Theoretical investigation on the healing mechanism of divacancy defect in CNT growth by C2H2 and C2H4

Experimental studies have shown that chemical vapor decomposition method by using C2H2/C2H4 as carbon source could dramatically decrease the defects in prepared CNT. However, the inherent mechanism with regards to reduction of defects is quite unclear. In the present paper, density functional theory is used to study the healing process of CNT with divacancy defect by C2H2/C2H4 molecule. The healing processes undergo three evolution steps: (i) the chemisorption of the first C2H2/C2H4 molecule on defective CNT; (ii) the insertion of C atoms from C2H2/C2H4 molecule into defective CNT; (iii) the removal of the H atoms on CNT, forming perfect CNT. The estimated adsorption energy barrier of C2H2/C2H4 molecules on defective CNT is within the range from 1.10 to 1.63 eV, and the eventual formation of CNT is strongly exothermic (4.40/4.54 eV in (8, 0) CNT). In light of the unique conditions of CNT synthesis, i.e., high temperature in a closed container, such healing processes could most likely take place. Therefore, we propose that during CNT synthesis procedures, both C2H2 and C2H4 could act as a carbon source and the defect healer.