The Study On Adhesion Of Nanobeam Under Van Der Waals Force

This work is focused on researching the influence of van der waals (vdw) forces on adhesion and pull-in stability of nanobeams which will be a reference in future NEMS design.First, the static adhesions of two silicon surfaces were studied under vdw forces when other surface forces were reduced by some technology. Considering the actual self-affine fractal surfaces contact model of two rough surfaces, the adhesion energy between two surfaces under vdw forces were calculated after adhesion due to elastic and plastic deformations. A general formula is deduced to calculate the adhesion energy and the effects of surface roughness on the adhesion energy of vdw forces were analyzed.Secondly, the pull-in phenomena of electrostatic actuated nanobeams which is widely used in MEMS/NEMS was studied under vdw forces. We extended the one-lumped model and energy-method model to study the relation between two pull-in voltages with or without vdw forces. The pull-in voltage of nano cantilevers and fixed-fixed beams under electrostatic and vdw forces were calculated by a number analysis method and contrast it to the value calculated by one-lumped model method. Then we analyzed the different structure's effect on pull-in voltage. It shows the pull-in deflection is one third of the initial gap under different voltages and structures. The static pull-in voltage with vdw force interaction is between one third and one fourth of the value without vdw forces.Thirdly, we simulated the deformation of nanobeams under the electrostatic and vdw forces by ANSYS software and compare the deflection of nanobeams with the value calculated by the number analysis method. We analyzed the influence of axial stretching of beam on the deflection. The deflection values of nanobeams with or without vdw forces interaction were compared with each other. It shows the deflection of nanobeam is reduced considering the axial stretching.At last, the dynamic deformation of nanobeams was study under the vdw forces and electrostatic forces. The static and dynamic pull-in voltages were compared. The natural frequency and modal of nanobeams were studied. The transient response was simulated by Ansys software. The influence of vdw forced on the pull-in time and dynamic pull-in voltage were analyzed. It shows the dynamic pull-in voltage is small than the static value. The pull-in time is reduced with vdw forces interaction.