The decomposition mechanism of p-chloromethylphenyltrimethoxysiloxane self-assembled monolayers on vacuum ultraviolet irradiation

Abstract

The decomposition mechanism of p-chloromethylphenyltrimethoxysiloxane (CMPS) self-assembled monolayers (SAMs) due to vacuum ultraviolet (VUV) irradiation at a wavelength of 172 nm has been studied based on water repellency, X-ray photoelectron spectroscopy (XPS) and Kelvin probe force microscopy (KPFM). The CMPS-SAMs were prepared through chemical vapor deposition at 100 °C. The water contact angle increased dramatically within the first 30 min, reaching a plateau at this point. The saturated water contact angle was 76°. Next, the CMPS-SAMs were irradiated at under 10 Pa from 0 to 30 min. The CMPS-SAMs irradiated for 15 and 30 min were covered with carboxylated hydrocarbon fragments and silanol groups, respectively. KPFM measurements for micro-patterned SAMs, i.e. CMPS/CO₂H and CMPS/SiOH, showed that the surface potential of the carboxylated and silanol regions were −16 and +19 mV vs. CMPS-SAM, respectively. The former negative surface potential difference originated in the electronegativity of the CO₂H fragments. These results provide us with a route to prepare an organic template for various fields such as bio-sensors, chemical sensors and electrolytes.