1. 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...

2. 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 +++ _ _ _ +++ _ _ _ x z 11 22

3. Dispersion Relation Faster phase velocity than in air Coupling light -> plasmon only possible in special geometries Grating (discreet, periodic sampling) Roughness Spheres (H. Räther, Surface Plasmons, Springer 1988)

4. Plasmons on a Sphere Lowest mode: dipole Higher modes Quadrupole - + - + etc. n=1 n=3n=2 n=6

5. Resonance Condition General for all modes: m=n 2 /n 1 Lowest (dipole) mode: n 1 =1, n=1 What – negative  n 2 2 = m 2 = - 2,  = -2 n2n2 n1n1 Bohren&Huffman, Absorption &Scattering of Light by Small Particles (Wiley 1983)

6. Dielectric Constant of Metals 0 at plasmon frequency Negative dielectric constant => imaginary index of refraction => reflection High frequencies => transparent Ag Free Electrons (Drude model) Bound electrons (Lorentz model)

7. Oldest Known Applications Colloidal gold in glasses: Lycurgus Cup (400 AD)Red color due to gold (1400 AD)

8. Main Plasmon Applications Today Measuring dielectric constant of solutions Guided plasmons -> plasmonics Forschungszentrum Jülich

9. 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

10. Challenges in Solar Cells Avoid reflection Shift resonance to visible region Cheap method of fabrication

11. Emission From Dipole Near Surface Reciprocity principle + frustrated total reflection =>emission into ”impossible angles”, guided modes Emission to front (reflection) reduced. -+-+ Mertz, J. 2002. Radiative abs.etc. J. Opt. Soc. Am. B. 17:1906–1913.

12. Shifting the Resonance Size Larger particles, higher modes contribute, each mode red-shifted Shape Elliptic shape, flatter particles have red-shifted resonance (and stronger coupling to guided modes?) Coating/substrate Resonance is given as a relative refraction index, changing surroundings changes resonance Arrays/clusters Loads of opportunities

13. How to Make? Requirements: Shape, size & position control + price Our hope: Deposit oxide + hydrogenation => hydrogen removes oxygen from structure, remaining metal forms nanoparticles. PLEASE HELP!

14. Thank you for your attention! - +