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1.
Sol–gel dip coating technique was employed to prepare Cu-doped SnO 2 thin films, which were able to detect H 2S gas at room temperature with high sensitivity and revealed fast response characteristics. The highest sensor response (the ratio of resistance in air versus in H 2S) was 3648 under H 2S concentration of 68.5 ppm at room temperature. Recoverability of the thin films appeared when the temperature raised to 50 °C. The films were analyzed by means of XRD and the dried gel powder was studied by TG-DTA test. Influences of sintering temperature and doping level on the H 2S response are discussed. The average grain size of the SnO 2 was about 25 nm. 相似文献
2.
A compact tubular sensor based on NASICON (sodium super ionic conductor) and V 2O 5-doped TiO 2 sensing electrode was designed for the detection of SO 2. In order to reduce the size of the sensor, a thick-film of NASICON was formed on the outer surface of a small Al 2O 3 tube; furthermore, a thin layer of V 2O 5-doped TiO 2 with nanometer size was attached on the NASICON as a sensing electrode. This paper investigated the influence of V 2O 5 doping and sintering temperature on the characteristics of the sensor. The sensor attached with 5 wt% V 2O 5-doped TiO 2 sintered at 600 °C exhibited excellent sensing properties to 1–50 ppm SO 2 in air at 200–400 °C. The EMF value of the sensor was almost proportional to the logarithm of SO 2 concentration and the sensitivity (slope) was −78 mV/decade at 300 °C. It was also seen that the sensor showed a good selectivity to SO 2 against NO, NO 2, CH 4, CO, NH 3 and CO 2. Moreover, the sensor had speedy response kinetics to SO 2 too, the 90% response time to 50 ppm SO 2 was 10 s, and the recovery time was 35 s. On the basis of XPS analysis for the SO 2-adsorbed sensing electrode, a sensing mechanism involving the mixed potential at the sensing electrode was proposed. 相似文献
3.
In this study, the nitrogen dioxide (NO 2) and ozone (O 3) sensing properties of a series bis[tetrakis(alkylthio) phthalocyaninato] lutetium(III) complexes [(C nH 2n+1S) 4Pc] 2Lu(III) ( n = 6, 10, 16) are investigated as a function of concentration in the temperature range between 25 °C and 150 °C. The concentration ranges were 1–10 ppm for NO 2, and 50 ppb–1 ppm for O 3. The response time and the sensor response to NO 2 are measured for approximately 1 min and 100% ppm −1, respectively, for compound 1 at room temperature. At room temperature, all compounds are in the solid phase. The response time decreases to a few seconds with increasing operation temperature to 150 °C. At this temperature, all compounds are in the liquid crystal phase. The fastest response to oxidizing gases is observed at the liquid crystal phase of the Pcs. It has also been observed that the response time and the sensor response depend on the alkyl chain lengths of the Pcs. The doping effect of oxygen has been determined under high purity nitrogen N 2 flow, after exposure to dry air, at a different period of time and after annealing. It has been found that the conductivities of [(C nH 2n+1S) 4Pc] 2Lu(III) thin films increased after exposure to dry air and the conduction mechanism also changed from ohmic behavior to space-charge-limited conduction. 相似文献
4.
Detection of low concentrations of petroleum gas was achieved using transparent conducting SnO 2 thin films doped with 0–4 wt.% caesium (Cs), deposited by spray pyrolysis technique. The electrical resistance change of the films was evaluated in the presence of LPG upon doping with different concentrations of Cs at different working temperatures in the range 250–400 °C. The investigations showed that the tin oxide thin film doped with 2% Cs with a mean grain size of 18 nm at a deposition temperature of 325 °C showed the maximum sensor response (93.4%). At a deposition temperature of 285 °C, the film doped with 3% Cs with a mean grain size of 20 nm showed a high response of 90.0% consistently. The structural properties of Cs-doped SnO 2 were studied by means of X-ray diffraction (XRD); the preferential orientation of the thin films was found to be along the (3 0 1) directions. The crystallite sizes of the films determined from XRD are found to vary between 15 and 60 nm. The electrical investigations revealed that Cs-doped SnO 2 thin film conductivity in a petroleum gas ambience and subsequently the sensor response depended on the dopant concentration and the deposition temperature of the film. The sensors showed a rapid response at an operating temperature of 345 °C. The long-term stability of the sensors is also reported. 相似文献
5.
An optical waveguide (OWG) pH sensor with two thin guiding layers (composite OWG) was fabricated, and its application to sensing extremely low concentrations of ammonia was demonstrated. The highly sensitive element based on a titanium dioxide (TiO 2) film was deposited onto the surface of a potassium ion (K +) exchanged glass OWG by RF sputtering. The surface of the TiO 2 film was coated with a thin film of a pH indicator dye (bromothymol blue, BTB) by spin coating. With optimum thickness of BTB film at about 46 nm and of TiO 2 films at 18–20 nm, this system proved to be an extremely sensitive ammonia sensor. The experimental results of the optimum conditions on BTB and TiO 2 film thicknesses were close to theoretically calculated values. The sensor easily detected 1 parts per trillion (ppt) ammonia reversibly, and had a short response time. The present sensor is also characterized by low cost, simple structure and facile fabrication. 相似文献
6.
Mesoporous TiO 2 nanoparticle thin films were prepared on MEMS microhotplate (μHP) platforms and evaluated as high-sensitivity conductometric gas sensor materials. The nanoparticle films were deposited onto selected microhotplates in a multi-element array via microcapillary pipette and were sintered using the microhotplate. The films were characterized by optical and scanning electron microscopies and by conductometric measurements. The thin films were evaluated as conductometric gas sensors based on the critical performance elements of sensitivity, stability, speed and selectivity. The nanoparticle films were compared with compact TiO 2 films deposited via chemical vapor deposition (CVD) and the nanoparticle films were found to demonstrate higher sensitivity to target analytes. The nanoparticle films were also stable with regard to both baseline conductance and signal response over 60 h of continuous operation at high temperatures (up to 475 °C). Sensor response times were evaluated and the TiO 2 nanoparticle films showed fast responses to the presence of analyte (≈5 s) and a response-time dependence on the analyte concentration. Control of the sensor operating temperature, an inherent benefit of the microhotplate platform, was employed to demonstrate the selectivity of the nanoparticle films. 相似文献
7.
This paper presents the ability of electrostatic sprayed tin oxide (SnO 2) and tin oxide doped with copper oxide (1, 2, and 4 at.% Cu) films to detect different pollutant gases, i.e., H 2S, SO 2, and NO 2. The influence of a copper oxide dopant on the SnO 2 morphology is studied using scanning electron microscopy (SEM) technique, which reveals a small decrease in the porosity and particle size when the amount of dopant is increased. The sensing properties of the SnO 2 films are greatly improved by doping, i.e., the Cu-doped SnO 2 films have large response to low concentration (10 ppm) of H 2S at low operating temperature (100 °C). Furthermore, no cross-sensitivity to 1 ppm NO 2 and 20 ppm SO 2 is observed. Among the studied films, the 1 at.% Cu-doped SnO 2 layer is the most sensitive in the detection of all the studied gases. 相似文献
8.
Pulsed laser deposited (PLD) Y-doped BaZrO 3 thin films (BaZr 1-xY xO 3-y/2, x = 0.2, y > 0), were investigated as to their viability for reliable humidity microsensors with long-term stability at high operating temperatures ( T > 500 °C) as required for in situ point of source emissions control as used in power plant combustion processes. Defect chemistry based models and initial experimental results in recent humidity sensor literature [1] and [2]. indicate that bulk Y-doped BaZrO 3 could be suitable for use in highly selective, high temperature compatible humidity sensors. In order to accomplish faster response and leverage low cost batch microfabrication technologies we have developed thin film deposition processes, characterized layer properties, fabricated and tested high temperature humidity micro sensors using these thin films. Previously published results on sputtering Y-doped BaZrO 3 thin films have confirmed the principle validity of our approach [3]. However, the difficulty in controlling the stoichiometry of the films and their electrical properties as well as mud flat cracking of the films occurring either at films thicker than 400 nm or at annealing temperature above 800 °C have rendered sputtering a difficult process for the fabrication of reproducible and reliable thin film high temperature humidity microsensors, leading to the evaluation of PLD as alternative deposition method for these films.X-ray Photoelectron Spectroscopy (XPS) data was collected from as deposited samples at the sample surface as well as after 4 min of Ar + etching. PLD samples were close to the desired stoichiometry. X-ray diffraction (XRD) spectra from all as deposited BaZrO 3:Y films show that the material is polycrystalline when deposited at substrate temperatures of 800 °C. AFM results revealed that PLD samples have a particle size between 32 nm and 72 nm and root mean square (RMS) roughness between 0.2 nm and 1.2 nm. The film conductivity increases as a function of temperature (from 200 °C to 650 °C) and upon exposure to a humid atmosphere, supporting our hypothesis of a proton conduction based conduction and sensing mechanism. Humidity measurements are presented for 200–500 nm thick films from 500 °C to 650 °C at vapor pressures of between 0.05 and 0.5 atm, with 0.03–2% error in repeatability and 1.2–15.7% error in hysteresis during cycling for over 2 h. Sensitivities of up to 7.5 atm −1 for 200 nm thick PLD samples at 0.058 atm partial pressure of water were measured. 相似文献
9.
Successive Ionic Layer Adsorption and Reaction (SILAR) was used to form Cd(OH) 2 thin films from aqueous cadmium–ammonia complex on glass substrates at room temperature and the thermal annealing effect on thin films was studied. The as-deposited films were annealed at 200, 300 and 400 °C for 1 h in an oxygen atmosphere for conversion from Cd(OH) 2 to CdO and change in the structural, optical and electrical properties of the films and the effect of the light on the electrical properties of the films were investigated. The structural and surface morphological properties of the films were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that Cd(OH) 2 phase is converted into the cubic CdO films by annealing. The band gap energy values of films decreased from 3.59 to 2.13 eV through increasing annealing temperature. It was found that the current increased with increasing light intensity and CdO films were more conductive than the as-deposited films. 相似文献
10.
The NO 2 gas sensing characteristics of semiconductor type gas sensors with channels composed of necked ZnO nanoparticles (NPs) were investigated in this study. The heat treatment of the NPs at 400 °C led to their necking and coarsening. The response of the necked-NP-based sensors was as high as 100 when exposed to 0.2 ppm of NO 2 at 200 °C. As the concentration of NO 2 increased to 5 ppm, their response was enhanced to approximately 400. During the repeated injection of NO 2 gas with a concentration of 0.4 ppm, the sensors exhibited stable response characteristics. Furthermore, the 90% response and recovery times of the gas sensor were as fast as 13 and 10 s, respectively. These observations indicate that the non-agglomerated necking of the NPs induced by the heat treatment significantly enhances the gas sensing characteristics of the NP-based gas sensors. 相似文献
11.
We report a novel route for the fabrication of highly sensitive and rapidly responding Nb 2O 5-based thin film gas sensors. TiO 2 doping of Nb 2O 5 films is carried out by co-sputtering without the formation of secondary phases and the surface area of TiO 2-doped Nb 2O 5 films is increased via the use of colloidal templates composed of sacrificial polystyrene beads. The gas sensitivity of Nb 2O 5 films is enhanced through both the TiO 2 doping and the surface embossing. An additional enhancement on the gas sensitivity is obtained by the optimization of the bias voltage applied between interdigitated electrodes beneath Nb 2O 5-based film. More excitingly, such a voltage optimization leads to a substantial decrease in response time. Upon exposure to 50 ppm CO at 350 °C, a gas sensor based on TiO 2-doped Nb 2O 5 film with embossed surface morphology exhibits a very high sensitivity of 475% change in resistance and a rapid response time of 8 s under 3 V, whereas a sensor based on plain Nb 2O 5 film shows a 70% resistance change and a response time of 65 s under 1 V. Thermal stability tests of our Nb 2O 5-based sensor reveal excellent reliability which is of particular importance for application as resistive sensors for a variety gases. 相似文献
12.
Different TiO2 synthesization processes give different properties. Most of researches in material studies only focus on the morphological and optical properties of TiO2 while lacking in the effort of achieving stable electrical properties of the material. In engineering, stable electrical properties are vital in order to develop a device. Moreover, current technology needs more nanostructure application to enhance the performance of devices. In this paper, TiO2 nanoparticle was synthesized by sol–gel method using 1:0.1:9 ratios of titanium isopropoxide:acetic acid:ethanol, respectively. This synthesized TiO2 was
able to respond in extremely small and consistent electrical reading (nanoampere). This metal oxide is good enough to be used as a material to develop ultra-high sensitive biosensor. Annealing process on the TiO2 film was able to improve its’ electrical conductivity. The three layers TiO2 coating were annealed at 400, 500, 600 and 700 °C and the surface morphologies, structural also electro-optical properties were studied using FESEM, XRD, UV–Vis and Keithley 6485 picoammeter. The XRD pattern shows the presence of stable anatase and rutile structures even at low temperature, whereas FESEM shows that annealing temperature affects the particle size. The optical band gap of TiO2 thin films decreases from 3.74 to 3.34 eV as the annealing temperature increases. The current-to-voltage characteristics show that the conductivity decreases as the annealing temperature varies from 400to 700 °C. The output measurements indicated an improvement in electrical properties with annealing temperature. 相似文献
13.
This paper reports the sensing response characteristics of rf-sputtered SnO 2 thin films (90 nm thick) loaded with platinum catalyst cluster of varying thickness (2-20 nm) for LPG detection. The enhanced response (5 × 10 3) was obtained for 200 ppm LPG with the presence of 10 nm thin and uniformly distributed Pt catalyst clusters on the surface of SnO 2 thin film at a relatively low operating temperature (220 °C). The high response for LPG is shown to be primarily due to the enhanced catalytic activity for adsorbed oxygen on the surface of SnO 2 thin film besides the spill over mechanism at elevated temperature. 相似文献
14.
Thin films of polymethylmethacrylate (PMMA) doped with perylene provide selective, robust and easily prepared optical sensor films for NO 2 gas with suitable response times for materials aging applications. The materials are readily formed as 200 nm thin spin cast films on glass from chlorobenzene solution. The fluorescence emission of the films ( λmax=442 nm) is quenched upon exposure to NO 2 gas through an irreversible reaction forming non-fluorescent nitroperylene. Infrared, UV–VIS and fluorescence spectroscopies confirmed the presence of the nitro adduct in the films. In other atmospheres examined, such as air and 1000 ppm concentrations of SO 2, CO, Cl 2 and NH 3, the films exhibited no loss of fluorescence intensity over a period of days to weeks. Response curves were obtained for 1000, 100 and 10 ppm NO 2 at room temperature with equilibration times varying from hours to weeks. The response curves were fit using a numerical solution to the coupled diffusion and a nonlinear chemical reaction problem assuming that the situation is reaction limiting. The forward reaction constant fitted to experimental data was kf∼0.06 (ppm min) −1. 相似文献
15.
The influences of La 2O 3 loading on the ethanol sensing properties of SnO 2 nanorods were investigated. An obvious enhancement of response was obtained. The response of 5 wt% La 2O 3 loaded SnO 2 nanorods was up to 213 for 100 ppm ethanol at low working temperature of 200 °C, while that of pure SnO 2 nanorods is 45.1. The improvement in response might be attributed to the presence of basic sites, which facilitated the dehydrogenation process. While the working temperature was increased to 300 °C, the sensor response decreased to 16 for 100 ppm ethanol. Additionally, the La 2O 3 loaded SnO 2 nanorods sensors showed good selectivity to ethanol over methane and hydrogen. Our results demonstrated that the La 2O 3 loaded SnO 2 nanorods were promising in fabricating high performance ethanol sensors which could work at low temperature. 相似文献
16.
The CuO-functionalized SnO 2 nanowire (NW) sensors were fabricated by depositing a slurry containing SnO 2 NWs on a polydimethylsiloxane (PDMS)-guided substrate and subsequently dropping Cu nitrate aqueous solution. The CuO coating increased the gas responses to 20 ppm H 2S up to 74-fold. The Ra/ Rg value of the CuO-doped SnO 2 NWs to 20 ppm H 2S was as high as 809 at 300 °C, while the cross-gas responses to 5 ppm NO 2, 100 ppm CO, 200 ppm C 2H 5OH, and 100 ppm C 3H 8 were negligibly low (1.5–4.0). Moreover, the 90% response times to H 2S were as short as 1–2 s at 300–400 °C. The selective detection of H 2S and enhancement of the gas response were attributed to the uniform distribution of the sensitizer (CuO) on the surface of the less agglomerated network of the SnO 2 NWs. 相似文献
17.
A thermally oxidized TiO 2 or Nb 2O 5 film equipped with a top Pd film electrode and a bottom Ti or Nb plate electrode (Pd/MO( n)/M, MO: oxide film, M: metal plate, n: annealing temperature (°C)) has been investigated as a diode-type H 2 sensor under air or N 2 atmosphere. Pd/TiO 2( n)/Ti sensors showed relatively poor H 2 sensing properties in air, in comparison with Pd/anodic-TiO 2( n)/Ti sensors constructed with an anodized TiO 2 film equipped with a top Pd film electrode and a bottom Ti plate electrode, which were reported in our previous studies. On the other hand, Pd/Nb 2O 5( n)/Nb sensors showed relatively larger H 2 response with fast response and recovery speeds than Pd/TiO 2( n)/Ti sensors in air under high forward bias conditions. A Pd/Nb 2O 5(450)/Ti sensor, which was fabricated by radio-frequency magnetron sputtering of Nb metal on a Ti substrate followed by thermal oxidation at 450 °C, showed the largest H 2 response and relatively fast response and recovery speeds in air, among the sensors tested. In addition, H 2 response of the Pd/Nb 2O 5(450)/Ti sensor in air was much lower than that in N 2, but the logarithm of H 2 response was almost proportional to the logarithm of H 2 concentration in a wide range of H 2 concentration (10–8000 ppm) in air, and the H 2 sensitivity in air was much higher than that in N 2. 相似文献
18.
Detection of sulfur dioxide (SO 2) at high temperature (600–750 °C) in the presence of some interferents found in combustion exhausts (NO 2, NO, CO 2, CO, and hydrocarbon (C 3H 6)) is described. The detection scheme involves use of a catalytic filter in front of a non-Nernstian (mixed-potential) sensing element. The catalytic filter was a Ni:Cr powder bed operating at 850 °C, and the sensing elements were pairs of platinum (Pt) and oxide (Ba-promoted copper chromite ((Ba,Cu) xCr yO z) or Sr-modified lanthanum ferrite (LSF)) electrodes on yttria-stabilized zirconia. The Ni:Cr powder bed was capable of reducing the sensing element response to NO 2, NO, CO, and C 3H 6, but the presence of NO 2 or NO (“NO x”, at 100 ppm by volume) still interfered with the SO 2 response of the Pt–(Ba,Cu) xCr yO z sensing element at 600 °C, causing approximately a 7 mV (20%) reduction in the response to 120 ppm SO 2 and a response equivalent to about 20 ppm SO 2 in the absence of SO 2. The Pt–LSF sensing element, operated at 750 °C, did not suffer from this NO x interference but at the cost of a reduced SO 2 response magnitude (120 ppm SO 2 yielded 10 mV, in contrast to 30 mV for the Pt-(Ba,Cu) xCr yO z sensing element). The powder bed and Pt–LSF sensing element were operated continuously over approximately 350 h, and the response to SO 2 drifted downward by about 7%, with most of this change occurring during the initial 100 h of operation. 相似文献
19.
Porous gas sensing films composed of TiO 2 nanotubes were fabricated for the detection of volatile organic compounds (VOCs), such as alcohol and toluene. In order to control the microstructure of TiO 2 nanotubular films, ball-milling treatments were used to shorten the length of TiO 2 nanotubes and to improve the particle packing density of the films without destroying their tubular morphology and crystal structure. The ball-milling treatment successfully modified the porosity of the gas sensing films by inducing more intimate contacts between nanotubes, as confirmed by scanning electron microscopy (SEM) and mercury porosimetry. The sensor using nanotubes after the ball-milling treatment for 3 h exhibited an improved sensor response and selectivity to toluene (50 ppm) at the operating temperature of 500 °C. However, an extensive ball-milling treatment did not enhance the original sensor response, probably owing to a decrease in the porosity of the film. The results obtained indicated the importance of the microstructure control of sensing layers in terms of particle packing density and porosity for detecting large sized organic gas molecules. 相似文献
20.
In situ patterned zinc oxide (ZnO) thin films were prepared by precipitation of Zn(NO 3) 2/urea aqueous solution and by microcontact printing of self-assembled monolayers (SAMs) on Al/SiO 2/Si substrates. The visible precipitation of Zn(OH) 2 from the urea containing Zn(NO 3) 2 solution was enhanced by increasing the reaction temperature and the amount of urea. The optimized condition for the ZnO thin films was found to be the Zn(NO 3) 2/urea ratio of 1/8, the precipitation temperature of 80 °C, the precipitation time of 1 h and the annealing temperature of 600 °C, respectively. SAMs are formed by exposing Al/SiO 2/Si to solutions comprising of hydrophobic octadecylphosphonic acid (OPA) in tetrahydrofuran and hydrophilic 2-carboxylethylphosphonic acid (CPA) in ethanol. The ZnO thin film was then patterned with the heat treatment of Zn(OH) 2 precipitated on the surface of hydrophilic CPA. The ZnO gas sensor was exposed to different concentrations of C 3H 8 (5000 ppm), CO (250 ppm) and NO (1000 ppm) at elevated temperatures to evaluate the gas sensitivity of ZnO sensors. The optimum operating temperatures of C 3H 8, CO and NO gases showing the highest gas sensitivity were determined to be 350, 400 and 200 °C, respectively. 相似文献
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