Surface Plasmons

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Surface Plasmons

• What They Are, and Their Potential Application in
  Solar Cells

Martin Kirkengen, AMCS, UiO Collaboration with
Joakim Bergli, Yuri Galperin, Alexander
Ulyashin Definitely work in progress...
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What is a Plasmon

• Surface plasmons surface plasmon polaritons
• Fluctuation in density of electrons
• Solution to Maxwell equations at metal/dielectric
  interface
• Exponentially decaying in z-direction

z
?1
x
_ _ _
_ _ _
?2


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Dispersion Relation
(H. Räther, Surface Plasmons, Springer 1988)

• Faster phase velocity than in air
• Coupling light -gt plasmon only possible in
  special geometries
• Grating (discreet, periodic sampling)
• Roughness
• Spheres

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Plasmons on a Sphere

• Lowest mode dipole
• Higher modes

n1
-
Quadrupole
etc.


-
n3
n2
n6
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Resonance Condition
BohrenHuffman, Absorption Scattering of Light
by Small Particles (Wiley 1983)

• General for all modesmn2/n1
• Lowest (dipole) moden11, n1
• What negative e?

n2
n1
n22 m2 -2, e -2
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Dielectric Constant of Metals

• 0 at plasmon frequency
• Negative dielectric constantgt imaginary index
  of refraction gt reflection
• High frequencies gt transparent

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Oldest Known Applications

• Colloidal gold in glasses

Lycurgus Cup (400 AD)
Red color due to gold (1400 AD)
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Main Plasmon Applications Today
Forschungszentrum Jülich

• Measuring dielectric constant of solutions
• Guided plasmons -gt plasmonics

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What about the Solar Cells?

• Proposed architecture (UNSW)
• Increased spread of incident light can replace
  texturing
• Possibly direct transitions from high-k Fourier
  components of the dipole field

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Challenges in Solar Cells

• Avoid reflection
• Shift resonance to visible region
• Cheap method of fabrication

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Emission From Dipole Near Surface
-
Mertz, J. 2002. Radiative abs.etc. J. Opt. Soc.
Am. B. 1719061913.

• Reciprocity principle frustrated total
  reflectiongtemission intoimpossible
  angles,guided modes
• Emission to front (reflection) reduced.

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Shifting the Resonance

• SizeLarger particles, higher modes contribute,
  each mode red-shifted
• ShapeElliptic shape, flatter particles have
  red-shifted resonance (and stronger coupling to
  guided modes?)
• Coating/substrateResonance is given as a
  relative refraction index, changing surroundings
  changes resonance
• Arrays/clustersLoads of opportunities

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How to Make?

• Requirements Shape, size position control
  price
• Our hopeDeposit oxide hydrogenationgt
  hydrogen removes oxygen from structure,remaining
  metal forms nanoparticles.
• PLEASE HELP! ?

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Thank you for your attention!