Particle-based display technologies - nanoparticles.orgnanoparticles.org/pdf/22-Morrison.pdf ·...
Transcript of Particle-based display technologies - nanoparticles.orgnanoparticles.org/pdf/22-Morrison.pdf ·...
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Particle-based display technologies
Ian MorrisonCabot Corporation
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Particle based displays• Reflective not emissive• “Adjusts” with ambient light• Thin, flexible, low power?• The electronics is a real challenge.
• Require high resistivity so particles move, not ions therefore – nonaqueous dispersions
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
To create a display – start with a print
and invent ways to make it change:
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
The Gyricon DisplayCharged,bichromalballs.
Suspendedin an oil.
Encased ina plasticsheet.
Addressedwith electrodes. That Xerox
built.
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
GyriconGyricon ball dynamics*ball dynamics*
X
Y
Zθψ
E
Switching Electrode
Ground Electrode
q+
q− d
Fluid Filled Cavity
Bichromal Ball
Critical-damped Over-damped
Un-damped Under-damped
(*Rick Lean, MIT)
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Suspended particle displays*
*Invented by E.H. Land in 1934
Particles. Suspendedin an oil.
Addressedwith electrodes,AC or DC.
Transparent
Transparent,or reflective.
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Electrophoretic displaysChargedpigmentparticles. Suspended
in a dyed oil.
Addressedwith electrodes.
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Problems with particle displays
Electrohydrodynamics:Sedimentation:
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
A solution - encapsulation
• “Solves”– Particle setting– Electrohydrodynamic effects
• “Creates”– Self-spacing electrodes– “Coatable” displays
Dark StateLight State
NOTE: These capsules are ~ 100 microns in diameter.
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Shutter modeChargedpigmentparticles. Suspended
in clear oil.
Addressedwith electrodes.
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Switching speed? – use two different pigments
• Switching time goes as square of thickness:
• The necessary thickness is determined by the optical density.
• Dye solutions have much lower optical density than pigments.
• Therefore dual pigments enables thinner.
2
transitdV
τμ
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Dual particle displays
Sony’s LIBRie EBR-1000EP from E Ink and Phillips Electronics
Negativelychargedpigmentparticles.
Positivelychargedpigmentparticles.
Suspendedin a clear oil.
Addressedwith electrodes.
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Dual particle displays
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
-
+
+ -
-+
Dispersions of oppositely charged particles
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
How to image with flocculated particles
1 2 1 2
total vdw elecseparation Force Force ForceField
q q q q+
= =− −
Practical considerations set an upper limit of about 0.5 V/μm.
The field necessary to separate charged particles is:
A steric barrier is necessary to limit the maximum attractive force.
n.b. The force varies with the product of particle charges, but the field also varies with the difference.
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Steric barrier necessary for typical pigments in oil
For particle radii of 150 nm, zeta potentials of +52 mV and –52 mV (corresponding to 12 charges per particle!), the background conductivity of 50pS/cm, and a Hamaker constant of 4.05x10-20 J.
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Control of interparticle spacing
•Electrostatic and dispersion forces are short range compared to the applied electric field.
•Therefore we produce particles that only move above a limiting electric field – an electric yield point.
•Manipulating the steric barriers and uneven surface charges controls the “yield” point.
•This enables simple threshold addressing – “line-by-line”.
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
From the physics of colloids:
•“Inverse” electrorheological fluids
•Field dependence of zeta potential
•AC electric fields – time dependencies
•Particle-particle or particle-wall adhesion
•Structures in fluid (particles or wide variety of polymer gels)
Threshold addressing by other means
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
What about color?
Color filter arrays
Simple, but 2/3rds loss in brightness.
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Photoelectrophoretic displays
• Photosensitive pigments• Light + electric field produces
change in charge• Particles migrate in the field – in or
out of view• Also a passive addressing scheme
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Color via plasmon resonance
Silver nanoparticles
http://physics.ucsd.edu/~drs/plasmon_research_home.htm#what
The magnitude, peak wavelength, and spectral bandwidth of theplasmon resonance associated with a nanoparticle are dependent on the particle’s size, shape, and material composition, as well as the local environment.
http://www.ece.rice.edu/~halas/
Au and thin gold layers on silica.
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Plasmon resonance – color depends on interparticle distance
E
E
E=0
Three color states when viewed from the top, depending on the electric field.
Blue Red Black
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Control of spacing with tethers
E E=0
Polymer tethers keep particles within 10’s of nanometers –switching times are very short.
On Off
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Quantum effects
Moungi Bawendihttp://web.mit.edu/chemistry/nanocluster/
Colloidal CdSe quantum dots dispersed in hexane. Quantum confinement effects allow quantum-dot color to be tuned with particle size. (Fluorescence shown.)
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Q-dot optics also depend on interparticle distance
•Large Q-dots quench smaller Q-dots
•Q-dots can be coated with a dielectric and charged
•Q-dots could be tethered to each other or to an electrode.
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
CdSeCdSe
Discoloration Coloration
Electron injection into quantum dots
http://dcwww.epfl.ch/lpi/electr.html
n.b. One electron per particle makes these 103 to 104 more sensitive than molecular electrochromics.
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Electrode Q Dot Layer
Dielectric layerITO on PE
Quantum dot electrochromic display
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June 10, 2004 ACS Summer School on Nanoparticle Materials
Particle-based display technologies
Cabot – We make fine particles by the ton.
www.cabot-corp.com