1. 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) 1

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

3. Motivation: Gas sensors for VOCs Certain VOCs in human breath = disease biomarkers: Examples for disease markers in human breath: 1 VOCs Disease Ethane and pentaneOxidative stress Methylated hydrocarbonsLung or breast cancer Hydrocarbons (especially ethane and pentane)Oxidative stress IsopreneCholesterol metabolism AcetoneDiabetes mellitus, ketonemia 3 – Acetone 2 – 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. 4 Eranna et al., Crit. Rev. Solid State Mater. Sci., 29, 2004, 171. Tin Oxides (35%)

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

6. 6 Zhao et al., Sens. Actuators, B., 115, 2006, 460. SnO 2 Dip coating 21 °C Dry Air d XRD = 5 nm Acetone(ppm) Sensitivity SnO 2 Sensitivity to Low Concentrations of Acetone

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 H 2 O, – H 2 O decreases SnO 2 resistivity. 3 7 1.Dang et al., J. Chromatogr., B810, 2004, 274. 2. Boguslaw et al., Biomed. Chromatogr., 21, 2007, 554. 3.Gaman et al., Russian Physics Journal, 51, 2008, 833.

8. Nanostructured SnO 2 Gas Sensitivity and Resistivity SnO 2 Bulk Thickness (nm) 10 11 10 10 9 10 8 10 7 10 6 0200 400600 800 50 60 20 0 320 °C, 10 ppm EtOH FSP 8 Xu et al., Sens. Act. B., 3, 1991, 149. 300 °C Dry Air 800 ppm H 2 300 °C Dry Air Tricoli et al., To be submitted. 800 ppm H 2 800 ppm CO

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

10. Advantages – Ag lowest resistivity of all metals Ag: 15.87 nΩ·m, 1 CuO: 0.1 Ω·m 2 (20°C). – Can produce metallic Ag by flames. 3 – Relatively cheap. 4 – Ag can enhance sensitivity. 4 10 Ag Nanoparticles as Nanoelectrodes 1.http://en.wikipedia.org/wiki/Resistivityhttp://en.wikipedia.org/wiki/Resistivity 2.Tsai et al., Acta Materialia, 57, 2008, 1570. 3.Keskinen et al., Journal of Nanoparticle Research. 9, 2007, 569. 4.http://www.kitco.com/market/us_charts.htmlhttp://www.kitco.com/market/us_charts.html 5.Kim et al., Thin Solid Films. 516, 2008,198.

11. FSP Direct Deposition and In-situ Flame Annealing SnO 2 : – 0.5M Tin (II) ethylhexanoate in Xylene Ag: – 0.01 M AgNO 3 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. 11 Tricoli et al. Adv. Mater., 20, 2006, 3005.

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

13. Deposition Time 13 15 seconds60 seconds

14. Deposition of Functional SnO 2 14 Ag on Alumina SubstrateSnO 2 on Ag and Alumina Substrate Ag-Bottom

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

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

17. Characterization of Ag Nanoelectrodes 17 320 °C Dry Air Substrate SnO 2 Ag-Bottom

18. 18 Substrate + + - - e-  e-  e-  O -O - O -O - O -O - O -O - O -O - O -O - CH 3 COCH 3 CO 2, H 2 O R SnO 2 R Ag 1/R =1/R Ag +1/R SnO2 R SnO2 CH 3 COCH 3 (gas) + 8O - (adsorbed)  3CO 2 (gas) +3H 2 O (gas) +8e - (conduction band) Qin et al., Nanotechnology. 19, 2008, 7. R Response S = R Dry Air /R Acetone

19. Reproducibility 19 320 °C 0% RH

20. Ag-Bottom vs. SnO 2 under Dry Conditions 20 320 °C Dry Air Wang et al., Chem. Mater.,20, 2008, 4894. 350 °C 10% Cr doped WO 3 ~40%

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

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

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

24. Conclusions Conductive path already with Ag 15 s, annealed. Detection of < 0.6 ppm acetone possible with ultra thin SnO 2 and nanostructured Ag/SnO 2. Ag-Bottom 40% more sensitive than SnO 2 0% RH, 9% in 80% RH, acetone. Ag-Bottom selective to acetone 0% RH. Acetone and ethanol sensitivity comparable 80% RH. 24

25. Outlook TiO 2 doped Ag-Bottom sensor testing- decrease cross sensitivity to humidity. Repetition ethanol humidity Testing. “Home-made” FSP-made sensor testing and characterization. 25

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

27. Thank you for your attention, Questions? 27

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

29. XRD Results 29 : SnO 2 : Ag : Al 2 O 3 : Au Au + Al 2 O 3 Substrate SnO 2 Filter d XRD = 12 nm Ag-Bottom Ag 8 min d XRD = 20 nm SnO 2 -Only 15 s. Deposition time

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

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

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. 32 Shyjumon et al. The Eur. Phys. J. D., 37, 2006, 309.

33. Ag Nanoparticles as Nanoelectrodes 33 Gibbs-Thomson Equation Shyjumon et al. The Eur. Phys. J. D., 37, 2006, 309. σ = 1.02 J/m 2 (surface energy) M = 107.9 g/mol (Molar mass) ρ = 10.5 g/cm 3 (density) ∆H m = 11.3 kJ/mol melting enthalpy T bulk = 1233K(bulk melting pt.) r = radius of cluster size.

34. Ag Nanoelectrodes 34 1 hour, O 2 Atmosphere Kim et al., Thin Solid Films. 2008, 516, 198

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

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

37. Portable Micro Gas Sensors 37 Kühne et al., J. Micromech. Microeng., 18, 2008, 035040Tricoli et al., Adv. Mater., 20, 2008, 3005 Baseline  10 9 ohm, Optimal Baseline  10 7 ohm Microhotplate  back-heating SnO 2 300  m

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

39. CO Response Compared 39 T = 320 °C Synthetic dry air O-O- O-O- O-O- O-O- O-O- O-O- O-O- e-  e-  e-  O-O- O-O- O-O- O-O- O-O- O-O- O2O2 Mädler et al. J. Mater. Res., 22, 2007, 854. COCO 2 Catalytic CO consumption without electron transfer