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(a) Optical micrograph of a bare micro-hotplate; (b) a typical device after deposition of the WO3 paste; (c) a gold wire-bonded microhotplate on a TO46 package and (d) SEM (250× magnification) of the surface of the deposited WO3 material.
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Semiconductor gas sensors based upon n-type WO3 nanoparticle powder were fabricated and their response from 100 ppb to ppm levels of H2S in air has been investigated. In this study, a low power MEMS based micro-hotplate was employed as the substrate and operated at a constant temperature of 350̊C. Experimental data demonstrate repeatable results ac...
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... this study, a low power MEMS based micro-hotplate gas sensor was used, and the operating temperature was controlled by an adjustable constant current circuit. The micro-hotplate is shown in Fig. 1a (CCS09C, Cambridge CMOS Sensors Ltd). The MEMS structure was fabricated in a commercial foundry and is based upon silicon-on- insulator (SOI) technology. In the membrane structure, a tungsten resistive micro-heater is embedded within a 5 m thick metal/oxide stack ensuring a low DC power consumption (e.g. 65 mW at 600C). The membrane is ...
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... solution (Figs. 1a and 1b). After deposition of the WO3 paste the substrate was left to dry in air at room temperature for ~12 h followed by annealing at 450C for 1 h, and then at 350C for about 23 h under ambient air to obtain the sensor element consisting of n-type WO3. Finally, the silicon die was wire-bonded onto a standard TO-46 header (Fig. 1c). Fig. 1d presents a scanning electron microscopy (SEM) image of the annealed paste with a porous microstructure showing a widespread grain size distribution with average particle size in hundreds of nm. The gas sensing measurements were performed at the Microsensors & Bioelectronics Laboratory at the University of Warwick using ...
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... (Figs. 1a and 1b). After deposition of the WO3 paste the substrate was left to dry in air at room temperature for ~12 h followed by annealing at 450C for 1 h, and then at 350C for about 23 h under ambient air to obtain the sensor element consisting of n-type WO3. Finally, the silicon die was wire-bonded onto a standard TO-46 header (Fig. 1c). Fig. 1d presents a scanning electron microscopy (SEM) image of the annealed paste with a porous microstructure showing a widespread grain size distribution with average particle size in hundreds of nm. The gas sensing measurements were performed at the Microsensors & Bioelectronics Laboratory at the University of Warwick using fully-automated ...
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Low cost air pollution sensors have substantial potential for atmospheric research and for the applied control of pollution in the urban environment, including more localized warnings to the public. The current generation of single-chemical gas sensors experience degrees of interference from other co-pollutants and have sensitivity to environmental...
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... The results of the interference between gas and TiO2 nanotubes showed that when the H2S gas was introduced, the resistance of the TiO2 nanotube sensor decreased. Figures 6-9 shows a typical response of the n-type gas sensor (TiO2 nanotubes) to the reducing gas (H2S), which was confirmed by the resistance in the air being greater than the resistance in the presence of the gas [38]. Response and recovery times are the primary concerns for gas sensing properties, particularly at low operating temperatures. ...
Serious gases have been highly related to being prejudiced against human life within the environment. The evolution of a trustworthy gas sensor with an elevated response is of major importance for detecting various hazardous gases. Titanium dioxide (TiO2) nanotubes (TNTs) are favorable candidates with considerable potential and stellar performance in gas sensor applications. In this work, we have studied the effect of voltage on preparing TiO2 nanotubular arrays via the anodization technique for gas sensor applications. A simple electrochemical anodization approach was used to synthesize titanium dioxide nanotubes. Diverse techniques of characterization were used to evaluate TNTs. The results gained from field emission scanning electron microscopy (FESEM), energy dispersion spectroscopy (EDS), and X-ray diffraction (XRD) indicate that TiO2 was formed. Gas sensors were created, and the gas detection characteristics were directed towards hydrogen sulfide (H2S), which is not a healthy gas. The sensor made from these nanotubes responds well to this gas at different temperatures and has high sensitivity. The H2S-detecting characteristics were evaluated at values ranging from room temperature up to 300 oC. Results show that the gas sensor TNTs that was prepared at 30 volt for H2S gas sensing has the highest sensitivity and shortest response time at room temperature.
... Rapid developments in industry and the community, including chemicals in industrial productions, have led to concern of air and water pollution that directly affects the health of human (Dhall et al., 2021). An example of this is hydrogen sulfide (H 2 S), which is flammable, toxic, corrosive, and hazardous to humans (Urasinska-Wojcik et al., 2016;Qu et al., 2016). Hence, gas sensing techniques in different configurations are highly essential. ...
In recent years, significant progress regarding energy harvesting has been made, owing to the need to replace conventional energy sources with alternative, green, and sustainable ones. Among them, mechanical energy harvesting is a promising strategy with outstanding characteristics of high conversion efficiency, facile fabrication process, simple structure, flexible selection of materials, and the ability to capture energy independent of season. Nowadays, the piezoelectric mechanism has gained attention from the research community as a prominent mechanical energy harvesting method. Diverse technologies in harvesting and sensing schemes have been innovatively developed alongside explorations of novel piezoelectric materials and the establishment of theoretical foundations. This article comprehensively reviews piezoelectric energy harvesting from the research background to its significance. The operation mechanisms of a piezoelectric nanogenerator (PENG) in various modes, including the theoretical principle of piezoelectricity, are discussed. Three generations of piezoelectric material development are explained, including structural designs of PENG for specific applications. Finally, highlighted applications of PENG in diverse fields such as energy harvesting and sensing, biomedical electronics, and novel intelligent sensing technologies, have been reviewed.
... Adsorbed H 2 S gases-WO 3 surface chemical reactions were explained by Urasinska-Wojcik et al. with the equation shown below [37]: ...
In this work, pure and nickel-doped WO3 films were produced by chemical bath deposition on In-doped SnO2 (ITO) substrates without annealing process. To synthesize the Ni:WO3 films, two different types of nickel precursors were used as NiSO4 and NiCl2. The influence of Ni doping using different Ni precursors on the structural, morphological, optical, and gas sensing properties of WO3 films toward H2S gas was investigated in detail. All samples have monoclinic WO3 polycrystallization where a substitution of Ni²⁺ ions with W⁶⁺ mı olmalı ions is detected from the slight shift in x-ray diffraction patterns with the Ni doping process. With nickel chloride source, the synthesized Ni:WO3 samples exhibit nano-ball shapes with different dimensions on the film surfaces. Optical band gap energy severely decreases with nickel doping due to increasing oxygen vacancies, especially when nickel chloride is used as a precursor source in Ni:WO3 samples. Ni²⁺ ions introduction in WO3 host lattice has improved H2S gas detection capability; however, the biggest positive effect came from the NiSO4 precursor with increasing solubility and improved growth process. The response to 50 ppb H2S gas at room temperature was calculated as 7%, 11%, and 23% for pure WO3, NiCl2-based Ni:WO3, and NiSO4-based Ni:WO3 sensors, respectively. When the gas selectivity property was studied for NiSO4-based Ni:WO3 sensors, they showed more selectivity against H2S gas compared to H2, benzene, methanol, etc. It is found that precursor type has an incredible impact on the H2S, reducing gas sensing properties in doped metal oxide gas sensor applications.
... Sensors based on metal oxide semiconductors have been extremely studied because of their high stability, low cost, and compatibility with microelectronic technology. Metal oxide semiconductors based on WO 3 are of special interest due to their structural simplicity, high sensitivity, low cost, and potential durability [1][2][3]. As a typical n-type semi-conductor material, WO 3 owns unique chemical and physical properties and excellent gas sensing characteristic for a series of target gases, including NO 2 , Cl 2 , CO 2 , H 2 S, and NH 3 [4]. ...
In this paper, the annealing effect of tungsten oxide (WO3) nanoparticles has been studied on different Si and PS substrates by spin coating technology to develop the gas sensor. WO3 thin film was prepared at RT, and 400∘C. XRD pattern shows all films are polycrystalline in nature, and have hexagonal structure. The annealed of WO3 thin film at 400∘C showed high intensity crystalline peaks with decreased in crystal size. The fine nanoparticles are fully agglomerate and their spherical shape increases upon annealing of the film. The energy gap of WO3 was 2.8 eV at RT, and it increased with increasing annealing temperature. The annealing temperature of 400 °C was selected and employed in gas sensors prepared on different substrates of Si and PS at RT, 100 °C, and 200 °C. The sensor was further fabricated to detect of nitrogen dioxide (NO2) and ammonia (NH3) gas at low concentration (8 ppm). The sensing effects toward NO2 and NH3 gases were compared between low- and high-temperature gases. The WO3/PS sample exhibited the highest sensitivity (144.1%) for NO2 gas at 200 °C. The sensitivity of both gases showed different results with regard to the response. However, the response and recovery time of both gases were moderate and decreased with increasing operating temperature.
... The challenges are related to the presence of relative humidity (RH), specific for in-field atmosphere and lack of reversibility upon H 2 S exposure at a low operating temperature, opposite to the higher effects recorded in sensitivity [5]. Several papers have reported hydrogen sulfide formation on the surface of the MOX layer [6][7][8][9][10]. However, there are few factors which downgrades the overall H 2 S sensing performance: Structure crystallinity reflected through the long term stability, low selectivity, and humidity interference [11]. ...
The paper presents the possibility of detecting low H2S concentrations using CuWO4. The applicative challenge was to obtain sensitivity, selectivity, short response time, and full recovery at a low operating temperature under in-field atmosphere, which means variable relative humidity (%RH). Three different chemical synthesis routes were used for obtaining the samples labeled as: CuW1, CuW2, and CuW3. The materials have been fully characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). While CuWO4 is the common main phase with triclinic symmetry, different native layers of CuO and Cu(OH)2 have been identified on top of the surfaces. The differences induced into their structural, morphological, and surface chemistry revealed different degrees of surface hydroxylation. Knowing the poisonous effect of H2S, the sensing properties evaluation allowed the CuW2 selection based on its specific surface recovery upon gas exposure. Simultaneous electrical resistance and work function measurements confirmed the weak influence of moisture over the sensing properties of CuW2, due to the pronounced Cu(OH)2 native surface layer, as shown by XPS investigations. Moreover, the experimental results obtained at 150 °C highlight the linear sensor signal for CuW2 in the range of 1 to 10 ppm H2S concentrations and a pronounced selectivity towards CO, CH4, NH3, SO2, and NO2. Therefore, the applicative potential deserves to be noted. The study has been completed by a theoretical approach aiming to link the experimental findings with the CuW2 intrinsic properties.
... The sensor device was found to be selective and sensitive towards NH 3 down to 25 ppm at 200°C. These, initial results suggest that with right choice of hybrid material and synthesis procedure, both selectivity as well as sensitivity of sensor can be tuned [12,13]. The sensor does not display a signal below 200°C. ...
Present work demonstrates the synthesis of MoS2/WO3 composite using a facile single step probe-sonication method. After probe sonication, obtained black powder was used for evaluating structural and gas sensing characteristics. Raman spectra not only revealed the presence of various first-order Raman active modes belonging to MoS2 but also the modes governed by the presence of defects. These defects may play a vital role in determining the interaction between adsorbed gas molecules and underlying semiconducting channel and may enhance the sensitivity of the obtained sensor device. The Raman spectra also revealed various Raman active modes corresponding to bending and stretching of O-W-O bonds, thus implying successful formation of the MoS2/WO3 composite. A relative response of nearly 70% was obtained at 200 °C for 200 ppm of NH3 and device was found to be more selective towards NH3 than ethanol and acetone and showed p-type semiconducting properties.
... WO 3 could be elaborated by different techniques such as: chemical vapor deposition [10,13], spray pyrolysis [14], sol gel [15], electrodeposition [16], and atomic layer deposition (ALD) [17]. In the literature, WO 3 used in gas sensors has been reported in different forms as nanowires [18,19], nanoparticles [20], thin films [21] permitting the detection of different gases: nitrogen dioxide (NO 2 ) [20,21], hydrogen sulfide (H 2 S) [22], ozone (O 3 ) [23], hydrogen [24], ethanol [24]. The WO 3 -based sensor response at an operating temperature is depending strongly on the substrate [21] and the microstructure features [25]. ...
In this work, we report on the gas-sensing properties of n-WO3/p-porous silicon (PS) structures. Nanostructured WO3 films are deposited by simple chemical method via dip-coating of PS in tungsten hexachloride solution. The morphological and structural properties of the elaborated structures were investigated using atomic force microscope (AFM), Raman and Fourier transform infrared (FTIR) spectrometers. The NO2-sensing performances of the sensor were measured at different operating temperatures ranging from room temperature to 250 °C, different NO2 concentrations, and different time exposure. The sensor showed a p-type semiconducting behavior which probably owning to the strong effect of the hetero-junction between the n-WO3 nanoparticles and p-porous silicon substrate. The obtained results confirm the suitability of these structures to detect low NO2 concentrations up to 1 ppm at moderate temperatures. These sensors exhibit fast response and recovery times.
... Herein, H 2 S sensing performance of the 30 h V 2 O 5 -W-C −650°C based sensor in this work is compared with those reported gas sensors in refs. [48][49][50][51][52][53][54][55], as shown in Table 3. Apparently, while the CuOfunctionalized WO 3 nanowires [48] were tested towards 100 ppm at same temperature used in this work, however, its response was roughly three times smaller. However, through careful comparison with WO 3 in Ref. [50], our 30 h V 2 O 5 -W-C −650°C based sensor actually showed even higher response at 5 ppm even though their working temperature was 350°C. ...
... [48][49][50][51][52][53][54][55], as shown in Table 3. Apparently, while the CuOfunctionalized WO 3 nanowires [48] were tested towards 100 ppm at same temperature used in this work, however, its response was roughly three times smaller. However, through careful comparison with WO 3 in Ref. [50], our 30 h V 2 O 5 -W-C −650°C based sensor actually showed even higher response at 5 ppm even though their working temperature was 350°C. In summary, the H 2 S sensing properties of the 30 h V 2 O 5 -W-C −650°C-based sensor is comparable or even much better than most of the previously reported H 2 S sensors. ...
... Index Terms-gas sensor, hydrogen environment, hydrogen sulfide 10 58, 75, 73, 54,24, 91 STD 4,19, ...
... The gas sensing measurements were performed at the Microsensors and Bioelectronics Laboratory at the University of Warwick using a fully-automated custom rig as illustrated earlier in [11,24]. The CMOS microhotplate substrates were connected to a custom made printed circuit board. ...
In this study we report for the first time detailed analysis of a p-type copper oxide based MEMS gas sensor to low ppm levels of hydrogen sulfide in a pure hydrogen environment and under various operating temperatures and humidity conditions. The p-type metal oxide sensing response to hydrogen sulfide seems to be reasonably stable and reversible under both dry and humid hydrogen ambiences. The response was sensitive to significant changes in ambient humidity, but was found to have no cross-sensitivity to carbon monoxide in dry and humid hydrogen. We believe that these copper oxide gas sensors could be exploited in harsh applications, i.e. in a gas contamination detector for testing the quality of hydrogen fuel.
... As we all know, environmentally hazardous gases can be classified into oxidizing gases (such as CO2 and Cl2) and reducing gases (such as H2S, CO, and C2H5OH) [1]. Among these gases, nitrogen oxide (NOx), which is a mixture of nitric oxide (NO) and nitrogen dioxide(NO2), is well known to be one of the major air pollutants containing oxidizing gas (NO2) and reducing gas (NO) [2][3][4]. ...
Reactive NOx is one of the major air pollutants, which also plays a key role as greenhouse gas. Many research efforts have been devoted to not only detection of NOx in air but also abatement of NOx emission. The aim of this mini review is to provide a panoramic snapshot of the electrochemical analysis methods for the emission and detection of NOx in atmosphere, with special emphasis on NOx sensor. The electrochemical detecting mechanism and materials for fabricating electrochemical gas sensors are discussed and the prospects and challenges in this area are also evaluated. This work will serve as a useful source to inform the interested audience of the latest developments and applications in the field of NOx emission and electrochemical detection.
