Multifunctional Particles for Crystalline Colloidal Array Sophisticated Photonic Crystals Optical Devices Sanford A. Asher Dept. of Chemistry University of Pittsburgh Pittsburgh, PA 15260 412-624-8570 asher@pitt.edu Sanford A. Asher, Department of Chemistry CRYSTALLINE COLLOIDAL SELF-ASSEMBLY: MOTIF FOR CREATING SUBMICRON PERIODIC SMART MATERIALS Sanford A. Asher, Department of Chemistry Outline CCA and PCCA Photonic Crystal Fabrication Spatial Control of Electromagnetic Field Maxima Ag@SiO2 Magnetically Controlled CCA – Superparamagnetic CCA – Ferromagnetic CCA ☺ Nothing@PS-Hollow Sphere CCA Crystalline Colloidal Arrays Self-Assembly fabricated from monodisperse, highly charged colloidal particles Dialysis / Ion Exchange Resin - + ++ - + +- - -+ + - ++-- +-+ + -+ + + - -- - +++ + - - + - + + + Self-assembly FCC ~ 1013 spheres/cm3 -+- - + + + +--+ + - - + +- + + + - - - + -- --+ - + ++ +- -- - + -+ - - + - + ++ -+ - - - + - - - -+ - - -- - + - + + - - +- -- + - - ---+ - - + -- -+ -- + + -- - -+ + - +- + - ++ -+ + + + + ++ -- - -+ -+ + + -+ - -- - + - - -- - - + - - ++ - - +-- - + ++ - - + -+ +- -- -- + + - - + +- - - - -+ -- + +-+ -+ -- --- + + -- -+ + - - +- + + -+ - -+ - + -+- - + Crystalline Colloidal Array spacing dependent only upon particle number density and crystalline structure Holtz, Asher et al J. Am. Chem. Soc. 1994, 116, 4497 Polystyrene Colloid Synthesis: EMULSION POLYMERIZATION Preparing ~ 100 nm Polystyrene Colloids 160 ml Water 60 ml Styrene (monomer) 2.00 g MA-80-1 (surfactant) 2.90 g COPS -1 (ionic co-monomer) 2.00 g Divinyl Benzene (crosslinker) 0.20 g Sodium Bicarbonate (buffer) 0.70 g Ammonium Persulfate (initiator) Polymerize at 70oC for 3 hrs. Temperature Controller N2 R• Long polymer chain TEM of polystyrene spheres + - - + N2 Surfactant + H2O R• Water Reese, Asher et al J. Colloid Interface Sci. 2000, 232, 76 What Drives CCA Self-Assembly? + + SO3- H H -O3S H+ -O S 3 H+ -O SO3-+ 3S H -O r H+ + SO3- H SO3- +H 3S 2 κa 2 ⎤ e − κr Z e ⎡ e U (r ) = ε ⎢⎣ 1 + κ a ⎥⎦ r 2 U 2a Negatively charged particle Sphere Radius Medium Dielectric Constant Interaction Potential Energy 2 4 π e (n p Z + ni ) κ2 = ε kB T Ionic Impurities Particle concentration Shear boundary Debye layer thickness 1 κ (in pure water ) ~ 700 nm r Sanford A. Asher, Department of Chemistry Crystalline Colloidal Array λ d θ - - +- - -+ - + + +-- -- -- -- - --- - - -- ++ - - --- - +- - --- +- -- + + -- -- - + -- - - +- - - -- - +- - ++ - -+- - - + + - -- - +- + - - -- -- - - -- +- - - -- + - -- - - --- -+ - + - + -- -- -+ -- -- + + +- -- +-- - + -- - - - ---+- +- ++ -- - - - -- - - + -- - -- - -- + +- -- +-- +- - -- -+-- + - --- +- --- - - - -- - -+ - - + - - - --+ - + + --- --- -+ - -+ + + + mλ = 2nd sin θ m = order of diffraction λ = diffracted wavelength n = refractive index of system d = spacing between diffracting planes θ = Bragg glancing angle + Bragg Diffraction λ0 + + + + - - - - - ------- - - + + + - - - - - ------ - - -+ θB + - - --------- - - -- + d ~ 200 nm + + - - - - - ------- - -+ + - - - - - ------- - + - - - - - -----+ - - - -- + d -- - - - ----- + ---- - - + (111) FCC CCA - - - - - ---------- - -+ + + + + + + - - - - - -------- - -- + + - - - - - ------- - - -+ -- - - - ------- - + + - - - - - -------- - - -- + + - - - - - ------ -+ -- mλo = 2ndsin θ + λ0 = wavelength of diffracted light n = refractive index of system d = interplanar spacing in crystal θB = Bragg glancing angle Diffracted Intensity, ID + + + - - - - - --------- - -- 500 600 700 Wavelength / nm 800 All Light Diffracted-Finite Widths-Top Hat Profiles Bandgap, Δλ↔Δθ Diffraction Phenomena of Photonic Crystals * Kinematic Diffraction x-rays: Atomic & Molecular Lattice wimpy scattering little attenuation each layer contributes similarly * Dynamical Diffraction strong scattering must consider coupled incident and diffracted wave * Theoretical Foundation Based on Work in 1930-1940 W.H. Zachariasen, The Theory of X-ray Diffraction in Crystals, Wiley, 1945. 3-D Photonic Bandgap Crystals-for much larger modulations of refractive index Dynamical Bragg Diffraction From Crystalline Colloidal Arrays, P. A. Rundquist, P. Photinos, S. Jagannathan, and S. A. Asher, J. Chem. Phys. 91, 4932-4941 (1989). Ultra Efficient Diffraction 0 91 nm PS CCA - Log T 2 100 μm = 400 layers 4 6 8 10 0 200 400 600 800 1000 Number of fcc (111) layers Britney Spears Britney Spears Photonic Crystal Site It is a little known fact, that Ms Spears is an expert in semiconductor physics. Not content with just singing and acting, she will guide you in the fundamentals of the vital laser components that have made it possible to hear her super music in a digital format. Bandgap causes standing wave where at the edges the electric field maxima occur within the high and low refractive index layers High refractive index layers Opportunity to spacially tune electric field maximum to region of high optical nonlinearities! Incident Diffracted Low refractive index layers Ag@SiO2 100 nm (EtO)4Si + H2O + AgNO3 hν Ag QD The monodisperse SiO2 spheres show a homogeneous incorporation of Ag quantum dot inclusions. dsphere=78+5.4 nm, dAg=3-8 nm. SiO2 . “Photochemical Incorporation of Silver Quantum Dots in Monodisperse Silica Colloids for Photonic Crystal Applications,” W. Wang and S. A. Asher, J. Am. Chem. Soc., 123, 12528-12535 (2001). Can Easily Vary Loading and Sizes A B C Ag QD Plasmon Resonance in Random Dispersion of Ag@SiO2 2.0 438 nm (a) Extinction, -log(I/I0) 1.5 1.0 (b) random dispersion in water (c) 0.5 (d) Refractive index matched (e) 0.0 300 400 500 Wavelength, nm Figure 11 600 700 fcc CCA mλ=2ndsinθ 605 nm 565 nm 0.5 521 nm 1.0 490 nm 288 nm 307 nm 1.5 457 nm 2.0 Plasmon Resonance 253 nm 266 nm Extinction, -logI/I 0 2.5 403 nm 425 nm 220 nm 235 nm 3.0 210 nm Ag@SiO2 CCA Diffraction as a Function of Lattice Spacing 0.0 200 300 400 500 Wavelength/nm 600 700 1.50 490 nm 425 nm Dependence of Plasmon Resonance Extinction on Bragg Condition 1.00 565 nm Extinction, -logI/I0 392 nm 1.25 0.75 0.50 0.25 Refractive Index Matched 0.00 Random 200 Dispersion Plasmon Resonance 300 400 500 600 Wavelength/nm 700 800 Spatial Concentration of Electromagnetic Field Increased plasmon absorption Decreased plasmon absorption Standing Wave Photonic Crystal Electromagnetic standing wave produced by incident and diffracted light Bormann Effect Dependence of Plasmon Resonance Extinction on CCA Ordering 408 nm 1.2 Refractive Index Matched Random Dispersion Plasmon Resonance Extinction, -logI/I0 1.0 0.8 λo/n = λin For λ at red edge of bandgap electric field maximum occurs in water! 0.6 0.4 In water Layer 0.2 In Ag@SiO2 Layer 0.0 200 300 400 Wavelength, nm 500 600 Ag quantum dot nav = Φ SiO2 nAg + (1-Φ) nw But on red edge of plasmon resonance nAg < 0, thus, nav < nw! Ag Electric Field is Localized • Increased nonlinear optical responses • Increased linear optical responses • Recent Example: Increased Absorbance of Dyes Towards Longer Wavelengths in Solar Cells-dramatically increased efficiencies:Tom Mallouk, Penn State • Method for increasing refractive index contrast Other Examples of Complex Particles • • • • • CdS@SiO2 CdS cores within SiO2 Spheres CdS shells around SiO2 cores Concentric CdS and SiO2 shells Synthesized during microemulsion condensation of (EtO)4Si "Preparation and Properties of Tailored Morphology, Monodisperse Colloidal Silica-Cadmium Sulfide Nanocomposites", S.-Y. Chang, L. Liu, and S. A. Asher, J. Am. Chem. Soc. 116, 6739-6744 (1994). "Creation of Templated Complex Topological Morphologies in Colloidal Silica", S.-Y. Chang, L. Liu, and S. A. Asher, J. Am. Chem. Soc. 116, 6745-6747 (1994). Sanford A. Asher, Department of Chemistry 100 nm TEM Picture of CdS@SiO 2 Compos ite Nanoparticles Sanford A. Asher, Department of Chemistry Outline • CCA and PCCA Photonic Crystal Fabrication • Spatial Control of Electromagnetic Field Maxima Ag@SiO2 • Magnetically Controlled CCA – Superparamagnetic CCA – Ferromagnetic CCA Nothing@PS-Hollow Sphere CCA Synthesis of Monodisperse Charged Superparagnetic Particles FeCl2.4H2O FeCl3.6H2O NH3.H2O Strong stirring Sonicate the precipitate in 1 M TMAOH solution Surface modified magnetic colloid Magnetic colloid St MMA NaSS H2O Oleic Acid/ SDBS Sonication 5hr Emulsion polymerization Black precipitate 70 0C APS Brown latex APS: Ammonium Persulfate MMA: Methyl Methacrylate NaSS: Sodium Styrene Sulfonate St: Styrene SDS: Sodium Dodecyl Sulfonate TMAOH: Tetramethylammonium Hydroxide Magnetic separation Iron Oxide ~ 10 nm Polystyrene-iron oxide composite ~ 135 nm, polydispersity 7.5% Ferrite content 17 wt% Magnetic Properties of Superparamagnetic Particles 80 60 40 nanosize iron oxide PSt-iron oxide composite particles σ / emu/g 20 0 -50 -40 -30 -20 -10 0 10 -20 -40 -60 -80 H / KOe 20 30 40 50 Magnetic Force on a Magnetic Moment -p +p H dH L dH L F = p( H + ) − p( H + ) dx 2 dx 2 dH F = pL dx dH F=m dx m=pL : magnetic moment dH dx : spatial derivative of magnetic field strength No magnetic field In magnetic field - - - - -- - - - - -- - - - - - - - -- - - -- Repulsive force between a pair of particles, Fe=πεζ2κae-κh - - - - - - -- - - -- Magnetic force at different position: Fm= (dM/dH•H+M) •dH/dL ε is the dielectric constant, ζ is the zeta potential of a particle, M is the magnet moment of each particle κ is the reciprocal double-layer thickness, a is the radius of the particles, and h is the interparticle distance . Part 2: Self-assembly of Superparamagnetic Particles Self-assembly of Superparamagnetic Particles Effect of External Magnetic Field Lattice Constant Effect of external magnetic field on on lattice constant 240 16 220 200 Relative Diffraction Intensity FCC 111 plane spacing / nm 14 L ( mm) (Left to right) 2,3,4,5,6,7,8,9,10,11 12 10 8 6 4 2 180 0 350 400 450 500 550 600 wavelength (nm) L 160 CCD fiber sample magnet 140 6 5 4 3 dH/dL / KOe/cm 2 1 Effect of external magnetic field on self-assembly Effect of external magnetic field on self-assembly 18 16 12 10 8 6 4 L CCD fiber sample magnet 910 Diffraction peak / nm Relative Intensity (a.u.) 14 L H d H/d L primary peak mm kOe KOe/cm nm 3 3.57 4.69 850 5 2.75 3.56 866 7 2.13 2.71 871 11 1.29 1.56 888 14 0.91 1.03 899 19 0.54 0.51 904 in absence 911 920 of magnet 900 890 880 870 860 850 2 0 400 0 1 2 3 4 5 dH/dL / KOe/cm 500 600 700 Wavelength / nm 800 900 Comparison of Electrostatic and Magnetic Force 7 Effective surface charge 1.5 μ C/cm 1.4 1.3 1.2 magnetic force 2 5 4 F / 10 -11 dynes 6 3 2 1 2 4 6 8 10 Distance from magnet / mm Charge renormalization Zeff= Z/4 12 Color Change of CCA in magnetic field deionization Red shift Blue shift NaCl added H More NaCl added Blue shift In magnetic field, CCA color changes with ionic strength. Magnetic field induced assembly in NaCl solution 6 220 Relative intensity FCC (111) plane spcaing / nm 240 200 180 NaCl Concentration (From left to right) 4.0mM, 2.0mM, 1.0mM, 0.67mM, 0.33 mM,0.16 mM, 0mM 4 2 0 350 400 450 500 550 600 650 700 wavelength (nm) 160 0 1 2 NaCl concentration / mM 3 4 Magnetic field induced assembly in organic polar solvents 50 40 Relative Intensity FCC (111) plane spacings / nm 220 From left to right Ethanol, M ethanol, Acetonitrile, Ethylene Glycol, DM SO, water 200 30 20 10 180 0 400 500 600 wavelength (nm ) 160 140 20 30 40 50 60 70 dieletric constant of medium 80 Magnetic Response of PCCA 788 before imposing magnet Time after imposing magnet (mins) 0 15 30 45 60 75 Relative Reflection Intensity 784 1.6 1.2 CCD 0.8 magnet 0.4 740 760 780 800 820 1.8 860 840 Wavelength / nm 780 776 0 30 60 Impose CCD 1.2 0.9 0.6 0.3 0.0 740 Impose magnet before removing magnet time after removing magnet (mins) 0 15 30 45 60 1.5 Relative reflection Intensity Bragg diffraction peak / nm 2.0 760 780 800 820 840 860 Wavelength /nm Remove magnet 90 Time / mins 120 150 180 Remove Synthesis of Ferromagnetic Charged Magnetic Particles Co2+ Fe2+ CoCl2.4H2O FeCl3.6H2O NH3.H2O Strong stirring Sonicate the precipitate in 1 M TMAOH solution Surface modified magnetic colloid Magnetic colloid St MMA NaSS H2O Oleic Acid/ SDBS Sonication 5hr Emulsion polymerization Black precipitate 70 0C APS Brown latex APS: Ammonium Persulfate MMA: Methyl Methacrylate NaSS: Sodium Styrene Sulfonate St: Styrene SDS: Sodium Dodecyl Sulfonate TMAOH: Tetramethylammonium Hydroxide Magnetic separation Ferromagnetic Composite Particles ~ 123 nm, ~ 14 wt% Cobalt Ferrite Reduced Magnetization (M/Ms) Magnetic Behavior of ferromagnetic particles in powder and dispersion 1.0 0.5 Dispersed in deionized water Dried Powder 0.0 -0.5 -1.0 -2000 -1500 -1000 -500 0 H / Oe 500 1000 1500 2000 External magnetic field controlled orientation of single ferromagnetic particles A B Gold nanocrystals H H H1 H2 Magnetic field H2 × Diffracted Light Intentsity Response of ferromagnetic PCCA to oscillating magnetic field CCD 543.5 nm Incident Light Diffracted λ= 2 n d sinθ light Relative Diffraction Intensity (a.u.) 12 10 8 6 External magnetic field controlled orientation of magnetic photonic crystals H /Oe 90 65 55 33 22 13 0 CCD CCD +H -H 4 H 2 0 500 600 700 Wavelength /nm 800 Incident Light 2.4 2.0 1.6 0.5 2.1 1.0 Time / sec 1.5 + H2 Relative Intensity 10 Hz 60 Hz - H2 1.8 1.5 0 Diffracted light × Relative Intensity /a.u. 1 Hz 4 HZ 2.8 H1 H1 H2 50 100 150 200 Time /ms 250 300 Relative amplitude /a.u. Magnetic Response Frequency Dependence of Magnetooptical Fluid 1.0 0.8 0.6 0.4 0.2 -1.0 -0.5 0.0 0.5 1.0 log( f /Hz) 1.5 2.0 Optical Switch Controlled by weak magnetic field CCD Fiber Optic N S N S water Front View Top View Optical Switch Fabricated with Ferromagnetic PCCA 6 -20 Oe -9 Oe +9 Oe +20 Oe Relative Intensity (a.u.) 5 5 4 686 nm 549 nm 4 3 3 N S S 2 N 2 1 1 500 600 700 Wavelength /nm -120 -90 -60 -30 0 30 H / Oe 60 90 120 Relative Intensity (a.u.) 6 Patterning Surfaces Using Paramagnetic Colloids S. Asher, X. Xu and G. Walker, Dept. of Chemistry, University of Pittsburgh and Prof. Gary Friedman, Dept. of Electrical Engineering, Drexel University Position Defined Assembly of Ferromagnetic Particles 20 18 16 350 nm 14 300 250 12 200 10 150 8 100 50 6 0 4 -50 2 0 0 5 10 15 20 μm Position Defined Assembly of Ferromagnetic Particles ys0915.018: Height 10 9 8 350 7 300 250 6 200 5 150 4 100 50 3 0 2 -50 1 0 0 2 4 6 8 10 Sanford A. Asher, Department of Chemistry Outline • CCA and PCCA Photonic Crystal Fabrication • Spatial Control of Electromagnetic Field Maxima Ag@SiO2 • Magnetically Controlled CCA – Superparamagnetic CCA – Ferromagnetic CCA Nothing@PS-Hollow Sphere CCA Nothing@Polystyrene Spheres • Synthesize SiO2 cores • Using emulsion polymerization synthesize PS shell • Etch out SiO2 cores with HF • Fill Hollow Cores with reagent • Introduce Reactants in Medium to diffuse into core and react to fill shell voids Relative Diffraction Intensity /a.u. 4 3 275 nm Silica 275/379nm Silica@PSt 379 nm Hollow PSt 2 1 0 400 600 800 Wavelength /nm 1000 ferrite Fabrication of particles with complex morphology. ~ 203 nm MPS modified silica particles A were first coated with a ~43 nm copolymer shell to give core-shell particles B (~289 nm). Particles B were further coated with a ~ 17 nm silica shell to produce particles C (~ 323 nm). Particles C were further coated with ~ an additional ~42 nm PS shell to produce composite particles D (~407 nm). When the composite particles D react with HF, polymeric particles E with concentric shells were produced. When the polymer component in the composite particles D is removed by calcination silica particles F occur Magnetic composite particles (25 wt%) self-assemble into CCA. 1st order diffraction 1007nm, 2nd order diffraction at 511 nm 3.5 4 Extinction /au. 3 2.5 2.0 2 1.5 1.0 1 0.5 0 400 600 800 1000 1200 Wavelength /nm 400 500 600 700 800 900 Wavelength /nm 0.0 Relative Intensity /au. 3.0 Conclusions • Possible to make complex particles • The photonic crystal structure allows localization of electromagnetic fields on colloidal particles • Important new phenomena • Future bright for new phenomena and new devices Acknowledgements Asher Research Group Members $: NIH, NCI, NASA and NSF