Electrochromic Nanocrystal Quantum Dots

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Electrochromic NanocrystalQuantum Dots

• Prof. Philippe Guyot-Sionnests group (Univ. of
  Chigaco)
• 1. Electrochromic Nanocrystal Quantum Dots,
  Science 2001
• 2. Electrochromic semiconductor nanocrystal
  films, APL 2002

Yingqi Jiang
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Video from Discovery Channel! Fabrication of
QD with Colloidal chemistry method!
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Quantum dots (QDs) definition

• Quantum dots are nanometre-scale semiconductor
  crystals.
• Nanometer scale each dimensionlt100nm
• Exactly to say, ltone electron Fermi wavelength
• Semiconductor crystal potential excellent
  optical and electronic properties
• Quisi-0 dimension quantum confinement, discrete
  energy levelsartificial atoms

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Structure vs. Energy
Bulk
Quantum Well
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Quantum Wire
Quantum Dot

• Density of states (DoS)

d(E)
Brad Gussin, John Romankiewicz
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Fabrication Methods

• 3 primary methods (to form 3-D confinements)
• Colloidal chemistry
• Precipitate QDs from solutions
• Size variations by reaction dynamics
• Epitaxy
• Stranski-Krastanov growth (MBE, MOCVD)
• Size and shape fluctuations, ordering
• Lithography
• Etch (EBL) pillars in heterostructures
• Slow, contamination, low density, defect formation

Victor I. Klimov, Los Alamos Science, 2003
T. Fukui et al. Appl. Phys. Lett. May, 1991
Colloidal chemistry method is cheapest and
fastest!
A. Scherer and H.G. Craighead. Appl. Phys. Lett.,
1986.
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QD applications

• Fluorescent biological markers
• Photovoltaic materials (solar cells)
• Lasers of very precise, chosen wavelengths
• More efficient, higher material gain, lower
  threshold
• Less thermal dependence, spectral broadening
• Quantum computing
• Represent binary information by charge
  configuration
• Potentially more! smart bombs,

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Fabrication of electrochromic QDs
The optical properties change in response to
application of an electric current.

1. CdSe nanocrystals capped with trioctylphosphine
   oxide
2. CdSe nanocrystals are cleaned and dried under
   vacuum, and then dissolved in 91 (V/V)
   hexaneoctane mixture.
3. A drop of the CdSe nanocrystal solution is placed
   on the surface of the working electrode and
   allowed to dry slowly to form an optically clear
   film
4. Test in a spectroelectrochemical cell

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Basic observation
5.4nm
7.0nm

• Size tunable absorption (smaller ?larger distance
  of discrete energies)
• Electrochromic tunable absorption

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Detailed electrochromic effects
Infra-red
Visible

• Strong infrared (IR) intraband absorption
• Complete bleach of the visible interband
  transition
• Two electrons are injected into 1Se orbital of
  every nanocrystal

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Reversibility

• Charging and discharging of the nanocrystal films
  occur at about the same fast rate
• Detailed investigations of the factors that
  influence the electron injection and ejection
  processes.

• Efficient and reversible electron injection
  simply by adjusting the applied potential.
• Changes in the visible and IR follow each other
  very closely, indicating that they are the
  results of the same electron injection and
  ejection process.

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Summary

• Essential reviews of QDs
• Definition nanoscale semiconductor crystal
• Mechanism 0-D structure
• Fabrications Colloidal chemistry is cheapest and
  fastest
• Applications promising optical and electrical
  applications
• Electrochromic properties of colloidal
  nanocrystals
• Charge tunable by electron injection
• Strong IR absorption 1Se?1Pe
• Complete bleach of visible interband transition
  two electons injection
• Reversibility potentially to help understand the
  process

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Thank you for your attention!