General Report - National Institute of Materials Physics

SCIENTIFIC REPORT
with regard to the implementation of
IDEAS project 77/2011 in
October 2011-December 2014
Project Director
Dr. Ioan Baltog
Senior Scientist I
National Institute of Materials Physics
Laboratory of Optical Processes in Nanostructured Materials
105 bis Atomistilor Street
P. O. Box MG-7, 077125 Bucharest-Magurele, Romania
Tel: 00 40 (0)21 3690170 / 113
Fax: 00 40 (0)21 3690177
E-mail: ibaltog@infim.ro
Web: http://www.infim.ro
1
Mesoscopic physics is a sub-discipline of condensed matter physics that deals with small
size materials, situated between the size of a few clusters of atoms like molecule, and micron
size. The properties of these materials are strongly dependent on the ratio between surface and
volume, which generates new properties very different compared to those observed in
macroscopic scale. An example is the "quantum confinement effect" whereby electronic
properties of solids are modified by decreasing particle size. This effect becomes more
pronounced when it reaches the nanometric scale. In this context, opaque substances become
transparent, inert material gain catalytic properties, stable materials become unstable and the
solids turn into liquids and insulators become conductors.
Understanding and explanation of physical processes generated in recent years an intense
research effort and turned to the study of optical processes that occur in disordered mesoscopic
media or rough surfaces. The interest of these studies is justified by understanding the role
played by interference and for light scattering effects. By analogy with the movement of
electrons in a solid with multiple electron localization defects, Anderson effect, propagation of
light in a strong diffusing medium generates localization effects known as Anderson localization
of light that is usually viewed through a back scattering of coherent light - coherent
backscattering. Although spectacular in the quantum description, this phenomen still remains in
the context of physical optics more on an intuitive level of understanding. When an optical
coherence radiation penetrates a set of particle (mesoscopic environment), the intensity of light
observed and projected on a screen is the result of multiple interference merge process caused by
optical path differences. In this context two physical processes are observed: i) coherent
backscattering of light by which radiation is diffused back into a very small solid angle of the
order 0.001Rad, consistent with preservation of property; ii) Raman backscattering which
consists of a radiation emission energy modified like energy through the material phonon
spectrum. The two branches of Raman emission to excitation radiation are called Raman Stokes
and Raman anti-Stokes respectively. The ratio of anti-Stokes and Stokes intensity for normal
Raman stimulated emission process is governed by Boltzmann law.
If coherent backscattering of light wave propagation is done by analogy with electronic
wave propagation, it’s leading to an Anderson localization process. Anderson localization
process refers to inhibition (reduction) of wave propagation in disordered scattering systems due
to interference, leading to the emergence of localized states at the expense of extended states.
2
Propagation of diffuse radiation is dependent on diffusion constant D, which can be expressed in
terms of l. Anderson localization of light is conditionated by Ioffe-Regel criteria, where kl  1
unde k = 2
is the wave vector of the incident radiation. Ioffe-Regel criteria states that
observing the coherent backscattering, that means the optical Anderson localization, is made in
optimal conditions for values in terms of l ~ 100 nm which involves size and distance between
particles. Intuitively, a high value of free medium path involves less disorder.
The second process, Raman scattering of light also has specific dependence to
mesoscopic sample degree which consists of observing a ratio of intensities anti-Stokes / Stokes
(IAS / IS) much more higher than the one established by Boltzmann law.
Such type of results called AASRE ( abnormal anti-stokes Raman scattering) originate in
an optical nonlinear process like CARS (Coherent anti-Stokes Raman Scattering) which at its
turn is dependent by the optical nonlinear material properties and it can be seen as a evidence of
Anderson light localization. A prori, this type of process can be observed on two categories of
materials: i) which have intrinsec optical nonlinear properties ( ex. LiNbO3, bismuth germanium
oxide: BGO, bismuth silicon oxide:BSO), CdS, etc) and ii) which become optic non-linear
under rezonant optical excitation radiation (phtalocyanine:CuPc; carbon nanotubes , conductive
polymers) .
The main results obtained during the project are:
1. Related studies with optical and electronic microscopy were performed for determining the
mesoscopic configuration of the samples in which can be observed
coherent backscattering effects and AASRE.
Fig.1a. Inorganic mesoscopic
powders with optical nonlinear
properties (CdS; LiNbO3)
Fig.1b. Rough SERS
substrates (Ag;Au) and
carbon nanotubes.
3
2. Inorganic nonlinear optical properties with mesoscopic POWDERS
There were performed studies of light scattering and anti-Stokes Raman spectroscopy to
demonstrate
coherent backscattering effect simultaneous occurrence and AASR in mesoscopic
2x10
3
a2
a1
medium like simultaneous expression of Anderson localization of light.
3
1x10
Studies
related to coherent backscattering and anti-Stokes Raman spectroscopy
performed on materials with different scattering output/power (crystal or powder) argued
0
3
33
2x10
ab1 I /I
1 exp Boltzmann
3
1x10
1x103
a2
b
2
-623
1.4
-996
1.7
0
0
-1000
-800
-600
LiNbO
single
crystal
LiNbO
powder
compressed
3
3
non-hydrostatically at 0.58 GPa
33
2x10
6.0x10
bc1 Iexp
Iexp/I/IBoltzmann
Boltzmann
1
1x1033
3.0x10
bc2
2
-623
-623
1.4
3.6
5.7
1.7
-996
-996
Raman intensity (counts/sec)
Raman intensity (counts/sec)
Anderson localization
of light-600
phenomenon
appearance . Ilustrativ for this are Fig.1a si1b.
-1000
-800
LiNbO single crystal
0
0.0
-1000
-1000
6.0x10
-800
-800
-600
-600
c1 Iexp/IBoltzmann
3.0x10 1.6
LiNbO3 powder
non-hydrostatically at 0.58 GPa
2 m
c2
-623
3.6
5.7
a
-996
3
Backscattered intensity normalized
to the diffusive background.
LiNbO3 powder compressed
Wavenumber (cm-1)
3
0.01.4
-1000
-800
-600
1
LiNbO3 powder
Wavenumber (cm-1)
2 m
1.2
2
3
1.0
-0.03 -0.02 -0.01
Fig.2a Anti-Stokes Raman spectra
at λexc=514.5 nm of LiNbO3 in two
morphological forms: (a)
single crystal and (c) micrometric
(~38 nm) LiNbO3 powder. Red
dashed lines show the anti-Stokes
replica
calculated
with
the
Boltzmann formulae applied to the
recorded Stokes spectra. On the
right side, the optical microscopic
images of the laser spot focused on
the respective samples are shown.
The illuminated area indicates a
stronger backscattering process.
0.00
0.01
0.02
0.03
Fig.2b Coherent back scattering at
λexc = 633 nm of LiNbO3 in
different morphological forms:
powder with particles of 38 µm
(black 1 curve) and platelets
obtained
by
non-hydrostatic
compression at 9 tons (red 2 curve).
The blue 3 curve indicates the
absence of a backscattering effect
for a LiNbO3 single crystal slide.
Radians
1.0
b
Enhancement
3a. Elucidating the role of the metallic support (Au, Ag), of nonresonant optical excitation and
resonant SERS spectroscopy for observation the effect AASR on thin film structures of nanometer
size.
2
0.5
1
0.0
-0.03 -0.02 -0.01
4
0.00
Radians
0.01
0.02
0.03
Nonlinear features of surface enhanced Raman scattering revealed under non-resonant
and resonant optical excitation.
By performing comparative Raman studies on nanometric thin films (9.5, 39, 88 and 185
nm) of copper phthalocyanine (CuPc) deposited on glass, Au and Ag supports, we have
demonstrated that the mechanism of the surface-enhanced Raman scattering (SERS) generated
on Au and Ag substrates differs in the Stokes and anti-Stokes Raman branches depending on
whether non-resonant (515.5 nm) or resonant (647.1 nm) optical excitation is applied. The
evaluation of the SERS effect via the IaS/IS ratio reveals that this ratio is smaller or larger than
that predicted by the Boltzmann law for non-resonant or resonant optical excitation, respectively.
In the former case, the enhancement of the Stokes Raman emission is similar to a stimulated
Raman process resulting from the plasmon coupling associated with the incident excitation light
and spontaneous Stokes Raman emission. For the latter case, the amplification of the anti-Stokes
Raman emission results from a wave-mixing process reminiscent of a single-beam CARS effect.
647.1 nm
514.5 nm
150
Stokes
Ag 150
100
100
Au Ag
glass
2
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
Fig 3. Diagrams of variations of
2
the anti-Stokes and Stokes Raman
CuPc film thickness : 9.5 nm
line at 1530 cm-1 of
Sc
anti-Stokes
Stokes
Ag
40
40
Au
20
Stokes
Ag
15
Au
anti-Stokes
20
Ag
15
Au
10
different excitation wavelength (
1
1
1
0
0
0
0
glass
non-resonant : 514.5 and resonant :
5
3
glass
1
Au Ag
glass
2
glass
5
3
2
2
2
647.1 nm), film thickness (9.5, 39
CuPc film thickness : 39 nm
Stokes
Ag 20
15
15
1
0
Au Ag
glass
2
Au
glass
5
3
Stokes
8
Ag
Ag
6
glass, Au and Ag. Intensities one
8
6
each branch were normalized to the
10
5
3
4
3
2
2
1
1
0
0
Au
glass
10
and 88 nm) and substrates used
anti-Stokes
20
glass
anti-Stokes
at
10
3
3
CuPc
Au
4
3
value measured on glass substrate.
2
1
0
CuPc film thickness : 88 nm
3b. Elaboration of the cinematic scheme for Stokes Raman emission degeneration like a Raman
stimulated emission process under non resonant optical excitation (3b1) and for anti-Stokes
emission as a CARS process CARS (3b2).
5
3b1 SERS Stokes Raman effect under non resonant optical excitation reminiscent to a stimulate
Raman effect
exc = 514.5 nm
no resonance
120
100
80
60
40
20
Ag
Au
120
100
80
60
40
20
4
glass
2
Stokes
Au
glass
Normalized Raman Intensity
4
Ag
ant-Stokes
2
0
0
exc = 647.1 nm
I( ) >> I( ) >> I( )
resonance
20
Au
15
5
4
glass
10
1
 SP(L)  surface plasmons associated to
aS
-9
30
10 25 10
SP( ) >>AuSP( 20) >> SP( )
Ag
25
S
-6
Stokes
Ag
L
S15
exc = 514.5 nm
10
0
the laser excitation light;
 SP(S) and SP(S)  surface plasmons
associated to the Stokes and anti-Stokes
spontaneous Raman emission, respectively.
aS
SP( )  SP(51 ) = SRS
no resonance
anti-Stokes
glass
30
51
L
ant-Stokes
L
Stokes
Ag
S
50
40
0
30
20
Au
glass
glass
2
10
Ag
Au
3b
effect under resonant optical excitation reminiscent to CARS effect.
1.0
1 2 SERS anti-Stokes Raman
0.5
0.0
0
exc = 647.1 nm
resonance
18
anti-Stokes
15
Ag
12
Stokes
18
Ag
Au
Au
15
12
9
6
6
3
0
glass
9
glass
Normalized Raman Intensity
3
3
0
I( ) >> I( ) ≈ I(  )
L
S
-6
aS
-7
1
10
10
SP( ) >> SP( ) > SP( )
L
S
aS
(2SP( ) ± SP(  ))  SP( )
L
S
aS
CARS
Schematic representation of the
occurrence of AASRE
6
Schematic representation of the occurrence of AASRE as single-beam coherent anti-Stokes
Raman scattering (CARS) type effect and coherent backscattering effect in mesoscopic
materials. As both effects are strongly dependent on an intense multiple light scattering process,
they are considered as a manifestation of the Anderson localization of light.
3c. According with the ec. (1)
scrupulous investigation revealed new dependences for AASRE: (i) the intensity of anti-Stokes
Raman lines increases with the vibration wavenumber (Fig.3c1);; (ii) a square dependence on the
film thickness (Fig.3c1); (iii) a square dependence on the exciting laser intensity (Fig.3c1);; (iv) a
linear dependence on the NA of the microscope objective used for the detection of the antiStokes emission;
Fig.3c1 Abnormal anti-Stokes Raman emission observed in
backscattering geometry on a nonlinear optical material (powder
of LiNbO3) at excitation kexc¼514.5 nm. In panels (a) and (b) are
presented two characteristics of the abnormal anti-Stokes Raman
emission: the increase of the ratio (Iexp/IBoltzmann)/IaS with the
Raman shift and exciting laser intensity, respectively.All
experimental Raman data were obtained with a microscope
objective of 0.55 numerical aperture.
Fig. 3c2. Stokes and anti-Stokes Raman spectra at kexc¼514.5 nm of LiNbO3 powder recorded
in backscattering geometry through a microscope objective of different NA, 0.25 (solid black
curves) and 0.55 (solid red curves). Dashed curves show the anti-Stokes spectra, for the two NA
used,calculated with the Boltzmann formulae applied to the recorded Stokes spectra.
7
4a. New features in the anti-Stokes and Stokes Raman spectra of single-walled carbon nanotubes
that are highly separated intotheir semiconducting and metallic nanotube components.
Surface-enhanced Raman scattering studies were performed using nonresonant (514.5
nm) and resonant (676.4 nm) optical excitations on single-walled carbon nanotubes thoroughly
separated into semiconducting (pure 99%) and metallic (pure 98%) components. Regardless of
the support (Au or Ag), the metallic nanotubes do not present an anomalous anti-Stokes Raman
emission. Regardless of whether an on-resonant or off-resonant optical excitation is used, only
the semiconducting nanotubes produce an abnormal anti-Stokes Raman emission that grows
when increasing the excitation light intensity or temperature.
Fig.4a1. Intensities of the anti-Stokes and Stokes
Raman lines at 1595cm-1 (G band) under 514.5nm excitation for metallic (M, ~98% pure) and
semiconducting (S, ~99% pure) single-walled
nanotube thin films deposited on glass, Au and
Ag supports. The intensity of the laser light
focused on all samples was 2 mW.
Fig.4a2. Intensities of the anti-Stokes and Stokes G
band (1595cm-1) Raman lines excited at 676.4nm
(normalized by the intensity obtained from samples
with the glass substrate) for the metallic (M, ~98%
pure) and semiconducting (S, ~99% pure) singlewalled carbon nanotube thin films deposited on glass,
Au and Ag supports. The intensity of the laser
light focused on the samples was 2 mW.
8
4b. The Raman studies under light polarized relative to the main nanotube axis demonstrate that
only semiconducting nanotubes are sensitive toward changes in the polarization of the excitation
light.
Fig.4b1. Anti-Stokes and Stokes Raman
spectra for the semiconducting (~99% pure; S1
and S2; black - top curve) and metallic (~98%
pure; M1 and M2; red - bottom curve) singlewalled carbon nanotubes excited at λexc=676.4
nm with light polarized along (LO) and
perpendicular (TO) to the axes of the tubes.
All spectra were obtained in a backscattering
geometry with a 2-mW laser focused through
a 100× microscope objective on a sample
deposited on an Au support. The inset from
the bottom figure shows the microscopic
picture of a one-dimensional bundle on which
measurements were made.
Fig.4b2. Anti-Stokes Raman intensity of the
Raman G band for the semiconducting (~99%
pure; a) and metallic (~98% pure; b) single-walled
nanotubes on a Ag support versus the intensity of
the excitation laser light. All data were obtained at
λexc = 676.4nm with light polarized along (LO)
and perpendicular (TO) to the axes of the tubes.
The spectra were recorded in a backscattering
geometry with the laser light focused through a
100× microscope objective.
4c. Anti-Stokes Raman Spectroscopy as a method to identify metallic c and mixed metallic/
semiconducting configurations of multiwalled carbon nanotubes.
Measurements were performed using two types of MWCNTs: a) commercial MWCNTs,
labeled as C-MWCNTs and purchased from Aldrich Sigma and consisting of a coaxial
architecture alternating between metallic and semiconducting nanotubes and b) metallic
MWCNTs (M-MWCNTs) produced in a carpet form by water assisted catalytic chemical vapor
deposition (CCVD) at the Institut de Materiaux Condensee, Lausanne (Switzerland) .
9
The absorption spectra of the two categories of MWCNTs are different. In the absorption
spectrum of the ALDRICH MWCNTs (Fig.1 black curve) are identified S11 and S22 bands
belonging semiconducting component and a band M11 illustrating the presence of metallic
component . Similarly, the absorption spectrum for metallic nanotubes (Fig.2; red curve) is
dominated by an absorption band ranging1.7-2.2 eV , which is associated with transition M11.
And in this case, high intensity and width of this band indicate the large number of metallic
nanotubes whose chirality is different.
Fig. 4c1 Absorption spectra of the AldrichMWCNTs and Metallic-MWCNT obtained
after baseline subtraction.
exc = 514.5 nm
M-MWCNTs
9.0x102
9.0x103
Stokes
anti-Stokes
D band
G band
Raman Intensity (couns/sec)
6.0x102
6.0x103
3.0x102
0.0
3.0x103
glass
Au
Ag
glass
Au
Ag
0.0
exc = 514.5 nm
Aldrich-MWCNTs
1.5x103
1.5x104
Stokes
anti-Stokes
D band
G band
1.0x103
1.0x104
5.0x102
0.0
Fig. 4c2 Intensities of the anti-Stokes and
Stokes Raman D and G lines using 514.5 nm
excitation light for M-MWCNTs (top) and
Aldrich-MWCNTs (bottom) in thin films
deposited on glass, Au and Ag supports. The
intensity of the laser light focused on all
samples was 2 mW.
5.0x103
glass
Au
Ag
glass
Au
Ag
0.0
Substrate
10
Fig. 4c3 Intensities of the anti-Stokes and
Stokes Raman D and G lines using 647.1 nm
excitation light for M-MWCNTs (top) and
Aldrich-MWCNTs (bottom) in thin films
deposited on glass, Au and Ag supports. The
intensity of the laser light focused on all
samples was 2 mW.
4d. Anti-Stokes Raman Scattering as efficient spectroscopic method in the study of polymers and
composite based on polymer/carbon nanotubes
AASRE of PEDOT and PEDOT/SWNTs composites reveals specific relationships: (a)
the quadratic increase of anti-Stokes Raman intensities of the main Raman lines of PEDOT with
the vibration wavenumber, (b) the square dependence of the AASRE on the film thickness, and
(c) the nonlinear dependence of the AASRE on the exciting laser intensity.
11
3000
a
2000
300
600
900
1200 1500
10000
10000
439
-439
b
5.1
7500
1424
(Iexp/Icalc)aStokes
7500
987
0
0
-1500 -1200 -900 -600 -300
300
600
900
437
(Iexp/Icalc)aStokes
b
3.9
4000
1200 1500
1424
-300
1000
4000
-439
-600
2000
18
-990
Raman intensity (counts/sec)
-991
0
-1500 -1200 -900
160
34
2500
0
-600
-300
300
Wavenumber / cm
600
900
2000
0
0
-1500 -1200 -900
986
2000
-988
21.2
-991
2500
990
5000
-1423
141
5000
-1424
Raman intensity (counts/sec)
1000
2000
0
3000
-1424
92
4000
13.3
a
6000
991
2000
-1424
-439
62
437
3.4
-438
1424
4.1
6000
4000
(Iexp/Icalc)aStokes
1424
8000
(Iexp/Icalc)aStokes
439
8000
0
-1500 -1200 -900 -600 -300
1200 1500
300
Wavenumber / cm
-1
Fig.4d1. SERS Stokes and anti-Stokes
Raman spectra at λexc = 752 nm of
PEDOT synthesized electrochemically
by cyclic voltammetry at -1V vs. Ag/Ag+
on Au substrate. Figures (a) and (b)
were obtained on PEDOT thin films of
25 and 50 nm thickness, respectively
under laser exciting power of 40 mW.
600
900
1200 1500
-1
Fig.4d2 SERS Stokes and anti-Stokes
Raman spectra at λexc = 752 nm of
PEDOT synthesized electrochemically
by cyclic voltammetry at -1V vs.
Ag/Ag+ on Au substrate. Figures (a) and
(b) were obtained on PEDOT thin films
of 100 nm thickness under laser exciting
power of 20 mW
Conclusions:
1. Research objectives that were set to launch the project were fully met during project
execution 2011-2014.
2. Papers published in the period 2011-2014
Abnormal anti-Stokes Raman emission as single beam Coherent Anti-Stokes Raman
Scattering like process in LiNbO3 and CdS powder. Ioan Baltog, Mihaela Baibarac, Serge
Lefrant. Journal of Applied Physics, 110, 053106, (2011);
Nonlinear optical processes manifesting as Anderson localization of light in mesoscopic
materials. I.Baltog, M. Baibarac, L. Mihut, I. Smaranda, S. Lefrant; Proceedings of the
Romanian Academy A, 13(2), 109-117, (2012);
12
Raman scattering and anti-Stokes luminescence in poly-paraphenylene vinylene/carbon
nanotubes composites. M. Baibarac, F. Massuyeau, J. Wery, I. Baltog, S. Lefrant;
Journal of Applied Physics, 111(8), 083109, (2012);
Abnormal Anti-Stokes Raman Emission and Infrared Dichroism Studies on
Poly
(paraphenylenevinylene)/Single-Walled Carbon Nanotube Composites; M. Baibarac, I.
Baltog, J. Wery, S. Lefrant, J. Y. Mevellec, Journal of Physical Chemistry C, 116,
25537-25545, (2012).
 New features in the Anti-Stokes and Stokes Raman spectra of single-walled carbon
nanotubes that are highly separated into their semiconducting and metallic nanotube
components. Mihaela Baibarac, Ioan Baltog, Lucian Mihut, Serge Lefrant; J. Raman
Spectroscopy, 45(5), 323-331, (2014);
 Abnormal anti-Stokes Raman scattering and coherent backscattering as manifestation
of Anderson localization of light in nonlinear mesoscopic materials. Ion Smaranda,
Lucian Mihut, Mihaela Baibarac, Ioan Baltog, Serge Lefrant; Optical Engineering,
53,(9),097109, (2014);
 Nonlinear features of surface-enhanced Raman scattering revealed under non-resonant
and resonant optical excitation. M Baibarac, I Baltog, L Mihut, A Matea, S Lefrant;
Journal of Optics 16; 035003, (2014);
Abnormal anti-Stokes Raman scattering and surface-enhanced infrared absorption
spectroscopy studies of carbon nanotubes electrochemically functionalized with a 2,2’bithiophene and co-pyrene. M. Baibarac, I. Baltog, I. Smaranda, M. Scocioreanu, J. Y.
Mevellec, S. Lefrant; Applied Surface Science, 309, 11-21 (2014);
 Anti-Stokes Raman Spectroscopy as a method to identify metallic and mixed
metallic/semiconducting configurations of multi-walled carbon nanotubes.
Mihaela Baibarac, Adelina Matea, Mirela Ilie, Ioan Baltog, Arnaud Magrez
Applied Surface Science, submitted (2015).
3. Master thesis:
Normal and abnormal Raman effect excited by surface plasmons.
Adelina Matea, Faculty of Physics, University of Bucharest, 2012
4. General seminars:
Abnormal Anti-Stokes Raman scattering as a manifestation of an Anderson localization
of the light in optical nonlinear mesoscopic materials.
I.Baltog, M.Baibarac, L.Mihut, I.Smaranda, T.Velula; INCDFM, 16-Oct-2012.
 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; INCDFM, 2013.
 Metallic and semiconducting properties of carbon nanotubes revealed by SERS
spectroscopy and photoluminescence studies.
I.Baltog, M.Baibarac, A.Matea, I.Smaranda, L.Mihut; INCDFM, oct-2014.
Signature
Dr.Ioan Baltog
13