Synthesis of ZnO Nanoparticles Using
  a Low Temperature Vapor Phase
          Transport Process
                         ...
Outline




2009 SPIE Photonics West, Jan. 24-29, 2009     Slide 2
ZnO Nanostructures for Novel Optoelectronic Devices

    Unique electronic properties of ZnO:                 thin film ZnO...
Chemical and Physical Synthesis of ZnO
   Nanostructures
 Chemical                Physical
 • sol-gel               • Vapo...
Low Temperature Physical Synthesis of ZnO
                   Quantum Dots




                       Lu et al. Applied Phy...
NEW APPROACH--Low Temperature Carbothermal
   Vapor Phase Synthesis of ZnO Nanoparticles


       • Inner tube allows for ...
Experimental Details




  Substrate: Si(100) with 3 nm thin
  film of Au deposited by thermal
  evaporation

  Precursor: ...
ZnO Mesoparticles (>100 nm) Formation

  Reaction Conditions
  • substrate Ts = 270 °C                                60° ...
Particle stacking is
                                                                 observed towards
                   ...
• No particle
                                                                    stacking
                               ...
Reaction Conditions and the Effect on Average
               Particle Diameter
                                           ...
EDX

    Composition and Crystalline Quality of
    Nanoparticles
                            EDX                         ...
Optical Quality - LT Photoluminescence
        Strong Luminescence and Optical Size-Effect Observed

 • Low Temperature PL...
Conclusions and Future Directions
   • Novel method for the physical synthesis of ZnO
       nanoparticles at substrate te...
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Low Temperature Synthesis of ZnO Nanoparticles

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Low Temperature Synthesis of ZnO Nanoparticles

  1. 1. Synthesis of ZnO Nanoparticles Using a Low Temperature Vapor Phase Transport Process Curtis Taylor University of Florida, Dept. of Mechanical and Aerospace Engineering, Gainesville, Florida Tarek Trad University of Texas-Brownsville, Dept. of Chemistry, Brownsville, Texas Kurt Eyink, David Look, and David Tomich United States Air Force Research Laboratory, Wright-Patterson AFB, Dayton, Ohio SPIE Photonics West 2009 Quantum Dots, Particles, and Nanoclusters 2009 SPIE Photonics West January 24-29, 2009, San Jose, California
  2. 2. Outline 2009 SPIE Photonics West, Jan. 24-29, 2009 Slide 2
  3. 3. ZnO Nanostructures for Novel Optoelectronic Devices Unique electronic properties of ZnO: thin film ZnO • Direct wide band gap = 3.37 eV transistor • Large exciton binding energy ~ 60 meV for transparent flex circuitry Applications: • high efficiency field emitters • piezoelectric transducers • transparent thin film transistors • light emitting diodes (LEDs) high efficiency • hybrid organic solar cells ZnO nanowire field emitters nanowire photodetector Hybrid polymer-nanowire solar cell D. Wang et al. Nano Letters 7(4), 1003-1009 (2007) 2009 SPIE Photonics West, Jan. 24-29, 2009 Slide 3
  4. 4. Chemical and Physical Synthesis of ZnO Nanostructures Chemical Physical • sol-gel • Vapor Liquid Solid (VLS) • polymer stabilization • Vapor Solid (VS) nanoparticles nanorods • reversed micelles • CVD • alkoxide-assisted • MOCVD • etc. Madler, L et al. Huang M. et al chemical: spray physical: VLS pyrolysis synthesis synthesis • Problem: ZnO nanostructures synthesized by wet chemical or physical methods at high temperatures (> 800 C) • wet chemical methods difficult to integrate with existing silicon fabrication and processing • physical methods generally provide higher crystalline quality material than chemical • physical methods not amenable to flexible electronics or substrates • Need for low-temperature physical synthesis techniques 2009 SPIE Photonics West, Jan. 24-29, 2009 Slide 4
  5. 5. Low Temperature Physical Synthesis of ZnO Quantum Dots Lu et al. Applied Physics Letters, 88, 063110, 2006 • Vapor Phase Transport (VPT) synthesis • Zinc acetate is used as a precursor • ZnO quantum dots are grown at ~ 500 °C 2009 SPIE Photonics West, Jan. 24-29, 2009 Slide 5
  6. 6. NEW APPROACH--Low Temperature Carbothermal Vapor Phase Synthesis of ZnO Nanoparticles • Inner tube allows for LT VPT synthesis by carbothermal decomposition of ZnO powder • Facile route to synthesis of high quality ZnO nanoparticles • Substrate temperatures as low as 225 °C • amenable for polymer and other flexible substrates • Tunable structural and electronic properties 2009 SPIE Photonics West, Jan. 24-29, 2009 Slide 6
  7. 7. Experimental Details Substrate: Si(100) with 3 nm thin film of Au deposited by thermal evaporation Precursor: 1:1 equimolar mixture of high purity ZnO/C ZnO + C Zn + CO 2Zn + O2 ZnO 2009 SPIE Photonics West, Jan. 24-29, 2009 Slide 7
  8. 8. ZnO Mesoparticles (>100 nm) Formation Reaction Conditions • substrate Ts = 270 °C 60° tilted image • precursor Tp = 950 °C Time: • 1 hour reaction time • faceted morphology • particle density gradient across substrate • multilayer formation at substrate edge 0.5 cm 2009 SPIE Photonics West, Jan. 24-29, 2009 Slide 8
  9. 9. Particle stacking is observed towards substrate edge Mesoparticles Ts ~ 270 °C Tp = 950 °C Reaction time = 1 hour Ar gas flow rate = 139 sccm Average particle diameter = 248 nm 2009 SPIE Photonics West, Jan. 24-29, 2009 Slide 9
  10. 10. • No particle stacking observed • Uniform dispersion of nanoparticles • Narrow size distribution Nanoparticles Ts ~ 270 °C Tp = 950 °C Reaction time = 10 minutes Ar gas flow rate = 139 sccm Average particle diameter = 80 nm 2009 SPIE Photonics West, Jan. 24-29, 2009 Slide 10
  11. 11. Reaction Conditions and the Effect on Average Particle Diameter Time Gas Flow Rate 300.00 400 Particle Diameter (nm) Particle Diameter (nm) 238.75 300 177.50 200 116.25 100 55.00 0 0 15 30 45 60 0 75 150 225 300 Time (minutes) Gas Flow (sccm) (a) (b) Temperature: (a) Tp = 950 °C, Ts = 275 °C for 1 hour dav = 277 nm (a) Tp = 900 °C, Ts = 225 °C for 1 hour dav = 113 nm 2009 SPIE Photonics West, Jan. 24-29, 2009 Slide 11
  12. 12. EDX Composition and Crystalline Quality of Nanoparticles EDX XRD EDX indicates no impurities XRD peaks indexed to ZnO present in ZnO formation structures 2009 SPIE Photonics West, Jan. 24-29, 2009 Slide 12
  13. 13. Optical Quality - LT Photoluminescence Strong Luminescence and Optical Size-Effect Observed • Low Temperature PL ~4K • Peak at 3.366 eV -- attributed to surface- surface exciton feature related exciton [D. Stichtenoth et. al, 2007] • Results corroborate 3.366 eV feature as surface related since it dominates with decrease in NP size -- increase in surface area 2009 SPIE Photonics West, Jan. 24-29, 2009 Slide 13
  14. 14. Conclusions and Future Directions • Novel method for the physical synthesis of ZnO nanoparticles at substrate temperatures as low as 225 °C • Tuning particle properties (size, photoluminescence, structural quality, and density) was realized by changing reaction conditions such as temperature, time, and carrier gas flow • ZnO nanoparticles show strong luminescence and optical size effects • Future directions: • Optimize reaction conditions to reach quantum confinement • Obtain high resolution structural characterization • Embed particles in polymer to fabricate novel hybrid (polymer/metal oxide) photovoltaic devices potentially on flexible substrates 2009 SPIE Photonics West, Jan. 24-29, 2009 Slide 14
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