  Due to their exceptional mechanical and optical properties, dielectric
silicon nitride (SiN) micromembrane resonators have become the centerpiece of
many optomechanical experiments. Efficient capacitive coupling of the membrane
to an electrical system would facilitate exciting hybrid optoelectromechanical
devices. However, capacitive coupling of such dielectric membranes is rather
weak. Here we add a single layer of graphene on SiN micromembranes and compare
electromechanical coupling and mechanical properties to bare dielectric
membranes and to membranes metallized with an aluminium layer. The
electrostatic coupling of graphene coated membranes is found to be equal to a
perfectly conductive membrane. Our results show that a single layer of graphene
substantially enhances the electromechanical capacitive coupling without
significantly adding mass, decreasing the superior mechanical quality factor or
affecting the optical properties of SiN micromembrane resonators.
