WO_3气敏薄膜的膜厚对气体响应时间的影响

用简单的模型分析了薄膜气体传感器敏感材料的膜厚对气体响应时间的影响,该模型适用于分析WO3薄膜气体传感器的敏感特性。薄膜气体传感器的敏感特性依赖于气体原子在薄膜内的扩散和与气敏材料的响应;而气体原子在薄膜内的扩散是由薄膜厚度决定的。经过推导得出理论上WO3薄膜对NH3的敏感特性,并将其与实验所得的数据进行比较。最后,给出了WO3薄膜气体传感器的气敏特性与气体在其膜内扩散和膜厚的关系。     

Fluctuation-enhanced scent sensing using a single gas sensor

Scent or aroma sensing during aromatherapy can be carried out by applying only a single resistance gas sensor (TGS - Taguchi Gas Sensors). This paper considers the efficiency of detection of essential oils by DC resistance and its fluctuations observed in TGS sensors. A detailed study has been conducted for scents emitted by five popular essential oils using three sensor types (TGS 2600, TGS 2602, TGS 823). The research was focused on the practical use in aromatherapy to assure the same intensity of scents which are sprayed by a glass nebulizer. The prepared system for scent emission and control of its intensity was presented as well.     

Micrometer-sized nanoporous tin dioxide spheres for gas sensing

We report the synthesis of mesoporous tin dioxide (SnO₂) materials with well-defined particle morphology. The products consist of uniform spheres with a diameter of 5 μm. The spheres are hierarchically porous with two distinct pore modes of 5.0 nm and 52 nm, respectively. This special porosity is the result of a synthesis procedure which involves a ‘hard templating’ (nanocasting) process. The product forms an approximately homogeneous monolayer of spheres on a sensor substrate and shows promising response to methane gas with low cross-sensitivity to water. The structural properties and gas-sensing performance are compared with a mesoporous SnO₂ material without defined morphology, prepared by a ‘soft templating’ procedure.     

Comparative gas sensing in copper porphyrin and copper phthalocyanine spin-coating films

Spin-coating films of tetra-(tert-butyl)-5,10,15,20-tetraazaporphyrin copper (CuTAP(t-Bu)₄) and tetra-(tert-butyl) phthalocyanine copper (CuPc(t-Bu)₄) was obtained and characterized by absorption spectra and atomic force microscopy. The gas sensing behaviors of the films were investigated with respect to NH₃ and NO₂ at room temperature. In addition, the interactions between complexes and gas analytes were also discussed. It was found that the devices exhibited better response and slow response-recovery times with increase of interactions between the complexes and analytes related with conjugated ability of complexes. This suggests that the response may imparted by use of strong interactions between the complexes and the analyte of interest at the expense of reversibility.     

Improvement of optimization algorithm in active gas/odor sensing system

In the field of gas or odor sensing, it is difficult to quantify the composition of a mixture of aromas accurately. We proposed earlier the method of active sensing for this purpose and quantification was successfully performed in principle. Here, an optimization algorithm such as the gradient descent method for quantifying the mixture composition is improved by the introduction of least-squares and singular-value decomposition methods so that the stability of the system can be improved. Better convergence is achieved after the improvement.     

The influence of additives on gas sensing and structural properties of In2O3-based ceramics

In this paper the influence of additives on gas response of In₂O₃-based one-electrode sensors is discussed. The analysis of Raman scattering of doped In₂O₃ ceramics was carried out, and the mechanism of doping influence on In₂O₃ grain structure is suggested. It is concluded that the appearance of the second phase in In₂O₃-based ceramics is the main factor controlling the change of gas sensing characteristics.     

Phthalocyanines as sensitive coatings for QCM sensors: Comparison of gas and liquid sensing properties

The quartz crystal microbalance (QCM) was used to investigate the liquid sensing properties of a set of phthalocyanines (Pcs) which were systematically varied by attaching the substituent 2,2,3,3-tetrafluoropropyloxy to different positions and by introducing a central metal ion (i.e. Ni²⁺, Zn²⁺, and Cu²⁺). The responses to low concentrations of organic compounds such as hydrocarbons and chlorocarbons dissolved in water were recorded. The materials were very sensitive to the tested compounds with detection limits in the lower parts-per-million range and they exhibited a good sensing performance as the sensors have been working fully reversibly and reliably over long periods of time. Besides, the influence of substitution pattern and choice of central metal ion on the liquid sensing properties of Pcs were studied for the first time. The results show that the responses differ notably from each other depending on the modifications made to the Pc. Finally, it is demonstrated that the gas and liquid sensing responses of the materials are highly correlated and can be linked to each other with the help of a basic physical model.     

Differential study of substituted and unsubstituted cobalt phthalocyanines for gas sensor applications

The conductivity of CoPc (cobalt phthalocyanine) and Co[(SO₃Na)_2,3Pc] was measured under a flow of two different gases (NH₃ and O₃), during exposure/recovery cycles. It appears that the relative responses are linearly related to the concentration, in the 20-200 ppb range for O₃ and in the 20-200 ppm range for NH₃. Observed during time, the sensing parameters allow a qualitative understanding of the kinetics. The comparative study of those products under both different gases gave interesting results for sensor applications. Whereas CoPc is sensitive to both gases, its sulfonated counterpart is only sensitive to NH₃.     

Biomorphic synthesis of ZnSnO3 hollow fibers for gas sensing application

Biomorphic ZnSnO₃ hollow fibers have been fabricated using cotton as biotemplates. Cotton fibers are infiltrated with zinc nitrate and stannic chloride solution and subsequently sintered in air at high temperatures to produce the final ZnSnO₃ hollow fibers. The samples have further distinctions in structure and morphology by X-ray diffraction and scanning electron microscopy. It showed that all the samples present an orthorhombic structure of high crystallinity, and the hollow fibers were composed of numerous ZnSnO₃ nanorods. Furthermore, gas sensors were fabricated and an investigation of ethanol sensing properties has been conducted. The sensor, based on ZnSnO₃ hollow fibers calcined at 500 °C, shows highly sensitive to ethanol with fast response, good selectivity and stability, indicating its potential applications for environment and food or the drinking status of drivers.     

介孔SnO2气敏性能研究

为了改善传感器的气敏性能,采用溶胶-凝胶法合成了介孔SnO2,并研究了其气敏性能.研究表明:与纳米SnO2相比,介孔SnO2气体传感器具有较高的酒精、二甲苯响应,在100～150℃对甲醛的响应也大大提升.在100～ 150℃,干扰气体为甲苯和二甲苯时,介孔SnO2表现远远优越于纳米SnO2的酒精选择性.在100,150,350℃,干扰气体为甲苯时,介孔SnO2也具有优越的甲醛选择性.介孔SnO2的响应时间较短,但恢复时间较长.     

Fabrication of gas sensing devices with ZnO nanostructure by the low-temperature oxidation of zinc particles

A method for low-temperature synthesis of a mixture of high-density ZnO nanoflakes and nanowires was developed to produce low-cost and high-efficiency gas sensors with ZnO nanostructures. ZnO nanoflakes and nanowires were grown on glass substrates by the RF sputter deposition of Zn particles and localized oxidation at a low temperature of 300 °C. The synthesized ZnO nanoflakes and nanowires were polycrystalline and had nanometer dimensions, as revealed by X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) measuring. A gas sensor based on the mixture of ZnO nanoflakes/nanowires responded rapidly and sensitively to ethanol. The sensing properties of the ZnO nanostructure sensor were approximately 72% for 50 ppm ethanol gas at an operating temperature of 100 °C. The response to 10 ppm of ethanol gas was 42% at the same temperature.     

Low temperature gas sensing applications using copier grade transparency sheets as substrates

Transparency sheets, coated with copper on both sides by means of thermal evaporation in vacuum, are patterned by direct chemical etching to realize sensing platforms having copper heaters on the backside, and resistances having calibrated temperature coefficient on the topside. The mechanical and thermal stability of these structures was demonstrated up to 70 °C. Bending tests also show that the metallic patterns do maintain unaltered performances after more than 10⁴ bending cycles. Resistance measurements show that the resistance on the patterned copper structures linearly increases with the temperature in the range between room temperature and 70 °C, while above this temperature an irreversible damage occurs. Experimental investigations demonstrate that the heaters on the backside of the sensing platforms allow to obtain a quite uniform temperature distribution on the top side over an area larger than 1 cm².Coating the flexible sensing platform by doped polyaniline and carbon nanotubes embedded in a polymer host, a chemoresistive system operating at low temperature is developed, which allows to perform tests at constant temperature, with the temperature being set and monitored by using the heater and the patterned resistance, respectively. The sensing performances of the films are evaluated by means of electrical measurements performed while exposing the samples to different relative humidity levels, and to calibrate ammonia pulses.     

多氯联苯分子空间坐标与气相色谱相对保留时间的QSPR研究

应用ChemWindow和ChembioOffice绘图软件对209种多氯联苯化合物(PCBs)作图,通过分子最低能量模块计算得到其空间稳定构型,空间构型对应着分子空间坐标,固定坐标原点,得到同一坐标系的分子空间坐标。对PCBs分子空间坐标研究,定义了2个描述符,原子距离指数(Y_S)和分子空间特征指数(Y_F)。用多元线性回归方法获得了多氯联苯化合物的气相色谱相对保留时间(GCRRT)与该空间距离指数之间良好的定量结构一性质相关(QSPR)模型,定义的指数易于计算和运用。模型相关性良好(R=0.990),具有较高的预测能力和可靠性,从另一角度为QSPR研究提供一个新的思路。     

Growth and gas sensing characteristics of p- and n-type ZnO nanostructures

ZnO nanoparticles (NPs) of 5-15 nm size and nanowires (NWs) of 50-100 nm dia., exhibiting p and n-type characteristics, respectively, have been synthesized using simple chemical process. ZnO NW-films exhibited good sensitivity and selectivity towards H₂S in ppm range with fast response and recovery times. Interestingly, ZnO NP-films showed p-type conductivity that has been obtained for the first time without intentional doping while NW-films showed n-type conduction as has also been reported in various earlier studies. The p- and n-type conductivities in NP- and NW-films have been confirmed using hot probe and Kelvin probe measurements. The n-type behavior of NW-films is attributed to oxygen vacancies, whereas the p-type nature of NP-films is attributed to the zinc vacancy, surface acceptor levels created by the adsorbed oxygen and/or the unintentional carbon doping in ZnO.     

One-step synthesis and gas sensing characteristics of hierarchical SnO2 nanorods modified by Pd loading

The hierarchical unloaded and Pd-loaded SnO₂ nanostructures, consisting of many aggregative nanorods were prepared by one-step hydrothermal method. A possible formation mechanism of these hierarchical structures was proposed. The butanone sensing properties of the sensors based on unloaded and hierarchical Pd-loaded SnO₂ nanorods were investigated. The results indicate that the response of sensor using hierarchical Pd-loaded SnO₂ nanorods to 1000 ppm butanone was 451 at 250 °C, which was about 10 times higher than that of sensor based on unloaded SnO₂. Such enhanced gas sensing performances can be attributed to both the chemical and the electrical contribution of Pd loading.     

Using a TiO2/ZnO double-layer film for improving the sensing performance of ZnO based NO gas sensor

NO gas sensors, based on ZnO thin film (ZnO_film), TiO₂ nanoparticulate film (TiO₂NP), and TiO₂NP/ZnO_film double-layer film, were fabricated, and their sensing characteristics towards NO gas were investigated in this study. The maximal response of a ZnO_film deposited onto a rougher Al₂O₃ substrate, towards NO gas, was higher than that of a ZnO_film deposited on a smoother glass substrate. Although the sensing response of the TiO₂NPs itself towards NO gas was minute, the TiO₂NP/ZnO_film double-layer film showed enhanced response as compared with TiO₂NP or ZnO_film single-layer film. In addition, the sensor response of the TiO₂NP/ZnO_film double-layer film was strongly influenced by the annealing time for the film preparation; the maximum response to NO was enhanced about 6.2 times as the annealing time was increased from 30 min to 2 h. Based on the XPS results, the increase in the transition zone between TiO₂NP and ZnO_film along with the appearance of Ti³⁺ state was noticed when the annealing time was increased. With the high sensitive TiO₂NP/ZnO_film/Al₂O₃ electrode, the limit of detection (S/N = 3) can be achieved at 8.8 ppb. The double-layer TiO₂NP/ZnO_film also showed improved selectivities with respect to NO₂ and CO.     

离散半圆柱体电阻式气体传感器的研究

气体传感器,作为一种先进的信息获取设备,在人们生产和生活中发挥着越来越大的作用。人们对其性能要求也越来越高,尤其是传感器的响应速度更是人们关注的重点。所以,本文提出了一种新型的气体传感器模型,即在连续平面敏感结构的基础上,将其离散化,成为离散半圆柱体阵列结构,根据平面和圆柱体扩散方程,分析了两者的响应时间和灵敏度,并进行比较,证明离散半圆柱体阵列敏感结构具有了更快的响应速度和更高的灵敏度。     

High-performance liquefied petroleum gas sensing based on nanostructures of zinc oxide and zinc stannate

Toxic and combustible gas detection plays a major role in environmental air quality monitoring. Real-time monitoring of hazardous gases and signal of accidental leakages is of great importance owing to the concern for safety requirements in industries and household applications. A simple and economical method for the fabrication of highly sensitive zinc oxide (ZnO) nanorods based gas sensors for detecting low concentrations of Liquefied Petroleum Gas (LPG) was studied in this work. Platinum (Pt) nanoparticles were deposited on the sensing medium which acts as catalysts to improve the sensor performance. The change in electrical resistance of the metal oxide semiconductor for varying concentrations of LPG was measured. Maximum response of 59% was achieved for 9000 ppm LPG at 250 °C. Further to improve the sensing performance of the sensor towards LPG, surface modification of ZnO nanorods using zinc stannate (Zn₂SnO₄) microcubes was performed. High response of 63% was observed for 3000 ppm LPG at 250 °C. Significant improvement in response of the sensor with Zn₂SnO₄ microcubes on ZnO nanorods was observed when compared to sensor with ZnO nanorods.     

一种压缩待测气体增强气体传感的方法

针对普通气体传感器在低体积分数的气体检测中灵敏度低的问题,提出将待测气体进行压缩以增强气体传感器响应的方法,根据检测压缩后的气体响应的特征,间接得到普通状态下该气体的体积分数。设计了一种小型的样机系统来进行气体压缩和气体传感器检测,描述了系统各个模块的设计,给出了该系统的软件设计和控制流程。以H2S气体为检测对象进行了实验,分析结果表明:该方法提高了现有传感器检测低体积分数气体的能力,尤其是提高了对毒害气体的及时发现和预警防范能力。样机的试制也为该压缩传感系统的进一步小型化和提升检测性能提供了条件,具有较高的应用价值。     

Limitations on the use of perovskite-structure oxides in gas sensing as a result of the concurrent operation of separate mechanisms

This paper addresses the consequences of operating a semiconducting oxide gas sensor with appreciable oxygen ion mobility within a temperature range where equilibration of the bulk oxygen content and surface reactions with reducing gases can proceed simultaneously. The investigations focus on the behaviour of an example of a perovskite material (LaFe_0.95W_0.05O₃) stemming from standard perovskites, but having all alkaline ions substituted by rare earth, on its resistance and stability against sulfur-containing gases (H₂S) and on its sensitivity towards some important reducing gases (carbon monoxide, ethanol, methane, propane). The experimental results provide responses to these latter four gases which are distorted by the superimposition of responses involving bulk oxygen equilibration upon the surface reactions with reducing gases. It is concluded that, although perovskite-structure oxides remain useful for oxygen monitoring at high temperature, their deployment for sensing reducing gases is problematical.