Title: Electrochromic Nanocrystal Quantum Dots
1Electrochromic 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
2Video from Discovery Channel! Fabrication of
QD with Colloidal chemistry method!
3Quantum 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
4Structure vs. Energy
Bulk
Quantum Well
1
Quantum Wire
Quantum Dot
d(E)
Brad Gussin, John Romankiewicz
5Fabrication 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.
6QD 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,
7Fabrication of electrochromic QDs
The optical properties change in response to
application of an electric current.
- CdSe nanocrystals capped with trioctylphosphine
oxide - CdSe nanocrystals are cleaned and dried under
vacuum, and then dissolved in 91 (V/V)
hexaneoctane mixture. - 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 - Test in a spectroelectrochemical cell
8Basic observation
5.4nm
7.0nm
- Size tunable absorption (smaller ?larger distance
of discrete energies) - Electrochromic tunable absorption
9Detailed 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
10Reversibility
- 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.
11Summary
- 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
12Thank you for your attention!