Photonic Crystal Sensors

Silicone Method

What are photonic crystals?

Repeating nanostructures that allow only certain wavelengths to go through the crystal Photons photonics as electrons electronics Band gaps in photonics and electronics

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Optical Properties of Photonic Crystals

Transmission and reflection spectrum Use of spectrometer

Applications

What can be sensed with photonic crystals?

Environmental Changes Temperature Ph Silicone Ultrasound

Bragg’s equation: the wavelength of the center of the stop band can be calculated since the band is a diffraction based phenomenon

How do Photonic crystals work?

Bragg’s equation in action

Changing angle at which the crystal is seen changes the color

Self Assembly Silicone Method: Materials -Polystyrene Beads (aqueous dispersions

0.2um and 0.35um 2.6%)-Substrate: glass slides -Plasma cleaner-Silicone fluids: DMS-T11 DMS-T00-Hot plate -PDMS+DMS(T11) +curing agent (ratio of

5:5:1)

Materials

Silicone Method Procedure:1. Put glass slides (substrate) in plasma cleaner for

about 5 minutes2. Place aqueous dispersions of PB beads on

substrate 3. Cover this liquid film with silicone liquid4. Place sample on hot plate and let water evaporate

for certain amount of time, depending on vitality of silicone.

5. Remove liquid silicone with Kim-Wipe6. Combine PDMS, DMS, and curing agent in a 5:5:1

ratio7. Let PDMS elsatometer to be cured and hardened.

Silicone Method How does it work?

- Water slowly evaporates by diffusing through the skin of silicone -Embedding crystal in an elastomer matrix made of PDMS.-PDMS fills the voids, expanding or contracting depending on the environmental change.

Characterizing the crystal through spectrometry

Graphs obtained: transmittance and reflectance

Problems encountered in experiments

Evaporation rings created by contact line.

Polystyrene spheres do not form an uniform structure. (cracks)

‘White crystals’

Detecting ultrasound

Transducer sends pulse that will contract or expand the PDMS in the crystal, which will change the wavelength. As this happens the reflection intensity decreases in compression and increases in expansion creates an attenuating signal of the laser reading as a function of time.