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Electrochromic Nanocrystal Quantum Dots

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Title: Electrochromic Nanocrystal Quantum Dots


1
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
2
Video from Discovery Channel! Fabrication of
QD with Colloidal chemistry method!
3
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

4
Structure vs. Energy
Bulk
Quantum Well
1
Quantum Wire
Quantum Dot
  • Density of states (DoS)

d(E)
Brad Gussin, John Romankiewicz
5
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.
6
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,

7
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

8
Basic observation
5.4nm
7.0nm
  • Size tunable absorption (smaller ?larger distance
    of discrete energies)
  • Electrochromic tunable absorption

9
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

10
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.

11
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

12
Thank you for your attention!
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