First-principles study of a new type nanojunction: Finite length carbon chain inserted into half of a carbon nanotube

Based on first-principles calculations, we investigate the structure and electronic properties of a carbon atomic chain in finite length inserted into half of a single walled carbon nanotube (SWCNT), which we called half chain@SWCNT or more generally HCS. Comparing the optimized structure of HCS with that of the same chiral indices SWCNT and all carbon chain inserted SWCNT, we find that the geometry of the tube in HCS is slightly altered due to the weakly interacting between the inserted chain and the outer tube wall of HCS. Our calculation of band structure indicates that the armchair (5, 5) HCS exhibits metallic character, which is as that of (5, 5) SWCNT and all carbon chain inserted (5, 5) SWCNT. The zigzag (8, 0) and (9, 0) HCSs have small change in the energy gap compared to the corresponding pristine ones. Due to the downshift of conduction bands originating from the carbon chain, the calculation of band structure shows that chiral (6, 4) HCS is a semiconductor system with a small band gap of 0.94 eV, less than 1.125 eV in pristine SWCNT. The studied HCSs with unique structure and electronic property may construct a new generation nanoscale junctions without the usual heptagon-pentagon defect pair considerations.