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Metal oxide nanostructures and their gas sensing properties: a review.

Sun YF, Liu SB, Meng FL, Liu JY, Jin Z, Kong LT, Liu JH - Sensors (Basel) (2012)

Bottom Line: When the particle size of metal oxide is close to or less than double thickness of the space-charge layer, the sensitivity of the sensor will increase remarkably, which would be called "small size effect", yet small size of metal oxide nanoparticles will be compactly sintered together during the film coating process which is disadvantage for gas diffusion in them.Besides, doping is also an effective method to decrease particle size and improve gas sensing properties.The effect of doping is also summarized and finally the perspectives of metal oxide gas sensor are given.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical and Automotive Engineering, Anhui Polytechnic University, Wuhu 241000, China. sunyufeng118@126.com

ABSTRACT
Metal oxide gas sensors are predominant solid-state gas detecting devices for domestic, commercial and industrial applications, which have many advantages such as low cost, easy production, and compact size. However, the performance of such sensors is significantly influenced by the morphology and structure of sensing materials, resulting in a great obstacle for gas sensors based on bulk materials or dense films to achieve highly-sensitive properties. Lots of metal oxide nanostructures have been developed to improve the gas sensing properties such as sensitivity, selectivity, response speed, and so on. Here, we provide a brief overview of metal oxide nanostructures and their gas sensing properties from the aspects of particle size, morphology and doping. When the particle size of metal oxide is close to or less than double thickness of the space-charge layer, the sensitivity of the sensor will increase remarkably, which would be called "small size effect", yet small size of metal oxide nanoparticles will be compactly sintered together during the film coating process which is disadvantage for gas diffusion in them. In view of those reasons, nanostructures with many kinds of shapes such as porous nanotubes, porous nanospheres and so on have been investigated, that not only possessed large surface area and relatively mass reactive sites, but also formed relatively loose film structures which is an advantage for gas diffusion. Besides, doping is also an effective method to decrease particle size and improve gas sensing properties. Therefore, the gas sensing properties of metal oxide nanostructures assembled by nanoparticles are reviewed in this article. The effect of doping is also summarized and finally the perspectives of metal oxide gas sensor are given.

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Device structure based on ceramic wafer substrate.
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f2-sensors-12-02610: Device structure based on ceramic wafer substrate.

Mentions: Gas sensors based on metal oxide nanostructures generally consist of three parts, i.e., sensing film, electrodes and heater. Metal oxide nanostructures react in the form of a film which will change in resistance upon exposure to target gases. A pair of electrodes is used to measure the resistance of the sensing film. Usually the gas sensors are furnished with a heater so that they are heated externally to reach an optimum working temperature. Currently, metal oxide nanostructures sensors have been characterized in three ways: conductometric, field effect transistor (FET) and impedometric ones [20]. FET type is usually exploited to fabricate sensors based on single or arrays of one-dimensional (1D) semiconducting nanomaterials, which have a complex fabrication process. Impedometric type sensors are based on impedance changes and are operated under alternating voltage upon exposure to target species, which has not yet attracted much attention. The conductometric type is the most common gas sensor which is suitable for most nanomaterials. There are two types of device structures in conductometric sensors: directly heated and indirectly heated. A directly heated type structure means the heater is contacted with the sensing material, which may lack stability and anti-interference ability, so most of the current nanostructure-based gas sensors are indirectly heated type structures which can be divided into two types, i.e., cylindrical and planar layouts, as shown in Figures 2 and 3. Alumina ceramics (wafers or tubes) are generally used as substrates to support sensing films. In the ceramic tube-based device, a piece of heating wire is placed in the interior of the ceramic tube, while, in the ceramic wafer-based device, heating paste is placed on the backside of the ceramic wafer. Some silica wafers can also be used as the substrate, which is advantageous in manufacturing small sized gas sensor because of its compatibility with integrated circuits.


Metal oxide nanostructures and their gas sensing properties: a review.

Sun YF, Liu SB, Meng FL, Liu JY, Jin Z, Kong LT, Liu JH - Sensors (Basel) (2012)

Device structure based on ceramic wafer substrate.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3376589&req=5

f2-sensors-12-02610: Device structure based on ceramic wafer substrate.
Mentions: Gas sensors based on metal oxide nanostructures generally consist of three parts, i.e., sensing film, electrodes and heater. Metal oxide nanostructures react in the form of a film which will change in resistance upon exposure to target gases. A pair of electrodes is used to measure the resistance of the sensing film. Usually the gas sensors are furnished with a heater so that they are heated externally to reach an optimum working temperature. Currently, metal oxide nanostructures sensors have been characterized in three ways: conductometric, field effect transistor (FET) and impedometric ones [20]. FET type is usually exploited to fabricate sensors based on single or arrays of one-dimensional (1D) semiconducting nanomaterials, which have a complex fabrication process. Impedometric type sensors are based on impedance changes and are operated under alternating voltage upon exposure to target species, which has not yet attracted much attention. The conductometric type is the most common gas sensor which is suitable for most nanomaterials. There are two types of device structures in conductometric sensors: directly heated and indirectly heated. A directly heated type structure means the heater is contacted with the sensing material, which may lack stability and anti-interference ability, so most of the current nanostructure-based gas sensors are indirectly heated type structures which can be divided into two types, i.e., cylindrical and planar layouts, as shown in Figures 2 and 3. Alumina ceramics (wafers or tubes) are generally used as substrates to support sensing films. In the ceramic tube-based device, a piece of heating wire is placed in the interior of the ceramic tube, while, in the ceramic wafer-based device, heating paste is placed on the backside of the ceramic wafer. Some silica wafers can also be used as the substrate, which is advantageous in manufacturing small sized gas sensor because of its compatibility with integrated circuits.

Bottom Line: When the particle size of metal oxide is close to or less than double thickness of the space-charge layer, the sensitivity of the sensor will increase remarkably, which would be called "small size effect", yet small size of metal oxide nanoparticles will be compactly sintered together during the film coating process which is disadvantage for gas diffusion in them.Besides, doping is also an effective method to decrease particle size and improve gas sensing properties.The effect of doping is also summarized and finally the perspectives of metal oxide gas sensor are given.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical and Automotive Engineering, Anhui Polytechnic University, Wuhu 241000, China. sunyufeng118@126.com

ABSTRACT
Metal oxide gas sensors are predominant solid-state gas detecting devices for domestic, commercial and industrial applications, which have many advantages such as low cost, easy production, and compact size. However, the performance of such sensors is significantly influenced by the morphology and structure of sensing materials, resulting in a great obstacle for gas sensors based on bulk materials or dense films to achieve highly-sensitive properties. Lots of metal oxide nanostructures have been developed to improve the gas sensing properties such as sensitivity, selectivity, response speed, and so on. Here, we provide a brief overview of metal oxide nanostructures and their gas sensing properties from the aspects of particle size, morphology and doping. When the particle size of metal oxide is close to or less than double thickness of the space-charge layer, the sensitivity of the sensor will increase remarkably, which would be called "small size effect", yet small size of metal oxide nanoparticles will be compactly sintered together during the film coating process which is disadvantage for gas diffusion in them. In view of those reasons, nanostructures with many kinds of shapes such as porous nanotubes, porous nanospheres and so on have been investigated, that not only possessed large surface area and relatively mass reactive sites, but also formed relatively loose film structures which is an advantage for gas diffusion. Besides, doping is also an effective method to decrease particle size and improve gas sensing properties. Therefore, the gas sensing properties of metal oxide nanostructures assembled by nanoparticles are reviewed in this article. The effect of doping is also summarized and finally the perspectives of metal oxide gas sensor are given.

Show MeSH
Related in: MedlinePlus