Thermal stability of self-assembled octadecyltrichlorosilane monolayers on planar and curved silica surfaces

Understanding the structural and functional integrity of self-assembled monolayers (SAMs) of alkytrichlorosilane on Si/SiO₂ interface with change in temperature is critical for realizing their utility as antistiction coatings during the fabrication and functioning of microelectromechanical systems. Here we describe the thermal stability of two dimensional (2D) octadecyltrichlorosilane (OTS) monolayers on both n-type Si substrate (planar surface) and silica spheres (curved surface) using results of various surface sensitive spectroscopic techniques like the grazing angle Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Densely packed OTS monolayer on n-type Si surface is found to be thermally stable up to 525 K, while a significant enhancement in the thermal stability is interestingly observed for the case of OTS SAM (up to 625 K) on freshly prepared spherical silica surfaces. Despite this difference in the thermal stability, the results of temperature dependent infrared spectra demonstrate monolayer decomposition in both cases through the involvement of both Si-C and C-C bonds leaving Si-O-Si bond intact.