Current Optics Research at the ElectroOptics Research Institute & Nanotechnology Center

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1 Current Optics Research at the ElectroOptics Research Institute & Nanotechnology Center Robert W. Cohn, Director ElectroOptics Research Institute & Nanotechnology Center University of Louisville

2 ElectroOptics Research Institute & Nanotechnology Center (ERINC) Background Information Established 1996 Includes 14 faculty from the U. Louisville & 13 affiliated scientists from outside laboratories Significant facilities provided including: 10,000 sq. ft. microfab cleanroom modern materials analysis and nanofabrication tools Traditional focus on electrooptics systems Increasing emphasis on nanomaterials and devices

3 ERINC Background Information Panel form ERINC brochure on NanoMaterials and Devices R&D

4 Current Optics Research at ERINC OUTLINE Visual Psychophysics Diffractive SLM s and Laser Trapping Nanomorphological materials for AR coatings, optical couplers, antennae Optical spectroscopy of nanowires Polymer fiber 3D MEMS/NEMS/MOEMS

5 VISUAL PSYCHOPHYSICS Contextual Scene Interpretation Psychophysics: The quantifiable measurement of perception Evolution has created retinal-neural hardware with preconditioned interpretations of natural scenes leading to ways to fool the eyes This overview only introduces the general field a it is being studied at UofL and elsewhere

6 VISUAL PSYCHOPHYSICS Contextual Scene Interpretation Background affects perception of shade and color

7 VISUAL PSYCHOPHYSICS: Hanging Chads

8 VISUAL PSYCHOPHYSICS: ILLUSORY MOTION

9 PROGRAMMABLE SPATIAL LIGHT MODULATORS APPLIED TO DIFFRACTION PATTERN GENERATION AND LASER TRAPPING

10 ASSEMBLY OF MICROSTRUCTURES IN LIQUIDS WITH PROGRAMMABLE LASER PATTERNS Laser first turned on 1 μm Laser on a while Programmed laser patterns

11 NANOWIRES, NANO-MORPHOLOGICAL MATERIALS, AND OPTICAL APPLICATIONS

12 UofL NANOWIRE GROWTH STRATEGIES Synthesis Strategy Ga melt + gas plasma Metal melt + O 2 /H 2 plasma Metal melt + N 2 /H 2 plasma Ga-CH 4 plasmas Ga/Mo melt + CH 4 /H 2 plasma CVD transport of W in O 2 Nano-droplets of melted metal + gas plasma Demonstrated Materials Si, SiO 2, Si 3 N 4 Ga 2 O 3 GaN Carbon W, WO 3 Ga 2 O 3 nanowebs Anticipated Materials Ge, Si x Ge 1-x, Bi, InN, AlN, oxides Al 2 O 3, SnO 2, ZnO, In 2 O 3 AlN, InN Inorganic Carbides Refractory metals and oxides Carbon nanotube networks, Nanowebs of HfO 2, TiO 2, etc. Nanowires and nanostructured materials grown to date at UofL: Si, Ge, Ni, Fe, Bi, W, GaN, InN, AlN, Si x N y, WN x GaP, InP, InSb, GaSb, Si x Ge y, Ga 2 S 3, In 2 S 3 SiO x, GeO x, In 2 O 3, Al 2 O 3, Ga 2 O 3, SnO 2, TiO 2 Nb 2 O 5, V 2 O 5, Ta 2 O 5, Bi 2 O 3, Fe 2 O 3, NiO

13 NANOMATERIALS IN SOLUTIONS AND COMPOSITES Commercial WO 3 Nanoparticles WO 3 Nanowires & Nanowire bundles Freshly Mixed After 4 Hours After 10 Days After 10 Days Nanowires readily form stable suspensions/solutions Length of nanowires appears to hinder clumping Good dispersions important for making composites

14 TOOLS BASED ON CVD GROWN NANOMATERIALS Carbon pipettes Tough and flexible graphene with 2nm tip radius Need to develop selective attachment method GaN Handles to nanowires Easier to pick up with micromanipulator Possible optical coupler 200 nm GaN 1 μm GaN plates Slab optical guides Potential seeds for low defect substrates Substrates for pick and place 3D MEMS assembly New morphologies being found on a regular basis GaN GaN 200 nm 500 nm GaN 500 nm

15 WHAT IS NANO-FAB/MANIPULATION? Small tools making smaller structures Enabling connections across scale sizes We continue to find uses for nanomanipulation in our SEM

16 ADDING NANOWIRES ONTO MEMS PLATFORM HCl etch removes native oxide on Ga producing sphere Needles as narrow as 25 nm have been made Silver coated cantilever Melted gallium 10 μm 50 nm

17 GOAL: INTERACTIVE DRAWING AND SENSING OF FIBER FORMATION HAPTIC AFM Force (μn) 40 0 Hard contact -40 Capillary breakup event 1.14 μn Liquid contact Extension Retraction tip wets Distance (μm) meniscus thins Force (μn) s In compression In tension 58 s 116 s 20 μm 192 s Distance (μm)

18 DIFFUSIVE CURRENT OPTICAL SPECTROSCOPY OF NANOMATERIALS

19 PHOTODETECTION FROM SINGLE NANOWIRES Nanoscale Structure AC Modulated Light Source Dielectric Ground Plate Vout Photocurrent (a.u.) Current Amplifier Displacement Photocurrent Method Photon Energy (ev) Carbon Nanotube Response Femtosecond laser pulses produce peaks at the bandgap energy Typical absorption spectroscopy is limited by small area of nanowire Narrow peaks support ID by color and laser frequency stabilization Detection limit of 6 nw/μm 2 with CW at off-peak wavelength

20 BIASED SPECTRAL RESPONSE OF SWNT MAT 300 nm Photocurrent Without bias With bias Wavelength (μm) Large 300 nm exciton shift Dual spectra support identification by color Detection limit with CW of 6 nw/μm 2 off-peak Will the linewidth narrow for single nanowires?

21 SPECTROSCOPY STUDY OF InN NANOWIRES Photocurrent (a.u.) Photocurrent (a.u.) 77 o K 300 o K Excitation Energy (ev) Excitation Energy (ev) 2.0 InN and oxided InN InN only Narrow photocurrent peak at InN 0.8 ev bandgap energy The previous literature reported 1.8 ev for the bandgap The previous measurements were actually of oxidized InN Comparisons with bulk and single nanowires is underway

22 SUSPENDED POLYMER FIBER 3D MEMS/NEMS/MOEMS

23 Fibers by capillary a thinning Directed Self-Assembly of Suspended Polymer Fibers for 3D Nanodevices Used in nanofab Sheet edge 200 nm Array of Tips Applied to nanodevices Tough flexible polymers fibers form in seconds at room temperature Extensive functionality added by macromolecular syntheses Nanodevices emphasizing fluidics, optics and mechanics are being fabricated and evaluated

24 LONG RANGE ORDER ACHIEVED WITH BRUSH ON METHOD Poly Vinyl Acetate (50,000 MW)

25 ADDITIONAL RESULTS WITH ARRAYS Pull normal to edge 50 μm 50 μm Pull normal to tips Fractal bifurcation Pull normal to surface (view 1) 20 μm 10 μm Fractal bifurcation (view 2)

26 CAPILLARIES TEMPLATED ON POLYMER FIBERS 1 μm Chrome Parylene Overcoat with metal, glass or parylene Dissolve polymer leaving capillary Gold 20 nm film 4 μm 10 μm 2μm Glass

27 GLASSBLOWING ANALOGY TO OUR POLYMER FIBER DRAWING METHOD Glass is custom drawn over a flame Polymer fibers are drawn from a pool of solvent-suspended polymer Each method makes custom structures

28 MULTIFUNCTIONAL MEMS PLATFORM: SOFT FIBERS SUSPENDED ON RIGID SUPPORT Laser input and output Output: light (electroluminescence) Evanescent mode coupler Unclad polyfiber Potential for standing wave resonance or lasing Laser-trapped micro-bead resonator Polyfiber templated capillary + - Inputs: liquid, gas, voltage Outputs: liquid, gas Inputs: liquid, gas

29 OPTICAL APPLICATIONS OF POLYFIBERS Very small and sensitive optical resonators and interferometers could be constructed 50 μm 2 μm δg π (nm) D n 2 D (nm) = n 1 n 1 n G 400 λ=514 nm, l=500 μm n 1 =1.45, n 2 =1.33 G (nm)

30 MULTIFUNCTIONAL MEMS PLATFORM: SOFT FIBERS SUSPENDED ON RIGID SUPPORT Laser input and output Output: light (electroluminescence) Evanescent mode coupler Unclad polyfiber Potential for standing wave resonance or lasing Laser-trapped micro-bead resonator Polyfiber templated capillary + - Inputs: liquid, gas, voltage Outputs: liquid, gas Inputs: liquid, gas

31 POLYFIBERS DRAWN WITH SHARP OR BLUNT TIPS AFM Tip Fibers drawn with micromill Draw fiber from 1 st polymer pool 200 μm Tapered junctions Polyfib on end of 100 μm glass fiber Hand twisted 2 μm 40 μm 50 μm

32 CURRENT NANOFABRICATION THEMES ø Smaller than ever before. Not so! Simpler, faster, easier, less costly. Yes! Avoid cleanroom when possible. Yes! Examples Dip pen nanolithography of alkanethiols Soft lithography with PDMS Nanoimprint lithography with PMMA Self assembly of colloidal crystals Electrostatically driven assembly of polymers

33 MEMS FROM THE BOTTOM UP INTEGRATION OF NANOWIRE MATERIALS INTO DEVICES AND MICROSYSTEMS Needs Platforms to host nanowire functions in conventional electronics and microsystems in non-traditional forms e.g. textiles, smart skins Simplified fabrication methods to reduce time to market for practical utilization of nanowire functions that enable nanowire integration with soft materials Examples of robust fabrication at room temperature Selective crystallization of Ga-Ag nanowires Self-assembly of suspended polymer nanofibers Mega -functional microsystems enabled by nanofibers

34 MEMS FROM THE BOTTOM UP: DIRECTED SELF-ASSEMBLY OF POLYMER AND METAL NANOSTRUCTURES SUMMARY Using appropriate materials systems, crude directives can evolve into ultra-precise structures These assembly processes have the potential to produce custom MEMS prototypes faster EE students are capable of, excited by and become active learners through involvement in this type of research Nano-methods are quickly being adopted by academic institutions worldwide because of their ease of use and low cost The interdisciplinarity of nanoscience requires and motivates improved learning, retention and the creative application of the fundamentals of science