Single and multiple-step dip-coating of colloidal maghemite (γ-Fe2O3) nanoparticles onto Si, Si3N4, and SiO2 substrates

The adsorption behavior of colloidal maghemite (gamma-Fe2O3) nanoparticles, passivated by oleic acid and dispersed in octane solution, onto three different substrates (Si, Si3N4, and SiO2) is investigated. The average nanoparticle size is 10 nm, with a size variation (sigma) less than 5%. The adsorption of particles is strongly dependent on both the type of substrate and the particle concentration in solution. By a single-dipping process, we have obtained a maximum coverage of 0.45 on a Si substrate but much less on other substrates (0.19 on Si3N4 and 0.14 on SiO2). The particle coverage was drastically increased by the multiple-adsorption process, where the process of dipping and drying was repeated multiple times. With this process, we can obtain a maximum particle coverage of about 0.75 on a Si substrate and 0.61 on a thermally grown SiO2 substrate.