In Mie Theory, when the size of the particle is much smaller than the wavelength of the incident light, the nanoparticle experiences a field that is spatially constant, but with a time dependent phase, which is known as the quasi-static limit. Why?
Because the wavelength of the incident of the much larger then the particle.
What this means is that if you think of the incident electric field as oscillating in the UP and DOWN directions and the wavelength of the light is lets say 800 nm then half of the period (or in half of the wavelength region 400 nm) it is pointing in one direction and if the nanoparticle is small (lets say 15 nm) then the whole particle feels the electric field pointing in one direction (Up for example). The whole nanoparticle volume is situated in a electric field that is similar in strength and pointing in one direction.
If the particle is bigger lets say 500 nm then part of the particle (for half of the wavelength 400nm) is in the spacial region where the electric field is pointing to the UP direction and it also has different electric field strengths (from zero to amplitude max) and a part of the nanoparticle is experiencing the electric field poinding in the DOWN direction.So the particle does not feel a homogeneous electric field over its whole volume.
This is also the reason why small particles have only one (dipolar mode) peak in the plasmonic extinction spectra and bigger particles have two or more peaks (dipolar mode, quadrupole mode..) in their spectra.
One very good source for understanding the optical properties of metal nanoparticles is the book from by Uwe Kreibig and Michael Vollmer. Optical Properties of Metal Clusters (Springer Series in Materials Science) 1995.
http://www.amazon.com/Optical-Properties-Clusters-Springer-Materials/dp/3540578366
I hope i helped.
Because the wavelength of the incident of the much larger then the particle.
What this means is that if you think of the incident electric field as oscillating in the UP and DOWN directions and the wavelength of the light is lets say 800 nm then half of the period (or in half of the wavelength region 400 nm) it is pointing in one direction and if the nanoparticle is small (lets say 15 nm) then the whole particle feels the electric field pointing in one direction (Up for example). The whole nanoparticle volume is situated in a electric field that is similar in strength and pointing in one direction.
If the particle is bigger lets say 500 nm then part of the particle (for half of the wavelength 400nm) is in the spacial region where the electric field is pointing to the UP direction and it also has different electric field strengths (from zero to amplitude max) and a part of the nanoparticle is experiencing the electric field poinding in the DOWN direction.So the particle does not feel a homogeneous electric field over its whole volume.
This is also the reason why small particles have only one (dipolar mode) peak in the plasmonic extinction spectra and bigger particles have two or more peaks (dipolar mode, quadrupole mode..) in their spectra.
One very good source for understanding the optical properties of metal nanoparticles is the book from by Uwe Kreibig and Michael Vollmer. Optical Properties of Metal Clusters (Springer Series in Materials Science) 1995.
http://www.amazon.com/Optical-Properties-Clusters-Springer-Materials/dp/3540578366
I hope i helped.
Dear Siim Pikker,
in Rayleigh regime ,the wavelength of the incident light higher than particle size and in Mie regime ,the wavelength of the incident light is comparable with particle size . but for metal nanoparticles that is assumed the wavelength of the incident light higher than particle size , why do we use from Mir theory?
Quick answer. Because it works ;) . But yes it gets complicated very fast and for very small metal nanoparticles. There is ton of articles/books which describe it more exactly than i ever could write here. Maybe this open article written by smarter guys than i am will help with your everlasting quest for wisdom and knowledge:
Light scattering and surface plasmons on small spherical particles
Xiaofeng Fan1, Weitao Zheng1 and David J Singh1,2
http://www.nature.com/lsa/journal/v3/n6/pdf/lsa201460a.pdf
- Badges
- Science topic
- Similar topics
- Chemistry
- Nanotechnology
- Nanostructured Materials
- Nanoparticles