Manipulation of Nanoparticles Using Dielectrophoresis

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Manipulation of Nanoparticles Using
Dielectrophoresis

• Matt Pappas
• Valparaiso University

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Outline

• Present talk structure
• Be brief
• Broad topics only

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Milieu

• Carbon nanotubes have very desirable electrical
  and mechanical properties, and are very promising
  for a variety of uses. Their discovery has
  prompted speculation of uses in everything from
  nanoscale electronics to reinforcement where
  carbon fibers are used today.
• It would be convenient to be able to measure
  electrical, mechanical, or electromechanical
  properties at will. For example, one might want
  to test the conductance of a batch of metallic
  nanotubes, or to measure the torsional strength
  of a batch made for structural reinforcement.

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Near the target

• Other groups have measured properties such as
  conductance, torsional strength, deflection, and
  buckling, but experiments are highly specialized.
  Many also involve growing nanotubes in situ,
  making such procedures unfit for batch testing.
• Measuring torsional strength, for example,
  involved creating a custom mask for the
  nanotubes were spread on a wafer, found using a
  scanning electron microscope, and a mask created
  to fit the dispersion.

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Dielectrophoresis, Distilled

• In an electric field, a neutral particle becomes
  polarized. If the field is non-uniform, the
  forces on each end of the dipole are also
  non-uniform, and the particle experiences a net
  force dependent upon the permittivity and
  conductivity of the particle and the media, as
  well as the field strength and frequency, but not
  the field polarity.

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Device Design

• We have constructed a 1 cm2 array of 20
  electrodes as shown
• Red represents electrodes, green represents
  photoresist patterned on top of the electrodes,
  and blue represents silicon dioxide.

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Trapping Detection

• The circuit below ensures that once a nanotube
  bridges the electrodes, the field will diminish
  substantially, preventing accumulation of
  nanotubes and/or other particulate matter in
  suspension. The gap can be modeled as a small
  capacitor.
• When the gap is bridged, a high voltage drop is
  measured across the resistor.

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Measurement of Properties

• Once trapped, the nanotube can be affixed to the
  electrode surface using an electron beam.
• The nanotube or electrode can then be manipulated
  with an atomic force microscope tip, or the
  electrodes can be deflected using a light beam.

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Versatility

• Different geometries allow different types of
  tests to be performed.
• The silicon dioxide can be chemically etched,
  giving deeper wells, which can be used to measure
  large deflections or large torsional deformations.

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Here and Now

• We have demonstrated attraction of CNTs to
  electrode gap, orientation of CNTs correct. We
  have not, however, detected bridging of a single
  nanotube.

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Summary

• Dielectrophoresis is a powerful way to place
  objects.
• Combining dielectrophoresis with a simple circuit
  and a versatile electrode device, virtually any
  property of nanotubes can be tested.

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Future Work?

• needed follow-up work
• new problems opened by your work

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Acknowledgements

• Special thanks to Prof. Nicolaie Moldovan,
  Professor Horacio Espinosa, and Mr. Changhong Ke.
• Extra special thanks to The National Science
  Foundation, whose funding made this work, and the
  above acknowledgements, possible.