Surface Effects on the Jump-in Instability of Nanomechanical Structures

Abstract

Surface effects are indispensable for crystalline materials when the characteristic size falls into nanoscale. In this paper, the size-dependent jump-in instability of an ultrathin film, omnipresent in nanoelectromechanical systems, is analyzed by incorporating the effects of surface energies. Based on a nonclassical thin plate theory including surface effects and the thermodynamic energy balance theorem, the jump-in instability mechanism of the film is established to determine the critical separation gap and contact length between the film and the substrate. We found that the dimensionless forms of these two mechanical properties depend on the thickness of the film. When the residual surface stress is ignored, the critical separation gap is affected by the surface elasticity, but the contact length is not. An aluminum film is considered as an illustrative example, for which the effect of residual surface stress is superior to that of surface elasticity.

Surface effects at the nanoscale based on Gurtin’s theory: a review

“…The importance of surface stress effects was illustrated by employing the energy minimization method within the framework of continuum mechanics. The finding of Lü et al [93] on the occurrence of jump-in instability in a nanoplate suggests that surface elasticity can affect the critical separation gap but not the contact length between the ultrathin Brought to you by | Western University Authenticated Download Date | 6/8/15 3:42 PM film and substrate. Another of their publications reported that the surface effect will become more significant and indispensable when the thickness of functionally graded films reduces to the intrinsic length scale [94].…”

Theory of energy harvesting from heartbeat including the effects of pleural cavity and respiration

“…When undergoing a large deformation (A > A c ) during the systole of the heart, the MEH device will contact with the surrounding tissues at the centre part. Here, the adhesion effect between the MEH device and the surrounding tissues is neglected, then the contact length will be zero [32,33], that is, the device will have only the centre point contacting with the surround tissues. For simplicity, the deformation of the surrounding tissues is further ignored or the surrounding tissues are assumed rigid when compared with the MEH device, then the displacement and the slope at the device centre will keep at w| x=0 = A c and w | x=0 = 0.…”

“…When undergoing a large deformation (A > A c ) during the systole of the heart, the MEH device will contact with the surrounding tissues at the centre part. Here, the adhesion effect between the MEH device and the surrounding tissues is neglected, then the contact length will be zero [32,33], that is, the device will have only the centre point contacting with the surround tissues.…”