Piezoelectric and pyroelectric properties of ferroelectric Langmuir–Blodgett polymer films

Abstract

, L.M.; Fridkin, V.M.; Palto, S.P.; Petukhova, N.N.; and Yudin, S.G., "Piezoelectric and pyroelectric properties of ferroelectric Langmuir-Blodgett polymer films" (1999 The piezoelectric and pyroelectric responses of ferroelectric Langmuir-Blodgett polymer films are less than the largest values measured with bulk films of the same composition. The films of the crystalline copolymer poly͑vinylidene fluoride trifluoroethylene͒ fabricated by the LangmuirBlodgett technique are 30 ML thick ͑15 nm͒ and are highly crystalline and oriented with polarization perpendicular to the film. Both piezoelectric and pyroelectric measurements show reversible ferroelectric switching. The films are suitable for use in pyroelectric infrared imaging and in piezoelectric acoustic transducers.

Intrinsic Ferroelectric Coercive Field

“…1. The time of switching varied from 1 to 10 s, so hysteresis loops were recorded by quasistatic pyroelectric [19,20] and capacitance [17] methods. The remanent polarization hysteresis loop measured by the Chynoweth pyroelectric method [19] at 25 ± C on a 30-ML is shown in Fig.…”

Ferroelectric nanomesa formation from polymer Langmuir–Blodgett films

“…Sample capacitance was measured with an impedance analyzer (HP 4192A) operating at 1 kHz with 0.1 V amplitude. The pyroelectric response of the capacitors, which is proportional to the net polarization, 15 was measured at zero bias by modulating the sample temperature with a 6 mW helium-neon laser beam modulated at 2 kHz, and recording the ac pyroelectric current from the sample with a lock-in amplifier.…”

Pyroelectric study of polarization switching in Langmuir-Blodgett films of poly(vinylidene fluoride trifluoroethylene)

“…There is evidence of a saturation of E c to its intrinsic value for very thin films, attributed to the suppression of switching nucleation and domain growth. 12 The switching in the thinnest films was found to be slow, in the range of seconds, 13,16 in sharp contrast to the microsecond switching times typical with much thicker films formed by solvent spinning. 24 Such a significant difference may be caused by suppression of nucleation or domain-wall motion.…”

“…The pyroelectric response of the LB films of the 70:30 P͑VDF/TrFE͒ copolymer does not differ much from much thicker solvent-formed films. 16 The stable polarization reversal was found even in thinnest films down to few transferred layers ͑Ͻ10 nm͒, showing no evidence of suppression of ferroelectricity by finite-size effects. 22 The LB films also have relatively high coercive field E c of the order of 100 MV/ m, increasing with decreasing thickness.…”

“…Another one, also proportional to the net polarization, arises from the secondary pyroelectric effect, which is the piezoelectric charge generated by the strain due to thermal expansion, and is influenced by constraints, such as the rigidity of the substrate. 15,16 Because both primary and secondary pyroelectricity are proportional to P s and , they need not be separated in the polarization reversal studies. In the PVDF family polymers with their complex morphology, a few other potential sources of current should be noted.…”