Preparation Of Mixed Self-Assembled Monolayers By Co-Adsorbed Method And Study On The Micro Tribological Properties

With the further study of SAMs technique on MEMS devices lubricating, the organic silane SAMs, especially the mixed SAMs consist of two or more than two kinds of silane molecules, have gained widely attention by researchers for its excellent antifriction performance. In this paper, the preparation and micro-tribological properties of APS-WD-10 mixed SAMs have been experimentally studied.In order to obtain the optimum mixed SAMs assembly process, MS was used to respectively establish Si(100), APS, WD-10 molecular model. The molecular system model, which contained SAMs layer and the silicon substrate layer, was established on the basis of the calculation of the substrate surface coverage of SAMs. Molecular dynamics simulations were performed on the established model molecular systems to discuss the effect of different assembly temperatures and molecular concentration ratio on the performance of mixed SAMs and provide a theoretical basis for the preparation of mixed SAMs.Orthogonal test table were formulated based on MS software simulation to prepare the mixed SAMs under the adequate consideration of the effect of temperature, molecular concentration ratio, assembly time and PH value of the solution in the preparation of APS and WD-10 mixed SAMs using self-assembly techniques. XPS and AFM were used to analyze the surface morphology and chemical composition of elements to obtain the optimal assembly conditions and preparation process.The thermodynamic calculation shows silane molecule could be spontaneously adsorbed on silicon substrate surface in the preparation of mixed SAMs by co-adsorbed techniques. The surface tension and surface energy of mixed SAMs were derived by the integral transformation and Maxwell relations, which demonstrated the decrease of the film surface energy was conductive to the spontaneous reaction of silane molecule substrate assembly. Also, the effect of environmental factors on the assembly mechanism of silane molecular substrate surface has been researched in the preparation process by co-adsorbed technique.At last, three different concentration ratio mixed SAMs were experimentally studied using UMT to explore antifriction property of the SAMs. The micro friction and wear behaviors of mixed molecular film were studied using MEMS micro friction testing machine, which analyzed the micro friction mechanism of SAMs, investigated the variation of friction coefficient of different concentration ratio of SAMs and silicon chips with the relative sliding velocity and discussed the effect of different loads on mixed SAMs friction coefficient.