Conduction Model of Metal Oxide Gas Sensors
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.
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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
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
Cites background from "Conduction Model of Metal Oxide Gas..."
...More details can be seen in reference [52-56]....
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...The latter may be influenced by adsorbed species acting as additional scattering centers [52]....
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1,789 citations
TL;DR: In this article, high performance gas sensors prepared using p-type oxide semiconductors such as NiO, CuO, Cr2O3, Co3O4, and Mn3O3 were reviewed.
Abstract: High-performance gas sensors prepared using p-type oxide semiconductors such as NiO, CuO, Cr2O3, Co3O4, and Mn3O4 were reviewed. The ionized adsorption of oxygen on p-type oxide semiconductors leads to the formation of hole-accumulation layers (HALs), and conduction occurs mainly along the near-surface HAL. Thus, the chemoresistive variations of undoped p-type oxide semiconductors are lower than those induced at the electron-depletion layers of n-type oxide semiconductors. However, highly sensitive and selective p-type oxide-semiconductor-based gas sensors can be designed either by controlling the carrier concentration through aliovalent doping or by promoting the sensing reaction of a specific gas through doping/loading the sensor material with oxide or noble metal catalysts. The junction between p- and n-type oxide semiconductors fabricated with different contact configurations can provide new strategies for designing gas sensors. p-Type oxide semiconductors with distinctive surface reactivity and oxygen adsorption are also advantageous for enhancing gas selectivity, decreasing the humidity dependence of sensor signals to negligible levels, and improving recovery speed. Accordingly, p-type oxide semiconductors are excellent materials not only for fabricating highly sensitive and selective gas sensors but also valuable additives that provide new functionality in gas sensors, which will enable the development of high-performance gas sensors.
1,642 citations
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.
1,416 citations
Cites background from "Conduction Model of Metal Oxide Gas..."
...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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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
Book•
20 Oct 2012
TL;DR: In this paper, the authors present an approach for the reconstruction of the surface of a solid with respect to the Fermi energy in the band diagram of the solid and its surface.
Abstract: 1. Introduction.- 1.1. Surface States and Surface Sites.- 1.1.1. The Chemical Versus Electronic Representation of the Surface.- 1.1.2. The Surface State on the Band Diagram.- 1.1.3. The Fermi Energy in the Surface State Model.- 1.1.4. Need for Both Surface Site and Surface State Models.- 1.2. Bonding of Foreign Species to the Solid Surface.- 1.2.1. Types of Interaction.- 1.2.2. The Chemical Bond.- 1.2.3. Acid and Basic Surface Sites on Solids.- 1.2.4. Adsorbate Bonding on Various Solid Types.- 1.2.5. Movement of Surface Atoms: Relaxation, Reconstruction, and Relocation.- 1.2.6. The Electronic Energy Level (Surface State) of a Sorbate/Solid Complex.- 1.3. Surface Hydration on Ionic Solids.- 1.4. Surface Heterogeneity.- 2. Space Charge Effects.- 2.1. General.- 2.1.1. The Double Layer Involving Two Planar Sheets of Charge.- 2.1.2. The Space Charge due to Immobile Ions: The Depletion Layer.- 2.1.3. The Double Layer in the Band Diagram, Fermi Energy Pinning.- 2.2. Space Charge Effects with Reactive Surface Species.- 2.2.1. The Accumulation Layer.- 2.2.2. The Inversion Layer.- 2.3. Electron and Hole Transfer between the Solid and Its Surface.- 2.3.1. Basic Physical Model of Electron and Hole Capture or Injection.- 2.3.2. Electron and Hole Transfer with Large Changes in the Surface Barrier.- 2.3.3. Charge Transfer to a Surface Species in a Polar Medium: The Fluctuating Energy Level Mechanism.- 3. Experimental Methods.- 3.1. Surface Measurements Based on Electrical and Optical Techniques.- 3.1.1. Work Function.- 3.1.2. Surface Conductivity.- 3.1.3. Electroreflectance.- 3.1.4. Field Effect.- 3.1.5. Surface Photovoltage.- 3.1.6. Capacity of the Double Layer.- 3.1.7. Channel Measurements.- 3.1.8. Powder Conductance.- 3.1.9. Ellipsometry.- 3.1.10. Other Electrical and Optical Measurements.- 3.2. The Surface Spectroscopies.- 3.2.1. Ultraviolet Photoelectron Spectroscopy (UPS).- 3.2.2. Energy Loss Spectroscopy (ELS).- 3.2.3. Soft X-Ray Appearance Potential Spectroscopy (SXAPS).- 3.2.4. Field Emission (FEM).- 3.2.5. Field Ion Microscopy (FIM).- 3.2.6. Ion Neutralization Spectroscopy (INS).- 3.2.7. Low-Energy Electron Diffraction (LEED).- 3.2.8. Methods of Chemical Composition Determination for the Surface.- 3.2.9. Studies of Chemical Reactions due to the Impinging Beam.- 3.3. Chemical Measurements.- 3.3.1. Infrared Absorption.- 3.3.2. Temperature-Programmed Desorption.- 3.3.3. Adsorption of Gaseous Acids and Bases or of Indicators.- 4. The Adsorbate-Free Surface.- 4.1. Introduction.- 4.1.1. The Classification of Solids.- 4.1.2. Preparation of a Clean Surface.- 4.2. Theoretical Models.- 4.2.1. Quantum Models.- 4.2.2. Semiclassical Models: The Madelung Model for Ionic Solids.- 4.2.3. Models for Electron Pair Sharing: Lewis and Bronsted Sites.- 4.2.4. Comparison of the Various Surface States and Sites.- 4.3. Measurements on Adsorbate-Free Ionic Solids.- 4.3.1. Reconstruction on Ionic Solids.- 4.3.2. Physical Measurements on Ionic Solids.- 4.3.3. Chemical Measurements on Ionic Solids.- 4.4. Measurements on Adsorbate-Free Covalent or Metallic Solids.- 4.4.1. Reconstruction on Covalent and Metallic Solids.- 4.4.2. Electrical Measurements of Intrinsic Surface States on Covalent Solids.- 4.4.3. Measurement by the Surface Spectroscopies.- 5. Bonding of Foreign Species at the Solid Surface.- 5.1. Reconstruction and Relocation in Bonding.- 5.2. The Semiclassical Model of Bonding: The Surface Molecule.- 5.2.1. Surface Molecule Versus Rigid Band Model.- 5.2.2. Adsorbate Bonding to Covalent or Metallic Solids.- 5.2.3. Adsorbate Bonding to Ionic Solids.- 5.2.4. Multilayer Adsorption: The Development of a New Phase.- 5.3. Quantum Models of the Adsorbate/Solid Bond.- 5.3.1. Solid State Theories: The Semi-infinite Crystal.- 5.3.2. Cluster Models.- 5.3.3. The Interacting Surface Molecule (the Model Hamiltonian Analysis).- 5.3.4. Other Quantum Models.- 5.3.5. Remarks.- 5.4. Measurement of Adsorbate Surface States on Covalent or Metallic Solids.- 5.4.1. Screening Shifts and Other Inaccuracies in Measurement.- 5.4.2. Bond Angles.- 5.4.3. Surface State Energy Levels of Sorbate/Sorbent Bonds.- 5.5. The Chemistry of Surface States.- 5.5.1. Change of Surface State Energy Associated with Bonding.- 5.5.2. The Influence of a Polar Medium or Coadsorbate on the Surface State Energy.- 5.5.3. Surface States due to Multiequivalent Foreign Adsorbates.- 5.6. The Formation of Surface State Bands.- 6. Nonvolatile Foreign Additives on the Solid Surface.- 6.1. General.- 6.2. Dispersion of Additives.- 6.2.1. Techniques for Dispersing Additives.- 6.2.2. Measurement of Dispersion.- 6.2.3. Sintering of Dispersed Particles: Surface Diffusion of Adsorbates.- 6.3. The Cluster, the Transition between a Molecule and a Solid.- 6.4. The Control of Surface Properties with Additives.- 6.4.1. Theoretical Discussion.- 6.4.2. Observations of Additive Effects.- 6.5. The Real Surface.- 7. Adsorption.- 7.1. Adsorption Isotherms and Isobars.- 7.1.1. Physical Adsorption.- 7.1.2. Heat and Activation Energy of Adsorption, Irreversible Chemisorption.- 7.1.3. The Adsorbate Superstructure.- 7.2. Ionosorption on Semiconductors.- 7.2.1. The Surface State Representation of Adsorbed Species.- 7.2.2. Observations of Ionosorption.- 7.3. Adsorption with Local Bonding.- 7.3.1. Adsorption on Ionic Solids.- 7.3.2. Adsorption on Platinum.- 8. The Solid/Liquid Interface.- 8.1. Introduction.- 8.2. Theory.- 8.2.1. Double Layers and Potentials in Electrochemical Measurements.- 8.2.2. Charge Transfer between the Solid and Ions in Solution.- 8.2.3. Energy Levels of Surface Species Relative to Band Edges.- 8.3. Observations with Semiconductor Electrodes.- 8.3.1. Measurement Methods.- 8.3.2. Radical Generation (Current Doubling).- 8.3.3. Measurements of Energy Levels and Band Edges.- 8.3.4. Other Charge Transfer Measurements, Capture Cross Section.- 8.4. Comparison of the Solid/Liquid with the Solid/Gas Interface.- 9. Photoeffects at Semiconductor Surfaces.- 9.1. General.- 9.2. Simple Hole/Electron Recombination.- 9.2.1. Theory.- 9.2.2. Experimental Results.- 9.3. Photoadsorption and Photodesorption.- 9.3.1. Theory.- 9.3.2. Experimental Observations of Photoadsorption and Photodesorption.- 9.4. Photocatalysis.- 9.4.1. Photodecomposition of Adsorbed Species.- 9.4.2. Photostimulated Catalytic Reactions.- 9.5. Direct Excitation of Surface States by Photons.- 10. Surface Sites in Heterogeneous Catalysis.- 10.1. General Concepts.- 10.1.1. The Role of the Catalyst.- 10.1.2. Some Correlations in Heterogeneous Catalysis.- 10.2. Surface Sites Associated with Steps and Other Geometrical Factors.- 10.3. The Role of Acid and Basic Sites in Catalytic Reactions.- 10.4. Covalent Bonding to Coordinatively Unsaturated Metal and Cationic Sites.- 10.5. Sites in Oxidation Catalysis.- 10.5.1. Introduction.- 10.5.2. Oxygen Exchange Sites in Oxidation Catalysis.- 10.5.3. Dangling Bonds as Active Sites for Adsorption and Electron Exchange.- 10.5.4. Wide Bands as Electron Sources and Sinks: n-Type and p-Type Semiconductors.- 10.6. Examples of Oxidation Catalysis.- 10.6.1. Platinum.- 10.6.2. Partial Oxidation Catalysts: Bismuth and Iron Molybdate.- References.- Author Index.
772 citations
"Conduction Model of Metal Oxide Gas..." refers background in this paper
...Morrison [ 5 ] is considered in the calculation to be 1 eV. The lower limit was assumed to be 0.5 eV. The temperature was fixed to 300 ◦ C, which is a typical temperature for a SnO2 sensor....
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...Desorption is controlled, from the very beginning, by both electronic and chemical parts; the activation energy is not changed during the process if the coverage is not high enough to provide interaction between the chemisorbed species [ 5 ]....
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...mechanisms are proposed by Heiland and Kohl [6] and the third, indirect, is suggested by Morrison and by Henrich and Cox [ 5 , 7]....
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...Morrison, as well as Henrich and Cox [ 5 , 7], consider an indirect effect more probable....
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TL;DR: In this paper, the authors investigated the interaction of tin oxide surface with oxygen, water vapor, and hydrogen using temperature-programmed desorption (TPD) chromatograms of oxygen.
736 citations