Preparation and tribological properties of multiply-alkylated cyclopentane (MAC)–octadecyltrichlorosilane (OTS) double-layer film on silicon

A double-layer lubricant film consisting of a multiply-alkylated cyclopentane (MAC) mobile lubricant on octadecyltrichlorosilane self-assembled monolayer (OTS-SAM) was prepared. Atomic force microscopy (AFM) was used to examine the film surface. MAC with thickness of 25 Å was successfully coated on the OTS-SAM surface. MAC was discretely distributed on the OTS-SAM surface, and the film contained evenly distributed islands with a typical diameter of 25 nm and an average height of 25 Å. The area covered by the MAC was approximately 70%. Measurements were also performed on 50 Å Zdol-2000 film and 25 Å OTS-SAM for comparisons. The film thickness was measured by Gaerter elipsometer and the static contact angle was measured using a Kyowa contact-angle meter. The thickness of the lubricant film determined by the AFM was consistent with that measured by ellipsometer. The measured static angle of the 50 Å MAC–OTS double-layer film was about 110°, slightly greater than that of 108° of 25 Å OTS-SAM and that of 106° of 50 Å Zdol-2000. Tribological properties of the three kinds of films were evaluated using a ball-on-plate type universal DF-PM unidirectional sliding tribometer. The worn surfaces of the films were examined using a high precision non-contact surface profiler. All the films exhibited similar friction coefficients of about 0.1 at a normal load of 0.5 N, but the MAC–OTS double-layer film exhibited extended durability and higher load-carrying ability compared with 50 Å Zdol-2000 film or 25 Å OTS-SAM.