1. EPL335
Study of Raman scattering
in Carbon-nanotubes
Presented by :
Ajay Singh (2010PH10821)

2. Graphene
Graphene is an allotrope
of carbon whose structure
is a single planer Sheet
of sp2 bonded carbon
atoms, that are densely
packed in a honeycomb
crystal lattice.
Carbon-nanotube
• Layers of graphite wrapped into cylinders
of few nanometers in diameters
• Depending on how the 2D graphene sheet
“rolled up ” three types of CNT : armchair
, zigzag and chiral.
• SWNT (Diameter 1-2 nm & length 100µm)
• MWNT ( interlayer distance in multiwalled 0.34 nm & outer diameter 5-15 nm)

3. Raman Scattering
• A small portion of the scattered radiation has frequencies different from
that of the incident beam, inelastic scattering.
• Wavenumber shift , the difference in wavenumbers (cm-1) between
the observed radiation and that of the source.
• Stoke scattering and Anti stock scattering.
• First order Raman scattering and second order Raman scattering.

4. 



First order Raman scattering
Second order Raman scattering
Resonance Raman scattering
Surface enhanced Raman scattering
HER = Hamiltonian for electron-radiation interaction
HEL = Hamiltonian for electron-phonon/lattice interaction

5. In second-order Raman scattering process, an incident photon excites the lattice
from an initial state to a virtual state. The lattice emits a scattered photon by
making a transition to a final state mediated by two phonons. The second-order
Raman process involves either the creation of a phonon and the annihilation of
another , or two successive first-order processes of Fig.2.14 (b).
(b)

6. Resonance Raman scattering
If the wavelength of the exciting laser coincides with an electronic absorption of a
molecule, the intensity of Raman- active vibrations associated with the absorbing
chromophore are enhanced by a factor of 102 to 104. Thus the resonance Raman
technique is used for providing both structural and electronic insight into species of
interest.
Surface Enhanced Raman Scattering (SERS)
The Raman scattering from a compound (or ion) adsorbed on or even within a few
Angstroms of a structured metal surface can be 103 to 106x greater than in solution.
This surface-enhanced Raman scattering is strongest on silver, but is observable on
gold and copper as well.
SERS arises from two mechanisms:
• The first is an enhanced electromagnetic field produced at the surface of the metal.
When the wavelength of the incident light is close to the plasma wavelength of the
metal, conduction electrons in the metal surface are excited into an extended
surface electronic excited state called a surface plasmon resonance. Vibrational
modes normal to the surface are most strongly enhanced.
• The second mode of enhancement is by the formation of a charge-transfer
complex between the surface and analyte molecule. The electronic transitions of
many charge transfer complexes are in the visible, so that resonance enhancement
occurs.Molecules with lone pair electrons or pi clouds show the strongest SERS.
SERS is commonly employed to study monolayers of materials adsorbed on
metals, including electrodes.

7. Raman spectroscopy
• A spectroscopic technique used to observe vibrational , rotational and
other low-frequency modes in a system.
• A laser beam is used to irradiate a spot on the sample under investigation.
• The scattered radiation produced by the Raman effect contains
information about the energies of molecular vibrations and rotations, and
these depend on the particular atoms or ions that comprise the
molecule, the chemical bonds connect them, the symmetry of their
molecule structure, and the physico-chemical environment where they
reside.
• Wave number displacement (ΔV) of
Raman lines is independent of the
frequency of the exciting line.

8. Raman spectra of a MWCNT
9000
1580(cmˉ¹)
8000
7000
2698(cmˉ¹)
1350(cmˉ¹)
6000
5000
Intensity
(a.u.)
4000
3000
2000
1000
0
0
500
1000
1500
2000
2500
3000
Raman shift (cmˉ¹)
Raman spectra of MWCNT measured with 514.5-nm excitation
3500

9. Raman spectra of 1-LG
Second
order
Raman peak
(depends on
laser excitation)
Defect induced
Raman peak
 Order of defects can be calculated ID/IG.
2D mode enhances due to double resonance effect.

10. Raman signal from three isolated semiconducting and three isolated
metallic SWNTs showing the G-and D-band profiles. SWNTs in good
resonance (strong signal with low signal to noise ratio) show practically no
D-band.
G-band for highly ordered pyrolytic graphite (HOPG), MWNT
bundles, one isolated semiconducting SWNT and one isolated
metallic SWNT. The multi-peak G-band feature is not clear for
MWNTs due to the large tube size.
A. Jorio, M. A. Pimenta, A. G. S. Filho, R. Saito, G.
Dresselhaus, and M. S. Dresselhaus, New J.
Phys., 2003, 5, 139.

11. Phonon dispersion of sp² Carbon
Raman spectrum of a graphene edge, showing
the main Raman features, the D, G and G’ bands
taken with a laser excitation energy of 2.41 eV.
phonon dispersion relation of graphene showing the
LO, iTO, oTO, LA, iTA, and oTA phonon branches.
Dresselhaus, M.S., Jorio, a. & Saito, R. Characterizing Graphene, Graphite, and Carbon
Nanotubes by Raman Spectroscopy. Annual Review of Condensed Matter Physics1, 089108 (2010).

12. Reference links:
http://en.wikipedia.org/wiki/Graphine
http://epsc.wustl.edu/haskin-group/Raman/faqs.htm
http://en.wikipedia.org/wiki/Raman_spectroscopy
http://en.wikipedia.org/wiki/Carbon_nanotube
http://scientificentrepreneur.wordpress.com/2011/12/21/
raman-spectroscopy-in-graphene-and-nanoribbons/
http://www.sciencedirect.com/science/article/pii/S0370157309000520

13. Thank you
for
your attention