Electrophoretic Deposition of Au Nanocrystals inside Perpendicular Mesochannels of TiO2

Au nanocrystals stabilized by dodecanethiol were deposited into 100−150 nm thick TiO2 films with evenly spaced perpendicular nanopillars and mesochannels on the order of 10 nm supported on conducting ITO/glass electrodes. Electrophoretic deposition was used to enhance nanocrystal deposition within the mesoporous TiO2 film. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy-dispersive X-ray (EDX), UV−vis spectroscopy, variable-angle spectroscopic ellipsometry (VASE), and scanning surface potential microscopy (SSPM) were used to characterize the resulting Au nanocrystal/TiO2 composites. Au nanocrystal loadings reached 21 wt % and were not kinetically limited at 10 min, relative to depositions performed for 20 h. Both VASE measurements of the anisotropy of the imaginary refractive index, k, and X-ray photoelectron spectroscopy (XPS) depth profiling studies indicate that Au nanocrystals are dispersed within the vertically aligned mesopores and distributed throughout the film. The mean penetration depth of a single nanocrystal penetrating inside the film is described with a model in terms of the electric field and a local deposition rate constant, which is influenced by ligand binding and architecture on the nanocrystal surface.