Metal oxide-based gas sensor research: How to?
TL;DR: In this article, the state of the art in the field of experimental techniques possible to be applied to the study of conductometric gas sensors based on semiconducting metal oxides is reviewed.
Abstract: The paper critically reviews the state of the art in the field of experimental techniques possible to be applied to the study of conductometric gas sensors based on semiconducting metal oxides. The used assessment criteria are subordinated to the proposed R&D approach, which focuses on the study, and subsequent modelling, of sensors’ performance in realistic operation conditions by means of a combination of phenomenological and spectroscopic techniques. With this viewpoint, the paper presents both the to-date achievements and shortcomings of different experimental techniques, describes – by using selected examples – how the proposed approach can be used and proposes a set of objectives for the near future.
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TL;DR: A brief review of changes of sensitivity of conductometric semiconducting metal oxide gas sensors due to the five factors: chemical components, surface-modification and microstructures of sensing layers, temperature and humidity.
Abstract: Conductometric semiconducting metal oxide gas sensors have been widely used and investigated in the detection of gases. Investigations have indicated that the gas sensing process is strongly related to surface reactions, so one of the important parameters of gas sensors, the sensitivity of the metal oxide based materials, will change with the factors influencing the surface reactions, such as chemical components, surface-modification and microstructures of sensing layers, temperature and humidity. In this brief review, attention will be focused on changes of sensitivity of conductometric semiconducting metal oxide gas sensors due to the five factors mentioned above.
2,122 citations
TL;DR: In this paper, a detailed study of semiconductor metal oxide (SMO) gas sensors is provided for a detailed comparison of SMO gas sensors with other gas sensors, especially for ammonia gas sensing.
Abstract: This review paper encompasses a detailed study of semiconductor metal oxide (SMO) gas sensors. It provides for a detailed comparison of SMO gas sensors with other gas sensors, especially for ammonia gas sensing. Different parameters which affect the performance (sensitivity, selectivity and stability) of SMO gas sensors are discussed here under. This paper also gives an insight about the dopant or impurity induced variations in the SMO materials used for gas sensing. It is concluded that dopants enhance the properties of SMOs for gas sensing applications by changing their microstructure and morphology, activation energy, electronic structure or band gap of the metal oxides. In some cases, dopants create defects in SMOs by generating oxygen vacancy or by forming solid solutions. These defects enhance the gas sensing properties. Different nanostructures (nanowires, nanotubes, heterojunctions), other than nanopowders have also been studied in this review. At the end, examples of SMOs are given to illustrate the potential use of different SMO materials for gas sensing.
1,296 citations
TL;DR: The most important advances with regard to fundamental research, sensing mechanisms, and application of nanostructured materials for room-temperature conductometric sensor devices are reviewed here and particular emphasis is given to the relation between the nanostructure and sensor properties in an attempt to address structure-property correlations.
Abstract: Sensor technology has an important effect on many aspects in our society, and has gained much progress, propelled by the development of nanoscience and nanotechnology. Current research efforts are directed toward developing high-performance gas sensors with low operating temperature at low fabrication costs. A gas sensor working at room temperature is very appealing as it provides very low power consumption and does not require a heater for high-temperature operation, and hence simplifies the fabrication of sensor devices and reduces the operating cost. Nanostructured materials are at the core of the development of any room-temperature sensing platform. The most important advances with regard to fundamental research, sensing mechanisms, and application of nanostructured materials for room-temperature conductometric sensor devices are reviewed here. Particular emphasis is given to the relation between the nanostructure and sensor properties in an attempt to address structure-property correlations. Finally, some future research perspectives and new challenges that the field of room-temperature sensors will have to address are also discussed.
1,096 citations
TL;DR: An overview of TMO-based device architectures ranging from transparent OLEDs to tandem OPV cells is given, and various TMO film deposition methods are reviewed, addressing vacuum evaporation and recent approaches for solution-based processing.
Abstract: During the last few years, transition metal oxides (TMO) such as molybdenum tri-oxide (MoO3), vanadium pent-oxide (V2O5) or tungsten tri-oxide (WO3) have been extensively studied because of their exceptional electronic properties for charge injection and extraction in organic electronic devices. These unique properties have led to the performance enhancement of several types of devices and to a variety of novel applications. TMOs have been used to realize efficient and long-term stable p-type doping of wide band gap organic materials, charge-generation junctions for stacked organic light emitting diodes (OLED), sputtering buffer layers for semi-transparent devices, and organic photovoltaic (OPV) cells with improved charge extraction, enhanced power conversion efficiency and substantially improved long term stability. Energetics in general play a key role in advancing device structure and performance in organic electronics; however, the literature provides a very inconsistent picture of the electronic structure of TMOs and the resulting interpretation of their role as functional constituents in organic electronics. With this review we intend to clarify some of the existing misconceptions. An overview of TMO-based device architectures ranging from transparent OLEDs to tandem OPV cells is also given. Various TMO film deposition methods are reviewed, addressing vacuum evaporation and recent approaches for solution-based processing. The specific properties of the resulting materials and their role as functional layers in organic devices are discussed.
1,023 citations
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References
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Book•
01 Jan 1994
TL;DR: In this paper, the electronic structure of transition metal-oxide surfaces is described. But the electronic structures of non-transition metaloxide surfaces have not been discussed, and they are not considered in this paper.
Abstract: 1. Introduction 2. Geometric structure of metal-oxide surfaces 3. Surface lattice vibrations 4. Electronic structure of non-transition metal-oxide surfaces 5. Electronic structure of transition metal-oxide surfaces 6. Molecular adsorption on oxides 7. Interfaces of metal oxides with metals and other oxides References Index.
2,523 citations
TL;DR: In this article, the authors provide a frame model that deals with all contributions involved in conduction within a real world sensor, and then summarize the contributions together with their interactions in a general applicable model for real world gas sensors.
Abstract: Tin dioxide is a widely used sensitive material for gas sensors. Many research and development groups in academia and industry are contributing to the increase of (basic) knowledge/(applied) know-how. However, from a systematic point of view the knowledge gaining process seems not to be coherent. One reason is the lack of a general applicable model which combines the basic principles with measurable sensor parameters. The approach in the presented work is to provide a frame model that deals with all contributions involved in conduction within a real world sensor. For doing so, one starts with identifying the different building blocks of a sensor. Afterwards their main inputs are analyzed in combination with the gas reaction involved in sensing. At the end, the contributions are summarized together with their interactions. The work presented here is one step towards a general applicable model for real world gas sensors.
2,247 citations
"Metal oxide-based gas sensor resear..." refers background in this paper
...2a (for details see [29]), for such layers the contribution of he metal-sensing layer resistance is made negligible by the large umber of grain–grain contributions....
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...a compact and a porous one, for an n-type material, are escribed in a simplified manner (for details, see [29])....
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...In the figure are presented the contribuions to the overall resistance corresponding to: the changes in he band bending at the material/grain surface and the potenial barriers that are appearing due to the metal/metal oxide ontact (the former depend on the changes in the ambient atmophere, the latter ones not [29]; they are still discussed because hey represent an add-on to the sensing material properties due he presence of the electrodes)....
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...It is ot difficult to show [29,56,57] that one can derive a relationship etween the band bending (VS) and QS, which has the form:...
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...[29] N....
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TL;DR: A review of surface science studies of single crystal surfaces, but selected studies on powder and polycrystalline films are also incorporated in order to provide connecting points between surface sciences studies with the broader field of materials science of tin oxide as discussed by the authors.
2,232 citations
"Metal oxide-based gas sensor resear..." refers background in this paper
...pectroscopic techniques; there is a wealth of data provided by urface physics studies performed on metal oxides [16–18]....
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...[16] M....
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