Casimir Force and In Situ Surface Potential Measurements on Nanomembranes

We present Casimir force measurements in a sphere-plate configuration that consists of a high quality nanomembrane resonator and a millimeter sized gold coated sphere. The nanomembrane is fabricated from stoichiometric silicon nitride metallized with gold. A Kelvin probe method is used in situ to image the surface potentials to minimize the distance-dependent residual force. Resonance-enhanced frequency-domain measurements of the nanomembrane motion allow for very high resolution measurements of the Casimir force gradient (down to a force gradient sensitivity of 3 mu N/m). Using this technique, the Casimir force in the range of 100 nm to 2 mu m is accurately measured. Experimental data thus obtained indicate that the device system in the measured range is best described with the Drude model.