Freestanding membranes of cross-linked gold nanoparticles: novel functional materials for electrostatic actuators

Their tunable electrical, optical, and mechanical properties make freestanding membranes of organically cross-linked gold nanoparticles (GNPs) interesting materials for applications in micro- and nanoelectromechanical systems. Here, we demonstrate the application of α,ω-alkanedithiol-cross-linked GNP membranes as electrostatically driven actuators. The devices were fabricated by depositing these membranes (thickness 29-45 nm) onto cylindrical cavities (diameter ∼200 μm; depth ∼8-15 μm), which were lithographically patterned in a SU-8 resist. Applying voltages of up to ±40 V across the membrane and the silicon substrate deflected the membranes by several hundreds of nanometers, as measured by atomic force microscopy, confocal microscopy, and interferometry. A simple electrostatic model, which takes into account the membranes' mechanical properties, was used to interpret the experimental data.