1,720,969 research outputs found
Polycrystalline and amorphous sol-gel derived WO3 thin films and their gas sensing properties
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Comparison of single and binary oxide MoO3, TiO2 and WO3 sol-gel gas sensors
No full textA systematic comparison of sol-gel prepared titanium dioxide (TiO2), WO3, and MoO3 single metal oxide based gas sensors was conducted. Process variables such as solution concentration, deposition parameters, gelling time, annealing time and temperature, remained constant. Sensors based on binary compound MoO3-TiO2 and MoO3-WO3 were also investigated to determine if the performance is superior to their single oxide constituents. The sensors were systematically exposed to O-2, O-3, CO and NO2 gases and ethanol vapor at concentration levels of particular interest. MoO3 binary compound based sensors showed promising O-3, CO and NO2 gas response. Their use as a sensing film for gas is limited due to the materials low evaporating temperature, limiting its operating temperature below 350 degreesC. However, the binary oxide of MoO3-WO3 showed a high response to ethanol vapor and a highly selective response to NO2. (C) 2002 Elsevier Science B.V. All rights reserved
Microstructure characterization of sol-gel prepared MoO3-TiO2 thin films for oxygen gas sensors
No full textBinary metal-oxide MoO3-TiO2 films have been prepared using the sol-gel technique. The thin films were annealed at several temperatures including 400, 450, 500, 550, and 600 degreesC for 1 h. The morphology, crystalline structure, and chemical composition of the films have been analyzed using scanning electron microscopy (SEM) and atomic force microscopy, x-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), and x-ray photoelectron spectroscopy (XPS) techniques. The SEM analysis showed that there are two different sizes of grains in the films annealed at temperatures of 400, 450, 500, and 550 degreesC. One grain type is small with 20-100 nm; the other is a large grain type several micrometers in length. The XRD analysis revealed that the films annealed at 400 degreesC were a mixture of orthorhombic and hexagonal MoO3 phases. The films annealed at 450 degreesC showed an increase in the hexagonal phase. A preferential orientation growth along the (100) plane of the hexagonal phase and the (010) plane of the orthorhombic phase has been found in both samples. RES and XPS analysis showed that the films were stoichiometric. When the annealing temperature was increased beyond 500 degreesC, the concentration ratio of MoO3-TiO2 decreased due to the evaporation of MoO3. For the study of the electrical and gas sensing properties, the films were deposited on sapphire substrates with interdigital electrodes on the frontside and a Pt heater on the backside. The MoO3-TiO2 thin films are sensitive to oxygen gas. The film has exhibited the O-2 response (S = R-g/R-b) of 2.1, 8.1 and 80 for 120, 1000, and 10000 ppm concentration of O-2, respectively. (C) 2001 American Vacuum Society. RI li , yongxiang/C-5059-2009; Russo, Salvy/E-5837-201
Selective NO2 gas sensing characteristics of sol-gel prepared MoO3-WO3 thin filmsSelective NO2 gas sensing characteristics of sol-gel prepared MoO3-WO3 thin films
No full textp- and n-type Fe-doped SnO2 gas sensors fabricated by the mechanochemical processing technique
No full textFe-doped SnO2 sensors were fabricated using micromechanical synthesis technique. The Fe-doped sensor was compared to pure SnO2. Fe-doped SnO2 responded as a p-type semiconductor to oxygen concentrations of up to 10% at 300 degreesC. As the temperature increased to 400 degreesC, the material responded as an n-type semiconductor. Furthermore, a higher surface area and smaller grains size diameters were achieved when doping SnO2 with Fe. This translated into improved dynamic gas sensing properties and also improved responses to gases such as ethanol. (C) 2003 Elsevier Science B.V. All rights reserved
Microstructural characterization of MoO3-TiO2 nanocomposite thin films for gas sensing
No full textThis paper focuses on the microstructural characterization of the MoO3-TiO2 nanocomposite thin films prepared by the sol-gel process. The MoO3-TiO2 thin films were prepared by Mo(OC2H5)(5) and Ti(OC4H9)(4) precursor solutions. Different atomic ratios of the two compounds were investigated. The thin films were deposited on silicon, quartz and sapphire substrates annealed at temperatures of 400, 450, 500 and 600 degreesC for 1 h. The XRD patterns revealed the structure of the molybdenum dominated films consisted mainly of an orthorhombic MoO3 phase with preferential orientation along the (0 1 0)plane. The TEM selected area diffraction patterns revealed the presence of orthorhombic MoO3 and anatase and brookite TiO2 phases. The XPS characterization indicated the films are stoichiometric (MoO3 and TiO2). The SEM analysis showed that the films annealed at 400 degreesC are smooth and uniform with 20-100 nm sized grains. The MoO3 dominated films annealed at high temperatures (T > 500 degreesC) have relatively large micrometer particles grown out of the film. The AFM images showed that the MoO3 dominated thin films possess a high surface roughness and the TiO2 dominated films have smooth and uniform nanosized grains. The TEM results showed that the TiO2 dominated films have an average grain size of 6 nm with a narrow distribution. The MoO3 dominated films have an average size of 5 nm but with a broad distribution. The morphological and physical properties of the MoO3-TiO2 nanocomposite can be tailored by altering the ratio of the two compounds. and hence, enhanced thin films for gas-sensing could be achieved. (C) 2001 Elsevier Science B.V. All rights reserved. RI li , yongxiang/C-5059-200
MoO3, WO3 single and binary oxide prepared by sol-gel method for gas sensing applications
No full textMoO3, WO3 single and Mo/W binary compounds at different Mo/W atomic percentages were deposited by sol-gel spin coating technique on Si/Si3N4 substrates provided with Pt interdigital electrodes and annealed at 450degreesC for 1 h. Films were characterized by SEM, grazing incidence XRD and XPS techniques. Electrical responses to different gases were obtained by exposing the films to 30 ppm CO and 1 ppm NO2. Increasing the Mo/W content the selectivity to NO2 is enhanced. Gas responses resulted to be influenced by the Mo/W weight ratio, films morphology and amount of crystalline phases. RI li , yongxiang/C-5059-200
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