Calibration of piezoelectric bimorphs for experiments in a surface forces apparatus

A simple interferometric method is described to measure the time-dependent deformation of piezoelectric bimorphs driven by ac voltage. Applying this m ethod to a bimorph assembly used to measure viscoelastic forces in a surfac e forces apparatus, we find that a sinusoidal-shaped harmonic drive voltage generates sinusoidal deformation but that a triangular-shaped harmonic dri ve voltage fails to produce triangular-shaped deformation if the drive freq uency exceeds 1/100 of the resonance frequency. Sinusoidal displacement amp litudes as small as 0.1 nm were resolved. (C) 2000 American Institute of Ph ysics. [S0034-6748(00)00110-6].