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2.
A light-addressable potentiometric sensing (LAPS) system has been applied to construct an oxygen sensor using a suspended-gate electrode. The sensor principally consists of an MIS structure, i.e., suspended gate/air gap/LaF 3/SiO 2/Si. The use of the suspended gate makes it possible to realize a contactless sensing system, which provides a flexible structure to integrate multiple sensing elements on a single-chip semiconductor surface. The sensor shows a stable response at room temperature to oxygen partial-pressure changes in the range 0.25-1.0 atm. The fabrication conditions of the LaF 2 film are also discussed. 相似文献
3.
Gibbs energy of hcp_A3 phase in the Ag–Sn binary system has been reassessed using compatible lattice stability. Combined with previous assessments of the Ag–Au and Au–Sn binary systems, the Sn–Ag–Au ternary system has been thermodynamically optimized using the CALPHAD method on the basis of available experimental information. The solution phases including liquid, fcc_A1, hcp_A3 and bct_A5, are modeled as substitutional solutions, while the intermediate compound Ag 3Sn is treated using a 2-sublattice model because Au can be dissolved to a certain degree. The solubility of Ag in the Au–Sn intermediate phases, D0 24, Au 5Sn, AuSn, AuSn 2 and AuSn 4, is not taken into account. Thermodynamic properties of liquid alloys, liquidus projection and several vertical and isothermal sections of this ternary system have been calculated, which are in reasonable agreement with the reported experimental data. 相似文献
5.
Potentiometric cell, Au/LiCoO 2 5 m/o Co 3O 4/Li 2.88PO 3.73N 0.14/Li 2CO 3/Au, has been fabricated and investigated for monitoring CO 2 gas. A LiCoO 2–Co 3O 4 mixture was used as the solid-state reference electrode instead of a reference gas. The idea is to keep the lithium activity constant on the reference side using thermodynamic equilibrium at a given temperature. The thermodynamic stability of the reference electrode was studied from the phase stability diagram of Li–Co–C–O system. The Gibb’s free energy of formation of LiCoO 2 was estimated at 500°C from the measured value of the cell emf. The sensors showed good reversibility and fast response toward changing CO 2 concentrations from 200 to 3000 ppm. The emf values were found to follow a logarithmic Nernstian behavior in the 400–500°C temperature range. CH 4 gas did not show any interference effect. Humidity and CO gas decreased the emf values of the sensor slightly. NO and NO 2 gases affect this sensor significantly at low temperatures. However, increased operating temperature seems to reduce the interference. 相似文献
6.
The nano–micro-integrated sensor has been fabricated by sol–gel depositing the nanocrystalline indium oxide (In 2O 3)-doped tin oxide (SnO 2) thin film on microelectromechanical systems (MEMS) device having interdigitated electrode configurations with two different electrode spacing (10 μm and 20 μm) and two different number of fingers (8 and 20). The present nano–micro-integrated sensor exhibits high H 2 sensitivity range ( S = 3–10 5) for the H 2 concentration within the range of 100–15,000 ppm at room temperature. It has been demonstrated that, the room temperature response kinetics of the present nano–micro-integrated sensor is a function of finger spacing, H 2 concentration and air-pressure, but independent of number of fingers. Such dependence has been explained on the basis of Le Chatelier's principle applied to the associated H 2 sensing mechanism and the role of above parameters in shifting the dynamic equilibrium of the involved surface reactions under the described test conditions. A new definition of the response time has been proposed, which is not only suitable for the theoretical analysis but also for the practical applications, where a gas-leak detection alarm is required to be triggered. 相似文献
8.
A coupled ab initio and thermodynamic study of the Al–H–Mg system has been carried out and a self-consistent thermodynamic database has been obtained. Magnesium alanate Mg(AlH 4) 2, a candidate material for hydrogen storage, has been included into the database. According to Density Functional first principles calculations, the alanate is an insulator and its thermodynamic properties have been obtained at room temperature. This compound has been found metastable at 298.15 K and 1 bar. The alanate has been found thermodynamically stable only at high pressure when the formation of the binary β-MgH 2 phase is neglected. A reassessment of thermodynamic parameters of the liquid phase in the binary Mg–H system has also been carried out in order to be consistent with the Al–H system. The present results can reproduce reasonably well the available experimental data. 相似文献
9.
The recent discovery of a new family of non-oxide glasses based on mixtures of ZrF 4 or HfF 4 with other metallic fluorides by M. Poulain and coworkers offers great potential in optical fiber, window and source/detector application. Due to the limited phase diagram data available for the binary, ternary and multicomponent fluoride systems currently employed to synthesize these glasses most of the progress in identifying new compositions has proceeded along empirical lines. In order to remedy this situation, the CALPHAD method for coupling phase diagram and thermochemical data has been applied to develop a data base covering metallic fluorides. The objective is to permit computation of multicomponent phase diagrams which can be used to identify the composition range where the liquid is most stable. The latter offers opportunities for glass formation as demonstrated by predictions of new metallic glasses. Currently the data base covers combinations of 0.2 ZrF 4(ZF), 0.25 LaF 3(LF) 0.333 BaF 2(BF), 0.333 PbF 2(PF), 0.5 NaF(NF), 0.5RbF(RF), O.5CsF(CF) and 0.5 KF(KF) which have been developed along the lines described earlier for III–V, II–VI and SIALON systems. These results were used to generate computed liquidus contours in LF-ZF-BF and BF-ZF-NF to disclose the range of composition in which the liquid has the greatest stability. These compositions agree well with those in which Poulain and coworkers have discovered glass formation. 相似文献
11.
Thin films of CdS, Bi 2S 3 and composite CdS–Bi 2S 3 have been deposited using modified chemical bath deposition (M-CBD) technique. The various preparative parameters were optimized to obtain good quality thin films. The as-deposited films of CdS, Bi 2S 3 and composite were annealed in Ar gas at 573 K for 1 h. A comparative study was made for as-deposited and annealed CdS, Bi 2S 3 and composite thin films. Annealing showed no change in crystal structure of these as-deposited films. However, an enhancement in grain size was observed by AFM studies. In addition change in band gap with annealing was seen. A study of spectral response, photosensitivity showed that the films can be used as a photosensor. 相似文献
12.
The ceramic powder prepared from the mixture of Mn 3O 4 and La 2O 3 have been characterized for NTC behavior and the same have been used as CT 2C (continuous thermocouple) sensor in the form of a thin metal cable to detect over-heating. These materials have mega ohm resistance at room temperature and showed exponential drop in resistance with the rise in temperature over a temperature range of 100–400 °C. It has been observed that as the concentration of La 2O 3 increases from 0 to 10% the NTC behavior drops from (400–260 °C) ±10%. The material was pressed into pellets and sintered at 700 °C for 3 h resulting in good bonding strength. Electrical characterization of the material was done by measuring the resistance over a temperature range of 100–400 °C. The material showed reproducible NTC characteristics over the temperature range 400, 370, 340, 280, and 260 °C with decreasing thermistor constant values ( B = 9588, 9210, 8500, 5170, 3330 K −1) and activation energy (Δ E = 826, 794, 733, 445, 287 meV), respectively. The decrease in activation energy of the ceramic powder with increase in La 2O 3 concentration makes it possible to fabricate thermal sensors which can be used in different temperature ranges. The microstructure was studied using SEM and evidence of a sintered body with grain size around 1 μm was observed in the material. XRD analysis indicated the single-phase tetragonal structure of the ceramic material. The process of using this ceramic material for fabrication of 10 ft continuous fire wire sensor has been explained. 相似文献
13.
The mixed aqueous electrolyte system consisting of ammonium and potassium sulfates has been studied using the hygrometric method at the temperature 298.15 K. The water activities are measured at total ionic strength values ranging from 0.60 to 8.25 mol kg −1 for different ionic strength fractions ( y) of (NH 4) 2SO 4 with y=0.20, 0.50 and 0.80. The obtained data allow the deduction of osmotic coefficients. The experimental results are compared with the predictions of the Zdanovskii–Stokes–Robinson (ZSR), Kusik and Meissner (KM), Robinson and Stokes (RS), Lietzke and Stoughton (LS II), Reilly–Wood and Robinson (RWR) and Pitzer models. From these measurements, the new Pitzer mixing ionic parameters are determined and used to predict the solute activity coefficients in the mixture. 相似文献
14.
The control of the technological steps such as calcination temperature and introduction of catalytic additives are accepted to be key points in the obtaining of improved sol–gel fabricated SnO 2 thick film gas sensors with different sensitivity to NO 2 and CO. In this work, after proving that the undoped material calcined at 1000°C is optimum for NO 2 detection, grinding is added as third technological step for further modification of particle surface characteristics, allowing to reduce cross-sensitivity to CO. The influence of grinding on the base resistance and on the sensor signals to NO 2 and CO is discussed in detail as a function of the structural differences of the sensing material. 相似文献
15.
Fused silica optical fibers have been used in an intrinsic mode optical configuration as biosensors for fluorescence based detection of hybridization of nucleic acids. In this work, the kinetics of hybridization of single-stranded oligonucleotides that were covalently immobilized were studied. The probe DNA was dT 20, and the target was Fluorescein-labeled non-complementary (dT 20) or complementary (dA 20) oligonucleotide. Chronofluorimetric monitoring of the adsorption and hybridization processes was used to investigate oligonucleotide films of different density, in different salt concentrations, at temperatures of 25 and 40 °C, with the concentration of the target DNA being 0.005–0.1 μM. Mathematical models based on first- and second-order Langmuir adsorption have been examined to describe both the adsorption and the hybridization processes. Experimental data were processed using the models, and the hybridization kinetics were calculated. Hybridization kinetics on these optical fiber DNA sensors was found to be up to three orders faster than results presented for a number of other experiments using different immobilization chemistries. 相似文献
17.
Ultrafine SmFe 0.7Co 0.3O 3 powder, prepared by a sol–gel method, shows a single-phase orthogonal perovskite structure. The influence of annealing temperature upon its crystal cell volume, microstructure, electrical and ethanol-sensing properties was investigated in detail. When the annealing temperature increases from 600 to 950 °C, the unit cell volume of the SmFe 0.7Co 0.3O 3 sample reduces, and its average grain size increases. When the annealing temperature increases from 600 to 850 °C, the optimal working temperature and response to ethanol of the SmFe 0.7Co 0.3O 3 sensor increase, and the response–recovery time shortens. But when the annealing temperature further increases from 850 to 950 °C, there are decreases of the optimal working temperature and sensor response, and the response–recovery time is prolonged. The results indicate that, as for sensor response, its optimal annealing temperature is about 850 °C, and the sensor based on SmFe 0.7Co 0.3O 3 annealed at 850 °C shows the highest response S = 80.8 to 300 ppm ethanol gas, and it has the best response–recovery and selectivity characteristics. When the ethanol concentration is as low as 500 ppm, the curve of its optimal response versus concentration is nearly linear. Meanwhile, the influence mechanisms of annealing temperature upon the conductance, the optimal working temperature and sensor response for SmFe 0.7Co 0.3O 3 were studied. 相似文献
18.
Polyacrylamide (PAA) and amine-functionalized PAA (AFPAA) nanoparticles with disulfonated 4,7-diphenyl-1,10-phenantroline ruthenium (Ru(dpp(SO 3) 2) 3) have been prepared. The nanoparticles produced have a hydrodynamic radius of 20–25 nm. The amount of singlet oxygen (1O2) produced by Ru(dpp(SO3)2)3 as been measured using anthracene-9,10-dipropionic acid (ADPA). A kinetic model for the disappearance of ADPA, by steady state irradiation of Ru(dpp(SO3)2)3 at 465 nm, has been developed taking also into account a consumption not mediated by 1O2. This direct consumption of ADPA is evaluated by irradiating in the presence of NaN3 and is about 30% of the total. All the experimental results are very well described by the model developed, both for free Ru(dpp(SO3)2)3 and with this dye incorporated in the nanoparticles. It is found that the polyacrylamide matrix does not quench the 1O2 produced, allowing it to reach the external solution of the nanoparticles and react with ADPA. When the matrix possesses amine groups, AFPAA, the amount of 1O2 that reacts with ADPA is slightly reduced, 60%, but most of the 1O2 produced can still leave the particles and react with external molecules. The particles produced may therefore be used as sources of 1O2 in photodynamic therapy (PTD) of cancers. The fact that those nanoparticles do not quench significantly the 1O2 makes possible the future development of 1O2 sensors based on PAA nanoparticles with the appropriate sensor molecule enclosed. 相似文献
19.
Enzyme sensors for glucose and uric acid have been developed based on a solid-electrolyte cell using NASICON (Na 3Zr 2Si 2PO 12). These potentiometric devices respond reversibly to glucose and uric acid over a concentration range of two orders of magnitude with sensitivities of −54 and −52 mV/decade, respectively. The sensors can be used for a batch-type as well as a flow-through-type measuring system. Primarily the sensors respond to the H 2O 2 that is produced by the enzymatic reactions. The role of the three-phase region, electrolyte solution, sensing electrode metal and NASICON has been investigated. The liquid electrolyte/sensing electrode metal interface is found to work as a potential-determining as well as a rate-determining interface for the enzyme sensor. 相似文献
20.
This paper presents the development of micromachined thin-film silicon microbolometers which can be used for detection of soft X-ray, UV, visible and infrared radiation. The detector structure is a 1 μm thick polysilicon/Si 3N 4 membrane suspended over a cavity. This structure has been obtained by anisotropic etching of silicon with a previously deposited polysilicon/Si 3N 4 sandwich. Alternatively, porous silicon has been used as the sacrificial layer. Devices have been characterized. Good values of the voltage responsivity and detectivity have been obtained. 相似文献
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