  The ultra-short range force, van der Waals force (VWF), will rise rapidly
when one nanoscale waveguide is close to another one, and be stronger than the
external transverse gradient force (TGF). We theoretically investigate the
giant influence of the VWF on the device performance in a typical
optomechanical system consisting of a suspended silicon waveguide and a silica
substrate including waveguide deformation stiction and failure mechanism. The
device shows unique optically-activated plastic/elastic behaviors and stiction
due to the VWF. When the input optical power is above the critical power, the
waveguide is sticking to the substrate and the deformation is plastic and
unrecoverable, even though the total force is less than the yield strength of
the waveguide material. This is important and helpful for the design and
applications of optomechanical devices.
