1. Influence of Solvent on Selective Deposition of Tungsten Oxide Nanostructures via AACVD Chris Blackman

2. 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?

3. Synthesis W.B. Cross et al, Chem. Mater., 2003, 2786 Precursor [W(OPh) 6 ] Solvent –Acetone –Methanol –Toluene Substrate 400 °C – 600 °C Carrier (N 2 ) Flow 200 cm 3 /min

4. Toluene Solution Results Y. Liu, M. Liu, Adv. Funct. Mater., 2005, 15

5. Acetone Solution Results

6. 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

7. Factors Affecting Nanostructure Morphology Influence of reactant diffusion –Principally dependent on precursor flux

8. 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

9. 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

10. Acknowledgements Dr Stella Vargas Mr Savio Moniz Dr Polona Umek (Jozef Stefan Institute, Slovenia)