Vapor-phase grafting of a model aminosilane compound to Al2O3, ZnO, and TiO2 surfaces prepared by atomic layer deposition

Atomic layer deposition (ALD) is a highly versatile surface functionalization technique that can conformally coat both planar and porous substrates. Here we use ALD metal oxide layers to establish a well-defined starting surface for vapor-phase surface organic modification. Vapor-phase (3-aminopropyl)triethoxysilane (APTES) surface silanization of ALD Al2O3, ZnO and TiO2 surfaces were studied at 100 degrees C, 150 degrees C and 200 degrees C. In situ quartz crystal microbalance (QCM) and Fourier-transform infrared (FTIR) spectroscopy measurements, and ex situ atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) measurements showed uniform monolayer silane formation through self-limiting APTES reaction. We observed a higher surface density of grafted APTES species following silanization at 100 degrees C compared to 200 degrees C, and we attribute this to the temperature-dependent reactivity of the surface hydroxyls and changes in the mode of APTES reaction. The FTIR and XPS measurements revealed that APTES reacts with Al2O3 and ZnO exclusively through metal siloxy bond formation. However, APTES reacts with TiO2 through both siloxy bond formation and ammonium salt formation via the amine group.

Automated summary

ALD metal oxide layers were surface modified with vapor-phase (3-aminopropyl)triethoxysilane (APTES) at different temperatures, showing uniform monolayer silane formation through various measurement techniques. Higher surface density of grafted APTES species was observed at lower temperature due to temperature-dependent reactivity of the surface hydroxyls. APTES reacted with Al2O3 and ZnO exclusively through metal siloxy bond formation, while with TiO2 through both siloxy bond formation and ammonium salt formation.