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1.
The NO2 gas sensing behavior of porous silicon(PS) is studied at room temperature with and without ultraviolet(UV) light radiation.The PS layer is fabricated by electrochemical etching in an HF-based solution on a p +-type silicon substrate.Then,Pt electrodes are deposited on the surface of the PS to obtain the PS gas sensor.The NO2 sensing properties of the PS with different porosities are investigated under UV light radiation at room temperature.The measurement results show that the PS gas sensor has a much higher response sensitivity and faster response-recovery characteristics than NO2 under the illumination.The sensitivity of the PS sample with the largest porosity to 1 ppm NO2 is 9.9 with UV light radiation,while it is 2.4 without UV light radiation.We find that the ability to absorb UV light is enhanced with the increase in porosity.The PS sample with the highest porosity has a larger change than the other samples.Therefore,the effect of UV radiation on the NO2 sensing properties of PS is closely related to the porosity. 相似文献
2.
We report synthesis of Spinel type magnesium ferrite (MgFe 2O 4) material by a simple, inexpensive combustion method with glycine as a fuel and their application as a gas sensor for reducing gases (LPG, Acetone, Ethanol, Ammonia). The dependence of reducing gas sensing properties on the structural and surface morphological properties has been studied as an effect of sintering temperatures. The structural and surface morphological properties were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The MgFe 2O 4 were highly oriented along (311) with the spinel type crystal structure. The SEM observation reveals that porous morphology decreases due to the grain growth as sintering temperature increases. The mechanism of reducing gas sensing by the MgFe 2O 4 pellets is explained on the basis of adsorbed oxygen on the sensor surface. The selectivity and maximum response of 71% to 2000 ppm of LPG was observed at 698 K with the (MgFe 2O 4) material sintered at 1173 K. 相似文献
3.
This work studied the possibility of using a sensor based on plasma-sprayed zinc oxide (ZnO) sensitive layer for NO 2 detection. The atmospheric plasma spray process was employed to deposit ZnO gas sensing layer and the obtained coating structure was characterized by scanning electron microscopy and X-ray diffraction analysis. The influences of gas concentration, working temperature, water vapor in testing air on NO 2 sensing performance of the ZnO sensors were studied. ZnO sensors showed a good sensor response and selectivity to NO 2 at an optimal working temperature. 相似文献
4.
A mixed potential type yttria-stabilized zirconia-based sensor using NiO sensing electrode and Pt reference electrode was fabricated, and its NO 2 sensing characteristics were examined at various operating temperatures in the range of 700–950 °C. It was observed that the sensitivity to NO 2 strongly depends on the operating temperature of the sensor; the sensitivity decreases with increasing operating temperature, while the response/recovery rates increase. To rationalize this temperature dependence of NO 2 response, polarization curves and complex impedances of the sensor were measured in the base gas and in the sample gas (400 ppm NO 2?+?base gas) at various operating temperatures. It turned out that the operating temperature had a strong influence on the rate of anodic reaction of oxygen; the increased rate of anodic reaction leads to lower NO 2 sensitivity and quicker response/recovery at higher operating temperature. 相似文献
5.
WO 3 nanoparticles were prepared by evaporating tungsten filament under a low pressure of oxygen gas, namely, by a gas evaporation method. The crystal structure, morphology, and NO 2 gas sensing properties of WO 3 nanoparticles deposited under various oxygen pressures and annealed at different temperatures were investigated. The particles obtained were identified as monoclinic WO 3. The particle size increased with increasing oxygen pressure and with increasing annealing temperature. The sensitivity increased with decreasing particle size, irrespective of the oxygen pressure during deposition and annealing temperature. The highest sensitivity of 4700 to NO 2 at 1 ppm observed in this study was measured at a relatively low operating temperature of 50 °C; this sensitivity was observed for a sensor made of particles as small as 36 nm. 相似文献
6.
Sub-stoichiometric tungsten trioxide (WO 3) thin films are deposited onto the glass substrates by spray pyrolysis technique using ammonium metatungstate. Effect of solution concentration on structural, morphological, optical, electrical and NO 2 sensing properties of WO 3 thin films is studied. Films are polycrystalline with monoclinic crystal structure and sub-stoichiometric as observed form the XRD and XPS studies, respectively. The SEM and AFM images show micro grained structure and surface roughness increases with increase in solution concentration. The PL studies revealed that the majority of the defects are the oxygen vacancies. From XPS and PL studies it is observed that, oxygen vacancies decrease with increase in solution concentration. The dielectric constant of the films as a function of frequency is in concurrence with resistivity measurements. Films show reproducible and reversible gas response at various operating temperatures and gas concentrations. Highest sensor response (38%) towards 200 ppm NO 2 concentration is observed for the film with 15 mM solution concentration at moderate operating temperature (200 °C). Pd sensitization enhanced gas response to 68% and improved kinetics of the sensor. Films are highly selective towards NO 2 as compared with the various gases such as SO 2, LPG, NH 3 and H 2S. 相似文献
7.
The dispersal of CuO catalyst on the surface of the semiconducting SnO 2 film is found to be of vital importance for improving the sensitivity and the response speed of a SnO 2 gas sensor for H 2S gas detection. Ultra-thin CuO islands (8 nm thin and 0.6 mm diameter) prepared by evaporating Cu through a mesh and subsequent
oxidation yield a fast response speed and recovery. Ultimately nanoparticles of Cu (average size = 15 nm) prepared by a chemical
technique using a reverse micelle method involving the reduction of Cu(NO 3) 2 by NaBH 4 exhibited significant improvement in the gas sensing characteristics of SnO 2 films. A fast response speed of ∼14 s and a recovery time of ∼60 s for trace level ∼20 ppm H 2S gas detection have been recorded. The sensor operating temperature (130° C) is low and the sensitivity ( S = 2.06 × 10 3) is high. It is found that the spreading over of CuO catalyst in the nanoscale range on the surface of SnO 2 allows effective removal of excess adsorbed oxygen from the uncovered SnO 2 surface due to spill over of hydrogen dissociated from the H 2S-CuO interaction. 相似文献
8.
In this paper, porous WO 3 films were prepared by anodic oxidation of metallic tungsten (W) films deposited on alumina substrates. The structural and morphological properties of the porous WO 3 films were investigated using field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD). A large number of cracks appeared on the surface of films after anodization, which makes the films porous. The porous WO 3 sensors achieved their maximum response values to NO 2 at a low operating temperature of 150 °C. The porous WO 3 sensors showed high response values, great stability and fast response-recovery characteristics to different concentration of NO 2 gas due to the high specific surface area and special structural and morphological properties. 相似文献
9.
Abstract A fiber-optic chemical sensor (FOCS) for detection of nitrogen dioxide (NO 2 ) molecules is reported. The FOCS presents an optropode structure because of the transmission properties of the sensitive material. The NO 2 FOCS is activated by using the semiconductor polymer: regioregular head-to-tail poly(3-octylthiophene-2,5-diyl). The operation wavelength of the sensor is 543.5 nm such that a simple LED and detector can be used for the design of this device. The sensor response decreases after each exposure, demonstrating the reduction in sensitivity as well as irreversibility lower than 5%. However, its properties such as rapid response, high selectivity, high sensitivity (0.43 ± 0.01 muW/ppm), hygroscopic properties, and its operation at room temperature make this kind of FOCS a good alternative for NO 2 toxic gas detection. 相似文献
10.
Nanostructured zinc oxide thin films were prepared by spray pyrolysis technique using Zn(NO 3) 2·6H 2O as the precursor solution. The resulting films were investigated by X-ray diffraction and scanning electron microscopy to know crystal structure, size of crystallites and surface morphology. The films have been found to be polycrystalline zinc oxide, possessing hexagonal wurtzite crystal structure and nanocrystallite with grain size of approximately 30-35 nm. The LPG sensing performance of the films has been investigated at various concentrations of LPG in air at operating temperatures varying from 225 to 400 °C. At 325 °C the maximum responses of 46.3% and 48.9% have been observed, respectively, for concentrations of 0.8 and 1 vol% of LPG in air (1 vol% of LPG in air corresponds to 50% LEL of LPG in air). The recovery time has been found to be less than the response time for all concentrations of LPG. A possible reaction mechanism of LPG sensing has been proposed. 相似文献
11.
Present paper reports the preparation and characterization of nanorods and mixed shaped (nanospheres/nanocubes) copper ferrite for liquefied petroleum gas (LPG) sensing at room temperature. The structural, surface morphological, optical, electrical as well as LPG sensing properties of the copper ferrite were investigated. Single phase spinel structure of the CuFe 2O 4 was confirmed by XRD data. The minimum crystallite size of copper ferrite was found 25 nm. The stoichiometry was confirmed by elemental analysis and it revealed the presence of oxygen, iron and copper elements with 21.91, 12.39 and 65.70 atomic weight percentages in copper ferrite nanorods. The band gap of copper ferrite was 3.09 and 2.81 eV, respectively for nanospheres/nanocubes and nanorods. The sensing films were made by using screen printing technology and investigated with the exposure of LPG. Our results show that the mixed shaped CuFe 2O 4 had an improved sensing performance over that of the CuFe 2O 4 nanorods, of which a possible sensing mechanism related to a surface reaction process was discussed. Sensor based on mixed shaped copper ferrite is 92% reproducible after one month. The role of PEG in the synthesis for obtaining nanospheres/nanocubes has also been demonstrated. 相似文献
12.
New morphologies often play an important role in deciding the properties of nanomaterials. In current study, we synthesize various types of low dimensional SnO 2 nanostructure materials using a simple hydrothermal process. We find that the SnO 2 nanorods, nanowires and nanosheets show higher gas response as well as lower operating temperature as compared to that of nanospheres. In addition, the obtained nanosheets SnO 2 are found to show best sensing performances owing to the largest surface area and porous structure providing many quick passages to absorb and desorb gas, suggesting that the gas sensing properties of nanocrystals can be significantly improved by tailoring the shape and morphology of nanocrystals. Such an unexpected morphology holds substantial promise for rendering low dimensional nano-SnO 2 as a potential gas sensing material for future sensor application. 相似文献
13.
The nanostructured thin NiO films with the thicknesses of 30–180 nm were examined as a sensing electrode (SE) for the planar
mixed-potential-type yttria-stabilized zirconia (YSZ)-based NO 2 sensor. The sensing characteristics were examined in the temperature range of 600–800 °C under the wet condition (5 vol.%
water vapor). Among the NiO-SEs tested, the 60 nm-thick NiO-SE sintered at 1,000 °C was found to give the highest NO 2 sensitivity in the NO 2 concentration range of 50–400 ppm accompanying with fast response/recovery at the operating temperatures of 600–700 °C. The
high NO 2 sensitivity was attributed to the high catalytic activity for both electrochemical reactions of O 2 and NO 2 at the interface of NiO-SE/YSZ. The ultrathin gold layer with the thickness of about 60 nm was additionally formed on the
60 nm-thick NiO-SE to fabricate the laminated-type (60 nm NiO/60 nm Au)-SE. It was demonstrated that the use of this laminated
(NiO–Au)-SE improved both the sensitivity and the selectivity to NO 2. 相似文献
14.
In 2O 3 is introduced into TiO 2 by sol-gel method to improve the response/recovery rate and expand the operating temperature, when the In 2O 3-TiO 2 mixed system is exposed to H 2/O 2. The sensor is fabricated by thick film technology. Influence of In 2O 3 on the film phase composition, microstructure and sensing characteristics is discussed. Dynamic response properties show that the operating temperature of the mixed system is at 500-800 °C, which is about 600-800 °C for pure TiO 2. Response time of the sensor is about 200-260 ms (millisecond) while recovery time is in a narrow range of 60-280 ms at 600-800 °C. The promoting mechanism is suggested to arise from the introduction of In 2O 3 and grain size effect of the sensing film. Then In 2O 3-TiO 2 thick films are surface-modified by Pt using chloroplatinic acid. The promoting effect of Pt dispersed on the mixed system is also investigated. 相似文献
15.
通过在水热合成后追加退火处理,制备了径向生长的具有分级结构的树枝状三维Co 3O 4晶体,并用X射线衍射仪、扫描电子显微镜和透射电子显微镜对其结构和形貌进行了表征. 在110 oC对其气体探测性能的研究表明这种Co 3O 4分级结构对氨气有较高的探测灵敏度和响应速度(10 s),性能稳定并具有可重复性. 同时,还在较低的探测温度下对酒精、丙酮和苯进行了气敏探测. 相似文献
16.
An optical fiber gas sensor using hollow-core photonic bandgap fiber as a gas cell is proposed to detect H 2S mixed with natural gas. This sensor is advantageous for eliminating instability of light source, impact of thermal zero drift, and zero shift of photoelectric device. The gas sensing probe of configuration is using two shorter pieces of hollow-core photonic bandgap fiber (HC-PBF) with the same overall length instead of one long piece of HC-PBF to improve the system response. The experimental dates indicate that a minimum detectivity of 10 ppm for the system configuration was estimated. 相似文献
17.
Electrochemical sensors using tubular yttria-stabilized zirconia (YSZ) and oxide sensing electrode (SE) were fabricated and
examined for NO x detection at high temperatures. The mixed-potential-type NO x sensor using ZnO-SE gave the highest sensitivity to NO x among other single-type oxides tested as SEs in the temperature range of 600–700 °C. The response of the ZnO-attached device
was a linear for the logarithm of NO 2 (NO) concentrations from 40 to 450 ppm. The sensing mechanism of the sensor was discussed on the basis of the gas adsorption-desorption
behavior, the catalytic activity data, and electrochemical behavior for oxides examined. 相似文献
18.
The present investigation has been carried out to optimize the pH level of lanthanum (La)-doped tin dioxide (SnO2) nanoparticles towards the potential application in gas sensor. The La-doped SnO2 nanoparticles were synthesized by sol-gel method in different pH values varying from acidic to base nature. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), ultraviolet (UV), photoluminescence (PL), and scanning electron microscopy (SEM) techniques. The XRD, UV, and PL analyses show the pH influences on the crystallite size of La-doped SnO2 nanoparticles. The SEM images show the formation of porous structure at pH 11. Also, the electrical conductivity of 1 mol% La-doped SnO2 at pH 3 and pH 11 were measured by impedance analyzer. In addition, we have fabricated and demonstrated device performance of synthesized La-doped SnO2 nanoparticles for gas-sensing application. Real-time current response and long-time response to the gas sensing were also studied for the fabricated device. 相似文献
19.
Na 2WO 4 films have been grown on Si (1 0 0) and glass substrate using ultrasonic spray pyrolysis. The films are prepared from aqueous solution containing Na 2WO 4·2H 2O at 475 °C temperature and characterized by XRD and SEM techniques and the chemical composition of the films have been verified by EDX and PIXE and its formula Na 2WO 4 is confirmed by XRD. The evolution of the crystallinity was studied as a function of film thickness ranging from 2500 to 4200 nm, which corresponds to a deposition time from 10 to 30 min, respectively. The crystalline quality was found to improve, where the grain size values increased with increasing thickness. Atomic Force Microscopy (AFM) was used to study the morphology evolution with the deposition time, where porous films were found due to the synthesis parameters, and a better sensing response to gases was developed with increasing thickness. Thus, this study demonstrates the possibility of utilizing Na 2WO 4 thick films as a sensor element for the detection of ethanol vapor at room temperature, where thicker films exhibit excellent ethanol vapor sensing properties with a maximum sensitivity at 25 °C in air atmosphere with fast response time. 相似文献
20.
利用溶剂热法合成了一维的氧化钨纳米线, 通过掺入适量单壁碳纳米管(SWNT)制备了基于氧化钨纳米线-SWNT 复合结构的室温气敏元件并评价了其对NO 2气体的室温敏感性能. 利用X射线与扫描电子显微镜表征了材料的微结构, 结果表明, 合成的氧化钨纳米线具有单斜的W 18O 49结构, 复合材料中SWNT被包埋在氧化钨纳米线中间. 气敏性能测试结果表明, 氧化钨纳米线-SWNT复合结构气敏元件在室温下对NO 2气体表现出了高的灵敏度和超快的响应特性; 较低的SWNT掺入量对获得好的气敏性能有利. 分析了基于复合结构材料气敏元件的可能的气敏机理, 认为元件良好的室温敏感性能与SWNT掺入在复合结构材料中引入大量的贯穿气孔和p-n异质结有关. 相似文献
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