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Influence of Solvent on Selective Deposition of Tungsten Oxide Nanostructures via AACVD PowerPoint PPT Presentation


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Influence of Solvent on Selective Deposition of Tungsten Oxide Nanostructures via AACVD. Chris Blackman. Background. The intrinsic properties of nanomaterials promise advances in a wide range of fields Vapour synthesis of nanomaterials – AACVD Increased atom efficiency

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Influence of Solvent on Selective Deposition of Tungsten Oxide Nanostructures via AACVD

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Influence of Solvent on Selective Deposition of Tungsten Oxide Nanostructures via AACVD

Chris Blackman


Background

  • The intrinsic properties of nanomaterials promise advances in a wide range of fields

  • Vapour synthesis of nanomaterials – AACVD

    • Increased atom efficiency

    • Reduced waste production

    • Compatible with device manufacture

    • Scalable

  • Synthesis often requires high temperatures

    • Device fabrication issues

    • Precursor design

    • Other factors?


Synthesis

  • Precursor [W(OPh)6]

  • Solvent

    • Acetone

    • Methanol

    • Toluene

  • Substrate 400 °C – 600 °C

  • Carrier (N2) Flow 200 cm3/min

W.B. Cross et al, Chem. Mater., 2003, 2786


Toluene Solution Results

Y. Liu, M. Liu, Adv. Funct. Mater., 2005, 15


Acetone Solution Results


Factors Affecting Nanostructure Morphology

  • Influence of evaporation time of aerosol droplets

  • ‘Normal’ view is complete evaporation of droplet

  • Incomplete evaporation can lead to formation of solid shell at droplet surface

  • Less volatile toluene has lower probability of forming solid shell


Factors Affecting Nanostructure Morphology

  • Influence of reactant diffusion

    • Principally dependent on precursor flux


Methanol-containing Solution Results

  • Addition of methanol causes dramatic reduction in temperature required for nanostructure formation

  • Methanol is known to decompose via a radical mechanism at temperatures as low as 220 °C

    • Formation of more reactive intermediate, i.e. methanol is not simply a ‘carrier’ solvent

  • Formation of particles (homogeneous reaction) at increased temperatures indicates a different chemical species (intermediate) may be involved compared to toluene or acetone


Conclusions

  • The use of different ‘carrier’ solvents influences the nanostructure morphology obtained

  • Differences between acetone and toluene may be related to:

    • Rate of droplet evaporation

    • Rate of reactant diffusion

  • Difference found with methanol may be related to chemical interaction between solvent and precursor


Acknowledgements

  • Dr Stella Vargas

  • Mr Savio Moniz

  • Dr PolonaUmek (Jozef Stefan Institute, Slovenia)


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