Papers by Keyword: Gas-Sensing

Abstract: In this work, the nanorod structure of Tin oxide (SnO₂) prepared by glancing angle deposition (GLAD) technique with different O₂ flow rate from 12 to 48 sccm. The surface and Crystal structure of SnO₂ thin films were characterized by scanning electron microscopy (SEM), X-raydiffraction (XRD) and tested toward ethanol gas sensing. Structural characterization showed that the morphological of all SnO₂ thin films prepared with different O₂ flow rates consists of columnar nanorod structures and the nanorod size which are likely to decrease as the O₂ flow rate increases. As the O₂ flow rate increases from 12 to 48 sccm, the crystal structure of SnO₂ nanorods changes from amorphous to crystalline and the crystallinity is improved by the increase of the O₂ flow rate. Gas sensing performances of SnO₂ nanorods have been characterized toward ethanol sensing. It was found that SnO₂ nanorods exhibit n-type conductivity with decreased resistance when exposed to ethanol, which is reducing gas. In addition, sensitivity to ethanol tend to improve as O₂ flow rate increases. Furthermore, the SnO₂ nanorods prepared at O₂ flow rates 48 sccm are detecting ethanol gas at concentrations lower than 50 ppm at operating temperature 250 °C.

Abstract: In order to reduce the complexity of the experiment processes for the study of gas-sensing material properties, we have designed programmed temperature control gas-sensing characteristic tester. To obtain the precise measurement of gas-sensing materials’ resistance and programmed output voltage, the tester has used ratio method, SCM control technology, basic circuit principles, A/D converter, D/A conversion, the feedback network. Test results show that this system provides a great convenience for gas-sensing materials testing.

Abstract: Ag nanoparticle functionalized TiO₂ nanowire (TiO₂ NW @ Ag NP) was synthesized and the gas sensing properties of the nanowire film was investigated. The size and the distribution density of Ag nanoparticles can be easily controlled. The sensor based on Ag nanoparticle functionalized TiO2 nanowire thin film has promising sensing properties, and at room temperature, its sensitivity towards H₂ and O₂ can reach 500 ppm and 1000 ppm respectively.

Abstract: In this paper, the precursors were synthesized by microwave hydrothermal method using SnCl4•5H2O and Ce(NO3)3·6H2O as raw material, CO(NH2)2 as precipitants, respectively. Pure SnO2 nanoparticles and cerium-doped SnO2 nanoparticles were obtained. Furthermore, five kinds of SnO2 thick film gas sensors were fabricated from the above SnO2 nanoparticles (the sensors denoted as sensor SC0, SC2, SC3, SC4 and SC6, respectively). The experiment results showed that, compared with pure SnO2 thick film gas sensor, the intrinsic resistance of cerium-doped SnO2 thick film gas sensors decreased, and their sensor responses to acetone vapor increased, which are discussed in relation to the SEM micrographs of thick film sensors.

Abstract: Nano crystalline SnO₂ was prepared by sol-gel with PEG surfactant. CuO was doped in the SnO₂ by mechanical mixture and reaction congelation from CuCl. The samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen adsorption isotherms (BET). The results indicated that the average crystal size of SnO2 at sintering temperature of 550 °C was 10 nm, the conglomeration size of SnO₂ was about 100 nm. The specific surface area of pure SnO₂, mechanical doping SnO₂ and reaction doping SnO₂ were 110, 84, 72 m²/g, respectively. The thick film gas sensors made from these samples were examined. SnO₂ doped by different methods had different electrical and gas-sensing properties. The sensors based on CuO doped SnO₂ films exhibited less sensitive to ethanol gas but extremely higher sensitivity to H₂S gas than that of pure SnO₂.

Abstract: Ag-doped porous SnO₂ nanopowders were synthesized via a facile glucan-assisted template method combined with subsequent calcinations. Morphology, crystal structure, and H₂S gas sensing properties of pure and Ag-doped porous SnO₂ nanopowders were investigated. In comparison with undoped SnO₂ nanopowders, the Ag-doped porous SnO₂ nanopowders demonstrated enhanced H₂S sensing behavior with high sensitivity, short response and recovery time, relatively low response concentration of 50 ppm, and good selectivity. The dramatic improvement in H₂S gas sensing characteristics was explained in terms of rapid gas diffusion onto the entire sensing surface due to the less-agglomerated and porous structure of SnO₂ nanopowders and the catalytic effect of doped-Ag element. The main objective of this research is to develop a new method to introduce catalysts on gas-sensing materials with less-agglomerated and porous structure.

Abstract: In(OH)₃ and InOOH were prepared through a simple hydrothermal method at different volume ratios of En and H₂O. C-In₂O₃ and H-In₂O₃ were obtained by annealing these two precursors at 400°C in air, respectively. One-step In₂O₃ was also synthesized via solvothermal process using DEG as solvents. The effects of reaction conditions on phase structures and morphologies were studied. The gas sensing properties of the obtained materials toward ethanol were measured and X-ray diffraction, field-emission scanning electron microscope and PL were used to characterize the as-obtained products.

Abstract: Polythiophene (PTP) coated V2O5 nanotubes were prepared by an in-situ polymerization of thiophene monomers in the presence of prepared V2O5 nanotubes. The nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which proved the polymerization of thiophene monomer and the strong interaction between polythiophene and V2O5 nanotubes (VONTs). The gas sensing properties of PTP coated V2O5 nanotubes were studied at room temperature, which was found that PTP coated V2O5 nanotubes could detect ethanol with much higher sensitivity than pure VONTs. The sensing mechanism of PTP coated V2O5 nanotubes to ethanol is presumed to be the synergetic interaction between polythiophene (PTP) and V2O5 nanotubes.

Abstract: Hollow-core photonic crystal glass fibers have a high potential for gas sensing applications, since large light-gas interaction lengths can be effectively attained. Nevertheless, in order to enhance effective diffusion of gas into the hollow-core fiber, multi-coupling gaps are often needed, which raise coupling loss issues that must be evaluated prior to the development of practical systems. In this paper, a study on the coupling losses dependence on lateral and axial gap misalignment for single-mode fiber and two different types of hollow-core photonic crystal glass fibers is carried out. In addition, an experimental technique on splicing these glass fibers is also described and some results are presented showing that low splice losses can be obtained with high reproducibility.

Abstract: In order to improve the gas sensitivity of SnO2, Ni-doped and Co-doped nano-powders were prepared by the homogenous co-precipitation method using analytical pure SnCl4•5H2O and NH3•H2O as main materials under different doped ratios n (M2+)/n (Sn4+). The gas sensors were made by the thick film technique on mica substrates. The structure and crystal properties of the samples were investigated by X-ray diffraction (XRD). The results indicated that Sn4+ in the crystal lattice of SnO2 was partly replaced by M2+, which resulted in the change of the M-O bond lengths and the lattice parameters. The sensitivities of the sensors in H2 atmosphere with different concentrations at 75°C were tested. As a result, doped M2+ especially Ni2+ improves its H2 sensitivity, the sensitivities increases linearly with the increasing H2 concentration, and the best doping n(M2+)/n(Sn4+) of preparing gas-sensing material were obtained. The results show that doping which leads to the asymmetry of electrovalent balance of M-O octahedrons improves the activities and semiconductor properties of the powders. These studies play an important part in detecting reductive gases in special environment.