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1
GRAZING INCIDENCE SMALL ANGLE X-RAY
SCATTERING (GISAXS) AS A TOOL FOR
CHARACTERIZATION AND OPTIMIZATION OF
POLYMER NANOSTRUCTURES
I. Martín-Fabiani1, E. Rebollar2, D.R. Rueda1, M.C. García-Gutiérrez1, S.
Pérez2, M. Castillejo2 and T.A. Ezquerra1
1 Instituto de Estructura de la Materia, IEM-CSIC, Madrid, Spain2 Instituto de Química Física Rocasolano, IQFR-CSIC, Madrid, Spain
Motivation
2
𝐿 =𝜆
𝑛 − 𝑠𝑒𝑛𝜃• Interference between incident and
reflected light generates ripples with
period L~λ
• It involves a feedback effect and thus
pulse repetition
Flexibility
POLYMERS
LIPSS Laser Induced Periodic Surface Structures
• High molecular weight (more
than 1000 atoms and up to
millions)
• Carbon-based
• Glass transition temperature (Tg)
Low cost
Durability
Light weight
GISAXS Grazing Incidence Small-Angle X-Ray Scattering
• Powerful synchrotron tool to characterize nanostructures
• 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
(LET´S SEE!!!)
3
Sample preparation
1 .Spin coating of polymer thin films on Si wafers
PTT
PC
PET2 . Repetitive laser irradiation
Nd:YAG laser in normal incidence
4th armonic (266 nm)
τ = 6ns ; f = 10 Hz
𝐿 =𝜆
𝑛 − 𝑠𝑒𝑛𝜃=
𝜆
𝑛
L close to laser wavelength
Rebollar, E.; Perez, S.; Hernandez, J. J.; Martin-Fabiani, I.; Rueda, D. R.; Ezquerra, T. A.; Castillejo, M., Langmuir 2011, 27, 5596-5606.
Atomic Force Microscopy
(tapping mode)
Fluence dependence
(Energy of a single pulse over a
determined area integrated over time,
mJ/cm2)
Number of pulses dependence
Good absorbance
in the UV range!
3 . Characterization in real space
PTT/TFA solution 20 g/l150 nm thick
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)
Characterization in real space: Atomic Force Microscopy
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 dependance of morphology with laser parameters
Is it possible to optimize
LIPSS formation with laser
parameters?
Grazing Incidence Small Angle X-ray Scattering (GISAXS)
5
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
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
GISAXS modelling
6
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)
Characterization in reciprocal space: number of pulses dependence
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
8
Characterization in reciprocal space: number of pulses dependence
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
9 mJ/cm2
13 mJ/cm2
9 mJ/cm2
13 mJ/cm2
Characterization in reciprocal space: fluence dependence
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
10
Characterization in reciprocal space: fluence dependence
• Structural order of LIPSS improves with increasing fluency!
• GISAXS and AFM information are in agreement and complement each other
11
LIPSS formation using ultrashort (femtosecond) pulses
LIPSS induced by femtosecond (fs = 10 -15) pulses in polymers
- scarcely reported in the literature
- formation mechanisms different
from the ns regime
Ti : sapphire laser in normal incidence
4th harmonic (λ = 265 nm)
τ = 120 fs ; f = 1 Hz
1.1 mJ/cm2 1.3 mJ/cm2 1.6 mJ/cm2
Dependence with fluence for a fixed number of pulses (5000)
Rebollar, E.; de Aldana, J. R. V.; Perez-Hernandez, J. A.; Ezquerra, T. A.; Moreno, P.; Castillejo, M., Appl. Phys. Lett. 2012, 100
• Period close to the wavelength
• Height increases with fluency
• There is a strong dependance of morphology with laser parameters
1.51 mJ/cm2
1.65 mJ/cm2
1.51 mJ/cm2
1.39 mJ/cm2
LIPSS formation using ultrashort (femtosecond) pulses
Rebollar, E.; Vazquez de Aldana, J. R.; Martin-Fabiani, I.; Hernandez, M.; Rueda, D. R.; Ezquerra, T. A.; Domingo, C.; Moreno, P.; Castillejo, M., Phys. Chem. Chem. Phys. 2013, 15 (27), 11287-11298
Dependence with fluence for a fixed number of pulses (5000)
-0.3 0.0 0.3
Experimental
Modelado
I/I 0
Cut at α = 0.2⁰ 1.65 mJ/cm2
-0.3 0.0 0.3
Experimental
Modelado
I/I 0
1.39 mJ/cm2
-0.3 0.0 0.3
Experimental
Modelado
I/I 0
LIPSS generated by ns laser
pulses can be described as
paracrystalline 1D lattices
Optimum value of fluency for a
fixed frequency!
JIP 2013
, 26-30 Mayo, 2013 13
Conclusions
• LIPSS on polymer thin films have been fabricated
by irradiation with nano and femtosecond laser
pulses varying laser parameters: fluence and
number of pulses
• Morphological characterization (AFM) is in
agreement with the structural characterization
(GISAXS) , and both techniques complement
each other
• The as-fabricated structures can be considered 1D
paracrystalline lattices
• It is possible to correlate the degree of structural
order of the patterned samples with the
irradiation parameters and achieve control over
formation of these nanostructures.
CONCLUSIONS