1) The document discusses the electrochemical deposition of polyaniline (PANI) on gold nanoelectrode crossbar structures.
2) Crossbar structures were fabricated using nanoimprint lithography with a soft Surlyn mold, but the mold required treatment to prevent photoresist from ripping off or not crosslinking.
3) PANI was electrochemically deposited on gold electrodes in an aniline solution to bridge the gaps between electrodes. Deposition times ranged from 45 minutes to over 1 hour and conductivity increased by orders of magnitude once bridging occurred.
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Electrochemical Deposition of Polyaniline on Nanoelectrode CrossBar Structures
1. MitgliedderHelmholtz-Gemeinschaft
2009 iNNIN REU
Electrochemical Deposition of Polyaniline on
Nanoelectrode CrossBar Structures
José Guevarra
Department of Mechanical Engineering
University of California, Santa Barbara
PI: Dr Dirk Mayer
Mentor: Nils Sanetra
2. 29. Januar 2015 Folie 2
Outline
• Motivation
Molecular bioelectronics
• The crossbar structure
• Polyaniline (PANI)
• Goals
• Methods
• Crossbar Structure Fabrication
• Electrochemical deposition of PANI on Au
• Summary and Outlook
• Acknowledgments
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Molecular electronics
What is molecular bioelectronics?
• Miniaturization
• Alternative to CMOS
Bioelectronics
• Biomolecule as active part
• Totally new functions (e.g.
sensor)
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The crossbar architecture
What is a crossbar?
• Two parallel planes of
nanoscale wire arrays
• Propterties of the crossbar
determined by interjunction
layer
• Metal-Bridge-Metal (MBM)
• For bioelectronics:
Interjunctionlayer: SAM
[Snider et al 2005]
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Polyaniline (PANI)
• Well documented conducting polymer
• Can be acid-doped to form conducting salt (emeraldine)
• Can be electrochemically deposited
• Cheap
Can it be used to close the interjunction gap?
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Goals
• Fabricate crossbar structures using a soft mold and lift-off
process
• Characterize pattern fidelity and compare to other methods
• Electrochemically deposit a conducting polymer (Polyanaline)
to bridge the junction gaps between crossbar junctions
• Electronic characterization of polyaniline, electrodes, and
junctions
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Fabrication Process (NanoImprint Lithography)
CF4 Etch
O2 Etch
Gold Deposition
Lift-Off
Using a soft mold (Surlyn) allows one to imprint a pattern from a
rigid mold multiple times, this extends the life of the rigid mold
Soft mold must be rigid enough to survive imprint process and
transparent to allow crosslinking of photoresist
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Transmission Characteristics
• NXR-2010 crosslinks between 220nm and 300nm
• Multiple layers of Surlyn and Surlyn with PDMS backplane should allow
crosslinking of photoresist
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Embossing Results
• 1 layer of Surlyn – hard to handle (flimsy and curls on itself)
• 2 layers of Surlyn – easier to handle
• 3 layers of Surlyn – semi-rigid
• 4 layers – difficult to emboss (many corrugations)
• Surlyn from SONY (130-170 microns) – fairly rigid
PDMS backplane must be spin coated to get uniform thickness
Embossing is easier with Surlyn squares that fit within radius of wafer
although the entire pattern may not be transfered
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Imprinting Results
• Attempted to use several types of underlayers (TI-Prime/PMMA/NXR-3010)
• Used NXR-2010 undiluted and NXR-2010 + MMA(1:1)
Typically, ended with two results
• Photoresist ripped off, leaving few or no structures
• No crosslinking, leaving no structures (Bikini-Waxing)
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Imprinting Results: Ripping of Photoresist
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Imprinting Results: Not a Total Loss
Some larger, partial structures
can be produced
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Imprinting Results
Conclusions:
1. Surlyn is too sticky
2. Thicker layers of Surlyn are not transparent
Recommendations:
1. Surlyn requires silanization or appropriate treatment
2. Create a rigid, negative mold using SiO2 wafer and NXR-2010 [1]
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Electrochemical Deposition of PANI on Au
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PANI Electrodeposition on Au
Basic Technique:
• Immerse electrodes in Aniline + H2SO4 solution
• Apply voltage bias across electrodes
• PANI will oxidize on cathode, grow, and “bridge” gap to the next electrode
Deposition Parameters:
• Voltage bias between electrodes (0.95V, 0.97, 1 V)
• Aniline Concentration (0.1 or 0.2 M Aniline)
• Deposition Times
Problems:
• Use of small drops to immerse electrodes can result in concentration
variation
• Little to no control of immersed electrode area
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PANI Electrodeposition on Au
Deposition Characteristics:
• Bridging times range from 45 minutes to
1.5 hours and more
• Conductance may grow steadily or rapidly in
orders of magnitude
• Bridging usually indicated by spikes in
current or relatively large current
• Current during deposition never
exceeds 10-4 A
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PANI Deposition on Au: Sample 5
Before Deposition
PANI Depositions
1. +0.95V, 1:10 hrs
2. +0.95V, 10 min
3. +0.95V, 5 min
Samples rinsed in Milli-Q water, blown dry, and
fresh Aniline solution added before each
deposit
After Deposition
After 3 depositions no
current between electrodes
when measured in air
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PANI Deposition on Au: Sample 5
No conduction because no bridging
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PANI Deposition on Au: Sample 5
Short period of low conductance to a jump in four orders of
magnitude in about 1 hr
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PANI Deposition on Au: Sample 5
Current on the order of 10-6 A, implies Aniline bridging between
electrodes
Non-linear characteristics
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PANI Deposition on Au: Sample 5
Some bridging between electrodes
Conductance ~ 10-6 A
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PANI Deposition on Au
Sample Average Deposition
Conductance (S)
Bridging Observed Conductance Near +1V
(S) measured in Air
3 10-9 No -
4 10-9 Yes 10-6
5 10-10 No
-
5b 10-4 Yes 10-6
6 10-9 Yes 10-7
7 10-7 Yes 10-6
8 10-9 No -
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PANI Deposition on Au: Voltage Dependence
0.1M Aniline, 0.95V
0.1M Aniline, 0.97V
0.1M Aniline, 1V
0.1M Aniline, 1V
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PANI Deposition on Au: Concentration Dependence
0.2M Aniline, 0.97V 0.2M Aniline, 0.95V
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Summary
Conclusions:
Surlyn soft molds need silanization
An SiO2 + NXR-2010 rigid mold may be an alternative to the soft mold
Deposition process not very predictable
Bridging will take 45 minutes or more
Use a funnel to control surface area and concentration
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Acknowledgments
Dr. Dirk Mayer
Dr. Andreas Offenhäusser
Nils Sanetra
Lynn Rathbun
Everyone from IBN-2
National Science Foundation
National Nanotechnology Infrastructure Network
Jennifer, Adam, and Kishore
Thanks For the Best Summer Ever!
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References
[1] Cross-linked Polymer Replica of a Nanoimprint Mold at 30 nm Half-pitch, Nano Lett., Vol. 5, No. 1,
2005