Functional Bragg reflectors: patterning a block copolymer

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Functional Bragg reflectors patterning a block
copolymer
Presenter Hilary McWilliams Mentor Michael
Birnkrant Advisor Christopher Li
Dream Program Drexel University, 3141 Chestnut
St., Philadelphia PA, 19104
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Motivation
Problem Lasers present a real danger to pilots.
U.S. Arrests Suspect in Shining of Laser at
Aircraft January 5, 2005, Wednesday DAMIEN
CAVE A man from Parsippany, N.J., was accused
on Tuesday of shining a laser pen into the
cockpits of a small passenger jet and a
helicopter over the last week, Late Edition -
Final , Section B , Page 1 , Column 2
Current research Variable wavelength laser
protection
Impact and Future work Producing heads up
displays with Inherent laser safety for pilots
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Photonic Crystal
Photonic crystals are optical materials with
periodically changing refractive indices. This
periodic change of refractive indices leads to
Photonic band gaps that confine light.
A Bragg reflector is a specific one
Dimensional photonic crystal that has a photonic
band gap in the range of the visible spectrum.
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Benefits and Applications of Photonic Crystals
Benefits

• Small size
• High integration density
• Ability to guide light

Applications

• Optical circuitry

• Telecommunications

• Highly integrated devices
• Microanalyzers

• Optical computers

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Photonic Crystal Fabrication Methods
Photonic crystal prepared by a lithographic
technique
Opal templates assembled by deposition of silica
from solution onto a silicon wafer
Photonic crystal prepared using Holographic
Photopolymerization
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Holographic Polymerization Process
Prepolymer Syrup containing reactive monomers
and block copolymer
Holographic writing of prepolymer syrup.
The standing wave pattern results in local areas
of higher polymerization rates Photopolymerizable
Monomers diffuse to those areas while PE-b-PEO
diffuses to areas vacated by the reactive
monomers.
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Results from Holographic Patterning of
Polyethylene Glycol
SEM shows Semi-continuous layering PEG, the
lighter regions, and Photopolymerized Monomers,
the dark regions.
?
PEG produces semi- continuous layers , Left
VS. liquid crystals patterning results In droplet
formation, Right
Reflected Wavelength ?0
Transmitted Light
Holographically Patterned Liquid Crystals

• Transmission spectra, below
• Sharp notch around 600nm
• Grating calculated 208 nm

The grating d-spacings, ?, 220nm
Christopher Y. Li, Michael J. Birnkrant, Timothy
J. Bunning et. al Soft Matter, 2005, in Press
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Dynamic Behavior Thermal Switching
The results found PEG-based gratings posses a
dynamic behavior with respect to thermal
stimulation. Thermal switching occurs
because PEG melts and Crystallizes

• Upon heating
• Reflected wavelength
• red-shifts
• Upon cooling
• Reflected wavelength
• And original position

Christopher Y. Li, Michael J. Birnkrant, Timothy
J. Bunning et. al Soft Matter, 2005, in Press
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Current Research Block Copolymers
Polyethylene glycol, which is known to form semi
continuous layers, is covalently linked to
polyethylene, which has limited solubility in the
prepolymer syrup to disperse PE evenly in the
Bragg Reflector.

• Tested the compatibility between PE-b-PEG and
  Norland optical resin
• Prepared pre-writing syrup
• Prepared CNT/Norland syrup

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Stepping into the Future

• Look at holographically patterned syrups using
  SEM
• Evaluate changes in the transmission spectrum as
  a function of temperature for PE-b-PEO

• Inclusion of proteins in BR
• Holographic patterning CNTs in BR
• Pattern functionalized CNTs into BR

Carbon nanotubes
Proteins
Functionalized carbon nanotubes