Synthesis And Characterization Of Individual ZnO Nanowires

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Synthesis And Characterization Of Individual ZnO Nanowires

  1. 1. Synthesis and characterization of individual ZnO nanowires M. Duchamp
  2. 2. “Nano” applications MEMs device to measure ZnO Piezoelectronic nanowires Young’s modulus Field Effect Transistor (FET) Xudong Wang et al. Nano Lett., Vol. 6, No. 12, 2006 R. Agrawal et al. Nano Lett., Vol. 8, No. 11, 2008
  3. 3. “Nano” applications • Direct-Current nanogenerator driven by ultrasonic waves Xudong Wang, et al. Science 316, 102 (2007)
  4. 4. Top-Down approach • Today technology: last Intel node Improved transistor density by 2 • Complex and expensive processes • Need of new materials
  5. 5. ZnO attractive properties • Hexagonal wurtzite structure • ZnO can be used as UV or blue emitting materials • Transparent in visible spectrum • Wide band gap: 3.36 eV at room temperature • Young’s modulus: 140 GPa
  6. 6. Chemical Vapor Deposition Synthesis • Using Vapor-Liquid-Solid (VLS) growth mode Dissolution Diffusion Super-saturation Oxidation 900°C for 20 minutes Argon and Oxygen gas
  7. 7. Diameter control  Minimum achievable diameter: 40nm
  8. 8. Gold colloid catalysts Density of Chemical colloid functionalization ∞ silicon substrate Immersion time
  9. 9. Zinc precursor How did we chose the Influence of zinc/oxygen reaction temperature? ratio in the gas phase ZnO (s) Zn (g) Lan Hong et al. Scandinavian Journal of Metallurgy, 171–176, 2006
  10. 10. Rajoute diffraction pattern Crystallographic orientation Sapphire (001) SrTiO3 (110) C-axis Lattice mismatches : Silicon (100) Lattice mismatch : 18.8% 1% and 9%
  11. 11. Dielectrophoresis of ZnO nanowires Parameters studied: • Dispersion • Solvents Repartion [%] • Substrates • Applied voltages Number of attracted Nws  Number of ZnO nanowires between electrodes can be controlled by the applied voltage M. Duchamp, Kyumin Lee et al. in preparation
  12. 12. Electrical measurements: contact effects Lithography Contact oxidation lift-off processes  Nitrogen doped Cr is used as metal  Cannot be oxidized Allen et al. Appl. Phys. Lett. 94 (2009)
  13. 13. Energy level in semiconductors • Schottky diode • Electron affinity ZnO: 4.5eV • Work function Cr: 4.5eV
  14. 14. Transport measurements 2 eV
  15. 15. Optical measurements Catholuminescence by Scanning Photoluminescence Tunneling Microscopy 3.3eV ZnO1 1.0 ZnO3 ZnO4 ZnO2 Intensity (a.u.) 0.8 2.1eV 0.6 0.4 3.3eV 2.4eV 0.2 0.0 200 400 600 800 1000 1200 1400 Wavelength (nm) Excitation: 330-360 nm Optical gap: 2.3eV
  16. 16. Mechanical properties TEM compatible substrate 32nm 120GPa
  17. 17. Young’s modulus of ZnO nanowire Catalyst free growth by CVD in oxygen rich atmosphere 32nm 40nm Young ‘s modulus higher than bulk value C. Q. Chen et al. PRL 96, 075505 (2006)
  18. 18. Conclusions • Control of the synthesis: – Diameter, Shape, Length • Semi-conducting properties of ZnO grown by VLS method have been extracted fom a single nanowire • Young modulus enhanced for stoichiometric nanostructures

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