Molecular Dynamics Simulations On Friction Properties Of The Silicon Micro-structure Surface

With the development of nanotechnology and the increase of social demands,the miniaturization of devices has become an inevitable trend.The miniaturization of devices leads to the increase of the specific surface ratio,and the surface effect is obviously enhanced,which makes the surface forces,such as adhesion and friction,become the key factors that affect device performance and service life.Surface microstructure texturing on device surface is one of the effective ways to solve this problem.It is helpful to study the friction behavior of the surface microstructure in micro/nano scale,which can deepen the understanding of surface friction principle and guide the manufacture and development of micro-nano devices.Molecular dynamics simulations are performed to establish the dry friction model of silicon surface at atomic scale.A silicon tip sliding on a silicon substrate,is simulated with three substrate surface microstructures,including stripe,grid and pit,to study the effects of various microstructure and their sizes on the friction properties.The results show that the sliding friction between the probe and silicon substrates is significantly reduced with the introduction of surface microstuctures,and the largest friction reduction occurs on grid surface microstructure,followed by that on the stripe surface microstructure,and the least one is on the pit surface microstructure.In addition,the friction force increases with the increasing width of pit and stripe surface microstructures,and the width of grid-shape microstructure has no obvious effects on the friction force.Furthermore,it is also found the friction force decreases with the increasing depth of all these three surface microstructures.Molecular dynamics simulation models are also established study the probe sliding on the wet silicon substrate surfaces,and to further investigate influences of the water film thickness,the shape and size of microstructures and the surface anisotropy on the wet friction.The results show that the friction increases with the introduction of water molecules on substrates,and the augment of friction is enhanced with the number of water molecules increasing firstly and then followed by slight reduction.The adhesion of water molecules to the probe is obviously weakened by the microstructure surfaces.For different surface microstructure widths,movement distances of the probe on various microstructure-shaped surfaces are diverse when water molecules are separated from it,however,all decrease with the increasing depth.For the stripe-shape surface microstructure,the friction force of the vertical stripe surface is less than that of the parallel one in wet friction state.But in dry friction state,the friction force on vertical stripe surface is greater than that of parallel one...