Research On Preparation And Tribological Characteristics Of Self-Assembled Monolayers

The lubrication in nano-scale in the techniques of microelectromechanical system and high-speed magnetic recording system is imperatively to be solved with the rapid development of nano-science and technology. The technology of self-assembled monolayers(SAMs) is one of effective techniques in nano-scale lubrication. The preparation and tribological characteristics of SAMs were studied in this paper. The mechanical model for atomic force microscopy (AFM) tip sliding on the surface of sample was also set up. The main conclusions were reached as follow:1. 3-Amino-Propyltrimethoxysilane(APS) SAMs were prepared on the substrate of Si/SiO2.With observing the topography under different reaction time by AFM, The formation mechanism of aminosilane SAMs was concluded. Experimental results indicated that there are two stages in the process of formation of SAMs. At first stage, the quantity of "island" increased with reaction time. At second stage, the "islands" grew up with reaction time.2. The relationship of frictional coefficients of OTS and APS and sliding velocity was analyzed under constant load by Universal micro-tribometer(UMT). And the relationship of frictional coefficients and load was also analyzed under constant velocity by UMT. Experimental results indicated that frictional coefficient of OTS film increased with sliding velocity increasing, whereas frictional coefficient of APS film decreased with sliding velocity increasing, frictional coefficients of both OTS and APS films decreased with load increasing. It is chain length that leads to the differences of two kind of films in tribological characteristics.3. The effects of interfacial contact characteristics on the friction properties ofSAMs were analyzed in the condition of different sliding velocity and load by UMT. The results indicated that the friction coefficients of Ni with both OTS and APS were larger than those of Cu with both OTS and APS. The friction coefficients of Cu and Ni for OTS increased with sliding velocity increasing and reduced with load increasing.The friction coefficient between Cu and APS reduced with sliding velocity increasing. The effect of load on friction was relatively low. However, the friction coefficient between Ni and APS increased with sliding velocity increasing and reduced with load increasing.4.The mechanical model for AFM tip sliding on the surface of sample was set up. Verification was conducted by experiment. The results indicated that the periodicity of frictional force curve increased and the amplitude decreased with the asperity space increasing. The interaction potential VQ represented the surface energy, the amplitude of frictional curve increased when VQ increased. The damping depended on the sliding velocities and the amplitude of frictional force curve was invariable, but the curves went down slightly with the damping reducing. The frictional force was independence of the sliding velocities in some range.