Local piezoelectric response and surface potential of dielectric and ferroelectric langmuir-blodgett films studied by electrostatic force microscopy

A comparative study of ultrathin dielectric (an azo-compound) and ferroelectric (copolymer PVDF-TrFE) Langmuir-Blodgett (LB) films has been carried out by Electrostatic Force Microscopy (EFM). Films were poled locally by a strong d.d. field applied between a conductive tip of an Atomic Force Microscope (AFM) and the bottom Al electrode. The electrically poled domain was studied by EFM using a weak a.c. electric field and a lock-in amplifier technique. Two modes, a contact and non-contact ones, allowed for the measurement of field E in the air gap between the film and the tip and the piezoelectric distortion of the film due to d.c. field aligned spontaneous polarization. Simultaneously the topographic relief of the same area was imaged. The results confirm unequivocally a possibility to switch ferroelectric LB film locally by an AFM tip.