.

Figure 1

(Color) Initial configuration of two crossed $(3,3)$ UTCNTs, with atoms (${\mathrm{a}}_1{\mathrm{-a}}_4$ and ${\mathrm{b}}_1{\mathrm{-b}}_3$) highlighted in blue which are included in bonding arrangement.

Figure 2

(Color) Snapshots from simulation of welding two crossed $(3,3)$ UTCNTs at $1800\mathrm{K}$ (side and top view). (a) After $0.53\mathrm{ns}$, two tubes approach each other and one new ${\mathrm{sp}}^3$-related intertube bond ${\mathrm{a}}_1{\mathrm{b}}_1$ with length of $1.434\mathrm{\AA }$ (in red) is formed (side view). (b) After $0.565\mathrm{ns}$, another intertube bond ${\mathrm{a}}_2{\mathrm{b}}_2$ (in red) is formed; resulting in a highly stressed and saturated intratube bond ${\mathrm{a}}_1{\mathrm{a}}_2$ denoted by green arrow (side view), which is. broken quickly (c) to release the stress (side view). (d) After $0.728\mathrm{ns}$, the third intertube bond ${\mathrm{a}}_3{\mathrm{b}}_3$ is generated (top view), and the strained ${\mathrm{sp}}^3$-related intratube bond ${\mathrm{b}}_1{\mathrm{b}}_3$ marked by green arrow in (c) is broken to reduce the total energy (e). (f) After $0.9\mathrm{ns}$, the fourth intertube bond is created, causing two ${\mathrm{sp}}^3$-related intratube bonds (${\mathrm{b}}_2{\mathrm{b}}_4$ and ${\mathrm{a}}_3{\mathrm{a}}_4$) marked by arrow, which are broken successively in (g) and (h). Connection between two tubes is established through four enneagons (in blue) and one enneagon is shown in (i). ${\mathrm{Sp}}^3$ atoms are highlighted, in red, and ${\mathrm{sp}}^2$ atom in topological defect in blue.

Figure 3

The variation of total energy for all the configurations (denoted by squares) during the welding process. Initial: the initial configuration of crossed $(3,3)$ tubes with wall to wall distance of $4.0\mathrm{\AA }$; $\mathrm{a-h}$: configurations corresponding to those in Figs. 2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h.

Figure 4

(Color) Figures 4a, 4b, 4c, 4d show the final configurations of the multi-terminal junctions between two crossed $(3,3)\text{−}(3,3)$, $(5,0)\text{−}(5,0)$, and $(3,3)\text{−}(5,0)$ UTCNTs at $1300\mathrm{K}$ (a), $1800\mathrm{K}$ (b), $2300\mathrm{K}$ (c), $2500\mathrm{K}$ (d), and $2800\mathrm{K}$ (e), with ${\mathrm{sp}}^3$ atoms in red, ${\mathrm{sp}}^1$ atoms in yellow, and ${\mathrm{sp}}^2$ atoms in topological defects in blue. Left column for $(3,3)\text{−}(3,3)$ tubes, middle column for $(5,0)\text{−}(5,0)$ tubes, and right column for $(3,3)\text{−}(5,0)$ tubes.