Transcript Electrochromic Nanocrystal Quantum Dots

Electrochromic Nanocrystal
Quantum Dots
Prof. Philippe Guyot-Sionnest’s
group (Univ. of Chigaco) :
1. Electrochromic Nanocrystal
Quantum Dots, Science 2001
2. 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
dN
dE
Bulk
E
Quantum Well
1
Quantum Wire
1/ E
Quantum Dot

Density of states (DoS)
dN
DoS 
dE
δ(E)
Brad Gussin, John Romankiewicz
Fabrication Methods

3 primary methods (to form 3-D confinements)
–
Colloidal chemistry


–
Epitaxy


–
Precipitate QDs from solutions
Size variations by reaction dynamics
Stranski-Krastanov growth (MBE, MOCVD)
Size and shape fluctuations, ordering
Lithography


Victor I. Klimov, Los Alamos Science, 2003
T. Fukui et al. Appl. Phys. Lett. May, 1991
Etch (EBL) pillars in heterostructures
Slow, contamination, low density, defect formation
Colloidal chemistry method is cheapest and fastest!
A. Scherer and H.G. Craighead. Appl. Phys. Lett., 1986.
QD applications



Fluorescent biological markers
Photovoltaic materials (solar cells)
Lasers of very precise, chosen wavelengths
–
–

Quantum computing
–

More efficient, higher material gain, lower threshold
Less thermal dependence, spectral broadening
Represent binary information by charge configuration
Potentially more! “smart bombs”,…
The optical properties change in
response to application of an
electric current.
Fabrication of electrochromic QDs
1.
2.
3.
CdSe Nanocrystal film
(0.5μm)
Teflon(300μm)
Light
6mm
4.
CdSe nanocrystals capped with
trioctylphosphine oxide
CdSe nanocrystals are cleaned and
dried under vacuum, and then
dissolved in 9:1 (V/V) hexane:octane
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
Optics sensor
Counter
Electrode(Pt)
Voltage
Working
Electrode (Pt)
Basic observation
5.4nm


7.0nm
Size tunable absorption (smaller larger distance of discrete energies)
Electrochromic tunable absorption
Infrared
Frequencies (Hz)
0.003 - 4 x 1014
Wavelengths (nm)
1 mm - 750
Quantum energies (eV) 0.0012 - 1.65
Visible Light
4 - 7.5 x 1014
750 - 400
1.65 - 3.1
Ultraviolet
7.5 x 1014 - 3 x 1016
400 - 10
3.1 - 124
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


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.
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
Thank you for your attention!