The creation of the piezoresponse force microscopy twenty-three years ago

In the late 80ths we constructed a light fibre interferometer, which could measure the voltage-induced thickness variations of piezoelectric samples down to some few picometres. The principle of the interferometer is explained and four methods to minimize noise. With this sensor, we started a home-made PFM in February 1993. The very first pictures are shown together with locally measured polarization cycles. We found out that the inverse piezoelectric effect dominates the first harmonic of the PFM.