LABORATOIRE DE PHYSIQUE DES LASERS Photonique Organique et Nanostructures Support de thèse : ANR OLD-TEA Direction de thèse : Alexis Fischer et Azzedine Boudrioua Encadrement : Mahmoud Chakaroun Assistance technologique Jeanne Solard Collaboration: Chii-Chang Chen,National Central University, Taiwan Investigation of photonic properties of self organized nanoparticles monolayers : application to photonic crystal cavities and patterned organic light emitting diodes Getachew T. AYENEW PhD defence : July 8th, 2014

Outline 1.Introduction ► Context ► State of the art ► Our approach 2.Photonic properties of monolayer of opals and inverse-opals ► Numerical study of photonic band gaps ► Numerical study of microcavities ► Experimental approach of characterizing monolayer of opals 3.Nanoparticle based 2D patterning of OLED ► 2D pattering of surfaces ► 2D patterning of OLEDs 4.Conclusion and perspectives 2

3 1D Vertical confinement Top downBottom up Small Mode volume High Q Extended cavity 1. Introduction Context :ANR OLD-TEA Axe 1 Organic Laser Diode : A Threshold-Less Experimental Approach Axe 2 2D lateral confinement Photonic CrystalOpals - Inverse Opals Low threshold organic diode laser 2D DFB lasers Light extraction in OLED Potential Applications

►Photonic properties of monolayer of nanoparticles and microcavities ►New patterning technique using nanoparticles 4 1. Introduction Objectives of the study Self-organized Nanoparticles Photonic crystalsOLED Nanostructuration Photonic crystal laser with defect microcavity 2D-DFB OLDLight extraction in OLED

►Photonic properties of monolayer of nanoparticles and microcavities ►Making nanostructures using nanoparticles 5 1. Introduction Objectives of the study Self-organized Nanoparticles Photonic crystalsOLED Nanostructuration Photonic crystal laser with defect microcavity 2D-DFB OLDLight extraction in OLED

6 State of the art Polymeric solid-state dye lasers resonator Shi et al. Appl. Phys. Lett. 98, (2011) Random lasing Dye doped photonic crystal Kim et al Chem. Mater., 2009, 21 (20), pp 4993–4999 Murai et al, Chemistry LettersVol. 39 (2010), No. 6 p.532 porous photonic film  enhanced stimulated emission  Lasing by randomly dispersing nanoparticles into a gain material multiple scattering highly-efficient low threshold laser Emission spectra of the resonator cavity below and above lasing threshold 2. Photonic properties of monolayer of opals and inverse-opals

► General objective ►Optimal design of planar photonic crystal using nanoparticles ? ►Microcavity ? ► Methodology ►Investigate numerically photonic band gaps in monolayer of dielectric spheres ►Investigate numerically quality factors of microcavities ►Experimental investigation of in-Plane propagation 7 glass General objective/Methodology 2. Photonic properties of monolayer of opals and inverse-opals

Opal without substrate Numerical studies Introduction Structures glass air 2r2r r glass a Inverse opal without substrate Opal with substrate Inverse opal with substrate r a a = period r = radius 2. Numerical study of photonic band gaps

Control parameters Rafractive index (n) for compact arrangement(r/a=0.5) 2. Numerical study of photonic band gaps 9 Refractive index (n) n of spheres in opals n of infiltrated material in inverse-opals Compactness of spheres, r/a ratio ( for n = 2.5, anatase TiO2) r/a=0.5, compact spheres r/a < 0.5 non- compact spheres r/a ratio determines the filling factor (ff) Filling factor Effective refractive index Unit cell

10 Parameters Rafractive index (n) for compact arrangement(r/a=0.5) ► Direction of propagation of the incident field with respect to the crystal ►  M ( TE, TM polarisations) ►  ( TE, TM polarisations) ►Symetries and rotation 2. Numerical study of photonic band gaps K MM KK

► Boundary conditions ►Perfectly matched layer (PML) ►Periodic Introduction to simulation Simulation condition ► 3D finite-difference time-domain(3D-FDTD) method 2. Numerical study of photonic band gaps Top view Cross section

►Photonic band gap►Gap maps 12 Photonic band gap(PBG) and construction of gap maps PBG n=3 n=2.1 PBG n=1.5 Photonic gapmap Transmission spectra n= Numerical study of photonic band gaps  M direction, TE polarization  direction, TE polarization (intersection) 'complete' bandgap

►Gap maps ► Different polarizations ►TE ►TM ► Different directions of propagation ►  M ►  K 13 Photonic band gap(PBG) and construction of gap maps 2. Numerical study of photonic band gaps

PBG 14 Inverse-opals without substrate Region for TE polarization r/a=0.5 TiO 2 (n=2.5) ►PBG exists for a wide range of refractive indices ►PBG exists for a wide range of compactnesses ►For n=2.5, Largest gap to mid-gap ratio for r/a=0.4, (TE) ΔfΔf f width of PBG = gap-mid-gap ratio= Δf/f 2. Numerical study of photonic band gaps n=2.5 r/a

►Opals without substrate exhibit PBGs for different compactness ►PBG appears narrower 15 n=2.5, TiO 2 Opals without substrate 2. Numerical study of photonic band gaps

►First conclusion- monolayer of inverse opal offers larger gap-to-midgap ratio 16 г M-TE Opal or inverse-opal ? 2. Numerical study of photonic band gaps OpalsInverse-Opals

►Losses to glass substrate ►No PBG for low ref. index materials ►Higher refractive index materials required 17 r/a=0.5 ►PBG observed with non-compact spheres ►Overlap of TE mode for non- compact spheres Substrate effect: inverse-opal with substrate 2. Numerical study of photonic band gaps TiO 2 (n=2.5) r/a

►Losses to glass substrate as r/a is lower ►More compact spheres favorable 18 n=2.5 Lossy region glass Substrate effect : opal with substrate 2. Numerical study of photonic band gaps

►Opals: as the spheres are more compact n eff increases  less loss ►Inverse opals: as the spheres are more compact n eff decreases  more loss 19 n=2.5 ►PBG observed when using non- compact spheres n=2.5 Substrate effect : effect of compactness on losses 2. Numerical study of photonic band gaps compact high n eff non-compact low n eff Less compact More losses compact low n eff non-compact high n eff More compact More losses larger filling factor smaller filling factor OpalsInverse-opals

20 ►PBG observed when using non- compact spheres Substrate effect : effect of compactness on losses 2. Numerical study of photonic band gaps Compact opals high n eff Non compact low n eff More losses compact low n eff Non compact Inverse -opal high n eff More losses

► General objective ►Optimal design of planar photonic crystal using nanoparticles ? ►Microcavity ? ► Methodology ►Investigate numerically photonic band gaps in monolayer of dielectric spheres ►Investigate numerically quality factors of microcavities ►Experimental investigation of in-Plane propagation 21 glass General objective/Methodology 2. Photonic properties of monolayer of opals and inverse-opals

► Investigation with respect to ►Various cavity geometries ►The r/a ratio ►with and without substrate (effect of the losses) 22 The Quality factor investigated with respect to: - with respect to the r/a ratio -the cavity type H1 L5 L3 H2 Microcavities ►Fixed refractive index n= 2.5 ►Defects in the periodicity monitor source 2. Numerical study of microcavities 22

►Without substrate: ►Cavity resonance in the PBG ►With substrate ►Significant resonant peaks observed for non-compact arrangement Microcavities in inverse-opals 2. Numerical study of microcavities 23

►Quality factor increases when r/a < 0.40 ►The presence of glass substrate reduces the quality factor ►The maximum of the Q-factor is obtained for 0.3 < r/a < Microcavities in inverse-opals with and without 2. Numerical study of microcavities

25 H2 Higher refractive index values needed in opals to achieve a resonance: (n~4 realistic?) ► The inverse-opal arrangement is more favorable to microcavities Higher refractive index of dielectric spheres needed in opals to have a resonance With the presence of glass substrate, the refractive index of the spheres needed is not feasible with available materials Microcavities in opals 2. Numerical study of microcavities n=4 n=3.2

► General objective ►Optimal design of planar photonic crystal using nanoparticles ? ►Microcavity ? ► Methodology ►Investigate numerically photonic band gaps in monolayer of dielectric spheres ►Investigate numerically quality factors of microcavities ►Experimental investigation of in-Plane propagation 26 glass General objective/Methodology 2. Photonic properties of monolayer of opals and inverse-opals

► Objectives ►Measure of the In-Plane transmission spectra as a function of ►Polarization (TE, TM) ►Crystal direction (  M,  K) ► Problem ►Arrangement of spheres – presence of multiple domains ►Several directions are probed at the same time ► Method ►Fabrication of a single domain monolayers ? ►Characterization of single domain ? 27 In plane transmission spectra characterisation of Monolayer dielectric spheres in optical regime  Problems Many crystal domains in self assembled monolayer of spheres Nanoparticles too small to be manipulated 2. Towards experimental study of in-plane propagation in opal monolayers Problem and method transmitted Direction of propagation

Light ΓMΓM ΓK Reference waveguide nanoparticles micro- hexagon ►Single domain fabrication ► Fabrication of micro-hexagons ►force nanoparticles organizaton in ordered manner ►Orientation of hexagons to fixe the direction of propagation ►Dimension calculated for given nanoparticle diameter ►Single domain characterization ► Waveguides Polymer waveguide on a glass substrate In- and out-coupling Single domain probing 2. Towards experimental study of in-plane propagation in opal monolayers Approach: single domain samples and characterization 28

29 10µm 2. Towards experimental study of in-plane propagation of opal monolayers Preliminary experimental results: Fabricated waveguides micro-hexagon waveguide ►Clearly defined waveguide structure and micro-hexagon ►Different orientations of the micro-hexagons

►The diameter of the microneedle is too large as compared to the size of the micro-hexagon ►Nanoparticles not in the target area 30 ►1.5µm spheres used for optimization of the process 2. Towards experimental study of in-plane propagation of opal monolayers Preliminary experimental results: Deposition of nanoparticles

31 2. Towards experimental study of in-plane propagation of opal monolayers Conclusion and perspectives on experiments part 1 ► Conclusion ► Method of micro-hexagon promising to make single-domain monolayers ► Waveguides can enable in- and out- coupling from the nanoparticles ► Deposition by micro-needles not successful ► Perspective ► Deposition by microfluidic channels – easy to deliver the nanoparticle solution to micro-hexagon Adv. Funct. Mater., Vol. 19, 1247–1253(2009)

32 Conclusion and perspectives part 1 ►Numerical investigation on opals and Inverse opals ► Photonics bandgap exist in Opals and Inverse-Opals ► The inverse-opal structure exhibits larger PBG than the opal structure ► Non-compact inverse-opal structure has highest Q-factor ► Opal micro-cavities require high refractive index to have cavity resonances ►Experimental study of propagation in opals ► In-plane propagation experiment of single domain opals ►Micro-hexagons ►Waveguide ►Perspectives : ►Simulation: Mode volume calculation ►Experiment: nanoparticle self-organization by micro-channels 2. Photonic properties of monolayer of opals and inverse-opals

►Photonic properties of monolayer of nanoparticles and microcavities ►Making nanostructures using nanoparticles OLED Nanostruturation Objectives of the study Self-organized Nanoparticles Photonic crystalsOLED Nanostructuration Photonic crystal laser with defect microcavity 2D-DFB OLDLight extraction in OLED

► Objectives ► Patterning OLEDs ►Light extraction : requires period of lattice ~1-2.5 µm. ►2D DFB laser : requires period of lattice < 500 nm. ► Issues ►E-beam ►Time consuming ►Expensive ► Method ►Principle of photolithography using nanoparticles ►Simulations ►Experiments ►Analysis OLED Nanostruturation Objectives of the study (Journal of Nanoscience, Volume 2014 (2014))

35 ► microsphere deposited every time patterning is made State of the art: Microsphere based patterning and OLED patterning 3. 2D nanostructuration of OLED ►Laser ablation Optical Engineering 491, Laser exposure ►Micro-lens focusing Nanoscale Res Lett., Vol. 3, 123–127(2008) OPTICS EXPRESS / 2005 / Vol. 13, No. 5 ► Electron-beam lithography ► Nanosphere lithography Nano Letters, 2002, 2 (4), pp 333–335

36 Our approach : self-organized nanoparticle photolithography 3. 2D nanostructuration of OLED Monolayer of nanoparticles UV development ► Nanoparticle based reusable photolithographic mask ► Photomask made with nanoparticles ► Light exposure ► Development and reproducing close-packed microsphere pattern on photoresist ► Process advantages Reusable mask Simple Cheap Large area to OLED processing patterned photoresist patterned OLED

37 Experiment : The process 3. 2D nanostructuration of OLED ► Process parameters ►Spin coating: 6000rpm ►Soft 90 sec. ►UV 0.9sec ►Developmenet: 9 sec ► Materials used ►Size and type of microspheres: ►SiO2- 800nm, 1µm, 1.25µm, 1.53µm, 1.68µm, 1.96µm, 2.34µm ►Polystyrene- 1.68µm ►Photoresist, Az-1505 ►Developer- MF-319

► Large area microsphere thin-film on the substrate cm 1.7cm ► SEM: Periodically arranged monolayer of micro nanoparticles – presence of defects in the crystal Results: photomask made with self-organized nanoparticles 3. 2D nanostructuration of OLED

1µm Made by 2.34 µmsize microspheres microspheres mask Result: Patterned photoresist 39 ► Homogenous pattern made by self-organized nanoparticles photolithography 3. 2D nanostructuration of OLED

On the same sample 40 Results: 2 kinds of patterns on the same sample ! UV half of the period of the monolayer mask the period of the monolayer mask reproduced 3. 2D nanostructuration of OLED

►Period of lattice less than 750nm ►hole diameter less than 405 nm ►Reduced-Period not observed for microsphere sizes of 800nm and 1 μm 41 Results: Different size of micro nanoparticles ► Different size of microspheres: 800nm, 1µm, 1.25µm, 1.53µm, 1.68µm, 1.96µm, 2.34µm ► Two contact modes of the mask aligner: hard contact and soft contact 3. 2D nanostructuration of OLED

42 Micro-ball Lens effect Phase-mask effect Simulation: 2 kinds of patterns ► Hard-contact and soft-contact modes of the mask aligner period of pattern = ½ * (period of microspheres) period of pattern = period of microspheres 3. 2D nanostructuration of OLED

► Micro ball-lens ► focal length ►Numerical aperture  max 43 Phase-mask ►Fundamental low of grating ►Transmitted angle  1 Analysis : self-oganized microparticles 3. 2D nanostructuration of OLED The array of self-organized micro nanoparticles is both a collection of ball-lenses and a 2D-phase mask 11

44 Red OLED Green OLED 3. 2D nanostructuration of OLED glass ITO patterned photoresist Micro-OLEDS: Organic hetero-structures - band diagram

D nanostructuration of OLED Micro-OLEDs: Images ► Micro -OLED sizes = 1.27µm ► Method compatible with OLED operation

D nanostructuration of OLED Micro-OLEDs: Spectra ► Emission under normal incidence ► Small spectral modification of emitted light as compared to large area OLED ► Perspectives ► Measurements for other angles of emission ► Edge emission ► Smaller period of pattern glass

► Conclusion ►Cheap, simple method to pattern 2D surfaces on large area ►The patterning method is compatible with OLED deposition 47 Conclusion and perspective part 2 ► Perspective ►Characterization of the emission Measurement of the emission diagram Edge emission ►Towards 2D-DFB laser : Smaller lattices : nm Lower exposure wavelength (<405nm) to increase the resolution of the nanoparticles lithography process Deep UV (DUV) lithography and DUV photoresist ►Use negative photoresist to make periodic pattern of micro nano-pillars 3. 2D nanostructuration of OLED

48 Photonic properties of opal and inverse-opal monolayers ►Monolayers of O and I-O do exhibit photonic bandgap ►The inverse-opal structure exhibits larger PBG ►Non-compact (r/a=0.4) TiO2 inverse-opals exhibit the largest PBG ►Highest Q-factor is obtained in inverse –opals for r/a ratio ~ ►Opal micro-cavities require high refractive index to exhibits cavity resonances ► Nanoparticle photolithography ►Monolayers of nanoparticles used to make periodic pattern on photoresist Lattice down to 750 nm Holes down to 450 nm ►Array of micro-OLEDs (size = 1.27µm) fabricated ►Perspectives : 2D-DFB organic laser fabrication requires Deep-UV photolithography (193 nm) Applications of the nanoparticle photolithography technique : Patterning surface with metal (SERS, Molecules detection, OLED efficiency increases via Surface Enhanced Plasmon Resonance. 4. General Conclusion

Thank you for your attention 49

►Conclusion ►Structures without substrate exhibit PBGs for wide range of refractive indices and compactness ► Generally inverse opals have larger photonic bandgap width ►Structures with substrate have losses for lower refractive index materials ► Considering n=2.5, lower compactness in inverse opals and higher compactness in opals result in lower losses to glass substrate ►Inverse-opal with lower compactness on glass substrate seems to be a good compromise between the losses and the width of PBG ►Thus microcavities designed in non-compact sphere inverse-opals are expected to have better confinement ►Calculation of quality factors is necessary to optimize the optimum r/a value for a given refractive index 50 Conclusion 2. Numerical study of photonic band gaps

►Highest Q-factor(~300) obtained for non-compact spheres in inverse-opals. ►With a glass substrate the Q factor is limited to Q~200 ►Glass substrate reduces Q-factors ►Micro-cavities in opals require refractive index larger than n=3.2 which is hardly feasible ►The literature presents much higher Q-factor in conventional Phc Slabs. 51 Conclusion on Microcavities 2. Numerical study of microcavities

52 sample 2. Towards experimental study of in-plane propagation of opal monolayers Preliminary experimental results: Deposition of nanoparticles Micro-needle and micro-syringe

53 ► Light extraction (lattice ~ µm) ► Light extraction ► DFB lasing Deep UV litho. Smaller lattice (<500 nm) Etching ITO Etching glass substrate Conclusion and perspectives 3. 2D nanostructuration of OLED

54 Conferences and papers ►Papers ► Getachew T. Ayenew, Alexis P.A. Fischer, Chia-Hua Chan, Chii-Chang Chen, Mahmoud Chakaroun, Jeanne Solard, Azzedine Boudrioua,”Two-dimensional patterning of organic light emitting diode based on self-organized nanoparticles photolithography” Submitted to optics Express (may 2014) ► F. Gourdon, A.P.A. Fischer, M. Chakaroun, G. Ayenew and Azzedine Boudrioua “Study of the organic layer thickness effect in a hybrid photonic crystal L3 nanocavity under optical pumping”, Accepted in Journal of Nanophotonics, 5 may 2014 ► Min Won Lee, Siegfried Chicot, Chii-Chang Chen, Mahmoud Chakaroun, Getachew Ayenew, Alexis Fischer, and Azzedine Boudrioua, Study of the Light Coupling Efficiency of OLEDs Using a Nanostructured Glass Substrate, Journal of Nanoscience, Volume 2014 (2014) ► Getachew T. Ayenew ; Mahmoud Chakaroun ; Nathalie Fabre ; Jean Solard ; Alexis Fischer ; Chii-Chang Chen ; Azzedine Boudrioua ; Chia-Hua Chan Photonic properties of two-dimensional photonic crystals based on monolayer of dielectric microspheres, Proc. SPIE 8424, Nanophotonics IV, 84242X (April 30, 2012); ► Sokha Khiev, Lionel Derue, Getachew Ayenew, Hussein Medlej, Ross Brown, Laurent Rubatat, Roger C. Hiorns, Guillaume Wantz and Christine Dagron-Lartigau,"Enhanced thermal stability of organic solar cells byusing photolinkable end-capped polythiophenes", Polym. Chem., 2013,volume 4, (2013) ► Conference ► Getachew T. Ayenew, Mahmoud Chakaroun, Nathalie Fabre, Jeanne Solard, Alexis Fischer, Azzedine Boudrioua, Chii-Chang Chen, Chia-Hua Chan, « Photonic properties of two-dimensional photonic crystals based on monolayer of dielectric nanospheres » Poster SPIE April 2012, Square Brussels Meeting Centre Brussels, Belgium. ► Getachew T. Ayenew, Anthony Coens, Mahmoud Chakaroun, Jean Solard, Alexis P. A. Fischer, Chii-Chang Chen, Chia-Hua Chan, Azzedine Boudrioua, Micro-Oled fabricated by microsphere based lithography, Optique Paris 13, 8 au 11 juillet 2013, Villetaneuse, Présentation Orale. ► Getachew T. Ayenew, Anthony Coens, Mahmoud Chakaroun, Jeanne Solard, Alexis P. A. Fischer, Chii-Chang Chen, Chia-Hua Chan, Azzedine Boudrioua, Micro-OLED fabricated by microsphere based photolithography, JNRDM 2013, Journées National du Réseau Doctoral en Micro-Nanotechnologies, juin 2013, Minatec Phelma, Grenoble, Poster

30 à 50% Analyse du problème de l'émission lumineuse La structure OLED Interfaces – ITO / Verre – Verre /air Impact sur l'extraction lumineuse Réflexions aux interfaces : – 0,8%<R ITO/Verre <19% – R Verre/air  4% Angles limites :  lim = Arcsin(n 2 /n 1 ) Réflexion totale interne (TIR) Modes guidés dans le verre : 30% Modes guidées dans l'ITO : 50% Taux de couplage : 15 à 20 % Aluminium Organique n=1,7 n=1,8 à 2,2 n=1,5 Verre 22 11  lim TIR 50 à 30% Mode s guidé s TIR ITO 22  lim Lumière extraite 15% à 20%

Impact des angles limites A partir de la loi de Descartes n 2 sin(   ) = n 1 sin(   ) Angles limites :  lim = Arcsin(n 2 /n 1 ) ITO/verre : 43°  lim <56° Verre/Air :  lim  42° ITO/air : 27°  lim <33° (  lim  pour n=2  Au delà de l'angle limite il y a réflexion totale interne (TIR) (onde guidée) Taux de couplage Ce qui est transmis :  T(  r 2 sin  d  T(  transmittance en fonction de l'angle Couplage externe ITO/Air : 15 % Transmission au delà des angles limites? Modification de la géométrie grâce aux nanoparticules ?  lim =5 6°  lim =4 2° Cône d'émission ITO /verre Cône d'émission verre/air  lim =30° Cône d'émission ITO/air

57 Organic compounds for OLED Standard chemical products Alq3; tris(8- hydroxyquinolinat o)aluminum; copper phthaloc yanines 4,4'-Bis(2,2-diphenylvinyl)-1,1'- biphenyl 2,9-dimethyl-4,7- diphenyl-1,10- phenanthroline/B athocuproine N,N’- Di(naphthalen -1-yl)-N,N’- diphenyl- benzidine

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