1. www.tyndall.ie
New Photonic Band Gap Materials via the
Synthesis and Assembly of Dielectric-
Metal-Dielectric Particles
Bartosz Iżowski
Advanced Materials & Surfaces Group
Warsaw University of Technology
Poland
2. www.tyndall.ie
“ If only were possible to make materials in which
electromagnetically waves cannot propagate at certain
frequencies, all kinds of almost-magical things would
happen”
Sir John Maddox, Nature (1990)
4. www.tyndall.ie
Introduction
Photonic Crystals – semiconductors of light
Semiconductors
Atomic length scales
Natural structures
Control electron flow
Photonic Crystals
Length scale ~ λ
Artificial structures
Control e.m. wave propagation
Photonic Crystals periodic dielectric structures
• interact resonantly with radiation with wavelengths comparable to the periodicity
length of the dielectric lattice
• dispersion relation strongly depends on frequency and propagation direction
Periodic array
of atoms
Periodic variation of
dielectric constant
9. www.tyndall.ie
Synthesis
• Silica colloids were prepared using the Stöber synthesis
Si(OC2H5)4 + 4 H2O Si(OH)4 + 4 C2H5OH
Si(OH)4 → SiO2↓ + 2 H2O
In ethanol, in presence of NH3
• These colloids are charged, stabilised in water and
in alcohols by electrostatic interactions
•Zeta potential = - 55.3 mV
EtOH
NH4OH
23. www.tyndall.ie
Reflectance spectra of silica@silver opal measured at incident
angles from 10 to 60 degrees to the normal
Optical properties
Bragg-Snell’s Law
λmax = 2d111 (neff – sin2
θ)1/2
24. www.tyndall.ie
Conclusions
• Prepared monodispersed silica nanoparticles
• Prepared silver decorated silica nanoparticles
• Attempted silica@silver@silica CSS particles
• Characterized different steps of the CSS particle formation by ZP
measurements, UV-vis absorption spectroscopy and TEM analysis
• Photonic crystals of these materials are prepared and photonic band gap
properties are compared.
• Photonic band gap of silica@silver particles show a red shift from that of
bare opal.
