- Email: [email protected]
graphene oxide nanocomposite film
Accepted Manuscript Title: Impedance analysis of quartz crystal microbalance humidity sensors based on nanodiamond/graphene oxide nanocomposite film Author: Yao Yao Yajuan Xue PII: DOI: Reference:
S0925-4005(15)00085-4 http://dx.doi.org/doi:10.1016/j.snb.2014.12.134 SNB 17985
To appear in:
Sensors and Actuators B
Received date: Revised date: Accepted date:
30-8-2014 4-12-2014 24-12-2014
Please cite this article as: Y. Yao, Y. Xue, Impedance analysis of quartz crystal microbalance humidity sensors based on nanodiamond/graphene oxide nanocomposite film, Sensors and Actuators B: Chemical (2015), http://dx.doi.org/10.1016/j.snb.2014.12.134 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
The QCM humidity sensor based on nanodiamond/graphene oxide composite films
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Impedance analysis of quartz crystal microbalance
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humidity sensors based on nanodiamond/graphene
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oxide nanocomposite film
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Yao Yao, Yajuan Xue
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College of Communication Engineering, Chengdu University of Information Technology, Chengdu 610225, People’s Republic of China.
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Corresponding author: Y. Yao
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Tel & Fax: +8628 85966249
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E-mail address: [email protected]
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
Abstract In
this
work,
detonation
nanodiamond
(DND)/graphene
oxide
(GO)
nanocomposites with various weight ratios were prepared. By combining with quartz
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crystal microbalance (QCM) technique, the humidity sensing properties of these
nanocomposites sensors, including response sensitivity, humidity hysteresis, dynamic
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response and recovery, were studied through an impedance analysis method. The test
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results indicated that DND/GO nanocomposites showed high humidity response sensitivity, logarithmic linear response, fast response/recovery and small humidity
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hysteresis. Moreover, the influence of DND content in nanocomposite on the humidity response sensitivity and quality factor of the sensors has also been discussed. The
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results revealed that the increase of DND content in nanocomposite could enhance the humidity response sensitivity, but reduce the quality factor of the sensor. So, it is very
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necessary to selectve a suitable DND content in nanocomposite for balancing the
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sensitivity and quality factor. In addition, the reasons for the enhanced humidity sensing
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performance have also been discussed in detail. This work demonstrated that DND/GO nanocomposite is promise candicate material for humidity sensing detection by combing with QCM technique.
Keywords: Detonation nanodiamond/graphene oxide nanocomposite; Quartz crystal microbalance; Humidity sensor; Impedance analysis.
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
1. Introduction The accurate and reliable detection of relative humidity have attracted a great deal of attention in the fields of meteorology, agriculture, electronics and food storage etc. [1,
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2]. The increasing demand of humidity sensor market promotes a large number of efforts to fabricate high performance humidity sensor. So far, a variety of transduction
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mechanisms, including capacitive [3, 4], resistive [5], gravimetric [6], optical [7], strain
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[8], etc., have been explored to develop humidity sensor. Among the existing mechanisms, humidity sensor using quartz crystal microbalance (QCM) technique has
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become more and more popular since the first report by King in 1969 [9]. The advantages of QCM humidity sensor include high sensitivity, low cost, digital
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frequency signal output and excellent stability [10]. The QCM humidity sensor is generally composed of a QCM tranducer and a layer of sensitive material deposited on
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the the electrode of QCM. The adsorption of water molecules onto sensitive material
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will make QCM yield a frequency response. Until now, many reaseachers have already
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devoted themself to enhance humidity response senstivity by developing various kinds of humidity sensitive materials. Beside humidity response senstivity, the stability of QCM humidity sensor, which is quantitatively described by quality factor (Q-factor), is also an important characteristic for evaluating sensor performance. In most cases, the sensitive materials used for QCM humidity sensor are not purely rigid. The introduction of the viscosity of non-rigid sensitive material, on one hand, will increase the sensor sensitivity according to equation (1) [11].
f non rigid
2 f 0 m L L f02 3 q q A q q
3
(1)
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
Where f0 is the resonant frequency, Δm is the additional mass on the electrode, A is the surface area of the electrode, ρq and μq are the density and shear modulus of quartz, ρL and ηL are the density and viscosity of sensitive material, respectively. On the other
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hand, the increase in viscosity of non-rigid sensitive material during water adsorption will damp the QCM and reduce the Q-factor of the sensor. So, it is very essential to pay
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special attention to the change of Q-factor besides response sensitivity.
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In the last two decades, nanostructure sensitive materials, especially nanocarbon materials, have already shown a great prospect in the field of gas/humidity sensor.
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Compared with bulk materials, nanostructure sensitive materials usually exhibit some obvious advantages for sensor application, such as large specific surface area,
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outstanding adsorption capacity, high mechanical stiffness and satisfactory stability. Up to now, a variety of carbon nanostructure materials, including zero-dimensional (C60)
[12],
one-dimensional
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fullerenes
carbon
nanotube
(CNT)
[13]
and
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two-dimensional graphene oxide (GO) [14], have been used for humidity sensor by
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combining with QCM. Among the three kinds of carbon nanostructure materials, GO is a promise candicate material for high precision detection of humidity. Our pervious studies demonstrated that GO based QCM humidity sensors displayed both large humidity response sensitivity and high frequency stability [10, 14]. Su et al. [6] experimentally compared the humidity response sensitivities of GO and CNT based QCM humidity sensors, and found that the sensitivity of GO based QCM humidity sensor was better than that of CNT based QCM humidity sensor. However, it is noteworthy that GO sheets should be aggregated to form a relatively compact film after drying. This property heavily reduces the specific surface area contributed by individual GO sheets. To address this drawback, a few studies presensted a new approach to
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
introduce nanoparticles into GO sheet for preventing the agglomeration of GO sheets in the process of drying [15, 16]. The GO/nanoparticles composite film displays microporous-layered nanostructures, and thereby can provide large specific surface area
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[15]. This approach is beneficial to acquire high sensor’s response sensitivity.
Detonation nanodiamond (DND) with typical sizes in the 5~10 nm range has
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recently been extensively concerned in the areas of tribology, biology and sensitive
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electronics due to its excellent mechanical properties, high surface areas and tunable surface structures [17]. The rich surface groups of DND, such as hydroxy and carboxyl
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groups, make DND expediently realize functionalization with other sensing material [17]. In this work, we considered to synthesis DND/GO nanocomposite and examine its
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humidity sensing properties by combining with QCM technique. The sensor performances, including humidity response sensitivity, humidity hysteresis, dynamic
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response and repeatability of the sensors, were experimentally studied. In addition, the
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discussed.
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effect of DND content in nanocomposite on humidity sensing performances was also
2. Experimental
2.1 Preparation of GO/DND composites Graphite oxide was synthesized by the oxidation of natural graphite powder by a
modified Hummers method [18]. Subsequently, single-layered GO sheets were achieved by the exfoliation of graphite oxide under ultrasonication in water. The concentration of the prepared GO dispersion was 1 mg/mL. DND powder with typical sizes in the 5~10 nm range was purchased from Nanjing Xianfeng Nano Co. Ltd. China. Based on its excellent hydrophilic property, DND can be readily dispersed in water. Then, 2.5, 5 or 10 mg of DND powder was added into 10 mL GO dispersion (1 mg/mL), respectively.
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
Successively, these mixtures were treated via ultrasonic treatment for 1 hour for obtaining homogeneous DND/GO nanocomposite in water. The weight ratios of GO and DND, which was defined as R, were calculated to be 4:1, 2:1 and 1:1, respectively.
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2.2 Fabrication of GO/DND composite based QCM humidity sensor
The QCM used in this research was a 8 mm diameter 10 MHz AT-cut quartz
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crystal with 5 mm diameter electrodes manufactured by Wuhan Hitrusty Electronics Co.
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Ltd. China. By the precise control of electrode thickness, the nominal frequency deviation of the QCM is less than 5 ppm (i.e. 50 Hz). The initial Q-factor of the QCM is
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beyond 75,000. Before use, the QCM was rinsed with deionized water and ethanol, respectively, and then dried in oven for 6 hours at 40°C.
The deposition of DND/GO
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nanocomposite films onto the electrode of QCM was achieved by using a drop-casting method. And the DND/GO nanocomposite films coated QCM was dried in oven for 6
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hours at 40℃. After the evaporation of water, DND/GO nanocomposite film based
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2.3 Apparatus
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QCM humidity sensor was obtained.
A schematic diagram of the experimental setup is shown in Fig. 1. Saturated LiCl,
MgCl2, Mg(NO3)2, NaCl, KCl, KNO3 and K2SO4 solutions were used to yield approximately 11.3%, 32.8%, 54.3%, 75.3%, 84.3%, 93.5% and 97.3% RH levels, respectively. Two kinds of testing methods, including static and dynamic humidity sensing tests, were adopted to evaluate humidity sensing performances of the sensors. A precision impedance analyzer (6500, Wayne Kerr, UK), which was connected to PC through a LAN interface for data acquisition, was used to measure the electro-acoustic parameters of the sensor near its resonance at different RH levels. The static parameters, including resonance frequencies, Q-factor and the equivalent circuit elements
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
parameters, can be obtained by analyzing the electro-acoustic spectrum of the sensors. A home-made oscillating circuit was used to excite the QCM sensor, and the frequency output was monitored by a frequency counter (53131A, Agilent), which was
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communicated to PC via a GPIB-USB adapter interface. The dynamic humidity sensing response of the sensors was recorded in real time during the change of humidty. The
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surface morphologies of GO, DND and GO/DND nanocomposite were characterized by
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a field-emission scanning electron microscope (FE-SEM, S-4800, Hitachi). The BET analysises of the materials were carried out by Nova2000e specific area and void ratio
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tester. All the experiments were carried out at room temperature (25±1°C) without special representation.
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3. Results and discussion
Fig. 2(a-c) shows the FE-SEM images of DND, GO and DND/GO nanocomposite
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(R=1), respectively. These images revealed that DND exhibited a nanoparticles
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structure with a diameter of 5-10 nm; GO displayed a remarkable layered structure and
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many individual GO sheets were stacked together to form a compact film; DND/GO nanocomposite film showed a microporous-layered nanostructure. Table 1 listed the BET analysis results of GO and DND/GO nanocomposite (R=1). It can be found that DND/GO nanocomposite (R=1) has much larger surface areas and pore volumes than GO. As shown in Table 1, the specific surface area and pore volume of DND/GO nanocomposite (R=1) are 49.573 m2/g and 0.109 cm3/g, which are nearly 5 times and 9 times than that of GO, respectively. The BET analysis results indicated that the introduction of DND nanoparticles in GO sheets dramaticlly increased the specific surface area of GO films.
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
The static humidity sensing response was measured by exposing these sensors to different humidity sources. When the resonance reached steady state at a given humidity, the electro-acoustic spectrum of the sensor was recorded. For a sensing film coated
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QCM, the electro-acoustic spectrum is usually described as impedance spectrum and
analyzed by a modified Butterworth-van-Dyke (mBVD) equivalent circuit model as
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shown in Fig. 3(a). In this circuit, R, L, C and C0 describes the initial quality,
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mechanical flexibility, energy dissipation of the blank QCM and additional capacitor between two electrodes, respectively; R1 and L1 describe extra energy dissipation and
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mass due to the adsorption of sensing films. Therefore, the total admittance (reciprocal
1
1 ( R R1 ) j ( L L1 ) jC
d
Y ( ) G ( ) jB ( )
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of impedance) spectrum of the sensing film coated QCM, Y (ω), is expressed as [19]:
L* L L1
(2)
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R* R R1
jC0
Where G and B are conductance and susceptance, respectively. In equation (2), R* and
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L* describe the total energy dissipation and mass increasement of sensing films coated QCM sensor. Fig. 3(b) shows the typical conductance spectrum and susceptance spectrum curves of films coated QCM sensor. By fitting the conductance spectrum and susceptance spectrum with the mBVD equivalent circuit, a series of resonance parameters of the sensors, including resonant frequency, Q-factor and equivalent circuit elements values, can be obtained. The frequency at the conductance peak is the resonant frequency (f) of the sensor. The Q-factor of QCM can be defined as the ratio of resonant frequency to half-band width of conductance peak (HBW) as shown in equation (3). Fig. 4 gives the conductance spectrum and susceptance spectrum curves of the GO and
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
DND/GO nanocomposite based QCM humidity sensors at various RH levels. It can be found that the conductance peak of each sensor move from a higher frequency to a lower frequency with increasing humidity, and the HBW also becomes broad with
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increasing humidity. Fig. 5 shows the frequency response and Q-factor of the GO and
DND/GO nanocomposite based QCM humidity sensors as a function of humidity. It can
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be seen that both resonant frequency and Q-factor decreased with increasing humidity
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level for all the sensors. The frequency shifts (i.e. sensitivity) of DND/GO nanocomposite based QCM humidity sensors are larger than that of GO based sensor.
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Also, with the increase of DND content in the nanocomposite, DND/GO nanocomposite film based QCM sensor’s sensitivity increases and its Q-factor decreases. When
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humidity changed from 11.3% to 97.3%, the frequency shifts of GO and DND/GO nanocomposite based QCM humidity sensors (R=4, R=2 and R=1) were 1645, 2637,
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2864 and 5467 Hz, respectively. Meanwhile, we can find that the frequency responses
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to humidity of the sensors exhibits a logarithmic tendency. Fig. 6 shows the linear
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fitting curves of the Log (Δf) versus humidity for all the sensors. The regression coefficients, R2, are 0.98605, 0.99322, 0.97696 and 0.97019 for GO, DND/GO (R=4), DND/GO (R=2) and DND/GO (R=1), respectively. The frequency shifts of all the sensors exhibit an acceptable logarithmic linear relationship with relative humidity. The enhancement sensitivity may be attributed to the increase of porosity and adsorption sites of DND/GO composite film. The introduction of DND nanoparticles in GO sheets, on one hand, can increase the active surface areas due to the formation of microporous-layered nanostructure, which has been confirmed by SEM and BET analysis.
One the other hand, the intrinsic hydrophilicity of DND nanoparticles is able
to provide more water adsorption sites. As a result, DND/GO nanocomposite sensor
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
(R=1) that owns the most number of DND nanoparticles exhibits the highest humdity response sentivity.
f HBW
(3)
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Q
However, it should also be noted that DND/GO nanocomposite sensors (R=2 and
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R=1) suffer a sharp decrease in Q-factor during humidity detection. Especially at high
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humidity (97.3% RH), their Q-factors are only about 6,300 and 2,144. The possible reason for the sharp decrease in Q-factor can be attributed to the increase in viscosity of
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DND/GO nanocomposite film under a large number of water adsorption [20]. Table 2 gives the equivalent circuit elements values of DND/GO composite based QCM
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humidity sensors (R=1 and R=4) at several humidity points by fitting the impedance spectrum with BVD equivalent circuit model. It can be found that R* element of
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DND/GO nanocomposite sensor (R=1) is far larger than that of DND/GO
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nanocomposite sensor (R=4) during humidity detection. So, in the practical application, it is very necessary to select the oscillation circuit with strong excitation and good
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stability to ensure the normal operation of DND/GO nanocomposite sensor (R=1) [21]. The humidity hysteresis characteristic of DND/GO nanocomposite film based
QCM humidity sensors was also examined. The sensors firstly underwent humidity variation from low to high humidity for water adsorption, and then from high to low humidity for water desorption. The humidity hysteresis curves of the sensors are shown in Fig. 7. It can be seen that, for all the sensors, the humidity-decreasing sensing curve of the sensor is close to its humidity-increasing sensing curve. The introduction of DND nanoparticles in GO sheets does not acutely increase the sensor’s humidity hysteresis. The possible interpretation about this result is that the introduction of DND nanoparticles in GO sheets yields a microporous-layered nanostructure. This structure is
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
very conducive to desorb water molecules from sensing films. By comparing the four sensors, we can find that the DND/GO nanocomposite film (R=4) owns the smallest humidity hysteresis (~3% RH).
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As is known to all, dynamic response and recovery behavior is an important factor
for evaluating the performance of humidity sensor. To measure the dynamic response
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and recovery, the sensor were firstly exposed to low humidity environment (11.3% RH)
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provided by saturated LiCl solution and the sealing sleeve was released. The output response was record in real-time until the output reached a stable value. Then the
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sealing sleeve was pulled up for isolating the sensor with the surrounding atmosphere, and the isolated sensor was exposed to high humidity environment (84.3% RH)
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provided by saturated KCl solution, and the sealing sleeve was released again for water adsorption. Finally, we repeated step 1 to 3 for obtaining another two cycle’s transient
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humidity response. Fig. 8 displays the dynamic response and recovery curves of the GO
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and DND/GO nanocomposite (R=2 and R=1) sensors which undergo the humidity
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change (low-high-low) for 3 cycles. The response and recovery times, in this work, are defined as the times required by a sensor to achieve 90% of the total frequency change. Compare the dynamic response and recovery behavior of the four sensors, it is clearly noted that both GO and DND/GO nanocomposite based QCM sensor possess a fast response and recovery. The response times of the sensors are within 25 s, and the recovery times of the sensors are within 5 s. Compared to the studies of QCM humidity sensors reported recently [22-24], the response and recovery times of DND/GO nanocomposite based QCM sensor are shorter. Meanwhile, it can be found that the sensing response and recovery of the sensors are entirely repeatable. For example, the frequency shift of DND/GO nanocomposite (R=1) sensor was less than 30 Hz at 11.3%
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
RH after the sensor underwent the humidity change from low to high RH for 3 cycles. The excellent dynamic response and recovery behavior of the DND/GO composite sensor is attributed to water adsorption mechanism and microstructure property of
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sensing material. The adsorption of water molecules on GO and DND nanocomposite is dominated by physisorption with a weak hydrogen bond, so the dynamic equilibrium
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between water adsorption and desorption can be quickly reached. In addition, the
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microporous-layered nanostructure characteristic of DND/GO films is beneficial to realize fast adsorption or desorption of water molecules.
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At last, these effects of environment temperature and interference gases on the sensitivity of DND/GO nanocomposite based QCM humidity sensor have also been
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examined. It should be noted that the environment temperature affects the relative humidity provided saturated salt solution according to the standard of saturated salt
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solution versus RH. Therefore, we used a temperature and humidity chamber, which can
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yield a series of specified humidity points at various temperatures, to measure the
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temperature effect of the sensor. Fig. 9(a) shows the humidity response of DND/GO nanocomposite (R=2) based sensor at three temperature points of 15°C, 25°C and 35°C. It can be found that environment temperature inevitably affects the frequency response of the sensor. On one hand, the QCM displays an inherent temperature-frequency effect [25]; on the other hand, the change of temperature makes DND/GO composite sensing films produce a slight deformation [26], which also causes QCM sensor yield a frequency output. Therefore, the compensation of temperature is necessary for the sensor. In addition, some gases, such as ethanol, acetone, benzene, and formaldehyde, have been used to examine the effect of interference gases on the sensor’s performance. In order to avoid the influence of water vapor, the gas sensing tests use N2 gas as carrier
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
gases since it can provide a very low RH level. Fig. 9(b) shows the frequency response of DND/GO nanocomposite (R=2) based sensor to various gases. It can be seen that DND/GO composite films based sensor was also sensitive to ethanol, acetone and
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formaldehyde vapor. Therefore, we should especially consider the influence of cross-sensitivity of the sensor at low RH since the humidity sensing response is relative
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low.
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4. Conclusion
In summary, we have examined the humidity sensing properties of DND/GO
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nanocomposite films by combining with QCM technique. A series of sensitive test results indicate that DND/GO nanocomposite films display excellent humidity sensing
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properties. The introduction of DND nanoparticles into GO sheets can significantly increase the humidity sensitivity of the sensor. The sensitivity enhancement of
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DND/GO nanocomposite films can be attributed to the microporous-layered
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nanostructure of DND/GO and added water adsorption sites provied by DND. However,
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the Q-factor of DND/GO nanocomposite films based QCM sensor sharply decreases with increasing the DND content of nanocomposite films especially during high humidity detection. So, it is very necessary to selectve a suitable DND content for balancing the sensitivity and Q-factor. Besides the sensitivity and Q-factor, the humidity hysteresis and dynamic response and recovery of DND/GO nanocomposite films based QCM sensor have also been studied. Thanks to the microporous-layered nanostructure, DND/GO nanocomposite film sensor displayed a very small difference between water adsorption and desorption process. In addtion, this structure is beneficial to realize fast water adsorption or desorption, resulting in a fast response and recovery. This study
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
demonstrates that DND/GO nanocomposite is promise candicate material for humidity sensing detection by combing with QCM technique. Acknowledgements
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This work was supported by the National Natural Science Foundation of China
(Nos. 61401047 and 41404102) and the Project of the Scientific Research Foundation
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of CUIT (No. KYTZ201409).
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colloid crystals coated on quartz crystal microbalance by the self-assembly method, Ceramics International. 39 (2013) 3621-3625. [25] F.L. Walls, J.J. Gagnepain, Environmental sensitivities of quartz oscillators, IEEE Trans. Ultrason. Ferroelec. Freq. Contr., 39 (1992) 241-249. [26] A. Domack, O. Prucker, J. Rühe, D. Johannsmann, Swelling of a polymer brush probed with a quartz crystal resonator, Phys. Rev. E, 56 (1997) 680.
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
Table 1 BET surface area analyses of GO and DND/GO nanocomposite (R=1). BET surface area (m2/g)
Pore volume (cm3/g)
Pore diameter (nm)
GO
10.333
0.011
3.713
DND/GO (R=1)
49.573
0.109
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Samples
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te
d
M
an
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cr
3.939
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
Table 2 The equivalent circuit elements parameters of DND/GO nanocomposite based QCM sensor at various humidity points Equivalent circuit elements parameters DND/GO nanocomposite sensor (R=4)
RH
DND/GO nanocomposite sensor (R=1)
L (mH)
C (fF)
C0 (pF)
Q
R* (Ω)
L* (mH)
C (fF)
C0 (pF)
Q
11.3%
7.72
26.27
9.66
7.38
78243
100.56
25.39
10.00
7.60
6348
32.8%
7.86
26.26
9.66
7.35
76938
100.35
25.47
9.97
7.36
6170
54.3%
8.25
26.22
9.68
7.39
73649
135.13
25.50
9.96
7.16
4465
75.3%
8.99
26.21
9.68
7.52
67645
186.35
25.17
10.09
7.45
3235
84.3%
10.21
26.29
9.63
7.69
61213
238.15
25.32
10.02
7.65
2555
97.3%
12.76
26.55
9.56
8.32
45951
287.03
25.51
9.96
8.00
2144
an
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cr
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R* (Ω)
Ac ce p
te
d
M
*
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
Figure Captions Fig. 1. Schematic diagram of humidity sensing experimental setup.
nanodiamond/graphene oxide nanocomposite.
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Fig. 2. SEM images of (a) nanodiamond; (b) graphene oxide and (c)
Fig. 3. (a) The modified Butterworth-van-Dyke equivalent circuit; (b) The typical
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conductance and susceptance spectrum of films coated QCM sensor.
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Fig. 4. The conductance spectrum of (a) GO, (b) DND/GO (R=4), (c) DND/GO (R=2), (d) DND/GO (R=1) and the susceptance spectrum of (e) GO, (f) DND/GO (R=4), (g)
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DND/GO (R=2), (h) DND/GO (R=1) at various RH points.
Fig. 5. (a) The frequency response and (b) Q-factor of the GO and DND/GO
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nanocomposite based QCM humidity sensors as a function of humidity. Fig. 6. The linear fitting curves of the Log (Δf) versus humidity for all the sensors.
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humidity sensors.
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Fig. 7. Humidity hysteresis curves of GO and DND/GO nanocomposite based QCM
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Fig. 8. The dynamic response and recovery of (a) GO, (b) DND/GO (R=2) and (c) DND/GO (R=1) based sensors between the changes in humidity from 11.3% to 84.3%. Fig. 9. The effect of (a) temperature and (b) interference gases on the performance of DND/GO nanocomposite (R=2) based QCM humidity sensor.
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
Biographies Yao Yao was born in Sichuan, China. He received his BS degree from the school of Information Science and Technology, Southwest Jiaotong University, Sichuan, China in
ip t
2006. He received his PhD degree at the Southwest Jiaotong University, Sichuan, China in 2013. He is currently a Lecturer in the College of Communication Engineering,
us
interests include carbon based electronics and acoustic sensors.
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Chengdu University of Information Technology, Sichuan, China. His current research
Yajuan Xue was born in Inner Mongolia, China, in 1980. She received the PhD degree
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from Chengdu University of Technology, Sichuan, China in 2014. She is currently an Associate Professor in the College of Communication Engineering, Chengdu University Her current research interests include
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of Information Technology, Sichuan, China.
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signal processing and acquisition of intelligent information.
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S0925-4005(15)00085-4 http://dx.doi.org/doi:10.1016/j.snb.2014.12.134 SNB 17985
To appear in:
Sensors and Actuators B
Received date: Revised date: Accepted date:
30-8-2014 4-12-2014 24-12-2014
Please cite this article as: Y. Yao, Y. Xue, Impedance analysis of quartz crystal microbalance humidity sensors based on nanodiamond/graphene oxide nanocomposite film, Sensors and Actuators B: Chemical (2015), http://dx.doi.org/10.1016/j.snb.2014.12.134 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
The QCM humidity sensor based on nanodiamond/graphene oxide composite films
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Impedance analysis of quartz crystal microbalance
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humidity sensors based on nanodiamond/graphene
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oxide nanocomposite film
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Yao Yao, Yajuan Xue
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College of Communication Engineering, Chengdu University of Information Technology, Chengdu 610225, People’s Republic of China.
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Corresponding author: Y. Yao
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Tel & Fax: +8628 85966249
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E-mail address: [email protected]
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
Abstract In
this
work,
detonation
nanodiamond
(DND)/graphene
oxide
(GO)
nanocomposites with various weight ratios were prepared. By combining with quartz
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crystal microbalance (QCM) technique, the humidity sensing properties of these
nanocomposites sensors, including response sensitivity, humidity hysteresis, dynamic
cr
response and recovery, were studied through an impedance analysis method. The test
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results indicated that DND/GO nanocomposites showed high humidity response sensitivity, logarithmic linear response, fast response/recovery and small humidity
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hysteresis. Moreover, the influence of DND content in nanocomposite on the humidity response sensitivity and quality factor of the sensors has also been discussed. The
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results revealed that the increase of DND content in nanocomposite could enhance the humidity response sensitivity, but reduce the quality factor of the sensor. So, it is very
d
necessary to selectve a suitable DND content in nanocomposite for balancing the
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sensitivity and quality factor. In addition, the reasons for the enhanced humidity sensing
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performance have also been discussed in detail. This work demonstrated that DND/GO nanocomposite is promise candicate material for humidity sensing detection by combing with QCM technique.
Keywords: Detonation nanodiamond/graphene oxide nanocomposite; Quartz crystal microbalance; Humidity sensor; Impedance analysis.
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
1. Introduction The accurate and reliable detection of relative humidity have attracted a great deal of attention in the fields of meteorology, agriculture, electronics and food storage etc. [1,
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2]. The increasing demand of humidity sensor market promotes a large number of efforts to fabricate high performance humidity sensor. So far, a variety of transduction
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mechanisms, including capacitive [3, 4], resistive [5], gravimetric [6], optical [7], strain
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[8], etc., have been explored to develop humidity sensor. Among the existing mechanisms, humidity sensor using quartz crystal microbalance (QCM) technique has
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become more and more popular since the first report by King in 1969 [9]. The advantages of QCM humidity sensor include high sensitivity, low cost, digital
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frequency signal output and excellent stability [10]. The QCM humidity sensor is generally composed of a QCM tranducer and a layer of sensitive material deposited on
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the the electrode of QCM. The adsorption of water molecules onto sensitive material
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will make QCM yield a frequency response. Until now, many reaseachers have already
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devoted themself to enhance humidity response senstivity by developing various kinds of humidity sensitive materials. Beside humidity response senstivity, the stability of QCM humidity sensor, which is quantitatively described by quality factor (Q-factor), is also an important characteristic for evaluating sensor performance. In most cases, the sensitive materials used for QCM humidity sensor are not purely rigid. The introduction of the viscosity of non-rigid sensitive material, on one hand, will increase the sensor sensitivity according to equation (1) [11].
f non rigid
2 f 0 m L L f02 3 q q A q q
3
(1)
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
Where f0 is the resonant frequency, Δm is the additional mass on the electrode, A is the surface area of the electrode, ρq and μq are the density and shear modulus of quartz, ρL and ηL are the density and viscosity of sensitive material, respectively. On the other
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hand, the increase in viscosity of non-rigid sensitive material during water adsorption will damp the QCM and reduce the Q-factor of the sensor. So, it is very essential to pay
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special attention to the change of Q-factor besides response sensitivity.
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In the last two decades, nanostructure sensitive materials, especially nanocarbon materials, have already shown a great prospect in the field of gas/humidity sensor.
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Compared with bulk materials, nanostructure sensitive materials usually exhibit some obvious advantages for sensor application, such as large specific surface area,
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outstanding adsorption capacity, high mechanical stiffness and satisfactory stability. Up to now, a variety of carbon nanostructure materials, including zero-dimensional (C60)
[12],
one-dimensional
d
fullerenes
carbon
nanotube
(CNT)
[13]
and
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two-dimensional graphene oxide (GO) [14], have been used for humidity sensor by
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combining with QCM. Among the three kinds of carbon nanostructure materials, GO is a promise candicate material for high precision detection of humidity. Our pervious studies demonstrated that GO based QCM humidity sensors displayed both large humidity response sensitivity and high frequency stability [10, 14]. Su et al. [6] experimentally compared the humidity response sensitivities of GO and CNT based QCM humidity sensors, and found that the sensitivity of GO based QCM humidity sensor was better than that of CNT based QCM humidity sensor. However, it is noteworthy that GO sheets should be aggregated to form a relatively compact film after drying. This property heavily reduces the specific surface area contributed by individual GO sheets. To address this drawback, a few studies presensted a new approach to
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
introduce nanoparticles into GO sheet for preventing the agglomeration of GO sheets in the process of drying [15, 16]. The GO/nanoparticles composite film displays microporous-layered nanostructures, and thereby can provide large specific surface area
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[15]. This approach is beneficial to acquire high sensor’s response sensitivity.
Detonation nanodiamond (DND) with typical sizes in the 5~10 nm range has
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recently been extensively concerned in the areas of tribology, biology and sensitive
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electronics due to its excellent mechanical properties, high surface areas and tunable surface structures [17]. The rich surface groups of DND, such as hydroxy and carboxyl
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groups, make DND expediently realize functionalization with other sensing material [17]. In this work, we considered to synthesis DND/GO nanocomposite and examine its
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humidity sensing properties by combining with QCM technique. The sensor performances, including humidity response sensitivity, humidity hysteresis, dynamic
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response and repeatability of the sensors, were experimentally studied. In addition, the
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discussed.
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effect of DND content in nanocomposite on humidity sensing performances was also
2. Experimental
2.1 Preparation of GO/DND composites Graphite oxide was synthesized by the oxidation of natural graphite powder by a
modified Hummers method [18]. Subsequently, single-layered GO sheets were achieved by the exfoliation of graphite oxide under ultrasonication in water. The concentration of the prepared GO dispersion was 1 mg/mL. DND powder with typical sizes in the 5~10 nm range was purchased from Nanjing Xianfeng Nano Co. Ltd. China. Based on its excellent hydrophilic property, DND can be readily dispersed in water. Then, 2.5, 5 or 10 mg of DND powder was added into 10 mL GO dispersion (1 mg/mL), respectively.
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
Successively, these mixtures were treated via ultrasonic treatment for 1 hour for obtaining homogeneous DND/GO nanocomposite in water. The weight ratios of GO and DND, which was defined as R, were calculated to be 4:1, 2:1 and 1:1, respectively.
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2.2 Fabrication of GO/DND composite based QCM humidity sensor
The QCM used in this research was a 8 mm diameter 10 MHz AT-cut quartz
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crystal with 5 mm diameter electrodes manufactured by Wuhan Hitrusty Electronics Co.
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Ltd. China. By the precise control of electrode thickness, the nominal frequency deviation of the QCM is less than 5 ppm (i.e. 50 Hz). The initial Q-factor of the QCM is
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beyond 75,000. Before use, the QCM was rinsed with deionized water and ethanol, respectively, and then dried in oven for 6 hours at 40°C.
The deposition of DND/GO
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nanocomposite films onto the electrode of QCM was achieved by using a drop-casting method. And the DND/GO nanocomposite films coated QCM was dried in oven for 6
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hours at 40℃. After the evaporation of water, DND/GO nanocomposite film based
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2.3 Apparatus
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QCM humidity sensor was obtained.
A schematic diagram of the experimental setup is shown in Fig. 1. Saturated LiCl,
MgCl2, Mg(NO3)2, NaCl, KCl, KNO3 and K2SO4 solutions were used to yield approximately 11.3%, 32.8%, 54.3%, 75.3%, 84.3%, 93.5% and 97.3% RH levels, respectively. Two kinds of testing methods, including static and dynamic humidity sensing tests, were adopted to evaluate humidity sensing performances of the sensors. A precision impedance analyzer (6500, Wayne Kerr, UK), which was connected to PC through a LAN interface for data acquisition, was used to measure the electro-acoustic parameters of the sensor near its resonance at different RH levels. The static parameters, including resonance frequencies, Q-factor and the equivalent circuit elements
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
parameters, can be obtained by analyzing the electro-acoustic spectrum of the sensors. A home-made oscillating circuit was used to excite the QCM sensor, and the frequency output was monitored by a frequency counter (53131A, Agilent), which was
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communicated to PC via a GPIB-USB adapter interface. The dynamic humidity sensing response of the sensors was recorded in real time during the change of humidty. The
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surface morphologies of GO, DND and GO/DND nanocomposite were characterized by
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a field-emission scanning electron microscope (FE-SEM, S-4800, Hitachi). The BET analysises of the materials were carried out by Nova2000e specific area and void ratio
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tester. All the experiments were carried out at room temperature (25±1°C) without special representation.
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3. Results and discussion
Fig. 2(a-c) shows the FE-SEM images of DND, GO and DND/GO nanocomposite
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(R=1), respectively. These images revealed that DND exhibited a nanoparticles
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structure with a diameter of 5-10 nm; GO displayed a remarkable layered structure and
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many individual GO sheets were stacked together to form a compact film; DND/GO nanocomposite film showed a microporous-layered nanostructure. Table 1 listed the BET analysis results of GO and DND/GO nanocomposite (R=1). It can be found that DND/GO nanocomposite (R=1) has much larger surface areas and pore volumes than GO. As shown in Table 1, the specific surface area and pore volume of DND/GO nanocomposite (R=1) are 49.573 m2/g and 0.109 cm3/g, which are nearly 5 times and 9 times than that of GO, respectively. The BET analysis results indicated that the introduction of DND nanoparticles in GO sheets dramaticlly increased the specific surface area of GO films.
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
The static humidity sensing response was measured by exposing these sensors to different humidity sources. When the resonance reached steady state at a given humidity, the electro-acoustic spectrum of the sensor was recorded. For a sensing film coated
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QCM, the electro-acoustic spectrum is usually described as impedance spectrum and
analyzed by a modified Butterworth-van-Dyke (mBVD) equivalent circuit model as
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shown in Fig. 3(a). In this circuit, R, L, C and C0 describes the initial quality,
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mechanical flexibility, energy dissipation of the blank QCM and additional capacitor between two electrodes, respectively; R1 and L1 describe extra energy dissipation and
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mass due to the adsorption of sensing films. Therefore, the total admittance (reciprocal
1
1 ( R R1 ) j ( L L1 ) jC
d
Y ( ) G ( ) jB ( )
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of impedance) spectrum of the sensing film coated QCM, Y (ω), is expressed as [19]:
L* L L1
(2)
te
R* R R1
jC0
Where G and B are conductance and susceptance, respectively. In equation (2), R* and
Ac ce p
L* describe the total energy dissipation and mass increasement of sensing films coated QCM sensor. Fig. 3(b) shows the typical conductance spectrum and susceptance spectrum curves of films coated QCM sensor. By fitting the conductance spectrum and susceptance spectrum with the mBVD equivalent circuit, a series of resonance parameters of the sensors, including resonant frequency, Q-factor and equivalent circuit elements values, can be obtained. The frequency at the conductance peak is the resonant frequency (f) of the sensor. The Q-factor of QCM can be defined as the ratio of resonant frequency to half-band width of conductance peak (HBW) as shown in equation (3). Fig. 4 gives the conductance spectrum and susceptance spectrum curves of the GO and
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
DND/GO nanocomposite based QCM humidity sensors at various RH levels. It can be found that the conductance peak of each sensor move from a higher frequency to a lower frequency with increasing humidity, and the HBW also becomes broad with
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increasing humidity. Fig. 5 shows the frequency response and Q-factor of the GO and
DND/GO nanocomposite based QCM humidity sensors as a function of humidity. It can
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be seen that both resonant frequency and Q-factor decreased with increasing humidity
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level for all the sensors. The frequency shifts (i.e. sensitivity) of DND/GO nanocomposite based QCM humidity sensors are larger than that of GO based sensor.
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Also, with the increase of DND content in the nanocomposite, DND/GO nanocomposite film based QCM sensor’s sensitivity increases and its Q-factor decreases. When
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humidity changed from 11.3% to 97.3%, the frequency shifts of GO and DND/GO nanocomposite based QCM humidity sensors (R=4, R=2 and R=1) were 1645, 2637,
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2864 and 5467 Hz, respectively. Meanwhile, we can find that the frequency responses
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to humidity of the sensors exhibits a logarithmic tendency. Fig. 6 shows the linear
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fitting curves of the Log (Δf) versus humidity for all the sensors. The regression coefficients, R2, are 0.98605, 0.99322, 0.97696 and 0.97019 for GO, DND/GO (R=4), DND/GO (R=2) and DND/GO (R=1), respectively. The frequency shifts of all the sensors exhibit an acceptable logarithmic linear relationship with relative humidity. The enhancement sensitivity may be attributed to the increase of porosity and adsorption sites of DND/GO composite film. The introduction of DND nanoparticles in GO sheets, on one hand, can increase the active surface areas due to the formation of microporous-layered nanostructure, which has been confirmed by SEM and BET analysis.
One the other hand, the intrinsic hydrophilicity of DND nanoparticles is able
to provide more water adsorption sites. As a result, DND/GO nanocomposite sensor
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
(R=1) that owns the most number of DND nanoparticles exhibits the highest humdity response sentivity.
f HBW
(3)
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Q
However, it should also be noted that DND/GO nanocomposite sensors (R=2 and
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R=1) suffer a sharp decrease in Q-factor during humidity detection. Especially at high
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humidity (97.3% RH), their Q-factors are only about 6,300 and 2,144. The possible reason for the sharp decrease in Q-factor can be attributed to the increase in viscosity of
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DND/GO nanocomposite film under a large number of water adsorption [20]. Table 2 gives the equivalent circuit elements values of DND/GO composite based QCM
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humidity sensors (R=1 and R=4) at several humidity points by fitting the impedance spectrum with BVD equivalent circuit model. It can be found that R* element of
d
DND/GO nanocomposite sensor (R=1) is far larger than that of DND/GO
te
nanocomposite sensor (R=4) during humidity detection. So, in the practical application, it is very necessary to select the oscillation circuit with strong excitation and good
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stability to ensure the normal operation of DND/GO nanocomposite sensor (R=1) [21]. The humidity hysteresis characteristic of DND/GO nanocomposite film based
QCM humidity sensors was also examined. The sensors firstly underwent humidity variation from low to high humidity for water adsorption, and then from high to low humidity for water desorption. The humidity hysteresis curves of the sensors are shown in Fig. 7. It can be seen that, for all the sensors, the humidity-decreasing sensing curve of the sensor is close to its humidity-increasing sensing curve. The introduction of DND nanoparticles in GO sheets does not acutely increase the sensor’s humidity hysteresis. The possible interpretation about this result is that the introduction of DND nanoparticles in GO sheets yields a microporous-layered nanostructure. This structure is
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
very conducive to desorb water molecules from sensing films. By comparing the four sensors, we can find that the DND/GO nanocomposite film (R=4) owns the smallest humidity hysteresis (~3% RH).
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As is known to all, dynamic response and recovery behavior is an important factor
for evaluating the performance of humidity sensor. To measure the dynamic response
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and recovery, the sensor were firstly exposed to low humidity environment (11.3% RH)
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provided by saturated LiCl solution and the sealing sleeve was released. The output response was record in real-time until the output reached a stable value. Then the
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sealing sleeve was pulled up for isolating the sensor with the surrounding atmosphere, and the isolated sensor was exposed to high humidity environment (84.3% RH)
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provided by saturated KCl solution, and the sealing sleeve was released again for water adsorption. Finally, we repeated step 1 to 3 for obtaining another two cycle’s transient
d
humidity response. Fig. 8 displays the dynamic response and recovery curves of the GO
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and DND/GO nanocomposite (R=2 and R=1) sensors which undergo the humidity
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change (low-high-low) for 3 cycles. The response and recovery times, in this work, are defined as the times required by a sensor to achieve 90% of the total frequency change. Compare the dynamic response and recovery behavior of the four sensors, it is clearly noted that both GO and DND/GO nanocomposite based QCM sensor possess a fast response and recovery. The response times of the sensors are within 25 s, and the recovery times of the sensors are within 5 s. Compared to the studies of QCM humidity sensors reported recently [22-24], the response and recovery times of DND/GO nanocomposite based QCM sensor are shorter. Meanwhile, it can be found that the sensing response and recovery of the sensors are entirely repeatable. For example, the frequency shift of DND/GO nanocomposite (R=1) sensor was less than 30 Hz at 11.3%
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
RH after the sensor underwent the humidity change from low to high RH for 3 cycles. The excellent dynamic response and recovery behavior of the DND/GO composite sensor is attributed to water adsorption mechanism and microstructure property of
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sensing material. The adsorption of water molecules on GO and DND nanocomposite is dominated by physisorption with a weak hydrogen bond, so the dynamic equilibrium
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between water adsorption and desorption can be quickly reached. In addition, the
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microporous-layered nanostructure characteristic of DND/GO films is beneficial to realize fast adsorption or desorption of water molecules.
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At last, these effects of environment temperature and interference gases on the sensitivity of DND/GO nanocomposite based QCM humidity sensor have also been
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examined. It should be noted that the environment temperature affects the relative humidity provided saturated salt solution according to the standard of saturated salt
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solution versus RH. Therefore, we used a temperature and humidity chamber, which can
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yield a series of specified humidity points at various temperatures, to measure the
Ac ce p
temperature effect of the sensor. Fig. 9(a) shows the humidity response of DND/GO nanocomposite (R=2) based sensor at three temperature points of 15°C, 25°C and 35°C. It can be found that environment temperature inevitably affects the frequency response of the sensor. On one hand, the QCM displays an inherent temperature-frequency effect [25]; on the other hand, the change of temperature makes DND/GO composite sensing films produce a slight deformation [26], which also causes QCM sensor yield a frequency output. Therefore, the compensation of temperature is necessary for the sensor. In addition, some gases, such as ethanol, acetone, benzene, and formaldehyde, have been used to examine the effect of interference gases on the sensor’s performance. In order to avoid the influence of water vapor, the gas sensing tests use N2 gas as carrier
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
gases since it can provide a very low RH level. Fig. 9(b) shows the frequency response of DND/GO nanocomposite (R=2) based sensor to various gases. It can be seen that DND/GO composite films based sensor was also sensitive to ethanol, acetone and
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formaldehyde vapor. Therefore, we should especially consider the influence of cross-sensitivity of the sensor at low RH since the humidity sensing response is relative
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low.
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4. Conclusion
In summary, we have examined the humidity sensing properties of DND/GO
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nanocomposite films by combining with QCM technique. A series of sensitive test results indicate that DND/GO nanocomposite films display excellent humidity sensing
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properties. The introduction of DND nanoparticles into GO sheets can significantly increase the humidity sensitivity of the sensor. The sensitivity enhancement of
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DND/GO nanocomposite films can be attributed to the microporous-layered
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nanostructure of DND/GO and added water adsorption sites provied by DND. However,
Ac ce p
the Q-factor of DND/GO nanocomposite films based QCM sensor sharply decreases with increasing the DND content of nanocomposite films especially during high humidity detection. So, it is very necessary to selectve a suitable DND content for balancing the sensitivity and Q-factor. Besides the sensitivity and Q-factor, the humidity hysteresis and dynamic response and recovery of DND/GO nanocomposite films based QCM sensor have also been studied. Thanks to the microporous-layered nanostructure, DND/GO nanocomposite film sensor displayed a very small difference between water adsorption and desorption process. In addtion, this structure is beneficial to realize fast water adsorption or desorption, resulting in a fast response and recovery. This study
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The QCM humidity sensor based on nanodiamond/graphene oxide composite films
demonstrates that DND/GO nanocomposite is promise candicate material for humidity sensing detection by combing with QCM technique. Acknowledgements
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This work was supported by the National Natural Science Foundation of China
(Nos. 61401047 and 41404102) and the Project of the Scientific Research Foundation
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d
M
an
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of CUIT (No. KYTZ201409).
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functionalized carbon nanomaterials measured by a quartz crystal microbalance, Sens. Actuators A: Phys. 205 (2014) 126-132. [7] F. Arregui, Y.J. Liu, I. Matias, R. Claus, Optical fiber humidity sensor using a nano Fabry–Perot cavity formed by the ionic self-assembly method, Sens. Actuators B: Chem. 59 (1999) 54-59.
[8] G. Gerlach, K. Sager, A piezoresistive humidity sensor, Sens. Actuators A: Phys. 43 (1994) 181-184. [9] W.H. King, Piezoelectric sorption detector, Anal. Chem. 36 (1964) 1735-1739.
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[10] Y. Yao, X.D. Chen, X.Y. Li, X.P. Chen, N. Li, Investigation of the stability of QCM humidity sensor using graphene oxide as sensing films, Sens. Actuators B: Chem. 191 (2014) 779-783.
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[11] Y. Dong, G. Feng, Effects of surface physical sorption on characteristic of coated quartz-crystal humidity sensor, Sens. Actuators B: Chem. 24 (1995) 62-64.
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[12] E. Radeva, V. Georgiev, L. Spassov, N. Koprinarov, S. Kanev, Humidity
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adsorptive properties of thin fullerene layers studied by means of quartz micro-balance, Sens. Actuators B: Chem. 42 (1997) 11-13.
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[14] Y. Yao, X. Chen, H. Guo, Z. Wu, Graphene oxide thin film coated quartz crystal microbalance for humidity detection, Appl. Surf. Sci. 257 (2011) 7778-7782.
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colloid crystals coated on quartz crystal microbalance by the self-assembly method, Ceramics International. 39 (2013) 3621-3625. [25] F.L. Walls, J.J. Gagnepain, Environmental sensitivities of quartz oscillators, IEEE Trans. Ultrason. Ferroelec. Freq. Contr., 39 (1992) 241-249. [26] A. Domack, O. Prucker, J. Rühe, D. Johannsmann, Swelling of a polymer brush probed with a quartz crystal resonator, Phys. Rev. E, 56 (1997) 680.
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Table 1 BET surface area analyses of GO and DND/GO nanocomposite (R=1). BET surface area (m2/g)
Pore volume (cm3/g)
Pore diameter (nm)
GO
10.333
0.011
3.713
DND/GO (R=1)
49.573
0.109
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3.939
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Table 2 The equivalent circuit elements parameters of DND/GO nanocomposite based QCM sensor at various humidity points Equivalent circuit elements parameters DND/GO nanocomposite sensor (R=4)
RH
DND/GO nanocomposite sensor (R=1)
L (mH)
C (fF)
C0 (pF)
Q
R* (Ω)
L* (mH)
C (fF)
C0 (pF)
Q
11.3%
7.72
26.27
9.66
7.38
78243
100.56
25.39
10.00
7.60
6348
32.8%
7.86
26.26
9.66
7.35
76938
100.35
25.47
9.97
7.36
6170
54.3%
8.25
26.22
9.68
7.39
73649
135.13
25.50
9.96
7.16
4465
75.3%
8.99
26.21
9.68
7.52
67645
186.35
25.17
10.09
7.45
3235
84.3%
10.21
26.29
9.63
7.69
61213
238.15
25.32
10.02
7.65
2555
97.3%
12.76
26.55
9.56
8.32
45951
287.03
25.51
9.96
8.00
2144
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R* (Ω)
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Figure Captions Fig. 1. Schematic diagram of humidity sensing experimental setup.
nanodiamond/graphene oxide nanocomposite.
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Fig. 2. SEM images of (a) nanodiamond; (b) graphene oxide and (c)
Fig. 3. (a) The modified Butterworth-van-Dyke equivalent circuit; (b) The typical
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conductance and susceptance spectrum of films coated QCM sensor.
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Fig. 4. The conductance spectrum of (a) GO, (b) DND/GO (R=4), (c) DND/GO (R=2), (d) DND/GO (R=1) and the susceptance spectrum of (e) GO, (f) DND/GO (R=4), (g)
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DND/GO (R=2), (h) DND/GO (R=1) at various RH points.
Fig. 5. (a) The frequency response and (b) Q-factor of the GO and DND/GO
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nanocomposite based QCM humidity sensors as a function of humidity. Fig. 6. The linear fitting curves of the Log (Δf) versus humidity for all the sensors.
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humidity sensors.
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Fig. 7. Humidity hysteresis curves of GO and DND/GO nanocomposite based QCM
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Fig. 8. The dynamic response and recovery of (a) GO, (b) DND/GO (R=2) and (c) DND/GO (R=1) based sensors between the changes in humidity from 11.3% to 84.3%. Fig. 9. The effect of (a) temperature and (b) interference gases on the performance of DND/GO nanocomposite (R=2) based QCM humidity sensor.
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Biographies Yao Yao was born in Sichuan, China. He received his BS degree from the school of Information Science and Technology, Southwest Jiaotong University, Sichuan, China in
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2006. He received his PhD degree at the Southwest Jiaotong University, Sichuan, China in 2013. He is currently a Lecturer in the College of Communication Engineering,
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interests include carbon based electronics and acoustic sensors.
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Chengdu University of Information Technology, Sichuan, China. His current research
Yajuan Xue was born in Inner Mongolia, China, in 1980. She received the PhD degree
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from Chengdu University of Technology, Sichuan, China in 2014. She is currently an Associate Professor in the College of Communication Engineering, Chengdu University Her current research interests include
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of Information Technology, Sichuan, China.
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signal processing and acquisition of intelligent information.
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