A brief analysis on a paper published on Optical Properties of Nanoparticles studied using Mie Theory.

1. Optical Properties of Nanoparticles
(Studied using Mie Theory)
by Achal Bhardwaj

2. Abstract
In this work, the optical properties of nanoparticles was studied using Mie theory.
This famous theory is suited to compute accurately the optical cross sections of a
spherical particle. According to this theory, we can calculate the place of surface
plasmon resonance in optical spectra of spherical nanoparticle. Matlab was used for
simulation of some optical properties like scattering, absorbtion and extinction
cross section area and of nanoparticles. Results show that front surface located
nanoparticles Ag and Au are the most widely used materials due to their surface
plasmon resonances located in the visible range and therefore interact more
strongly with the peak solar intensity.

3. About Authors
Hossein Ghaforyan
Department of Physics, Payame
Noor University,
Sara Mohammadi Bilankohi
Department of Physics, Payame
Noor University,
Majid Ebrahimzadeh
Department of Physics, Payame
Noor University,

4. Introduction
The optical properties of nanoparticles are highly dependent on
the particle size, shape, chemical composition, and the local
dielectric environment.
it is possible to selectively tune these properties to suit a given
application
Many studies have explored the optical properties of metal
nanoparticles using simulations, that are useful in applications
including solar cell, imaging, sensing and constructing
nanostructures.
Metal nanoparticles are widely used to construct structures that
possess unique electronic, photonic and catalytic properties such
as local surface plasmon resonance (SPR).
Surface plasmon resonance of metallic nanoparticles is one of the
reasons of their unique optical properties.

5. Surface Plasmon Resonance (SPR)
What is SPR?
It is the resonant oscillation of conduction
electrons at the interface between a negative
and positive permittivity material simulated by
incident light.
The resonance condition is established when
the frequency of incident photons matches the
natural frequency of surface electrons
oscillating against the restoring force of
positive nuclei.
Why it is important??
Investigating the relationship between the sizes
of nanoparticle with surface plasmon frequency
in simple shapes such as spherical shape of
nanoparticles is possible using the Mie theory.
According to this theory, we can calculate the
place of surface plasmon resonance in optical
spectra of metallic spherical nanoparticle.

6. Mie Theory
According to this theory, we can calculate the
place of surface plasmon resonance in optical
spectra of metallic spherical nanoparticle.
Matlab program was used for simulation of
some optical properties such as scattering and
extinction cross section area and influence of
embedded metal nanoparticles on FeS2 (Pyrite)
solar cells.

7. Methodology of Study
The Mie scattering theory allows describing the scattering of a plane monochromatic wave by a
homogeneous sphere surrounded by a homogeneous medium for any particle radius and of any material.
Mie scattering theory does not deal with the problem of surface electron density oscillations (surface
plasmons) coupled to surface localized electromagnetic fields, although usually positions of successive peaks
appearing in light scattering spectra of conducting particles obtained with Mie theory, are interpreted as
directly related to positions of surface plasmon resonances.
Once the Mie coefficients are determined, we can calculate the extinction, absorption and scattering cross
sections or the electromagnetic fields inside and outside of the spherical particle.
Mie theory codes were used to simulate the optical properties of spheres nanoparticles.When the dimensions
of the particles are smaller than the light wavelength it is possible to employ the so-called quasistatic
approximation.

8. Mie theory codes were used to simulate the optical properties of spheres nanoparticles.When the dimensions
of the particles are smaller than the light wavelength it is possible to employ the so-called quasistatic
approximation.
Otherwise if the investigated structures have spatial dimensions say 50 nm, we can connect the macroscopic
dielectric function with the microscopic polarizability (alpha).
The elastic scattering of light can then be described in terms of Rayleigh scattering. Expressing the dipole
moment P through the local microscopic electric field on one hand, and connecting it with the dielectric
function (through D = εE = E+4πP) on the other hand, leads to the Clausius-Mossotti relation for
spherical particles.

9. Observations
Below are the Simulated optical extinction (black lines), scattering (red lines) and
absorption (green lines) efficiencies of 10 nm and 100 nm diameter Ag spheres.

10. Below are the Simulated optical extinction (black lines), scattering (red lines) and
absorption (green lines) efficiencies of 10 nm and 100 nm diameter Au spheres.

13. Influence of metal nanoparticle embedded on FeS 2 (Pyrite)
Solar Cells
Pyrite, formally known as Iron disulfide, is the most
abundant naturally occurring of the sulfide minerals.
It has a crystal structure that resembles the fluorite
structure. Iron disulfide has a yellow-brass, metallic
luster that is sometimes incorrectly recognized as
gold.
Due to this mistaken identity it is often referred to as
“fool’s gold”.As the result of sparks generated when
struck against metal, pyrite was used as a source of
ignition for early firearms.
We considered the metal nanoparticles are on FeS 2
surface.

14. Below figure shows the calculated extinction spectrum of a 60 nm diameter Ag and Au nanosphere
embedded in FeS 2 .

15. Conclusion
For solar cell applications, we need high
scattering and low absorption across the solar
spectrum. Scattering in the near-infrared
(NIR) is particularly desirable in solar cell,
because this property lead to produce current
at night too. As a result Ag and Au are more
preferred for solar applications.

16. Thank You