1
FABRICATING POLYMER NANOSTRUCTURES
WITH CONTROLLED MORPHOLOGY:
DIFFERENT TOP-DOWN APPROACHES
Ignacio Martín-Fabiani
Instituto de Estructura de la Materia, IEM-CSIC, Madrid, Spain
Motivation
POLYMERS
• High molecular weight (more than 1000 atoms and
up to millions)
• Carbon-based
• Unique internal structure: amorphous and crystalline
phases coexist
FlexibilityLow cost
Durability Light weight
Functionality
2
Natural
Synthetic
~ 10-5 - 10-6 m
Spherulites
~ 10-8 m
Crystalline lamellae
~ 10-9 m
Unit cell
• Glass transition temperature (Tg)
Motivation
POLYMERS
NANOSTRUCTURATION
• Laser Induced Periodic Surface Structures (LIPSS)
• Nanoimprint Lithography (NIL)
• Imprinting of Optical Near Fields (ONFs)
• Melt Wetting of Nanoporous Templates
APPLICATIONS
Flexibility
Low cost DurabilityLight weight
Functionality
Photovoltaics
Electronics
Photonics
• Feasibility of nanostructuration methods in polymers
• Appropiate characterization techniques
• Optimization of the process/nanostructures
• Understanding of the physics that lie underneath
Plasmonics
LET´S GO!
Preparation and characterization of polymer thin films
𝜔a 𝜔a
PTT
PC
PET
Spin coating of a PTT/TFA solution (20 g/l)
on a Si substrate
10 x 10 μm2 5 x 5 μm2
Atomic Force Microscopy (tapping mode) Absorbance
Good absorbance only in the near UV range
190 nm < λ < 400 nmRugosity 1,1 ± 0,5 nm
Film thickness 147 ± 25 nm
Preparation and characterization of polymer thin films
Tg = 44ºC ; Tm = 232 ºC
Laser Induced Periodic Surface Structures (LIPSS)
5
Laser light 𝜃
Original surface
LIPSS
𝑛
𝐿
𝐻
• Interference between incident and reflected
light generates ripples with period L~λ
• It involves a feedback effect and thus pulse
repetition
• Rugosity plays a relevant role
• Can we assess the structural order of LIPSS on polymer films?
• Is it possible to optimize LIPSS formation with laser parameters?
Bolle, M.; Lazare, S., Appl. Surf. Sci. 1993, 69 (1-4), 31-37 Csete, M.; Bor, Z., Appl. Surf. Sci. 1998, 133 (1-2), 5-16
𝐿 =𝜆
𝑛 − 𝑠𝑒𝑛𝜃
Nd:YAG laser (λ = 266 nm)
Linearly polarized
τ = 6ns ; f = 10 Hz
Nnormal incidence (θ = 0⁰)
𝐿 =𝜆
𝑛 − 𝑠𝑒𝑛𝜃=
𝜆
𝑛
Fluence dependence
(Energy of a single pulse over a
determined area integrated over time,
mJ/cm2)
Number of pulses dependence
Laser Induced Periodic Surface Structures (LIPSS)
Irradiation of polymer thin films
Open questions
Characterization
AFM in tapping mode
100 300 1200 6000
4 mJ/cm2 9 mJ/cm213 mJ/cm25 mJ/cm2
Dependence with number of pulses for a fixed fluence F = 7 mJ/cm2
Dependence with fluence for a fixed number of pulses (600)
Martin-Fabiani, I.; Rebollar, E.; Perez, S.; Rueda, D. R.; Garcia-Gutierrez, M. C.; Szymczyk, A.; Roslaniec, Z.; Castillejo, M.; Ezquerra, T. A., Langmuir 2012, 28 (20), 7938-7945.
• Period close to the wavelength
• Height increases with number of pulses
• There is a strong dependence of morphology with laser parameters
Is it possible to optimize
LIPSS formation with laser
parameters?
Laser Induced Periodic Surface Structures (LIPSS)
7
Grazing Incidence Small Angle X-ray Scattering (GISAXS)
Correlations parallel to the
sample plane
𝑞𝑧 =2𝜋
𝜆𝑠𝑒𝑛𝛼𝑖 + 𝑠𝑒𝑛𝛼
𝑞𝑦 =2𝜋
𝜆𝑠𝑒𝑛𝜔𝑐𝑜𝑠𝛼
Correlations perpendicular to
the sample plane
• Allows characterizing submicrometric
films
• Reflection geometry is extremely
sensitive to surface features
• By changing the incidence angles
different depths within the sample can
be probed
• Powerful tool to characterize
nanostructures
DESY, Hamburg (Germany)
BW4 beamline (Doris ring)
λ = 0.14 nm
MARR CCD pixel size 79.1 x 79,1 µm2
αi ≈ 0.4⁰
Muller-Buschbaum, P., Analytical and Bioanalytical Chemistry 2003, 376 (1), 3-10
Detector
Sample
αi
αi
ω
αf
Incident beam
hh’ α=0
qy
qz
m
m’ ω=0
Grazing Incidence Small Angle X-Ray Scattering
8
LL+ΔL1 L
L-ΔL2
• The probability of finding the next
box at a distance L is determined
by a Gaussian function
𝑝 𝑥 =1
𝜎 2𝜋𝑒𝑥𝑝 −
(𝑥 − 𝐿)2
2𝜎2
Hosemann, R., Zeitschrift Fur Physik 1950, 128, 465-492 Lazzari, R., Journal of Applied Crystallography 2002, 35, 406-421
Paracrystalline lattice
IsGISAXS software – Freeware
http://ln-www.insp.upmc.fr/axe4/Oxydes/IsGISAXS/isgisaxs.htm
• Central geometrical parameters
determined by AFM, assuming
a variation
𝜎𝑅
𝑅~
𝜎𝐻
𝐻~0.1
𝑔 = 𝜎/𝐿
• Paracrystalline distortion parameter
𝑔 = 0 Crystalline lattice
𝑔 → ∞ Disordered system
Local monodisperse aproximation (LMA) (monodisperse domains that interfere incoherently
between them)
𝑑Σ
𝑑Ω 𝑞 =< 𝐹 2> 𝑆 𝑞 α 𝐼𝑠𝑐𝑎𝑡𝑡𝑒𝑟𝑒𝑑
Distorted Wave Born Approximation (DWBA)(4 contributions to the form factor)
GISAXS modeling of nanostructures
Dependence with number of pulses for a fixed fluence F = 7 mJ/cm2
AFM
100
Modelling
300
6000
300
6000
100
GISAXS
100
300
6000
Cut at α = 0.2 ⁰
Laser Induced Periodic Surface Structures (LIPSS)
10
Optimum
LIPSS formation
𝑔 = 𝜎/𝐿
Paracrystalline distortion
parameter
𝑔 = 0 Crystalline lattice
𝑔 → ∞ Disordered system
• LIPSS generated by ns laser pulses can be described as paracrystalline 1D lattices
• Optimum value of the number of pulses for a fixed frequency!
• GISAXS and AFM information are in agreement and complement each other
Laser Induced Periodic Surface Structures (LIPSS)
9 mJ/cm2
13 mJ/cm2
9 mJ/cm2
13 mJ/cm2
AFM
5 mJ/cm2
GISAXS
5 mJ/cm2
Modelling
5 mJ/cm2
9 mJ/cm2
13 mJ/cm2
Dependence with fluence for a fixed number of pulses (600)
Cut at α = 0.2 ⁰
Laser Induced Periodic Surface Structures (LIPSS)
12
• Structural order of LIPSS improves with increasing fluency!
• GISAXS and AFM information are in agreement and complement each other
Laser Induced Periodic Surface Structures (LIPSS)
13
Laser Induced Periodic Surface Structures (LIPSS)
Formation mechanism𝜕2𝑇(𝑥, 𝑡)
𝜕𝑥2− 𝑎2
𝜕𝑇 𝑥, 𝑡
𝜕𝑥=
𝛼
𝜅𝑃 𝑡 exp −αx 𝐹0
Rebollar, E.; Perez, S.; Hernandez, J. J.; Martin-Fabiani, I. et al. Langmuir 2011, 27, 5596-5606.
Solving numerically the heat equation in one dimension:
The Raman spectra of irradiation samples remain
unaffected except for a slight oxidation in the case
of high number of pulses
• The maximum temperatures reached on the
surface of the polymer film are around 87 -
203 ⁰C.
• These temperatures are well above Tg and
below Tm, suggesting that a reorganization
of material takes place in the formation of
LIPSS (no ablation).
14
Laser Induced Periodic Surface Structures (LIPSS)
Au-coated polymer LIPSS as Surface-Enhanced
Raman Scattering (SERS) substrates
Rebollar, E. et al. Phys. Chem. Chem. Phys. 2012, 14, 15699-15705.
Thinner Au coatings yield higher
enhancements
Linear relationship between analyte
concentration and Raman intensity
PTT LIPSS Au-coated LIPSS
Pulsed Laser Deposition
Nd:YAG laser
λ = 213 nm; τ = 15 ns
Ν = 10 Hz
The presence of metallic nanoparticles can
enhance dramatically the Raman intensity
A SERS enhancement of an
order of magnitude is obtained
• These hybrid substrates require a small
amount of gold
• They benefit from the light weight,
flexibility and durability of polymeric
materials
• The linear relationship of the Raman
intensity with analyte concentration is
advantageous for potential application
in sensors
Nanoimprint Lithography (NIL)
15
PressNanoimprint Lithography (NIL)
• Lithographic process which involves the
transfer of nanometric motifs from a hard
mold to a soft substrate
• Requires the use of white rooms
• The transfer is optimized when motifs in
the mold are protruding from the
substrate.
Wet etchingOptic Lithography
16
Fabricación del molde I: mesa
Si wafer
UV light
Resist
Mask
HNO3
HF
H2O
Nanoimprint Lithography (NIL)
Fabrication of a mesa-type structure
17
Fabricación del molde I: mesa
Wafer
Resist
Nanoimprint Lithography (NIL)
Fabrication of a mesa-type structure
AFM
Height ≈ 650 nm
(2) e-beam lithography
(4) Removal of
redundant resist
and metal
(3) Development
+ Metalization
PMMA
Si
(1) spin- coating
e-e-
SF6C4F8 O2
(5) Reactive Ion Etching (6) Mold
300 nm
300 nm
Nanoimprint Lithography (NIL)
Fabrication of motifs on the mesa structure
Nanoimprint Lithography (NIL)
Silanization process: Avoids sticking of the polymer
to the Si mold
TFOCS
60nm
200 x 200 µm2
Mesa
Si mold
• GISAXS arc-like pattern
• Radius depends on αi
• Spacing 300 nm
LET´S IMPRINT!
300 nm
SEM AFM
60 nm100 nm
Qin, D.; Xia, Y. N.; Whitesides, G. M. Nat. Protoc. 2010, 5, 491-502.
20
Nanoimprint Lithography (NIL)
Polymer replicaSi mold
52 nm300 nm
60 nm
150 ºC 40 bar
5 minC
• Scattered intensity in the vertical direction
300 nm
60 nm100 nm
150 ºC 40 bar
5 minC
• AFM images shows regions where the effective
length of the motifs is reduced
Nanoimprint Lithography (NIL)
(⁰)
(⁰)
(⁰)
(⁰) (⁰)
(⁰)
(⁰)
(⁰)
ModelingGISAXSAFM
200 μm
150 μm
1 μm(⁰)
(⁰)(⁰)
(⁰)
LIPSS
Polymer replica
Si mold
Effective length of
the motifs decreases
22
Nanoimprint Lithography (NIL)
W/R = 1000
W/R = 100
W/R = 10
(⁰)
(⁰)
(⁰)
(⁰)
(⁰) (⁰)
(⁰)
(⁰)(⁰)
(⁰)
(⁰)
(⁰)
(⁰)
(⁰)
(⁰)
Rueda, D. R.; Martin-Fabiani, I.; Soccio, M. et al. J. Appl. Crystallogr. 2012, 45, 1038-1045.
Form FactorGISAXS Interference function
The transition from an arc-like pattern, characteristic of polymer
grating replicas fabricated by NIL, to a fringe pattern,
characteristic of LIPSS, is determined by a reduction of the
effective length of the motifs
Cut at ω = 0 ⁰
Imprinting the Optical Field dispersed by a dielectric microsphere
Nanostructuring with Optical Near Fields (ONFs)
pfw
b
sin1fwpa
pbw
sin1bwpr
θ
Shadow region
Far field approximation
• CD and DVD optical systems
(phase change memories)
• Microscopy (SNOM)
• Sensors
• Materials processing
Vicinity of the sphere
Period in the
backward direction Period in the
forward direction
Optical Near Fields
allow to overcome the
diffraction limit
(≈ λ/2)
Kuehler, P. et al. Small 2009, 5, 1825-1829.
Carried out in several inorganic materials:
silicon, amorphous silica, aluminium oxide,
Ge2Sb2Te5…
Never in
polymers!
It is possible to visualize
or imprint structures with
resolution of λ/2 or
smaller
Applications
Laser light
θLaser light
Ablation hole The sphere can be considered a point scatterer
100 µm
Nanostructuring with Optical Near Fields (ONFs)
1. Sample preparation: spin-coating of SiO2 microspheres (ϕ = 4.6 µm) on PTT
polymeric thin films
2. Irradiation: single pulse from an excimer laser ArF at normal incidence (θ = 0⁰) or
θ = 54⁰. Fluences around 300-350 mJ/cm
3. Characterization of the irradiated zone
θ = 0⁰, F=300mJ/cm2
OM AFM
Dendritic morphology!
GIWAXS Raman Spectroscopy
Crystallinity hints?
Increased fluorescence
Might be related to parallel
arrangement of phenyl
rings in PTT
Some incipient
shoulders
corresponding to
Bragg peaks
appear
Luo, W.-a. et al. Macromolecules 2008, 41, 7513-7518.
150x150 µm2 10x10 µm2
θ = 54⁰, F = 350 mJ/cm2
100 µm
107 nm
Asymptotical
value in the
far field
sin1bwp
Nanostructuring with Optical Near Fields (ONFs)
• Near-field induced topography modulation
extends over the entire film thickness.
• Regions of local fluence enhancement
correspond to topographic regions below the
initial film surface
• Values of the period tend to reach the
asymptotical value predicted in the far field
25 x 25 μm2
L1L2
25 x 25 μm2
Zoom in the
backscattering
region
Nanostructuring with Optical Near Fields (ONFs)
10 nm
0 nm
10 nm
0 nm
Formation mechanism: patterning of GST single pulse from an excimer laser ArF
Fluences around 75 mJ/cm2
Topographic contrast originates from the
different density of both phases, the amorphous
one being lower yielding to an elevation of the
amorphous regions over the crystalline film (no
ablation)
θ = 54⁰, F = 75 mJ/cm2
Raman spectroscopy
Siegel, J. et al. Appl. Phys. 2008, 023516.1-7
Under these irradiation conditions PTT
presents chemical stability
Melt wetting of nanoporous AAO membranes
27
Zhang, M. F.; Dobriyal, P.; Chen, J. T.;
Russell, T. P.; Olmo, J.; Merry, A. Nano Lett.
2006, 6, 1075-1079.
Garcia-Gutierrez, M.-C.; Linares, A.; Hernandez,
J. J.; Rueda, D. R.; Ezquerra, T. A.; Poza, P.;
Davies, R. J. Nano Lett. 2010, 10, 1472-1476.0
1D confinement
Length scales imposed
by external geometry
Length scales imposed by
internalcooperativity
Competition
• Electrospinning
• Self-assembly
• Nanoporous templates
2D confinement
• Crystalline unit cell
• Chain folding
• Size of crystalline lamellae
• Pore diameter
• Pore depth
• Pore density
Versus
Bulk
Restricting dimensions
Under these conditions interesting effects may arise!
Shin, K.; Xiang, H. Q.; Moon, S. I.; Kim, T.;
McCarthy, T. J.; Russell, T. P. Science 2004, 306, 76-76.
28
500 nm
Disordered
AAO membranes
500 nm
TOP – Pore size ~ 20 nm
BOTTOM – Pore size ~ 200 nm
0
N2
PTT
/nanocomposite
film
(200 µm thick)
AAO membrane
Melt wetting
1h at 253 ºC
Semicrystalline
nanorods
Cooling @ 3ºC/min
Solving AAO in NaOH
Are you sure they are crystalline?
Are they oriented?Let´s check it!
Poly (trimethylene terephthalate)
(PTT)
Tg = 44ºC ; Tm = 232 ºC
PTT/SWCNTs nanocomposite (0.5 % weight
concentration)
Prepared by in-situ polimerization
SWCNTs: diameter 0.6 – 1.4 nm
Melt wetting of nanoporous AAO membranes
X-Ray Microdiffraction setup
29
ESRF (Grenoble)ID13 Microfocus beamline
λ = 0,09951 nm
1 µm beam diameter
FReLoN detector
Transmission geometry
Scan
direction
Residualfilm
Infiltrated AAO
template
Interface
XBeam orthogonal to the
slide plane
Step scan (1 µm resolution)
We record a 2D diffraction pattern
each single micrometer containing
WAXS and SAXS information
WAXS
SAXS
• Crystallographic
planes
• Orientation
• Orientation of
crystalline
lamellae
• Long spacing
Bulk
002
010
01210201-2
Wide Angle X-Ray Scattering (WAXS)
30
Main nanopore axis
Bulk
002
01001-2012
102
Inside AAO
01001-2
012102
0kl reflections concentrated in the meridian
in both infiltrated PTT and nanocomposite!!
Triclinic unit cella=0.46nm ; b=0.61 nm ; c
=1.86 nm ; α=97.5º ; β=92.1º ;
γ =110º
Wang, B. J et al.
Polymer 2001, 42, 7171-
7180.
a
c
b
PTT
PTT/SWCNTsInside AAO
01001-2
012102
a-axis lies in the equator, b and
c can rotate
ac
b
a-axis is the radial
growth direction for
PTT spherulites!
Ho, R. M. et al.
Macromolecules
2000, 33, 7529-
7537.
Steinhart, M. et al.. Phys. Rev. Lett. 2006, 97.
Kinetic selection
Wide Angle X-Ray Scattering (WAXS)
31
Bulk Interface Inside AAOFull Width at Half
Maximum of the 102
reflection
102
Azimutal integration
Crystalline orientation
• Orientation improves with pore depth!
• Template has been filled completely
Increase of intensity related to:
• Augmented amount of
material
• Increase in orientation
AAO vs SWCNTs
32
Do the SWCNTs
enter the pores?
Yes, they do!
Ma, Y.; Hu, W. B.; Hobbs, J.; Reiter, G. Soft Matter 2008, 4, 540-543
Slippery walls
Sticky walls
Obtained
ac
b
Expected : Shish – Kebab?
SWCNT
Main polymer chain paralell to
the AAO wall (edge-on)
Main polymer chain orthogonal
to the AAO wall (flat-on)
Polymer melts – Low surface energy
AAO – High surface energy
The formation of flat-on lamellae is
favored by the strong polymer-AAO
interaction
This interaction, toguether with the
kinteic selection, prevails over the
templating features of the SWCNTs
Small Angle X-Ray Scattering (SAXS)
33
Main nanopore axis
PTT
PTT/
SWCNTs
Residual film Infiltrated AAO
Scan direction
Isotropic Edge-onEdge-on +
Flat-on No long spacing
No long spacing4-point
patterns
(shish-kebab)
Slight increase in flat-on
population
(SWCNTS alignment with
the pores)
70 µm away 25 µm away 5 µm away
Model for PTT
34
Edge-on/ flat-
on lamellae
WAXS
002
010
01-2
012 102
Bulk polymer Flow zone Interface
010
01-2 012 102
WAXS
ac
b
Confinement zone
IsotropicEdge-on
lamellae
SA
XS
Kinetic selection AAO-polymer interactionMartin-Fabiani, I. et al. ACS Applied Materials & Interfaces 2013, 5, 5324-5329.
Conclusions
35
Conclusions
• It has been proven that controlled nanostructuration of
polymeric materials can be achieved by using laser light
(LIPSS and imprinting of ONF), NIL and melt wetting of
nanoporous AAO membranes.
• It was demonstrated that nanosecond laser pulses can be used
in order to obtain LIPSS on polymer thin films. In addition, it
has been proven that the characterization of LIPPS in real
space by AFM can be complemented with the corresponding
characterization in the reciprocal space by GISAXS.
• It was shown that numerical modeling of the GISAXS
diagrams of LIPSS structures provides a description of them
in terms of one-dimensional paracrystalline lattice of
parallelepipeds. In addition to this, the study of the
dependence of the paracrystalline distortion parameter has
allowed determining the values of laser fluence and number
of pulses that optimize LIPSS formation.
• The potential of hybrid gold-polymer LIPSS as SERS
substrates has been proven.
Conclusions
36
Conclusions
• Hard silicon mold nanogratings have been imprinted on polymeric
thin films by NIL, fabricating successfully their replicas in the
polymer.
• Numerical modeling of the GISAXS diagrams has allowed
concluding that the transition from an arc-like pattern,
characteristic of polymer grating replicas fabricated by NIL, to a
fringe pattern, characteristic of LIPSS, is determined by a
reduction of the effective length of the motifs.
• The nanostructuration by imprinting of ONF has been applied
for the first time on a polymeric material. Structuration by ONF
takes place by polymer ablation and the nature of the laser used
determines the appearance of dendritic structures on the polymer
film surface.
• It has been proven that the one-dimensional confinement of
PTT in AAO nanopores induces the growth axis of the crystalline
lamellae to align with the main axis of the nanopores.
• The template effect of the SWCNTs in the crystallization process
of polymer nanocomposites is inhibited by the one-dimensional
confinement in AAO membranes.
Acknowledegements
37
Acknowledgements
Soft and Polymeric Matter group• T.A. Ezquerra
• A. Linares
Collaborators• E.Rebollar (IQFR-CSIC)
• J. Siegel (IO-CSIC)
• F. Pérez-Murano (
• J. Boneberg
38
Thanks for your attention!
Soft and Polymeric Matter grouphttp://www.iem.cfmac.csic.es/fmacro/softmatpol/