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

JIP 2013

, 26-30 May, 2013 14

Thanks for your attention!

Soft and Polymeric Matter grouphttp://www.iem.cfmac.csic.es/fmacro/softmatpol/