Low Temperature Synthesis of ZnO Nanoparticles

Synthesis of ZnO Nanoparticles Using a Low Temperature Vapor Phase Transport ProcessCurtis TaylorUniversity of Florida, Dept. of Mechanical and Aerospace Engineering, Gainesville, FloridaTarek TradUniversity of Texas-Brownsville, Dept. of Chemistry, Brownsville, TexasKurt Eyink, David Look, and David TomichUnited States Air Force Research Laboratory, Wright-Patterson AFB, Dayton, OhioSPIE Photonics West 2009Quantum Dots, Particles, and Nanoclusters2009 SPIE Photonics WestJanuary 24-29, 2009, San Jose, California Outline2009 SPIE Photonics West, Jan. 24-29, 2009Slide 2ZnO Nanostructures for Novel Optoelectronic Devices Unique electronic properties of ZnO:thin film ZnO • Direct wide band gap = 3.37 eVtransistor• Large exciton binding energy ~ 60 meVfor transparent flex circuitryApplications:• high efficiency field emitters• piezoelectric transducers• transparent thin film transistors• light emitting diodes (LEDs)high efficiency • hybrid organic solar cellsZnO nanowire field emittersnanowire photodetectorHybrid polymer-nanowire solar cellD. Wang et al. Nano Letters 7(4), 1003-1009 (2007) 2009 SPIE Photonics West, Jan. 24-29, 2009Slide 3Chemical and Physical Synthesis of ZnO NanostructuresChemicalPhysical• sol-gel• Vapor Liquid Solid (VLS)• polymer stabilization • Vapor Solid (VS) nanoparticlesnanorods• reversed micelles• CVD• alkoxide-assisted• MOCVD• etc.Madler, L et al. Huang M. et alchemical: spray physical: VLS pyrolysis synthesissynthesis• 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 techniques2009 SPIE Photonics West, Jan. 24-29, 2009Slide 4Low Temperature Physical Synthesis of ZnO Quantum DotsLu 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 °C2009 SPIE Photonics West, Jan. 24-29, 2009Slide 5NEW 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 properties2009 SPIE Photonics West, Jan. 24-29, 2009Slide 6Experimental DetailsSubstrate: Si(100) with 3 nm thin film of Au deposited by thermal evaporationPrecursor: 1:1 equimolar mixture of high purity ZnO/CZnO + C Zn + CO2Zn + O2 ZnO 2009 SPIE Photonics West, Jan. 24-29, 2009Slide 7ZnO Mesoparticles (>100 nm) FormationReaction Conditions60° tilted • substrate Ts = 270 °C image• precursor Tp = 950 °C Time:• 1 hour reaction time • faceted morphology• particle density gradient across substrate • multilayer formation at substrate edge0.5 cm2009 SPIE Photonics West, Jan. 24-29, 2009Slide 8Particle stacking is observed towards substrate edgeMesoparticlesTs ~ 270 °C Tp = 950 °C Reaction time = 1 hourAr gas flow rate = 139 sccmAverage particle diameter = 248 nm2009 SPIE Photonics West, Jan. 24-29, 2009Slide 9• No particle stacking observed• Uniform dispersion of nanoparticles• Narrow size distributionNanoparticlesTs ~ 270 °C Tp = 950 °C Reaction time = 10 minutesAr gas flow rate = 139 sccmAverage particle diameter = 80 nm2009 SPIE Photonics West, Jan. 24-29, 2009Slide 10