Plasmons
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Plasmons are quanta of plasma oscillations that can be excited by light under certain conditions. There are two types of plasmons: bulk plasmons, which depend only on electron density, and surface plasmons, which are collective oscillations of electrons at a surface. Metallic nanoparticles support surface plasmons - when illuminated by light, the electromagnetic field causes electrons within the nanoparticle to oscillate at a resonant plasmonic frequency, generating an enhanced local electric field. Efficient energy transfer can occur between metal nanoparticles and semiconductors if their plasmons are resonantly coupled, allowing light absorption and energy transfer.
Plasmons
- 2. Presentation Layout What are plasmons Plasma Frequency Physical meaning of surface plasmon Bulk plasmon and surface plasmon
- 3. 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
- 4. 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
- 5. 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.
- 6. 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.
- 7. 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.
- 8. 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.