Jordan University Of Science and Technology. Faculty of science . Faculty of science Department of physics Seminar title Raman scattering Presented by : Sakher Abed Al Razaq Hayajneh Superviser name : Dr. Fedda Alzoube 1 st semester 2007/ 2008. . TABLE OF CONTENTS :.
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Faculty of science
Faculty of science
Department of physics
Presented by :
Sakher Abed Al Razaq Hayajneh
Superviser name :
Dr. Fedda Alzoube
. Types scattering of photon
. Raman scattering explanation
. Application for Raman scattering
. Key feature of SERS
. Mechanism of SERS
. Application for SERS
The scattering of light may be thought of as the redirection of light that takes place when an Electromagnetic (EM) wave (i.e. an incident light ray) encounters an obstacle or nonhomogeneity, In our case, the scattering material (solid, liquid or gas).
As the EM wave interacts with the matter, the electron orbits within the constituent molecules are perturbed periodically with the same frequency (no) as the electric field of the incident wave.
The oscillating induced dipole moment is manifest as a source of EM radiation,
thereby resulting in scattered light.
The majority of light scattered is emitted
at the identical frequency (no) of the incident light, a process referred to as elastic scattering.
Raman scattering is one such example of inelastic scattering.
In summary, the above comments describe the process of light scattering as
a complex interaction between the incident EM wave and the material’s molecular/atomic structure, which is useful to study the microscopic structure .
1 - Thomson scattering
2 - Compton scattering
3 - Raman scattering
The last one will be discussed in details.
Describe electromagnatic radiations in a simple classical process scatter by the electron of ionized gas.where thomson cross-section
Where ro = classical radius of electron
In other words. The photon energy is mush less than the rest mass of the electron .
Compton scattering is observed in x-rays passing through a solid or gas.
The essential interaction is between higher photon energy and individual electrons. wether or not that electron is bond to atomic nucleus.
Where λ΄ is the wavelength of the scattered photon & λ is the wavelength of incident photon
The spentaneous raman effect was discovered by C .V Raman 1928 ,he was a distinguished indian physist who was awarded the noble prize in 1930 for his work on the scattering of light and for the discovery of raman effect .
Raman scattering results from the interaction of light with the vibrational modes of molecules constituting the scattering medium raman scattering can equivalently be described as the scattering of light from optical phonons .
The difference energy between the incident photon and the raman scattered photon is equal to the energy of a vibration
Of the scattering molecules and its described is inelastic scattering .
“ Stokes lines ” .
. Diagram illustrate raman shift
Light is treated as a electromagnatic wave and the molecules is modeled as small spheres connected by spring.
The incident light can be described by following equations :
E (x, t) = E0 Cos (wℓ t - k’x), …eq (3)
The induced dipole is
µ = α . E , …eq (4)
α is the polarizability tensor , substitute
in the electric field of light
µ = αE0 Cos (wℓ t) , …eq (5)
the conformation of the molecule,
it changes as the molecule vibrate .
But α = α (Q ) , …eq (6)
Q is the normal vibrational coordinates .
We can expand α as tayler series ,
α = αo + [ ∂ (α)/ ∂ (Q )](Q - 0) +……eq (7)
where Q = Q0 Cos (wm t), …eq (8)
Wm is the frequency for the molecule vibrate
µ = αoE0 Cos (wℓ t) + [∂ (α)/ ∂ (Q )]. Q0E0 Cos (wℓ t) .Cos (wm t) , …eq (9)
µ = αoE0 Cos (wℓ t) + [∂ (α)/ ∂ (Q )] .
Q0E0 [Cos ((wℓ - wm )t) +
Cos ((wℓ + wm )t)] , …eq (10)
mean the incident light frequency is the same
for the scattered light frequency which was
mentioned ( Reyliegh scattering ) .
2nd term L.H.S
[∂(α)/ ∂ (Q )]. Q0E0 [Cos ((wℓ - wm )t) ,
mean lower shift of frequency which was mentioned (Raman stokes shift )
[∂ (α)/ ∂ (Q )]. Q0E0 [Cos ((wℓ + wm )t) , mean higher shift of frequency which was mentioned (Raman anti stokes shift ) .
Note that ,the Raman scattering intensity proportional to
[∂ (α)/ ∂ (Q) ]^2 .
- The selection rule for raman scattering is
∂ (α)/ ∂ (Q) ≠ 0
Surface enhanced raman scattering spectroscopy (SERS).
This review covers from the basic principles of raman spectroscopy to the advanced technique of surface enhanced raman scattering (SERS) spectroscopy.
In 1977 found the rough sliver electrode produce raman spectrum that is a million fold more intense than was expected .
This enormously strong signal debuted surface enhanced raman scattering (SERS) .
- SERS occurs when molecules are brought to the surface of metal in a variety of
- large enhancement are observed from silver ,gold and copper ,the particles size for enhancement raman to happen ranges from
20 nm - 300nm.
- Molecules adsorbed in the first layer on the surface show largest enhancements (large range effect 10 nanometer ) .
- several years ago few were fully convinced that SERS enhancement could be as high as 15 orders of magnitude and SERS active materials would include
a variety of transition metals and probably semi-conductors .
When the shape of particle was sharp
The electric field near the sharp tip would be greatly enhanced , then if we collect two or more particles gather together the electric field could be collective resonance of free electron of the surface of the metal particles which provides great enhancement .
SERS used in detection of DNA & RNA
- Procedure :
the gold particles were designed in special
way to make use of SERS the dye CY3 was
attached to the gold particles and the target
was attached to the CY3 then the gold
particle thrown onto the DNA chip After that
add some silver particles to the solution
which gather around the gold particles which give SERS effect .
“ fingerprint ” of the DNA & RNA .
As previous overview the important factor for raman scattering that it is more sensitive to different vibrational modes this is the reason why its called “ fingerprint of molecules” after SERS was discovered .
SERS is among the most sensitive techniques available to surface science .
its capability to delivering specific chemical identification and to couple this with a wide range of instruments, has led to its continuing use in both new and traditional areas of surface science .
Finally , SERS became a good tool in all advanced techniques .
Physicists study to increase surface enhancement using nano wires technology .
- MIT course 6.975 handout ,Katrin Kneipp(200)
- Introductory Raman Spectroscopy,R.LFerraro,academic
- Introduction to modern optics, Grant R.Fowles,2nd edition,
- The new interfacial ubiquity of surface enhanced Raman
spectroscopy, NM ,J.Weaver (2000)
- Surface enhanced Raman spectroscopy
- Electromagnetic Mechanism of surface enhanced
Spectroscopy ,G,C,Schatz,759-774 (2002)
- M.Moskovits ,D.P.Dilella,in surface enhanced Raman
Scattering, R.K.Chang new work, 243-273(1982)