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Electron beam evaporated carbon nanotube dispersed SnO2 thin film gas sensor
Abstract
Carbon nanotube (CNT) is a useful material for gas-sensing applications because of its high surface to volume ratio structure.
In this work, multi-wall CNTs are incorporated into tin oxide thin film by means of powder mixing and electron beam evaporation
and the enhancement of gas-sensing properties is presented. The CNTs were combined with SnO2powder with varying concentration in the range of 0.25–5% by weight and electron beam evaporated onto glass substrates. From
AFM and TEM characterization, CNT inclusion in SnO2thin film results in the production of circular cone protrusions of CNT clusters or single tube coated with SnO2layer. Experimental results indicate that the sensitivity to ethanol of SnO2thin film increases by the factors of 3 to 7, and the response time and recovery time were reduced by the factors of 2 or
more with CNT inclusion. However, if the CNT concentration is too high, the sensitivity is decreased. Moreover, the CNT doped
film can operate with good sensitivity and stability at a relatively low temperature of 250–300∘C. The improved gas-sensing properties should be attributed to the increasing of surface adsorption area of metal oxide produced
by CNT protrusion.
... This synthesis is done in an autoclave in which the concentration of the solution, the time, and the temperature of the reaction are controlled [48]. Solvothermal [49], pulse laser deposition (PLD) [50], atomic layer deposition (ALD) [51], RF sputtering [52], thermal evaporation [53], E-beam evaporation [54], electrospinning [55], the facile solution method [56], sol-gel [57], and chemical vapor deposition (CVD) [58] are also employed for the synthesis of metal oxide nanostructure films. SnO 2 is a widely researched n-type metal oxide material that can be applied in many practical commercial devices. ...
... the reaction are controlled [48]. Solvothermal [49], pulse laser deposition (PLD) [50], atomic layer deposition (ALD) [51], RF sputtering [52], thermal evaporation [53], E-beam evaporation [54], electrospinning [55], the facile solution method [56], sol-gel [57], and chemical vapor deposition (CVD) [58] are also employed for the synthesis of metal oxide nanostructure films. ...
Atmospheric pollution has become a critical problem for modern society; therefore, the research in this area continually aims to develop a high-performance gas sensor for health care and environmental safety. Researchers have made a significant contribution in this field by developing highly sensitive sensor-based novel selective materials. The aim of this article is to review recent developments and progress in the selective and sensitive detection of environmentally toxic gases. Different classifications of gas sensor devices are discussed based on their structure, the materials used, and their properties. The mechanisms of the sensing devices, identified by measuring the change in physical property using adsorption/desorption processes as well as chemical reactions on the gas-sensitive material surface, are also discussed. Additionally, the article presents a comprehensive review of the different morphologies and dimensions of mixed heterostructure, multilayered heterostructure, composite, core-shell, hollow heterostructure, and decorated heterostructure, which tune the gas-sensing properties towards hazardous gases. The article investigates in detail the growth and interface properties, concentrating on the material configurations that could be employed to prepare nanomaterials for commercial gas-sensing devices.
... Les résultats montrent d'une part une amélioration de la sensibilité des capteurs MWNTs/SnO 2 par rapport aux capteurs à base de SnO 2 seuls et d'autre part l'importance de la teneur en nanotubes dans les couches hybrides. Van Hieu et al. [86] Wisitoraat et al. [87] Wei et al. [88] Espinosa et al. [87] Bittencourt et al. [89] Balàzsi et al. [30] Liu et al. [95] I. 5 ...
... Les résultats montrent d'une part une amélioration de la sensibilité des capteurs MWNTs/SnO 2 par rapport aux capteurs à base de SnO 2 seuls et d'autre part l'importance de la teneur en nanotubes dans les couches hybrides. Van Hieu et al. [86] Wisitoraat et al. [87] Wei et al. [88] Espinosa et al. [87] Bittencourt et al. [89] Balàzsi et al. [30] Liu et al. [95] I. 5 ...
L’objectif de cette étude est le développement d’un capteur de gaz à base de couche hybrideSnO2/SWNTs dans le but d’améliorer les performances des capteurs chimiques « classiques »uniquement constitués de dioxyde d’étain. En premier lieu, afin de maîtriser la synthèse dumatériau sensible, nous avons validé l’élaboration d’une couche sensible à base de dioxyded’étain préparée par procédé sol-gel. Le matériau synthétisé a été déposé par la technique ‘microgoutte’sur une micro-plateforme permettant simultanément le chauffage de la couche sensible etla mesure de sa conductance. L’étude des réponses électriques du capteur de gaz en présence dubenzène a permis de valider la possibilité d’utilisation du sol d’étain préparé pour la réalisation decouches sensibles aux gaz. En effet, des traces de benzène (500 ppb) ont été détectées à latempérature optimale de couche sensible de 420°C.Le second volet de cette étude repose sur la fabrication du matériau hybride obtenu par dispersiondes nanotubes de carbone dans un sol d’étain. Les couches sensibles élaborées par dip-coating àpartir du sol d’étain modifié par les nanotubes de carbone ont clairement montré la possibilité dedétection de divers gaz (ozone et ammoniac) à température ambiante. Ce résultat constitue l’undes points importants de ce travail de thèse dans la mesure où jusqu’à présent les capteurschimiques à base de dioxyde d’étain ne présentaient une forte sensibilité aux gaz que pour destempératures de fonctionnement de l’ordre de 350-400°C. Pour les deux gaz cibles étudiés dans lecadre de ce travail, la limite de détection à température ambiante a été évaluée à 1 ppm enprésence de NH3 et est inférieure à 20 ppb en présence d’ozone.La dernière partie de ce travail a porté sur l’optimisation des performances de détection descouches hybrides. Dans ce cadre, les expérimentations ont porté sur l’étude de l’influence dedivers paramètres tels que la quantité de nanotubes dans le matériau hybride, la température decalcination de la couche sensible, la température de fonctionnement ou encore les propriétésphysico-chimiques des nanotubes de carbone (mode de synthèse, diamètre,…) sur l’efficacité dedétection des couches sensibles. Les résultats ainsi obtenus en termes de performance de détectionont été discutés en relation avec les paramètres expérimentaux utilisés.
... As it was mentioned above, combination of metal oxides and CNTs has been recently used as a material for manufacture of semiconductor gas sensors, lithium-ion batteries and catalysts [72][73][74][75][76][77][78][79]. Gas sensors can be realized on the base of SnO 2 /CNTs, TiO 2 /CNTs, Fe 2 O 3 / CNTs, WO 3 /CNTs and Co 3 O 4 /CNTs composites. ...
... Gas sensors can be realized on the base of SnO 2 /CNTs, TiO 2 /CNTs, Fe 2 O 3 / CNTs, WO 3 /CNTs and Co 3 O 4 /CNTs composites. [77][78][79]. For example, the NH 3 gas sensors based only on CNTs [80,81] and SnO 2 [82][83][84][85][86] have been extensively investigated. ...
Gas sensors made of carbon nanotubes without their doping and functionalization have serious shortcomings. Analysis of physics and technics of functionalization of carbon nanotubes by organic polymers, impurities, metalic nanoparticles/nanoclusters and use of nanotube in metaloxide nanocomposites for realization of detectors of different important gases with dramatically improved response, better time characteristics and smaller consumed power is carried out.
... On the other hand, the composite based sensors (e.g. SnO 2 /CNT) operating at room temperatures is expensive as their fabrication needs sophisticated instruments and expertise [22][23][24][25][26][27]. However, metal oxide sensors are inexpensive, have long term stability and can be efficient room *Address correspondence to this author at the Department of Nanotechnology, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad 431004, Maharashtra, India; Tel: +91-9730283381, +91-240-2403254; +91-240-2403284; E-mail: anighule@gamil.com ...
... SnO 2 is one of the promising metal oxide semiconductor gas sensing materials with sensible gas response to numerous varieties of poisonous gases and organic vapours [31][32][33][34][35][36][37][38][39][40]. Specifically, SnO 2 -based gas sensors can detect NH 3 gas with good sensitivity and response-recovery time [26,41,42]. A variety of ways for the preparation of SnO 2 nanoparticles have been proposed viz. ...
Tin oxide (SnO2) nanoparticles are prepared by simple and cost-effective biosynthesis method, wherein, tin chloride (SnCl4) reacts with Bengal gram bean (Cicer arietinum L.) extract. The assynthesized SnO2 nanoparticles were coated onto the glass substrates using doctor blade method to form thin films. The films were further annealed at 250 degrees C and used for characterization and gas sensing applications. Alternatively, the SnO2 nanoparticles were biosynthesized using carbohydrate (starch) and also by chemical precipitation method. A comparative study of structural and morphological properties of chemical and biosynthesized SnO2 nanoparticles is also carried out. Further, room temperature ammonia gas sensing properties of the biosynthesized SnO2 nanoparticles thin films are studied.
... CNTs electric properties are altered by adsorption of gaseous molecules onto the surface and become enabled to act as gas sensors [12]. Improvement of sensing properties by adding functionalized CNTs to SnO 2 have been reported in various studies [12][13][14][15]. ...
... 0.25-5.0 wt% MWCNTs incorporated into tin oxide thin films have increased the specific surface areas of the samples and improved sensors responses to ethanol [15]. Carbon nanotubes added to alpha-Fe 2 O 3 gas sensors have shown enhanced selectivity and gas sensing properties [16]. ...
Multiwall carbon nanotubes (MWCNTs)/SnO2 nanocomposites were synthesized by ultrasonic-assisted deposition–precipitation method and used for detection of acetone in the same range of concentrations as in diabetes mellitus breath. The nanocomposite samples were characterized by BET, FE-SEM, XRD and TEM. MWCNTs with an average size of about 60 nm are coated with and uniformly dispersed in 5–10 nm SnO2 nanoparticles matrix. To diagnose diabetes, the sensors responses to ppm concentrations of acetone were measured in a flow system at various temperatures and 85% relative humidity. Addition of MWCNTs dramatically enhances the sensors response to acetone. Moreover, the sensors response to ethanol, as an interfering species with acetone in human breath, was also measured. Breath humidity increases the conductivity of the sensing materials and therefore, lowers the sensors response to acetone.
... 0.5 and 1 wt% CNTs) were E-beam evaporated over interdigitated electrode through another electroplated shadow mask with square window pattern aligned to interdigitated area. The deposition rate and ion source parameters including ion driving voltage, and ion flux current were based on previous studies by A. Wisitsoraat et al. [9,10]. The film thickness of sensing materials is ~300 nm. ...
... Nevertheless, if CNT amount exceed, the gas sensitivity will be reduced because the CNTs begin to connect together and result in shorter resistance path. The gas-sensing current of the metal oxide layer is shunted [9]. ...
In this paper, a mobile electronic nose (E-nose) based on novel hybrid carbon nanotube-SnO2 gas sensors is described. The instrument combines new feature extraction techniques including integral and primary derivative, which leads to higher classification performance comparing with the classical features ( Delta R and Delta R/R0). The results show that doping of carbon nanotube (CNT) improves the sensitivity of hybrid gas sensors while quantity of CNT has a direct effect on selectivity to volatile organic compounds, i.e. MeOH and EtOH. The real-world applications of this E-nose were also presented. Based on the proposed methods, this instrument can monitor and classify 1% vol. of MeOH contamination in whiskey.
... Recent developments in nanotechnology have helped considerably in achieving these objectives. Mainly, metal-oxides [1], conducting polymers [2], carbon nanotubes (CNTs) [3][4][5][6][7][8][9][10][11] and their composites [12][13][14] have been tried for chemical sensing applications. Metal-oxide based sensors have been known for a long time. ...
... and polymers [12][13][14]. Thus, technological hurdle imposed by the difficulty in obtaining pure SWNTs of desired geometry and the long recovery time are the challenges still to be met on the way of development of effective gas sensors based on carbon nanotubes. ...
The objective of the present study is to investigate temperature and chemical sensitivity of carbon nanofilms made on diamond surface by high temperature surface modification followed by plasma treatment. The carbon nanofilms made this way were characterized by electrical measurements, Raman spectroscopy and atomic force microscopy. The nanofilms were found amorphous in nature. They showed significant sensitivity of their electrical conductance to temperature and exposure to vapors of different organic compounds. The fast response and recovery of the conductance make the carbon nanofilms on diamond substrates promising for development of all-carbon chemical sensors which could be suitable for biological and medical applications.
... Green synthesis is defined as the use of environmentally compatible materials such as bacteria, fungi and plants in the synthesis of nanoparticles [1] . These green and economical strategies are free of the short falls associated with conventional synthetic strategies, i.e. they are environment-friendly [2,3] . We have synthesized a carbon dot compositor with SnO 2 nanoparticles by green preparation method and gas sensors are widely used in hydrothermal processing [4] . ...
SnO 2 /Carbon Quantum Dots (CQDs) were synthesized by a hydrothermal method using grape fruit juice. The nanocomposites (NC) were characterized by means of XRD and Gas sensing properties. The sensor devices were fabricated using SnO 2 /CQDs NC as sensing materials. The effect of the CQDs content on the gas-sensing responses and the gas-sensing selectivity was investigated. In this work, the gas sensor developed is exposed to carbon monoxide polluting gas like at different temperatures to determine the optimum operating temperatures which allow obtaining the highest sensitivity for gas.
... Green synthesis is defined as the use of environmentally compatible materials such as bacteria, fungi and plants in the synthesis of nanoparticles [1] . These green and economical strategies are free of the short falls associated with conventional synthetic strategies, i.e. they are environment-friendly [2,3] . We have synthesized a carbon dot compositor with SnO 2 nanoparticles by green preparation method and gas sensors are widely used in hydrothermal processing [4] . ...
SnO2/Carbon Quantum Dots (CQDs) were synthesized by a hydrothermal method using grape fruit juice. The nanocomposites (NC) were characterized by means of XRD and Gas sensing properties. The sensor devices were fabricated using SnO2/CQDs NC as sensing materials. The effect of the CQDs content on the gas-sensing responses and the gas-sensing selectivity was investigated. In this work, the gas sensor developed is exposed to carbon monoxide polluting gas like at different temperatures to determine the optimum operating temperatures which allow obtaining the highest sensitivity for gas. Keywords: Green synthesis, Grape fruit, SnO2 nanoparticles, CQDs, Gas sensor.
... Stability can be increased by calcinations and annealing as post-processing treatment and also by lowering the working temperature of the sensor. Besides this, the doping of metal particles as well as the synthesis of mixed oxides can also increase stability which is reported in [104,105]. Mani et al. [106] presented the long term stability of 60 days for Ni-doped ZnO thin films not only in air but also towards 500 ppm of ammonia as compared to pure ZnO. Jain et al. [107] reported the sensing capability of CuCO 2 O 4 (CCO) towards ammonia gas and observed that there is a slight gradual drop in the response over the first couple of days, but the response remains relatively constant over the period of 15 days. ...
This review paper encompasses a study of metal-oxide and their composite based gas sensors used for the detection of ammonia (NH3) gas. Metal-oxide has come into view as an encouraging choice in the gas sensor industry. This review paper focuses on the ammonia sensing principle of the metal oxides. It also includes various approaches adopted for increasing the gas sensitivity of metal-oxide sensors. Increasing the sensitivity of the ammonia gas sensor includes size effects and doping by metal or other metal oxides which will change the microstructure and morphology of the metal oxides. Different parameters that affect the performances like sensitivity, stability, and selectivity of gas sensors are discussed in this paper. Performances of the most operated metal oxides with strengths and limitations in ammonia gas sensing application are reviewed. The challenges for the development of high sensitive and selective ammonia gas sensor are also discussed.
... These CNT-based nanocomposites have several important applications in chemical sensors, biological systems, and energy storage devices [27][28][29]. Previously, combination of CNT and ZnO has been reported to improve the sensing properties [30][31][32][33][34]. Herein, we would like to report the preparation of a new ZnO-functionalized multiwall carbon nanotubes nanocomposite employing it as a NO x sensor for the first time. ...
Synthesis of nano-zinc oxide-oxidized multiwall carbon nanotubes (ZnO-OMWCNTs) nanocomposite with different weight percentages of OMWCNTs via a multistep procedure has been described. The structure of this newly synthesized ZnO-OMWCNT was fully characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and Fourier-transform infrared (FT-IR) techniques. In this research, nano-ZnO-OMWCNTs with different weight percentages of oxidized multiwall carbon nanotubes (X = 0, 0.1, 0.5, 1, and 2 wt%) were prepared. Alumina substrate with gold electrodes was labeled by sputtering, and then, the nanocomposite was deposited using spin coating machine. The sensor efficiency of nano-ZnO-OMWCNTs as recyclable nanosensor was explored in probe of nitrous oxide (NOx) gas at the concentration of 20–40 ppm NOx and evaluated at different temperatures (150–300 °C). Detection of NOx gas by ZnO-OMWCNTs sensor was studied under different experimental conditions, and the results were compared by previous studies with ZnO and another metal oxide. The results show that the responsiveness, detection range, and optimum temperature of ZnO-OMWCNTs sensor performance at 250 °C were improved compared to other works. Also, adding 1 wt% of multiwall carbon nanotubes functionalized (FMWCNT) leads to an increase in sensitivity and reduces the operating temperature to 150 °C.
... 27 In this chapter, we are specifically interested in the hybridized MOX gas sensors based on MOX and carbon nanotube (CNT) composites. 28,29 For more information about the modification of the MOXs with other additives, other chapters in this book or the current reference section should be consulted. 30 MOXs are a very robust technology mostly adopted commercially for semiconductor gas sensors. ...
... As a consequence, the local electric field favorable for the gas-sensing reaction is improved. According to Wisitsoraat, the sensing mechanism is connected with an increase in the surface area due to the formation of CNT protrusions [33]. The authors of study [11] propose that the enhancement effect is attributed to the nanochannels formed by CNTs embedded in MOX. ...
The aim of the study was to present the possibility of the sensitivity improvement of the electronic nose (e-nose) and to summarize the detection mechanisms of trace gas concentrations. Our main area of interest is graphene, however, for the better understanding of the sensing mechanisms, it is crucial to review other sensors of similar functions. On the basis of our previous research, we explained the detection mechanism which may stay behind the graphene sensor's sensitivity improvement. We proposed a qualitative interpretation of detection mechanisms in graphene based on the theory regarding the influence of metals and substituents on the electronic systems of carbon rings and heterocyclic aromatic ligands. The analysis of detection mechanisms suggests that an increase of the electronic density in graphene by attaching a substituent and stabilization of electronic charge distribution leads to the increase of graphene sensor conductivity. The complexation of porphyrins with selected metals stabilizes the electronic system and increases the sensitivity and selectivity of porphyrin-based sensors. Our research summary and proposed conclusions allow us to better understand the mechanisms of a radical change of graphene conductivity in the presence of trace amounts of various gases.
... It has been realized that special geometries and properties of the hybrid materials offer great potential applications as high performance gas-sensor devices. Previous works have demonstrated that the hybrid materials can be used to detect various gases such as NH 3 , NO 2 , H 2 , CO, LPG, and Ethanol [7][8][9][10][11][12]. These works also reported that the hybrid gas sensors have a better performance compared to SMO-as well as ...
Recently, novel materials such as semiconductor metal oxide (SMO) nanowires (NWs), carbon nanotubes (CNTs), and hybrid materials SMO/CNTs have been attractively received attention for gas sensing applications. These materials are potential candidates for improving the well known “3S”: Sensitivity, Selectivity and Stability. In this article, we describe our recent studies on synthesis and characterizations of nanomaterials for gas-sensing applications. The focused topics include are: (i) various system of hybrid materials made CNTs and SMO; and (ii) quasi-one-dimension (Q1D) nanostructure of SMO materials. The synthesis, characterizations and gas-sensing properties are deal thoroughly. Gas-sensing mechanism of those materials, possibility producing new novel materials and other novel applications are also discussed
... The authors concluded that a higher sensing behavior originated from a common interface with CNTs, since the morphology and surface area of the hybrid sensors were similar to those of the pure SnO 2 and the observed sensitivities increased with increasing CNT loading. Wisitsoraat et al. [28] reported that electron beam evaporation of a powder mixture of (multi-wall) MWCNTs and SnO 2 could enhance the ethanol sensing via an increase in the surface area of SnO 2 . Espinosa et al. [29] reported that the pure WO 3 sensors, which are insensitive to NO 2 at Fig. 1. ...
This review focuses on the recent developments of carbon/metal oxide hybrids for gas and biological sensing, which is one of the most important fields where these hybrids are efficiently applied. Carbon and metal oxides are excellent complementary materials: in hybrids, they compensate for the shortcomings of the single components and their combination creates new advantageous features. Intensive research has advanced the understanding of these materials, however, the complex array of possible carbon nanostructure shapes and different metal oxides present many unexplored areas. Current results are already exciting and promise even bigger improvements in sensing. We introduces the recent progress in this field and the key advantages of some nanostructures over each counterpart are discussed and compared, presenting examples and emphasizing the most promising routes.
... Combinations of metal oxides and CNTs have been recently used as a material for manufacture of semiconductor gas sensors, lithium-ion batteries and catalysts [47][48][49][50][51][52][53][54]. Gas sensors can be realized on the base of SnO 2 /CNTs, TiO 2 /CNTs, Fe 2 O 3 /CNT, WO 3 /CNT and Co 3 O 4 /CNT composites. ...
Gas sensors made from carbon nanotubes without their doping and functionalization have serious shortcomings. Analysis of physics and techniques of decoration (functionalization) of carbon nanotubes using organic polymers, doping with impurities, metallic nanoparticle/nanoclusters is carried out. The development of metal oxide nanocomposite sensors decorated with carbon nanotubes is very promising for realization of detectors of different important gases with dramatically improved response, better time characteristics and smaller consumed power.
... 27 In this chapter, we are specifically interested in the hybridized MOX gas sensors based on MOX and CNT composites. 28,29 For more information about the modifi cation of the MOXs with other additives, other chapters in this book or the references should be consulted. 30 AQ1 AQ2 AQ3 11_p386-407.indd ...
This chapter discusses nanocomposites based on carbon nanotubes (CNTs) and metal oxides (MOX) for gas sensing applications. The chapter first reviews the historical background of the MOX and the hybridized MOX/CNT composite gas sensors. It then describes several popular methods for preparation of MOX/CNT sensing films such as spin-coating, drop-coating, screen-printing, dip-coating, and electron beam evaporation techniques. The ways to characterize MOX/CNT materials with their basic theories including raman spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy have been presented. Finally, the sensing mechanism of a MOX/CNT gas sensor based on p-n heterojunctions has been highlighted.
... The preparation of composite materials containing CNTs and TiO 2 in the previous hydrogen storage studies reported by Mishra et al. [24] and Rather et al. [25] involved chemical vapor deposition and ultrasonication respectively. Reports by Wisitsoraat et al. [32] and Madhusudhana and Chanodrkar [33] have demonstrated that the structure of CNTs does not undergo any deformation while its deposition (MWCNT-SnO 2 , MWCNT-WO 3 ) using electron beam (EB) evaporation technique. Hence, the present study focusses on the investigation of hydrogen storage in single walled carbon nanotubestitanium dioxide (SWCNTs-TiO 2 ) composite prepared by EB evaporation technique. ...
The composite material made up of carbon nanotubes (CNTs) and metal oxide nanostructures have been investigated for hydrogen storage application. The present experimental work deals with the investigation of hydrogen storage in single walled carbon nanotubes-titanium dioxide (SWCNTs-TiO2) composite. The SWCNTs-TiO2 composite has been made by depositing the pellet containing the mixture of SWCNTs and TiO2 using electron beam (EB) evaporation technique in hydrogen ambient. The preparation and hydrogenation of the SWCNTs-TiO2 composite have been done in a single-step. The characterization results expose that the deposition of SWCNTs with TiO2 material is possible using EB evaporation technique without any significant structural decomposition of SWCNTs. The amount of hydrogen incorporated is found to be 3.2 wt.%, and it is attributed to both the synergetic action of SWCNTs-TiO2 nanostructures and the method of preparation. The stored hydrogen is found to be released completely in the temperature range of 120-215 degrees C. Copyright
... Furthermore, single-crystalline SnO 2 NWs (100-150 m in length, 16-60 nm in diameter) synthesized by chemical vapor deposition (CVD) at 800 • C offered excellent performances with high selectivity and short response time to ethanol vapor and H 2 S at 320 • C [41]. From these studies, 1D SnO 2 nanostructures such as NWs, nanobelts, nanorods and other special 1D nanostructures are considered to be highly promising for gas sensing because of superior performances, which may be attributed to higher effective surface-to-volume ratio and single crystalline properties [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. However, common synthesis methods of 1D SnO 2 nanostructures including thermal evaporation [31,36,37,39], CVD [33,40], sol-gel [34] and DC-sputtering [35] have some particular disadvantages such as poor control of nanostructures, metal catalyst contamination, expensive instrumentation, complicated synthesis process and high processing temperature. ...
... Most of the recent studies on CNT/SnO 2 composite hybrid sensors were based on their response towards ethanol, methanol, H 2 S, NO 2 and NH 3 gases [25,26]. However, there are no reports on the response of such CNT-SnO 2 composite sensors towards H 2 . ...
Nanosized SnO2/carbon nanotube composite gas sensing material has been synthesized by a wet chemical method. The gas sensing studies were performed against a wide range of concentration of hydrogen gas. The sensing performance of the composite was compared with the bulk tin oxide nanoparticles and pure CNT. At 200 degrees C, 0.1% CNT/SnO2 composite sensor exhibited 84% sensitivity against 4% hydrogen gas with a relatively low recovery time of 120 s. It has been demonstrated that SnO2/CNT composite sensor is highly suitable for sensing hydrogen gas at comparatively lower operating temperatures and has the ability to arrest the effect of moisture, by which the stability of the sensors are enhanced markedly, in spite of the lower operating temperatures.
... Wei et al. [4] reported that a hybrid of SnO 2 /SWNTs revealed an enhanced sensitivity for NO 2 . Wisitsoraat et al. [5] reported that electron beam evaporation of a powder mixture of MWNTs and SnO 2 can enhance the ethanol sensing via an increase in the surface area of SnO 2 . Composite nanobers of MWNTs and tin oxide were synthesized by electrospinning and were subsequently calcined in air for CO gas sensor application [6]. ...
We introduce a simple method to synthesize one-dimensional tin-oxide-coated single-wall carbon nanotubes (SWNTs) for gas sensor applications The SWNTs are synthesized directly on a Sio 2/Si substrate with comb-type electrodes via the arc-discharge method. Metallic Sn thin layers with various thicknesses are deposited over the grown SWNTs. After that. a rheotaxial and thermal oxidation is performed to spread and convert the tin metal on the surfaces of the SWNTs into tin oxide. The electrical and the NO Xgas sensing properties of the sensor devices are then investigated. The as-grown SWNTs sensor exhibited a p-type semiconducting property whereas the tin-oxide-coated SWNTs exhibited an n-type semiconducting property. Moreover.the one-dimensional tin-oxidecoated SWNTs sensor exhibited a higher sensitivity than the pure SWNTs sensor.
... The preparation methods for CNT-inorganic hybrid materials can be divided into two classes: vacuum technique [6,9] and wet solution methods [10][11][12][13]. These methods, however, usually incur high costs because of complicated processing and costly equipment during from device fabrication, especially for producing high vacuum [6] and high pressure [12,13] conditions. ...
This chapter provides an overview of nano metal oxide as nanosensors in agriculture and the environment. Sensors are used at all stages of the life cycle of agricultural products. They are used in preparatory and growth stages, control of soil, water, air, and feed, and control of various auxiliary stages. Currently, the development of new sensors with improved characteristics is an urgent task. Modern sensors are a variety of nanostructured organic, inorganic, and combined materials. The most significant numbers of sensors presented in the literature and used in agriculture are organic. In this chapter, only nano metal oxide as nanosensor is considered, including the analysis of used metal oxides, methods of their synthesis. A wide range of examples of the use of nano metal oxide nanosensors are presented in agriculture and environmental monitoring.
Carbon nanomaterials have gained significant attention for numerous applications. Their outstanding physical and chemical properties have triggered substantial research to evaluate their potential as gas sensing materials. Herein, we present an overview discussing the recent progress in the utilization of carbon nanomaterials and their composites in gas sensing devices. The sensing mechanism, design, and preparation techniques of such sensors are introduced. The modification of the carbon-based nanostructure with other nanomaterials and its effect on the sensing performance is also discussed. Finally, the existing challenges facing the practical application are presented, together with some possible improvement opportunities for future work.
Hydrogen sulfide (H2S) is a poisonous gas and corrosive with a characteristic rotten egg smell. Exposure to a higher concentration of H2S gas leads to death. Research groups across the globe have been working on developing a gas sensor composed of novel sensing materials to monitor deadly H2S gas for over a decade. Carbon-based materials such as single-wall carbon nanotubes, multi-wall carbon nanotubes, graphene, and graphene derivatives have been incorporated with metal oxides to improve H2S gas sensing properties. Carbon-based composites have unique physicochemical properties which provide the sensor possessing superior sensitivity, selectivity, stability, quick response time, etc. This review highlights the importance of H2S sensors based on rGO/MOx and CNT/MOx, their enhanced sensitivity and selectivity to H2S.
Due to the confinement effect, nanotubes (NTs) are believed to be a highly promising platform for gas detection. In this work, combining density functional theory calculations with non-equilibrium Green's-function-based simulations, we systematically investigate the sensing performance of SnOX (X = S, Se) NTs toward NH3, NO, and NO2. Our results reveal that the novel SnOX NTs with a built-in electric field have ultrahigh stability and can be spontaneously formed from their monolayer counterparts. NH3 can be chemically captured by the inner side of the tube with moderate bonding strength. Combining this with a short recovery time and high sensitivity, SnOX NTs are believed to be a promising platform for sensing NH3. In contrast, NO and NO2 both interact physically with the NTs, and their different interaction mechanisms, i.e., electrostatic interactions and dipole-dipole interactions, account for the different sensing behavior. Due to the obvious perturbation of their electronic properties and ultrafast recovery time, SnOX NTs show high sensitivity toward NO2. However, due to the relatively weak interactions and relatively lower perturbation of their electronic properties, SnOX NTs show weak sensitivity toward sensing NO. The intrinsic dipole of the NTs is found to play different roles in detecting these N-containing polar gases. Transport calculations further verify that the SnOSe NTs are the most promising materials for sensing NH3 and NO2. Our results may provide a new idea for the artificial control and tailoring of the sensing performance based on the intrinsic dipole of the NTs.
The emergence of two-dimensional (2D) materials enables enormous progress in the development of high-performance chemical sensors facilitating exotic structural and material properties. In this review, we focus on the rational design and synthesis strategies of various 2D metal oxide-based for chemiresistive gas sensors. We first discuss various synthesis strategies for 2D metal oxides such as thin-film manufacturing, exfoliation of layered metal oxides, templating route using sacrificial layer, and template-free synthesis route to elucidate the basic design principles of metal oxide nanosheets both from the top-down and bottom-up perspectives and their efficacy toward gas sensing applications. Then, we discuss assembly strategies of 2D metal oxide nanosheets for hierarchical and hybrid nanostructures with increased design complexity in terms of morphology and/or composition, which boosted their sensing performances. Finally, we conclude by providing an outlook of development in 2D metal oxides for realizing practical gas sensing devices. Through this article, not only did we elucidate the representative synthesis strategies for 2D metal oxides for applications in gas sensors, but we also provided a rich insight into their fundamental design principles to help propel the future development of high-performance gas sensors.Graphic abstract
Nowadays air pollution created by chemical gaseous pollutants becomes the major concern for the adverse effect on human health, plant or animal life, or the welfare of man. Thus miniaturized low-cost sensor device based on nanomaterials can be introduced for an observable signal, or warning bell may be set to control the pollution level of outdoor as well as indoor air. Exploring the present state-of-the-art inorganic, organic, or even hybrid nanomaterials used as receptor in chemical sensors to detect the pollutants in the air is briefly considered here.
This chapter presents the fundamental properties of polymer nanocomposites (PNCs) and their characteristics that play a significant role in deciding their capability for the advanced energy storage devices. The various synthesization methods used for the preparation of polymer electrolytes are described followed by the characterization techniques used for the analysis. The properties of the polymer host, salt, nanofiller, ionic liquid, plasticizer, and nanoclay–nanorod–nanowire are described. Various ion transport mechanisms with different nanoparticle dispersions in polymer electrolytes are highlighted. Various important results are summarized, and a pathway is built to fulfill the dream of the future renewable source of energy that is economical and environmental benign. Chapter motivation is focused on the investigation of the role of polymer host, aspect ratio, surface area, nanoparticle shape, and size in terms of boosting the electrolytic–electrochemical properties of PNC. It will certainly help in order to open new doors toward the development of advanced polymeric materials with overall balancing property for enhancement of the fast solid-state ionic conductor which would revolutionize the energy storage–conversion device technology.
Analysis of Denton E-Beam 2 Nanofabricated Thin Films by Metrology - Volume 25 Supplement - Ronald Reliford, Jafar F. Al-Sharab
This paper describes a simple, low cost and effective route to fabricate CNT-based chemical sensors, which operate at room temperature. Firstly, the incorporation of silk fibroin in vertically aligned CNT arrays (CNTA) obtained through a thermal chemical vapor deposition (CVD) method makes the direct removal of CNT arrays from substrates without any rigorous acid or sonication treatment feasible. Through a simple one-step in situ polymerization of anilines, the functionalization of CNT arrays with polyaniline (PANI) significantly improves the sensing performance of CNT-based chemical sensors in detecting ammonia (NH3) and hydrogen chloride (HCl) vapors. Chemically modified CNT arrays also show responses to organic vapors like menthol, ethyl acetate and acetone. Although the detection limits of chemically modified CNT-based chemical sensors are of the same orders of magnitudes reported in previous studies, these CNT-based chemical sensors show advantages of simplicity, low cost and energy efficiency in preparation and fabrication of devices. Additionally, a linear relationship between the relative sensitivity and concentration of analyte makes precise estimations on the concentrations of trace chemical vapors possible.
In this work, hydrogen storage property of single walled carbon nanotubes-tungsten trioxide (SWCNTs-WO3) composite is investigated. The composite is prepared and hydrogenated by electron beam (e-beam) evaporation technique. Hydrogenation is carried out during the preparation of the composite itself. The amount of hydrogen uptake by the composite is 2.7 wt%, which is due to the collective adsorption of hydrogen by CNTs and WO3 nanostructured materials, the method of preparation and hydrogenation involved. The incorporated hydrogen is completely (100%) released in the temperature range of 175-305 °C which in turn infers that the hydrogenated composite is stable at room temperature. The stored hydrogen has the average binding energy of 0.4 eV and the nature of binding is found to be weak chemisorption. Spillover mechanism is attributed for the hydrogen uptake of the composite.
Carbon nanotubes gas sensors are attracted more attentions for its exceptional properties of lower work temperature and detection limit. While the oxide semiconductor doping with carbon nanotubes gas sensors have the advantages both of carbon nanotubes gas sensors and oxide semiconductor gas sensors, such as higher sensitive, lower work temperature and detection limit. The progress and gas-sensing mechanism of this two kinds of gas sensors are introduced and summarized in this paper, and also the problems and developing tendency are pointed out.
Tin oxide nanoparticles are synthesized using solution combustion technique and tin oxide – carbon composite thick films are fabricated with amorphous carbon as well as carbon nanotubes
(CNTs). The x-ray diffraction, Raman spectroscopy and porosity measurements show that the as-synthesized nanoparticles are having rutile phase with average crystallite size ∼7 nm and ∼95 m2/g surface area. The difference between morphologies of the carbon
doped and CNT
doped SnO2 thick films, are characterized using scanning electron microscopy and transmission electron microscopy. The adsorption-desorption kinetics and transient response curves are analyzed using Langmuir isotherm curve fittings and modeled using power law of semiconductor gas sensors.
A La-doped SnO2 (La-SnO2) nano sol solution containing multi-wall carbon nanotubes (MWCNTs) was prepared by hydrothermal reaction and the gas sensing characteristics of the La-SnO2/MWCNT composite sensors were investigated at various heat treatment temperatures (HTTs). The MWCNTs were unaffected, partially decomposed, and completely decomposed by the heat treatment at 500, 600, and 700 degrees C in air, respectively. However, regardless of the HIT variation, the gas responses to C2H5OH al: 400 degrees C were increased 1.4-2.5 times by the addition of 0.1 wt% MWCNTs and the sensors showed selective detection to C2H5OH. The mechanisms for the enhancement of gas response are discussed in relation to the decomposition of MWCNTs and its consequent effect on the gas sensing reaction.
This paper reports electrochemical sensing of salbutamol, a prohibited drug in sports, with a new working electrode based on vertically aligned carbon nanotubes (V-CNT). V-CNTs were synthesized by chemical vapor deposition using acetylene and argon gases at 700 °C on gold coated silicon substrates. A simple electrochemical cell including V-CNTs, silver wire (Ag) and platinum (Pt) wire was designed. Electrochemical characterization by cyclic voltammetry (CV) was carried out with different salbutamol concentrations ranging from 10−7 to 10−4 mol·l−1. CV curves exhibited irreversible oxidation peak at ∼0.7 V. The current response was linear with sensitivity of 0.13 A/mol·l−1 and a minimum detection of 3 × 10−7 mol·l−1. In addition, its pharmaceutical applications were demonstrated. The direct analysis of salbutamol in pharmaceutical products yielded a good analytical feature with wide dynamic working range (0.5 to 100 M) and matrices' interference was found to be negligible. Thus, V-CNTs electrode is a potential candidate for the electrochemical detection of salbutamol.
In this work, CNTs–MoOx nanocomposite thin film is prepared by a new method based on powder mixing and electron beam evaporation. The CNT powder was thoroughly mixed with MoOx commercial powder by 0.5% wt. ratio and then evaporated on to silicon and alumina substrates by electron beam at a vacuum of 10–5 Torr. The surface and chemical structure of the materials were characterized by means of scanning electron microscopy, transmission electron microscopy and X-ray diffraction. Structural characterization showed that undoped MoOx and CNTs–MoOx nanocomposite thin films posses similar surface morphology and orthorhombic crystal structure and CNTs were incorporated in MoOx thin film in the form of small clusters uniformly dispersed within MoOx matrix. It was found from gas-sensing characterization that CNTs incorporation led to an order of magnitude decrease of electrical conductivity in the temperature range between 200–400 °C. The sensitivity to ethanol was found to considerably enhance by a factor of 3–6 with CNTs incorporation. The sensors exhibit maximized response of ∼115 to 1000 ppm of ethanol at 400 °C.
Nano-SnO2 flat-type coplanar 2-Methyl-2,4-pentanediol (MPD) gas sensor arrays were fabricated by a screen-printing technique based on nano-SnO2 powders prepared by a hydrothermal method. The results show that the fabricated gas sensor arrays have good MPD gas sensing characteristics, such as good selectivity and response-recovery characteristics. Especially, they can be used for detecting the concentration of MPD gas as low as 1 ppm which is much lower than the legal concentration of 20 ppm or 25 ppm. The good sensing properties indicate that the SnO2 gas sensor arrays have great potential for on-line or portable monitoring of MPD gas in practical environments.
This paper presents the results of study of the electrophysical and gas-sensitive properties of a SnO2-based film nanocomposite with the addition of multiwalled carbon nanotubes (to 7 wt %), produced by the hydrolysis of aqueous-alcoholic solutions of tin salts. The dependences of the free carrier mobility and concentration on the number of nanotubes in the composite, and the temperature dependences of the gas sensitivity to ethanol, acetone, and propanol vapors in air are studied. It is shown that the gas sensitivity of the nanocomposite containing ∼1.75 wt % of nanotubes is 10–15 times higher in comparison with that of the pure SnO2 film.
The present experimental work deals with the investigation of hydrogen uptake study of single-walled carbon nanotubes (SWCNTs-Ti)-titanium metal composite. The mixture containing SWCNTs and Ti powder is made into tablet by cold pressing. The composite has been prepared and hydrogenated by evaporating the tablet in hydrogen ambient on glass substrates using electron beam (EB) evaporation technique. Efficient hydrogen uptake of 4.74 wt.% is achieved with the composite and the adsorbed hydrogen posses the average hydrogen binding energy of 0.4 eV. The obtained hydrogen uptake is due to the cumulative adsorption of hydrogen by CNTs and Ti nanostructured materials. The physical properties are characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction study (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Raman analysis. Hydrogenation and dehydrogenation behavior of the composite are studied using CHN-elemental analysis and thermo gravimetric/thermal desorption spectroscopy (TG/TDS) studies, respectively. The stored hydrogen is found to be 100% reversible in the temperature range of 160-310 degrees C. Copyright
characterized by scanning electron microscopy and transmission electron microscopy. Various gases with variable concentrations were used to test the sensing properties and selectivity of the gas sensors at different operating temperatures. Based on the operating temperatures within a range of 350-400 DC, the Sn02 and W03 gas sensors were found to exhibit good response to alcohol and hydrogen, respectively. Doping CNT in Sn02 and W03 dramatically improves the sensitivity and selectivity of the gas sensors. Moreover, CNT can reduce the operating temperature (from around 350-400°C to 250°C) leading to reduction in power consumption which is one of the major problems for metal oxide gas sensor. The sensing mechanism of these gas sensors will be demonstrated.
A SnCl2 solution was used to prepare SnO2-coated multi-walled carbon nanotubes (SnO2/MWCNTs), and their hydrogen sensing properties at room temperature was studied. SEM and TEM observations indicate that SnO2 nanoparticles with a size of 5 nm are uniformly coated on the MWCNTs, forming a continuous SnO2 coating. The SnO2/MWCNTs are sensitive to 10-4 hydrogen at room temperature. During the sensing measurement at room temperature for 10-3 hydrogen mixed with argon gas, the current change with gas concentration is reversed after the mixed gas is switched to air. This can be ascribed to the reaction between O2 in air and residual H2 around the SnO2/MWCNTs to form adsorbed H2O and the subsequent desorption of H2O by substitution adsorption of O2 in air. The H2O adsorption may lead to a decrease of the electric resistance of SnO2/MWCNTs and thus an increase of current measured. The reversal of current implies that the SnO2/MWCNTs may possess a good sensitivity to humidity at room temperature.
Hydrogen intake study on single walled carbon nanotubes (SWCNTs)-tin oxide (SnO2) nano composite films have been performed. The composite is prepared on glass substrates in hydrogen atmosphere by electron beam evaporation (e-beam) technique. The process of hydrogenation has been done during the preparation of hydrogen storage medium itself, as one-step process. The amount of hydrogen incorporated in the composite is found to be 2.4 wt.%. The entire (100%) amount of stored hydrogen is released in the temperature range of 200–350 °C. The stored hydrogen has weak chemical binding in the SWCNTs-SnO2 nano composite.
Electronic carbon nanostructures have been fabricated on diamond substrates by focused ion beam (FIB) irradiation. Fabrication of planar nanowire/nanodot structures at a scale below 10 nm (e.g. all-carbon single electron transistor with island size of 7 nm) has been shown. FIB-written carbon nanostructures may reveal non-linear conductivity, current injection trough insulating diamond, bistability of current flow, and coulomb blockade at room temperature. Also we developed methods of fabrication of large uniform areas of amorphous carbon and/or graphene films on diamond and quartz substrates using combination of graphitization/CVD deposition/plasma etching processes. Arrays of carbon nanowires/nanodots, amorphous carbon films on diamond and graphene films on quartz have been shown to possess remarkable electronic properties and selective chemical sensitivity. A model of continuum carbon phase transitions has been developed to explain the experimental data. The problem of two-dimensional (2D) nucleation has been approached theoretically using the concept of escape time (phase-transition time) and direct computer simulations. It is shown that the transition state of graphite/diamond phase system gains thermodynamic stability in a closed nano-volume and, in case of 2D nucleation, there is a critical thickness above which the growing layer manifests the stable phase.
A kinetic theory combined with an effective medium theory in a nonlinear basis is used to compute the effective dielectric of single-walled carbon nanotubes (SWNTs) in the presence of gas molecules. The effect of the change of SWNT volume fraction on the response to gas molecules is investigated to find the optimum SWNTs embedded in the system. The computational results obtained show that the effective dielectric of the system increases explicitly with increasing dielectric and volume fraction of SWNTs. The effects of molecular adsorption on the effective dielectric of the system are also examined. This investigation showed that the effective dielectric of the system increases with increasing collision frequency and decreases with increasing electron density. This work is helpful for designing SWNT gas sensors.
Seit ihrer Entdeckung im Jahr 1991 haben Kohlenstoff-Nanoröhren ein riesiges Interesse erfahren. Grund ist ihr enormes Anwendungspotenzial, und Forscher unterschiedlicher Fachrichtungen arbeiten heute gemeinsam daran, die elektronische Struktur und das Reaktionsverhalten von Kohlenstoff-Nanoröhren aufzuklären. Da ihre elektronische Struktur leicht von wechselwirkenden Molekülen beeinflusst wird, reagieren Kohlenstoff-Nanoröhren extrem empfindlich auf Änderungen in der lokalen chemischen Umgebung. Dies macht sie zu idealen Kandidaten für den Einsatz in chemischen Sensoren, und es wurden bemerkenswerte Fortschritte bezüglich der Empfindlichkeit und chemischen Selektivität gegenüber einer Vielzahl chemischer Spezies erzielt. Trotz der zahlreichen Verbesserungen sind aber noch einige wichtige Probleme zu lösen, bevor Kohlenstoff-Nanoröhren mit den modernsten Feststoff-Sensormaterialien konkurrieren können. Die Entwicklung von Sensoren auf der Basis von Kohlenstoff-Nanoröhren befindet sich zwar noch im Anfangsstadium, aber bei weiteren Fortschritten erscheint ihre Integration in kommerziell tragfähige Sensoren, die sich dann durch eine konkurrenzlose Empfindlichkeit und außerordentlich kleine Abmessungen auszeichnen werden, möglich.
TiO2 and SnO2 are the well-known sensing materials with a good thermal stability of the former and a high sensitivity of the latter. Carbon nanotubes (CNTs) have also gas sensing ability at room temperature. CNTs-included SnO2/TiO2 material was a new exploration to combine the advantages of three kinds of materials for gas-sensing property. In this work, a uniform SnO2/TiO2 solution was prepared by the sol–gel process with the ratio 3:7 in mole. The CNTs with contents in the range of 0.001–0.5 wt% were dispersed in a mixed SnO2/TiO2 matrix by using an immersion-probe ultrasonic. The SnO2–TiO2 and the CNTs-included SnO2–TiO2 thin films were fabricated by the sol–gel spin-coating method over Pt-interdigitated electrode for gas-sensor device fabrication and they were heat treated at 500 °C for 30 min.FE-SEM and XRD characterizations indicated that the inclusion of CNTs did not affect the particle size as well as the morphology of the thin film. The sensing properties of all as-fabricated sensors were investigated with different ethanol concentrations and operating temperatures. An interesting sensing characteristic of mixed SnO2/TiO2 sensors was that there was a two-peak shape in the sensitivity versus operating temperature curve. At the region of low operating temperature (below 280 °C), the hybrid sensors show improvement of sensing property. This result gives a prospect of the stable gas sensors with working temperatures below 250 °C.
Ordered mesoporous SnO2 was prepared from sodium stannate by utilizing the self-assembly of a cationic surfactant (n-cetylpyridinium chloride (C16PyCl)) and its thermal stability was improved by the treatment with phosphoric acid (PA) prior to calcination. Under the most suitable preparation conditions, an ordered mesoporous structure ( nm) with a large specific surface area (ca. 305 m2 g−1) was obtained after calcination of the resultant solid product (having ordered mesopores of nm) at 600 °C for 5 h. The sensitivity of a thick film-type sensor (ca. 85 μm thick) fabricated with the mesoporous SnO2 to 500 ppm H2 (maximum sensitivity kM,H2=22.9 at 350 °C) was much higher than that to 500 ppm CO (kM,CO=3.72 at 450 °C). The H2 sensitivity of the mesoporous SnO2 sensor was superior to that of a conventional SnO2 sensor fabricated from tin oxalate, whereas the enhancement in H2 sensitivity due to the development of mesopores was not so remarkable in spite of the large specific surface area (ca. 305 m2 g−1) and small crystallite size (ca. 2 nm). The main reason for the unexpected low H2 sensitivity may arise from agglomeration of mesoporous SnO2 particles, i.e. the potential barrier height at the boundaries between agglomerated particles may be less-sensitive to H2, while that at grain boundaries of SnO2 crystallites is highly sensitive.
Electrical properties of the metallic oxide semiconductor, such as tungsten trioxide (WO3) thin films, deposited on SiO2/Si substrates by RF reactive magnetron sputtering system from a metallic tungsten target and argon–oxygen mixture gas have been investigated. This study is devoted to analyse the relationship between the electrical properties and the WO3 thin film deposition parameters (substrate temperature, oxygen partial pressure, annealing) and the sensitivity and stability of these WO3 gas sensors. The surface morphology evolution of these films has been investigated by atomic force spectroscopy (AFM). Two types of electrical measurements were performed: conductivity versus temperature and some tests under ozone at different temperatures. The activation energy evolution is correlated with the reactivity of surface sensors under oxygen partial pressure.
Structural and NO2 and H2S gas-sensing properties of nanocrystalline WO3 powders are analysed in this work. Sensor response of thick-film gas sensors was studied in dry and humid air. Interesting differences were found on the sensor response between sensors based on 400 and 700 °C-annealed WO3, what motivated a structural study of these materials. Crystalline structure and defects were characterised by X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). Experimental results showed that both triclinic and monoclinic structures are present in the analysed materials, although their amount depends on the annealing treatment. Crystalline shear planes, which are defects associated to oxygen deficient tungsten trioxide, were found in 400 °C-annealed WO3 and their influence on XRD spectra was analysed by XRD simulations. Moreover, XRD and Raman spectra were also acquired at normal metal oxide-based gas sensor working temperatures in order to relate both crystalline structure and sensor response.
The experimental results show, that the doping of the SnO2 thin films with molybdenum ions increases the sensor response to alcohols and downshifts the sensor operating temperature. The effect is caused by the formation of substitutional solid solution of molybdenum ions in the SnO2 crystal lattice with stabilized interstitial Mo(V) ions. The formation of Mo(V) ions proceeds by the capturing the conductivity electrons localized in the oxygen vacancies by nearest neighbor Mo(VI) ions and their shift from the regular positions into interstitials of the rutile-type SnO2 lattice, causing the decrease of the electric conductance. The enhancement of SnO2 sensitivity to alcohols in the presence of homogeneously distributed molybdenum additive is closely connected with the high catalytic activity of molybdenum ions in the reactions of oxidizing dehydration of alcohols. The reaction proceeds by the radical mechanism with the elimination of hydrogen form CH2-group in the alcohol molecule. Hydrogen generated by the reaction reduces the oxide surface and thus increases the sensor conductivity.
The Pd‐doped SnO 2 thin film detector for gaseous components has been developed, whose detection is based on the fact that the adsorption and desorption of gases cause the remarkable change in electrical resistivity of the semiconductor. This property of SnO 2 film is applicable to the preferential detector for gaseous components, especially ethanol gas. SnO 2 thin film was prepared on the polished ferrite substrate which SiO was precoated. Both the preparation and the precoating were done by vacuum deposition. Subsequently the oxidation for SnO 2 film in air was done at 500–550 °C for 30–60 min. The rise rate and fall rate of temperature were 2.5 and 1.7 °C/min, respectively. The thickness of SnO 2 film was about 0.3–0.35 μm.
Thin-film SnO2 gas sensors are fabricated using an electron-beam evaporation method at pre-optimized substrate temperatures and post-deposition heat-treatment temperature. The response of these sensors is studied for various operating temperatures and reducing gas ambients. Reducing gases used for testing the response are hydrogen, carbon monoxide and methane, as they belong to three distinct chemical families. It is observed that the response of these sensors follows a power-law relationship, with the exponent value always remaining less than one at higher concentrations of reducing gas. Films deposited at 25 and 350 °C and heat treated at 650 °C in O2 ambient for 2 h are found to be more suitable for sensor application compared to films deposited at intermediate temperatures and heat treated under identical conditions. Further, the response of the sensor is found to deteriorate with a decrease in operating temperature. It is also concluded from the results that a thin-film SnO2 sensor can be used as a selective sensor for H2 at either low operating temperature or under very low background concentrations of other reducing gases. Finally, the above-mentioned results are explained using existing physical models.
Hydrogen gas, within the concentration range of 100 ppm–4 vol.%, is successfully sensed at lower operating temperatures, 25 and 50 °C, using the Pt-sputtered sol–gel dip-coated nanocrystalline (6–7 nm) 6.5 mol% In2O3-doped SnO2 semiconductor thin (100–150 nm) film sensor. Typically, for 1000 ppm of hydrogen, the maximum sensitivity values of 32 and 1600% are observed at 25 and 50 °C, respectively; while for 2 vol.% hydrogen, the maximum sensitivity values of 50 and 70,000% are recorded at 25 and 50 °C, respectively. At 25 °C, for 4 vol.% (explosive limit as set by NASA) hydrogen, the maximum hydrogen gas sensitivity values of 107,887 and 2083% are observed for the Pt-sputtered thin films calcined at 500 and 600 °C, respectively.
Sn-W-O thin films, deposited by rheotaxial growth and thermal oxidation (RGTO) technique, have been investigated. The aim of this work is the compositional and sensing characterization, in order to obtain stable materials for gas sensing. Two kinds of SnO2 based sample are realized: W deposited just after Sn deposition and W deposited on SnO2 already oxidized.The compositional characterization is performed by means of XPS depth profiling technique. Surface topography is studied by means of AFM measurements.Electrical measurements were performed in the presence of some gases of interest in polluting area (CO, NO2 and CH4), in breath analysis (ethanol) and in food control (ethylene).