Effect of solvent and silicon substrate surface on the size of iron nanoparticles

The diameter of carbon nanotubes is strongly related the geometric sizes of the metal particles upon which they are nucleated. To improve the control over the nanoparticle sizes derived from iron acetate and deposited on Si substrates, two different approaches were employed; manipulation of the solvent chemistry and manipulation of the Si substrate surface. The iron acetate was dissolved separately in pure water and ethanol and in binary ethanol/water mixtures. Silicon substrates, with either smooth surface or nano-porous surface, were dip coated using these solutions. The dip-coated substrates were first thermally oxidised at 400 °C in air followed by reduction at 800 °C in an Ar/H₂ gas mixture. As derived particles were measured by scanning electron microscopy, and the average size and size distribution were determined by statistical analysis. Electron microscopy and statistical analyses demonstrated that metal particles deposited onto the smooth Si wafer have sizes ranging from 18 to 160 nm based on the solvent used, where the pure solvents resulted in a narrower size distribution when compared to the water/ethanol mixtures. When nano-porous Si wafer is used as a substrate, the metal particle diameter distributions are reduced to a range from 11 to 17 nm contingent upon the solvent used. The role of the ethanol/water interactions investigated by vibrational (IR and Raman) and ¹H nuclear magnetic resonance spectroscopy on nanoparticle sizes and size distributions is discussed.