Toward Dynamic Control over TiO2 Nanocrystal Monolayer-by-Monolayer Film Formation by Electrophoretic Deposition in Nonpolar Solvents

摘要

The controlled electrophoretic deposition ofnmonolayers and ultrathin films of 4.0 nm TiO2 nanocrystalsnfrom stable, nonpolar solvent-based suspensions is reported.nStable suspensions were prepared in hexane, and the electrophoreticnmobility of the nanocrystals was enhanced by ancombination of a liquid−liquid extraction followed by mechanicalnsurfactant removal by high-speed centrifugation. The controllednevolution of the density of TiO2 nanocrystal monolayers wasnstudied by transmission electron microscopy and opticalntransmittance spectroscopy. Ultrathin films were assembled while maintaining monolayer-by-monolayer growth and uniformndensity of the film. A time-dependent, equivalent circuit model has been proposed to characterize the electrophoretic current thatnwas recorded during our experiments. Further, we demonstrate that the proposed model, coupled with the mobility, provides anmeans to estimate the deposition rate and, hence, the time necessary to fabricate a submonolayer, a monolayer, and multilayers ofnnanocrystals.