Pyrolysis of self-assembled organic monolayers on oxide substrates

Abstract

The pyrolysis of siloxy-anchored, organic self-assembled monolayers (SAMs) on oxide substrates [titanium dioxide powder; hydrolyzed silicon dioxide on (100) silicon] was studied using x-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and mass spectroscopy (MS). Pyrolysis in air began on heating at 200 °C and was complete by 400 °C for both octadecyltrichlorosilane (OTS) and C16-thioacetate (TA) SAMs, as observed in TGA of SAM-coated TiO2 powders, and in XPS studies of TA-SAM-coated TiO2 powders and Si wafers after various heat treatments. In low-oxygen environments, pyrolysis of SAMs began at higher temperatures: between 250 and 400 °C for heating in ultrahigh vacuum (10−8 Torr) as observed in XPS studies of TA-SAMs on Si, and between 300 and 400 °C in nitrogen, as observed in TEM analysis of sulfonate SAMs under a TiO2 thin film on Si substrates.