  Using the measured optical response and surface roughness topography as
inputs, we perform realistic calculations of the combined effect of Casimir and
electrostatic forces on the actuation dynamics of micro-electromechanical
systems (MEMS). In contrast with the expectations, roughness can influence MEMS
dynamics even at distances between bodies significantly larger than the
root-mean-square roughness. This effect is associated with statistically rare
high asperities that can be locally close to the point of contact. It is found
that, even though surface roughness appears to have a detrimental effect on the
availability of stable equilibria, it ensures that those equilibria can be
reached more easily than in the case of flat surfaces. Hence our findings play
a principal role for the stability of microdevices such as vibration sensors,
switches, and other related MEM architectures operating at distances below 100
nm.
