gas sensing characteristics and porosity control of nanostructured films

Sensors and Actuators B 137 (2009) 513–520
Contents lists available at ScienceDirect
Sensors and Actuators B: Chemical
journal homepage: www.elsevier.com/locate/snb
Gas sensing characteristics and porosity control of nanostructured films
composed of TiO
2
nanotubes
ଝ
Min-Hyun Seo
a
, Masayoshi Yuasa
b
, Tetsuya Kida
b
, Jeung-Soo Huh
c
, Kengo Shimanoe
b,∗
, Noboru Yamazoe
b
a
Department of Molecular and Material Sciences, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
b
Department of Energy and Material Sciences, Faculty of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
c
Department of Materials Science and Metallurgy, Kyungpook National University, Daegu 702-701, South Korea
article info
Article history:
Received 15 August 2008
Received in revised form 19 December 2008

Accepted 30 January 2009
Available online 10 February 2009
Keywords:
TiO
2
nanotube
VOC
Porosity control
Porous film
Hydrothermal treatment
abstract
Preparation and morphology control of TiO
2
nanostructured films for gas sensor applications were inves-
tigated. To examine the effect of the morphology of sensing films on the sensing characteristics, TiO
2
with
different morphologies, nanoparticles and nanotubes, were used for the film preparation. TiO
2
nanotubes
were prepared by a hydrothermal treatment of TiO
2
nanoparticles in a NaOH solution at 160, 200, and
230
◦
C for 24 h and subsequent washing with an HCl solution. Uniform sized TiO
2
nanotubes of 1 ␮min
length and 50 nm in diameter were formed at 230
◦

C. The sensing films composed of nanotubes prepared
at 230
◦
C showed a high sensor response to toluene at 500
◦
C as compared with those composed of TiO
2
nanoparticles. Scanning electron microscope (SEM) analysis and pore size distribution measurements
indicated that the sensing films composed of the TiO
2
nanotubes had a high porous morphology with a
peak pore size of around 200 nm, which can promote the diffusion of toluene deep inside the films and
improve the sensor response. The obtained results demonstrated the importance of microstructure con-
trol of sensing layers for improving the sensitivity to large size molecules like volatile organic compounds
(VOCs).
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
Semiconductor gas sensors based on metal oxides have aroused
considerable interest owing to their high sensitivity to pollutant
gases, low cost, and small size [1–3]. Various oxide materials such
as SnO
2
[4],WO
3
[5],TiO
2
[6–9], and ZnO [10] have so far been
used for gas sensors. Among them, TiO
2
is a well-known important

functional material used for a variety of applications such as pho-
tocatalysts [11], dye-sensitized solar cells [12], batteries [13], and
pigments [14]. For gas sensor applications, it has been reported that
TiO
2
with a large surface area shows good sensing properties to CO
[7],H
2
[8], and NO
x
[9]. The important feature of TiO
2
-based gas
sensors is that they can be operated at high temperature because
of the good chemical stability of TiO
2
.
Recently, utilization of nanostructured TiO
2
for various devices
has attracted much attention due to prospects for upgrading
the device performance through the nanostructure control of
devices [15,16]. Various nanostructured TiO
2
such as nanorods [17],
ଝ
Paper presented at the International Meeting of Chemical Sensors 2008 (IMCS-
12), July 13–16, 2008, Columbus, OH, USA.
∗
Corresponding author. Tel.: +81 92 583 7876; fax: +81 92 583 7538.

E-mail address: (K. Shimanoe).
nanowires [18], nanosheets [19], and nanotubes [20–23] have been
prepared by wet-chemical methods. TiO
2
nanotubes were firstly
reported by Kasuga et al. in 1998 [20]. Since then, the chemical and
physical properties of TiO
2
nanotubes have been studied intensively
due to the ease of the preparation using a simple hydrothermal
method. The nanotubular architecture can achieve high specific
surface area and thus TiO
2
nanotubes prepared by a hydrother-
mal method have been successfully utilized for photocatalysis [24],
dye-sensitized solar cells [25], and lithium-ion batteries [26].
TiO
2
nanotubes and nanofibers prepared by anodization and
electrospinning methods have been used for the detection of H
2
[27,28],NO
2
[29], and water vapor [30,31]. Varghese et al. reported
a large change in the electric resistance of arrays of TiO
2
nan-
otubes in response to H
2
[27,28]. However, the sensing mechanism

of nanostructured TiO
2
films composed of nanotubes or nanofib ers
has not yet been understood well. It is thus of considerable interest
and importance to examine the detailed gas sensing properties of
nanostructured films base d on TiO
2
nanotubes.
For semiconductor gas sensors, the porosity of sensing films is
an important parameter [32–34]; porous sensing films can facilitate
gas diffusion deep inside the films and reach high gas sensitivity. In
particular, the microstructure control is important to detect large
size molecules such as volatile organic compounds (VOCs). Note
that it is possible to prepare porous gas sensing films using TiO
2
0925-4005/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.snb.2009.01.057
514 M H. Seo et al. / Sensors and Actuators B 137 (2009) 513–520
Fig. 1. SEM images of the sensing films composed of (a) commercial TiO
2
nanoparticles (P-25) and those hydrothermally treated at (b) 160, (c) 200 and (d) 230
◦
C. (a’)–(d’)
show the corresponding images after calcination at 600
◦
C.
nanotubes because of their high anisotropic shape; packing tubular
particles would produce loosely-packed particulate films with ran-
domly distributed pores while hindering intimate contacts among
the particles. Such a porous film is expected to show sensitivities

to large sized gas molecules like VOCs.
In this study, we fabricated porous gas sensing filmscomposed of
TiO
2
nanotubes prepared by a hydrothermal treatment and studied
the gas sensing properties of the porous TiO
2
nanotubular films.
The investigation was carried out with a particular emphasis on
the promotion of the gas sensitivity through the porosity control of
gas sensing films.
2. Experimental
TiO
2
nanotubes were prepared by a hydrothermal method as
reported in the literature [18].0.5gofaTiO
2
commercial powder
(Degussa P-25 (mean particle size: ca. 20 nm)) was hydrothermally
treated with 30 mL of a NaOH solution (10 mol/L) at 160, 200 and
Fig. 2. TEM images of TiO
2
aggregates and nanotubes prepared by the hydrothermal treatment at (a) 160, (b) 200 and (c) 230
◦
C, followed by calcination at 600
◦
C.
M H. Seo et al. / Sensors and Actuators B 137 (2009) 513–520 515
Fig. 3. Pore size distribution of the sensing films composed of (a) commercial TiO
2

nanoparticles (P-25) and those hydrothermally treated at (b) 160, (c) 200 and (d)
230
◦
C. They were calcined at 600
◦
C.
230
◦
C for 24 h in a Teflon-lined autoclave. After the treatment, the
TiO
2
powder was washed with 50 mL of a HCl solution (0.2 mol/L)
under ultrasonic irradiation for 1 h. Then, the obtained products
were filtered and dried to recover TiO
2
nanotubes. The resulting
products were characterized by X-ray diffraction (XRD) with Cu-K␣
radiation, scanning electron microscopy (SEM), and transmission
electron microscopy (TEM).
For electrical and sensing characterizations, TiO
2
thick films
were fabricated by a screen-printing method. By using a binary
dispersant of ␣-terpineol (95 mass%) mixed with ethyl cellulose
(5 mass%), the sensor material was converted into a paste, which
was screen-printed on an alumina substrate attached with a pair of
Au electrodes (line width: 180 ␮m, distance between lines: 90 ␮m,
sensing layer area: 64 mm
2
). After screen-printing, the fabricated

sensor devices were calcined at 600
◦
C for 1 h. The porosity of the
films was measured by mercury porosimetry.
The electrical and gas sensing properties of the films were tested
using CO, H
2
, ethanol, and toluene as target gases at 450–550
◦
C.
Measurements were performed using a conventionalgas flow appa-
ratus equipped with an electric furnace at a gas flow rate of
Fig. 4. XRD patterns of (a) commercial TiO
2
nanoparticles (P-25) and those
hydrothermally treated at (b) 160, (c) 200 and (d) 230
◦
C.
Fig. 5. XRD patterns of (a) commercial TiO
2
nanoparticles (P-25) and those
hydrothermally treated at (b) 160, (c) 200 and (d) 230
◦
C. They were calcined at
600
◦
C.
100 cm
3
/min. The sensor response was defined as R

air
/R
gas
, where
R
air
and R
gas
are the electric resistances in air and that in a test gas,
respectively.
3. Results and discussion
3.1. Characterization of nanotubular TiO
2
films
Fig. 1 shows SEM images of the surface of TiO
2
thick films com-
posed of TiO
2
nanotubes prepared by the hydrothermal treatment
at 160, 200, and 230
◦
C, together with that of a film composed of
commercial TiO
2
nanoparticles (P-25). The surfaces of the films
were observed before and after calcination at 600
◦
C. It is obvious
that the morphology of the films was significantly changed after the

hydrothermal treatment, depending on the treatment temperature.
The treatment at 160
◦
C produced heavily aggregated TiO
2
particles,
as shown in Fig. 1(b). On the other hand, the treatment at 200 and
230
◦
C resulted in the formation of tubular TiO
2
of 1 ␮m and 50 nm
in length and diameter, respectively, as shown in Fig. 1(c) and (d).
With increasing the temperature of the hydrothermal treatment,
the length of the tubes increased and the distribution of the diam-
eter became narrower. Nanotubes with a more uniform size were
formed by the hydrothermal treatment at 230
◦
C. The SEM images
confirm that the films composed of the TiO
2
nanotubes are more
porous than those composed of TiO
2
nanoparticles, as expected. It
is also noted that the calcination induced no drastic change in the
morphology of TiO
2
, but resulted in slight sintering of TiO
2

aggre-
gates and nanotubes obtained at 160 and 200
◦
C, respectively, as
shown in Fig. 1(b’) and (c’).
The nanostructures of the TiO
2
nanotubes calcined at 600
◦
C
were observed by TEM, as shown in Fig. 2. The TEM observation
Table 1
Specific surface area of commercial TiO
2
nanoparticles (P-25) and those hydrother-
mally treated at 160, 200 and 230
◦
C, together with the peak pore size of the sensing
films composed of the particles. They were calcined at 600
◦
C.
Sample Specific surface area (m
2
/g
−1
) Peak pore size (nm)
Commercial TiO
2
(P-25) 46.3 36.0
160

◦
C 76.4 20.4
200
◦
C 22.7 138.6
230
◦
C 23.1 201.3
516 M H. Seo et al. / Sensors and Actuators B 137 (2009) 513–520
Fig. 6. Electric resistance in air as a function of operating temperature for the thick
films composed of (a) commercial TiO
2
nanoparticles (P-25) and those hydrother-
mally treated at (b) 160, (c) 200 and (d) 230
◦
C.
revealed that the tubular structure is stable even after calcination at
600
◦
C and TiO
2
aggregates obtained at160
◦
C have no tubular struc-
ture. The wall thickness of nanotubes prepared at 200 and 230
◦
Cis
estimated to be ca. 5 nm from the TEM images. In addition, a uni-
form size distribution was confirmed for the nanotubes treated at
230

◦
C, suggesting that the optimum temperature of the hydrother-
mal treatment is 230
◦
C. The mechanism of the nanotube formation
by a hydrothermal treatment has been reported as follows [23];
first, TiO
2
transformed into a layered compound of Na
2
Ti
2
O
5
·H
2
O
by NaOH. The washing of the product with HCl results in the ion
exchange of Na
+
with H
+
. The HCl treatment removes Na
+
from the
layered compound to form exfoliated sheets. The sheets roll up to
form tube-like particles. The TEM image shown in Fig. 2(c) also con-
firms the rolling up of nanosheets into nanotubes. On the basis of
the above mechanism, it is considered that the treatment at higher
temperature of 230

◦
C promoted the transformation of TiO
2
parti-
cles into nanosheets and resulted in the formation of more uniform
nanotubes, as observed in SEM and TEM images.
Fig. 3 shows the pore size distribution of the films composed
of TiO
2
nanoparticles, aggregates, and nanotubes after calcination
at 600
◦
C. The distribution of pores peaks at approximately 36 and
138 nm for the films composed of commercial TiO
2
particles and
TiO
2
nanotubes obtained at 200
◦
C, respectively, indicating that
the porosity of the film was increased by using the nanotubular
particles. Furthermore, the peak pore size of the TiO
2
nanotubes
obtained at 230
◦
C increased, while the porosity of the TiO
2
aggre-

gates obtained at 160
◦
C decreased. The observed trend is in good
agreement with the SEM results. The pore size at the maximum
pore volume for the films composed of TiO
2
nanoparticles, aggre-
gates, and nanotubes is summarized in Table 1, together with the
specific surface area of TiO
2
measured by the B.E.T. method. The
surface area of calcinated nanotubes was lower than that of TiO
2
nanoparticles. A peculiar feature was observed in the TiO
2
aggre-
gates obtained at 160
◦
C that show a high surface area but a small
peak pore size.
The crystal structure of the obtained TiO
2
nanotubes was ana-
lyzed by XRD. Fig. 4 shows the XRD patterns of the products
hydrothermally treated at different temperatures. The patterns
show that the crystal phase of TiO
2
changed from a mixed phase
of rutile and anatase to that of H
2

Ti
3
O
7
and anatase after the
hydrothermal treatment, irrespective of reaction temperature. The
Fig. 7. Sensor responses to (a) CO (500 ppm), (b) H
2
(500 ppm), (c) ethanol (47 ppm), and (d) toluene (50 ppm) gases in the temperature range of 450–550
◦
C for the devices
using commercial TiO
2
nanoparticles (P-25) and those hydrothermally treated at 160, 200 and 230
◦
C.
M H. Seo et al. / Sensors and Actuators B 137 (2009) 513–520 517
Fig. 8. Sensor responses to CO (500 ppm), H
2
(500 ppm), ethanol (47 ppm), and toluene (50 ppm) gases at 500
◦
C for the devices using (a) commercial TiO
2
nanoparticles
(P-25) and those hydrothermally treated at (b) 160, (c) 200 and (d) 230
◦
C.
main peak for the TiO
2
nanotubes was assigned to H

2
Ti
3
O
7
accord-
ing to recent structural characterizations [35,36], although different
assignments of nanotubes to H
2
Ti
2
O
5
·H
2
O and H
2
Ti
4
O
9
·H
2
Ohave
also been reported [23,37]. Fig. 5 shows the XRD patterns of the
products after calcination at 600
◦
C. The crystallization of H
2
Ti

3
O
7
to anatase occurred in the TiO
2
nanotubes obtained at 200 and
230
◦
C, although the H
2
Ti
3
O
7
phase remained. On the other hand,
for TiO
2
aggregates obtained at 160
◦
C, the H
2
Ti
3
O
7
phase com-
pletely transformed into the anatase phase after calcination. It has
been reported that the thermal stability of the protonated titanate
phase is improved by the presence of sodium ions and the removal
of sodium ions promotes the thermal conversion to anatase [35].It

is suggested that the reaction of TiO
2
with NaOH is incomplete at
160
◦
C to produce partly Na-intercalated layered compounds on the
basis of the proposed mechanism discussed above and the SEM and
TEM results, and that the subsequent washing with HCl effectively
removed sodium ions from the layered compounds. Consequently,
the low sodium content in aggregates obtained at 160
◦
C may assist
in the formation of the anatase phase.
3.2. Gas sensing properties of nanotubular TiO
2
films
Fig. 6 shows the electrical resistances in air as a function of
temperature ranging from 450 to 550
◦
C for the fabricated films
composed of TiO
2
nanoparticles, aggregates, and nanotubes. The
film using TiO
2
nanotubes obtained at 230
◦
C gave the highest resis-
tance, reflecting their higher porosity than the other films. However,
the electric resistance of the other films was not correlated well

with their porosity. This is because the electric resistance is depen-
dent on various parameters such as grain size, tube length, film
thickness, crystal structure, and physical parameters such as car-
rier density and effective mobility. In addition, the observed thin
wall thickness (ca. 5 nm) of the nanotubes may also be responsible
for the high electric resistance.
The electric resistance decreased with increasing the operating
temperature, following the typical behavior of oxide semiconduc-
tor. However, the electric resistance at lower than 500
◦
C exceeded
10
9
, which is too high to be measured using a conventional elec-
tric circuit. Thus, the optimal operating temperature is judged to be
500
◦
C from a practical point of view.
The sensor response of the fabricated films composed of TiO
2
nanoparticles, aggregates, and nanotubes was examined against
traces of CO, H
2
, ethanol, and toluene gases at 450, 500, and 550
◦
C,
as shown in Fig. 7. The fabricated sensors using TiO
2
(n-type semi-
conductor) responded to the target gases by a decrease in the

electric resistance. Thus, the probable sensing mechanism is that
Fig. 9. Schematic model of diffusion of toluene gas inside a porous nanotubular film.
518 M H. Seo et al. / Sensors and Actuators B 137 (2009) 513–520
the target gas molecules diffuse into the sensing layer through
pores and react with adsorbed oxygen on TiO
2
, as reported [1].
This reduces the thickness of the surface depletion layer in TiO
2
,
thereby decreasing the electric resistance. Fig. 8 summarizes the
sensor response of the devices to the test gases at 500
◦
C. The film
using commercial TiO
2
nanoparticles exhibited the highest sensor
responses to all gases. We have recently developed a new model on
the roles of shape and size of component crystals in semiconductor
gas sensors on the basis of electron-depleted conditions in com-
ponent crystals [38]. The model confirms that the gas sensitivity
increases with decreasing the crystal size as experimentally proved
for many cases, and predicts that crystals in spherical shape would
show higher sensitivity than those in columnar shape. Thus, the
observed higher sensor response of commercial TiO
2
nanoprticles
than nanotubes is consistent with the developed model.
On the other hand, the film using TiO
2

nanotubes prepared at
230
◦
C showed comparably high sensitivity to toluene among the
gases tested, despite their lower surface area than that of com-
mercial TiO
2
nanoparticles. As noted above, for semiconductor gas
sensors, target gases diffuse in a sensing film through pores and
react with surface oxygen adsorbed on component particles to
induce the resistance change. The concentration of the target gases
decreases inside the sensing film as they diffuse. The component
particles located deep inside the film may remain intact or inacces-
sible for the target gases provided that the film is not sufficiently
porous. This would lead to a decrease in the sensor response due to
a decrease in the utility factor of the sensing film or a decrease in
the accessibility of the target gas. Thus, the effect of the porosity of
sensing films on the sensor response is more pronounced for target
gases with large molecular sizes. As revealed by the pore size dis-
tribution measurements, the film using TiO
2
nanotubes prepared
at 230
◦
C has the peak pore size of around 200 nm, which is much
larger than those for the film using TiO
2
aggregates and nanotubes
prepared at 160 and 230
◦

C, respectively. Such macropores can pro-
vide high-diffusivity paths for large toluene molecules and improve
the utility factor of the sensing film. Thus, the observed particular
Fig. 10. Response transients to toluene (50 ppm) at 500
◦
C for the devices using
(a) commercial TiO
2
nanoparticles (P-25) and (b) those hydrothermally treated at
230
◦
C.
increase in the sensor response to toluene for the film using TiO
2
nanotubes prepared at 230
◦
C can be ascribed to the high porosity
of the nanotubular film, as is schematically shown in Fig. 9. In addi-
tion, almost constant sensor responses to CO and H
2
were observed
for the films using TiO
2
aggregates and nanotubes. This is probably
because more combustible gases than toluene are difficult to dif-
fuse deep inside the films and tend to burn at the film surfaces even
if the porosity of the films is high. Importantly, the selective detec-
tion of toluene was achieved by the porosity improvement of the
sensing film and the high temperature operation.
There have been some papers reporting the response charac-

teristics of TiO
2
-based sensors to VOCs. Teleki et al. reported the
sensor response of S = 6 to ethanol gas (30–300 ppm) in dry air at
400
◦
C for TiO
2
doped with Nb [39]. On the other hand, Gessner et
Fig. 11. SEM images of the TiO
2
nanotubular films calcined at (a) 600 and (b) 700
◦
C. (a’) and (b’) show the corresponding high magnification images.
M H. Seo et al. / Sensors and Actuators B 137 (2009) 513–520 519
Fig. 12. Sensor responses to toluene (50 ppm) for the TiO
2
nanotubular films cal-
cined at (a) 600 and (b) 700
◦
C.
al. reported the sensor response of S = 4 to toluene gas (100 ppm)
in dry air at 400–50 0
◦
C [40]. Although the preparation methods of
TiO
2
and the experimental conditions are different from those in
the present study, the reported sensor responses were lower than
our results. Therefore, our approach of controlling the film pore size

is quite effective in improving the sensor performance to large size
molecules like ethanol and toluene.
Fig. 10 shows the response transients to toluene (50 ppm) at
500
◦
C of the sensors using TiO
2
nanotubes prepared at 230
◦
C and
commercial TiO
2
nanoparticles (P-25). Even if a difference in the
response transients is seen by both sensors, it seems not to be the
important difference because the speed of response and recovery
depends on dead volume in the equipment, as reported by Kida et
al. [41]. According to a basic viewpoint of gas diffusion [42],itis
know that the diffusion through the microstructure affects sensor
response (R
air
/R
gas
). From the above, it is thought that the sensor
response of nanotubes observed in Fig. 10 is as high as that of
nanoparticles.
To provide a further experimental evidence of supporting the
above discussions, the porosity of the nanotubular film was con-
trolled by calcination and then the sensor response was tested
again. Fig. 11 shows the SEM images of the film composed of
TiO

2
nanotubes prepared at 230
◦
C after calcination at 600 and
700
◦
C. From the SEM images, it appears that the porosity obviously
decreased due to sintering of nanotubes after calcination at higher
temperature. As a result, the sensitivity to toluene gas significantly
decreased, as shown in Fig. 12. Thus, the results obtained indicate
again the importance of themicrostructure control ofsensing layers
for detecting large sized gas molecules.
4. Conclusion
TiO
2
nanotubes of 1 ␮m in length and 50 nm in diameter were
formed by the hydrothermal treatment of TiO
2
nanoparticles with
NaOH at 200 and 230
◦
C. Uniform sized nanotubes were obtained at
230
◦
C. The tubular structure of the TiO
2
nanotubes was stable even
after calcination at 600
◦
C for 1 h. The calcination of the nanotubes

resulted in the formation of the anatase phase. A porous film with a
peak pore size of around 200 nm was successfully formed using the
TiO
2
nanotubes obtained at 230
◦
C. The sensing film using the nan-
otubes exhibited higher sensor response to toluene at 500
◦
C than
CO and H
2
. The porous morphology of the nanotubular films facili-
tated diffusion of large sized molecules like toluene through pores
in the film, leading to the improved sensor response and selectivity
to toluene.
Acknowledgement
This study was partly supported by NISSAN Science Foundation,
a Grant-in-Aid for Exploratory Research (No. 19659402) from the
Ministry of Education, Culture, Sports, Science and Technology of
Japan, and by Environmental Research and Technology Develop-
ment Fund from the Ministry of Environment of Japan.
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Biographies
Min-Hyun Seo received his M. Eng. Degree in Dept. of sensor and display in 2007
from Kyungpook National University. He is currently a Ph.D. course student at the
Department of Molecular and Material Sciences in Kyushu University. His current
research interests include the development of gas sensors and nanoparticle process-
ing.
Masayoshi Yuasa has been an Assistant Professor at Kyushu University since 2005.
He received his M. Eng. Degree in materials science in 2003. His current research
interests include the development of gas sensors and active electrocatalysts for
oxygen reduction.
Tetsuya Kida has been an Associate Professor at Kyushu University since 2006. He
received his M. Eng. Degree in materials science in 1996 and his Dr. Eng. Degree in
2001 from Kyushu University. His current research interests include the develop-
ment of gas sensor, nanoparticle processing, and self-assembled inorganic–organic
hybrid materials.
Jeung-Soo Huh has been a Professor of Kyungpook National university, Korea since
1995. He received B.S. and M.S. from Dept. of Materials Science & Engineering, Seoul
National University in 1983 and 1985. He obtained his Ph.D. in Electronic Materials
from M.I.T (Massachusetts Institute of Technology) in 1993. His current research
interests include gas sensor, odor sensing and medical application of these sensors.
Kengo Shimanoe has been a Professor at Kyushu University since 2005. He received
the B.E. Degree in Applied Chemistry in 1983 and the M. Eng. Degree in 1985 from
Kagoshima University and Kyushu University, respectively. He joined Nippon Steel
Corp. in 1985, and received his Dr. Eng. Degree in 1993 from Kyushu University.
His current research interests include the development of gas sensors and other

functional devices.
Noboru Yamazoe had been a Professor at Kyushu University since 1981 until he
retired in 2004. He received his M. Eng. Degree in Applied Chemistry in 1963 and his
Dr. Eng. Degree in 1969 from Kyushu University. His research interests were directed
mostly to the development and application of functional inorganic materials.