The formation and stability of junctions in single-wall carbon nanotubes.

ABSTRACT

The structure and stability of molecular junctions, which connect two single-wall carbon nanotubes (SWCNTs) of different diameters and chiral angles, (n 1, m 1)-(n 2, m 2), are systematically investigated by density functional tight binding calculations. More than 100 junctions, which connect well-aligned SWCNTs, were constructed and calculated. For a highly stable junction between two chiral (n 1, m 1) and (n 2, m 2) SWCNTs with opposite handedness, the number of pentagon-heptagon (5/7) pairs required to build the junction can be denoted as ∣∣n 2 - n 1∣ - âˆ£m 2 - m 1∣∣+min{∣n 2 - n 1∣, ∣m 2 - m 1∣} with (n 2, m 2) rotating π/3 angle or not. While for a junction connected by two zigzag, armchair or two chiral SWCNTs with the same handedness, the number of 5/7 pairs is equal to ∣n 1 - n 2∣ + âˆ£m 1 - m 2∣. Similar to the formation energies of grain boundaries in graphene, the curve of the formation energies vs. chiral angle difference present an 'M' shape indicating the preference of ∼30 degree junctions. Moreover, the formation energies of the zigzag-type and armchair-type junctions with zero misorientation angles are largely sensitive to the diameter difference of two sub-SWCNTs.