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SnO 2 with Ag Nanoelectrodes for Sensing Ultra Low Acetone Concentrations Final Presentation Semester Project FS09

SnO 2 with Ag Nanoelectrodes for Sensing Ultra Low Acetone Concentrations Final Presentation Semester Project FS09. E. Buitrago Advisors: Dr. H. Keskinen and A. Tricoli Particle Technology Laboratory Swiss Federal Institute of Technology (ETHZ). Outline. Motivation Tin Oxide Silver

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SnO 2 with Ag Nanoelectrodes for Sensing Ultra Low Acetone Concentrations Final Presentation Semester Project FS09

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  1. SnO2 with Ag Nanoelectrodes for Sensing Ultra Low Acetone ConcentrationsFinal PresentationSemester Project FS09 E. Buitrago Advisors: Dr. H. Keskinen and A. Tricoli Particle Technology Laboratory Swiss Federal Institute of Technology (ETHZ)

  2. Outline • Motivation • Tin Oxide • Silver • Experimental • Results • Conclusion • Outlook • Questions?

  3. Motivation: Gas sensors for VOCs • Certain VOCs in human breath = disease biomarkers: • Acetone2 • diabetic patients: 1.8 ppm • healthy individuals: 0.8 ppm. • 1.Boguslaw et al., Biomed. Chromatogr., 21, 2007, 544. • 2. Wang et al., Chem. Mater.,20, 2008, 4894.

  4. Tin Oxides (35%) Eranna et al., Crit. Rev. Solid State Mater. Sci., 29, 2004, 171.

  5. Sensing of different metal oxides to various gaseous species. Eranna et al., Crit. Rev. Solid State Mater. Sci., 29, 2004, 171.

  6. SnO2 Sensitivity to Low Concentrations of Acetone SnO2 Dip coating 21 °C Dry Air dXRD = 5 nm Sensitivity Acetone(ppm) Zhao et al., Sens. Actuators, B., 115, 2006, 460.

  7. Acetone in Breath Detection Challenges • > 200 VOCs in human breath. 1 • VOCs present at trace levels: • i.e. ammonia: 0.8 ppm , ethanol: 0.1 ppm.2 • Breath saturated in H2O, • H2O decreases SnO2 resistivity.3 • Dang et al., J. Chromatogr., B810, 2004, 274. • Boguslaw et al., Biomed. Chromatogr., 21, 2007, 554. • Gaman et al., Russian Physics Journal, 51, 2008, 833.

  8. Nanostructured SnO2Gas Sensitivity and Resistivity 1011 60 300 °C Dry Air 320 °C, 10 ppm EtOH FSP 300 °C Dry Air 1010 50 800 ppm H2 Dry Air 109 Baseline Resistance RAir, Ohms Sensitivity 108 800 ppm H2 800 ppm CO 20 107 0 106 400 600 0 200 800 SnO2 Bulk Thickness (nm) Xu et al., Sens. Act. B., 3, 1991, 149. Tricoli et al., To be submitted.

  9. Film Resistance and Sensitivity • Electrode geometry and minimal distance.1 • Film characteristics (porosity, thickness, material, etc.). • Divide Sensitive and Conductive Functions!2 Interdigitated Electrodes • Shukla et al., International Journal of Hydrogen Energy. 33, 2008, 470. • Tricoli et al., To be submitted.

  10. Ag Nanoparticles as Nanoelectrodes • Advantages • Ag lowest resistivity of all metals Ag: 15.87 nΩ·m,1 CuO: 0.1 Ω·m2 (20°C). • Can produce metallic Ag by flames.3 • Relatively cheap.4 • Ag can enhance sensitivity.4 • http://en.wikipedia.org/wiki/Resistivity • Tsai et al., Acta Materialia, 57, 2008, 1570. • Keskinen et al., Journal of Nanoparticle Research. 9, 2007, 569. • http://www.kitco.com/market/us_charts.html • Kim et al., Thin Solid Films. 516, 2008,198.

  11. FSP Direct Deposition and In-situ Flame Annealing • SnO2: • 0.5M Tin (II) ethylhexanoate in Xylene • Ag: • 0.01 M AgNO3 in ethanol, ethylhexanoate acid (1:1 ratio) 5/5 Flame Dep time: 15 s • Anneal: • Xylene • 12/5 Flame • Anneal time: 25 s Mädler et al. Sens. Actuators, B. 2006. Tricoli et al. Adv. Mater., 20, 2006,3005.

  12. Ag Nanoelectrodes-Anneal Before in-situ anneal 15 s After in-situ anneal

  13. Deposition Time 15 seconds 60 seconds

  14. Deposition of Functional SnO2 Ag on Alumina Substrate SnO2 on Ag and Alumina Substrate Ag-Bottom

  15. Qualitative Effect of Anneal on Glass Substrate ~3.3 μm ~0.4 μm Ag-Bottom- No Anneal Glass Substrate Ag-Bottom- Annealed

  16. Sensor Testing T = 320 °C Synthetic dry air Water Vapor Acetone S = Rair/Ranalyte (1) Tubular furnace, (2) Quartz tube (3) Sensor, (4) Gold wiring Teleki et al., Sens. Actuators, B.,119, 2006, 684.

  17. Characterization of Ag Nanoelectrodes Substrate 320 °C Dry Air Ag-Bottom SnO2

  18. Response R 1/R =1/RAg +1/RSnO2 CH3COCH3 CO2, H2O RSnO2 O- O- O- O- O- O- R SnO2 e-  e-  e-  + - R Ag Substrate S = RDry Air/RAcetone CH3COCH3(gas) + 8O-(adsorbed) 3CO2(gas) +3H2O (gas) +8e-(conduction band) Qin et al., Nanotechnology. 19, 2008, 7.

  19. Reproducibility 320 °C 0% RH

  20. Ag-Bottom vs. SnO2 under Dry Conditions ~40% 320 °C Dry Air 350 °C 10% Cr doped WO3 Wang et al., Chem. Mater.,20, 2008, 4894.

  21. Effect of RH, Closer to Real Conditions ~9% 320 °C 80% RH S =RRH=80%/RAcetone RH=80%

  22. Ag-Bottom Selectivity under Dry Conditions ~40% 320 °C Dry Air

  23. Ag-Bottom Acetone Selectivity 80% RH 320 °C 80% RH

  24. Conclusions • Conductive path already with Ag 15 s, annealed. • Detection of < 0.6 ppm acetone possible with ultra thin SnO2 and nanostructured Ag/SnO2. • Ag-Bottom 40% more sensitive than SnO2 0% RH, 9% in 80% RH, acetone. • Ag-Bottom selective to acetone 0% RH. • Acetone and ethanol sensitivity comparable 80% RH.

  25. Outlook • TiO2 doped Ag-Bottom sensor testing- decrease cross sensitivity to humidity. • Repetition ethanol humidity Testing. • “Home-made” FSP-made sensor testing and characterization.

  26. Acknowledgments • Dr. Helmi Keskinen • Antonio Tricoli • PTL Lab

  27. Thank you for your attention, Questions?

  28. Appendix • XRD • Thermal Stability Ag • Effect Ag addition, Resistance • Dry and Humid Air Trace • Portable Gas sensors • High Concentration mini-p results

  29. : SnO2 : Ag : Al2O3 : Au XRD Results Ag 8 min dXRD = 20 nm SnO2 Filter dXRD = 12 nm Ag-Bottom 15 s. Deposition time SnO2-Only Au + Al2O3 Substrate

  30. Ag Nanoparticles as Nanoelectrodes • Disadvantages • Low thermal stability in air, < 500°C. Akhavan et al. Applied Surface Science., 2007, 254, 548.

  31. Low Thermal Stability High Resistances • As deposited Ag • 500 °C • 700 °C • 1 hour anneal in dry air Sheet resistance variation with Ag Thickness, different temperatures. SEM. Akhavan et al. Applied Surface Science., 254, 2007, 548.

  32. Ag Nanoparticles as Nanoelectrodes • Disadvantages • Low thermal stability at low temperatures in air, < 500°C.1 • Melting point depression for decreasing grain sizes. 10 nm  < 760 K, bulk: 1233 K. Shyjumon et al. The Eur. Phys. J. D., 37, 2006, 309.

  33. Ag Nanoparticles as Nanoelectrodes Gibbs-Thomson Equation σ = 1.02 J/m 2 (surface energy) M = 107.9 g/mol (Molar mass) ρ = 10.5 g/cm3 (density) ∆Hm = 11.3 kJ/mol melting enthalpy Tbulk = 1233K(bulk melting pt.) r = radius of cluster size. Shyjumon et al. The Eur. Phys. J. D., 37, 2006, 309.

  34. Ag Nanoelectrodes 1 hour, O2 Atmosphere Kim et al., Thin Solid Films. 2008, 516, 198

  35. Sensitive to Ultra Low Concentrations of Acetone Ag-Bottom 320 °C 0% RH S= RDryAir/RAnalyte

  36. Ag-Anneal 80%, Acetone Response 80% RH, 0 ppm Acetone 0.1 ppm 0.2 ppm 0.5 ppm 0.6 ppm S= RRH=80%/RRH=80%, Analyte

  37. Portable Micro Gas Sensors Microhotplateback-heating SnO2 300 mm Baseline  109 ohm, Optimal Baseline  107 ohm Kühne et al., J. Micromech. Microeng., 18, 2008, 035040 Tricoli et al., Adv. Mater., 20, 2008, 3005

  38. Acetone Sensor Response, Low Concentrations S = Rair/Ranalyte T = 320 °C Synthetic dry air

  39. CO Response Compared CO CO2 O2 e-  e-  e-  e-  e-  e-  O- O- O- O- O- T = 320 °C Synthetic dry air O- O- O- O- O- O- O- O- Catalytic CO consumption without electron transfer Mädler et al. J. Mater. Res., 22, 2007, 854.

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