Carbon Nanotube “T Junctions”: Formation Pathways and Conductivity

Using tight-binding molecular dynamics we simulate the formation of single wall carbon nanotube T junctions via the fusing of two nanotubes. We propose energetically efficient pathways for this process in which all atoms maintain their $s{p}^2$ arrangements throughout. Recent experimental advances have greatly increased the plausibility of synthesizing T junctions as proposed in the simulations. We further report $I\mathrm{\text{−}}V$ characteristics of the formed junctions.

Figure 1

Simulation results showing different steps leading up to the formation of the $(9,0)\mathrm{\text{−}}(10,0)\mathrm{\text{−}}(9,0)$ T junction. The defect rings are shown in red and include five-, seven-, eight-, and ninefold rings. All the atoms in the junction region are $s{p}^2$ bonded. The final structure contains eight heptagons and two pentagons.

Figure 2

Simulation results showing different steps leading up to the formation of the $(5,5)\mathrm{\text{−}}(10,0)\mathrm{\text{−}}(5,5)$ T junction. The defect rings are shown in red and include five-, seven-, and eightfold rings. All the atoms in the junction region are $s{p}^2$ bonded. The final structure contains six heptagons and no pentagons.

Figure 3

Relative energies at each step of the formation of $(9,0)\mathrm{\text{−}}(10,0)\mathrm{\text{−}}(9,0)$ and $(5,5)\mathrm{\text{−}}(10,0)\mathrm{\text{−}}(5,5)$ T junctions (large circles and large squares, respectively), as calculated using the GTBMD scheme. Intermediate energy points are represented by small circles and squares.

Figure 4

The $I\mathrm{\text{−}}V$ characteristics of the $(9,0)\mathrm{\text{−}}(10,0)\mathrm{\text{−}}(9,0)$ T junction obtained in the simulations shown in Fig. 1 for different values of gate voltages. The current direction is taken to be positive when flowing toward the junction region and negative otherwise. The figure shows current in the primary channel $I_s$ as a function of the bias voltage $V_s$ for five different values of the gate voltage $V_g$. The figure shows asymmetry in the $I\mathrm{\text{−}}V$ behavior with current saturation for positive values of $V_s$ for all values of $V_g$. The main effect of the variation in $V_g$ is the modulation of the current.