Preparation and tribological behaviors of an amide-containing stratified self-assembled monolayers on silicon surface

An amide-containing stratified self-assembled film is grafted on a silicon surface by a simple two-step method. First, N-[3-(trimethoxylsilyl)propyl]ethylenediamine (DA) molecules are self-assembled on silicon surfaces followed by deriving with stearoyl chloride (STC) through a surface coupling reaction. The films are characterized by means of contact angle measurement, ellipsometry, and attenuated total reflectance Fourier transformed infrared (ATR-FTIR) spectra. STC forms an ordered and hydrophobic film over the DA layer with a water contact angle of nearly 110 degrees. A microtribological study of the films is carried out on an atomic force microscope (AFM), and the wear-resistant property is tested on a ball-on-plate tribometer. Compared to the films in our previous study, the friction-reducing and load-affording abilities of the film are greatly improved. We contribute the improvements to the existence of two layers of hydrogen bonds, which can enhance the stability of the film by double in-plane cross-linking.