Chirality Selective Growth of Aligned Single-Walled Carbon Nanotubes on Graphite Surface
How to realize the chirality controlled growth of single-walled carbon nanotubes (SWNTs) in chemical vapor deposition (CVD) system has been viewed with the greatest challenge due to lack of the basic guidelines and characterization methods. Although a few reported cases showed the produced SWNTs with chirality selectivity, actually the catalyst nanoparticles with a narrow size distribution were mostly used to refine the diameters of produced SWNTs rather than their chiralities. Meanwhile, SWNTs with the similar diameters and chiral angles display a marginal difference of physical properties. So, a prominent method is essential to distinguish the tiny difference. As we known, the SWNT can be considered as a seamless cylinder formed by rolling a piece of graphene. In this way, each SWNT with specific (n, m) index should possess its own optimum orientation on graphite surface due to their lowest interaction.
Herein, the graphite substrates were used to grow SWNTs in CVD system. It was found that the chiralities of aligned SWNTs strongly related to their grown directions. In short, few layer graphene or graphite was mechanically exfoliated onto Si substrates (300 nm oxide layer) by scotch type. Following the lattice-directed and kite-flying growth mechanism, the nanodiamonds were used as non-metallic nucleated centers to grow SWNTs at 850 oC and 950 oC, respectively. AFM images showed the obtained SWNTs presented the fancy topographies with some special angles like 30o, 60o, 150o, 180o, etc. on the graphite surfaces. The Raman spectra of SWNTs from 13CH4 appeared the typical RBM and G bands. Meanwhile, the STM results with atomic resolution proved the identical benzene ring arrangements between SWNT and its graphite surface. Furthermore, the density functional theory simulation also showed that the global minimum of the potential energy surface appeared at the alignment angles of α = 30o - θ, where α was the orientation of the tube on the graphene surface. In conclusion, the SWNTs with chirality selectivity were successfully produced on few layer graphene or graphite surfaces. We hope that the obtained SWNTs should have more applications in nanoelectronics field.