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

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 vertical bar vertical bar n(2) - n(1)vertical bar - vertical bar m(2) - m(1)vertical bar vertical bar + min{vertical bar n(2) - n(1)vertical bar, vertical bar m(2) - m(1)vertical bar} with (n(2), m(2)) rotating pi/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 vertical bar n(1) - n(2)vertical bar + vertical bar m(1) - m(2)vertical bar. 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 similar to 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.