AFM characterisation of silicon-on-insulator push-in plates for Casimir force measurements

The use of silicon-on-insulator (SOI) material to fabricate a set of push-in plates for Casimir force measurements is reported. These plates have the advantage of being parallel as fabricated, which is an essential criterion for accurate Casimir force measurements. The roughness of the inner SOI silicon surfaces after the removal of the sacrificial buried oxide and subsequent CO2 critical point drying is characterised. The root-mean-square (RMS) surface roughness measured by atomic force microscopy (AFM) is of the order of 0.25 nm and is shown by calculation to be an insignificant contribution to the measurement of the Casimir force with these plates.