Transcript Principe de fonctionnement du SNOM

Static and dynamic studies using linear
reflectance and second harmonic
generation of molecular and metallic
nanoparticles films at the air/water
interface.
Gaëlle Gassin-Martin
Nonlinear Optics and interfaces
Laboratoire de Spectrométrie Ionique et Moléculaire (LASIM)
– Lyon -
Aims
General idea: Nanometric studies using nonlinear optics
o Bi-dimensional films upon compression
Control of the average distance between nanoobjects
Vary the amplitude of the interactions
o Optical measurement of the electronic delocalisation
Molecular systems (molecular aggregates)
Metallic systems (nanoparticles)
Overview
o Molecular film
o Langmuir film formation
o Importance of optical measurement
o Properties upon compression
 Polarisation resolved Second Harmonic Generation (SHG)
o Metallic nanoparticles film
o Evolution of interactions upon compression
 Linear reflectance
 SHG
o Film dynamics at the air/water interface
 Intensity correlation analysis
Molecule : DiA
air
water
hydrophilic
head
hydrophobic
tail
o Amphiphilic molecule
o Large nonlinear response (electrons
delocalised, « push-pull » structure)
 Excellent surface SHG probe
p
Molecular films
Langmuir trough
barrière
Eau Pure
(sous phase)
compression
 Control the density in situ
Densification
film 2D
Film isotherms
Condensed liquid
Pression de surface /mN/m
30
25
Expanded liquid
20
compression
15
10
5
0
20
30
40
50
Surface /cm
60
70
80
2
Compression
 Knowledge of certain macroscopic states (S, P, T, pH…)
all along the film formation
 Control of interactions in the system
Polarisation resolved SHG of a film
- Experimental set up -
 Polarisation measurement
o A l/2 wave plate permits
the variation of the
incident light polarisation
Filter
l/2
Lens
Photon
counter
Laser
femto
Analyser
Above
Chopper
Langmuir trough
Mirrors
Langmuir trough
70°
Pressure
Measurement

E
o An analyser to select the
emergent light polarisation
 Experimental curves
interpretation, exit S
polarised
S
profile
Langmuir trough
k
E 2
k 2
Second harmonic generation
SHG process : brings into play
the second order polarisation
P
P
1
P

2

P

3
 ...
2

  0    E   0    : EE   0    : EEE  ...
1
/u.a.
4000
Intensité SHG
5000
3000
2
Excitation
at 800 nm
3
SHG
measurement
I SHG  G 
SHG
 2
2
( I (  ) )2
2 nd order
susceptibility
tensor
2000
1000
0
360
380
400
Longeur d'onde
420
/nm
440
Centrosymmetric property
Z
 2
P  0 
 2
: EE
M(x, y, z)
M’(-x, -y, -z)
O
Y
E  E
  E 
 P 2   0   2 :  E
Centrosymmetric
medium
X

The symmetry is very important for
this process

SHG is always null in centrosymmetric
medium
 P 2   P 2 

 2
0
Wide interest with the surface which represents a
symmetry break
(2)

exclusive measurement of surface properties ( surf )
Microscopic dimension
Induced dipole defined by :
(t )  0   .E   : EE  ...
polarisability
Hyperpolarisabilty
1st order
o Hyperpolarisabilty tensor β microscopic parameter which
characterises the molecule.
o Susceptibility tensor χ macroscopic parameter which
characterises the surface.
0
( 2)
N 
( 2)
space
Molecular film collapse
-DiA molecular film -
o High monolayer compression
o Simultaneous measurements :
Molecular Density : 0.4 to 3 nmoles/cm²
 Surface pressure :
continuous growing

(2)
surf
0
centrosymmetry
/ua
/uamN/m
Signal
SHG
Signal
SHG
Pression
de surface
( 2)
1000
1000
40
40
800
800
600
600
30
30
/mN/m
 0  information
 N remain
Some
inaccessible by surface
pressure measurement.
(2)
Non
SHG

0
technique
convincing
surf
centrosymmetry
( 2)
50
Contre-ions
Pression de surface
 SHG: Signal falls at
high density
1200
1200
50
400
400
20
20
200
200
Micelle
0.5
0.50.5
1.0
1.0
1.0
1.5
1.51.5
2.02.0 2.0
DensitéDensité
moleculaire
nmol/cm²
/nmol/cm²
Densité /nmol/cm²
2.5
2.5 2.5
SHG signal
related
to multilayer
DiA : 2falls
carbon
chains
formation
 liquid film with
a lot of defects
Polarisation analysis
-DiA molecular film -
eee
Pi(2) (2)   ijk
E j ()Ek ()
j,k
ED Approximation (electric dipolar)
Isotropic surface
Cv
eee
zzz
eee
 zxx   eee
zyy
eee
eee
eee
eee






xxz
yyz
xzx
yzy
I
DE
s
 a1 
eee
yyz
sin 2
Molecular Density : 0.43 nmoles/cm²
Signal SHG
/ua
400
2
300
200
100
0
50
100
150
200
Angle de polarisation incidente
incident polarisation
angle
250
300
350
/deg
 High degree of symmetry
Isotropic chiral Surface
-DiA molecular film -
 Monolayer compression
Chiral isotropic surface
C
CV
Molecular Density : 0.8 nmoles/cm²
ED Approximation
400
400
eee
zzz
eee
 zxx   eee
zyy
eee
eee
eee
 xxz   yyz   eee


xzx
yzy
DE
DE
ss
II
Signal
Signal
SHG
/ua
SignalSHG
SHG /au
/au
eee
eee
eee
eee






xyz
xzy
yxz
yzx
300
300
300
(Chiral)
a
sin 22 
a  sin 2
a  cos2 
eee
1 eee
yyz
1 yyz
eee
7 yxz
200
200
200
100
100
100
2
0
00
0
50
50
50
100
100
100
150
150
200
250
150
200
Angle de polarisation
incidente 250
//deg
deg
Angle de polarisation incidente /deg
300
300
350
350
 Chirality
with EDorigin
approximation
Unique possible
for 90° angle
deformation
is chirality's phenomenon
not
sufficient
Introduction of magnetic components
-DiA molecular film -
eee
eem
Pi(2) (2)   ijk
E j ()Ek ()   ijk
E j ()Bk ()
Isotropic chiral Surface C
eee
zzz
eee
 zxx   eee
zyy
eee
eee
eee
 xxz   yyz   eee


xzx
yzy
350
(Chiral)
300
Signal SHG
/au
MD Approximation
eem
 eem
xyz   yzx
eem
 eem
xzy   yzx
eem
 eem
zxy   zyx
j,k
Molecular Density : 0.8 nmoles/cm²
ED Approximation
eee
eee
eee
eee






xyz
xzy
yxz
yzx
eem
zzz
eem
 zxx  eem
zyy
eem
eem
 xxz   yyz
eem
eem
xzx   yzy
j,k
eem
 eem
xyz   yzx
eem
 eem
xzy   yzx
eem
 eem
zxy   zyx
250
200
150
100
(Chiral)
50
a1 
eee
yyz
 (a10 
eem
yxz
eee
eem
I sDE  DM   a7  yxz
 a9  yzy
eem
 a8  yyz
 a11 
eem
yzx
)sin 2
cos 2 
sin 2 
2
0
50
100
150
200
Angle de polarisation incidente
250
300
350
/deg
 Chirality with MD
approximation adapted
Evolution of S-polarised curves
all along compression
-DiA molecular film -
DE
D
300
800
1400
40
50
1500
1200
E
F
A
C
E
BG
G
F
D
Pression de surface
Signal
SHG
/ua
Pression
deSHG
surface
/mN/m
Signal
SHG
/ua
/au
Signal
/ua
Signal
SHG
/ua
Signal
SHG /ua
Signal
SHG
/ua
70
1800
2000
1600
1000
350
50
2000
1600
60
1400
/mN/m
50
30
20
10
250
1500
1200
C
40
A
B
0.4
0.6
30
1000
800
800
1000
150
20
400
20
600
600
100
10
400
200
10
500
400
500
A
50
200
0
50
0.4
50
50
50
50
100
0.6
100
100
100
100
1.0
1.2
/nmol/cm²
Progressive
symmetry
breaking all along
the compression
B
00 000
0.8
Densité
C
40
1000
600
30
1000
200
F G
150
150
150
150
0.8
200
200
200
200
Densité
/nmol/cm²
Angle
de
polarisation
incidente
Anglede
de
polarisation
incidente
Angle
Angle
de
polarisation
polarisation
incidente
incidente
250
1.0
250
250
250
/deg
/deg
/deg
300
300
300 1.2
350
350
Molecular
Density : 0.2 Tensor
to 1.4 nmoles/cm²
Fitting
curves
elements which translate
threshold : 0.5 nmoles/cm²
surface state all along compression
Chiral tensor element 
-DiA molecular film1800
eee
eem
eem
a1  yyz
 (a10  yxz
 a11  yzx
)sin 2
200
eee
eem
I sDE  DM   a7  yxz
 a9  yzy
cos 2 
a 
sin 
100
0
50
eem
8 yyz
Angle de polarisation
incidente
100
150
200
2
Increase chiral tensor
eem
element  yyz
eee

Becomes comparable to
1600
1400
/ua
300
Signal SHG
/ua
400
Signal SHG
eem
yyz
2
250
300
350
/deg
1200
1000
800
600
400
100
200
0
50
50
150
200
250
300
350
/deg

/ua
Sign change
/ua
1000
eem
yyz
Signal SHG hH
0
1500
Signal SHG
2000
1500
/au
100
Angle de polarisation incidente
2000
1000
500
-50
500
0
50
100
150
200
Angle de polarisation incidente
-100
0
0.4
0.6
Densité
0.8
1.0
/nmol/cm²
Compression
1.2
250
300
350
/deg
 Uncertainty about the
origin of chiral tensor
evolution
Microscopic Interpretation
-DiA Molecular film Even if we lack some information we know :
DiA non chiral molecule
 eem
yyz attest an isotropic chiral surface
 Progressive formation of chiral structures
upon compression
o Microscopic models of chiral aggregates
It drives us to think about:
 Helix aggregates
Model: an electron along an helix
Conclusions
-DiA molecular film-
Langmuir technique : squeeze the molecules to form a 2D film
Chiral aggregates formation
SHG technique : sensible to surface phenomenon
Measure electronic delocalisation effects in these
chiral aggregates upon compression
Molecular Films
Nanoparticles Films
Overview
o Molecular Film
o Langmuir films
o Importance of optical measurement
o Proprieties under compression
 SHG resolved in polarisation
o Film of metallic nanoparticles
o Evolution of interactions upon compression
 linear reflectance
 SHG
o Film dynamic at the air/water interface
 Intensity correlation analysis
Nanoparticles Synthesis
Metallic Nanoparticles
Gold and Sliver
Ø 7 nm
Brust
Method
 Surface capped thioalkanes
hydrophobic particles adapted to
2D film formation
Silver Nanoparticles
in chloroform
Chain length variation:
Nano
Particle
• Chains C18 limited interactions
• Chains C12 , C6 … allowed interactions
C12
Thioalkanes
Collaboration LPCML ( Olivier Tillement, Stéphane Roux)
Nanoparticles Films
-Aims-
 Consequences on optical
response
(new resonances,
Nanoparticles
Filmthanks to
field
enhancement…)
deposit
acompression
microlitric
syringe
 Aggregates formation
 Emergence of interactions
upon compression
Linear reflectance and SHG of a film
-experimental set up-
Detection
Detection
Lampe
femto
HaDe
Laser
Filter
Objective
Filter
Beam
splitter
Beam splitter
Dichroïc
mirror
Objective
Objective
Pressure
Measurement
Langmuir
trough
Langmuir
trough
Reflected Spectrum
at 90° incidence on
the surface
Sources :
Linear measurements :
HaDe lamp
Nonlinear measurements :
femtosecond laser
Langmuir
trough
Metallic Nanoparticles
capped C18
Linear reflectance
-Silver nanoparticles film-
Reflectance is the ratio
o Disappearance
ofspectrum
between reflection
of the film to the
fluctuations
forreference
high
reflection spectrum
density
2 consecutive measurements
for each compression
-3
-3
40x10
35
Réflectance
Réflectance
o Strong fluctuations of
reflectance
Surface density :
3, 4 and 7x1014 particles /m²
30
25
25
20
20
400
400
400
500
500
500
600
600
600
Longueurd'onde
d'onde/nm
/nm
Longueur
Longueur
d'onde
/nm
700
700
700
800
800
800
Linear reflectance
-Silver nanoparticles film-
Surface density:
3, 4 et 7x1014 particles /m²
The behaviour is easily
observed after normalised
of the reflectance
spectra
1.8
Reflectance normalisée
o Maximum reflectance
Amplitude increases at
660 nm with compression
2.0
1.6
1.4
1.2
1.0
300
400
500
600
Longueur d'onde /nm
700
800
Linear reflectance modelling
-Silver nanoparticles film-
Simulations
Simulations
withwith
hypothesis
hypothesis
of nonof
particles
aggregated
particles
aggregate
Surface density : 9x1014 particles /m²
2.0
2.0
2.0
Broaden
=
heterogeneous
1.8
1.8
1.8
set
of ellipsoid
Effective film
theory
for spherical
particles
2.0
2.0
2.0
1.8
1.8
1.8
Réflectance
Réflectance exp
exp
Isolated particles
(weak surface
Particles in strong
fraction )
interaction equivalent to an
ellipsoid (model)
High surface fraction
1.6
1.6
1.6
1.4
1.4
1.4
1.4
1.4
1.4
1.2
1.2
1.2
Effective film
theory for ellipsoidal
particles
1.0
1.0
1.0
400
400
400
50 nm
Réflectance theo
1.6
1.6
1.6
500
500
500
600
600
Longueur d'onde
d'onde /nm
/nm
Longueur
700
700
1.2
1.2
1.2
1.0
1.0
1.0
800
800
2nd resonance shows the beginning of interactions
Conclusions
-Silver nanoparticles filmDiluted system (surface filling factor = 3%)
Long alcane Chains C18
Expect : No aggregation
No interaction
Strong fluctuations at weak compression which disappear at high density
Prove : Inhomogeneous surface, existence of domains
Domains movements frozen
2nd plasmon resonance increases
Prove : Interactions appear upon compression
Compression
Modification of
for the particles

SHG

SHG of particles films
-Gold nanoparticles film0.12
420 nm
/ua
0.08
Signal bruit
0.10
0.06
25
20
15
10
0.02
5
0
0
50
100
150
200
temps
380
390
400
longueure d'onde
410
420
signal
/ua
25
Few sharp picks
20
0.06
15
0.04
10
0.02
5
0.00
0
0
50
100
150
temps
200
/s
250
300
/ mN/m
0.0
30
400 nm
0.10
Signal SHG
0.1
/s
pression de surface
Measured SHG
300
0.12
0.08
0.2
250
Compression
0.4
Measured
noise
/ mN/m
0.04
0.00
0.3
Pression de surface
o Continuous compression
o Density: 2 to 11x1014 particles/m²
30
Non linear signal
-Gold nanoparticles film-
0.12
30
/ua
25
20
0.06
15
0.04
10
0.02
5
0.00
0
0
50
100
150
temps
200
250
300
/s
Intensity histograms
Log normal fit
/ mN/m
Signal SHG
0.08
pression de surface
6 temporal domains
0.10
For each average
density:
o
o
I
I
Nonlinear signal
-Gold nanoparticles film-3
I SHG  G 
35x10
I  N2
Signal SHG moyen
/ua
30
20
( I )2
15
10
0
0.0
60x10
/u.a.
2
 0  ( 2)  N  ( 2)
25
5
Largeur de la distribution
 2
0.5
1.0
1.5
2.0
-22.5
densité moyenne de particule /m
3.0
15
3.5x10
II N
N 



II
N

N
-3
50
 Necessity to introduce the tensor
 . It proves the presence of
interactions between particles
40
30
20
10
0
5
10
15
Intensité moyenne
 Density variation
N
N
1

N
N
I
But
do not decrease
I
20
/u.a.
25
30x10
-3
Conclusion
-Silver nanoparticles filmDiluted system (surface filling factor = 3%)
Long alkane Chains C18
Expect: No aggregation
No interaction
 Necessity to introduce the element  (2) at high compression
Prove: Existence of interactions in compressed film
 Link with the increase of the second resonance plasmon concerning
reflectance measurements
Recurrence of these fluctuations phenomenon
 Reflectance
 SHG
Signal Fluctuations
To extract quantitative information from this
systematic observation
 Analysis using autocorrelation calculation
Autocorrelation function
SHG signal intensity
1600
1.8
1.8
1.8
1.7
1.7
1.7
1200
1.6
1.6
1.6
1000
gg ((t t) )
Intensité SHG
/u.a.
1400
800
600
1.5
1.5
1.5
1.4
1.4
1.4
400
1.3
1.3
1.3
200
0
1000
2000
3000
4000
Temps /s
5000
6000
hydrophilic silver Nanoparticles
Ø 7 nm
7000
0.001
0.001
0.001
2 distinct
characteristic
times
0.01
0.01
0.01
0.1
0.1
0.1 temps
temps
temps
111
/s
/s
/s
10
10
10
100
100
100
Autocorrelation calculation
Signal memory measurement
between t et t + 
Two characteristic values:
Function at the origin
g(0)
Decorrelation characteristic
C
time
g( ) 
I( t  )I( t )
I
2
Reflectance fluctuation all along compression
-Silver nanoparticles film-
Signal intensity
3
100x10
3
100x10
3
3
140x10
100x10
3
Density
Autocorrelation function
1.6
14:part/m²
4.4x1014 part/m²
: Density
3.2x10
part/m²
1.7x1014
100x10
1.5
90
1.4
1.4
80
80
80
100
Autocorrelation
Autocorrelation
Autocorrelation
Autocorrelation
Intensité
/cps
Intensité/cps
/cps
Intensité
Intensité
/cps
120
80
70
60
60
80
60
60
1.3
1.3
c = 40 seconds
1.2
1.2
1.2
60
40
50
40
40
40
Density: :5.3x10
8x101414 part/m²
Density
40
0000
c >> 100 seconds
1.1
1.1
1.1
20
20
20
20
20
40
40
40
40
40
6060
60
60
60
8080
80
80
temps
/s
temps
/s
temps/s/s
100
100
100
100
second
c c = =62 1seconds
1.0
1.0
1.0
-6
-6
-6
10
-6
10
10
10
-5
-5
-5
10
-5
-5
10
10
10
-4
-4
-4
10
-4
-4
10
10
10
10
-3
-3
-3
10
-3
-3
10
10
10
10
-2
-2
-2
10
-2
-2
10
10
10
10
temps
temps
/s/s
temps/s
-1
-1
-1
10
-1-1
10
10
10
10
Linear signal study
Silver
nanoparticles
 Characteristic
fluctuation time increases
Ø7
nmg(0) value decreases
capped C12
0
00
10
00
10
10
10
10
1
11
10
11
10
10
10
10
2
22
10
22
10
10
10
10
Evolution of the parameter g(0)
1.6
autocorrelation à tau=0 eau pure
autocorrelation à tau=0 film Ag
g(0) decreases
1.5
/ AU
1.3
g(o)
1.4
1.2
1
g(0) 
N
1.1
g(0)
1.0
20
30
40
50
surface
60
/ cm²
70
Compression
80
90
Density of particles
aggregates increases
under the laser spot
Evolution of the parameter 
10
tau
/s
10
10
10
10
10
c
5
4
Characteristic time
increases
 Frozen movements
on the surface for
high density
3
2
1
0
20
30
40
50
surface
60
/ cm²
70
Compression
80
90
Agreggate size evolution
from nm to µm
Autocorrelation curve fitting
-Silver nanoparticles film-
Checked : No disregard waves
Autocorrelation function
2
Brownian diffusion
g( )  1 
Spot light
Seff
1
dom
Domain
1
eff

1
D
e
  
1
 
 e  1 
D
1.5
Lateral flow
vi
Autocorrelation
1.4
1.3
1.2
1.1
Autocorrelation
function from a
silver
nanoparticles film
density 2x1014
part/m²
1.0
0.001
0.01
0.1
1
temps /s
10
100
Conclusions
-Nanoparticles films-
Compression
Compression
Some interactions between particles appear when the
surface is compressed :
 Linear reflectance
 SHG
Possibility to measure the dynamics of the film :
 Presence of moving nanoparticules domains
 Dynamic evolution during compression
General Conclusions
o Bi-dimensional Langmuir films studies:
Control the distance between nano-objects
Modulate the interactions between nanoobjects
nano-objects
without interaction
2D system
with interaction
o Molecular films upon compression:
Molecular aggregates arrangement
Presence of chirality in aggregates
Evidence of electronic delocalisation in aggregates
o Metallic nanoparticles films:
Beginning of interactions upon compression
Observation of the film dynamics
Have a look to my PhD group …
Thank you every one ! !
Pierre-François Brevet, Emmanuel Benichou, Guillaume Bachelier,
Isabelle Russier-Antoine, Christian Jonin,
Guillaume Revillod, Chawki Awada, Yara El Harfouch, Julien Duboisset, Lin Pu