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428 KiB

Open AccessArticle

Oxidation of Hydrocarbons on the Surface of Tin Dioxide Chemical Sensors

by Helena Teterycz, Patryk Halek, Kamil Wiśniewski, Grzegorz Halek, Tomasz Koźlecki and Izabela Polowczyk

Sensors 2011, 11(4), 4425-4437; https://doi.org/10.3390/s110404425 - 15 Apr 2011

Cited by 17 | Viewed by 9483

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 electrical [...] 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)

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604 KiB

Open AccessArticle

A High Temperature Capacitive Humidity Sensor Based on Mesoporous Silica

by Thorsten Wagner, Sören Krotzky, Alexander Weiß, Tilman Sauerwald, Claus-Dieter Kohl, Jan Roggenbuck and Michael Tiemann

Sensors 2011, 11(3), 3135-3144; https://doi.org/10.3390/s110303135 - 14 Mar 2011

Cited by 44 | Viewed by 14539

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 temperature [...] 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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615 KiB

Open AccessArticle

Application of V₂O₅/WO₃/TiO₂ for Resistive-Type SO₂ Sensors

by Noriya Izu, Gunter Hagen, Daniela Schönauer, Ulla Röder-Roith and Ralf Moos

Sensors 2011, 11(3), 2982-2991; https://doi.org/10.3390/s110302982 - 7 Mar 2011

Cited by 52 | Viewed by 11036

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 oxide [...] 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)

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284 KiB

Open AccessArticle

Effects of Calcination Temperature and Acid-Base Properties on Mixed Potential Ammonia Sensors Modified by Metal Oxides

by Atsushi Satsuma, Makoto Katagiri, Shiro Kakimoto, Satoshi Sugaya and Kenichi Shimizu

Sensors 2011, 11(2), 2155-2165; https://doi.org/10.3390/s110202155 - 11 Feb 2011

Cited by 35 | Viewed by 8882

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 metal [...] 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 WO_3,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)

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538 KiB

Open AccessArticle

Effect of TiO₂ on the Gas Sensing Features of TiO₂/PANi Nanocomposites

by Duong Ngoc Huyen, Nguyen Trong Tung, Nguyen Duc Thien and Le Hai Thanh

Sensors 2011, 11(2), 1924-1931; https://doi.org/10.3390/s110201924 - 1 Feb 2011

Cited by 107 | Viewed by 11662

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 with [...] 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% TiO₂shows 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)

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812 KiB

Open AccessArticle

Preparation of Mesoporous and/or Macroporous SnO₂-Based Powders and Their Gas-Sensing Properties as Thick Film Sensors

by Luyang Yuan, Takeo Hyodo, Yasuhiro Shimizu and Makoto Egashira

Sensors 2011, 11(2), 1261-1276; https://doi.org/10.3390/s110201261 - 25 Jan 2011

Cited by 16 | Viewed by 8918

Abstract

Mesoporous and/or macroporous SnO₂-based powders have been prepared and their gas-sensing properties as thick film sensors towards H₂ and NO₂have been investigated. The mesopores and macropores of various SnO₂-based powders were controlled by self-assembly of sodium [...] Read more.

Mesoporous and/or macroporous SnO₂-based powders have been prepared and their gas-sensing properties as thick film sensors towards H₂ and NO₂have 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)

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742 KiB

Open AccessArticle

Flame-Made Nb-Doped TiO₂ Ethanol and Acetone Sensors

by Sukon Phanichphant, Chaikarn Liewhiran, Khatcharin Wetchakun, Anurat Wisitsoraat and Adisorn Tuantranont

Sensors 2011, 11(1), 472-484; https://doi.org/10.3390/s110100472 - 5 Jan 2011

Cited by 67 | Viewed by 11396

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 (SSA_BET) of the [...] 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 (SSA_BET) of the nanoparticles was measured by nitrogen adsorption. The trend of SSA_BET on the doping samples increased and the BET equivalent particle diameter (d_BET) (rutile) increased with the higher Nb-doping concentrations while d_BET (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)

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277 KiB

Open AccessArticle

Improving the Performance of Catalytic Combustion Type Methane Gas Sensors Using Nanostructure Elements Doped with Rare Earth Cocatalysts

by Ying Wang, Min Ming Tong, Dan Zhang and Zhen Gao

Sensors 2011, 11(1), 19-31; https://doi.org/10.3390/s110100019 - 23 Dec 2010

Cited by 42 | Viewed by 11695

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 nanostructure [...] 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)

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1572 KiB

Open AccessArticle

Using a Floating-Gate MOS Transistor as a Transducer in a MEMS Gas Sensing System

by Mario Alfredo Reyes Barranca, Salvador Mendoza-Acevedo, Luis M. Flores-Nava, Alejandro Avila-García, E. N. Vazquez-Acosta, José Antonio Moreno-Cadenas and Gaspar Casados-Cruz

Sensors 2010, 10(11), 10413-10434; https://doi.org/10.3390/s101110413 - 18 Nov 2010

Cited by 13 | Viewed by 14310

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 are [...] 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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622 KiB

Open AccessArticle

Polypyrrole Porous Micro Humidity Sensor Integrated with a Ring Oscillator Circuit on Chip

by Ming-Zhi Yang, Ching-Liang Dai and De-Hao Lu

Sensors 2010, 10(11), 10095-10104; https://doi.org/10.3390/s101110095 - 10 Nov 2010

Cited by 42 | Viewed by 10716

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)

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353 KiB

Open AccessArticle

Detection of Greenhouse Gas Precursors from Diesel Engines Using Electrochemical and Photoacoustic Sensors

by Geórgia Mothé, Maria Castro, Marcelo Sthel, Guilherme Lima, Laisa Brasil, Layse Campos, Aline Rocha and Helion Vargas

Sensors 2010, 10(11), 9726-9741; https://doi.org/10.3390/s101109726 - 1 Nov 2010

Cited by 25 | Viewed by 12878

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 present [...] 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, NO_xand 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)

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223 KiB

Open AccessArticle

A Sulfur Hexafluoride Sensor Using Quantum Cascade and CO₂ Laser-Based Photoacoustic Spectroscopy

by Mila Rocha, Marcelo Sthel, Guilherme Lima, Marcelo da Silva, Delson Schramm, András Miklós and Helion Vargas

Sensors 2010, 10(10), 9359-9368; https://doi.org/10.3390/s101009359 - 18 Oct 2010

Cited by 9 | Viewed by 11987

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 gas [...] 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 CO₂laser and 50 ppbv for quantum cascade laser were obtained. Full article

(This article belongs to the Special Issue Gas Sensors - 2010)

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767 KiB

Open AccessArticle

Study of a QCM Dimethyl Methylphosphonate Sensor Based on a ZnO-Modified Nanowire-Structured Manganese Dioxide Film

by Zhifu Pei, Xingfa Ma, Pengfei Ding, Wuming Zhang, Zhiyuan Luo and Guang Li

Sensors 2010, 10(9), 8275-8290; https://doi.org/10.3390/s100908275 - 2 Sep 2010

Cited by 40 | Viewed by 11479

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 enhances [...] 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 MnO₂nanofibers. 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)

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1296 KiB

Open AccessArticle

Flame-Spray-Made Undoped Zinc Oxide Films for Gas Sensing Applications

by Nittaya Tamaekong, Chaikarn Liewhiran, Anurat Wisitsoraat and Sukon Phanichphant

Sensors 2010, 10(8), 7863-7873; https://doi.org/10.3390/s100807863 - 23 Aug 2010

Cited by 46 | Viewed by 11737

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 nanorods [...] 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 SO₂were 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)

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870 KiB

Open AccessArticle

Multi-Walled Carbon Nanotube-Doped Tungsten Oxide Thin Films for Hydrogen Gas Sensing

by Chatchawal Wongchoosuk, Anurat Wisitsoraat, Ditsayut Phokharatkul, Adisorn Tuantranont and Teerakiat Kerdcharoen

Sensors 2010, 10(8), 7705-7715; https://doi.org/10.3390/s100807705 - 17 Aug 2010

Cited by 106 | Viewed by 14571

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 the [...] 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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1288 KiB

Open AccessArticle

The Effects of the Location of Au Additives on Combustion-generated SnO₂ Nanopowders for CO Gas Sensing

by Smitesh D. Bakrania and Margaret S. Wooldridge

Sensors 2010, 10(7), 7002-7017; https://doi.org/10.3390/s100707002 - 21 Jul 2010

Cited by 33 | Viewed by 9891

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 500 [...] 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

963 KiB

Open AccessReview

Resistive Oxygen Gas Sensors for Harsh Environments

by Ralf Moos, Noriya Izu, Frank Rettig, Sebastian Reiß, Woosuck Shin and Ichiro Matsubara

Sensors 2011, 11(4), 3439-3465; https://doi.org/10.3390/s110403439 - 24 Mar 2011

Cited by 95 | Viewed by 16308

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 sensor [...] 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)

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277 KiB

Open AccessReview

Physiological Sensing of Carbon Dioxide/Bicarbonate/pH via Cyclic Nucleotide Signaling

by Jochen Buck and Lonny R. Levin

Sensors 2011, 11(2), 2112-2128; https://doi.org/10.3390/s110202112 - 11 Feb 2011

Cited by 38 | Viewed by 11180

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 are [...] 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)

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1306 KiB

Open AccessReview

Low-Dimensional Palladium Nanostructures for Fast and Reliable Hydrogen Gas Detection

by Jin-Seo Noh, Jun Min Lee and Wooyoung Lee

Sensors 2011, 11(1), 825-851; https://doi.org/10.3390/s110100825 - 13 Jan 2011

Cited by 139 | Viewed by 15359

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 in [...] 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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841 KiB

Open AccessReview

Hydrogen Sensors Using Nitride-Based Semiconductor Diodes: The Role of Metal/Semiconductor Interfaces

by Yoshihiro Irokawa

Sensors 2011, 11(1), 674-695; https://doi.org/10.3390/s110100674 - 11 Jan 2011

Cited by 37 | Viewed by 12137

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 of [...] 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)

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Femtosecond Laser Filamentation for Atmospheric Sensing

by Huai Liang Xu and See Leang Chin

Sensors 2011, 11(1), 32-53; https://doi.org/10.3390/s110100032 - 23 Dec 2010

Cited by 154 | Viewed by 15518

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 of [...] 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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