Polypyrrole Nanoribbon Based Nano Gas Sensors

1. Polypyrrole Nanoribbon Based Nano Gas Sensors Sergio Martin Hernandez August 20th, 2009 Department of Chemical and Environmental Engineering University of California, Riverside BRITE Symposium

2. Outline • Sensor Outlook • Objectives • Motivation • PPY Fabrication process • Apparatus • Sensing Conditions • Results • Summary • Future work • Acknowledgements and References

3. Sensors Outlook Industrial Emissions Automobiles Environmental Monitoring Gas Sensors Food & Agriculture Space Exploration Medical Diagnostics Homeland Security nssdc.gsfc.nasa.gov/image/spacecraft/mir.jpg

4. Dynamic range (Property) / Property Sensitivity UDL LDL Concentration of analyte Gas Sensor Overview Gas/Analytes Chemical reaction (e.g., protonation) Sensitive layer Transducer Interface circuitry Response signal (e.g., Voltage)

5. Objectives • In our research we are using polypyrrole nanoribbons as sensing materials, • The main objective is to analyze the sensing of analytes such as water vapor, acetone, methanol, ethanol, isopropanol, MEK, and carbon dioxide using polypyrrole nanoribbons as a sensing materials. • Eventually we will try to improve the sensitivity by functionalizing the polypyrrole nanoribbons with other materials.

6. Motivation • Conducting polymers are new class of material with fascinating electron-transport behavior. This provides them with many technical applications. The simplicity of processing polymers together with chemically tunable properties makes them especially useful in electronic, optoelectronic and electromechanical devices. One such area where the conducting polymers have shown great promise is in sensory applications. In an attempt to increase the sensitivity of sensing materials, research has focused in utilizing nanowires as their primary focus. In our research we are using polypyrrole nanoribbons as sensing materials, because they are highly sensitive and relatively stable. • A variation of polypyrrole nanostructures fabrication techniques have been developed such as template synthesis and dip-pen lithography; however they require expensive equipment such as AFM, FIB and E-Beam Lithography. Additionally, the device assembling process is very extensive. On the other hand Lithographically Patterned Nanowire Electrodeposition (LPNE) technique has been demonstrated as cost-effective technique in fabrication of nanowires in pre-determined locations on substrates with precisely controlled height and width. Another notable characteristic of this technique is that it combines photholithography and electrodeposition approaches.

7. Lithographically Patterned Nanowire Electrodeposition (LPNE) • P-type Si wafer with 1000Å SiO2 layer • Deposition 100nm thickness of sacrificial layer (Ni) • Spin coating of photoresist (PR) S1813

8. Lithographically Patterned Nanowire Electrodeposition (LPNE) • Exposure under UV light for 7 second • Develop pattern in developer(AZ400Z)-water mixture solution

9. Lithographically Patterned Nanowire Electrodeposition (LPNE) • Chemical etching with Ni Etchant TFB • Electrochemical etching • Electrolyte: 0.1M KCl + 24mM HCl • Eapplied = 0.02V vs. SCE with Pt counter electrode

10. Lithographically Patterned Nanowire Electrodeposition (LPNE) • Electropolymerization of PPy • Electrolyte: 0.5M Pyyrole + 0.2M LiClO4 • Eapplied = 0.7V vs. SCE with Pt counter electrode

11. Lithographically Patterned Nanowire Electrodeposition (LPNE) E Ni SiO2 layer • Removal of PR by acetone • Integration of gold electrode by lift-off photolithography • Thickness of chrome = 20 nm • Thickness of gold = 180 nm

12. Lithographically Patterned Nanowire Electrodeposition (LPNE) • Removal of Ni by 2% HNO3

13. Wafer Scale Fabrication of PPy Nanoribbons

14. Gas Sensing Apparatus

15. Gas Sensing Apparatus

16. Conditions and Protocol Percent Saturation 1% , 5% , 10% , 20%, 50% ,100%

17. Conditions and Protocol • Measurement of resistance • Make the electrical connections in the EP board by wire bonding • Purge air for 15 minutes • Hook up the EP board to sensor Actual Experiment Starts • 1 hour exposure to air (purging/ to establish a base line) • 15 minutes exposure of water vapor (1) • 20 minutes of recovery (only air) (2) • (1) and (2) are repeated five more time respectively because we are using six exposures. • Total flow rate: 200 sccm

18. Resistance and Sensitivity of Alcohol Group

19. Resistance and Sensitivity of the Ketone Group

20. Summary • Water vapor had a very high negative response. • In the alcohol group methanol , ethanol, and isopropanol was tested; with methanol clearly having the highest response, and ethanol the lowest. • In the ketone group MEK and Acetone was tested; MEK having the highest response. • Comparing both groups it is clear that the alcohol group produced the higher response. Even ethanol had a larger response than MEK. • Carbon Dioxide was also tested; however it seems to produce no response.

21. Future Work • In the future work, the sensing performance of the polypyrrole nanoribbons will be further improved by functionalizing them with other materials such as gold , palladium and platinum.

22. Acknowledgements and References • I acknowledge my mentor and graduate student Dr. Myung and Nicha Chartuprayoon from the department of Chemical and Environmental Engineering, in the University of California, Riverside; and the Financial support from the BRITE program and the University of California, Riverside. • 1. Skotheim, T. A.; Reynolds, J. R., Handbook of conducting polymers. 3rd ed.; CRC: Boca Raton, Fla., 2007; p 2 v. • 2. Menke, E. J.; Thompson, M. A.; Xiang, C.; Yang, L. C.; Penner, R. M. Nature Materials 2006, 5, (11), 914-919.