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Special Issue "Gas Sensors - 2010"

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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Chemical Sensors".

Deadline for manuscript submissions: closed (31 December 2010)

Special Issue Editor

Guest Editor
Prof. Dr. Michael Tiemann (Website)

Department of Chemistry, Faculty of Science, University of Paderborn, Warburger Str. 100, D-33098 Paderborn, Germany
Interests: porous materials; semiconducting; gas sensors; nanoparticles; in-situ studies; chemical synthesis; functional materials

Special Issue Information

Dear Colleagues,

The science and development of gas sensors continues to be a vivid field of research. Recent advances in chemical synthesis and microfabrication provide us with new sensing materials and novel devices with substantially enhanced properties. At the same time, fundamental knowledge about sensing mechanisms has greatly improved by sound theoretical models as well as in situ spectroscopic studies. This special issue on “gas sensors” aims to cover all various aspects, such as (but not limited to) the preparation of functional materials and micro-fabricated systems for gas sensing, new insights in gas-sensing mechanisms, and the large number of different types of gas-sensing principles (resistive, mechanical, capacitive, etc.).

Prof. Dr. Michael Tiemann
Guest Editor

Keywords

  • metal oxide gas sensors
  • thin films
  • porous materials / nanostructures
  • microfabrication / MEMS
  • resistive gas sensors
  • electrochemical gas sensors
  • optical gas sensors
  • thermometric gas sensors / pellistors
  • acoustic wave / crystal microbalance gas sensors
  • cantilever gas sensors
  • capacitive humidity sensors
  • field-effect gas sensors

Published Papers (21 papers)

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Research

Jump to: Review

Open AccessArticle Oxidation of Hydrocarbons on the Surface of Tin Dioxide Chemical Sensors
Sensors 2011, 11(4), 4425-4437; doi:10.3390/s110404425
Received: 2 March 2011 / Revised: 1 April 2011 / Accepted: 6 April 2011 / Published: 15 April 2011
Cited by 7 | PDF Full-text (428 KB) | HTML Full-text | XML Full-text
Abstract
The paper presents the results of our investigation on the effect of the molecular structure of organic vapors on the characteristics of resistive chemical gas sensors. The sensors were based on tin dioxide and prepared by means of thick film technology. The [...] Read more.
The paper presents the results of our investigation on the effect of the molecular structure of organic vapors on the characteristics of resistive chemical gas sensors. The sensors were based on tin dioxide and prepared by means of thick film technology. The electrical and catalytic examinations showed that the abstraction of two hydrogen atoms from the organic molecule and formation of a water in result of reaction with a chemisorbed oxygen ion, determine the rate of oxidation reactions, and thus the sensor performance. The rate of the process depends on the order of carbon atoms and Lewis acidity of the molecule. Therefore, any modification of the surface centers of a sensor material, modifies not only the sensor sensitivity, but also its selectivity. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
Open AccessArticle A High Temperature Capacitive Humidity Sensor Based on Mesoporous Silica
Sensors 2011, 11(3), 3135-3144; doi:10.3390/s110303135
Received: 30 January 2011 / Revised: 20 February 2011 / Accepted: 25 February 2011 / Published: 14 March 2011
Cited by 17 | PDF Full-text (604 KB) | HTML Full-text | XML Full-text
Abstract
Capacitive sensors are the most commonly used devices for the detection of humidity because they are inexpensive and the detection mechanism is very specific for humidity. However, especially for industrial processes, there is a lack of dielectrics that are stable at high [...] Read more.
Capacitive sensors are the most commonly used devices for the detection of humidity because they are inexpensive and the detection mechanism is very specific for humidity. However, especially for industrial processes, there is a lack of dielectrics that are stable at high temperature (>200 °C) and under harsh conditions. We present a capacitive sensor based on mesoporous silica as the dielectric in a simple sensor design based on pressed silica pellets. Investigation of the structural stability of the porous silica under simulated operating conditions as well as the influence of the pellet production will be shown. Impedance measurements demonstrate the utility of the sensor at both low (90 °C) and high (up to 210 °C) operating temperatures. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
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Open AccessArticle Application of V2O5/WO3/TiO2 for Resistive-Type SO2 Sensors
Sensors 2011, 11(3), 2982-2991; doi:10.3390/s110302982
Received: 11 February 2011 / Revised: 1 March 2011 / Accepted: 3 March 2011 / Published: 7 March 2011
Cited by 17 | PDF Full-text (615 KB) | HTML Full-text | XML Full-text
Abstract
A study on the application of V2O5/WO3/TiO2 (VWT) as the sensitive material for resistive-type SO2 sensor was conducted, based on the fact that VWT is a well-known catalyst material for good selective catalytic nitrogen [...] Read more.
A study on the application of V2O5/WO3/TiO2 (VWT) as the sensitive material for resistive-type SO2 sensor was conducted, based on the fact that VWT is a well-known catalyst material for good selective catalytic nitrogen oxide reduction with a proven excellent durability in exhaust gases. The sensors fabricated in this study are planar ones with interdigitated electrodes of Au or Pt. The vanadium content of the utilized VWT is 1.5 or 3.0 wt%. The resistance of VWT decreases with an increasing SO2 concentration in the range from 20 ppm to 5,000 ppm. The best sensor response to SO2 occurs at 400 °C using Au electrodes. The sensor response value is independent on the amount of added vanadium but dependent on the electrode materials at 400 °C. These results are discussed and a sensing mechanism is discussed. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
Open AccessArticle Effects of Calcination Temperature and Acid-Base Properties on Mixed Potential Ammonia Sensors Modified by Metal Oxides
Sensors 2011, 11(2), 2155-2165; doi:10.3390/s110202155
Received: 24 December 2010 / Revised: 20 January 2011 / Accepted: 10 February 2011 / Published: 11 February 2011
Cited by 7 | PDF Full-text (284 KB) | HTML Full-text | XML Full-text
Abstract
Mixed potential sensors were fabriated using yttria-stabilized zirconia (YSZ) as a solid electrolyte and a mixture of Au and various metal oxides as a sensing electrode. The effects of calcination temperature ranging from 600 to 1,000 °C and acid-base properties of the [...] Read more.
Mixed potential sensors were fabriated using yttria-stabilized zirconia (YSZ) as a solid electrolyte and a mixture of Au and various metal oxides as a sensing electrode. The effects of calcination temperature ranging from 600 to 1,000 °C and acid-base properties of the metal oxides on the sensing properties were examined. The selective sensing of ammonia was achieved by modification of the sensing electrode using MoO3, Bi2O3 and V2O5, while the use of WO3, Nb2O5 and MgO was not effective. The melting points of the former group were below 820 °C, while those of the latter group were higher than 1,000 °C. Among the former group, the selective sensing of ammonia was strongly dependent on the calcination temperature, which was optimum around melting point of the corresponding metal oxides. The good spreading of the metal oxides on the electrode is suggested to be one of the important factors. In the former group, the relative response of ammonia to propene was in the order of MoO3 > Bi2O3 > V2O5, which agreed well with the acidity of the metal oxides. The importance of the acidic properties of metal oxides for ammonia sensing was clarified. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
Open AccessArticle Effect of TiO2 on the Gas Sensing Features of TiO2/PANi Nanocomposites
Sensors 2011, 11(2), 1924-1931; doi:10.3390/s110201924
Received: 11 January 2011 / Revised: 25 January 2011 / Accepted: 28 January 2011 / Published: 1 February 2011
Cited by 39 | PDF Full-text (538 KB) | HTML Full-text | XML Full-text
Abstract
A nanocomposite of titanium dioxide (TiO2) and polyaniline (PANi) was synthesized by in-situ chemical polymerization using aniline (ANi) monomer and TiCl4 as precursors. SEM pictures show that the nanocomposite was created in the form of long PANi chains decorated [...] Read more.
A nanocomposite of titanium dioxide (TiO2) and polyaniline (PANi) was synthesized by in-situ chemical polymerization using aniline (ANi) monomer and TiCl4 as precursors. SEM pictures show that the nanocomposite was created in the form of long PANi chains decorated with TiO2 nanoparticles. FTIR, Raman and UV-Vis spectra reveal that the PANi component undergoes an electronic structure modification as a result of the TiO2 and PANi interaction. The electrical resistor of the nanocomposite is highly sensitive to oxygen and NH3 gas, accounting for the physical adsorption of these gases. A nanocomposite with around 55% TiO2 shows an oxygen sensitivity of 600–700%, 20–25 times higher than that of neat PANi. The n-p contacts between TiO2 nanoparticles and PANi matrix give rise to variety of shallow donors and acceptor levels in the PANi band gap which enhance the physical adsorption of gas molecules. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
Open AccessArticle Preparation of Mesoporous and/or Macroporous SnO2-Based Powders and Their Gas-Sensing Properties as Thick Film Sensors
Sensors 2011, 11(2), 1261-1276; doi:10.3390/s110201261
Received: 13 December 2010 / Revised: 10 January 2011 / Accepted: 19 January 2011 / Published: 25 January 2011
Cited by 9 | PDF Full-text (812 KB) | HTML Full-text | XML Full-text
Abstract
Mesoporous and/or macroporous SnO2-based powders have been prepared and their gas-sensing properties as thick film sensors towards H2 and NO2 have been investigated. The mesopores and macropores of various SnO2-based powders were controlled by self-assembly of [...] Read more.
Mesoporous and/or macroporous SnO2-based powders have been prepared and their gas-sensing properties as thick film sensors towards H2 and NO2 have been investigated. The mesopores and macropores of various SnO2-based powders were controlled by self-assembly of sodium bis(2-ethylhexyl)sulfosuccinate and polymethyl-methacrylate (PMMA) microspheres (ca. 800 nm in diameter), respectively. The introduction of mesopores and macropores into SnO2-based sensors increased their sensor resistance in air significantly. The additions of SiO2 and Sb2O5 into mesoporous and/or macroporous SnO2 were found to improve the sensing properties of the sensors. The addition of SiO2 into mesoporous and/or macroporous SnO2 was found to increase the sensor resistance in air, whereas doping of Sb2O5 into mesoporous and/or macroporous SnO2 was found to markedly reduce the sensor resistance in air, and to increase the response to 1,000 ppm H2 as well as 1 ppm NO2 in air. Among all the sensors tested, meso-macroporous SnO2 added with 1 wt% SiO2 and 5 wt% Sb2O5, which were prepared with the above two templates simultaneously, exhibited the largest H2 and NO2 responses. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
Open AccessArticle Flame-Made Nb-Doped TiO2 Ethanol and Acetone Sensors
Sensors 2011, 11(1), 472-484; doi:10.3390/s110100472
Received: 23 October 2010 / Revised: 24 November 2010 / Accepted: 29 December 2010 / Published: 5 January 2011
Cited by 24 | PDF Full-text (742 KB) | HTML Full-text | XML Full-text
Abstract
Undoped TiO2 and TiO2 nanoparticles doped with 1–5 at.% Nb were successfully produced in a single step by flame spray pyrolysis (FSP). The phase and crystallite size were analyzed by XRD. The BET surface area (SSABET) of [...] Read more.
Undoped TiO2 and TiO2 nanoparticles doped with 1–5 at.% Nb were successfully produced in a single step by flame spray pyrolysis (FSP). The phase and crystallite size were analyzed by XRD. The BET surface area (SSABET) of the nanoparticles was measured by nitrogen adsorption. The trend of SSABET on the doping samples increased and the BET equivalent particle diameter (dBET) (rutile) increased with the higher Nb-doping concentrations while dBET (anatase) remained the same. The morphology and accurate size of the primary particles were further investigated by high-resolution transmission electron microscopy (HRTEM). The crystallite sizes of undoped and Nb-doped TiO2 spherical were in the range of 10–20 nm. The sensing films were prepared by spin coating technique. The mixing sample was spin-coated onto the Al2O3 substrates interdigitated with Au electrodes. The gas sensing of acetone (25–400 ppm) was studied at operating temperatures ranging from 300–400 °C in dry air, while the gas sensing of ethanol (50–1,000 ppm) was studied at operating temperatures ranging from 250–400 °C in dry air. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
Open AccessArticle Improving the Performance of Catalytic Combustion Type Methane Gas Sensors Using Nanostructure Elements Doped with Rare Earth Cocatalysts
Sensors 2011, 11(1), 19-31; doi:10.3390/s110100019
Received: 11 November 2010 / Revised: 30 November 2010 / Accepted: 30 November 2010 / Published: 23 December 2010
Cited by 10 | PDF Full-text (277 KB) | HTML Full-text | XML Full-text
Abstract
Conventional methane gas sensors based on catalytic combustion have the drawbacks of high working temperature, low thermal stability and small measurement range. To improve their performance, cerium, which possesses high oxygen storage and release ability, was introduced via nanotechnology to prepare Ce-contained [...] Read more.
Conventional methane gas sensors based on catalytic combustion have the drawbacks of high working temperature, low thermal stability and small measurement range. To improve their performance, cerium, which possesses high oxygen storage and release ability, was introduced via nanotechnology to prepare Ce-contained nanostructure elements. Three kinds of elements with different carriers: Al2O3, n-Al2O3 and n-Ce-Al2O3 were prepared and separately fabricated (Pt-Pd/Al, Pt-Pd/n-Al, Pt-Pd/n-Ce-Al). The performances of Wheatstone Bridges with three different catalytic elements were tested and compared. The results indicated that the cerium-containing element exhibited better performance than other elements regarding activity, anti-sulfur ability and thermal stability. Moreover, a constant temperature circuit was also applied in this system. The measurement range was extended from 4% to 10% by automatically decreasing the working current in a reasonable range. The maximum error for 0%–10% CH4 was controlled below 5%, which fully meets the measurement requirements. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
Open AccessArticle Using a Floating-Gate MOS Transistor as a Transducer in a MEMS Gas Sensing System
Sensors 2010, 10(11), 10413-10434; doi:10.3390/s101110413
Received: 30 September 2010 / Revised: 28 October 2010 / Accepted: 10 November 2010 / Published: 18 November 2010
Cited by 5 | PDF Full-text (1572 KB) | HTML Full-text | XML Full-text
Abstract
Floating-gate MOS transistors have been widely used in diverse analog and digital applications. One of these is as a charge sensitive device in sensors for pH measurement in solutions or using gates with metals like Pd or Pt for hydrogen sensing. Efforts [...] Read more.
Floating-gate MOS transistors have been widely used in diverse analog and digital applications. One of these is as a charge sensitive device in sensors for pH measurement in solutions or using gates with metals like Pd or Pt for hydrogen sensing. Efforts are being made to monolithically integrate sensors together with controlling and signal processing electronics using standard technologies. This can be achieved with the demonstrated compatibility between available CMOS technology and MEMS technology. In this paper an in-depth analysis is done regarding the reliability of floating-gate MOS transistors when charge produced by a chemical reaction between metallic oxide thin films with either reducing or oxidizing gases is present. These chemical reactions need temperatures around 200 °C or higher to take place, so thermal insulation of the sensing area must be assured for appropriate operation of the electronics at room temperature. The operation principle of the proposal here presented is confirmed by connecting the gate of a conventional MOS transistor in series with a Fe2O3 layer. It is shown that an electrochemical potential is present on the ferrite layer when reacting with propane. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
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Open AccessArticle Polypyrrole Porous Micro Humidity Sensor Integrated with a Ring Oscillator Circuit on Chip
Sensors 2010, 10(11), 10095-10104; doi:10.3390/s101110095
Received: 25 September 2010 / Revised: 28 October 2010 / Accepted: 28 October 2010 / Published: 10 November 2010
Cited by 25 | PDF Full-text (622 KB) | HTML Full-text | XML Full-text
Abstract
This study presents the design and fabrication of a capacitive micro humidity sensor integrated with a five-stage ring oscillator circuit on chip using the complimentary metal oxide semiconductor (CMOS) process. The area of the humidity sensor chip is about 1 mm2 [...] Read more.
This study presents the design and fabrication of a capacitive micro humidity sensor integrated with a five-stage ring oscillator circuit on chip using the complimentary metal oxide semiconductor (CMOS) process. The area of the humidity sensor chip is about 1 mm2. The humidity sensor consists of a sensing capacitor and a sensing film. The sensing capacitor is constructed from spiral interdigital electrodes that can enhance the sensitivity of the sensor. The sensing film of the sensor is polypyrrole, which is prepared by the chemical polymerization method, and the film has a porous structure. The sensor needs a post-CMOS process to coat the sensing film. The post-CMOS process uses a wet etching to etch the sacrificial layers, and then the polypyrrole is coated on the sensing capacitor. The sensor generates a change in capacitance when the sensing film absorbs or desorbs vapor. The ring oscillator circuit converts the capacitance variation of the sensor into the oscillation frequency output. Experimental results show that the sensitivity of the humidity sensor is about 99 kHz/%RH at 25 °C. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
Open AccessArticle Detection of Greenhouse Gas Precursors from Diesel Engines Using Electrochemical and Photoacoustic Sensors
Sensors 2010, 10(11), 9726-9741; doi:10.3390/s101109726
Received: 6 August 2010 / Revised: 9 September 2010 / Accepted: 29 October 2010 / Published: 1 November 2010
Cited by 9 | PDF Full-text (353 KB) | HTML Full-text | XML Full-text
Abstract
Atmospheric pollution is one of the worst threats to modern society. The consequences derived from different forms of atmospheric pollution vary from the local to the global scale, with deep impacts on climate, environment and human health. Several gaseous pollutants, even when [...] Read more.
Atmospheric pollution is one of the worst threats to modern society. The consequences derived from different forms of atmospheric pollution vary from the local to the global scale, with deep impacts on climate, environment and human health. Several gaseous pollutants, even when present in trace concentrations, play a fundamental role in important processes that occur in atmosphere. Phenomena such as global warming, photochemical smog formation, acid rain and the depletion of the stratospheric ozone layer are strongly related to the increased concentration of certain gaseous species in the atmosphere. The transport sector significantly produces atmospheric pollution, mainly when diesel oil is used as fuel. Therefore, new methodologies based on selective and sensitive gas detection schemes must be developed in order to detect and monitor pollutant gases from this source. In this work, CO2 Laser Photoacoustic Spectroscopy was used to evaluate ethylene emissions and electrochemical analyzers were used to evaluate the emissions of CO, NOx and SO2 from the exhaust of diesel powered vehicles (rural diesel with 5% of biodiesel, in this paper called only diesel) at different engine rotation speeds. Concentrations in the range 6 to 45 ppmV for ethylene, 109 to 1,231 ppmV for carbon monoxide, 75 to 868 ppmV for nitrogen oxides and 3 to 354 ppmV for sulfur dioxide were obtained. The results indicate that the detection techniques used were sufficiently selective and sensitive to detect the gaseous species mentioned above in the ppmV range. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
Open AccessArticle A Sulfur Hexafluoride Sensor Using Quantum Cascade and CO2 Laser-Based Photoacoustic Spectroscopy
Sensors 2010, 10(10), 9359-9368; doi:10.3390/s101009359
Received: 30 August 2010 / Revised: 29 September 2010 / Accepted: 3 October 2010 / Published: 18 October 2010
Cited by 4 | PDF Full-text (223 KB) | HTML Full-text | XML Full-text
Abstract
The increase in greenhouse gas emissions is a serious environmental problem and has stimulated the scientific community to pay attention to the need for detection and monitoring of gases released into the atmosphere. In this regard, the development of sensitive and selective [...] Read more.
The increase in greenhouse gas emissions is a serious environmental problem and has stimulated the scientific community to pay attention to the need for detection and monitoring of gases released into the atmosphere. In this regard, the development of sensitive and selective gas sensors has been the subject of several research programs. An important greenhouse gas is sulphur hexafluoride, an almost non-reactive gas widely employed in industrial processes worldwide. Indeed it is estimated that it has a radiative forcing of 0.52 W/m2. This work compares two photoacoustic spectrometers, one coupled to a CO2 laser and another one coupled to a Quantum Cascade (QC) laser, for the detection of SF6. The laser photoacoustic spectrometers described in this work have been developed for gas detection at small concentrations. Detection limits of 20 ppbv for CO2 laser and 50 ppbv for quantum cascade laser were obtained. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
Open AccessArticle Study of a QCM Dimethyl Methylphosphonate Sensor Based on a ZnO-Modified Nanowire-Structured Manganese Dioxide Film
Sensors 2010, 10(9), 8275-8290; doi:10.3390/s100908275
Received: 10 August 2010 / Revised: 20 August 2010 / Accepted: 31 August 2010 / Published: 2 September 2010
Cited by 16 | PDF Full-text (767 KB) | HTML Full-text | XML Full-text
Abstract
Sensitive, selective and fast detection of chemical warfare agents is necessary for anti-terrorism purposes. In our search for functional materials sensitive to dimethyl methylphosphonate (DMMP), a simulant of sarin and other toxic organophosphorus compounds, we found that zinc oxide (ZnO) modification potentially [...] Read more.
Sensitive, selective and fast detection of chemical warfare agents is necessary for anti-terrorism purposes. In our search for functional materials sensitive to dimethyl methylphosphonate (DMMP), a simulant of sarin and other toxic organophosphorus compounds, we found that zinc oxide (ZnO) modification potentially enhances the absorption of DMMP on a manganese dioxide (MnO2) surface. The adsorption behavior of DMMP was evaluated through the detection of tiny organophosphonate compounds with quartz crystal microbalance (QCM) sensors coated with ZnO-modified MnO2 nanofibers and pure MnO2 nanofibers. Experimental results indicated that the QCM sensor coated with ZnO-modified nanostructured MnO2 film exhibited much higher sensitivity and better selectivity in comparison with the one coated with pure MnO2 nanofiber film. Therefore, the DMMP sensor developed with this composite nanostructured material should possess excellent selectivity and reasonable sensitivity towards the tiny gaseous DMMP species. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
Open AccessArticle Flame-Spray-Made Undoped Zinc Oxide Films for Gas Sensing Applications
Sensors 2010, 10(8), 7863-7873; doi:10.3390/s100807863
Received: 7 July 2010 / Revised: 16 August 2010 / Accepted: 20 August 2010 / Published: 23 August 2010
Cited by 19 | PDF Full-text (1296 KB) | HTML Full-text | XML Full-text
Abstract
Using zinc naphthenate dissolved in xylene as a precursor undoped ZnO nanopowders were synthesized by the flame spray pyrolysis technique. The average diameter and length of ZnO spherical and hexagonal particles were in the range of 5 to 20 nm, while ZnO [...] Read more.
Using zinc naphthenate dissolved in xylene as a precursor undoped ZnO nanopowders were synthesized by the flame spray pyrolysis technique. The average diameter and length of ZnO spherical and hexagonal particles were in the range of 5 to 20 nm, while ZnO nanorods were found to be 5–20 nm wide and 20–40 nm long, under 5/5 (precursor/oxygen) flame conditions. The gas sensitivity of the undoped ZnO nanopowders towards 50 ppm of NO2, C2H5OH and SO2 were found to be 33, 7 and 3, respectively. The sensors showed a great selectivity towards NO2 at high working temperature (at 300 °C), while small resistance variations were observed for C2H5OH and SO2, respectively. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
Open AccessArticle Multi-Walled Carbon Nanotube-Doped Tungsten Oxide Thin Films for Hydrogen Gas Sensing
Sensors 2010, 10(8), 7705-7715; doi:10.3390/s100807705
Received: 20 June 2010 / Revised: 15 July 2010 / Accepted: 30 July 2010 / Published: 17 August 2010
Cited by 41 | PDF Full-text (870 KB) | HTML Full-text | XML Full-text
Abstract
In this work we have fabricated hydrogen gas sensors based on undoped and 1 wt% multi-walled carbon nanotube (MWCNT)-doped tungsten oxide (WO3) thin films by means of the powder mixing and electron beam (E-beam) evaporation technique. Hydrogen sensing properties of [...] Read more.
In this work we have fabricated hydrogen gas sensors based on undoped and 1 wt% multi-walled carbon nanotube (MWCNT)-doped tungsten oxide (WO3) thin films by means of the powder mixing and electron beam (E-beam) evaporation technique. Hydrogen sensing properties of the thin films have been investigated at different operating temperatures and gas concentrations ranging from 100 ppm to 50,000 ppm. The results indicate that the MWCNT-doped WO3 thin film exhibits high sensitivity and selectivity to hydrogen. Thus, MWCNT doping based on E-beam co-evaporation was shown to be an effective means of preparing hydrogen gas sensors with enhanced sensing and reduced operating temperatures. Creation of nanochannels and formation of p-n heterojunctions were proposed as the sensing mechanism underlying the enhanced hydrogen sensitivity of this hybridized gas sensor. To our best knowledge, this is the first report on a MWCNT-doped WO3 hydrogen sensor prepared by the E-beam method. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
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Open AccessArticle The Effects of the Location of Au Additives on Combustion-generated SnO2 Nanopowders for CO Gas Sensing
Sensors 2010, 10(7), 7002-7017; doi:10.3390/s100707002
Received: 9 June 2010 / Revised: 16 July 2010 / Accepted: 19 July 2010 / Published: 21 July 2010
Cited by 17 | PDF Full-text (1288 KB) | HTML Full-text | XML Full-text
Abstract
The current work presents the results of an experimental study of the effects of the location of gold additives on the performance of combustion-generated tin dioxide (SnO2) nanopowders in solid state gas sensors. The time response and sensor response
to [...] Read more.
The current work presents the results of an experimental study of the effects of the location of gold additives on the performance of combustion-generated tin dioxide (SnO2) nanopowders in solid state gas sensors. The time response and sensor response
to 500 ppm carbon monoxide is reported for a range of gold additive/SnO2 film architectures including the use of colloidal, sputtered, and combustion-generated Au additives. The opportunities afforded by combustion synthesis to affect the SnO2/additive morphology are demonstrated. The best sensor performance in terms of sensor response (S) and time response (t) was observed when the Au additives were restricted to the outermost layer of the gas-sensing film. Further improvement was observed in the sensor response and time response when the Au additives were dispersed throughout the outermost layer of the film, where S = 11.3 and t = 51 s, as opposed to Au localized at the surface, where
S = 6.1 and t = 60 s. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
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Review

Jump to: Research

Open AccessReview Resistive Oxygen Gas Sensors for Harsh Environments
Sensors 2011, 11(4), 3439-3465; doi:10.3390/s110403439
Received: 30 January 2011 / Revised: 14 March 2011 / Accepted: 15 March 2011 / Published: 24 March 2011
Cited by 34 | PDF Full-text (963 KB) | HTML Full-text | XML Full-text
Abstract
Resistive oxygen sensors are an inexpensive alternative to the classical potentiometric zirconia oxygen sensor, especially for use in harsh environments and at temperatures of several hundred °C or even higher. This device-oriented paper gives a historical overview on the development of these [...] Read more.
Resistive oxygen sensors are an inexpensive alternative to the classical potentiometric zirconia oxygen sensor, especially for use in harsh environments and at temperatures of several hundred °C or even higher. This device-oriented paper gives a historical overview on the development of these sensor materials. It focuses especially on approaches to obtain a temperature independent behavior. It is shown that although in the past 40 years there have always been several research groups working concurrently with resistive oxygen sensors, novel ideas continue to emerge today with respect to improvements of the sensor response time, the temperature dependence, the long-term stability or the manufacture of the devices themselves using novel techniques for the sensitive films. Materials that are the focus of this review are metal oxides; especially titania, titanates, and ceria-based formulations. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
Open AccessReview Physiological Sensing of Carbon Dioxide/Bicarbonate/pH via Cyclic Nucleotide Signaling
Sensors 2011, 11(2), 2112-2128; doi:10.3390/s110202112
Received: 3 January 2011 / Revised: 28 January 2011 / Accepted: 10 February 2011 / Published: 11 February 2011
Cited by 21 | PDF Full-text (277 KB) | HTML Full-text | XML Full-text
Abstract
Carbon dioxide (CO2) is produced by living organisms as a byproduct of metabolism. In physiological systems, CO2 is unequivocally linked with bicarbonate (HCO3) and pH via a ubiquitous family of carbonic anhydrases, and numerous biological processes [...] Read more.
Carbon dioxide (CO2) is produced by living organisms as a byproduct of metabolism. In physiological systems, CO2 is unequivocally linked with bicarbonate (HCO3) and pH via a ubiquitous family of carbonic anhydrases, and numerous biological processes are dependent upon a mechanism for sensing the level of CO2, HCO3, and/or pH. The discovery that soluble adenylyl cyclase (sAC) is directly regulated by bicarbonate provided a link between CO2/HCO3/pH chemosensing and signaling via the widely used second messenger cyclic AMP. This review summarizes the evidence that bicarbonate-regulated sAC, and additional, subsequently identified bicarbonate-regulate nucleotidyl cyclases, function as evolutionarily conserved CO2/HCO3/pH chemosensors in a wide variety of physiological systems. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
Open AccessReview Low-Dimensional Palladium Nanostructures for Fast and Reliable Hydrogen Gas Detection
Sensors 2011, 11(1), 825-851; doi:10.3390/s110100825
Received: 2 November 2010 / Revised: 22 December 2010 / Accepted: 10 January 2011 / Published: 13 January 2011
Cited by 54 | PDF Full-text (1306 KB) | HTML Full-text | XML Full-text
Abstract
Palladium (Pd) has received attention as an ideal hydrogen sensor material due to its properties such as high sensitivity and selectivity to hydrogen gas, fast response, and operability at room temperature. Interestingly, various Pd nanostructures that have been realized by recent developments [...] Read more.
Palladium (Pd) has received attention as an ideal hydrogen sensor material due to its properties such as high sensitivity and selectivity to hydrogen gas, fast response, and operability at room temperature. Interestingly, various Pd nanostructures that have been realized by recent developments in nanotechnologies are known to show better performance than bulk Pd. This review highlights the characteristic properties, issues, and their possible solutions of hydrogen sensors based on the low-dimensional Pd nanostructures with more emphasis on Pd thin films and Pd nanowires. The finite size effects, relative strengths and weaknesses of the respective Pd nanostructures are discussed in terms of performance, manufacturability, and practical applicability. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
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Open AccessReview Hydrogen Sensors Using Nitride-Based Semiconductor Diodes: The Role of Metal/Semiconductor Interfaces
Sensors 2011, 11(1), 674-695; doi:10.3390/s110100674
Received: 21 December 2010 / Accepted: 6 January 2011 / Published: 11 January 2011
Cited by 15 | PDF Full-text (841 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, I review my recent results in investigating hydrogen sensors using nitride-based semiconductor diodes, focusing on the interaction mechanism of hydrogen with the devices. Firstly, effects of interfacial modification in the devices on hydrogen detection sensitivity are discussed. Surface defects [...] Read more.
In this paper, I review my recent results in investigating hydrogen sensors using nitride-based semiconductor diodes, focusing on the interaction mechanism of hydrogen with the devices. Firstly, effects of interfacial modification in the devices on hydrogen detection sensitivity are discussed. Surface defects of GaN under Schottky electrodes do not play a critical role in hydrogen sensing characteristics. However, dielectric layers inserted in metal/semiconductor interfaces are found to cause dramatic changes in hydrogen sensing performance, implying that chemical selectivity to hydrogen could be realized. The capacitance-voltage (C-V) characteristics reveal that the work function change in the Schottky metal is not responsible mechanism for hydrogen sensitivity. The interface between the metal and the semiconductor plays a critical role in the interaction of hydrogen with semiconductor devises. Secondly, low-frequency C-V characterization is employed to investigate the interaction mechanism of hydrogen with diodes. As a result, it is suggested that the formation of a metal/semiconductor interfacial polarization could be attributed to hydrogen-related dipoles. In addition, using low-frequency C-V characterization leads to clear detection of 100 ppm hydrogen even at room temperature where it is hard to detect hydrogen by using conventional current-voltage (I-V) characterization, suggesting that low-frequency C-V method would be effective in detecting very low hydrogen concentrations. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)
Open AccessReview Femtosecond Laser Filamentation for Atmospheric Sensing
Sensors 2011, 11(1), 32-53; doi:10.3390/s110100032
Received: 19 November 2010 / Revised: 10 December 2010 / Accepted: 13 December 2010 / Published: 23 December 2010
Cited by 52 | PDF Full-text (343 KB) | HTML Full-text | XML Full-text
Abstract
Powerful femtosecond laser pulses propagating in transparent materials result in the formation of self-guided structures called filaments. Such filamentation in air can be controlled to occur at a distance as far as a few kilometers, making it ideally suited for remote sensing [...] Read more.
Powerful femtosecond laser pulses propagating in transparent materials result in the formation of self-guided structures called filaments. Such filamentation in air can be controlled to occur at a distance as far as a few kilometers, making it ideally suited for remote sensing of pollutants in the atmosphere. On the one hand, the high intensity inside the filaments can induce the fragmentation of all matters in the path of filaments, resulting in the emission of characteristic fluorescence spectra (fingerprints) from the excited fragments, which can be used for the identification of various substances including chemical and biological species. On the other hand, along with the femtosecond laser filamentation, white-light supercontinuum emission in the infrared to UV range is generated, which can be used as an ideal light source for absorption Lidar. In this paper, we present an overview of recent progress concerning remote sensing of the atmosphere using femtosecond laser filamentation. Full article
(This article belongs to the Special Issue Gas Sensors - 2010)

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