Organosilane self-assembled monolayers directly linked to the diamond surfaces

Abstract

An amino-terminated self-assembled monolayer (SAM) was prepared from p-aminophenyltrimethoxysilane (H2N(CH)6Si(OCH3)3,APhS) on diamond substrates irradiated by vacuum ultraviolet (VUV) light (wavelength: 172nm) through chemical vapor deposition. Furthermore, the APhS-SAM was irradiated by VUV light in air. After the VUV irradiation, only one layer of siloxane (SiOx) was left as a result of the selective decomposition of organic compounds. APhS-SAM was reprepared on the SiOx surface. The evidence as to the respective processes was clearly obtained by x-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Based on the chemical bonding states analysis, APhS-SAMs were confirmed to be directly linked to the diamond substrates and SiOx layers with bonding types of Si–O–C and Si–O–Si, respectively. The compositions obtained by XPS measurement indicate that the thickness of the SiOx layer was increased gradually by repeating the APhS-SAM formations and VUV irradiations in this order. Finally, we are successful in controlling the nano-scale thickness of the SiOx layer, which is the interface between APhS-SAMs and diamond substrates.