PLASMONICS AND APPLICATIONS RENJITH MATHEW ROY

CLASSICAL FOUNDATION In a conducting metal each atoms give electrons and are shared among atoms, and free to move around the positive ions Call it electron sea(sea electron model) or free electron gas 2

PLASMONS Electron gas is like plasma and as we say photon as quantum of electromagnetic field, plasmon is a quantum of plasma oscillation. A plasmon is a quasi particle and is described by a collection of particle(here electrons) which occur on the surface of a metal and consists of collective oscillations of free electron gas. A plasmon is a density wave in an electron gas. It is analogous to a sound wave, which is a density wave in a gas consisting of molecule. the oscillations happens when light wave(EM wave) hit on metal surfaces 3 particles/

PLASMON NANO PARTICLES Plasmons are on surface If I confine the size of surface into nano particles –plasmons cover the whole surface. When light interact, magic happens The size changes the possible wavelength the plasmons can have they cannot have all wavelengths as in the bulk metal. Depends on size 4

5 PLASMON RESONANCE Right at the plasmon frequency  p the electron gas has a resonance, it oscillates violently. This resonance frequency increases with the electron density n. (Drude model) If wavelength of light hitting nanoparticles are greater than the size of particle, electron cloud is excited by the external electric field and causes distortion in electron cloud. If the light is at resonance absorbance happens(why metals are opaque)

Oscillation of electrons when a wave is present. Surface plasmons (SPs) are coherent delocalised electrons oscillations that exist at the a metal-dielectric interface, such as a metal sheet in air. The charge motion in a surface plasmon always creates electromagnetic fields outside (as well as inside) the metal 6 SURFACE PLASMONS Electromagnetic mode Electron oscillation Surface waves

APPLICATIONS OF PLASMONS 7 1.Biomedical sensing 2.Super resolved imaginary 3.Energy harvesting 4.Next generation optical circuits 5.Surface enhanced Raman spectroscopy 6.Plasmonic laser-property of confining light 7.Superlenses

8 1.SURFACE ENHANCED RAMAN SPECTRSCOPY RAMAN SPECTROSCOPY Raman spectroscopy is a spectroscopic technique based on inelastic scattering of monochromatic light. Photons are absorbed by the sample and then reemitted. Frequency shift provides information about vibrational, rotational and other transitions in molecules. LIMAITATIONS 1.Week signals. 2.Donot work well for low concentration or low quantity of samples

Raman scattered intensity coming from the molecule in the vicinity of the nano structured metallic surface excited by visible light can be enhanced. Even a single molecule can be detected Molecule get adsorbed on rough metal surface. Excitation of localised surface plasmons 9 NANOSTRUCTURED PLASMONS Nano particles Creates a localised field Which polarises molecule and strong Raman scattering will happen

2.BIOSENSING USING SURFACE PLASMON RESONANCE 10 CREATING SURFACE WAVE A prism with a designed refractive index and Particular angle of incidence to get total internal reflection. Wave coming in,excites evanescent field(confined energy).Spatial frequency excites surface plasmons. Reflection spectrum 1.When total internal reflection happens 2.Drop in reflection –due to the creation of surface wave,plasmons absorb energy at resonance frequency hence reflection intensity decreases.

11 BIOSENSING USING SPR CONTINUED… If I pass my analyte on to the surface of gold sensor which has acceptors on which analyte sticks to. Surface wave generated on boundary are very sensitive to any change in the boundary (like adsorption of biomolecule on the surface of metal) Causes a change in refractive index of the medium directly in contact to metal surface(gold) (Acceptors for molecule to get attached)

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