  We have designed photonic crystal suspended membranes with optimized optical
and mechanical properties for cavity optomechanics. Such resonators sustain
vibration modes in the megahertz range with quality factors of a few thousand.
Thanks to a two-dimensional square lattice of holes, their reflectivity at
normal incidence at 1064 nm reaches values as high as 95%. These two features,
combined with the very low mass of the membrane, open the way to the use of
such periodic structures as deformable end-mirrors in Fabry-Perot cavities for
the investigation of cavity optomechanical effects
