Perfecting the Carbon Nanotube Forest

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Perfecting the Carbon Nanotube Forest

• James Harper
• Robert Mifflin

Advisors Prof. Prab Bandaru Prof. SungHo
Jin Prof. Frank Talke
June 7th, 2007 Jacobs School of
Engineering University of California San Diego
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Outline

• Introduction
• Selecting the Area of Nanotechnology to Enhance
• Why is this area important?
• Does it pass the Moral / Ethics Test?
• Background
• Growth and Chirality
• Separation Techniques
• Analyses of Separation Techniques
• Dielectrophoresis
• Flow Fractionalization Analysis and Improvement
• Pulsed dielectrophoresis
• Creating Pure Lines of Carbon Nanotubes
• Selection and Release
• The Perfect Carbon Nanotube Forest
• Conclusion

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Area of Nanotechnology to Enhance

• Generating Pure Sets of CNTs on Demand
• Why is this area important?

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Area of Nanotechnology to Enhance

• Carbon nanotubes can be used to enhance materials
  and create new sensors that impact everyday life
• Electrical arena
• Wires, Batteries and
  Capacitors, Flex displays

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Area of Nanotechnology to Enhance

• Carbon nanotubes can be used to enhance materials
  and create new sensors that impact everyday life
• Electrical arena
• Conductive plastics, adhesives
• Structural Arena
• Adhesives, Flexible circuits,
  Composites

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Area of Nanotechnology to Enhance

• Carbon nanotubes can be used to enhance materials
  and create new sensors that impact everyday life
• Electrical arena
• Conductive plastics, adhesives
• Structural Arena
• Adhesives, textiles, composites
• Bio-molecule sensing

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Area of Nanotechnology to Enhance

• Does it pass the Moral / Ethics Test?

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Background

• Growth and Chirality of Carbon Nanotubes
• Formed from several processes, resulting in a
  sheet of graphene in the form of a hollow
  continuous tube.
• Differences between SWCNT, MWCNT,M-SWCNT, S-SWCNT

SWCNT Single Wall CNT MWCNT Multi-Wall
CNT M-SWCNT Metallic SWCNT S-SWCNT
Semiconductor SWCNT
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Background

• Unbundling Carbon Nanotubes
• Use sonication and ultra-centrifugation to
  separate hydrophobic clumps of CNTs
• Buffer with a surfactant sodium dodecyl sulphate
  (SDS)

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Background

• Unbundling Carbon Nanotubes
• Use sonication and ultra-centrifugation to
  separate hydrophobic clumps of CNTs
• Buffer with a surfactant sodium dodecyl sulphate
  (SDS)
• Purification / Sorting Techniques
• Ultra-centrifugation
• Optical sorting
• Fluid flow fractionalization
• Dielectrophoresis

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Background

• Purification / Sorting Techniques
• Ultra-centrifugation

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Background

• Purification / Sorting Techniques
• Optical sorting

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Background

• Purification / Sorting Techniques
• Optical sorting

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Background

• Purification / Sorting Techniques
• Fluid flow fractionalization

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Background

• Purification / Sorting Techniques
• Dielectrophoresis

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Background

• Unbundling Carbon Nanotubes
• Use sonication to separate clumps and
  ultra-centrifugation
• Purification / Sorting Techniques
• Ultra-centrifugation
• Optical sorting
• Fluid flow fractionalization
• Dielectrophoresis
• Problem?
• Each technique allows for partial separation of
  the desired carbon nanotubes from the bulk
  solution However

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Background

• There is an overlap of sorting parameters!
• Use of one technique independently will not
  discriminate nanotubes with overlapping parameters

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Background

• There is an overlap of sorting parameters!
• And the number of parameters that can vary is
  large!

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Background

• Partial Solution?
• Multiple techniques must be used for to obtain a
  rough sort of the material.
• Ultra-centrifugation
• Optical sorting
• Fluid flow
  fractionalization
• 
  Dielectrophoresis
• And the resulting subset will still have a
  mixture of different nanotubes - albeit a set
  with many overlapping attributes.

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Solution

• Realize that absolute purity of nanotubes through
  top down or bottom up fabrication may not be
  achievable.
• Recast the problem what other system/industry
  has high variability yet desires near exact to
  exact duplicates be used?

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Solution

• Look to the Bio Labs
• Generating a clone murine line for laboratory
  study.

Maps to --- CNT rough sort desired
CNTs --- CNT individual capture --- Check the
Chirality using Raman scattering
and conduction properties --- Release the
individual CNT --- Clone the CNT
Bio Process Select an species Isolate the
individual Sequence the DNA Release the
individual(into a controlled environment) Clone
the individual
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Solution

• Can all of these steps be done?
• If so, perfect sorting may not be required.

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Outline

• Introduction
• Selecting the Area of Nanotechnology to Enhance
• Why is this area important?
• Does it pass the Moral / Ethics Test?
• Background
• Growth and Chirality
• Separation Techniques
• Analyses of Separation Techniques
• Dielectrophoresis
• Flow Fractionalization Analysis and Improvement
• Pulsed dielectrophoresis
• Creating Pure Lines of Carbon Nanotubes
• Selection and Release
• The Perfect Carbon Nanotube Forest
• Conclusion

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Dielectrophoresis

• Uncharged particle  non-uniform electric field
  force
• Caused by uneven charge distribution
• Depends strongly on
• Mediums and particles' electrical properties
• Particles' morphology
• Frequency of the electric field
• More polarizable particles move toward stronger
  electric field
• For CNTs,
• where ,
  and

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Dielectrophoresis
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Dielectrophoresis
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Flow Fractionalization Analysis and
Improvement

• CNTs with dissimilar conductivitiesand
  morphologies develop differentterminal
  velocities within a fluid flow,as described by
• Separation is most efficient when vT
• of different sizes of CNTs is most
• dissimilar.
• Adjust friction factor f by changing orientation

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Flow Fractionalization Analysis and
Improvement

• Three possible orientations
• Parallel
• Because ,
• vT a
  f -1 when u is constant.

• Perpendicular

• Random

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Flow Fractionalization Analysis and
Improvement
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Flow Fractionalization Analysis and
Improvement
Orientation Inverse of Friction Factor (s/kg) Inverse of Friction Factor (s/kg) Difference (s/kg)
Orientation 100 nm length 2 µm length Difference (s/kg)
Perpendicular 4.5 105 51.3 105 46.8 105
Random 6.4 105 76.8 105 70.4 105
Parallel 8.9 105 103.0 105 94.1 105

• Maximum difference attained with parallel
  orientation
• 34 larger difference than random orientation
• Significant?
• May be difficult to implement in practice
• Possibly use dielectrophoretic force itself to
  orient nanotubes parallel to flow

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Pulsed Dielectrophoresis

• Difference between Dielectrophoresis (DEP) and
  Pulsed Dielectrophoresis (PDEP)
• DEP is typically set up for an asymmetrical field
  with constant frequency. We would like to look
  at varying the duty cycle to try to separate CNT
  that have very closely overlapping properties.
• Example - Lets look at some cells

Distributed populations of spherical shell models
of mammalian cells. (Top Left) 10 variation
across all three DEP parameters, radius,
permittivity, and conductivity. (Top Right)
Constant conductivity with varying permittivity
and radius. (Lower Left) Constant radius. (Lower
Right) Constant permittivity.
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Pulsed Dielectrophoresis

• Difference between Dielectrophoresis (DEP) and
  Pulsed Dielectrophoresis (PDEP)

Distributed populations of spherical shell models
of mammalian cells. (Top Left) 10 variation
across all three DEP parameters, radius,
permittivity, and conductivity. (Top Right)
Constant conductivity with varying permittivity
and radius. (Lower Left) Constant radius. (Lower
Right) Constant permittivity.
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Pulsed Dielectrophoresis

• The equations
• Complex Permittivity
• Permittivity of CNT
• Metallic 2000
• Media 18.6
• Modified Clausius Mossotti
• E field between electrodes volts
  per meter
• And the friction factor

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Actual Simulation Failed! Agh!
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Capture of subset of CNTs

• Capture occurs due to Dielectrophoresis
  attracting the CNT dipoles.
• CNT lands on the probes and
• causes the field to be modified
• Thus self assembly/placement
• Modify the probe surface with LBL deposited
  materialfor sticktion and later lift off

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Analysis of subset of CNTs

• Use Raman scattering and conduction parameters to
  analyze the CNTs
• Electronic and mechanicallystringency wash
  cartridge.

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Release the desired CNTs

• Decorate CNTs with bio-particles to ease later
  handling.
• CNTs are then released as
• needed from the storage
• cartridge.
• Moved to cloning cell off chip

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Release the desired CNTs

• Sonicated into seeds
• Embedded into an LBL deposited layer
• Used to grow Final CNTs

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Conclusions

• Sorting of CNTs difficult, yet improvable
• Flow fractionalization
• Pulsed dielectrophoresis
• Best solution avoid problem of perfect sorting
  with capture and release of CNTs
• The perfect carbon nanotube forest

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References

• Pictures
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More references available for this document upon
request.
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