AVS 54th International Symposium | |
Nanometer-scale Science and Technology | Thursday Sessions |
Session NS-ThM |
Session: | Nanotube Devices and Processes |
Presenter: | Y. Suda, Hokkaido University, Japan |
Authors: | Y. Suda, Hokkaido University, Japan T. Saito, Hokkaido University, Japan A. Okita, Hokkaido University, Japan J. Takayama, Hokkaido University, Japan J. Nakamura, Tsukuba University, Japan Y. Sakai, Hokkaido University, Japan H. Sugawara, Hokkaido University, Japan |
Correspondent: | Click to Email |
Oxidant has been used for growth promotion of carbon nanotubes (CNTs) in CVD since the work by Hata, et al.1 We report the effect of CO2 addition to CH4 gas on CNT growth. The CVD chamber is evacuated down to 10-6 Torr by a turbo-molecular pump followed by a rotary pump. We used Mo(0.025)/Fe(0.05)/MgO(0.925) or Mo(0.025)/Ni(0.05)/MgO(0.925) as a catalyst, H2 gas as a reductant and CH4 gas as a feedstock.2 CO2 gas was introduced during the CNT growth at a temperature of 800°C and its concentration in CH4 was varied from 0.0037% (37 ppm) to 50%. The other experimental parameters are as follows: H2 gas pressure = 100 Torr and flow rate = 100 sccm for reduction; CO2/CH4 gas pressure = 100 Torr and flow rate = 76 sccm for growth. The CNT yield and the G/D ratio in the Raman spectra of CNTs grown in 10%-CO2/CH4 were slightly higher (~86%) than that grown in CH4 only (~71%). However, CNTs were hardly grown when the CO2 concentration was more than 20%. Decreasing the CO2 concentration down to 37 ppm, it was found that single-walled CNTs (SWCNTs) with a yield of ~10% were grown and that the yield for 60 min was 1.5 times higher than that for 10 min. This suggests that the SWCNT growth in a CO2/CH4 gas mixture continued for 60 min. The G/D ratio obtained from 37 ppm-CO2/CH4 was almost the same as that grown from CH4 only. The radial breathing mode (RBM) obtained by a 632.8 nm excitation shows that the SWCNT diameter ranges from 0.9 to 1.3 nm and that a few metallic SWCNTs were eliminated but most of semiconducting SWCNTs remained.
1K. Hata, et al, Science, 306 (2004) 1362-1364
2L.-P. Zhou, et al, J. Phys. Chem. B, 109 (2005) 4439-4447.