Functional Bragg reflectors: patterning a

block copolymer

Functional Bragg reflectors: patterning a

block copolymerPresenter: Hilary McWilliams Mentor: Michael Birnkrant

Advisor: Christopher Li

Dream ProgramDrexel University,3141 Chestnut St., Philadelphia PA, 19104

MotivationMotivation

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

Problem:

Lasers present a real dangerto pilots.

Impact and Future work:

Producing heads up displays withInherent laser safety for pilots

Photonic CrystalPhotonic 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 aspecific one Dimensionalphotonic crystal that has a photonic band gap in the range of the visiblespectrum.

Benefits and Applications of Photonic CrystalsBenefits and Applications of Photonic Crystals

• Small size

• High integration density

• Ability to guide light

Benefits

•Highly integrated devices

•Microanalyzers

Applications

•Optical computers

•Optical circuitry•Telecommunications

Photonic Crystal Fabrication MethodsPhotonic Crystal Fabrication Methods

Opal templates assembled by deposition of silica from solution onto a silicon wafer

Photonic crystal prepared by a lithographic technique

Photonic crystal prepared using Holographic Photopolymerization

Holographic Polymerization ProcessHolographic Polymerization Process

Holographic writing of prepolymer syrup.

27% PE-b-PEO 70% Photopolymerizable Monomers

Prepolymer Syrup containing reactive monomers and block copolymer

The standing wave pattern results inlocal areas of higher polymerization rates;

Photopolymerizable Monomers diffuse to those areaswhile PE-b-PEO diffuses to areas vacated by

the reactive monomers.

Incident Laser Beam

}Standing wave pattern

Results from Holographic Patterning of Polyethylene Glycol

Results from Holographic Patterning of Polyethylene Glycol

PEG produces semi-continuous layers , Left

VS.liquid crystals patterning results

In droplet formation, Right

Holographically Patterned Liquid

Crystals

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

Transmitted Light

Reflected Wavelengt

h λ0

Λ

Christopher Y. Li, Michael J. Birnkrant, Timothy J. Bunning et. al Soft Matter, 2005, in

Press

SEM shows Semi-continuous layering PEG, the lighter regions, and Photopolymerized Monomers, the dark regions.

The grating d-spacings, Λ, ~220nm

Dynamic Behavior: Thermal SwitchingDynamic Behavior: Thermal Switching

The results found PEG-based gratings posses a dynamic behavior with respect to thermal stimulation.

Thermal switching occurs becausePEG 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

Current Research: Block CopolymersCurrent Research: Block Copolymers

The Final Product =PhotoPolymerized Monomers =

Λ

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

Stepping into the FutureStepping into the Future

1.Inclusion of proteins in BR2.Holographic patterning CNTs in BR3.Pattern functionalized CNTs into BR

The Final Product =PhotoPolymerized Monomers =

Λ

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

ProteinsCarbon nanotubes

Functionalized carbon nanotubes