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Search Results: 1 - 10 of 1636 matches for " semiconductor oxides "
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Metal Oxide Semi-Conductor Gas Sensors in Environmental Monitoring
George F. Fine,Leon M. Cavanagh,Ayo Afonja,Russell Binions
Sensors , 2010, DOI: 10.3390/s100605469
Abstract: Metal oxide semiconductor gas sensors are utilised in a variety of different roles and industries. They are relatively inexpensive compared to other sensing technologies, robust, lightweight, long lasting and benefit from high material sensitivity and quick response times. They have been used extensively to measure and monitor trace amounts of environmentally important gases such as carbon monoxide and nitrogen dioxide. In this review the nature of the gas response and how it is fundamentally linked to surface structure is explored. Synthetic routes to metal oxide semiconductor gas sensors are also discussed and related to their affect on surface structure. An overview of important contributions and recent advances are discussed for the use of metal oxide semiconductor sensors for the detection of a variety of gases—CO, NOx, NH3 and the particularly challenging case of CO2. Finally a description of recent advances in work completed at University College London is presented including the use of selective zeolites layers, new perovskite type materials and an innovative chemical vapour deposition approach to film deposition.
A Perspective on the Flame Spray Synthesis of Photocatalyst Nanoparticles
Wey Yang Teoh
Materials , 2013, DOI: 10.3390/ma6083194
Abstract: The synthesis of functional nanoparticles via one-step flame spray pyrolysis (FSP), especially those of catalytic nature, has attracted the interests of scientists and engineers, as well as industries. The rapid and high temperature continuous synthesis yields nanoparticles with intrinsic features of active catalysts, that is, high surface area and surface energetics. For these reasons, FSP finds applications in various thermally inducible catalytic reactions. However, the design and synthesis of photocatalysts by FSP requires a knowledge set which is different from that established for thermal catalysts. Unknown to many, this has resulted in frustrations to those entering the field unprepared, especially since FSP appears to be an elegant tool in synthesising oxide nanoparticles of any elemental construct. From simple oxide to doped-oxide, and mixed metal oxide to the in situ deposition of noble metals, this Perspective gives an overview on the development of photocatalysts made by FSP in the last decade that led to a better understanding of the design criteria. Various challenges and opportunities are also highlighted, especially those beyond simple metal oxides, which perhaps contain the greatest potential for the exploitation of photocatalysts design by FSP.
Aplicación de peliculas delgadas de SnO2 y SnO2:Ru como sensores de propano
Aguilar-Leyva, J.;Maldonado, A.;Olvera, M. de la L.;
Superficies y vacío , 2012,
Abstract: in this work we report the sensing properties of undoped and ruthenium-doped tin oxide thin films (sno2, sno2:ru) with different thicknesses, in a controlled atmosphere of propane gas (c3h8) at different operation temperatures. the films were deposited onto soda-lime glass substrates by the spray pyrolysis technique at different deposition temperatures, namely, 300, 350, 400, and 450°c. all the films were annealed in vacuum at 400°c during 1 h in order to stabilize the surface physical characteristics. the sensing properties of the films were characterized by the surface electrical resistance ratio in a c3h8 atmosphere, and air as reference. maximum sensitivities, on the order of 1.4 and 7.4 were obtained for undoped sno2, and, sno2:ru thin films, respectively.
Improved acetone sensing properties of flat sensors based on Co-SnO2 composite nanofibers
Lei Hu,Yi Li
Chinese Science Bulletin , 2011, DOI: 10.1007/s11434-011-4558-0
Abstract: Co-SnO2 composite nanofibers were synthesized by an electrospinning method and characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. Gas sensors were fabricated by spinning these nanofibers onto flat ceramic substrates, which had signal electrodes and heaters on their top and bottom surfaces, respectively. Compared with sensors loaded with pure SnO2 nanofibers, the Co-SnO2 nanofiber sensors exhibited improved acetone sensing properties with high selectivity and rapid response and recovery times. The response was 33 when the sensors were exposed to 100 μL/L acetone at 330°C, and the corresponding response with 100 μL/L of ethanol was only 6. The response and recovery times to acetone were about 5 and 8 s, respectively. These results indicate Co-SnO2 composite nanofibers are good candidates for fabrication of high performance acetone sensors for practical application.
Hydrogen Gas Sensors Based on Semiconductor Oxide Nanostructures
Haoshuang Gu,Zhao Wang,Yongming Hu
Sensors , 2012, DOI: 10.3390/s120505517
Abstract: Recently, the hydrogen gas sensing properties of semiconductor oxide (SMO) nanostructures have been widely investigated. In this article, we provide a comprehensive review of the research progress in the last five years concerning hydrogen gas sensors based on SMO thin film and one-dimensional (1D) nanostructures. The hydrogen sensing mechanism of SMO nanostructures and some critical issues are discussed. Doping, noble metal-decoration, heterojunctions and size reduction have been investigated and proved to be effective methods for improving the sensing performance of SMO thin films and 1D nanostructures. The effect on the hydrogen response of SMO thin films and 1D nanostructures of grain boundary and crystal orientation, as well as the sensor architecture, including electrode size and nanojunctions have also been studied. Finally, we also discuss some challenges for the future applications of SMO nanostructured hydrogen sensors.
Calibration of GaAlAs Semiconductor Diode  [PDF]
S. B. Ota, Smita Ota
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.310184
Abstract: The forward voltage of GaAlAs semiconductor diode has been measured in the temperature range 50 K - 300 K and for current values between 10 nA and 450 μA. The forward voltage as a function of temperature is least-squares fitted and the coefficients are given. The 1st and 2nd order least-squares fitting has high temperature root between 400 K and 950 K. The presence of the high temperature root indicates that the fitted polynomials are of similar character. The high temperature root is found to increase for the least squares fitted polynomials corresponding to higher current values.
A Theoretical Study on Van Der Pauw Measurement Values of Inhomogeneous Compound Semiconductor Thin Films  [PDF]
Toru Matsumura, Yuichi Sato
Journal of Modern Physics (JMP) , 2010, DOI: 10.4236/jmp.2010.15048
Abstract: The influence of intermixing heterogeneous regions that have different electrical properties from the base materials on van der Pauw measurement values was theoretically studied by computer simulation using the finite-element method. The measurement samples selected were thin films of inhomogeneous semiconductors. Calculated electrical properties, such as resistivity, carrier density, and mobility of the thin films, varied in predictable ways when heterogeneous regions were dispersed in wide ranges over the samples. On the other hand, the mobility of the thin films showed a different change when heterogeneous regions were locally concentrated in the measurement samples.
A Dependence of Crystallinity of In2O3 Thin Films by a Two-Step Heat Treatment of Indium Films on the Heating Atmosphere  [PDF]
Yuichi Sato, Fumito Otake, Hirotoshi Hatori
Journal of Modern Physics (JMP) , 2010, DOI: 10.4236/jmp.2010.16051
Abstract: A difference in crystallinity of In2O3 thin films on sapphire substrates by heat treatment of indium films was reported. Indium films were heated in an inert atmosphere or in air until they reached a specified temperature and then oxidized in air at much higher temperatures. Crystallinity of the In2O3 thin film which was heat-treated in air from room temperature was quite poor. On the other hand, narrow X-ray rocking curves of the In2O3 films were obtained when the temperature was increased in an inert atmosphere to a specified tem-perature.
Cr+3 Distribution in Al1 and Al2 Sites of Alexandrite (BeAl2O4: Cr3+) Induced by Annealing, Investigated by Optical Spectroscopy  [PDF]
Neilo M. TRINDADE, Rosa M. F. SCALVI, Luis V. A. SCALVI
Energy and Power Engineering (EPE) , 2010, DOI: 10.4236/epe.2010.21004
Abstract: In order to investigate optical properties of alexandrite, the present work deals with the influence of thermal annealing on optical absorption and luminescence spectra of natural samples. The exposure time to heat treatment at 1000oC is taken into account. Possible migration of Cr3+ ions from Al1 (inversion site) to Al2 (reflection site) is detected. Sample composition is obtained through Scanning Electron Microscopy (SEM) measurements and points to a rearrangement of Cr+3 and Fe3+ ions in the alexandrite crystalline structure, un-der thermal annealing influence. This feature may be used to control the optical properties of natural alexan-drite, which can be associated to the observed laser emission effect.
Formation characterization and rheological properties of zirconia and ceria-stabilized zirconia  [PDF]
Arvind K. Nikumbh, Parag V. Adhyapak
Natural Science (NS) , 2010, DOI: 10.4236/ns.2010.27086
Abstract: Zirconia and ceria-stabilized zirconia (12Ce-TZP) were synthesized by the dicarboxylate coprecipitation technique such as fumarate, succinate, tartarate and adipate. The formation of these dicarboxylate precursors was studied by elemental analysis, thermal analysis and infrared spectroscopy. The precursors were further decomposed at 650oC for 2 hours to form respective zirconia and ceria-stabilized zirconia. The composition of these oxides was checked by Atomic absorption spectrometer and Energy dispersive X-ray analysis. The structural and morphological characterization of these oxides was done by using X-ray diffraction analysis, surface area, scanning electron micrographs and particle size distribution analysis. These properties were found depending to great extent on the nature of the precursors. The zirconia and ceria-stabilized zirconia obtained from adipate precursor were found to be good for slip- casting. The slips (i.e., suspensions) of these oxides with different solid contents were prepared at different pH with distilled water and ethanol as dispersing agents, with and without deflocculant. The suspension rheological flow (i.e., variation of shear stress and viscosity with shear rate) was determined. The minimum viscosities were observed at pH = 10.16 for ZrO2- water and pH = 10.26 for 12Ce–TZP-water system. The slip, green and sedimentation bulk density were measured.
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