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)