0 10 20 30 40 50 60 70 800.00

0.02

0.04

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RR

0

Percent Saturation (%)

Sensitivity of MEK

n=3

humidity Methanol Ethanol Isopropanol

-1.2

-1.0

-0.8

-0.6

-0.4

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R/R

0 Analyte

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0.0

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R/R

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Sensitivity of Methanoln=3

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tance(k)

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ent S

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ration

(%

)

Polypyrrole Nanoribbon Based Nano Gas Sensors 

Sergio Hernandez, Nicha Chartuprayoon and Nosang V. Myung Department of Chemical and Environmental Engineering, University of California, Riverside,

Riverside, CA 92521

AbstractAbstract

Introduction & MotivationIntroduction & Motivation

Polypyrrole nanoribbon is an effective sensing material because of high sensitivity and good stability. The simplicity of processing polymers together with chemically tunable properties makes them ideal materials for electronic, optoelectronic and electromechanical devices. Conducting polymer (i.e. polypyrrole) nanoribbon based gas sensors were fabricated using Lithography Patterned Nanowire Electrodeposition (LPNE) which combines the advantages of top-down lithographic patterning and bottom-up electrodeposition to form high density nanostructures in pre-determined location. The synthesized polypyrrole nanoribbons were used as sensing/transducing materials to detect various analytes including water vapor, acetone, methanol, ethanol, isopropanol, MEK, and carbon dioxide. The change of resistance upon exposure to analytes was monitor by applying a constant voltage of 0.5 V. The preliminary results show that polypyrrole nanoribbons are highly sensitive to VOCs with greatest sensitivity toward methanol. In the future work, the sensing performance will be further improved by functionalizing them with other materials.

ObjectivesObjectives

Wafer Scale Fabrication of PPy Nanoribbons

Gas Sensing Apparatus

Electrical conductivity at Room Temperature

Temperature Dependent Measurement

-1.50 -0.75 0.00 0.75 1.50

-225

-150

-75

0

75

150

225

Curr

ent (n

A)

Voltage (V)

Resistance = 5.64 MΩConductivity = 5.91 S/cm

410μm

Summary

Future Work

Acknowledgements

Reference

Resistance and Sensitivity of Alcohol GroupResistance and Sensitivity of Alcohol Group

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0-200

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295K 273K 250K 230K 210K 190K 170K 150K 130K 110K 90K 70K 50K 30K

Curr

ent (n

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Voltage (V)

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tance(k)

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ent S

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ration

(%

)

Resistance and Sensitivity of the Ketone Resistance and Sensitivity of the Ketone GroupGroup

MEK Acetone0.00

0.03

0.06

0.09

0.12

0.15

R/R

0

Analyte

Lithographically Patterned Nanowire Lithographically Patterned Nanowire Electrodeposition (LPNE)Electrodeposition (LPNE)

• P-type Si wafer with 1000Å SiO2 layer • Deposition 100nm thickness of sacrificial layer (Ni)• Spin coating of photoresist (PR) S1813

• Electropolymerization of PPy• Electrolyte: 0.5M Pyyrole + 0.2M LiClO4

• Eapplied = 0.7V vs. SCE with Pt counter electrode

• Exposure under UV light for 7 second• Develop pattern in developer(AZ400Z)-water mixture solution

• Chemical etching with Ni Etchant TFB• Electrochemical etching

• Electrolyte: 0.1M KCl + 24mM HCl•Eapplied = 0.02V vs. SCE with Pt counter electrode

•Removal of Ni by 2% HNO3

• Removal of PR by acetone•Integration of gold electrode by lift-off photolithography

•Thickness of chrome = 20 nm•Thickness of gold = 180 nm

E

SiO2 layerNi

• 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.

• 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.

0.00 0.01 0.02 0.03 0.040

1

2

3

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6

ln(R

)

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Resis

tance (M

Ohm

)

Temperature (K)

15 meV/K

60 meV/K

• 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.

• 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.

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.

Conducting polymers are new class of material with fascinating electron-transport behavior that 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.