Dislocation Dynamics in Multiwalled Carbon Nanotubes at High Temperatures

Dislocation dynamics dictate the mechanical behavior of materials. Dislocations in periodic crystalline materials have been well documented. On the contrary, dislocations in cylindrical carbon nanotubes, particularly in multiwalled carbon nanotubes (MWCNTs), remain almost unexplored. Here we report that a room temperature $\frac{1}{2}⟨0001⟩$ sessile dislocation in a MWCNT becomes highly mobile, as characterized by its glide, climb, and the glide-climb interactions, at temperatures of about $2000°\mathrm{C}$. The dislocation glide leads to the cross-linking of different shells; dislocation climb creates nanocracks; and the interaction of two $\frac{1}{2}⟨0001⟩$ dislocations creates kinks. We found that dislocation loops act as channels for mass transport. These dislocation dynamics are drastically different from that in conventional periodic crystalline materials due to the cylindrical, highly anisotropic structures of MWCNTs.

Figure 1

In situ dislocation dynamics in a MWCNT. Arrowheads and slim arrows point out the dislocation cores and the dislocation lines, respectively. The fat arrow points out a kink. The voltage applied to the nanotube was 2.55 V. The dislocation climb velocity is $19\mathrm{nm}/\min$. The core of the edge and screw dislocations in (e)–(i) is marked in red, and green, respectively: (a) A dislocation with a Burgers vector of $\frac{1}{2}[0001]$ is nucleated. (b) The dislocation climbs up. (c) A dislocation with a Burgers vector of $\frac{1}{2}[000\overline{1}]$ is formed, and it interacts with the climbing-up $\frac{1}{2}[0001]$ dislocation. (d) The $\frac{1}{2}[0001]$ dislocation annihilates with the $\frac{1}{2}[000\overline{1}]$ dislocation, forming a kink, (e)–(f) An atomic structural model of the dislocation in (c). The atoms marked in blue are for reference, (g)–(i) Schematic structural model explaining the kink formation due to the dislocation interaction.

Figure 2

In situ dislocation dynamics in a MWCNT. The voltage applied to the nanotube was 2.55 V. The dislocation migration velocity is $8.5\mathrm{nm}/\min$. Arrowheads and dashed lines in (a)–(c) denote the dislocation cores and the dislocation lines, respectively. The stars mark nanocracks. The dislocation in the lower part of (a) climbs up, and it interacts with another dislocation (b), forming a dislocation loop (c). (d)–(e) An atomic structural model of the dislocation in (a). The atoms marked in blue are for reference. (f)–(k) Interactions of two dislocation loops, (f) the loop A is a pure edge dislocation loop (as shown by a symbol “$\perp$”) that encloses the tube hollow and tube axis. The loop B is a mixed loop located on one side of the tube hollow, and it does not enclose the tube hollow. The loop A climbs up to meet with the loop B (g). Part of the loop A and part of the loop B annihilate with each other forming a new dislocation loop C (h). The arrowheads in the figure show the climb direction of the dislocations, (i)–(k) Atomic structural models of the dislocation loops shown in (f)–(k), respectively.

Figure 3

In situ dislocation dynamics in a MWCNT. The dashed lines in (a)–(c) denote the dislocation lines. The voltage applied to the nanotube was 2.55 V. The dislocation core is marked in red (edge components) and green (screw components) in (d)–(j). As the dislocation climbs up, it also glides from underneath the surface shell [(a),(b)] to the nanotube surface (c). The dislocation migration velocity is $1.8\mathrm{nm}/\min$. (d)–(g) Schematic drawing explaining the dislocation dynamics in (a)–(c). (d)–(e) An edge dislocation. (f) The edge dislocation slips out partly. (g) The dislocation slips completely out to the surface. (h)–(j) An atomic structural model of the dislocation in (f). The inner tube walls are shown in blue and the outer tube walls are shown in black.