Study On The Influence Of Separation Speed On Micro-nano Adhesion Based On AF

In the field of MEMS,instruments are prone to adhesion between two surfaces due to abnormally large surface to body ratios.Adhesion problem is an important cause of failure in MEMS,and separation speed is a major factor affecting adhesion problem.Therefore,it is an urgent need to solve the problem of micro nano adhesion by analyzing the mechanism of separation speed.Therefore,this article explores the mechanism of adhesion through a large number of experiments and theories.The specific research conclusions are as follows:At moderate relative humidity,the adhesion on different material surfaces(with different hydrophilicities)was measured using AFM silicon microcantilever,and the separation rate dependence of adhesion was investigated.The variation range of separation speed exceeds four orders of magnitude.The results indicate that the speed dependence of adhesion separation is related to the surface material.On different material surfaces,the adhesive force exhibits different behaviors as the separation speed increases:(1)it is independent below the critical speed and decreases above it;(2)Large amplitude at low speeds,independent at high speeds;(3)Independence within the full speed range;(4)Independent at low speeds and large amplitude at high speeds;(5)Increase exponentially.The decreasing trend at high separation speeds is attributed to the instability of the liquid bridge during the separation process(low viscosity of the liquid bridge).The phenomenon of large amplitude at high separation speeds is attributed to the viscous force during separation(high liquid bridge viscosity).The independence within the full speed range is attributed to the balance and compromise between separation instability and viscous forces(liquid bridge viscosity medium).The phenomenon of exponential increase is attributed to the crack propagation process at the interface during separation.Based on experimental results,it is recommended to select a value less than 10 in the conventional adhesion measurement of AFM 10 μm/s Separation speed of m/s.The adhesion between silicon microcantilever and three surfaces(silica,monolayer graphene attached to silica surface,and HOPG)was measured using AFM at low,medium,and high relative humidity(～10%,～58%,～90%),and the effect of separation speed on adhesion was investigated at different residence times.The results show that there is a certain correlation between the separation speed dependence of adhesive force and its contact time dependence.The specific details are as follows:(1)At low,medium,and high relative humidity,the adhesion of the silicon dioxide interface increases with the increase of residence time(with a dependence on contact time).This is attributed to the increase in interfacial liquid bridges with contact time,which ultimately leads to an increase in capillary force.However,the adhesion between silicon graphene and silicon HOPG interfaces does not vary with residence time(no contact time dependence).This is attributed to the liquid bridge being able to reach saturation in a short period of time.(2)Under the conditions of low,medium,and high relative humidity and different residence times,the adhesion of the silicon dioxide interface tends to decrease with the separation speed.This trend includes two behaviors:continuously decreasing with increasing separation speed,and initially remaining unchanged and decreasing at high speeds with increasing separation speed.In addition,when the residence time is zero or a small value,the decrease in adhesion is greater,while in the case of long residence time,the decrease in adhesion is smaller.This decreasing trend is attributed to the dependence of contact time and instability during interface separation at high speeds.The higher the separation speed,the smaller the movement time,resulting in a smaller contact time(=residence time+movement time),which ultimately leads to a decrease in adhesion.(3)Under the conditions of low and medium relative humidity and different residence times,the adhesion at the silicon graphene interface exhibits two behaviors as the separation speed increases: maintaining the same behavior,and decreasing at high speeds.However,at high humidity,its adhesion remains unchanged or slightly decreases at low to medium separation speeds,while suddenly becomes extremely small at high separation speeds.(4)Under the conditions of low and medium relative humidity and different residence times,the adhesion force at the silicon HOPG interface also exhibits two behaviors as the separation speed increases: maintaining the same behavior,and increasing with the separation speed.However,at high humidity,its adhesion remains unchanged at low to medium separation speeds,while it may continue to remain unchanged or become very small at high separation speeds(i.e.,there are two different states).