22B09
Chirality distribution control of single-walled carbon nanotubes fromnonmagnetic catalyst by diffusion plasma CVD
非磁性触媒利用拡散プラズマCVDによる単層カーボンナノチューブの構造制御合成
Koushi Murakoshi, Toshiaki Kato, Zohreh Ghorannevis, Toshiro Kaneko,
and Rikizo Hatakeyama
村越幸史, 加藤俊顕, ゴラネビスゾーレ, 金子俊郎, 畠山力三
Department of Electronic Engineering, Tohoku University
6-6-05 Aobaku, Sendai, 980-8579, Japan
東北大学 大学院工学研究科 電子工学専攻 〒980-8579 仙台市青葉区荒巻字青葉6-6-05
Single-walled carbon nanotubes (SWNTs) take on hollow cylinders formed by rolling up a graphenesheet made up of hexagonally bonded sp2 carbon atoms. The direction and magnitude of a roll-up vector
prescribe the chirality and diameter of the resulting tube, respectively. These geometric parameters in turn
determine the tube's electronic band structure. However, making SWNTs of defined structures still
remains to be a major challenge in the fundamental studies and applications of SWNTs. In this paper weshow the first result on the narrow-chirality distributed SWNTs using a gold-catalyzed plasma chemicalvapor deposition (PCVD) method through adjusting the H 2 gas and their electronic properties.

1. Introduction
Onedimensional
single-walledcarbonnanotubes (SWNTs) are potential materials for
future nanoelectronics [1]. Since the electronic andoptical properties of SWNTs strongly depend on
their diameter and chiral angle, the selective
synthesis of SWNTs with desired chiralities is oneof the major challenges in nanotube science andapplications [2]. Some progress has been made bysilica supported CoMo [3] and zeolite supported
FeCo [4] catalysts. FeRu [5] and FeNi [6] catalysts
have also been developed for the narrow chirality
distribution. Noticeably, all of these results on thenarrow chiraity distribution growth have been
limited to the case of using magnetic catalysts. In
spite of recent improvements in the SWNTs
growth with nonmagnetic catalysts [7-8], thediameter and chirality (n,m) distribution control
with the nonmagnetic catalysts is still highly
required for the variety of applications.
2. Experimental
Figure 1 represents the schematic of experimental
apparatus. The electrode distance (dele) is 10 mm andthe anode-substrate distance (dsub) is 50 mm. It is
possible to generate plasmas under various pressures
ranging from 50 Pa (low) to 10 kPa (high) in thissystem. On purpose to supply feedstock gases
uniformly, mesh grids are used as the electrodes. Since

Fig. 1: Schematic of experimental apparatus.

growth process is carried out in a diffusion plasma
region, the high quality SWNTs growth is considered tobe realized.
The SWNTs production is performed on a substratelayered with Au, Al2O3, SiO2, and Si. The gas pressure(Pg) is 60 Pa and the growth time (t) of SWNTs is 1min.
3. Results and Discussion
Here we demonstrate a narrow-chirality
distributed growth of SWNTs from an Au catalyst.
The chirality and diameter distribution is analyzed
by photoluminescence excitation/emission (PLE)
spectroscopy, UV-vis-NIR absorption spectroscopy,

Intensity (arb.units)625
500
750625500
750625500

of cap structures, which satisfy the isolated
pentagon rule, is highly limited for small diameter
SWNTs, and (6,5) is known to have one of thestable cap structures in this diameter range.

(d)9001150

Absorbance (arb.units )Excitation wavelength (nm)750400600800

1000

Wavelength (nm)1400Emission wavelength (nm)Fig. 2: PLE maps of SWNTs from Au catalyst by
PCVD at (a) 0-sccm, (b) 3-sccm, and (c) 7-sccm H2
flow rates, respectively. (d) UV-vis-NIR spectrum of
SDS-dispersed SWNTs from Au catalyst at 7-sccm
H2 flow rate.

and Raman scattering spectroscopy withmulti-lasers excitation. Based on the systematicinvestigation using the different combinations ofcatalyst types (magnetic or nonmagnetic) andchemical vapor deposition (CVD) methods (thermalCVD (TCVD) or plasma CVD (PCVD) [9]), PCVD
with the nonmagnetic catalyst under an appropriate
H2 concentration is found to be critical. Figures 2(a-c) and (d) show the PLE mapping and theUV-vis-NIR optical absorbance spectrum of the Au
synthesized SWNTs by the PCVD method with(6,5) dominant SWNTs, respectively. We have forthe first time demonstrated the selective growth of(6,5) rich SWNTs from the nonmagnetic catalyst[10].
This indicates hydrogen-assisted Au catalyzationis one of the critical factors to realize the narrowchirality distribution, which is in good agreementwith theoretical predictions. The first-principle
calculation by Yazyev et al. reveals that coinage
metals such as Cu, Ag, and Au produce narrowchirality distributions [11]. Ding et al. report theSWNTs diameter is larger on the surface of Fe, Co,and Ni particles than Cu, Pd, and Au particles
because of the different bond energies on thecatalyst surface [12]. Following these theoreticalmodels, we can explain the effect of H2-assisted Au
catalyzation on the narrow chirality distirbution as
follows. Since the binding energy of hydrocarbons
on the Au surface is much weaker than that on theFe surface, it is difficult in the large-diameter caseof Au catalyst to achieve the cap formation [12].
Additonal H2 also enhances the etching of carbon
precursor from the catalyst surface, which strongly
suppresses the growth of large diameter SWNTs,
and hence the chirality distribution grown from theAu catalyst can be narrower than that from the Fe
catalyst. The stability of the cap structure migh be apossible reason why the (6,5) tube is dominant inthis small diameter Au-PCVD SWNTs. The number

4. Conclusion
In conclusion, we have for the first timedemonstrated the narrow-chirality distributed
growth of SWNTs from the nonmagnetic catalyst.
The Au catalzed PCVD growth under theappropriate hydrogen concentration is figured to be
the critical factor in achieving the narrow chirality
distribution. This narrow-chirality distributed
SWNTs selectively grown from the nonmagnetic
catalyst could be attractive to both fundamental
studies of intrinsic magnetic properties of SWNTs
and industrial applications to nanoelectronics.
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