Stimulated
Raman Scattering
Coherent
anti-Stokes Raman Scattering
A. Surface Enhanced Raman Scattering (SERS) as
nonlinear optical effect.
B. New features of the Raman spectra of single-walled
carbon nanotubes highly separated into
semiconducting (99%) and metallic (98%) components.
I.Baltog, M.Baibarac, L.Mihut,
Outline
A • Background of Raman light scattering
• Methods of amplification of the Raman emission
• Surface Enhanced Raman Scattering (SERS) via plasmons excitation
• SERS mechanism as a nonlinear optical process.
B• Brief introductions in the Raman spectroscopy of carbon nanotubes
• Abnormal Anti-Stokes SERS spectra of single-walled carbon nanotubes as
single beam CARS effect .
• Anti-Stokes and Stokes SERS spectra of single-walled carbon nanotubes
highly separated into semiconducting (99%) and metallic (98%) nanotube
components.
C • Summary
I aS
IS
Excitation
Raman anti-Stokes
Raman Stokes
v3
v2
v1
v0
4
  l   
 h 

 exp 

    
kT



 l
Electronic levels
Excitation
Excitation
Raman anti-Stokes
v3
v2
v1
v0
Raman Stokes
Excitation
Virtual levels
     aS

   
 S

1
Raman light scattering is an complex interaction of photons
and intrinsic molecular bonds
E = E0cos2lt
incident electromagnetic wave (laser beam)
P = E =  E0cos2lt
induced electric dipole moment ;  is the polarizability
𝐼=
164 4 4
 𝑃
3𝑐 3 𝑙
classical expression of total scattered light

 = o + 𝑄
𝑘
0
𝑄𝑘 +
Rayleigh
scattering
…
is polarizability that changes by molecular
vibration; Q is coordinate that describes molecular
vibration
Anti-Stokes
Stokes
Raman scattering
1
2
P = E = o E0cos2lt + E0 𝑄𝑘
Intensity
Values at
~ 1500 cm-1
0
I(l) >> IS >> IaS
1 >> 10-6 >> 10-9

[cos2(l + )t + cos2(l - )t ]
𝑄𝑘 0
Both branches are amplified equally
with the excitation light intensity
I aS
IS
     aS

   
 S

4
  l   
 h 

 exp 

    
kT



 l
1
Information from Raman spectroscopy
║
┴
Characteristic Raman
frequencies
PbI2 ; ZnO ; CCl4 ; TiO2
C60; SWNTs; graphene
Changes in frequency
of Raman peak
Chemical interaction;
stress; strain; temperature
Polarization
of Raman peak
Crystal symmetry ;
orientation; antenna effect.
Width
of Raman peak
Morphology: crystal;
mesoscopic and nanometric
structures;
Intensity
of Raman peak
 Amount of material;
film thickness;
 Nonlinear optical
effects
Methods of amplification of the Raman emission
Resonant excitation
SERS effect
chemical + plasmons
B.V
514.5 nm
676.4 nm
B.C
SERS
chemical
x 104
x104 -106
SERS plasmons
Stimulated Raman effect
CARS effect
ωS
ħ(2ωP – ωS)
ωaS = 2ωP – ωS
kaS =2kP -kS
ħω1
ωp
ωp-ωS=Ω
x104-108
x104-1010
k(ω0)
k(ω0)
Abnormal anti-Stokes SERS spectra of CuPc under resonant
excitation
180
36000
A
1
I(514+647)/I514
1.67
exc = 514.5 nm
exc = (514.5 +647.1) nm
24000
120
1.68
1.66
60
Raman intensity (counts/sec)
2
1
12000
0
0
-1600
-1500
-1400
-1300
1300
1400
1500
1600
700
7000
B
1
exc = 647.1 nm
I(647+514)/I647
exc = (647.1+514.5) nm
1
1
1
350
3500
2
Absorbance
647.1
0
-1600
-1500
-1400
-1300
1300
1400
1500
0
1600
-1
Wavenumber (cm )
exc = 647.1 nm is resonant for CuPc
514.5
I aS
400
500
600
700
Wavelength (nm)
800
IS
     aS

   
 S

4
  l   
 h 

 exp 

    
kT



 l
1
Surface plasmons as a channel to generate by optical
pumping non-linear effects.
Second harmonic
generation
CARS effect
Stimulated Raman
effect
 Single beam :
I.Baltog et al. Phys. Rev. B,72,(24), 245402,(2005)
J.Appl.Phys,110, 053106,(2011)
 Double beams
IL >> IS
ωL +  ☛ CARS
ω = ωL± (ωL – ωS) =
ωS ☛ Stimulated
I.Baltog et al. J.Opt.Soc.Am.,13, 656,(1996)
J.L.Coutaz et al. Phys Rev B,32,227,(1985)
Raman
C.Steuwe, et al. Nano Lett. , 11, 5339;(2011)
RL Aggarwal ; et al. Appl. Spectrosc.. 67 ,
132-135 ,(2013)
Second harmonic
generation
Stimulated Raman
effect
s-polarization:
E-field is perpendicular to the
plane of incidence
(German senkrecht = perpedicular)
p-polarization:
E-field is parallel to the plane
of incidence
Ez
Hz
E
Hy
z
Ey
Ex
q1
z=0
y
H
x
e1
e2
Hx
q1
z=0
y
q2
x
e1
e2
q2
z
Any linearly polarized radiation can be represented as a superposition of
p - and s - polarization.
p-polarized incident radiation will
create polarization of charges at
he interface.
These charges give rise to a
surface plasmon modes
Boundary condition:
(a) transverse component of E is conserved,
(b) normal component of D is conserved
E1z
E1
z=0
y
z
H1y
x
E1x
E2z
H2y
E2
E2x
e1
e2
creation of the polarization charges
if one of the materials is metal, the electrons
will respond to this polarization. This will
give rise to surface plasmon modes
s-polarized incident radiation
does not create polarization
charges at the interface. It thus
can not excite surface plasmon
modes
Boundary condition
(note that E-field has a transverse
component only):
transverse component of E is conserved,
H1z
H1
z=0
y
z
E1y
x
H1x
H2z
E2y
H2
H2x
e1
e2
no polarization charges are created 
no surface plasmon modes are excited!
Maxwell’s equations
Surface Enhanced Raman Scattering
(SERS)
via plasmons excitation
Charge neutrality,  = 0
No direct current, j = 0
Non-magnetic materials, r = 1 ( = 0)
condition imposed on k-vector
E1z
E1
dielectric e1
y
x
z
metal e2
wave propagating
in x-direction
intensity
E1x
~e
ik z z
;
k z   i z
localized surface mode = surface plasmon
decaying into both materials
Caracteristicile undelor de suprafata = plasmoni de suprafata (SP) :
(i) undele de suprafata rezulta din oscilatiile colective ale electronilor din stratul
metalic ; pot fi excitate numai cu radiatie cu polarizata p (TM), care are o
componenta EM perpendiculara la suprafata
(ii) undele de suprafata sunt propagative in lungul suprafetei de separare dintre
doua medii (metal-dielectric) aflate in contact;
pentru λexc = 500 nm; Lpropagare≈ 25 μm
(ii) unde evanescente pentru care amplitudinea scade exponential cu distanta de la
suprafata de separare –
pentru : λexc = 500 nm; hpenetrare ≈ 12 nm in metal si ≈ 95 nm in aer
(iii) amplitudinea undei evanescente este maxima in lungul suprafetei lor de separare
(iv) Metale active Pb, In, Hg, Sn, Cd  UV si Cu, Au, Ag  VIS
METHODS OF PLASMON EXCITATION
dielectric e1
q1
prism
coupling gap
metal
Otto geometry
q1
metall
e2
prism
metal
Kretschmann-Raether
geometry
Grating
 rough surface 
kx  0
kx  kx  Gx
'
Gx  
2
d
kx  
'
2
d
Experimental
Material:
- copper-phthalocyanine (CuPc)
- SWNTs highly separated in semiconducting (99%) and metallic (98%)
components
Sample form :
- thin films (9.5; 39; 88; 185 nm thickness ) deposited on glass and
rough Au and Ag supports with different SERS activity;
motivation: SERS(Au) << SERS(Ag)
Measuring geometry : Backscattering under focused light ; x50 aperture objective
Excitation laser light : 514.5 ; 647.1;676.4 nm ensuring non-resonant and
resonant optical excitation
Abnormal anti-Stokes SERS spectra of CuPc under resonant
excitation
180
36000
A
1
I(514+647)/I514
1.67
exc = 514.5 nm
exc = (514.5 +647.1) nm
24000
120
1.68
1.66
60
Raman intensity (counts/sec)
2
1
12000
0
0
-1600
-1500
-1400
-1300
1300
1400
1500
1600
700
7000
B
1
exc = 647.1 nm
I(647+514)/I647
exc = (647.1+514.5) nm
1
1
1
350
3500
2
Absorbance
647.1
0
-1600
-1500
-1400
-1300
1300
1400
1500
0
1600
-1
Wavenumber (cm )
exc = 647.1 nm is resonant for CuPc
514.5
I aS
400
500
600
700
Wavelength (nm)
800
IS
     aS

   
 S

4
  l   
 h 

 exp 

    
kT



 l
1
A. SERS spectroscopic studies on CuPc thin films under
non-resonant ( 514.5 nm) and resonant (647.1 nm) optical excitation.
0
-1500
-1400
-1300
1300
1400
1500
Raman intensity
25
500
600
700
800
1600
Wavelength (nm)
Au
15000
10
10000
5
5000
-1500
-1400
-1300
1300
1400
1500
30
1528
1452
1306
25000
1342
-1342
-1306
-1452
exc = 647.1 nm
-1500
-1400
-1300
1300
1400
1500
1000
20000
15
Ag
0
-1600
25000
20
0
-1600
500
514.5
400
50000
-1528
Raman intensity (counts/sec)
0
-1600
1000
647.1
50000
1454
-1454
50
exc = 514.5 nm
1342
-1530
100000
Ag
Absorbance
-1342
1530
100
0
1600
50000
Au
500
0
-1600
25000
-1500
-1400
-1300
1300
1400
1500
glass
60
3000
20
1200
10
600
40
0
0
-1400
-1300
1300
1400
1500
2000
20
SRS
-1500
0
1600
4000
1800
glass
-1600
0
1600
1600
1000
CARS
0
-1600
0
-1500
-1400
-1300
1300
1400
1500
1600
Wvenumber (cm-1)
-1
Wvenumber (cm )
Anti-Stokes and Stokes Raman spectra of CuPc thin
Films of 39 nm thickness deposited on Ag, Au and
glass supports. Red curves show the anti-Stokes spectra
calculated with the Boltzmann formulae applied to the
corresponding Stokes Raman spectra.
Anti-Stokes and Stokes Raman spectra of CuPc thin
Films of 39 nm thickness deposited on Ag, Au and
glass supports. Red curves show the anti-Stokes
spectra calculated with the Boltzmann formulae
applied to the corresponding Stokes
Raman spectra.
for a Raman line at ~1500 cm-1
Ag
Stokes
50
40
4
30
1
Au
Ag
20
Au
glass
2
glass
10
1.0
0.5
0.0
0
v3
v2
v1
v0
exc = 647.1 nm
resonance
Stokes
anti-Stokes
18
Ag
15
12
18
Ag
Au
Au
12
6
6
0
glass
9
3
I(L) >> I(S) >> I(aS)
1
10-6
10-9
SP(L) >> SP(S) >> SP(aS)
SP(L)  SP(S) = SRS
I(L) >> I(S) ≈ I(aS)
1
10-6
10-6
15
9
glass
Normalized Raman Intensity
3
Excitation
anti-Stokes
Raman Stokes
5
Excitation
no resonance
Raman anti-Stokes
exc = 514.5 nm
3
0
Intensities of the anti-Stokes and Stokes Raman lines
at 1530 cm-1 of 39-nm-thick CuPc films deposited on
glass, Au and Ag supports. Raman measurements were
performed in a backscattering geometry under non-resonant
(514.5 nm) and resonant (647.1 nm) optical excitations.
Data were all obtained at the same laser intensity (2 mw)
focused by a 50x objective onto the surface sample.
Data for each Raman branch were normalized to the
intensity measured on the film deposited on a
glass support.
SP(L) >> SP(S) > SP(aS)
SP(L)  SP(S)
SRS
(2SP(L) ± SP(S))  SP(aS) CARS
SRS
647.1 nm
514.5 nm
150
Stokes
Ag 150
100
100
glass
2
Au Ag
3
2
2
1
1
1
0
0
0
50
Au
glass
3
25
20
15
10
5
3
1
0
Au
Au
glass
50
Stokes
Ag
anti-Stokes
Ag
glass
anti-Stokes
25
20
15
10
5
3
2
and Stokes Raman line at 1530 cm-1 of
CuPc film thickness : 9.5 nm
anti-Stokes
Stokes
Ag
40
Au
20
Stokes
Ag
15
Au
anti-Stokes
40
20
Ag
15
Au
10
10
2
1
1
1
1
0
0
0
0
glass
Au Ag
5
3
glass
2
2
glass
5
3
glass
3
3
Diagrams of variations of the anti-Stokes
2
CuPc at different excitation wavelength
( non-resonant : 514.5 and resonant :
647.1 nm), film thickness (9.5, 39 and 88 nm)
and substrates used glass, Au and Ag.
CuPc film thickness : 39 nm
Intensities one each branch were normalized
Stokes
anti-Stokes
20
Ag 20
15
15
1
0
Au Ag
glass
2
Au
glass
5
3
Ag
Ag
6
8
6
10
5
3
4
3
2
2
1
1
0
0
Au
CuPc film thickness : 88 nm
glass
10
Stokes
8
glass
anti-Stokes
Au
4
3
2
1
0
to the value measured on glass substrate.
A2
Film thickness matched by plasmons
wave penetration depth
exc = 514.5 nm
no resonance
Stokes
Au
Ag
Au
120
100
80
60
40
20
4
glass
2
ant-Stokes
2
0
0
exc = 647.1 nm
resonance
30
ant-Stokes
25
20
1
0
glass
10
30
Ag
25
I(L) >> I(S) ≈ I(aS)
1
10-6
10-6
20
Au
15
5
Stokes
Ag
Au
glass
Normalized Raman Intensity
4
Ag
glass
120
100
80
60
40
20
15
10
5
1
0
Intensity of the anti-Stokes and Stokes Raman line at
1560 cm-1 of CuPc thin films of 9.5 nm thickness
deposited on glass, Au and Ag supports under
non-resonant (514.5 nm) and resonant (647.1 nm)
laser excitation.Data were normalized to the intensity
obtained on glass support.
SP(L) >> SP(S) ≈ SP(aS)
SRS
SP(L)  SP(S)
CARS
(2SP(L) ± SP(S))  SP(aS)
 SERS mechanism can be considered a nonlinear optical process ?
 Yes, this is demonstrated by the deviations from the Boltzmann law.
4
1
     aS    l   
Plasmons coupling mechanism
I aS
 h 

 exp 








I





kT
I(l) > I(S) > I(aS)


S
 S 
l


SPs(l) > SPs(S) > SPs(aS)
𝑰𝒂𝑺
𝑰𝑺 𝑺𝑹𝑺
<
𝑰𝒂𝑺
<
𝑰𝑺 𝑩𝒐𝒍𝒕𝒛𝒎𝒂𝒏𝒏
mixing of surface waves (SW)
SW(1) + SW(S) + SW(aS)
ωmix = ωL± (ωL – ωs)
ωmix = ωL- (ωL – ωs) = ωs
lower frequencies are amplified at the
expense of the higher frequencies
Stimulated Stokes Raman effect (SRS)
SRS
ωmix = ωL+ (ωL – ωs) = 2ωL- ωS = ωL+ Ω = ωaS
higher frequencies are amplified at the
expense of the lower frequencies
Coherent anti-Stokes Raman effect (CARS)
CARS
𝑰𝒂𝑺
𝑰𝑺 𝑪𝑨𝑹𝑺
Carbon allotropic particles
Graphite
Graphene
metallic
semiconductor
Diamond
Single wall carbon nanotubes
Fullerene : C60
Multi-wall carbon
nanotubes
Carbon nanoparticles
Robert F. Curl Jr.,
Nobel prize
Harold W. Kroto,
Chemistry
Richard E. Smalley
Fullerene
Raman intensity
1996
Ag(2)
Ag(1)
Hg(1) 494
272
1468
Hg(2)
433
200
400
600
800 1400
1600
Wavenumber (cm-1)
2008
Inaugural
Sumio Iijima
Kavli Prize
Carbon
nanotubes
exc = 647.4 nm
exc = 514.5 nm
RBM
175
1540
G
1593
2D
2612 2G
3187
D
1310
for
Nanoscience
1200 1400 1600 1800 2400 3200
100200
Wavenumber (cm-1)
Andre Geim,
Graphene
1200
1.5
1400
1600
2800
D
A 1362
1.0
G
2D
1582
2717
3000
3200
SDS
(28722975)
3400
H2O
2011
exc = 457.9 nm
1623
0.0
1.5
G
B
1582
exc = 457.9 nm
(2D)h
2752
1.0
(2D)l
2D'
2714
0.5
3250
Konstantin
Novoselov
0.5
0.0
1.0
C&D
G
1582
(2D)l (2D)h
SDS
2715 2754
(28722975)
D
0.5
1362
1625
Nobel prize
Physics
Normalized Raman Intensity
D'
0.0
1200
1400
1600
2D'
3250
2800
3000
3200
Wavenumber (cm-1)
3400
Geometry of single-walled carbon nanotube
(SWNT)
d = Ch / π = 31/2aC-C(m2 + mn + n2)1/2/ π
q= tan-1[31/2m/(m+2n)]
N(hex/u.c) = 2(m2 + mn + n2)/d
(n,m) denote the number of unit vectors na1 si ma2
q
in the hexagonal honeycomb lattice contained in the
vector Ch
chiral angle
aC-C = 1.421 Ǻ is the nearest-neighbor C-C distance in
graphite
q = 00 ; q = 300 ; 0<q<300
n,m,q
define a specific SWNT:
► Armchair (n = m,q =300 ),
► Achiral or zig-zag (n ≠ 0 or m = 0 ; q = 00 )
► chiral (n ≠ m ≠ 0 ; 00<q <300 ).
- for n-m = 3k , k = 1,2,3..
- for n-m ≠ 3k
Metallic properties
Semiconducting properties
Electronic structure
- SWNT has one-dimensional (1D) electronic density of states
- 1D electronic band structure derive from the 2D band structure
of the graphene honeycom sheet.


  y 0 1  4 cos 




E2D
E 2 D   y0
k a

3k a
x C  C  cos  y C  C


2
2



k a

2 y C  C
 4 cos


2



E 11  2 a C  C  0 / d
S
E 11  6 a C  C  0 / d
M
2 . 7   0  3 eV




1/ 2
► The structure of electronic bands density of an one dimensional system (1D- carbon nanotube) derives from
the bi dimensional structure (2D) of graphite
► A set of 1D energy dispersion relations is obtained by slicing up the 2D energy band structure of graphite in the
circumferential direction.
1/ 2

 m 
 ka 
2  ka  
E  k     0 1  4 cos 
 cos 
  4 cos 

 5 
 2 
 2 

where a = 1.42 x Ǻ =2.46 Ǻ is lattice constant of two dimensional graphite kx and ky are the corresponding basis vectors
of the reciprocal lattice; γ0 is nearest-neighbor transfer integral
a
m
For an armchair SWNT tube the 1D energy dispersion relation is:


E 2 D k x , k y     0 1  4 cos 



 k ya 
3k x a 
 cos 

 2   4 cos
2 


2
 k y a 


 2 


1/ 2
(-π < ka < π ); m = 1,.....,5 ;
Similarly for a zig-zac SWNT tube:
z
Em


 k     0 1  4 cos 



3 ka 
 m 
2  m 
 cos 

4
cos




2 
 9 
 9 
1/ 2
 
 
 ka 


3
3

m = 1,.....,9 ;
k is one dimensional vector along the tub axis
► The calculations for the electronic structure of SWNTs show that about 1/3 of the nanotubes are metallic and 2/3
are semiconducting , depending on the nanotube diameter dt and chiral angle θ.
►The metallic SWNT have a small non-vanishing 1D density of states at the Fermi level while for the semiconducting
1D SWNT the density of states is zero.
► The band gap for isolated semiconducting carbon nanotubes is proportional to the reciprocal nanotube diameter 1/dt
The tubes diameter and calculated band gap energies as
function of n,m, q parameters .
514.5 nm
2.4 eV
676 nm
1.83 eV
0.3
ES
11
1064 nm
1.16 eV
Absorbance
0.68
0.2
ES
22
1.28
0.1
EM
11
1.82
0.0
0.5
1.0
1.5
2.0
2.5
Energy (eV)
Absorption spectrum of SWNT
Electronic structure
a
1593
excit1064 nm
164
2537
Raman intensity (a.u.)
178
RBM
= α/d (nm ) ;
3
175
excit 676.4 nm
1590
1313
2613
2
1591
radial breathing modes RBM
(cm-1)
3182
1275
180
excit 514.5 nm
1340
2682
1
0
500
1000
223.75<α<248
1500
2000
2500
Wavenumber / cm
3000
3500
-1
164
1593
c
178
b
3178
1275
3
3
175
1590
1313
176
1591
1340
1
Electronic 1D density of states for two
(n,0) zig-zag nanotubes.Dotted line
shows the density of states for the 2D
graphene sheet
(R.Saito,M.S Dresselhaus et al J.Appl.Phys
73,494,(1993))
1300
1250
1.0
1.5
2.0
514.5 nm
d
1350
1
1200 1400 1600
-1
Wavenumber / cm
676.4 nm
1400
1064 nm
Peak position of the
-1
D band. (cm )
-transversal axial
150
225
-1
Wavenumber / cm
2
2.5
457.9 nm
164
2
3.0
Energy (eV)
SERS spectra on carbon nanotubes films (thickness of ca.150 nm)
deposited on rough Au support .
-longituginal
SERS spectra of mixture semiconductor (66%) and metallic (33%)
carbon nanotubes packed in bundles
Stokes and anti-Stokes SERS spectra
on SWNTs films of different thicknesses
(h1<h2<h3, i.e about 30, 60 and 120nm )
recorded through a microscope objective
of x0.55 numerical aperture under
excitation wavelengths
of 676.4 and 514.5 nm.
The IaS/IS ratio was estimated for
the G band. Au as metallic SERS support
Explanation:
Single beam CARS effect
I.Baltog et al .Phys Rev B,72,(24), 245402,(2005)  SWCNTs
J. Raman Spectrosc,42,303,(2011)  conducting polymers
J. Appl. Phys., 110, 053106, (2011)  nonlinear optical
materials
Abnormal anti-Stokes Raman scattering under resonant optical excitation
of SWNTs is a process reminiscent to a single beam CARS effect.
where : Il - incident pump intensity;
χ(3) - the dielectric susceptibility; d - slab
thickness; Δk - the phase-mismatch requirement
 (Δk = kas – (2 kI– kS) ; kas, kS ,kI are the wave
vectors); NA is the numerical aperture of the
collecting lens.
ICARS ~ NA ωaS2d2 |χ(3)|2 I2l.IS sinc2(|Δk|.d/2)
80
2
8
60
(Iexp/Icalc)aS
a
40
q1
1

q

q1
q

4
20
q
0
q
0
-1600
-1400
0
250 500 750 1000 1250 1500
-1200
1200
-1
Wavenumber (cm )
q1
1400
4
2
q
q
q1
0.0
-1600
-1400
-1200
1200
1400
~ 0.5 for h2
2.5
1.5
q
(IAS/IS) ~ 4.0 for h3
0
1600
q
1542
G
3.0
b
5.0
G
exc = 676.4 nm
a
-1584
Raman intensity (arb.units)
Raman intensity (arb.unit.)
5.0
q
~ 0.1 for h1
D
h2
D
h2
h1
-1314
h3
-1600
1.5
-1400
G
b -1590
-1200
1200
1400
Stokes
45
1592
(IAS/IS) ~ 0.06 for h3
h3
0.0
1600
G
exc = 514.5 nm
1.0
0
a-Stokes
1314
h3
0.0
2.5
h1
h1
30
~ 0.02 for h2
~ 0.004 for h1
1600
0.5
15
h2
-1
Wavenumber (cm )
D
h1
D
-1342
1342
0.0
h3
0
-1600
-1400
-1200
1200
1400
-1
Wavenumber (cm )
Baltog et all. Journal of Optics A: Pure and Applied Optics 7, 1-8, (2005) ;
Phys Rev B,72,(24), 245402-245413,(2005) ;
1600
weak temperature
dependence
M22
1.77
S11
S22
0.68
-*
3.2
M11
0.50
4.5
1.24
B. Anti-Stokes and Stokes SERS spectra of single-walled
0.25
carbon nanotubes
highly separated into semiconducting (99%)
S
and metallic (98%)
nanotube components.
A
2.47
33
0.00
0
1
2
3
5
6
B1. Absorption
spectra
of4 semiconducting
(99%) and metallic (98%) SWNT
S11
0.68
514.5
nm
S22
S
1.24
514
-*
0
1
2
4
0
S22
1
6
M
4.5
3.2
0.68
5
-*
M22
S11
676
4.5
3
M11
1.77
1.21
Absorbance
2.47
S33
676.4
nm
2
Calculated Kataura plots of
van Hove singularities
Energy vs. tub diameter
3
Energy (eV)
4
5
6
Fano asymmetry
Breit-Wigner-Fano (B WF) profile :
I=I0{1+(0 - )/}2/{1+[(0 - )/]2}
 = line width ;
 = parametre of asymetery
●The quantum interference between two
configurations in the transition process
into a final state with the same energy:
one direct <2α2|0> and one indirect via a
discrete state <2W|1> <1α1|0> , where W is
a
matrix
element
describing
a
nonradiative transition from discrete to
continuum.
●The energy continuum of these
transitions overlaps with the energy of the
discrete Raman active optical phonon of
the same symmetry and an interference
between the phonon and the electronic
transition takes place.
M.A.Pimenta, …,G.Dresselhaus, and M.S.Dresselhaus..,
Phys.Rev.B 58,R16016-R16019,(1998)
TO
Stokes and anti-Stokes Raman spectra for
SWNT’s of d~1.49 nm taken at four different
values of E laser
LO
S. D. M. Brown et al. Phys. Rev. B 61, R5137(2000)
Raman G+ and G- peaks associated to LO and TO
phonons for semiconducting and metallic SWNTs
S. Piscanec et al. Phys. Rev. B 75, 035427(2007)
?
LO
TO
 Since metals are infinitely polarizable, it is hard to see how a vibration of the atoms
in the crystal lattice could cause a change in the polarizability.
 Raman activity of metals may be generated by small clusters of metal atoms, and in
the case of metallic nanotubes by their association in bundles
 Fano Raman profile
K.Kempa et al. Phys Rev B 66, 161404 (2002);
66, 195406 (2002)
The relative BWF intensity is always weak for thin
bundles or individual tubes but varies for thicker
bundles. The solid lines show estimated relative intensities
for pure metallic bundles and bundles containing isolated
or noninteracting metallic tubes.
G Raman band profiles of metallic ( 98%) and semiconductor (99%)
carbon nanotubes
Supports:  glass ;  Au;  Ag
exc = 514.5 nm
a2
300
Metallic
25000
50
0
-1650
-1600
-1550
1550
1600
0
1650
800
400000
b1
b2
Semiconductor
200000
400
0
-1650
-1600
-1550
1550
Wavenumber (cm-1)
1600
0
1650
200
a2
exc = 647.1 nm
Metallic
100
0
200
30000
0
1450 1500 1550 1600 1650
4000
40000
b1
b2
Semiconductor
30000
2000
20000
1000
10000
0
60000
a2
a1
exc = 676.4 nm
-1586
45000
15000
-1650 -1600 -1550 -1500 -1450
3000
300
60000
a1
Raman intensity (counts/sec)
a1
Raman intensity (counts/sec)
400
50000
Raman intensity (counts/sec)
100
1583
40000
Metallic
100
20000
0
0
-1600
600
-1500
1500
1600
45000
-1589
b1
1589
b2
Semiconductor
400
30000
200
15000
0
-1650 -1600 -1550 -1500 -1450
1450 1500 1550 1600 1650
Wavenumber (cm-1)
0
0
-1600
-1500
1500
Wavenumber (cm-1)
Anti-Stokes (a1;b1) and Stokes (a2;b2) G Raman band profiles of metallic (~98%
pure, a1;a2) and semiconductor (~99% pure, b1;b2) SWNTS deposited in a thin
layer on glass (black), Au (red) and Ag (blue) supports. All spectra were recorded
in a backscattering geometry with 2 mW of laser intensity focused on the sample
through a 50x objective.
1600
SERS evidence of anomalous behavior in anti-Stokes Raman branch
of metallic nanotubes.
Metallic
4
3
0
Semiconductor
Stokes Ag
30
30
Au
1
1
0
Semiconductor
anti-Stokes
5
5
4
Stokes
Ag
Ag
20
10
2
3
Au
glass
glass
glass
Ag
Au
4
Au
1
1
1
0
0
0
0
glass
1
Au
2
Ag
1
0
0
Semiconductor
Stokes
anti-Stokes
4
Ag
2
4
Ag
3
2
1
exc = 514.5 nm
2
glass
Ag
2
0
3
10
Au
glass
20
2
3
Au
3
Au
glass
1
anti-Stokes
4
Stokes
3
Au
2
0
anti-Stokes
Ag
3
glass
Ag
glass
Au
4
4
Stokes
Au
glass
1
anti-Stokes
Ag
3
glass
2
4
glass
Ag
Normalized Raman Intensity
Stokes
3
Normalized Raman intensity
Stimulated
Raman
Scattering
effect
anti-Stokes
Normalized Raman intensity
4
Metallic
Metallic
Au
2
1
1
0
0
exc = 676.4 nm
exc = 647.1 nm
CARS effect
Intensities of the anti-Stokes and Stokes G Raman lines (1595 cm-1) under 514.5;
647.1 and 676.4 nm excitation light (normalized by the intensity obtained from
samples with the glass substrate) for metallic (M, ~98 % pure) and semiconductor
(S, ~99% pure) C-SWNT thin films deposited on glass, Au and Ag supports. The
intensity of the laser light focused on all samples was 2 mW.
9000
100
6000
50
3000
0
300
Supports:
 glass
 Au
 Ag
0
-1600
-1400
-1200
1200
1400
1600
150
6000
exc = 647.1 nm
b1
b2
100
4000
MWNT
LAUSANNE
12000
a2
exc = 514.5 nm
a1
200
8000
100
4000
0
0
-1600
-1400
-1200
1200
1400
1600
600
6000
b1
b2
exc = 647.1 nm
400
4000
200
2000
Metallic
50
2000
0
0
0
-1200
1200
1400
0
-1600
1600
-1400
exc = 514.5 nm
4
Ag
and b1, b2 , respectively ,
2
1
0
0
MWNT
Au
Ag
anti-Stokes
Ag
Stokes
4
0
Ag
glass
1
Au
2
0
0
exc = 647.1 nm
anti-Stokes
5
Stokes
Ag
4
5
Ag
4
3
Semiconductor
Au
2
Metallic +
Au
1
2
1
0
3
2
Au
Au
glass
exc = 647.1 nm
5
1
ALDRICH
3
1600
Stokes
anti-Stokes
Anti-Stokes and Stokes
Raman spectra of MWNT
(ALDRICH)
4
4
deposited on glass, Au and Ag supports (curves black,red
Ag and blue)
recorded at3the excitation light of 514.5 and 647.1 nm, figures
3 a 1, a2
2
Au
1
4
1400
exc = 514.5 nm
5
glass
glass
Au
glass
Anti-Stokes and Stokes Raman spectra of MWNT (Crpet-metallic)
anti-Stokes
deposited
on
glass, Au and Ag supports (curves
Stokes black,red3and blue)
3
recorded at excitation light of 514.5 and 647.1 nm, figures
a 1, a2
Ag
and b12, b2 , respectively ,
1200
Wavenumber (cm-1)
Wavenumber (cm-1)
4
-1200
glass
-1400
glass
-1600
glass
Raman intensity (counts/sec)
a2
exc = 514.5 nm
a1
Raman intensity (counts/sec)
150
3
2
1
1
0
0
Insulator, semiconductor and metal
Clasification based on bandstructure
Conduction
band
EF
Conduction
band
Eg
Energy
Vibration
levels
Valence
band
METAL
INSULATOR or
SEMICONDUCTOR
Absorption: Semiconductors
• Absorption by electron transition occurs if h > Egap
Energy of electron
unfilled states
incident photon
energy h
Egap
typical resonance
Io
filled states
Optical Properties of Metals: Absorption
• Absorption of photons by electron transition:
Energy of electron
unfilled states
h
Io
E = h required covers a large
spectral range ; no typical
resonance
filled states
• Metals have a fine succession of energy states that causes absorption and reflection;
• Normally, the Raman activity is conditioned of the vibrations which change the
poalarizability of the molecule or material.
• Because the visible light cannot penetrate the metals , Raman scattering results from
the modulation of the electronic susceptibility by the optical vibration modes within
the skin depth by the optical vibration modes .
• Inside the medium, the amplitude of the electric field decays to zero rapidly with
distance.
Variation with excitation laser intensity and temperature of the anti-Stokes
Raman G band of semiconductor and metallic carbon nanotubes
50
150
exc = 676.4 nm
S
100
10
1
M
50
0.2
2
mW
Normalized (IaS/IS)G ratio
SRS
100
Normalized Raman intensity
Typical non-linear
dependence for
a non-linear optical process
25
0
0
0.0
0.4
0.8
1.2
1.6
mW
incident laser power
Intensities of Stokes (filled symbols) and anti-Stokes (open
symbols) Raman lines at 1595 cm-1 (G band) measured in a
backscattering geometry for semiconducting (~99% pure; up
triangles) and metallic (~98% pure; down triangles) of CSWNTs under 676.4 nm excitation light focused through a
50x microscope objective. The samples were in the form of
thin films layered on a glass (triangles) substrate or Ag SERS
supports (stars). The Raman intensity was normalized to the
signal measured at the lowest excitation intensity (0.2 mW).
2.0
0
100
200
300
400
500
600
Temperature (K)
Variation with temperature of the IaS/IS ratio associated with
the Raman G band (1590 cm-1) for semiconducting (~99%
pure, red symbols) and metallic (~98% pure, blue symbols)
of C-SWNTs deposited on a glass substrate. All data were
obtained at exc = 676.4 nm with 2 mW of laser power
focused on the sample through a 50x microscope objective.
The green line illustrates the variation allowed by applying
the Boltzmann law to the recorded Stokes Raman spectra for
metallic tubes.
1554
S1
-1583
4500
[(IaS/Is)LO]1583 = 0.47
1583
Polarized Raman spectra of isolated
semiconducting and metallic nanotubes
9000
S2
[(IaS/Is)TO]1583 = 0.057
6000
3000
1313
1500
0
0
-1500
1400
1500
M1
200
1583
[(IaS/Is)LO]
1547
300
1600
= 0.055
1583
-1600
-1584
Raman intensity (counts/sec)
-1563
3000
6000
M2
[(IaS/Is)TO]1583 = 0.042
4000
100
2000
0
0
-1600
-1500
1400
1500
1600
Wavenumber (cm-1)
Anti-Stokes and Stokes Raman spectra for semiconductor
(~99% pure; S1,S2; black curve) and metallic (~98% pure;
M1,M2; red curve) C-SWNTs excited at exc = 676.4 nm
with light polarized along (LO) and perpendicular (TO) to
the tubes’ axes.
Anti-Stokes Raman intensity of the Raman G band for
semiconductor (~99% pure; a) and metallic (~98% pure; b)
SWNTs on a Ag support versus the intensity of excitation
laser light. All data were obtained at exc = 676.4 nm with
light polarized along (LO) and perpendicular (TO) to the
tubes’ axes.
Conclusion:
i) SERS effect manifests differently under non-resonant and resonant optical excitations, it
results from the coupling of plasmons associated with the incident light with the plasmons
associated with the Stokes and anti-Stokes spontaneous Raman emissions.
ii) Under non-resonant and resonant optical excitation SERS manifests as stimulated Raman
process and CARS effect, respectively.
iii) Contrary to the results reported so far , and regardless of whether the optical excitation was
non-resonant or resonant and regardless of whether glass, Au or Ag was used as the substrate,
the metallic single wall carbon nanotubes (SWNTs) do not show an anomalous anti-Stokes
Raman emission.
iv) Semiconducting SWNTs always show an anomalous anti-Stokes Raman emission that grows
further under increases in the excitation light intensity or temperature.
v) Semiconducting SWNTs behave differently than metallic SWNTs because of the splitting
of electronic levels into a vibration structure, which under resonant optical excitation
changes the polarizability of the material by overpopulating the states and contributes
to an enhancement of the anti-Stokes Raman emission;
vi) Metallic SWNTs (like any metal) are infinitely polarizable at very short distances, fact
which determines the invariance of the Stokes Raman spectrum under changes of
the polarization of the excitation light
Own contributions:
Appl Phys Lett 66,1187-1190,(1995)
J Opt Soc Am B 13, 656-660, (1996)
Pure Appl. Opt. 5 , 645–653,(1996)
J. Raman Spectrosc. 29, 825È832 (1998)
Phys Rev B 65, 235401,(2002)
Carbon, 40,2201-2211,(2002)
J. Opt. A: Pure Appl. Opt. 7,632–639,(2005)
Phys. Rev. B,72,(24), 245402-245413,(2005)
Carbon, 43,1-9,(2005)
J Raman Spectrosc 36,676-698, (2005)
Physica E: 40(7),2380,(2008)
J. Phys:Condensed Matter. 20,(27), 275215, (2008)
Physica Status Solidi (b) 245, (10), 2221, (2008)
Carbon ,47, (5),1389-1398,(2009)
Synthetic Metals 159 , 2173,(2009)
J Raman Spectrosc ,42,(3),303, (2011 )
J. Phys. B: At. Mol. Opt. Phys. 44,095401, (2011)
Optical Materials, 33, (9), 1410,(2011)
J Appl Phy, 110, 053106, (2011)
Proc. Romanian Acad., Series A, 13, (2), 109–117, (2012)
J Phys Chem. C, 116, 25537−25545, (2012)
Optics Communication : submitted, (2013)
J Raman Spectrosc, submitted, 2013
Journal of Optics : submitted, (2013)
WEB of Science
2000-2012
9,089 records. Topic = (Raman carbon nanotubes)
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Field: Authors
Record Count
% of 8993
1
DRESSELHAUS MS
236
2.624 %
2
SAITO R
146
1.623 %
3
JORIO A
127
1.412 %
4
DRESSELHAUS G
122
1.357 %
5
KATAURA H
117
1.301 %
6
KUZMANY H
113
1.257 %
7
LEFRANT S
94
1.045 %
8
PIMENTA MA
94
1.045 %
9
THOMSEN C
94
1.045 %
10
IIJIMA S
76
0.845 %
11
KAVAN L
75
0.834 %
12
ROTH S
74
0.823 %
13
SOUZA AG
71
0.790 %
14
ENDO M
69
0.767 %
15
PICHLER T
68
0.756 %
16
BAIBARAC M
65
0.723 %
17
BALTOG I
65
0.723 %
18
DUNSCH L
64
0.712 %
19
SAUVAJOL JL
64
0.712 %
20
KIM YA
61
0.678 %
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Thanks for your attention
Carbon allotropic particles
Graphite
Graphene
metallic
semiconductor
Diamond
Single wall carbon nanotubes
Fullerene : C60
Multi-wall carbon
nanotubes
metallic
What is the wavelength of the surface plasmon ?
 
2
k
let us find k:
substitute
kx  k
k1 z  
 n1 k 2  k 12x
k2z  
 n1 k 2  k 22 x
e r 1e r 2
e r1  e r 2
kx
The surface plasmone mode always
lies beyond the light line, that is it

has greater momentum than a free
kx 

e r 1e r 2
c
e r1  e r 2
k
photon of the same frequency 