MODELING OPTICAL PROPERTIES OF PLASMONIC NANOPARTICLES USING FINITE DIFFERENCE TIME DOMAIN1 Mary Fleck, 2 Holden T. Smith, 2 Louis H. Haber, 1,2 Kenneth Lopata1Center for Computation & Technology, LSU – Baton Rouge, LA2Department of Chemistry, LSU – Baton Rouge, LA
LIGHT & MATTER
The way that light interacts with metal nanostructures• Light: electromagnetic radiation• Metals: good conductors, lots of electrons
that are free to move• Electrons: Motion is affected by other
electromagnetic fields• When light meets electrons in metal
nanoparticles, electron density rapidly oscillates
Plasma oscillations, plasmonic nanoparticles
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PLASMONIC NANOPARTICLES
Localized surface plasmon resonances characterized by the coherent oscillations of free electrons of the metal.
Plasmonic nanoparticle are of great interest for applications such as:• Molecular Sensing• Catalysis• Solar Cells• Photothermal Cancer Therapy
3Cobley, C.; Chen, J.; Cho, E. C.; Wang, L. V.; Xia, Y.; Chem. Soc. Rev. 2011, 40, 44.Plech, A.; Kotaidis, V.; Lorenc M.; Boneberg J.; Nature Physics 2006, 2, 44.
|E(w)|2
-----------|E0(w)|2
Field enhancement =
OVERVIEW
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Core-shell nanoparticles composed of silver and gold• Gold and silver nanoparticle surfaces are very
attractive for biological applications• Nanoparticles with CSS structure have more
flexible optical properties• Create significant plasmonic enhancements
when exposed to a variety of wavelengths of light
I sought to:• Use FDTD to model extinction and compare with experimental data• Identify plasmon modes involved • Use FDTD code to compute field enhancements• Optimize enhancement by tuning optical properties• Use data from experiments to generate electrodynamic simulationsG
OALS
This material is based upon experiments conducted by
collaborators of the Louis H. Haber group at the Louisiana State
University Department of Chemistry.
CLASSICAL TREATMENT
• Large size of Nanoparticles allows for a classical treatment
• Computationally cheaper
• Finite Difference Time Domain (FDTD)• Approximates the Electromagnetic Field
in both time and space.
Maxwell’s Equations
𝜕𝐻(𝑟, 𝑡)
𝜕𝑡= −
1
𝜇𝛻 × 𝐸
𝜕𝐸(𝑟, 𝑡)
𝜕𝑡=1
𝜀𝛻 × 𝐻 −
1
𝜀
𝜕𝐽(𝑟, 𝑡)
𝜕𝑡
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CORE-SHELL-SHELL NANOPARTICLES
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• Concentric metallic gold and silver shells encapsulating a metallic gold core
Karam et. al, J. Phys. Chem. C (2015), 119 (32), 18573-18580
• Gold nanoparticle surfaces are very attractive for biological applications due to their ability for size-controlled synthesis, stabilization, functionalization, and bio-compatibility.
• Gold-silver-gold core-shell-shell nanoparticles can be easily thiolated and functionalized for potential biochemical applications.
GOLD SEEDS AND GOLD-SILVER CORE-SHELL NANOPARTICLES
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12nm gold nanoparticle
Au-Ag Core-Shell nanoparticle with 12nm Au Core and 12nm Ag Shell Karam et. al, J. Phys. Chem. C (2015), 119 (32), 18573-18580
12 nm Au nanoparticles
CORE-SHELL-SHELL: VARYING WIDTH OF SHELLS
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Core-shell-shell nanoparticles with 12 nm gold cores, 12 nm silver shells, and gold shells of 15 nm (top left), 20 nm (top right), and 30 nm (bottom right)
20 nm
Karam et. al, J. Phys. Chem. C (2015), 119 (32), 18573-18580
PHOTOTHERMAL CANCER THERAPY
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Temperature change after irradiation with a 1.7 W defocused
laser pulse centered at 800 nm.
Core-shell-shell nanoparticles
have 12 nm gold cores, 13 nm
silver shells, and 30 nm gold shells
Karam et. al, J. Phys. Chem. C (2015), 119 (32), 18573-18580
MY CONTRIBUTIONUse FDTD to model extinction and compare with experimental data Identify plasmon modes involved Use FDTD code to compute field enhancements• Optimize enhancement by tuning optical properties• Use data from experiments to generate electrodynamic simulations
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Timeline
Silver Nanoparticle Plasmonics
Silver-GoldCore-Shell Analysis
Silver-GoldCore-Shell Plasmonics
Analysis and Reflection
SILVER NANOPARTICLES
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Extinction and field enhancement
well-known
Ag
SILVER-GOLD CORE-SHELL NANOPARTICLES
• Not so simple:• Need for convergence on all parameters according to Mie theory• Need for analysis of size distribution
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FUTURE WORK
Extension of core-shell work to Ag-Au-Ag core-shell-shell• Extinction• Field Enhancement
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This material is based upon work supported by the National Science Foundation under award OCI-1560410 with additional support from the Center for Computation & Technology at Louisiana State University.
Acknowledgements
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• Prof. Kenneth Lopata• Holden T. Smith• Prof. Louis Haber
QUESTIONS?Thanks for listening!