logging in or signing up Working Principle of SMO Gas Sensors mehulmatrix Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 4137 Category: Entertainment License: All Rights Reserved Like it (5) Dislike it (1) Added: July 29, 2008 This Presentation is Public Favorites: 3 Presentation Description Explains the basics of Semiconducting Metal Oxides based Gas Sensors. Comments Posting comment... By: agnivesh1989 (3 month(s) ago) thanks but how can i download Saving..... Post Reply Close Saving..... Edit Comment Close By: atomic3 (35 month(s) ago) HI Mehul, Thanks, but still not able to download - says that presenter is not allowing such. Indeed, I'd not pass it on, but rather use some of it in a techical analysis that I'm preparing for a client. I'll definitely attirbute what I use to you, and will share with you what I write. BTW I am a physicist having spent some 45 yeaers in sensor development/ use, am retired from industry having worked previously for a non-pfrofit, the Department of Defense, industry,, and univeristies, and am doing consulting now. MIght I ask the nature of your involvement in SMOs? Best regards, John John P Carrico johnpcarrico9@msn.,com Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript Working Principle of Semi-conducting Gas Sensors : Working Principle of Semi-conducting Gas Sensors Outline of Presentation : Outline of Presentation Applications of Gas Sensors & Emerging Markets Features of SMO Gas Sensors History Basis of MO Semiconductor Gas Sensors Effect of Reducing & Oxidizing Gases Why Metal-Oxides? Sensor Mechanism parameters Influence of Catalysts Importance of nano-size particles Important Characterization parameters Few examples Applications of Gas Sensors : Applications of Gas Sensors Safety Applications* Slide 4: Environmental Control* *FiS Sensors,Japan. Emerging Markets : Emerging Markets Sensing of O2 containing CO2,NOx & SO2. Detection of N2O & Ethylene- -oxide in hospitals. Chemical reagents like NH3, HNO3, HF, & PH3 in silicon machining industries. Auto-damper Systems (ADS) for car ventilation. House-hold applications. Features of SMO Gas Sensors : Features of SMO Gas Sensors Small Size, High Sensitivity, Low Price, Long Life- Around 10 years compared to, Maintenance-free 1-2 yrs for catalytic/electrochemical types, Feasibility to combine control circuit, signal-conditioning. History : History Brattain & Bradeen in 1953 demonstrated change in ‘Contact Potential’ based on changes in ambient conditions.* Oxygen, water vapor, OH radicals, alcohol,etc were found to effect the contact potential. In 1962, Seiyama demonstrated a ZnO film gas sensor based on adsorption & desorption of gases.** Also he found that the process was affective at temperatures near 400C. *- The Bell System Technical Journal,January 1953. **- Analytical Chemistry,Vol 34,No 11. Basis of MO Semiconductor Gas Sensors : Basis of MO Semiconductor Gas Sensors Semi-conducting gas sensors basically operate on bulk changes & surface changes mechanism. 1st class sensitive to only oxygen partial pressure & oxide defect chemistry is of central importance. Operate in the temp range of 700C & above. Typically they are used as Oxygen Sensors in exhausts of combustion engines. Adsorption-desoprtion of Oxygen on the surface the driving mechanism for 2nd class. O2 can be thought of as a surface trap for electrons. Slide 10: Oxygen adsorbates will build a space-charge region i.e electron-depleted layer. Reversible change in resistance based on O2 adsorption-desorption. In temperature range 300-500C can be used to detect impurity/minority gases. The temperature dependence is due to differing stabilities of oxygen- species & different oxidizing temperatures of gases. Why only adsorption of Oxygen is so significant? Slide 11: Oxygen adsorbates will build a space-charge region i.e electron-depleted layer. Reversible change in resistance based on O2 adsorption-desorption. In temperature range 300-500C can be used to detect impurity/minority gases. The temperature dependence is due to differing stabilities of oxygen- species & different oxidizing temperatures of gases. Why only adsorption of Oxygen is so significant? Effect of Reducing & Oxidizing Gases : Effect of Reducing & Oxidizing Gases Space-charge layer will be over the grain boundary area. Consider the following reaction: 2CO + O2- 2CO2 + e- CO will react with the adsorbed O2 species & donate an electron to the surface( reduction process). The surface could be n-type or p-type & determines the change in resistance. Slide 14: Reducing Gases: H2, Hydrocarbons, CO. Oxidizing Gases: Cl, NO2. Oxidizing agents normally don’t react with Oxygen species', chemisorption more dominant. Humidity interference is also a concern. Products of catalytic reactions can accumulate & cause surface poisoning. Why Metal Oxides? : Why Metal Oxides? Certain kinds of surface reactions are to be avoided. Growth of oxide layer, etching of the surface. High operating temperatures & some MOs exhibit stoichiometry changes. Electronic Structure of Metal oxides also important.* Transitional MO with filled d0 & d10 electronic configurations imp for gas sensing applications. Post-transitional MOs like ZnO & SnO2 have filled d10 configurations. d0 configuration found in binary MO likes TiO2,V2O5,WO3. *- G. Korotcenkov / Materials Science and Engineering B 139 (2007) 1–23 Sensing Mechanism Parameters : Sensing Mechanism Parameters Sensing mechanism based on*: i) Receptor Mechanism & ii) Transducer Mechanism. Receptor function based on the Surface properties Diffusion of the analyte gas** Adsorption/Desorption Parameters Transducer function based on interaction with the particles. Oxidation of analyte gas Barrrier Height at grain boundaries Grain Size Film Thickness** Band Gap *G. Korotcenkov / Materials Science and Engineering B 139 (2007) 1–23 **- S&A B 80 (2001) 125-131 Slide 17: Parameters for Characterization Influence of Catalysts : Influence of Catalysts Catalysts improve speed of response & selectivity. Two main mechanisms through which catalysts influence sensing mechanism: Spill Over. Fermi Energy Control. Normally noble metals like Palladium & Platinum used as catalysts. Why materials like Platinum only? Slide 19: As illustrated, the catalyst will dissociate the molecule & then the atoms will ‘spill over’ the surface. Slide 20: ‘Fermi Energy Control’ simply means that the adsorbed oxygen will remove electrons from the catalyst & catalyst will effectively remove from the SC film. Importance of nano-sized particles. : Importance of nano-sized particles. Possible states of materials Amorphous, glass-state, nanocrystalline, polycrystalline & single crystalline. Nano & polycrystalline form are the most suitable forms. Amorphous & Glassy state are unstable at high temperatures. High cost & difficulties for single crystalline material manufacture limit their applications. Slide 22: Specific surface area increases with a decrease in grain size. Comparability of the grain size (D) with space-charge layer (Ls) increases the sensitivity.* *N. Yamazoe, Sens. Actuators B: Chem. 5 (1991) 7–18. Examples : Examples http://www.grc.nasa.gov/WWW/chemsensors/ Slide 24: http://www.hwsensor.com/English/products/sensor/Semiconductor.htm You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.
Working Principle of SMO Gas Sensors mehulmatrix Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 4137 Category: Entertainment License: All Rights Reserved Like it (5) Dislike it (1) Added: July 29, 2008 This Presentation is Public Favorites: 3 Presentation Description Explains the basics of Semiconducting Metal Oxides based Gas Sensors. Comments Posting comment... By: agnivesh1989 (3 month(s) ago) thanks but how can i download Saving..... Post Reply Close Saving..... Edit Comment Close By: atomic3 (35 month(s) ago) HI Mehul, Thanks, but still not able to download - says that presenter is not allowing such. Indeed, I'd not pass it on, but rather use some of it in a techical analysis that I'm preparing for a client. I'll definitely attirbute what I use to you, and will share with you what I write. BTW I am a physicist having spent some 45 yeaers in sensor development/ use, am retired from industry having worked previously for a non-pfrofit, the Department of Defense, industry,, and univeristies, and am doing consulting now. MIght I ask the nature of your involvement in SMOs? Best regards, John John P Carrico johnpcarrico9@msn.,com Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript Working Principle of Semi-conducting Gas Sensors : Working Principle of Semi-conducting Gas Sensors Outline of Presentation : Outline of Presentation Applications of Gas Sensors & Emerging Markets Features of SMO Gas Sensors History Basis of MO Semiconductor Gas Sensors Effect of Reducing & Oxidizing Gases Why Metal-Oxides? Sensor Mechanism parameters Influence of Catalysts Importance of nano-size particles Important Characterization parameters Few examples Applications of Gas Sensors : Applications of Gas Sensors Safety Applications* Slide 4: Environmental Control* *FiS Sensors,Japan. Emerging Markets : Emerging Markets Sensing of O2 containing CO2,NOx & SO2. Detection of N2O & Ethylene- -oxide in hospitals. Chemical reagents like NH3, HNO3, HF, & PH3 in silicon machining industries. Auto-damper Systems (ADS) for car ventilation. House-hold applications. Features of SMO Gas Sensors : Features of SMO Gas Sensors Small Size, High Sensitivity, Low Price, Long Life- Around 10 years compared to, Maintenance-free 1-2 yrs for catalytic/electrochemical types, Feasibility to combine control circuit, signal-conditioning. History : History Brattain & Bradeen in 1953 demonstrated change in ‘Contact Potential’ based on changes in ambient conditions.* Oxygen, water vapor, OH radicals, alcohol,etc were found to effect the contact potential. In 1962, Seiyama demonstrated a ZnO film gas sensor based on adsorption & desorption of gases.** Also he found that the process was affective at temperatures near 400C. *- The Bell System Technical Journal,January 1953. **- Analytical Chemistry,Vol 34,No 11. Basis of MO Semiconductor Gas Sensors : Basis of MO Semiconductor Gas Sensors Semi-conducting gas sensors basically operate on bulk changes & surface changes mechanism. 1st class sensitive to only oxygen partial pressure & oxide defect chemistry is of central importance. Operate in the temp range of 700C & above. Typically they are used as Oxygen Sensors in exhausts of combustion engines. Adsorption-desoprtion of Oxygen on the surface the driving mechanism for 2nd class. O2 can be thought of as a surface trap for electrons. Slide 10: Oxygen adsorbates will build a space-charge region i.e electron-depleted layer. Reversible change in resistance based on O2 adsorption-desorption. In temperature range 300-500C can be used to detect impurity/minority gases. The temperature dependence is due to differing stabilities of oxygen- species & different oxidizing temperatures of gases. Why only adsorption of Oxygen is so significant? Slide 11: Oxygen adsorbates will build a space-charge region i.e electron-depleted layer. Reversible change in resistance based on O2 adsorption-desorption. In temperature range 300-500C can be used to detect impurity/minority gases. The temperature dependence is due to differing stabilities of oxygen- species & different oxidizing temperatures of gases. Why only adsorption of Oxygen is so significant? Effect of Reducing & Oxidizing Gases : Effect of Reducing & Oxidizing Gases Space-charge layer will be over the grain boundary area. Consider the following reaction: 2CO + O2- 2CO2 + e- CO will react with the adsorbed O2 species & donate an electron to the surface( reduction process). The surface could be n-type or p-type & determines the change in resistance. Slide 14: Reducing Gases: H2, Hydrocarbons, CO. Oxidizing Gases: Cl, NO2. Oxidizing agents normally don’t react with Oxygen species', chemisorption more dominant. Humidity interference is also a concern. Products of catalytic reactions can accumulate & cause surface poisoning. Why Metal Oxides? : Why Metal Oxides? Certain kinds of surface reactions are to be avoided. Growth of oxide layer, etching of the surface. High operating temperatures & some MOs exhibit stoichiometry changes. Electronic Structure of Metal oxides also important.* Transitional MO with filled d0 & d10 electronic configurations imp for gas sensing applications. Post-transitional MOs like ZnO & SnO2 have filled d10 configurations. d0 configuration found in binary MO likes TiO2,V2O5,WO3. *- G. Korotcenkov / Materials Science and Engineering B 139 (2007) 1–23 Sensing Mechanism Parameters : Sensing Mechanism Parameters Sensing mechanism based on*: i) Receptor Mechanism & ii) Transducer Mechanism. Receptor function based on the Surface properties Diffusion of the analyte gas** Adsorption/Desorption Parameters Transducer function based on interaction with the particles. Oxidation of analyte gas Barrrier Height at grain boundaries Grain Size Film Thickness** Band Gap *G. Korotcenkov / Materials Science and Engineering B 139 (2007) 1–23 **- S&A B 80 (2001) 125-131 Slide 17: Parameters for Characterization Influence of Catalysts : Influence of Catalysts Catalysts improve speed of response & selectivity. Two main mechanisms through which catalysts influence sensing mechanism: Spill Over. Fermi Energy Control. Normally noble metals like Palladium & Platinum used as catalysts. Why materials like Platinum only? Slide 19: As illustrated, the catalyst will dissociate the molecule & then the atoms will ‘spill over’ the surface. Slide 20: ‘Fermi Energy Control’ simply means that the adsorbed oxygen will remove electrons from the catalyst & catalyst will effectively remove from the SC film. Importance of nano-sized particles. : Importance of nano-sized particles. Possible states of materials Amorphous, glass-state, nanocrystalline, polycrystalline & single crystalline. Nano & polycrystalline form are the most suitable forms. Amorphous & Glassy state are unstable at high temperatures. High cost & difficulties for single crystalline material manufacture limit their applications. Slide 22: Specific surface area increases with a decrease in grain size. Comparability of the grain size (D) with space-charge layer (Ls) increases the sensitivity.* *N. Yamazoe, Sens. Actuators B: Chem. 5 (1991) 7–18. Examples : Examples http://www.grc.nasa.gov/WWW/chemsensors/ Slide 24: http://www.hwsensor.com/English/products/sensor/Semiconductor.htm