Nanostructures. Laser Induced Nanostructures on Polymeres. Tuesday, June 9, 2009

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1 Nanostructures Laser Induced Nanostructures on Polymeres 1

2 Which Polymers? PET PI PS 2

3 Polyethylene Terephtalate as Polyester in textiles as PET in bottles 3

4 Polyimide orange color eg. insulation in electronics 4

5 Polystyrene Yoghurt Cups Petri Dishes CD Cases 5

6 Controlled Microprocessing with Lasers Direct Writing Mask Projection 6 SNOM Interference Illustrations: Bäuerle, Laser Processing and Chemistry, Springer

7 Self Organized Nanostructure Formation Large area of constant illumination Nanosecond pulsed laser radiation polymers 7

8 Pulsed laser Laser Ablation Threshold Fluence 8 Graph: Bäuerle, Laser Processing and Chemistry, Springer

9 Structures Walls periodic, φ > φthr Naps periodic, φ > φthr Dendrites aperiodic, φ φthr Cones periodic, φ φthr Ripples periodic, φ < φthr 9

10 Walls and Naps Periodic structures φ > φthr Caused by mechanical stress Dependance on direction 10 Heitz et al; Femtosecond excimer-laser-induced structure formation on polymers; Applied Physics A 59

11 Walls and Naps PET foils are stretched in one or two directions. The polymere chains are frozen in place. Laser radiation heats the surface and allows the material to relax. Model: Cracks forming due to internal tension. 11 Heitz et al; Femtosecond excimer-laser-induced structure formation on polymers; Applied Physics A 59

12 Cones Periodic φ φthr Selective Etching Impurities shield laser radiation Krajnovich, Vazquez; Formation of intrinsic surface defects during 248nm photoablation of polyimide; Journal of Applied Physics 73 12

13 Cones Impurity at cone tip prevents ablation Effective Fluence along slope: φ = φ0 cos α Equilibrium when φ = φthr Many pulses necessary 13

14 Cones Krajnovich, Vazquez; Formation of intrinsic surface defects during 248nm photoablation of polyimide; Journal of Applied Physics 73 Example: Polyimide Cone shape influenced by atmosphere 14

15 Ripples Periodic φ < φthr Dimensions similar to laser wavelength Single beam interference Many Pulses Ripples on PET Foil; taken from Heitz et al; Femtosecond excimerlaser-induced structure formation on polymers; Applied Physics A 59 15

16 Ripples Scattering parallel to surface at existing protrusions Interference between incident wave and scattered wave At places of constructive interference, polymer chains break into smaller pieces and bulge 16

17 Ripples Example: Polystyrol after treatment with 6000 laser pulses periodicity: 40nm, 70nm, 80nm, 100nm Ripples on Polystyrol, 2x2µm AFM images; taken from Rebollar et al., Proliferation of aligned mammalian cells on laser-nanostructured polystyrene, Biomaterials 29 (2008) 17

18 Dendrites Aperiodic φ φthr Single Pulse Crystalline Heitz et al., Growth of excimer-laser-induced dendritic surface structures on polyethylene-terephtalate AFM 15x15µm, ~70nm high 18

19 Dendrites After Laser radiation, the sample surface becomes amorphous. During annealing, redeposited material and short polymer chains from the surface recrystalize Structures reach into the surface. Heitz et al., Growth of excimer-laser-induced dendritic surface structures on polyethylene-terephtalate AFM 15x15µm, ~70nm high 19

20 Applications? 20

21 Possible Applications Optical Gratings Modification of Surface Properties Opacity Adhesion Interaction with biological cells 21

22 Rebollar et al., Proliferation of aligned mammalian cells on lasernanostructured polystyrene, Biomaterials 29 (2008) Cell Alignment 22

23 Cell Alignment Rebollar et al., Proliferation of aligned mammalian cells on laser-nanostructured polystyrene, Biomaterials 29 (2008) Biological cells align along the ripple structure on PS. This occurs even though the structure is much smaller than the cells. 23

24 Sources D. Bäuerle; Laser Processing and Chemistry; Springer Heitz, Arenholz, Bäuerle, Sauerrey, Phillips; Femtosecond excimer-laser-induced structure formation on polymers; Applied Physics A 59 (1994) Heitz, Arenholz, Bäuerle, Schilcher; Growth of excimer-laser-induced dentritic structures on PET; Applied Surface Scienc 81 (1994) E. Rebollar, I. Frischauf, M. Olbrich, T. Peterbauer, S. Hering, J. Preiner, P. Hinterdorfer, C.Romanin, J. Heitz; Proliferation of aligned mammalian cells on laser-nanostructured polystyrene; Biomaterials 29 (2008) Structure formulas taken from Wikipedia 24