The effect of defects upon the static first hyperpolarizability (β0) for topological Stone-Wales, single-vacancy and double-vacancy defects was studied. For eight carbon nanotubes with defects and one relevant perfect nanotube, the obtained order of the β0 values was 0 (perfect) < 5.0 x 102 (DV585-z) < 5.3 × 102 (SW5577-z) < 4.6 x 103 (DV585-xz) < 6.0 x 103 (DV555777) < 7.3 x 103 (SV-xz) < 1.1 x 104 (SV-z) < 3.3 x 104 (SW5577-xz) < 2.2 x 105au (SW57-75). The results showed that the defect played an important role in greatly enhancing the β0 value due to lowering the transition energy. Four interesting relationships between the defect and the β0 value were observed. The defects caused a large increase in the β0 values. For Stone-Wales and double-vacancy defects, the direction of the defect was an important factor in enhancing the β0 value. Thus the β0 values of SW5577 structures were 3.3 x 10 4 (near xz direction) ≫ 5.3 x 102au (the z direction along the tube axis). Not vacancy defects, but topological defects, could produce the largest β0 value (2.2 x 105au for SW57-75). For topological Stone-Wales defects, the separate pentagon-heptagon pair defect (57-75, β0 value of 2.2 x 105au) could be more efficient than the fused one (5577, 3.3 x 104au) in enhancing the β0 value. This suggested a new strategy for introducing the correct defect into carbon nanotubes so as to enhance the non-linear optical response.

What Is the Role of Defects in Single-Walled Carbon Nanotubes for Nonlinear Optical Property? Z.B.Liu, Z.J.Zhou, Z.R.Li, Q.Z.Li, F.Y.Jia, J.B.Cheng, C.C.Sun: Journal of Materials Chemistry, 2011, 21[24], 8905-10