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1. Please cite this article in press as: N. Van Quy, et al., Gas sensing properties at room temperature of a quartz crystal microbalance coated with
ZnO nanorods, Sens. Actuators B: Chem. (2010), doi:10.1016/j.snb.2010.10.030
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Contents lists available at ScienceDirect
Sensors and Actuators B: Chemical
journal homepage: www.elsevier.com/locate/snb
Gas sensing properties at room temperature of a quartz crystal microbalance
coated with ZnO nanorods
Nguyen Van Quy, Vu Anh Minh, Nguyen Van Luan, Vu Ngoc Hung∗
, Nguyen Van Hieu∗
International Training Institute for Materials Science (ITIMS), Hanoi University of Science and Technology (HUST), No. 1 Dai Co Viet Road, Hanoi, Viet Nam
a r t i c l e i n f o
Article history:
Received 19 March 2010
Received in revised form 18 October 2010
Accepted 21 October 2010
Available online xxx
Keywords:
QCM
ZnO nanorods
Gas sensors
a b s t r a c t
Gas sensors based on a quartz crystal microbalance (QCM) coated with ZnO nanorods were developed for
detection of NH3 at room temperature. Vertically well-aligned ZnO nanorods were synthesized by a novel
wet chemical route at a low temperature of 90 ◦
C, which was used to grow the ZnO nanorods directly
on the QCM for the gas sensor application. The morphology of the ZnO nanorods was examined by field-
emission scanning electron microscopy (FE-SEM). The diameter and length of the nanorods were 100 nm
and 3 ␮m, respectively. The QCM coated with the ZnO nanorods gas sensor showed excellent performance
to NH3 gas. The frequency shift ( f) to 50 ppm NH3 at room temperature was about 9.1 Hz. It was found
that the response and recovery times were varied with the ammonia concentration. The fabricated gas
sensors showed good reproducibility and high stability. Moreover, the sensor showed a high selectivity to
ammoniac gas over liquefied petroleum gas (LPG), nitrous oxide (N2O), carbon monoxide (CO), nitrogen
dioxide (NO2), and carbon dioxide (CO2).
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
In recent years, many semiconductor metal-oxide materials,
such as SnO2, TiO2, CuO, and In2O3, have been used for gas
sensors [1–5]. In these, the ZnO nanomaterial possesses certain
unique properties, such as a direct band gap (3.37 eV), large exci-
ton binding energy (60 meV), high thermal and chemical stability,
transparence, biocompatibility, and wide electrical conductivity
range [6–8]. Moreover, one-dimensional (1D) ZnO nanostructures
have attracted much attention due to their large aspect ratio, which
makes them a good candidate for gas sensing applications [9,10].
Most gas sensors using semiconductor metal-oxide materials are
based on the change in electrical conductivity with the compo-
sition of the surrounding gas atmosphere. Major challenges in
conductivity-based gas sensors are the high operating tempera-
ture, poor gas selectivity, and unstableness. These sensors are based
on the changes in electrical resistance of the materials upon gas
adsorption. Thus, a high temperature is required for charge car-
riers of the semiconductor materials to overcome the activation
energy barrier. Therefore, almost all conductivity-based gas sensors
operate at high temperatures [2–4,9,10].
In gas sensor structures, the principle naturally requires a larger
surface-area-to-volume ratio for high sensitivity; for this matter,
∗ Corresponding authors. Tel.: +84 4 38680787; fax: +84 4 38692963.
E-mail addresses: hungvungoc@itims.edu.vn (V.N. Hung), hieu@itims.edu.vn
(N. Van Hieu).
1D nanostructures have been extensively studied. However, in the
conductivity-based sensors, the sensing layer is required to be con-
tinuous to ensure that conductivity exists in two electrodes of
the sensor. Therefore, the sensing layers usually consist of the 1D
nanostructures in parallel orientation with the substrate. Hence,
the exposing area of the sensing layer is reduced significantly. In
particular, many sensors based on semiconductor metal oxide have
extensively been used for detecting toxic gases such as COx, NOx,
CH4, and NH3 [4,11–13]. Among these, NH3 gas presents much haz-
ard to both humans and the environment. Due to its highly toxic
characteristics, even low level concentrations (ppm) pose a serious
threat. Nowadays, there are many fields of technological impor-
tance that need to detect NH3 gas in low concentrations, such as
food technology, chemical engineering, medical diagnosis, environ-
mental protection, and industrial processes. Thus, the requirement
of using ammonia gas sensors is becoming greater. In previous
works, we have developed a room temperature NH3 gas sensor
based on the composites of SnO2/carbon nanotube and polypyr-
role/carbon nanotubes [14,15]. The limitations of these sensors are
their poor selectivity and non-detect of NH3 gas at much lower
levels (ppb).
In this study, we developed a highly sensitive and reproducible
ammonia gas sensor with a combination of ZnO nanorods and
quartz crystal microbalance (QCM). In the past decades, the QCM
technique has been developed as a sensitive tool that utilizes the
piezoelectric properties of quartz crystals to measure the attached
mass on an electrode surface. Change in the resonant frequency
can be related to change in the mass according to the Sauerbrey
0925-4005/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.snb.2010.10.030

2. Please cite this article in press as: N. Van Quy, et al., Gas sensing properties at room temperature of a quartz crystal microbalance coated with
ZnO nanorods, Sens. Actuators B: Chem. (2010), doi:10.1016/j.snb.2010.10.030
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equation [16]. As such, QCM technique has been applied in bio-
chemistry, analytical science, and other fields [17–20]. Abe and
colleagues fabricated a QCM sensor array on a single crystal of a
quartz plate (one-chip multichannel QCM). The QCM sensor array,
which has different resonance frequencies, can be applied to detect
various kinds of gases [18]. On the other hand, QCM coated with a
sensing layer was also applied to the sensor due to its high repro-
ducibility and stability [21,22]. As the QCM is an extremely sensitive
mass device that can detect the change in mass of a molecule, sen-
sors based on the QCM have high sensitivity and accuracy. The
operating principle of the QCM coated with ZnO nanorods sensor is
based on the change in mass of the adsorbed gas in the sensing layer.
Thus, mass-based gas sensors measure directly the adsorption
process and do not require the charge carriers of the semiconduc-
tor materials to be the sensing layer to overcome the activation
energy barrier. The gas sensor based on the QCM coated with
ZnO can usually be operated at room temperature. Various meth-
ods have been reported for the synthesis of ZnO nanorods, such
as reactive magnetron sputtering, pulsed laser ablation, thermal
evaporation, vapor phase transport, and chemical vapor deposi-
tion [2,23–25]. However, these methods usually require expensive
equipments and high synthesizing temperatures, which are not
compatible with the QCM substrate in the operating frequency of
the quartz. The wet chemical route was chosen due to its obvious
advantages of low synthesizing temperature, simple equipment,
and easy operation. Moreover, this technique can synthesize on
any substrate with a large-scale area, precise position control, and
easy control of synthesis conditions. An important advantage of
the method is its ability to synthesize the vertically well-aligned
ZnO nanorods with high quality and uniform length and distribu-
tion. In the present paper, the fabrication processes of mass-based
gas sensor using QCM coated with a sensing layer of vertically
well-aligned ZnO nanorods were reported. The characteristics,
including sensitivity, reproducibility, response, and recovery times
of as-fabricated sensors, were investigated with different ammonia
concentrations.
2. Experiment
For fabrication of the QCM device, both-side polished AT-cut
quartz crystal plates with dimensions of 25 mm × 20 mm and thick-
ness of 300 ␮m were used. Two circular electrodes with diameters
of 12 and 6 mm were deposited on both sides of the quartz plate
by sputtering method and were patterned by the lithography
technique. The circular electrodes were composed of a 40 nm Cr
under-layer surface and a top 100 nm Au layer.
Vertically aligned ZnO nanorods were directly grown on the Au
electrode of the QCM device by a wet chemical route. First, zinc
acetate [Zn(COOCH3)2·2H2O] diluted in butanol was coated on the
Au electrode by the drop-coating technique and was followed by
heat-treatment at 300 ◦C in air for 30 min to form a seed layer of
ZnO nanocrystals. Subsequently, the QCM coated with the seed
layer was vertically floated upside down on the aqueous solution
surface of equal molar zinc nitrate [Zn(NO3)2·6H2O] and hexam-
ethylenetetramine (HMTA) (C6H12N4). The hydrothermal process
was conducted at 90 ◦C for 2 h. After reactions, the substrates were
removed from the solution, rinsed with de-ionized water, and dried
with N2 blow. ZnO nanorods form by the hydrolysis of zinc nitrate
in water in the presence of HMTA. The chemical reactions for the
formation of the ZnO nanorods on ZnO-coated substrates are [26]:
C6H12N4 + 6H2O → 6CH2O + 4NH3 (1)
NH3 + H2O ↔ NH4
+
+ OH−
(2)
Zn2+
+ 2OH−
→ ZnO + H2O (3)
Fig. 1. Diagram of the testing gas system.
X-ray diffraction (XRD) and field emission scanning electron
microscopy (FE-SEM) were used to analyze the crystal structure
and morphology of the as-grown ZnO nanorods.
Gas sensing measurement of the QCM coated with ZnO nanorods
was conducted using a gas sensing system, as shown in Fig. 1. A
flow-through technique with a constant flow rate (15 sccm) was
employed for the gas sensing test. The gas concentration was con-
trolled by changing the mixing ratio of the parent gases on MFC1
and synthetic air on MFC2 in a mixing chamber. The testing process
was conducted by two steps as follows. At the beginning, air flow
of 15 sccm (MFC4) was flowed through the chamber to obtain the
baseline of the frequency. Balance NH3 gas flow of 15 sccm (MFC3)
was then flowed through the chamber to replace the air flow. The
frequency shifts of the sensors were monitored by a frequency
counter, QCM200, which was connected to a computer system via
the SRSQCM200 software program and stored in a PC. The resonant
characteristics of the fabricated QCM device were examined using
an R37CG Network Analyzer (30 kHz–3.8 GHz).
3. Results and discussion
Fig. 2 shows a photograph and the resonant characteristics of
the as-fabricated QCM device using AT-cut quartz crystal plate as
a precursor substrate. The AT-cut quartz crystal is well known as
a piezoelectric material suitable for the QCM due to its high sen-
sitivity to mass change on the surface. The resonant frequency (f0)
in this work was evaluated from the conductance peak. It has been
observed that the conductance versus frequency curve shows a fun-
damental resonance peak at 5.48 MHz (Fig. 2b). The ZnO nanorods
were then grown on one side of the Au electrode-coated QCM by the
wet chemical route. Fig. 3 shows SEM images of the top-view (3a)
and side-view (3b) of as-grown ZnO nanorods on the Au electrode
of the QCM. The morphology of the ZnO nanorods with a hexagonal
structure was vertically well-aligned and uniformly distributed on
the Au electrode of the QCM. This shows that the exposed area of the
sensing layer was remarkably enhanced compared with the sensing
layer of the ZnO nanowires [27]. The average diameter and length
of ZnO nanorods were around 100 nm and 3 ␮m, respectively. In
comparison with the ZnO nanowires that were first synthesized
by evaporating high purity zinc pellets at 900 ◦C and were then
distributed on the QCM [27], the wet chemical route has many
advantages such as low cost, low temperature operation, high pre-
ferred orientation, and environmental friendliness. This method
can also directly grow ZnO nanorods with high uniform distribution
on a large area.
The XRD pattern of the as-grown ZnO nanorods grown on the
Au electrode of QCM is shown in Fig. 4. The XRD diffraction peaks
at 31.28◦, 34.64◦, 36.32◦, 47.90◦, and 62.90◦ represent the (1 0 0),
(0 0 2), (1 0 1), (1 0 2), and (1 0 3) planes, respective, of the hexago-
nal ZnO structure with lattice constants of a = 3.24 ˚A and c = 5.20 ˚A
in accordance with the JCDPS card 36-1451. The over-whelmingly

3. Please cite this article in press as: N. Van Quy, et al., Gas sensing properties at room temperature of a quartz crystal microbalance coated with
ZnO nanorods, Sens. Actuators B: Chem. (2010), doi:10.1016/j.snb.2010.10.030
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Fig. 2. (a) Optical image and (b) conductance characterization of the fabricated QCM.
high intensity of the (0 0 2) reflection peak compared to the other
crystallographic planes directly implies that a majority of the ZnO
nanorods grew with the c-axis direction perpendicular to the sub-
strate. Higher peak ratios of (0 0 2)/(1 0 0) and (0 0 2)/(1 0 1) were
observed, suggesting the vertical alignment of the nanorods.
Fig. 5a shows the response transients of the ZnO nanorod-coated
QCM sensor to switching-on and off of the NH3 gas-flow with dif-
ferent concentrations (50, 100, and 200 ppm) at room temperature
(25 ◦C). In the first stage, the sensor flushed a reference air gas flow
of 15 sccm to obtain a baseline. The sensor was then exposed to a
NH3 gas flow of 15 sccm with a certain concentration, which leads
to frequency response until a steady stage was reached, indicating
maximum adsorption of NH3 gas onto the QCM sensor. The NH3
gas flow was finally replaced by the air gas flow and the sensor
returned back to its baseline. In this experiment, the flow rate of
the diluted ammonia gas and dry air was fixed at 15 sccm. Hence, in
the gas sensing chamber, the flow and pressure were ensured to be
constant. The change in resonant frequency of a QCM ( f) can be
related to the change in mass ( m) due to the adsorption of NH3
gas molecules on ZnO nanorods using the Sauerbrey equation as
follows [16].
f =
−2f 2
0
A q q
m, (4)
where A is the active area of the QCM electrode in cm2, f0 is the
resonant frequency of the QCM in hertz (Hz), m is the change in
the oscillating mass in grams (g), q is the density of quartz, and q
is the shear wave velocity in the quartz.
Fig. 5a also shows three time-cycling responses of the sensors for
each NH3 gas concentration (50, 100, and 200 ppm). The sensor had
almost the same response for the three cycles, indicating that the
sensor had good reproducibility. Additionally, we found that when
Fig. 3. SEM images of ZnO nanorods grown by wet chemical bath deposition: (a)
top-view and (b) side-view.
the NH3 gas flow was replaced by air flow, the resonant frequency
returned to its original value. This indicates that the absorbed NH3
molecules were completely removed. The vertically aligned ZnO
nanorods grown on the QCM electrodes might have enhanced this
fact. The temporary change in frequency during the exposure of
NH3 was supposed to be due to the weak physical adsorption of
Fig. 4. X-ray diffraction pattern of ZnO nanorods.

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Fig. 5. (a) Reproducibility and (b) proportion test for the frequency shift of the sensor
based on QCM coated with ZnO nanorods with different NH3 concentrations.
NH3 onto the ZnO, as the chemical adsorption of NH3 on the ZnO
nanorods could not be rinsed with the air flow [27,28]. However, the
theory calculation of the adsorption of NH3 gas on 1D ZnO nanos-
tructures was chemical adsorption as previously reported [29]. This
means neither the experimental data nor the theory calculation
data as previously reported can be used to explain our observation.
Thus, we propose the NH3 sensing mechanism of our sensor as fol-
lows. The H2O molecules from air (moisture) could be expected to
adsorb physically on the surface of the ZnO nanorods at room tem-
perature. Upon exposure to ammonia, the surface reaction of NH3
with the physical adsorption H2O could occur:
NH3(g) + H2O(surface) → NH4OH(g) (5)
Ammonium hydroxide, NH4OH, produced during the surface reac-
tion is volatile in nature. The high volatility of NH4OH explains the
complete recovery of the sensor by rinsing the air flow.
Fig. 5b shows the frequency shift as a function of NH3 gas con-
centration. It is obvious that the frequency shift linearly increases
with an increase in the NH3 gas concentration in the range of
50–200 ppm. This indicates that more NH3 molecules are adsorbed
on the ZnO nanorods with the increase in the NH3 gas concentra-
tion. Although a higher NH3 gas concentration was not tested in this
work due to a limitation in our testing system, we recognize that the
increase in the shift frequency tends to saturate with the increase in
concentration, as previously reported [27]. It can be also observed
that the shift frequency upon exposure to 50 ppm is about 9.1 Hz.
This suggests that ZnO nanorod-coated QCM sensor can detect NH3
Fig. 6. High magnification of the response and recovery time of the fabricated sensor
to (a) 50, (b) 100, and (c) 200 ppm of NH3 concentrations.
gas at lower concentration and even at the ppb level. Our group is
currently working on this.
In order to study the response and recovery times of the sen-
sor, the high magnification of the frequency shift versus time at
each concentration of NH3 is plotted in Fig. 6. The times to reach
90% variation in the frequency shift upon exposure to gas and air
were defined as the 90% response time [t90%(air-to-gas)] and the 90%
recovery time [t90%(air-to-gas)], respectively. The 90% response time
for gas exposure [t90%(air-to-gas)] and that for recovery [t90%(gas-to-air)]
were calculated from the frequency shift–time data from Fig. 6.
The t90%(air-to-gas) values in the sensing of 50, 100, and 200 ppm NH3
were 226, 231, and 239 s, respectively, while the t90%(gas-to-air) value
in the sensing of that were 368, 394, and 398 s, respectively. The
response and recovery times slight increased with an increase in the
NH3 gas concentration. It can be seen that the response times were
also relatively shorter than the recovery time. This means that the
adsorption process of NH3 was faster than the desorption process.
This observation agrees well with the previous reports [27,28].
One of the most important characteristics of the gas sensor is
its selectivity. To examine the selectivity of the QCM coated with
ZnO nanorods gas sensor, we tested the sensitivity of the sensor
with several gases including of carbon monoxide, carbon dioxide,
nitrogen dioxide, nitrous oxide and LPG (which consists of hydro-

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ZnO nanorods, Sens. Actuators B: Chem. (2010), doi:10.1016/j.snb.2010.10.030
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Table 1
Brief summary of results reported on the response of NH3 gas sensors.
No. Gas sensor types Testing gases Response, S Reference
S = % R/R
1 Ru-doped ZnO sensor NH3, 1000 ppm 430 [30]
Alcohol, 1000 ppm 190
LPG, 1000 ppm 40
H2, 1000 ppm 25
NOx, 1000 ppm 10
S = % R/R
2 Polypyrrole-based gas
sensor
1% NH3 + N2 51.2 [31]
2% CO + N 0.4
0.7% CH4 + N2 0.5
5% Hz + N2 0.6
100% O2 1.2
S =
Ri/R0−1
˙n
j=1
Rj/R0−1
3 Ionic conductor (CuBr)
film-based gas sensor
NH3, 200 ppm 1 [32]
C2H2, 200 ppm No appreciable change
H2S, 200 ppm 0.16
NO, 200 ppm No appreciable change
S = R
4 Pt-doped WO3 sensor NH3, 4000 ppm 15 [33]
NO2, 400 ppm 4
CO, 400 ppm 1
Ethanol, 80 ppm 1
S = f
5 QCM-ZnO nanorods NH3, 200 ppm 24.1 This work
N2O, 5000 ppm 0.45
NO2, 1000 ppm 0.85
CO2, 20 000 ppm 0.67
LPG, 20 000 ppm 0.91
CO, 150 ppm 0.62
carbons like CH4, C3H8, C4H10). The conductivity-based gas sensor
using ZnO thin film indicates significant sensitivity to LPG signifi-
cantly [28]. For the gas sensing properties, the fabricated sensors
were not responsive at a concentration of about 1% LPG. The change
in frequency of the sensors was realized when the concentration of
LPG was about 2%. Fig. 7 shows the comparison of the resonant
frequency of the device exposed to N2O, CO, NO2, CO2, and LPG
with that exposed to ammonia. Although the concentration of LPG
was 2%, the frequency shift of the sensor only changed by 0.8 Hz.
In comparison with 50, 100, or 200 ppm NH3, the response of the
sensor with LPG was insignificant. Specially, our NH3 sensors are
also good selective over the compound of nitrogen (N2O and NO2).
We have tested sensor with 0.5% N2O and 0.1% NO2 concentration
7006005004003002001000
Time (s)
0.5% N2
O
150 ppm CO
0.1% NO2
2% CO2
2% LPG
50 ppm NH3
Gas
in
Air
in
-5
0
Δf(Hz)
Fig. 7. Comparison of the frequency change of the fabricated sensor when exposed
to LPG, CO2, N2O and NH3.
the frequency shift are about 0.4 Hz and 0.6 Hz, respectively. It can
be recognized that the compound of nitrogen gas as concentra-
tion of few hundred ppm cannot interfere the sensor to NH3 gas. A
good selectivity of the sensors to NH3 gas was also observed when
exposed to carbon monoxide (CO) and carbon dioxide (CO2). The
frequency shift of the sensors with both of carbon monoxide and
carbon dioxide was even less than that with the LPG. Fig. 7 shows
clearly the frequency shift of the sensor when exposed to them. At
150 ppm carbon monoxide and 2% carbon dioxide concentrations,
the change in frequency was only 0.5 and 0.6 Hz, respectively.
We have made comparison the selectivity of our QCM-coated
ZnO nanorods sensors to various kind of the sensors recently
reported as presented in Table 1 [30–33]. It can be seen that Ru-
doped ZnO-based sensor has quite good selectivity to NH3 gas
compared with the other sensors (see Table 1). For instance, the
ratio of response of NH3 to LPG and NO2 (SNH3
/SLPG and SNH3
/SNO2
)
at 1000 ppm is around 10.7 and 43, respectively. These ratios in our
sensor are comparable with reported results, which are round 26
and 28.3. It should be noted that we have tested our sensor with
lower NH3 concentration and higher concentration of LPG and NO2.
The good selectivity to NH3 gas of the QCM coated with ZnO
nanorods is an important factor for developing NH3 gas sensor. This
characteristic is difficult to achieve with resistive-sensors based on
the semiconductor metal oxides. For further application of the sen-
sors, the mechanism of this issue needs to be elucidated in detail.
Although present study cannot fully understand the mechanism, it
can be somehow explained based on the viewpoint of Eq. (4).
4. Conclusion
In this paper, we presented the first study on the use of ZnO
nanorods-coated quartz crystal microbalance as a NH3 sensor.
Vertically well-aligned ZnO nanorods were successfully grown
on the Au electrode of QCM by the wet chemical method. The

6. Please cite this article in press as: N. Van Quy, et al., Gas sensing properties at room temperature of a quartz crystal microbalance coated with
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ZnO nanorods were uniformly distributed on the substrate with
a diameter and height of around 100 nm and 3 ␮m, respectively.
As-developed sensor showed a good response to NH3 gas at room
temperature and it could be used detect at low level concentration
of NH3 gas. Additionally, the sensor has a good selectivity to NH3
gas over various gases such as LPG, N2O, NO2, CO, and CO2. This plat-
form provides a promising NH3 gas sensor with high response, high
selectivity, rapid response, and operating at room temperatures.
Acknowledgment
This work was supported by the application-oriented basic
research program (2009-2012, Code: 05/09/HÐ-ÐTÐL).
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Biographies
Nguyen Van Quy received his M.S and Ph.D degrees from Materials Science and
Engineering at Chungnam National University, South Korea in 2006 and 2009,
respectively. He is currently a research lecturer at International Training Institute
for Materials Science (ITIMS), Hanoi University of Science and Technology (HUST),
Vietnam. His research interests include synthesis of carbon nanotubes and applica-
tions to nano-electronic devices of field emission, solar cell and sensors, MEMS, and
sensitive materials.
Vu Anh Minh received his B.S and M.S degrees from Faculty of Physics at Hanoi Uni-
versity of Science, Vietnam National University, in 1992 and 2001, respectively. He
is currently a Ph.D student at International Training Institute for Materials Science
(ITIMS), Hanoi University of Science and Technology (HUST), Vietnam. His current
interests include nanomaterials synthesis, characterizations, and applications to
electronic devices, gas sensors and biosensors.
Nguyen Van Luan received his B.S from Institute of Engineering Physics (IEP), Hanoi
University of Science and Technology (HUST), Vietnam. He is currently a master
course student Department of Energy Science, Sungkyunkwan Advanced Institute
of Nanotechnology, Sungkyunkwan University, South Korea.
Vu Ngoc Hung received the B.S. degree in physics from Kishinev University (USSR), in
1979 and the Ph.D. degree from Hanoi University of Science and Technology (HUST),
Vietnam in 1991. He is currently an Associate Professor at the International Training
Institute for Materials Science (ITIMS), HUST. His current research interests are in
the area of MEMS inertial and QCM sensors.
Nguyen Van Hieu joined the International Training Institute for Material Science
(ITIMS) at Hanoi University of Science and Technology (HUST) in 2004, where he is
currently associate professor. He received his PhD degree from the Faculty of Electri-
cal Engineering at University of Twente, The Netherlands in 2004. In 2007, he worked
as a post-doctoral fellow at the Korea University. Currently, he is the vice director
of ITIMS and chairs the research group of gas sensors. His current research inter-
ests include nanomaterials, nanofabrications, characterizations and applications to
electronic devices, gas sensors and biosensors.