This work covers the analysis of the nonmagnetic-catalyzed plasma chemical vapor deposition (PCVD) of single walled carbon nanotubes (SWNTs). The selective growth of SWNTs by the nonmagnetic catalyst using PCVD is realized for the first time. Experimental investigations are presented, which allow to get a comprehensive picture of the nonmagnetic catalytic growth of SWNTs by PCVD. The PCVD growth of SWNTs is performed on an alumina supported Au catalyst using methane as a carbon source. The methodologies to accomplish the controlled growth of SWNTs, i.e., diameter, density, and chirality are investigated. The Au catalyst can afford the SWNTs growth with narrow diameter and chirality distribution with PCVD by carefully adjusting the experimental parameters. Methane PCVD on the Au catalyst under well-defined conditions produced predominantly (6,5) SWNTs according to Raman, UV-Vis-NIR absorption, and photoluminescence excitation/emission (PLE) spectroscopic characterizations. The high yield of (6,5) semiconducting SWNTs produced by the structure controlled synthesis described above is promoted us to directly use the as-synthesized SWNTs for constructing nanotube field effect transistors (FETs), which suggests the SWNTs grown from the nonmagnetic catalyst with PCVD display the best device performance in comparison with thermal chemical vapor deposition (TCVD) synthesized and magnetic catalyzed SWNTs based devices. Based on the magnetic measurements with the Au catalyzed SWNTs, we observe that the nonmagnetic catalyzed SWNTs show ferromagnetic features, which suggest that the ferromagnetic features might come from the SWNTs itself. Hence this narrow-chirality distributed Au catalyzed SWNTs selectively grown with PCVD could be attractive to both fundamental studies of intrinsic magnetic properties of SWNTs and industrial applications to nanoelectronics.

In situ plasma analysis was performed during the single-walled carbon nanotubes (SWNTs) growth from nonmagnetic catalysts with plasma chemical vapor deposition (PCVD). The system based on optical emission spectroscopy (OES) was dedicated for in situ diagnostics of PCVD processes. The SWNTs growth was performed for a various H2 flow rates with 50W of an radio frequency (RF) power. Nonmagnetic metal particles were found to have catalytic activity for the growth of SWNTs under a specific plasma condition. The plasma analysis revealed that the intensities of Ha and CH radicals remarkably increased and decreased by increasing the H2 flow rate, respectively. Based on the comparison between the growth condition of SWNTs and results of plasma analysis, it was found that the intensity ratio of CH/ Ha shows fairly similar tendency to the yield of SWNTs as a function of H2 flow rate, i.e. SWNTs could be grown from nonmagnetic catalysts only when CH/ Ha is high. This indicates that the intensity ratio of CH/ Ha could be useful to optimize the growth condition of SWNTs with Au catalyst.

This paper describes experimental research on synthesis of single walled carbon nanotubes (SWNTs) from nonmagnetic catalysts with plasma chemical vapor deposition (PCVD). Nonmagnetic metal particles were found to have catalytic activity for the growth of SWNTs under a specific plasma condition. An actinometry method based on optical emission spectroscopy (OES) measurements was also used to determine the molar fraction of monoatomic hydrogen and carbon species produced in plasma. We found that Methane conversion is remarkably promoted using plasma which enhances growth of SWNTs over nonmagnetic catalysts. It is well known that metals such as Au, Ag, and Pt have low adsorption and dissociation for catalytic reactions. Hence external forces such as methanehydrogen discharge are required for high dissociation of hydrocarbons. Plasma–catalyst reaction system is able to generate desired reactants for SWNTs growth from nonmagnetic catalysts.

Optical emission spectra (OES) of a CH4-H2 plasma during synthesis of single walled carbon nanotubes (SWNTs) using an Au catalyst were in-situ examined for the purpose of understanding the formation mechanism of SWNTs over the Au catalyst. From OES analysis, it was shown that changing the hydrogen related radicals, which are regarded as etching species in SWNTs growth by varying the H2 flow rate made effects on the diameter and yield of the SWNTs. Also OES investigations during the SWNTs growth suggest that CH/Ha can be useful for finding the optimum condition for the SWNTs growth by plasma chemical vapor deposition (PCVD) method.