Nanoconfined Chemistry

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Computational Nanophotonics -- S. K. Gray
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Computational Nanophotonics Stephen K.
GrayChemistry DivisionArgonne National
LaboratoryArgonne, IL 60439gray_at_tcg.anl.govTel
630-252-3594
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Motivation

• Wish to control light or electromagnetic energy
  in nano-sized optical devices
• Problem optical light has wavelength gtgt 1nm
• Possible Solution
• - use near-field coupling of light
• with surface plasmons of
• metal nanoparticles
• gt arrays of metal nanoparticles
• become photonic devices
• gt steady or pulsed modes
• of illumination

surface-plasmon resonance in Au nanoparticles
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Excitation Transfer in Nanophotonics
Want Simulations to Guide Experiment

• arrays of metal nanoparticles substrate
  represented by
• spatially varying dielectric constant
• discretized fields E and H on 3D grids
• finite difference solution to Maxwells (curl)
  equations for
• time and spatial dependence of E and H fields

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Finite Difference Time Domain (FDTD) Method

• Maxwells PDEs ,
• outside nanoparticle inside
  nanoparticle
• ?E(x,t)/?t ? x H(x,t)/e(x) ?E(x,t)/?t ?
  x H(x,t) - J(x,t)/e8
• ?H(x,t)/?t -? x E(x,t)/µo ?H(x,t)/?t
  -? x E(x,t)/µo
• ?J(x,t)/?t eowp2 E(x,t)/µo
• 
  
  -nJ(x,t)
• are discretized in space and time in general,
  6 or more components
• are represented on a 3D spatial grid and
  propagated in discrete time
• steps

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FDTD Basics Yee Algorithm based on staggered
space and time grids
Space

• Each E component surrounded by 4 H components
• Each H component surrounded by 4 E components

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E and H Leapfrog in time
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More Explicitly Continuous Equations such as
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Get Replaced by Equations Like
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Current ANL Calculations

• 2D uniform grids (2000 x 2000) over 10000 time
  steps
• Silver nanowire (nanoscale radius infinite
  cylinder) arrays considered
• Variety of array configurations examined

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Example pulse of vertically polarized, 400 nm
light shows 100 nm scale localization when
passing (left to right) through a funnel
configuration of 30 nm diameter silver
nanowiresS. K. Gray and T. Kupka, Phys. Rev. B,
submitted (2003).
600 nm
0
0
600 nm
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Future Work Includes

• 3D Extensions for arbitrary shapes
• The FD algorithm parallelization

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Some Useful References Quinten et al., Optics
Letters 23, 1331 (1998) Maier et al., Advanced
Materials 13, 1501 (2001) Maier et al., Appl.
Phys. Lett. 81, 1714 (2002) Krenn et al.,
Europhys. Lett. 60, 663 (2002) Kottmann and
Martin, Optics Express 12, 655 (2001)