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Development of High Sensitivity Ethanol Gas Sensors Based on Pt-Doped SnO2 Surfaces
Abstract
This paper describes how thick-film technology was used to fabricate small, robust, sensitive, and selective semiconductor metal oxide (SMO) sensors to detect traces of ethanol vapours in air. The sensing parameters of several active layers were studied including: sensitivity, response repeatability, stability and selectivity. The response to different species of five differently doped SnO2 sensors and a commercially available one were measured at concentrations between 1 ppb and 1000 ppm. Interaction was extremely high when ethanol came into contact with the Pt-doped SnO2 surface. The change in resistance of the Pt-doped sensors was between 2 and 55 times higher than the change in the commercial one. The Pt-doped SnO2 material is less resistant, more sensitive and shows faster response to ethanol than pure SnO2. Since the detection limit for ethanol is at sub-ppb level, the fabricated sensors could be used for alcoholmeters or for on-line monitoring and controlling the concentration of ethanol in fruit ripening storage chambers.
... To further improve the response of gas sensing devices and improve the sensitivity and selectivity, it is common to add porous materials and catalytically active agents 15,16 . Doping the metal oxide -such as SnO 2 -based sensor promotes the physicochemical reactions between the surface and the gas 17 www.nature.com/scientificreports/ ...
The increasing demand of efficient optoelectronic devices such as photovoltaics has created a great research interest in methods to manipulate the electronic and optical properties of all the layers of the device. Tin dioxide (SnO2), due to his charge transport capability, high stability and easy fabrication is the main electron transport layer in modern photovoltaics which have achieved a record efficiency. While the wide band gap of SnO2 makes it an effective electron transport layer, its potential for other energy applications such as photocatalysis is limited. To further improve is conductivity and reduce its bandgap, doping or co-doping with various elements has been proposed. In the present density functional theory (DFT) study, we focus on the investigation of vanadium (V) and tantalum (Ta) doped SnO2 both in the bulk and the surface. Here we focus on interstitial and substitutional doping aiming to leverage these modifications to enhance the density of states for energy application. These changes also have the potential to influence the optical properties of the material, such as absorption, and make SnO2 more versatile for photovoltaic and photocatalytic applications. The calculations show the formation of gap states near the band edges which are beneficial for the electron transition and in the case of Ta doping the lowest bandgap value is achieved. Interestingly, in the case of Ta interstitial, deep trap states are formed which depending of the application could be advantageous. Regarding the optical properties, we found that V doping significantly increases the refractive index of SnO2 while the absorption is generally improved in all the cases. Lastly, we investigate the electronic properties of the (110) surface of SnO2, and we discuss possible other applications due to surface doping. The present work highlights the importance of V and Ta doping for energy applications and sensor applications.
... The electrical sensitivity values under an atmosphere of CO/Air showed that the response of pure SnO2 films is lower than Pt-doped films; also, the response of the sol−gel films is lower than inverted opal films. P. Ivanov used a valuable, thick-film technique to manufacture robust, small, and sensitive semiconductor metal oxide sensors to reveal traces of ethanol vapors in the air [78]. The alteration in resistance of the Pt-doped sensors is from two to fifty-five times larger than the alteration in the mercantile sensor. ...
Metal oxide gas sensors have many advantages over other solid-state gas monitoring devices, including low cost, ease of manufacture, and small design. However, the shape and structure of sensing materials have a considerable impact on the performance of such sensors, posing a significant challenge for gas sensing properties on materials or dense films to attain high-sensitivity characteristics. Various tin dioxide (SnO2) nanostructures have been devised to increase gas sensing characteristics such as sensitivity, selectivity, and response time, among other characteristics. An overview of the most well-known techniques for synthesizing gas-sensing films, as well as the influence of doping with various metal oxides, nanoparticle size, and operating temperature on the gas-sensing properties of such films, is discussed in this work. The gas sensing mechanisms and the gas detection techniques are presented in detail. The metal oxide doped SnO2 showed a strong response for SO2 and NO2 gases, whereas nanoparticle doping plays a crucial effect in increasing SnO2 sensitivity towards H2, H2S, NO2, CO, Ethanol, etc. Furthermore, the effect of operating temperature on SnO2 response is discussed in this report. SnO2 has a high sensitivity over a wide temperature range (100-350 C).
... [163] The smaller the grain size, the higher the surface area, and the larger the change in electrical conductivity upon exposure to reducing gas species. For comparison, a porous film gas sensor consisting of large SnO 2 particles showed a sensitivity of 15 when exposed to 100 ppm ethanol at 300°C, [182] while our sensor with nanosize grains displayed a sensitivity of 280 under the same conditions. The relative conductance changes are also plotted on a logarithmic scale in Figure 5-6(b) as a function of ethanol concentration. ...
... The electrical sensitivity values under an atmosphere of CO/Air showed that the response of pure SnO2 films is lower than Pt-doped films; also, the response of the sol−gel films is lower than inverted opal films. P. Ivanov used a valuable, thick-film technique to manufacture robust, small, and sensitive semiconductor metal oxide sensors to reveal traces of ethanol vapors in the air [78]. The alteration in resistance of the Pt-doped sensors is from two to fifty-five times larger than the alteration in the mercantile sensor. ...
Metal oxide gas sensors have many advantages over other solid-state gas monitoring devices, including low cost, ease of manufacture, and small design. However, the shape and structure of sensing materials have a considerable impact on the performance of such sensors, posing a significant challenge for gas sensing properties on materials or dense films to attain high-sensitivity characteristics. Various tin dioxide (SnO2) nanostructures have been devised to increase gas sensing characteristics such as sensitivity, selectivity, and response time, among other characteristics. An overview of the most well-known techniques for synthesizing gas-sensing films, as well as the influence of doping with various metal oxides, nanoparticle size, and operating temperature on the gas-sensing properties of such films, is discussed in this work. The gas sensing mechanisms and the gas detection techniques are presented in detail. The metal oxide doped SnO2 showed a strong response for SO2 and NO2 gases, whereas nanoparticle doping plays a crucial effect in increasing SnO2 sensitivity towards H2, H2S, NO2, CO, Ethanol, etc. Furthermore, the effect of operating temperature on SnO2 response is discussed in this report. SnO2 has a high sensitivity over a wide temperature range (100-350 C).
... Another study on detection of volatile organic compounds (VOCs) demonstrates that Ti 3 C 2 T x MXene gas sensors performs quite effectiveness sensing 50-100 ppb for VOC gases at room temperature surpassing the best sensors known [4]. More related topics including detection of hazardous gases, physical measures and precautions taken against environmental and health issues can be found elsewhere [5][6][7][8][9][10]. Among these, metal oxide semiconductor sensors are renowned for their high precision in gas detection under high temperature conditions [11][12][13][14]. ...
An alternative oxygen sensor to conventional ZrO2 based automotive oxygen sensors (COS) was successfully manufactured. ZrO2 nanoparticles were used as base material and nanofibers were fabricated via electrospinning using polyvinyl alcohol and ZrO2 solution (ZrO2+PVOH) to obtain active surface of the sensor where the engine exhaust gas interacts and chemisorption reactions take place prior to calcination process of nanofibers at 700 oC. Thanks to operating temperature control and high surface/volume ratio of nanofibrous structure, the ZrO2+PVOH nanofibrous sensor demonstrated similar performance with COS under increasing exhaust gas percentage (until 50-60%) along with increasing operating temperature conditions. For ZrO2+PVOH nanofibrous sensor, maximum sensing performance (Ra/Re) of 7.24 was achieved at sensor operating temperature of 700 oC and exhaust gas concentration of 50% whereas it was 8.11 for EOS under same conditions. The ZrO2+PVOH nanofibrous sensor performed acceptable performance throughout wider operating temperature range (270-900 oC) compared to conventional COS. Though an average of 15% reduction in sensing performance was observed for ZrO2+PVOH nanofibrous sensor, the promising results of this alternative oxygen sensor will be a good guide for more comprehensive future works focusing on oxygen sensors with very rapid response-recovery time and light-off capability.
... SnO 2 nanoparticles and nanocomposites are utilized in environmental remediation, public safety, and health by several researchers. 233,234 Gas, electric, and chemical sensing Q31 ...
In view of their inimitable characteristics and properties, SnO2 nanomaterials and nanocomposites have been used not only in the field of diverse advanced catalytic technologies and sensors but also in the field of energy storage such as lithium-ion batteries and supercapacitors, and in the field of energy production such as solar cells and water splitting. This review discusses the various synthesis techniques such as traditional methods, including processes like thermal decomposition, chemical vapor deposition, electrospinning, sol-gel, hydrothermal, solvothermal, and template-mediated methods and green methods, which include synthesis through plant-mediated, microbe-mediated, and biomolecule-mediated processes. Moreover, the advantages and limitations of these synthesis procedures and how to overcome them that would lead to future research are also discussed. This literature also focuses on various applications such as environmental remediation, energy production, energy storage, and removal of biological contaminants. Therefore, the rise and journey of SnO2-based nanocomposites will motivate the modern generation of chemists to modify and design robust nanoparticles and nanocomposites that can effectively tackle significant environmental challenges. This overview concludes by providing future perspectives on research into tin oxide in synthesis and its various applications.
... 2 thermally activated gas sensors commonly are employed at temperatures more than 150 • C [16][17][18][19][20][21][22][23]. Although, usage of high temperature influences excess power consumption, economic facets, and long-term stability of the sensing device [24]. ...
Here, the photo-enhanced behavior in LPG sensing of hydrothermally synthesized BaFe12O19 nanorods at room temperature under visible light radiation has been thoroughly inspected and reported. The sensing element is observed to be poorly responsive towards LPG in dark conditions at room temperature, while it reveals a good photo response in presence of visible light of 30 mW/cm², and the visible light aids in improving the LPG sensing response up to a great extent at room temperature. Under the irradiation, the nanorods are found to detect the presence of LPG molecules of concentration as small as 0.5 vol.% at the response and recovery times ~5.02 sec and ~10.10 sec respectively. The sensitivity of the visible-light induced material was evaluated ~ 41.27 sensor response/vol.% with the maximum sensor response as high as 108, whereas, in dark, the same material showed a maximum response of ~6.64 with a sensitivity of merely 1.94 sensor response/vol.%. The photo-generated carriers are suggested to be responsible for achieving a significant, stable, fast response in presence of LPG. This is the first ferrite based visible light-induced LPG sensor.
... This in turn results in a change in its stoichiometry, and thereby carrier concentration and the electrical resistance of the material at the end [27,28]. Therefore, the key performance parameters, such as the response, the response time, selectivity, and stability would largely depend on the structure, morphology, composition, crystallite size, surface-to-volume ratio of the sensing/active material [29][30][31][32]. For example, the sensitivity of a gas sensor may maximize when the crystallite/particle diameter of the sensing material would approximately be equal to the length of the carrier depletion/accumulation depth, resulting from the adsorption of the target gas species [33]. ...
Printed vapor and moisture sensors are essential components of the multi-sensor platforms that the pharmaceutical and food safety industries require in large quantities; however, fully-printed gas or volatile organic compounds (VOCs) sensors have rarely been reported in the literature. In this regard, we demonstrate the fabrication of high surface-to-volume ratio co-continuous mesoporous tin oxide based fully-printed chemiresistive-type ethanol gas sensors. Herein, a soft templating method that mimic evaporation induced self-assembly (EISA) process has been utilized with amphiphilic triblock co-polymer pluronic F127 (PEO106-PPO70-PEO106) as the templating agent and a low-cost swelling agent ´xylene´ as the micelle expander to obtain pore diameter in the range of 10-25 nm. The tuned pore size at this range is found optimal for high surface area and high pore volumes, at the same time. The fully-printed ethanol sensors fabricated with such mesoporous SnO2 active elements show highly selective sensitivity towards ethanol with an average response of 1050 for 100 ppm and a very short response and recovery time of 9 and 129 s, respectively. The observed high response can be attributed to the high density and easily accessible active sites and simultaneous high mobility electron transport through the well-crystalline and co-connected tin oxide ligaments.
... This 1-D morphology also provides a unidirectional flow of charge carriers which again enhance the gas sensing properties [11][12][13][14][15]. Different strategies have been followed for the improvement of gas sensing properties such as sensing response, selective detection of specific analyte gas etc. Among them, functionalization with the noble metal nanoparticles like silver, palladium, gold, and platinum is a promising method to modulate the sensing properties of the sensor [16][17][18]. The enhanced gas sensing properties of noble metal doped MOS gas sensor is mainly due to the catalytic activity of noble metal nanoparticles and the work function difference between the MOS and noble metal nanoparticles which results in the formation of Schottky junction. ...
One dimensional pristine and Au doped tin oxide (SnO2) nanofibers were successfully synthesised by versatile electrospinning technique followed by calcination at 600°C for 2h. As-synthesized nanofibers were characterized by X-ray diffraction (XRD), scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray spectroscopy (EDAX), transmission electron microscopy (TEM), and UV visible spectrophotometer. The response of the sensors strongly depends on the operating temperature and the amount of additives. The optimum performance was obtained at 370°C for 3 wt% Au doped SnO2 sample. The fabricated devices show response to reducing gases like hydrogen sulphide (H2S), acetone, ammonia, ethanol, propanol etc. and the lowest detectable concentration was 1 ppm for H2S and 10 ppm for all other gases. Thus, the device can be used for the selective detection of H2S avoiding the problem of cross linking response of other reducing gases with concentration below 10 ppm. The theoretically calculated detection limit for H2S is 550 ppb. Hence, the device can be used for the diagnosis of halitosis since the concentration level of H2S in the exhaled breath of halitosis patient is found to be in the range of 80 ppb-2 ppm.
... Introduction of dopants, such as Pt and Pd, evenly dispersed on SnO 2 grain surfaces, has led to improved gas sensing performance of SnO 2 to gases such as CO, CH 4 , and NO 2 [70]. Pt doping of SnO 2 has resulted in lower overall resistance, increased sensitivity, and faster response to ethanol [71]. Pt doping of SnO 2 nanofibers obtained by electrospinning improved significantly the response to H 2 S [72]. ...
This paper presents an overview of semiconductor materials used in gas sensors, their technology, design, and application. Semiconductor materials include metal oxides, conducting polymers, carbon nanotubes, and 2D materials. Metal oxides are most often the first choice due to their ease of fabrication, low cost, high sensitivity, and stability. Some of their disadvantages are low selectivity and high operating temperature. Conducting polymers have the advantage of a low operating temperature and can detect many organic vapors. They are flexible but affected by humidity. Carbon nanotubes are chemically and mechanically stable and are sensitive towards NO and NH3, but need dopants or modifications to sense other gases. Graphene, transition metal chalcogenides, boron nitride, transition metal carbides/nitrides, metal organic frameworks, and metal oxide nanosheets as 2D materials represent gas-sensing materials of the future, especially in medical devices, such as breath sensing. This overview covers the most used semiconducting materials in gas sensing, their synthesis methods and morphology, especially oxide nanostructures, heterostructures, and 2D materials, as well as sensor technology and design, application in advance electronic circuits and systems, and research challenges from the perspective of emerging technologies.
... These processes allow designers to accumulate different sensor arrays on a single sensor platform that can be utilized for mass-production at a low cost [113]. Nanoscale MOS materials integrated with MEMS technology are widely employed in gas sensing applications due to the drastically reduced size, low cost and significantly lower power consumption of such devices [114][115][116]. In comparison with traditional MOS-based gas sensors ( Fig. 12(a)), MEMS-based gas sensors that use MOS materials typically consist of three basic components: (i) a micro-heater, (ii) a sensing material in the form of a thin film (receptor layer), and (iii) interdigited electrodes ( Fig. 12(b)). ...
With the tremendous advances in technology, gas-sensing devices are being popularly used in many distinct areas, including indoor environments, industries, aviation, and detectors for various toxic domestic gases and vapors. Even though the most popular type of gas sensor, namely, resistive-based gas sensors, have many advantages over other types of gas sensors, their high working temperatures lead to high energy consumption, thereby limiting their practical applications, especially in mobile and portable devices. As possible ways to deal with the high-power consumption of resistance-based sensors, different strategies such as self-heating, MEMS technology, and room-temperature operation using especial morphologies, have been introduced in recent years. In this review, we discuss different types of energy-saving chemisresitive gas sensors and their application in the fields of environmental monitoring. At the end, the review will be concluded by providing a summary, challenges and future perspectives.
... The incorporation of Cr metal into the structure increases the interaction between the gas molecules and surface area. The response value of the gas sensor can be calculated as [44]: ...
The goal of in this paper has to design, fabricate and test gas sensors based on chromium (Cr) doped titanium dioxide (TiO
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) thin films for propane gas detection. Cr doped TiO
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thin films with different power on the Cr target ranging from 5 to 20 W were deposited by confocal magnetron sputtering at same deposition conditions. The effect of Cr concentrations on structural, morphological and optical properties of the films have been investigated in detail. The thin film characterizations were performed by using X-Ray Photoelectron Spectroscopy (XPS), Energy-Dispersive X-Ray Spectroscopy (EDX), Secondary Ion Mass Spectroscopy (SIMS), Atomic Force Microscope (AFM), UV-Vis-NIR spectrometer and Photoluminescence (PL) systems. The sensing behavior of the sensors was tested with gas testing system to propane gas at 250, 500 and 1000 ppm. The high sensor performance was observed in gas detection behavior with increasing Cr content. In particular, the obtained gas sensor with Cr RF power of 20 W exhibited higher sensor response in the detection of propane at working temperature of 300 °C.
... 6−11 The chronic exposure of people to NO 2 at concentrations above 40−100 μg/m 3 may cause pulmonary edema and respiratory diseases. 12,13 According to clinical statistics, continuous exposure to NO 2 within the environment is associated with increased risks of cardiovascular disease, 14 incident chronic kidney disease, or cancer, 15 where a 10 μg/m 3 change in NO 2 generates a relative mortality risk of 1.012. 16 In the United States, approximately 6.3% of the adult population diagnosed with chronic obstructive pulmonary diseases (COPD) is ascribed to exposure to NO 2 . ...
Fossil fuel internal combustion engines generate and release a huge amount of nitrogen dioxide, leading to respiratory and allergic diseases such as asthma, pneumonia and possibly tuberculosis. Here we develop an alveolus-inspired membrane sensor (AIMS) for self-powered wearable nitrogen dioxide detection and personal physiological assessment. The bionic AIMS exhibits an excellent sensitivity up to 452.44%, a good linearity of 0.976, and superior selectivity under the NO2 concentration of 100 ppm. Furthermore, AIMS can also be employed to diagnose human breath behaviors for breath analysis. The fundamental sensing mechanism is established using a combination of thermodynamic analysis, finite-element analysis, and phase-field simulations. It is found that the depolarization field inside the sensitive materials plays a crucial role in the self-powered gas sensing performance. This work not only provides an efficient, low cost, portable and environment-friendly means for active environmental assessment and personal biomonitoring, but also renders the community a deep understanding of the gas sensing mechanisms.
... Out of these growth techniques, vapor transport method, using vapor-liquid-solid (VLS) growth mechanism or VS growth, is one of the finest growth techniques used for the growth of metal oxide semiconductor nanostructures. It is a cost-effective easy method used to create many single-crystalline 1-D nanostructures [3][4][5][6][7][8][9][10][11]. ...
... The challenging part is to find an effective doping method that can be used to introduce the dopants to the sensing material. Several methods have been used such as mixing [25], dip coating [26], and RF-magnetron/reactive DC sputtering [27]. ...
This paper presents the development of a metal oxide semiconductor (MOS) sensor for the detection of volatile organic compounds (VOCs) which are of great importance in many applications involving either control of hazardous chemicals or noninvasive diagnosis. In this study, the sensor is fabricated based on tin dioxide (SnO2) and poly(ethylene oxide) (PEO) using electrospinning. The sensitivity of the proposed sensor is further improved by calcination and gold doping. The gold doping of composite nanofibers is achieved using sputtering, and the calcination is performed using a high-temperature oven. The performance of the sensor with different doping thicknesses and different calcination temperatures is investigated to identify the optimum fabrication parameters resulting in high sensitivity. The optimum calcination temperature and duration are found to be 350 °C and 4 h, respectively and the optimum thickness of the gold dopant is found to be 10 nm. The sensor with the optimum fabrication process is then embedded in a microchannel coated with several metallic and polymeric layers. The performance of the sensor is compared with that of a commercial sensor. The comparison is performed for methanol and a mixture of methanol and tetrahydrocannabinol (THC) which is the primary psychoactive constituent of cannabis. It is shown that the proposed sensor outperforms the commercial sensor when it is embedded inside the channel.
... The development of new materials based on different methods, techniques and working principles has been carried out to achieve the best performance. However, the operating temperatures of metal oxide gas sensors are usually above 150 • C to activate the absorption and desorption processes between the targeted gases and the surfaces of the materials [1][2][3][4][5][6][7][8]. The high operating temperature is one of the main drawbacks of metal oxide-based gas sensors because it ultimately results in high power consumption and undesirable long-term drift problems caused by sintering effects in the metal oxide grain boundaries, yielding poor selectivity and stability [9,10]. ...
In this work, we present conductometric gas sensors based on p-type calcium iron oxide (CaFe2O4) nanoparticles. CaFe2O4 is a metal oxide (MOx) with a bandgap around 1.9 eV making it a suitable candidate for visible light-activated gas sensors. Our gas sensors were tested under a reducing gas (i.e., ethanol) by illuminating them with different light-emitting diode (LED) wavelengths (i.e., 465–640 nm). Regardless of their inferior response compared to the thermally activated counterparts, the developed sensors have shown their ability to detect ethanol down to 100 ppm in a reversible way and solely with the energy provided by an LED. The highest response was reached using a blue LED (465 nm) activation. Despite some responses found even in dark conditions, it was demonstrated that upon illumination the recovery after the ethanol exposure was improved, showing that the energy provided by the LEDs is sufficient to activate the desorption process between the ethanol and the CaFe2O4 surface.
... A group of response signals continuously delivered from the MOS sensor array is analyzed via pattern-recognition techniques for characterizing and quantifying gases to which the array is exposed. However, such multi-sensor arrays suffer from contaminant doping in the sensing area during the manufacturing process, which unpredictably alters the resistance of the sensing elements in the sensor array [14,15]. ...
Microelectronic gas-sensor devices were developed for the detection of carbon monoxide (CO), nitrogen dioxides (NO2), ammonia (NH3) and formaldehyde (HCHO), and their gas-sensing characteristics in six different binary gas systems were examined using pattern-recognition methods. Four nanosized gas-sensing materials for these target gases, i.e., Pd-SnO2 for CO, In2O3 for NOX, Ru-WO3 for NH3, and SnO2-ZnO for HCHO, were synthesized using a sol-gel method, and sensor devices were fabricated using a microsensor platform. Principal component analysis of the experimental data from the microelectromechanical systems gas-sensor arrays under exposure to single gases and their mixtures indicated that identification of each individual gas in the mixture was successful. Additionally, the gas-sensing behavior toward the mixed gas indicated that the traditional adsorption and desorption mechanism of the n-type metal oxide semiconductor (MOS) governs the sensing mechanism of the mixed gas systems.
... Many works of transition-metal-doped metal oxide materials, namely Pt -doped TiO 2 [1], utile TiO 2 doped with 4d transition [2], Fe 2 O 3 nanoparticles doped with transitionmetal [3], ZrO 2 doped with Ag [4], Ag-and Au-doped ZnO nanomaterial [5], and Pt-doped SnO 2 surfaces [6], have been widely investigated for several purposes such as gas sensing and gas storage materials. Transition-metal elements doped on graphene have widely studied as hydrogen storage materials, namely Cu and Pd-decorated graphene [7], Pd and Pt decorated graphene nano-particles [8], Pd-decorated graphene [9,10] and dual Ni and Al doped graphene composites [11], Zr-doped graphene [12], Co-doped graphene [13]. ...
Adsorptions of Zr atom onto the perfect rutile TiO2(110) and the oxygen vacancy rutile TiO2 (110) ([TiO2+Vo]) to form Zr–TiO2 and Zr‒[TiO2+Vo] were studied using periodic density functional theory (DFT) method. Three configurations of both Zr–TiO2 and Zr‒[TiO2+Vo] surfaces were found and binding energies of Zr atom of the most stable Configurations of Zr–TiO2 and Zr‒[TiO2+Vo] surfaces are respectively −3.36 and −3.26 eV. The most stable Configurations of the Zr–TiO2 and Zr‒[TiO2+Vo] surfaces were selected in hydrogen adsorption study. Adsorption energies of single H2 molecule on the most stable Zr–TiO2 and Zr‒[TiO2+Vo] are −1.43 and −1.45 eV, respectively. Based on the second H2 molecular adsorption on the hydrogen pre‒adsorbed Zr–TiO2 and Zr‒[TiO2+Vo] surfaces, adsorption energies of −1.90 and −2.55 eV were found, respectively. The second H2 molecule adsorption was found to be much stronger than the first H2 molecule adsorbed onto the Zr–TiO2 and Zr‒[TiO2+Vo] surfaces by 32.9% and 75.9%, respectively. Either the Zr–TiO2 or Zr‒[TiO2+Vo] surface is suggested as hydrogen–storage material and the Zr–TiO2 can be proposed as an electrical resistance‒based hydrogen sensor.
... The intensification of environmental pollution due to industrialization, fuel burning, agriculture, and leakage of poisonous gases is a threat to human life. 1 A timely discovery and the monitoring of toxic and harmful gases are essential for the environmental protection. 2 Recently, gas sensors based on semiconductor metal oxides (SMOs) have become one of the most dominant research topics owing to their resistance change induced by the interaction of gas and solid materials on the surface of the semiconductors. 3,4 Additionally, metal oxide (MO) can be readily synthesized with various methods (e.g., physical and chemical methods). ...
The application of metal oxide-based sensors for the detection of volatile organic compounds is restricted because of their high operating temperatures and poor gas sensing selectivity. Driven by this fact, we report the low operating temperature and high performance of C3H7OH and C2H5OH sensors. The sensors comprising SnO2 hollow spheres, nanoparticles, nanorods, and fishbones with tunable morphologies were synthesized with a simple hydrothermal one-pot method. The SnO2 hollow spheres demonstrated the highest sensing response (resistance ratio of 20) toward C3H7OH at low operating temperatures (75 °C) compared to other tested interference vapors and gases, such as C3H5O, C2H5OH, CO, NH3, CH4, and NO2. This improved response can be associated with the higher surface area and intrinsic point defects. At a higher operating temperature of 150 °C, a response of 28 was witnessed for SnO2 nanorods. A response of 59 was observed for SnO2 nanoparticle-based sensor toward C2H5OH at 150 °C. This variation in the optimal temperature with respect to variations in the sensor morphology implies that the vapor selectivity and sensitivity are morphology-dependent. The relation between the intrinsic sensing performance and vapor selectivity originated from the nonstoichiometry of SnO2, which resulted in excess oxygen vacancies (VO) and higher surface areas. This characteristic played a vital role in the enhancement of the target gas absorptivity and the charge transfer capability of SnO2 hollow sphere-based sensor.
... Although the metal oxides have a simple working principle, they have proven to be excellent in sensor applications due to their long-term stability, durability and price. In addition to these advantages, thanks to nano-sized materials, the sensors are more sensitive for gas detection and can operate at lower operating temperatures [10]. ...
... Tin dioxide has been extensively studied for a long time for use as transparent oxide films in optoelectronic devices such as sensor, solar cells, liquid crystal displays (LCD), photocatalysis, lithium ion batteries, wastewater treatment, and large area flat panel displays [1][2][3][4][5][6][7]. The SnO 2 thin films can be doped with a wide variety of transition metal ions [8][9][10][11][12][13][14] to meet the demands of these many practical applications. Among the various dopants, indium (In) [15][16][17] and fluorine (F) [18][19][20] were found to be more effective to improve the n-type conductivity of SnO 2 thin films. ...
Pure and antimony doped tin oxide films (SnO2:Sb) have been prepared by a chemical spray technique on silica glass substrates. X-ray diffraction (XRD), atomic force microscopy (AFM), UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), electrochemical impedances spectroscopy (EIS) and electrochemical photocurrent (ECP) measurements were used to characterize the obtained films. The results of XRD indicated that all films exhibited tetragonal cassiterite SnO2 structure. The Sb-doped films showed a transparency more than 70% in the visible region and the Sb inclusion in the cassiterite lattice reduced the transparency in this region. EIS spectra have a single semi-circle in the high frequency region and the diameter of half-circle was found to decrease in the presence of small amount of Sb doping (2%). Electrochemical photocurrent test showed that the maximum increasing current under ultraviolet light was obtained for a doping level of 4%.
... In order to secure the environment from these poisonous and toxic chemicals, it is necessary to monitor and detect these chemicals in an effective way. Materials exhibiting chemical sensing properties play a vital role in detection and monitoring mechanisms and researchers are recently trying to develop chemical sensors with astonishing performance [1,2]. Adsorption of chemicals on to the surface of sensing materials resulted in change of their chemical, physical and electrical which then transformed in to measurable quantities [3][4][5]. ...
Synthesis of magnesium doped zinc oxide nanostructures has been carried out by vapor transport method and characterization of the samples have been performed regarding methane (CH4) gas sensing in addition to their structural, morphological, chemical composition and optical properties. The un-doped and magnesium doped zinc oxide nanostructures were synthesized on silicon substrates at 900 °C through vapor liquid solid mechanism. Powder X-ray diffraction study confirmed the growth of material exhibiting crystalline wurtzite (hexagonal) structure. Scanning electron microscopy revealed that morphology of grown material is in the form of nanorods and nanobelts with average diameter and thickness of 12.66 ± 3.72 µm and 1.88 ± 0.70 µm, respectively. Energy dispersive X-ray analysis was used to examine the stoichiometry of the samples. Optical characterizations were carried out by photoluminescence, diffused reflectance spectroscopy, voltage dependent photo-current response and Time dependent photocurrent response. A significant change in energy bandgap has been observed after Mg incorporation in ZnO. For doped ZnO samples, the observed value of band gap is 3.32 eV which is higher than that for undoped ZnO (3.18 eV).The nanostructures were tested for UV and gas sensing properties based on the change in resistance in UV light when exposed to CH4 gas. The gas sensing response was recorded for temperature ranging from 50 to 200 °C for 400 ppm concentration of methane gas. The sensing response of Mg-doped ZnO nanobelts was found as high as 54%. The Mg-doped ZnO nanobelts showed significant, stable and enhanced sensing properties (54%) towards 400 ppm of CH4 gas at optimal temperature of 200 °C. The observations revealed that Mg doping in ZnO nanostructures would help to improve the CH4 and UV sensing of these materials.
... Bracelet with the three MOX sensors 2.4.SnO2 sensors for transdermal ethanol monitoring 2.4.1.Sensitive material SnO2We selected tin dioxide based sensitive layer relying on the results reported in the literature.Tin dioxide is n-type semiconductor oxide with a wide-band-gap (3.6 eV), and a wide range of applications for various types of oxidizing or reducing gas/vapor detection. It is one of the most sensitive layer used[25][26][27][28][29][30][31]. Our SnO2 sensitive thin layers were deposited by RF reactive magnetron sputtering technique on transducers patented by the CNRS-AMU-IM2NP laboratory. ...
The aim of this study is to develop the first system based on chemical MOX sensors for monitoring ethanol on the skin after consumption. Thus, non-invasive measurements to monitor alcohol concentration and their correlation with blood and breathe Alcohol become possible. Transdermal alcohol emissions by perspiration have been investigated during clinical trials to demonstrate the relevance of this method. First, three commercial MOX sensors were used after calibration in respect of the thermodynamic conditions of the skin surface. Then, six volunteers have been selected for clinical trials with two cohorts of BAC target: 0.5 g/l and 0.8 g/l, and the three different sensors have been integrated in a wristband. We observed that the skin emits ethanol concentrations and we found a consistent correspondence between the kinetics of blood, breath and perspiration. MOX sensors can reliably estimate whether a drinker consumed a low or significant amount of alcohol. After validating this method, we developed our sensors based on tin dioxide thin sensitive layers with thickness of 50 nm. Sensitive properties of the films to ethanol were studied in the conditions of the skin surface. The sensor shows a higher response to ethanol (r = 7.8 for 50 ppm) with relative humidity of 50% and a lower consumption (55 mW) than commercial sensors (MICS 5524: 65 mW).
... High sensitivity, low cost, fast response and easy miniaturization are the main advantages of semiconducting SnO2 gas sensors. State-of-the-art techniques to manufacture gas sensitive layers are sputtering [31], spin coating [32], or screen printing [33]. Extensive summaries can be found in [22,23,26]. ...
The Aerosol Deposition (AD) method has the unique property to allow for manufacturing dense ceramic films at room temperature. As found in many publications, the deposition process is very sensitive to powder properties. In particular, powders of nano-sized particles and grains, e.g., from precipitation, are usually beyond the conventional size range of AD processability, yielding chalk-like films of low mechanical stability. Thus, the conventional AD process is limited in applicability. In this study, we try to overcome this problem by adapting the standard milling treatment of powders for improved deposition by additional temperature pre-treatment. Using commercial tin dioxide and including a temperature treatment for grain growth, makes the powder accessible to deposition. In this way, we achieve optically translucent and conductive SnO2 thick films. With the application such as a gas sensitive film as one of many possible applications for SnO2 thick-films, the sensors show excellent response to various reducing gases. This study shows one exemplary way of extending the range of adequate powder and applications for the AD method.
... Pt as a catalytic additive has been proven to be effective in improving gas-sensing performance. Ivanov et al. [25] has shown that the Pt-doped SnO 2 material is less resistant, more sensitive, and shows faster response to ethanol than pure SnO 2 ; what's more, the response of the Pt-doped sensors was between 2 and 55 times higher than the commercial one. Wang et al. ...
Pristine and Pt-doped CuO nano-flowers were synthesized by a simple water bath heating method in this paper. Highly sensitive hydrogen sulfide (H2S) gas sensors based on Pt-doped CuO nano-flowers were fabricated. Scanning electron microscopy, X-ray diffraction, inductively coupled plasma atomic emission spectrometry, and energy dispersive X-ray spectroscopy were used to examine the characteristics and morphology of materials. The sensing performances of sensors with different concentrations of Pt dopants were evaluated at different operating temperatures. The results indicated that the CuO sensor doped with 1.25 wt % Pt exhibited the highest response (Rg/Ra, where Rg is the resistance in gas, and Ra is the resistance in air) of 135.1 to 10 ppm H2S at 40 ∘C, which was 13.1 times higher than the response of a pure CuO sensor. Pt doping also plays an important role for the enhancement of H2S selectivity against C2H5OH, NH3, H2, CH3COCH3, and NO2.
... ZnO is direct band gap semiconductor with 3.2-3.7 eV (Norton et al. 2006;Jain et al. 2007). High transparency in visible light, piezoelectricity, low electric resistant and chemical stability (Look 2001) are unique properties of ZnO that can be used for many applications such as sunscreens, sun glasses, gas sensors, water pollution sensors and temperature and magnetic field sensors (Qi et al. 2009;Ivanov et al. 2004). Pure ZnO nanolayer is a semiconductor that has advantageous properties which lead to application of it in optoelectronic devices. ...
Pure and doped zinc oxide nanofilms were deposited onto glass substrates by the sol–gel method. Doping can change structural, optical and magnetic properties of matter. In this research, transition elements (Fe, Co, Ni and Mn) were chosen as dopants because of their ferromagnetic property at room temperature. Structural, optical and magnetic properties of pure and doped zinc oxide were experimentally investigated. The band gap and absorption edge of nanofilms were determined, and the optical constants of films were calculated by the Cauchy formula. Transmittance spectrum, XRD diffraction and hysteresis loop were measured, and spontaneous and saturation magnetic moment of samples was calculated. Results of our measurements show Mn-doped samples are paramagnetic and the others are ferromagnetic, and band gap variation does not follow a specific pattern. Controlling dopant concentrations improves matter properties, so different Mn and Ni concentrations on ZnO nanolayers were prepared and investigated for finding out the effect of different concentrations of dopants on ZnO properties. In the case of different Mn concentrations, the band gap was decreased in low doping (Mn < 3%) and increased for high concentration (Mn > 3%), and this is due to the exchange interaction between the localized d shell electrons of the magnetic ions and the delocalized band states. Results of investigating different concentrations of Ni indicate that low Ni concentration slightly increases the band gap and high concentration of Ni leads to a decrease in the band gap. This phenomenon is due to the magnetic property of Ni and quantum confinement that can increase the band gap.
... It comes out by combustion of fuels from the vehicles in huge amount. The dissolution of NO 2 from industrial sewage and runoff water from agricultural lands into running as well as underground water may result threat to environment [3,4]. Thereby, ultimate finding and monitoring of these hazardous and poisonous gases is essentially important for an environmental safety. ...
Zinc oxide (ZnO) films of nanograins were obtained on a glass substrate by simple and rapid chemical bath deposition method with zinc nitrate and urea as precursors at low pH condition (∼9) without adding any complexing agent. The structure, morphology and surface chemistry were confirmed from the XRD, EDX, Raman spectroscopy, x-ray photoelectron spectroscopy, BET, FE-SEM and TEM imaging measurements. Chemiresitive selectivity and sensitivity of ZnO film sensor toward NO2 gas was better than other target gases like methanol, ethanol, hydrogen sulphide and chlorine. Remarkable high sensitivities from 176% to 610% towards NO2 gas have been obtained under variation of concentration from 10 ppm to 200 ppm @200 °C operating temperature. Large response about 84.42% against first day measurement on 15th day supports chemical stability and mechanical robustness of ZnO film-based sensor. Hence, the present study signifies the potentiality of ZnO in fabricating low-cost and high-performance NO2 gas sensors.
Hybridizing hierarchically structured Sm2O3 with multi-walled carbon nanotube (MWCNTs) is highly desirable for improving the performance of Sm2O3-based gas sensors. In this work, we developed a simple solvothermal method combined with heat treatment for the preparation of flower-like Sm2O3/MWCNTs nanocomposites with a flexible three-dimensional nanostructure. The characterization results showed that 4–8 μm Sm2O3 flower-like structures, formed by Sm2O3 nanosheets, were attached to the MWCNTs surface. The Sm2O3-MWCNTs composite possesses a SBET of 212.5 m2g−1 and higher VTot of 0.756 cm3g−1. Gas sensors based on the Sm2O3/MWCNTs nanocomposites exhibited a greater response, better selectivity, lower operating temperature, and good recovery towards acetone compared with pure Sm2O3. Additionally, the sensors show a total recovery of their baseline resistance and reasonable response and recovery times. 5.0 wt% MWCNT-doped Sm2O3 sample is the most sensitive sensor towards LPG and ethanol and the related response value are 18.2 and 14.3. Moreover, the Sm2O3/MWCNT hybrid sensor delivers a response and recovery time of 7 and 10 s, respectively. In addition, the fabricated sensor showed high stability, which is conducted by long period (60 days) sensing response for both gases. The improved mechanism of the fabricated sensor was also discussed in detail.
(Left panel) A schematic of SO 2 gas sensor devices with two Au electrodes and a central region based on TM doped HfS 2 monolayers (TM = Ni, Pd or Pt). (Right panel) I – V relationship of the Pt-doped HfS 2 monolayer-based sensor.
The increasing demand for efficient sensing devices with facile low-cost fabrication has attracted a lot of scientific research effort in the recent years. In particular, the scientific community aims to develop new candidate materials suitable for energy-related devices, such as sensors and photovoltaics or clean energy applications such as hydrogen production. One of the most prominent methods to improve materials functionality and performance is doping key device component(s). This paper aims to examine in detail, both from a theoretical and an experimental point of view, the effect of halogen doping on the properties of tin dioxide (SnO2) and provide a deeper understanding on the atomic scale mechanisms with respect to their potential applications in sensors. Density Functional Theory (DFT) calculations are used to examine the defect processes, the electronic structure and the thermodynamical properties of halogen-doped SnO2. Calculations show that halogen doping reduces the oxide bandgap by creating gap states which agree well with our experimental data. The crystallinity and morphology of the samples is also altered. The synergy of these effects results in a significant improvement of the gas-sensing response. This work demonstrates for the first time a complete theoretical and experimental characterization of halogen-doped SnO2 and investigates the possible responsible mechanisms. Our results illustrate that halogen doping is a low-cost method that significantly enhances the room temperature response of SnO2.
The production of a large number of metal oxide semiconductor materials is more for design needs, while theoretical exploration is relatively less concerned. In this work, WO3 nanoparticles were prepared by the tungstic acid thermolysis method, and the catalysts of Pt and Ru were loaded on the surface of nanoparticles with a wet impregnation method. As expected, the sensitive responses were enhanced significantly with the additional loading of Pt, which revealed that bimetallic loading could achieve better properties with a smaller loaded amount than single metal. According to the power-law response to oxygen and H2-TPR results, the sensitization mechanism of noble metals loaded WO3 to acetone as the typical VOCs was investigated. The results showed that the sensing processes were dominated by oxygen adsorption behavior and there was no difference with the loading of Ru. Furthermore, the power-law coefficient n became smaller with Pt loading. It is proposed that oxygen adsorbates on the surface become more active due to Pt. We would like to propose further a perspective, i.e., polymetallic loading that utilizes the properties of different metals to achieve synergism.
Metal oxide semiconductor gas sensors (MOS) based on tin oxide have excellent performance in ethanol gas detection and have been widely used in industrial production, environmental protection, and road safety detection. However, conventional tin oxide sensors can only show excellent detection performance for ethanol gas above 250 °C. In this work, nano-size tin oxide particles were grown on the micron hollow carbon spheres derived from the biomaterial chlorella by a gel method. This three-dimensional hierarchical porous structure can enrich ethanol gas at a certain temperature. Ethanol gas sensor fabricated with this material has better sensing performance at low temperature (168 °C to 200 °C).
The demand of portable and wearable chemical or biosensors and their expeditious development in the recent years has created a scientific challenge in terms of their continuous powering. As a result, the mechanical energy harvesters such as piezoelectric and triboelectric generator (TEG) have been explored recently either as sensors or harvesters to store charge in small, but long‐life, energy storage devices to power the sensors. The use of energy harvesters as sensor is particularly interesting as with such multifunctional operations it is possible to reduce the number devices needed in a system, which also helps overcome the integration complexities. In this regard, TEGs are promising, particularly for energy autonomous chemical and biological sensors, as they can be developed with wide variety of materials and their mechanical energy to electricity conversion can be modulated by various analytes. This review focusses on this interesting dimension of TEGs and presents various self‐powered active chemical and biological sensors. A brief discussion about the development of TEG based physical, magnetic and optical sensors is also included. The influence of environmental factors, various figures of merit, and significance of TEG design are explained in context with the active sensing. Finally, the key applications, challenges and future perspective of chemical and biological detection via TEG are discussed with a view to drive further advances in the field of self‐powered sensors. This article is protected by copyright. All rights reserved
During the process of metal oxide semiconductors (MOS) gas sensing, the chemisorbed oxygen on the surface plays a significant important role, which determines the surface reactivity and controls the film conductivity. Therefore, it is necessary to improve the amount of chemisorbed oxygen on MOS surface. In this paper, the effect of doping on the accumulation of chemosorbed oxygen on SnO2 surface was studied. SnO2, Co-SnO2 and Nb-SnO2 were successfully synthesized via nonaqueous sol-gel method to study the effect of acceptor doping and donor doping on accumulation of chemosorbed oxygen and gas response. And dynamic program cooling (DPC) was also carried out in different concentrations of acetone and different gases respectively to obtain the R-T curve and gas response. The results showed that the Co doped SnO2 obviously improved the accumulation of chemosorbed oxygen and dynamic gas response, while the Nb doping has little improvement. The reason of these results was also analyzed by band theory in this paper.
The present study demonstrates the facile synthesis of SnO2 (tin oxide) 2D nanoflakes (2-dimensional) for sonophotocatalytic tetracycline hydrochloride (TcH) degradation. TcH is known to be widely used antibiotic, but even minute concentrations of it make the aqueous environment unsafe for living beings. As-synthesized SnO2 was thoroughly characterized to reveal its morphology, crystal structure and other intrinsic properties. SnO2 2D nanoflakes possessed excellent photocatalytic TcH degradation under visible light. Preliminary investigation inferred that sonophotocatalytic mode of TcH degradation was efficient over other modes with respect to degradation efficiencies for 20 mg L⁻¹ TcH and 20 mg of SnO2. The optimum degradation of TcH was observed to be 88.82% in 135 min under LED (9 W, 220 V) irradiation with 30 mg of SnO2 dosage and 40 kHz ultrasound. The degradation dynamics complied with pseudo-first-order kinetics where the kinetic rate constant (k) was 0.02 min⁻¹. Hence, SnO2 2D nanoflakes were promising in mineralization of the biotoxin (TcH) in aqueous environments that accent its application to treat real-time water and wastewater.
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Much recent attention has been focused on the development of field-effect transistors based on low dimensional nanostructures for the detection and manipulation of molecules. Because of their extraordinarily high charge sensitivity, InAs nanowires present an excellent material system in which to probe and study the behaviour of molecules on their surfaces and elucidate the underlying mechanisms dictating the sensor response. So far, chemical sensors have relied on slow, activated processes restricting their applicability to high temperatures and macroscopic adsorbate coverages. Here, we identify the transition into a highly sensitive regime of chemical sensing at ultra-low concentrations (< 1 ppm) via physisorption at room temperature using field-effect transistors with channels comprised of several thousand InAs nanowires and ethanol as a simple analyte molecule. In this regime, the nanowire conductivity is dictated by a local gating effect from individual dipoles leading to a non-linear enhancement of the sensitivity. At higher concentrations (> 1 ppm), the nanowire channel is globally gated by a uniform dipole layer at the nanowire surface. The former leads to a dramatic increase in sensitivity due to weakened screening and the one-dimensional geometry of the nanowire. In this regime, we detect concentrations of ethanol vapour as low as 10 ppb, 100 times below the lowest concentrations previously reported. Furthermore, we demonstrate electrostatic control of the sensitivity and dynamic range of the InAs nanowire-based sensor and construct a unified model that accurately describes and predicts the sensor response over the tested concentration range (10 ppb to 10 ppm).
0.5 mol% Pt decorated SnO
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(Pt-SnO
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), 0.5 mol% Pd decorated SnO
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(Pd-SnO
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), 0.5 mol% Pt decorated WO
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(Pt-WO
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), and 0.5 mol% Pd decorated WO
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(Pd-WO
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) gas sensing films were fabricated by screen printing. Subsequently, SiO2 membrane was deposited in situ by CVD. The response of the sensing films to CO, NO, H
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, and NO
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were investigated. Pt-SnO
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, and Pt-WO
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with SiO2 membrane deposited for 20 min (Pt-WO
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-SiO
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showed highly sensitive and selective to CO, NO, H
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, and NO
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at each optimal operating temperature respectively. Different enhancements of response to target gases might be associated to the combined effects of electronic, chemical sensitizations, and “support effect”. The highly sensitive and selective gas sensors in this paper can be integrated into a gas sensor array to fabricate an electronic nose for H
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, CO, NO, and NO
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detection.
The development of mesoporous metal/metal oxide nanohybrids in the field of gas sensor has attracted intensive research interest in the last years due to their increasing number of applications in the industrial and private sectors. The role of gas sensors for the control of technical processes, automobiles, healthcare and environment monitoring is increasing exponentially every day. Therefore the development of sensors with improved sensitivity, good linearity, fast response/recovery, good stability, excellent reproducibility and impressive selectivity to the target gases at ppm concentrations is the subject area of intensive research. Considering this aspect, the mesoporous metal/metal oxide materials with novel fundamental characteristics including high-specific surface area, ordered mesoporous structure and good interconnectivity, have emerged as the potential candidate for the development of futuristic sensors. This book chapter highlights the recent developments and reflects the impact of mesoporous metal/metal oxide nanohybrid materials on sensor technology.
In this work, a high-performance p-type semiconducting gas sensor was successfully fabricated based on a SnO-SnO2 p-n heterojunction thin-film formed via a radio-frequency (RF) -magnetron sputtering process. The structure, morphology, and chemical composition of the deposited thin-film were investigated using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, indicating that the thin-film had a microcrystalline structure and a mixed SnO and SnO2 phase. Compared to the previously reported p-type metal oxide semiconductor-based gas sensors, the gas sensor in this study exhibited competitive sensing performance for NO2 gas with a maximum response of 4.35–10 ppm NO2 at a low operating temperature of 60 °C, although it was fabricated via a simple RF- magnetron sputtering process. Moreover, the SnO-SnO2 p-n heterojunction thin-film gas sensor exhibited a high sensing selectivity to NO2 gas. The enhanced NO2-sensing performance of the fabricated gas sensor at low operating temperatures is possibly attributed to the formation of the SnO-SnO2 p-n junctions at the surface of the thin-film. The importance of this work is in the successful fabrication of the high-performance p-type semiconducting gas sensor using a simple and conventional RF- magnetron sputtering process.
Les travaux présentés dans ce manuscrit concernent la réalisation et la caractérisation d?un capteur de gaz à base de dispositifs à ondes élastiques de surfaces, SAW (Surface Acoustic Wave). Pour obtenir et exploiter de telles ondes, deux transducteurs inter-digités (IDT), l'un servant d'émetteur et l'autre de récepteur, sont déposés sur un substrat piézoélectrique. Une tension alternative appliquée aux bornes de l'IDT émetteur génère une onde se propageant le long du substrat. Lorsque cette onde arrive sur l'IDT récepteur, elle est convertie en tension électrique. A partir de ce dispositif, la spécificité du capteur est obtenue par l'ajout d'une couche sensible sur le chemin de propagation de l'onde, entre les deux IDTs. L'adsorption du gaz sur la couche sensible perturbe la propagation de l?onde et modifie ainsi sa vitesse et son amplitude. La structure du capteur développé et caractérisé au cours de cette thèse est la suivante : Polyaniline/ZnO/Quartz. Le substrat bicouche ZnO/Quartz pour une direction de propagation particulière (90°) constitue la partie génératrice d'ondes de Love et la polyaniline, polymère fonctionnalisable est utilisée en tant que couche sensible. La structure génératrice d'ondes a été entièrement réalisée en salle blanche avec notamment l?optimisation des paramètres de dépôt du film de ZnO par pulvérisation réactive RF magnétron et la photolithographie des IDTs. Elle a ensuite été étudiée et caractérisée, avant et après dépôt de la couche sensible, par des mesures expérimentales confrontées aux estimations théoriques. Pour finir, nous avons procédé à des tests sous gaz (NO2, SO2 et éthanol) avec notre capteur. Nous avons ainsi pu montrer le potentiel d?utilisation de la structure Polyaniline/ZnO/Quartz en tant que capteur de gaz.
La détection et la surveillance des gaz est un enjeu important tant pour la sécurité industrielle que pour la protection de l’environnement et des personnes. Le dihydrogène, prend une place de plus en plus importante en tant que combustible et vecteur énergétique mais il est extrêmement inflammable et explosif dans un large domaine de 4 à 75% dans l’air. De même, l’ammoniac est très utilisé dans l’industrie comme gaz réfrigérant ou comme élément de base pour la production chimiques d’autres composés. Ce gaz présente des risques sur l’environnement et sur les êtres vivants et peut former des mélanges explosifs avec l’air dans les limites de 15 à 28% en volume. Les capteurs de gaz permettant d’indiquer la présence et/ou la quantification de ces gaz prennent alors toute leur importance. Dans la continuité de nos nombreux travaux sur les capteurs résistifs à base d’assemblages discontinus de nano-objets, l’objet de ce travail de thèse a été de préparer des capteurs résistifs pour la détection de H2 et NH3. Ces capteurs sont à base d’assemblages 2D de nanoparticules de compositions complexes. Trois types de nanoparticules cœur-coquille ont été synthétisés : Au@ZnO, Au@SnO2 et Au@Ag. Différentes techniques physico-chimiques (UV-Visible/TEM / DRX etc) ont permis de caractériser les particules obtenues. L’étape suivante a consisté à les assembler en monocouches compactes. Les films ont été obtenus par la méthode d’assemblage de Langmuir-Blodgett. Après transfert à la surface d’un substrat en verre supportant des électrodes inter digitées, les performances de détection des capteurs résistifs fabriqués ont été alors évaluées. Les capteurs à base de Au@ZnO et Au@SnO2 ont été testés sous H2, tandis que les capteurs à base de Au@Ag l’ont été sous NH3. Les capteurs fabriqués ont montré des performances attractives de détection de H2 et NH3 dans des gammes de concentration étendues. Une autre contribution importante de ce travail concerne la compréhension des mécanismes de détection. Diverses techniques analytiques, tels que la TPD (Température désorption Programmed) et la TPR (Température de réduction programmée) ont été utilisés pour permettre la discussion des les mécanismes impliqués.
A series of pure and iron doped strontium titanate, (SrFexTi1-xO3; x = 0, 0.1 and 0.2) powders were synthesized, characterized and used to fabricate ethanol sensors for low concentration. X-Ray Diffraction (XRD) technique was used to confirm the single phase formation. Microstructural properties of the powders were investigated using scanning electron microscopy (SEM). Electrical conductivity of all the samples at room temperature (RT) was measured. Sensors were optimized for best responsiveness by varying the operating temperature from 350 °C to 500 °C.The sensor with doping x = 0.2 exhibited best sensing response at 400 °C for ethanol gas. The undoped sensor demonstrated a decrease in resistance on exposure to ethanol gas whereas Fe-doped sensors showed increase in resistance. The doping induced changeover from n to p behavior in the sensing response on doping has been investigated and corroborated with an observed shift in the Fermi level position by X-ray photoelectron spectroscopy (XPS). The disparity in gas sensing response clearly demonstrates inter-connection of multiple influencing factors such as electrical conductivity, morphology, porosity and change in chemical composition on doping. The sensors were exposed to ethanol, nitrogen dioxide, carbon monoxide, butane gases at concentration between 5 ppm and 50 ppm. The sensor exhibited much reduced relative response to all gases other than ethanol which can be utilized for wide range of applications.
A number of sensor types were fabricated and tested for their electrical resistance changes to compounds known to be evolved by potato tubers with soft rot caused by the bacterium Erwinia carotovora. On the basis of these tests, three sensors were selected for incorporation into a prototype device. The device was portable and could be used without computer control after threshold values and sensor settling criteria had been downloaded. The prototype was assessed for its discriminating power under simulated storage conditions. The device was capable of detecting one tuber with soft rot in 100 kg of sound tubers in a simulated storage crate. The device was also able to detect a tuber inoculated with E. carotovora, but without visible signs of soft rot, within 10 kg of sound tubers. The same system was able to follow the progression of the disease in a tuber stored amongst 10 kg of sound tubers when operated at 4 °C and 85% relative humidity (conditions typical of a refrigerated storage facility).
Nanostructured (3-6 nm) thin films (80 nm) of SnO2 and Pt-doped SnO2 were obtained by a new sol-gel route using tetra(tert-butoxy)tin(IV) and bis(acetylacetonato)platinum(II) as precursors. EPR and XPS investigations, performed on thin films after interaction with CO, demonstrated that singly ionized oxygen vacancies (V-o(.)) fully transferred their electrons to the noble metal and reduced Pt(IV) to Pt(ll). Contact with air at room temperature led to the reduction of O-2 to O-2(-), therefore, re-oxidizing metal centers. The reaction mechanism concords with the high electrical sensitivity of this material. (C) 2001 Elsevier Science B.V. All rights reserved.
The preparation of γ-Fe2O3 by the thermal decomposition of Fe3O4 obtained from the hydrazine reduction of ferric nitrate was studied employing differential thermal analysis (DTA), and X-ray diffraction (XRD). Here we report a simple technique that does not need any explosive or high-energy reactions to obtain γ-Fe2O3. The ethanol sensitivity of pure and Pt doped γ-Fe2O3 were investigated by studying the electrical resistance characteristics of sensor elements prepared from this material. The Pt doped sensor elements showed a linear response of sensitivity, in the range of 1–1000 ppm ethanol in air, in the logarithmic scale. γ-Fe2O3 behaves as an n-type basic semiconducting oxide when exposed to ethanol vapors and in turn ethanol probably decomposes via the route of CH3CHO to form CO2 and H2O. The maximum sensitivity after Pt incorporation is found at 175°C. The high sensitivity of the sensor to ethanol can be explained on the basis of a catalytic activity that invokes the acid base properties of the test gas and the sensor surface. The response time of the elements to 10 ppm ethanol in air is less than 30 s. Cross sensitivity to other gases like liquefied petroleum gas (LPG), CO, CH4, H2, H2S and NH3 was also studied.
SnO2 and SnO2:Pt thin films, prepared by chemical spray deposition, have been used as gas sensors. The electrical characterization results and their sensing properties in the presence of CO are reported. The films were grown by chemical spray deposition on glass substrates at different temperatures. The initial solution was obtained by diluting SnCl4·5H2O in ethyl alcohol at 0.2 M. In the case of the doped films we have added PtCl2 to the initial solution in the following proportions: 3, 5 and 8% at. The conductance of the films was calculated from the electrical resistance which was measured as a function of measuring temperature, thickness and Pt concentration in the solution. The values of the sensitivity for 3.8 torr of CO partial pressure are as high as 5 for SnO2 and 4×102 for SnO2:Pt. Additionally we report results on surface topography and crystalline structure.
A gas sensor that operates by the detection of changes in the bulk conductivity of a bismuth molybdate semiconductor catalyst is presented. The reduction of the catalyst by organic vapours produces highly mobile oxygen vacancies, which have a direct effect on the carrier density throughout the sample. This reaction is completely reversible in air. The sensor can be prepared as a mixture of the alpha and gamma phases of bismuth molybdate evaporated onto a quartz substrate. The prototype sensors studied show long-term stability of response and insensitivity to water vapour. A degree of selectivity to alcohols and ketones and some alkenes over other reducing agents such as alkanes, hydrogen and carbon monoxide is shown. At an operating temperature of 330 °C, increases in conductivity of a factor of 30 after exposure to 200 ppm of ethanol were commonly observed, with sensitivities down to 5 ppm. Eventually this class of sensors may find use in breathalyser devices.
An SnO2 thin film ethanol gas sensor has been fabricated by electron-gun evaporation and proper annealing in ambient oxygen gas. This processing yielded an SnO2 thin film with fine particles and good structure, thus providing a sensor with a high sensitivity and selectivity in detecting ethanol gas.
The main part of this paper is a report of the detailed preparation conditions, experimental data on sensing characterization and performance of the sensor.
The selectivity of SnO2 gas sensor for a hydrocarbon gas like i-C4H10 has been improved through the serial connection of a compensating element which is sensitive to the interfering gas. The devices were fabricated in 2mm×2mm through the screen-printing technique. The sensing material, made of SnO2, was doped with Sb2O5 and treated with Pt catalyst to detect a hydrocarbon gas. The compensating material was composed of Sb2O5-doped SnO2 with Pd catalyst to detect interfering gas such as ethanol. The amount of resistance change in each material upon exposure to gas is differed depending on the kind of gas to be exposed, giving rise to an improvement in the selectivity of the device.
Nanocrystalline Fe2O3(0.9)–SnO2(0.1) powders have been prepared using a hydrazine method by adding hydrazine monohydrate to an aqueous solution of ferric nitrate nanohydrate, (Fe(NO3)3·9H2O) and tin tetra chloride (SnCl4), followed by washing and drying. This material has been characterized by different techniques such as gravimetric-differential thermal analysis (TGA/DTA), X-ray diffraction (XRD). Sensors made from this material have been proved to be highly sensitive and selective in the detection of ethanol. The sensitivity for ethanol has been compared with a 10wt.% of ZrO2 and SnO2 loaded in Fe2O3. The ethanol sensitivity of pure and Pt doped Fe2O3(0.9)–SnO2(0.1) and Fe2O3(0.9)–ZrO2(0.1) has been investigated for its electrical resistance. The high sensitivity of the sensor to the ethanol could be explained on the basis of a SnO2, ZrO2 activity that invokes the acid–base properties of sensing materials towards the sensitive detection of ethanol vapor in air. Its cross-sensitivity to other gases like CH4, CO, and H2 has also been carried out.
To increase CO sensitivity, SnO2 sensors are doped with a palladium compound. A procedure has been developed to determine quantitatively the ratio Pd/SnO2. It is possible to derive the amount of impregnated Pd in the samples using ICP-MS with a precision of approximately 5%.
Derived from a concept suggested by E. M. Logothetis et al., Proc. 2nd Int. Meet. Chemical Sensors, Bordeaux, France, 1986, p. 175, two differential sensing devices, based on the different catalytic properties of palladium and platinum, are proposed. The first one consists in covering two screen-printed layers of pure tin dioxide by Pd and Pt-doped filters. No major difference is observed between these sensors, probably because of the lack of thickness of the screen-printed filters. In the second device, tin dioxide is directly doped with palladium for one sensor and with platinum for the other. The difference in the response to methane is now sufficient to consider the feasibility of a differential device. However, such sensors have no long-term stability which can only be achieved by covering the layers with inert filters. These filtered SnO2:Pd and SnO2:Pt sensors, now satisfactory as far as differential sensitivity and long-term stability are concerned, also exhibit an important differential response to ethanol, but fortunately reverse to that to methane. The latter result enables a sensing device to be constructed which is selective to methane with respect to ethanol, and insensitive to changes in relative humidity and/or gas flow.
The sensitivity and selectivity of SnO2-based elements to ethanol vapour (1000 ppm) in air at 300 °C are found to be markedly promoted by the addition of several basic oxides, among which La2O3 is the most influential. The promoting effect seems to appear through a change of the reaction selectivity between the two oxidation routes for C2H5OH. Although these elements are rather slow in response rate, this can be improved significantly by loading the elements further with noble metal (Pd or Pt). The doubly promoted elements, Pd(0.5 wt.%)La2O3(5 wt.%)SnO2 and Pt(0.5 wt.%)La2O3SnO2, show excellent sensing properties to ethanol vapour in the range 100–10000 ppm at 300 °C.
SnO2 semiconductor gas sensors undoped and doped with Pt and Pd are prepared by the thick-film technique on Al2O3 substrates with different electrode structures. The SnO2 layer structure is characterized by scanning electron microscopy (SEM) and X-ray diffraction. The temperature dependence of the conductance of these sensors is measured by d.c. and a.c. techniques up to 300 kHz in the temperature range 300 to 800 K under synthetic air and air/250 ppm CO mixtures, as well as the sensor response time due to gas changes from air to air/CO.The results show a temperature-activated conduction mechanism which is discussed using a barrier model. The response time is governed by diffusion processes of the gas into the porous SnO2 layer and surface reaction times.
Thin films of polycrystalline Pd-doped tin dioxide SnO2(Pd), widely used as sensitive element in gas sensors devices for atmospheric pollutant as CO, have been deposited on Si substrates through the ultrasonic aerosol pyrolysis technique. It is firstly shown that the sensitivity S=(G−G0)/G0 to CO at low temperature (80–120°C), measured on steady state regime by conductance–temperature characteristics, depends on the concentration x of Pd incorporated into the film and on the SnO2 grain size D. The highest sensitivity S corresponds to a very sharp (x, D) domain. Secondly, the films synthesised under these optimal conditions have been integrated to a silicon-based prototype of micro-sensor. This device provides stable response in dynamic regime (S=17) at low temperature (∼100°C) to 50 ppm CO by using a short-term annealing (Tannealing=350°C, tannealing=5 min) before each measurement.
Influences of various oxide additives on C2H5OH sensing properties of SnO2-based elements were examined. The sensitivity and selectivity of the elements could be markedly promoted with the addition of basic oxides represented by La2O3. The promoting effect was estimated to be related with selectivity in oxidation reaction of C2H5OH.
In this paper, SnO2 thin films doped with Sb, In, Pd and Pt were prepared by the Sol–Gel technique. The influence of the dopants on the electronic structures of SnO2 film was studied using X-ray photoelectron spectroscopy (XPS). It was observed that the dopants shifted the binding energies of the Sn3d and O1s orbitals, which was possibly caused by the changes of the Fermi level of the SnO2. The changes of the Sn M4,5N4,5N4,5 Auger line shapes of doped SnO2 films demonstrated the influences of the dopants on the distribution of the electron state density of Sn 4d orbital.
SnO2 is Pd doped by using two different methods. In the first method, SnO2 and PdCl2 powders are simply mixed in a mixer, then cold pressed and sintered at high temperature. In the second one, a fixation method is used: a PdCl42− complex is chemically fixed on the surface of the SnO2 powder, the fixed species subsequently being reduced to metallic Pd; powder is then cold pressed and sintered at 650 °C. Pd dispersion is lower in the case of the mixing method, but electrical properties are about the same for the two kinds of sensors realized by Coreci Company. On the one hand, CH4 and aliphatic hydrocarbons are selectively detected at high temperature (400–450 °C). On the other hand, CO detection is possible at low temperature (50 °C, for example). Nevertheless, response time is long and can be improved by two different working modes: continuous pulsed temperature plus cleaning pulse, or isothermal measurement plus cleaning pulse. By doing this, the CO sensitivity is greatly increased, and the humidity variations are easy to compensate. However, the use of a carbon-based filter is necessary in order to avoid the presence of NOx which is a great interferent. These two kinds of sensors can be used eithe as a domestic alarm in order to control CH4 or CO leaks, or as a control sensor in order to monitor car pollution.
A highly sensitive and selective H2S gas sensor has been developed. An SnO2 thin film is deposited on an alumina substrate by the r.f. reactive sputtering method. The influence of the preparation conditions, such as the calcination temperature and the film thickness, has been examined. The sensitivity and the selectivity to H2S are improved by increasing the calcination temperature from 500 to 600°C and by decreasing the film thickness. The optimized sensor shows high sensitivity and good selectivity to H2S, a short response time and long-term stability over 90 days. The relationship between the preparation conditions and the morphologies of SnO2 thin films is also discussed.
Sensors consisting of mixtures of tin dioxide and zinc oxide powders in a range of proportions were constructed. Each mixture was applied to an electrode-bearing alumina substrate either as a paste, or by screen printing. The responses of these sensors, and of three commercially-available Figaro sensors, to ethanol vapour in the 1–1000 parts-per-billion (ppb) range were measured. At 100 ppb of ethanol vapour, the most sensitive paste sensor (25% SnO2/75% ZnO) exhibited a response that was more than twice that of the screen-printed sensors, and almost 60 times greater than that of the most sensitive Figaro sensor (TGS822).
The paper reports the successful fabrication of ethanol gas sensors with tin-dioxide (SnO2) thin films integrated with a solid-state heater, which is realized with technologies of micro-electro-mechanical systems (MEMS), and are compatible with VLSI processes. The main sensing part with dimensions of 450×400 μm2 in this developed device is composed of a sensing SnO2 film, which is fabricated by electron-gun evaporation with proper annealing in ambient oxygen gas to yield fine particles and good structure. An integrated solid-state heater with a 4.5 μm-thick cantilever bridge (1000×500 μm2) structure is made of silicon carbide (SiC) material by MEMS technologies. The sensitivity for 1000 ppm ethanol gas reaches as high as 90 with 10 s and 2 min for the response and recovery time, respectively, at an operating temperature of 300°C. Those experimental results also exhibit a much superior performance to that of a popular commercial ethanol gas sensor TGS-822. Therefore, the developed sensor with high performance is a good candidate for some specific application in automobile to detect drink-drive limit and allows an array integration available with various films for controlling each element at separate resistance.
LaFEO3 and CaxLa1−xFeO3 ceramic powders have been prepared by the coprecipitation method from La(NO3)3, Fe(NO3)3 and Ca(NO3)2 aqueous solutions. The orthorhombic perovskite phases of LaFeO3 and CaxLa1−xFeO3 are characterized by X-ray diffraction patterns. The sensors fabricated with those powders have high sensitivity to alcohol. Partial substitution of La3+ in LaFeO3 with Ca2+ can enhance the sensitivity of the materials to reducing gases. The resistance of an LaFeO3 sensor in air, vacuum and alcohol-containing air has been measured. Complex impedance spectroscopy has been used to try and analyse the gas-sensing mechanism. According to the experimental results, it can be deduced that the surface adsorptive and lattice oxygen govern the sensing properties of LaFeO3 and CaxLa1−xFeO3 ceramics.
In this paper, the structure of SnO2 thin films doped with Pd, Sb, Pt and In, especially the effects of dopants on the electronic structure of SnO2 were studied by XPS and TEM. It was observed that the dopants not only changed the Fermi level but also influenced the distribution of electron state density (DESD) of Sn4d valence band. We also studied the electronic structure change of the doped SnO2 after H2 adsorption.
This paper reports the development of a methane analyser, which meets some of the requirements of a reliable domestic methane detector. The equipment is based on a five-element array that includes four tin oxide gas sensors and a humidity sensor. The pattern recognition engine is based on multilayer perceptron (MLP) neural networks trained with the back-propagation algorithm. Both static and dynamic signals from the sensors are fed into the neural networks to identify and quantify methane and ethanol. The system identifies and quantifies unknown samples of these contaminants, even when the ambient relative humidity varies broadly (from 25% to 80%). As a result, the equipment detects methane, rejects false alarms caused by ethanol and complies with some aspects of the European directive for domestic methane detectors.
It is demonstrated that the sensing characteristics of a semiconductor gas sensor using SnO2 can be improved by controlling fundamental factors which affect its receptor and transducer functions. The transducer function is deeply related with the microstructure of the elements, i.e., the grain size of SnO2 (D) and the depth of the surface space-charge layer (L). The sensitivity is drastically promoted when D is made comparable to or less than 2L, either by control of D for pure SnO2 elements or by control of the Debye length for impurity-doped elements. On the other hand, the receptor function is drastically modified by the introduction of foreign receptors on the surface of SnO2. In the particular cases of Pd and Ag promoters, the oxides (PdO and Ag2O) formed in air interact with the SnO2 surface to produce an electron-deficient space-charge layer, and this contributes much to promoting the gas sensitivity. For a test gas having a specific reactivity, such specificity can be utilized for exploiting gas-selective receptors, as exemplified by CuOSnO2 and La2O3SnO2 elements, which detect H2S and ethanol gas respectively very sensitively.
Gas sensing properties and mechanism of Ca x La 1−x FeO 3 ceramics
- L Kong
- Y S Shen
L. Kong, Y.S. Shen, Gas sensing properties and mechanism of
Ca x La 1−x FeO 3 ceramics, Sens. Actuators B Chem. 30 (1996) 217-221.
Electrical apparatus for detection of combustible gases in domestic premises
CENELEC, Electrical apparatus for detection of combustible gases
in domestic premises, Ref. No. prEN 50194: 1996E.
Preparation of -Fe 2 O 3 by the hydrazine method. Application as an alcohol sensor
- C V Reddy
- K Seela
- S V Manorama
C.V. Gopal Reddy, K. Kalyana Seela, S.V. Manorama, Preparation of
-Fe 2 O 3 by the hydrazine method. Application as an alcohol sensor,
Int. J. Inorg. Mater. 2 (2000) 301-307.
Preparation of χ-Fe2O3 by the hydrazine method. Application as an alcohol sensor
- Gopal Reddy