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Electrochromic NanocrystalQuantum Dots
Prof. Philippe Guyot-Sionnest’s group (Univ. of Chigaco) :1. Electrochromic Nanocrystal Quantum Dots, Science 20012. Electrochromic semiconductor nanocrystal films, APL 2002
Yingqi Jiang
Video from Discovery Channel! —Fabrication of QD with Colloidal chemistry method!
Quantum dots (QDs) definition
Quantum dots are nanometre-scale semiconductor crystals.– Nanometer scale: each dimension<100nm
Exactly to say, <one electron Fermi wavelength
– Semiconductor crystal: potential excellent optical and electronic properties
– Quisi-0 dimension: quantum confinement, discrete energy levels——“artificial atoms”
Structure vs. Energy
Brad Gussin, John Romankiewicz
Bulk
Quantum Well
Quantum Wire
Quantum Dot
dNDoS
dE
Density of states (DoS)
dE
dN
E
E1/
1
δ(E)
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
A. Scherer and H.G. Craighead. Appl. Phys. Lett., 1986.
Colloidal chemistry method is cheapest and fastest!
T. Fukui et al. Appl. Phys. Lett. May, 1991
Victor I. Klimov, Los Alamos Science, 2003
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”,…
Fabrication of electrochromic QDs
WorkingElectrode (Pt)
CounterElectrode(Pt) Voltage
Optics sensor
Light
Teflon(300μm)
6mm
CdSe Nanocrystal film (0.5μm)
1. CdSe nanocrystals capped with trioctylphosphine oxide
2. CdSe nanocrystals are cleaned and dried under vacuum, and then dissolved in 9:1 (V/V) hexane:octane 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
The optical properties change in response to application of an electric current.
Basic observation
Size tunable absorption (smaller larger distance of discrete energies) Electrochromic tunable absorption
5.4nm 7.0nm
Detailed electrochromic effects
Infrared Visible Light Ultraviolet Frequencies (Hz) 0.003 - 4 x 1014 4 - 7.5 x 1014 7.5 x 1014 - 3 x 1016 Wavelengths (nm) 1 mm - 750 750 - 400 400 - 10 Quantum energies (eV) 0.0012 - 1.65 1.65 - 3.1 3.1 - 124
Strong infrared (IR) intraband absorption
Complete bleach of the visible interband transition
Two electrons are injected into 1Se orbital of every nanocrystal
Infra-red Visible
Reversibility
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.
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.
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: 1Se1Pe
– Complete bleach of visible interband transition: two electons injection
– Reversibility: potentially to help understand the process
Thank you for your attention!