esearch Highlights

esearch Highlights

Development of Carbon Nanotubes
with High Electrical Conductivity

Development of High Performance
Photocatalyst-Coated Film

- Application to Nanowiring and Transparent Electrodes -- Realizing a Corrosive Gas Decomposition Rate 30 Times
Faster than the Conventional Technology -Nano Frontier Materials Group, Nano System Functionality Center

Advanced Materials Research Group, Photocatalytic Materials Center
Group Leader

Managing Director

Satoshi Ishii, Yoshihiko Takano

Fig.1

CarbonNanotube

5 µm
Scanning electron microscope image of a boron-doped CNT
with a nanofabricated four terminals.

1x104
Boron-doped Carbon Nanotuube

Titanium oxide photocatalysts are applied as environmental purification materials in a variety of products. In actuality, a titanium oxide photocatalyst is usually coated on
the surface of a substrate of ceramic, glass, metal, or othermaterials in the purification devices for decomposition ofharmful substances in the air.
In conventional titanium oxide photocatalytic filters, aslurry (a liquid dispersed with titanium oxide) mixed with asilica-based binder (a component which fixes the titaniumoxide on the substrate surface) is coated on a porous ceramicmaterial and fixed by heat treatment. However, for various
reasons, the films produced by this process did not posses adequate photocatalytic activity. For example, in addition to thefact that a sufficient reaction surface area was not secured,
light failed to reach the film interior, and the film contained
heterogeneous silica compounds.
To solve these problems, we conducted a joint researchon the development of new photocatalyst-coated films with
Meidensha Corporation. First, we produced the films on
glass plates in which the slurry and binder component weresystematically adjusted, and investigated the crystallinity,surface morphology, film thickness, strength, and isopropyl
alcohol (IPA) decomposition activity by the photocatalytic
reaction of these films. Fig. 1 shows a part of the results. The
ordinate is the amount of acetone formed by decompositionof IPA. The formation rate with sample A is as much as 15Fig.1
1x1021x101

1x100

Commercially available
Carbon Nanotube

050100150200250

Temperature [K]Temperature dependency of electrical conductivity.

300Fig.270605040302010001050203040Light irradiation time (min)60

Results of a preliminary experiment using a titanium oxidecoated film with a controlled morphology. The properties ofsample A, which is characterized by numerous fine cracks,are superior.

08

Internationaltimes faster than that with sample B. This result is attributable to the fact that, with sample A, numerous fine cracks areformed in the surface, as shown in the photograph (inset),
and these increase the surface area that contributes to the reaction. As a further development based on these preliminary
experimental results, micro-sized acrylic beads were introduced in a titanium-based binder component on an actual porous ceramic substrate. Because these beads are decomposed
upon heat treatment, a coated film having a structure of micro-sized holes was obtained (Fig. 2). This resulted in a total
increase in the amount of photoreaction due to a large increase in the effective surface area of the titanium oxide, andthe penetration of light to the deep parts of these holes, etc.
In a photocatalytic test for decomposition of hydrogen sulfide using the developed photocatalyst-coated film, a hydrogen sulfide decomposition rate more than 30 times fasterthan that of the conventional product was achieved.
In addition to corrosive gases such as hydrogen sulfide,the photocatalytic filter developed in this research also enables highly efficient removal of various species of harmful
molecules in the atmosphere, such as formaldehyde, sulfur
dioxide, ammonia, nitric oxide, and the like. In the future,application to diverse types of air purification devices is expected.

1x103

Acetone concentration (ppm)

Fig.2

Conductivity [ǡ-1࡮cm-1]

Beautiful diamond jewels, graphite used in pencil leads,
soccer ball-shaped C60, fullerenes, and carbon nanotubes(CNTs); they all consist of single element, carbon. Because
CNTs have a fine straw shape with a diameter of less than
one ten-thousandth of a millimeter and is light and strong,these novel properties make them potentially useful for a variety of applications in fields, such as nanowiring for future
LSIs, and transparent electrodes. However, depending on the"handedness," or chirality, of CNTs, its properties differ
greatly, for example, showing metal-like conductivity or theproperties of a semiconductor. To date, attempts to control
the chirality have not been successful.
In order to use CNTs for nanowiring and similar applications, high electrical conductivity independent of chirality
is necessary. We have successfully fabricated boron-doped
CNTs by a simple chemical vapor deposition method employing an electric furnace. Using electron beam lithography,
four terminals were fabricated on a CNT and its electricalconductivity was measured (see Fig. 1). The results showedthat the electrical conductivity of the CNTs at room temperature is one to two orders of magnitude higher than that ofconventional multi-walled CNTs. Furthermore, it was also
found that the CNTs retain its high electrical conductivity at
down to extremely low temperatures (see Fig. 2).
Our group is conducting research on high electric conductivity and superconductivity that are found to occur whenboron is added to diamond. Similarly, in CNTs, we assume
that hole carriers are introduced into carbon when doped withboron, making it possible to obtain high electrical conductivity independent of the chirality of CNTs. In the future, superconductivity could also be found in boron-doped CNTs.
This new method has applications in a wide range offields, including transparent electrodes and conductive films
produced by adding CNTs to resins, nanowiring for future
LSIs, CNT field effect transistors (FET), probes for scanningprobe microscopes, electron emission devices, and fuel cells.

Defa Wang, Tetsuya Kako, Jinhua Ye

NONE

SEI

15.0kV

X1.00010µm WD 10.0 mm

Surface SEM image of the photocatalyst-coated film
fabricated by the new technique developed in this research.
The baking temperature was 500 °C. A large number ofmicro-sized holes can be observed.

International09