GRAZING INCIDENCE SMALL ANGLE X-RAY SCATTERING (GISAXS) AS A TOOL FOR CHARACTERIZATION AND OPTIMIZATION OF POLYMER NANOSTRUCTURES

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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-Fabiani 1, E. Rebollar 2, D.R. Rueda 1, M.C. García-Gutiérrez 1, S. Pérez 2, M. Castillejo 2 and T.A. Ezquerra 1 1 Instituto de Estructura de la Materia, IEM-CSIC, Madrid, Spain 2 Instituto de Química Física Rocasolano, IQFR-CSIC, Madrid, Spain 1

2 POLYMERS High molecular weight (more than 1000 atoms and up to millions) Carbon-based Glass transition temperature (T g ) Durability Motivation Low cost Flexibility Light weight LIPSS Laser Induced Periodic Surface Structures Interference between incident and reflected light generates ripples with period L~λ L = λ n senθ It involves a feedback effect and thus pulse repetition GISAXS Grazing Incidence Small-Angle X-Ray Scattering (LET S SEE!!!) 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), Csete, M.; Bor, Z., Appl. Surf. Sci. 1998, 133 (1-2),

3 Sample preparation 1.Spin coating of polymer thin films on Si wafers PTT/TFA solution 20 g/l 150 nm thick PC PTT 2. Repetitive laser irradiation PET Nd:YAG laser in normal incidence 4 th armonic (266 nm) τ = 6ns ; f = 10 Hz Good absorbance in the UV range! L = λ n senθ = λ n L close to laser wavelength 3. Characterization in real space Fluence dependence (Energy of a single pulse over a determined area integrated over time, mj/cm 2 ) Number of pulses dependence Atomic Force Microscopy (tapping mode) Rebollar, E.; Perez, S.; Hernandez, J. J.; Martin-Fabiani, I.; Rueda, D. R.; Ezquerra, T. A.; Castillejo, M., Langmuir 2011, 27,

4 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), Dependence with number of pulses for a fixed fluence F = 7 mj/cm Dependence with fluence for a fixed number of pulses (600) 4 mj/cm 2 5 mj/cm 2 9 mj/cm2 13 mj/cm 2 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?

5 Grazing Incidence Small Angle X-ray Scattering (GISAXS) Grazing Incidence Small Angle X-ray Scattering (GISAXS) Correlations perpendicular to the sample plane Allows characterizing submicrometric q z = 2π λ senα i + senα Correlations parallel to the sample plane q y = 2π λ senωcosα 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 µm 2 α i 0.4⁰ Muller-Buschbaum, P., Analytical and Bioanalytical Chemistry 2003, 376 (1),

6 GISAXS modelling Local monodisperse aproximation (LMA) (monodisperse domains that interfere incoherently between them) Distorted Wave Born Approximation (DWBA) (4 contributions to the form factor) dσ dω q =< F 2 > S q α Is cattered Central geometrical parameters determined by AFM, assuming a variation σ R R ~ σ H H ~0.1 The probability of finding the next box at a distance L is determined p x = 1 (x L)2 exp σ 2π 2σ 2 by a Gaussian function Paracrystalline lattice Paracrystalline distortion parameter L L+ΔL 1 L L-ΔL 2 IsGISAXS software Freeware g = σ/l g = 0 Crystalline lattice g Disordered system Hosemann, R., Zeitschrift Fur Physik 1950, 128, Lazzari, R., Journal of Applied Crystallography 2002, 35,

7 Characterization in reciprocal space: number of pulses dependence 100 AFM Dependence with number of pulses for a fixed fluence F = 7 mj/cm 2 GISAXS 100 Cut at α = 0.2 ⁰ Modelling

8 Characterization in reciprocal space: number of pulses dependence Paracrystalline distortion parameter g = σ/l g = 0 Crystalline lattice g Disordered system Optimum LIPSS formation 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 8

9 AFM 5 mj/cm 2 Characterization in reciprocal space: fluence dependence Dependence with fluence for a fixed number of pulses (600) GISAXS 5 mj/cm 2 Cut at α = 0.2 ⁰ Modelling 5 mj/cm 2 9 mj/cm 2 9 mj/cm 2 9 mj/cm 2 13 mj/cm 2 13 mj/cm 2 13 mj/cm 2

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 10

11 LIPSS formation using ultrashort (femtosecond) pulses LIPSS induced by femtosecond (fs = ) pulses in polymers Ti : sapphire laser in normal incidence 4 th harmonic (λ = 265 nm) τ = 120 fs ; f = 1 Hz Dependence with fluence for a fixed number of pulses (5000) - scarcely reported in the literature - formation mechanisms different from the ns regime 1.1 mj/cm mj/cm mj/cm 2 Period close to the wavelength Height increases with fluency There is a strong dependance of morphology with laser parameters Rebollar, E.; de Aldana, J. R. V.; Perez-Hernandez, J. A.; Ezquerra, T. A.; Moreno, P.; Castillejo, M., Appl. Phys. Lett. 2012, 10011

12 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), Dependence with fluence for a fixed number of pulses (5000) 1.65 mj/cm 2 Cut at α = 0.2⁰ 1.65 mj/cm 2 Experimental Modelado I/I mj/cm Experimental Modelado 1.51 mj/cm 2 I/I mj/cm 2 I/I Experimental Modelado 1.39 mj/cm 2 LIPSS generated by ns laser pulses can be described as paracrystalline 1D lattices Optimum value of fluency for a fixed frequency!

13 Conclusions 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. JIP 2013, Mayo,

14 Thanks for your attention! Soft and Polymeric Matter group JIP 2013, May,