Plasmons

Presented By:

Anuradha Verma

Presentation Layout

What are plasmons

Plasma Frequency

Physical meaning of surface plasmon

Bulk plasmon and surface plasmon

What are Plasmons

Plasmons are a unit of collective oscillations of electrons Or

Quantum of plasma oscillation Photons-

electromagnetic vibrations

Light is a wave that is oscillating electro-magnetic field, plasmons can be excited by light under specific conditions. (And conversely, in some cases light can be emitted by plasmons as well.)

Phonons-

mechanical vibrations

Bulk Plasmon and Surface Plasmon

• Collective oscillation of conducting electrons

• Bulk plasmon energy depends only on electron density n

Bulk Plasmon

• Wave nature: Charge density waves at surface.

Surface Plasmon

ωp= bulk plasmonfrequency

ωp(s)= surface plasmonfrequency

Physical Meaning of Surface Plasmons

Nanoparticles- Lattice of ionic cores with conduction electron moving almost freely

inside the NP.

Particle illumination: EMF of the light exerts

a force on these conduction electrons

moving them towards the NP surface.

Electrons are confined inside NP, negative charge and positive

charge accumulate on opposite side, creating

an electric dipole

Dipole generates an electric field inside the NP opposite to that of the light that will

force the electrons to return to the equilibrium

position.

electrons are displaced from the equilibrium position and the field is removed later, they will oscillate with a certain frequency that is

called the resonant frequency called plasmonic frequency.

Metallic nanoparticles (NPs)-

Electrons are confined in 3D.

Electron oscillations induce an electric field

around the NP that can be much larger than

the incident light one.

Photoanode (Au-ZnO photoelectrode) capture solar light, simultaneously generates photoelectrons that migrates to the CB of ZnO.

Simultaneously, the Au nanostructure absorbs plasmon-induced irradiation, generating hot electrons and an electromagnetic field.

The plasmon-induced hot electrons were injected into CB of ZnO and they were driven to the photocathode, where they reacted with protons to form H2 .

Now excited Au nanoparticles can generate holes to accept electrons from electrolyte (water) and form O2

Plasmon-induced electromagnetic field creates additional vacancies at the bottom of the conduction band, facilitating the generation of photoelectrons by

photoexcitation.

Efficient energy transfer can occur between metal and

semiconductor if resonant coupling is present between the

plasmonic metal nanoparticles and semiconductor.

In case of low overall light absorption:

Plasmonic metal nanoparticles can be used to capture the light.

When the photons are not absorbed in the desired location,

metal nanoparticles can be used to absorb photons and then

transfer the energy to an adjacent semiconductor.

Metal nanoparticle be energetically coupled to the semiconductor

to transfer its excitation energy and produce an electron-hole pair

in the semiconductor.