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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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13

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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!