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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
W.B. Cross et al, Chem. Mater., 2003, 2786
• Precursor [W(OPh)6]
• Solvent– Acetone– Methanol– Toluene
• Substrate 400 °C – 600 °C• Carrier (N2) Flow 200 cm3/min
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
• 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
Methanol-containing Solution Results
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 Polona Umek (Jozef Stefan Institute, Slovenia)
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