Nanoscale polarization patterning of ferroelectric Langmuir-Blodgett P(VDF-TrFE) films

This paper reports nanoscale piezoelectric measurements on ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) films prepared by the Langmuir-Blodgett (LB) technique. Polarization patterning, piezoelectric hysteresis and relaxation after poling are studied in this work by piezoresponse force microscopy. High quality P(VDF-TrFE) films with a copolymer content of 30% were fabricated using a Schaefer monolayer transfer setup permitting precise control of the film microstructure. The thickness of the films deposited with 100 transfers was ∼64 nm. Local switching resulted in written polarization lines with the lateral size in the range 70-300 nm depending on polarization time. Local hysteresis loop (at a fixed tip position) demonstrated clear ferroelectric switching with the coercive voltage ≈8-10 V that corresponds to a macroscopic switching field (∼1.5 MV cm^-1) at a ∼10 nm depth below the tip. Relatively slow ageing after poling was observed with the characteristic relaxation time of about 1500-2000 s depending on the polarization direction. The obtained results demonstrate that the stable polarization patterns can be created in LB P(VDF-TrFE) films and attest them as suitable candidates for memory and nanotemplate applications.