University of Ioannina Department of Materials Science & Engineering Computational Materials Science

Elefterios Lidorikis Materials Science & Engineering, University of Ioannina, Greece

Plasmonic Near-Field Enhanced Absorption and Scattering

Crete, 8-11 June 2011

June 8-11, 2011 Crete, Greece

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•  Inside an electric field a nanoparticle gets polarized

•  Surface plasmon resonance

•  Strong scattering •  Strong absorption •  Strongly enhanced near fields

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Outline

•  We will use a point-dipole approximation and consider two applications: –  Enhanced solar cell absorption –  Enhanced Raman scattering

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•  Metallic nanoparticles and/or nanostructures can be used: –  on the surface –  inside the semiconductor –  on the back contact

•  Enhancement due to: –  scattering –  LSPR near-fields

back metal contact

metal nanoparticles

back metal contact

metal nanodisks or nanowires

back metal contact

metal nanodisks or nanowires

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x y

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k,ω E0

2a Au nanoparticle

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x y

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k,ω E0

for a<<λ

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for r<<λ the dominant term is the

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absorption enhancement

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Absorption enhancement •  at a point

•  on a plane

•  within a volume

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–  Multiple scattering → Claussius-Mossotti

–  Absorption in the nanoparticle → reduced field strength

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Planar absorption enhancement

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Volume enhancement of composites

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Schedin et al., ACS Nano 4, 5617 (2010)

virtual energy level

vibrational state ground state

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Theory of SERS in 2d

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Theory of SERS in 2d

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This excites a Raman dipole

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Theory of SERS in 2d

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This excites a Raman dipole

which re-radiates exciting a secondary dipole in the nanoparticle

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Theory of SERS in 2d

φ

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This excites a Raman dipole

which re-radiates exciting a secondary dipole in the nanoparticle

ks,ωs

total particle-induced Raman emission

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Theory of SERS in 2d

Normalize with the signal I0 expected without nanoparticles

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assume square array with side L

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Validation of 2d SERS theory

Ex

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10nm nanoparticles 140nm nanoparticles

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Au Cr SLG

Drude-Lorentz model: 1 free electron & N bound electrons

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monitor the field at graphene

Fourier transform

normalize to field without Au disks

absorption enhancement

emission enhancement

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Raman enhancement absorption enhancement

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Conclusions and acknowledgements

•  Simple description of plasmonic near-field effects based on a discrete dipole –  enhanced absorption in

semiconductors –  SERS in 2d materials

•  insight for designing plasmonic response

Happy Birthday Costa!

Computing time provided by RCSS Ioannina

Semiconductor absorption •  University of Patras

–  M.M Sigalas

•  N.C.S.R “Demokritos” –  N. Lagos

SERS in graphene •  Cambridge University

–  A.C. Ferrari –  A. Lombardo

•  University of Manchester –  K.S. Novoselov –  A.K. Geim –  A.N. Grigorenko –  F. Schedin –  V.G. Kravets

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•  Include polarization terms in Maxwell’s equations

reflection transmission

absorption effective medium

band structure