  The electrostatic pull-in instability (EPI), within the framework of the
nanoelectromechanical systems (NEMS) has been shown as a robust and versatile
method for characterizing mechanical properties of nanocantilevers. This paper
aims to investigate the surface effects, specifically residual surface stress
and surface elasticity, on the EPI of micro and nano-scale cantilevers as well
as double clamped beams. Since the cantilever has one end free, it has no
residual stress, thus the strain-independent component of the surface stress or
intrinsic surface stress has no influence on the EPI, as long as it has small
deformation. The strain-dependent component of the surface stress or surface
elasticity changes the bending stiffness of the cantilever and, consequently,
induces shifts in the EPI. For double clamped beams, the effective residual
surface stress comes into play and modifies the effective residual stress of
the beam. The nonlinear electromechanical coupled equations, which take into
account the surface effects are solved numerically. The theoretical results
presented in this paper indicate that the EPI is very sensitive to the surface
effects, especially when a double clamped beam is employed. The results show
that the influence of surface effects on the EPI of cantilevers become more
profound when the thickness is below 50 nm, while the influence on double
clamped beams is significant even at sub-micron scale. The present study can
provide helpful insights for the design and characterization of NEMS switches.
Moreover, the results can be used to provide the proof of concepts of a new
surface stress sensing method using EPI in nanomechanical sensor systems.
