JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構

4-03
Synthesis of Single-Crystalline and Amorphous SiC
Nanotubes by Ion-Irradiation Technique
T. Taguchi a) , S. Yamamoto b) , K. Kawaguchi b) , K. Kodama a) and S. Shamoto a)
a) Neutron Material Research Center, QuBS, JAEA,
b) Environment and Industrial Materials Research Division, QuBS, JAEA
Since the discovery of carbon nanotubes (CNTs) in 1991,
significant numbers of researchers have synthesized new
one-dimensional nanostructured materials such as nanotubes,
nanorods and nanowhiskers for potential applications.
Some of them have reported that many nanomaterials such
as TiC, NbC, BN, SiO 2 and GaN nanostructures are
fabricated from CNTs as the template. SiC is one of the
most important wide-band-gap semiconducting materials for
high temperature and high power. And SiC is also one of
the most important structural materials at high temperature.
Therefore, SiC offers exciting opportunities in electronic
devices and in structural materials at high temperature.
We reported that the C-SiC coaxial nanotubes, which were
CNTs sheathed with SiC, were formed. Furthermore, the
single-phase SiC nanotubes were successfully synthesized
by heating the C-SiC coaxial nanotubes in air 1, 2) . However,
many grain boundaries exist in SiC nanotubes because SiC
nanotubes fabricated in this study are polycrystalline.
Grain boundaries degrade the electronic and mechanical
properties of SiC nanotubes. Therefore, the synthesis of
single-crystalline and/or amorphous SiC nanotubes without
the grain boundary is required. The purpose of this study is
to synthesize single-crystalline and amorphous SiC
nanotubes by ion-irradiation technique.
Carbon nanotubes (GSI Creos Corporation, Tokyo,
Japan) were used as the template. The C-SiC coaxial
nanotubes were synthesized by heating CNTs with Si
powder (The Nilaco Corporation, Tokyo, Japan) at 1,200 ºC
for 100 h in a vacuum. Single-phase SiC nantoubes were
formed by the heat treatment of C-SiC coaxial nanotubes at
600 ºC for 2 h in air. Thin films of single-phase SiC
nanotubes were prepared on the alumina plates by
depositing with the single-phase SiC nanotubes dispersed in
50 nm
Fig. 1 TEM image of a single-crystalline SiC nanotube.
JAEA-Review 2010-065
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ethanol. These thin films of single-phase SiC nanotubes
were irradiated with 3-MeV Si 2+ ions at 190 ºC and 900 ºC.
The ion fluence was 6.4 × 10 20 ions/m 2 .
According to TEM observations, a few single-crystalline
SiC nanotubes were formed by the ion irradiation at 900 ºC.
Figure 1 shows the typical TEM image of single-crystalline
SiC nanotubes. Because grain growth in the SiC nanotubes
occurred by the ion irradiation at 900 ºC, polycrystalline SiC
nantoubes were transformed to single crystalline SiC
nanotubes. However, the number of single-crystalline SiC
nanotubes synthesized by this process was very small.
On the other hand, many amorphous SiC nanotubes were
formed by the ion irradiation at 190 ºC. Figure 2 shows the
typical TEM image of amorphous SiC nanotubes. No
microstructural change in SiC nanotubes occurs only by
thermal annealing up to 900 ºC because synthesis
temperature is 1,200 ºC. As well as single-phase SiC
nanotubes, polycrystalline C-SiC coaxial nanotubes were
transformed to single-crystalline C-SiC coaxial nanotubes
by the ion-irradiation at 900 ºC and to amorphous C-SiC
coaxial nanotubes by the ion irradiation at 190 ºC,
respectively. By the ion irradiation using a slit or a mesh,
the SiC composite nanotubes with two or more different
crystallinities and microstructures such as polycrystal-
amorphous, single crystal-polycrystal and single crystal-
amorphous in a SiC nanotube can be synthesized in the near
future.
References
1) T. Taguchi et al., J. Am. Ceram. Soc. 88 [2] (2005)
459-461.
2) T. Taguchi et al., Physica E 28[4] (2005) 431-438.
100 nm
Fig. 2 TEM image of an amorphous SiC nanotube.