Vapor-Phase Grafting of Functional Silanes to Al2O3, ZnO, and TiO2 Surfaces Prepared By Atomic Layer Deposition

Abstract

Atomic layer deposition (ALD) is a highly versatile surface functionalization technique that can conformally coat both planar and porous substrates. Surface modification of ALD films with organic species is an ideal way to tailor the surface properties for applications such as water treatment, sensors, gas capture and drug delivery. Here we demonstrate ALD metal oxide layers to establish a well-defined starting surface for vapor-phase surface organic functionalization. We investigated the surface chemistry of ALD Al2O3, TiO2, and ZnO and the grafting of six different bifunctional silanes at 100 ℃, 150 ℃ and 200 ℃. 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 show the uniform monolayer silane formation through self-limiting reaction. We observed a higher surface reactivity of grafted silane species at 100 ℃ compared to 200 ℃, which is attributed to temperature-dependent reactivity of the surface hydroxyls and the type of silane binding. The FTIR and XPS measurements also reveal that silanes react differently depending on the metal oxide surfaces.