Growth Promotion and Etching of Carbon Nanotubes by Carbon Dioxide in Chemical Vapor Deposition using Methane Gas
- PDF / 547,446 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 59 Downloads / 249 Views
1057-II05-15
Growth Promotion and Etching of Carbon Nanotubes by Carbon Dioxide in Chemical Vapor Deposition using Methane Gas Yoshiyuki Suda1, Junichi Takayama1, Takeshi Saito1, Atsushi Okita1, Junji Nakamura2, Yosuke Sakai1, and Hirotake Sugawara1 1 Hokkaido University, Sapporo, 060-0814, Japan 2 University of Tsukuba, Tsukuba, 305-8573, Japan ABSTRACT We report the effect of CO2 addition to CH4 gas on carbon nanotube (CNT) growth by chemical vapor deposition. CO2 gas was introduced during the growth of CNTs on Fe0.05Mo0.025MgO0.925 and Ni0.05Mo0.025MgO0.925 catalysts by CH4 gas at a temperature of 800−850oC, and its concentration in a fraction of the gas flow rate was varied from 5×10-3 to 50%. In the experimental condition of the preferential growth of multi-walled CNTs, the carbon yield and the G/D ratio in the Raman spectra of the CNTs grown in 10%-CO2/CH4 were slightly higher than that grown in CH4 only. However, CNTs hardly grew when the CO2 concentration was more than 10%. We then prepared CO2 gas diluted with Ar gas (CO2/Ar) and varied its flow rate between 0 and 10 sccm. As the CO2/Ar gas flow rate was increased, the number of RBM peaks decreased even though the G/D ratio gradually decreased. The decrease in the RBM intensities of CNTs on the FeMoMgO catalyst was more significant than that of NiMoMgO. INTRODUCTION Chemical vapor deposition (CVD) has been a major technique for the growth of highlypurified carbon nanotubes (CNTs) since the works by Colomer et al [1] and Maruyama et al [2]. An excellent work by Hata et al [3] has led to the use of various oxidants to promote the growth of high-quality CNTs. Hata et al succeeded in the growth of mm-length single-walled CNTs (SWCNTs) by adding a minute amount of H2O (~175 ppm) in C2H4. Nasibulin et al clarified that CO2 was generated from the iron-containing chamber wall when CO was used for the disproportionation reaction of SWCNT growth, and reported the elongation of SWCNTs by adding ~1000-ppm CO2 in the CO environment [4]. CO2 was also used with CH4 gas for the improvement of purity and yield in SWCNTs growth [5]. In remote-plasma CVD, Zhang et al reported that the introduction of O2 in the CH4 gas generates OH radicals which subsequently reduces the number density of H radicals, which is not favorable for sp2 bond formation in SWCNTs [6]. These studies tell us that oxidants have a role of elongating CNTs. Meanwhile, the etching of particular CNTs using oxidants has been reported. Huang et al showed that metallic SWCNTs were selectively removed by laser irradiation with a fluence of ~1 mW/µm2 in air for 10 min [7]. Yang et al studied a gas phase reaction of SWCNTs with F2 gas, followed by a heat treatment, and removed metallic SWCNTs with certain diameters [8]. Here, we focus on the selective growth technique for forming metallic/semiconducting SWCNTs, in order to realize potential electronics applications of CNTs. It is known that CO2 has a weak oxidizing ability and etches the CNT surface [9]. Very recently, Wen et al showed that CO2 has a suppression e
Data Loading...
