Monolayer formation of colloidal nanoparticles on various substrates by single and multiple dip-coating process

The adsorption behavior and monolayer formation of colloidal nanoparticles on various substrates are investigated by employing the single and multiple dip-coating process. The colloidal particles passivated by the surfactant and dispersed in the solvent are found to adsorb on the substrate within the solution. The particle layer formed by the adsorption of particles has the coverage proportional to the interaction between particle and substrate. For example, the 10 mn-size maghemite (gamma-Fe2O3) particles, passivated by oleic acid and dispersed in octane solution adsorb on three different substrates (Si, Si3N4, and SiO2) and have the coverage of 0.45 on Si and much less in other substrates (0.19 on Si3N4 and 0.14 on SiO2). In addition, the particle coverage was drastically increased by the multiple-adsorption process, repeating the process of dipping and drying multiple times. With this process, we can obtain the maximum coverage of particles up to about 0.76 on a Si substrate and 0.61 on a thermally grown SiO2 substrate. These phenomena were reproducibly demonstrated in other particle-substrate systems, for example, CdSe particles on Si and PEDOT substrate.