Modifying the zeta potential of silica particles via atomic layer deposition of nanoscale oxide coatings

Atomic layer deposition (ALD) shows promise for purposefully modifying the surface chemistry of powders because it has excellent control over the thickness of the applied coatings. ALD can precisely deposit coatings with a resolution approaching 0.1 nm, providing intricate control over surface properties. However, few studies have investigated the potential to systematically vary the surface potential of powders using this precision in ALD’s deposition process. In this work, titanium oxide thin films are deposited onto silicon oxide nanoparticles via ALD to create silica–titania core-shell nanoparticles. The change in the isoelectric points of the particles is investigated as a function of the thickness of the ALD deposited TiO2 layer. For films deposited at 1 nm thickness and below, the isoelectric point changes approximately linearly with coating thickness. For films thicker than 1 nm, the isoelectric point no longer changes, indicating that the surface potential is no longer influenced by the underlying silicon oxide core. We investigate the conformality of the coating with electron microscopy, x-ray photoelectron spectroscopy, and energy-dispersive x-ray (EDX) analysis. Additionally, we introduce a model to estimate layer thickness from the EDX measurements based on simple geometric and stoichiometry assumptions.