Characterization of Gas-Expanded Liquid-Deposited Nanofilms with Size-Controlled Gold and Iron Oxide Nanoparticles

Alkanethiol-stabilized gold nanoparticles and oleic acid-stabilized iron oxide nanoparticles were deposited via a gas-expanded liquid (GXL) technique utilizing CO₂-expanded hexane onto substrates of different surface energy. The different surface energies were achieved by coating silicon (100) substrates with various organic self-assembled monolayers (SAMs). The films were characterized and the rms surface roughness values were obtained to determine the nanoparticle film deposition and growth characteristics. Based on the critical surface tension of the SAMs, the film growth indicates a shift between layer-by-layer deposition and island formation, which also results in a change in the surface roughness. Moreover, the surface roughness is influenced by the concentration of the nanoparticle solution, the average size, size distribution of nanoparticles and the nature of the nanopartcle surface chemistry. The manner in which the surface roughness was affected was investigated by using nanoparticles with different sizes. Based on this information, the potential exists to engineer nanoparticle films with desired morphologies and characteristics.