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 poly(vinylidene fluoride trifluoroethylene) fabricated by the Langmuir–Blodgett technique are 30 ML thick (15 nm) 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.

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Piezoelectric and pyroelectric properties of ferroelectric Langmuir-Blodgett polymer films

In this review the physical properties, mechanisms and models are reviewed which explain the high piezoelectricity of the ferroelectric polymers of the polyvinylidene fluoride (PVDF) family, the odd nylons, the vinylidene cyanide (VDCN) copolymers and polyurea. Because PVDF and its copolymers with trifluoroethylene (TrFE) and tetrafluoroethylene (TFE) have been studied extensively in the last 25 years the main part of the review deals with these polymers. Additionally a short summary of the different piezoelectric applications of PVDF is presented. The odd nylons, the VDCN copolymers and the polyurea are compared with PVDF to show the different stabilization mechanisms of the remanent polarization and the different temperature behavior of the piezoelectricity. This review not only concentrates on the work done in the last few years but in order to describe the behavior of these polymers in detail, it is necessary to go back to the roots. Therefore many articles from the late seventies and early eighties are included.

Piezoelectric polymer electrets

The article presents the recent research development in controlling molecular and microstructures of thin ferroelectric polymer films for the application of non-volatile memory. A brief overview is given of the history of ferroelectric memory and device architectures based on ferroelectric polymers particularly emphasizing on the device elements such as metal/ferroelectric/metal type capacitor, metal-ferroelectric-insulator-semiconductor (MFIS) diodes and ferroelectric field effect transistor (FeFET) with ferroelectric poly(vinylidene fluoride) (PVDF) and its copolymers with trifluoroethylene (TrFE). Key material and process issues for optimizing the memory performance in each device architecture and thus realizing non-volatile ferroelectric polymer memory are in details discussed, including the control of crystal polymorphs, film thickness, various hetero-material interfaces between ferroelectric polymer and either metal or semiconductor, crystallization and crystal orientation. The current effort of micro and nanopatterning techniques is also addressed for high density and flexible memory arrays.

Control of thin ferroelectric polymer films for non-volatile memory applications

A surface X-ray diffraction study is presented showing that highly ordered and uniaxially aligned hexa(3,7-dimethyl-octanyl)hexa-peri-hexabenzocoronene (HBC-C8,2) films can be fabricated by crystallization from solution onto friction-transferred poly(tetrafluoroethylene) (PTFE) layers. Three crystalline HBC-C8,2 majority phases result. In all three phases, the HBC-C8,2 molecules self-organize into columns which are uniaxially aligned along the direction defined by the PTFE macromolecules of the substrate. The three phases are quite similar, the major difference being their orientation with respect to the substrate. A quasi-2D epitaxial growth mechanism with a grapho-epitaxial component for one of the three phases explains the formation of the three rotational HBC-C8,2 variants. A method to obtain a thin film with only one phase is proposed. The results show that standard THETAV;-2THETAV; X-ray diffraction and transmission electron diffraction can be very misleading tools to estimate the crystalline quality in a thin film of complex structure.

Induced alignment of a solution-cast discotic hexabenzocoronene derivative for electronic devices investigated by surface X-ray diffraction.

A remanent polarization of 130±3 mC/m2, large among the values reported for organic materials, and rectangular D–E hysteresis curves were realized in synthesized vinylidene fluoride (VDF) oligomer [CF3(CH2CF2)17I] film evaporated onto a platinum surface around liquid nitrogen temperature. The results suggested that the VDF oligomer film has an extremely high crystallinity, and the electric dipoles arrange almost perfectly perpendicular to the film surface, and that a Lorentz local field factor of ferroelectric VDF oligomer crystals is nearly zero. Moreover, the obtained value of the coercive field, which was larger than those of ferroelectric polymers, might be attributed to the steric hindrance arising from the existence of iodine atoms at the VDF oligomer chains.

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Remanent polarization of evaporated films of vinylidene fluoride oligomers

Highly crystalline and uniaxial-oriented polytetrafluoroethylene films, nanostructured in one dimension, were used to produce a fully crystalline, thermoreversible morphology in the ferroelectric copolymer poly[vinylidenefluoride-trifluoroethylene]. The resulting state is built up of regularly stacked lamellar crystals of about 100 nm thickness and lateral dimensions of about 6 \ensuremath{\mu}m.

Surface-induced organization of linear molecules on nanostructured polytetrafluoroethylene: Crystalline state of poly[vinylidenefluoride-trifluoroethylene]

Within this work we present Brillouin and ultrasonic investigations performed on the liquid crystals p-methoxybenzylidene p-(n-butylaniline) (MBBA), p-azoxyanisol (PAA), 4-cyano-4-n-alkylbiphenyles (nCB), and 4-n-pentoxybenzylidene-4'-n-octoaniline (5O.8). Special attention has been paid to the evolution of a significant splitting of the two longitudinal polarized acoustic modes within the nematic phase. Angle-resolving Brillouin spectroscopy allowed the determination of the complete stiffness tensors and hence a discussion of the propagation of quasitransverse polarized acoustic modes in the nematic state of liquid crystals. We analyze the behavior of the eigenvectors of the relevant acoustic modes and discuss their significance for the propagation of quasishear modes. For 5O.8 we report an acoustic instability within its nematic state. We confirm the existence of a universal thermal relaxation mechanism of weak activation energy for the nematic state of classical liquid crystals. The observed hypersonic anisotropy is discussed in terms of that relaxation mechanism and is compared with that of glass-forming liquid crystals.

Second-order elasticity of liquid crystals within their nematic state at high frequencies

Universal relaxation behavior of classical liquid crystals at hypersonic frequencies

Phase-transition behavior of n-alkanes on nanostructured polytetrafluorethylene films : brillouin spectroscopic and calorimetric investigations on pen tacosane

Taking advantage of the surface-induced orientation of linear molecules on highly oriented nanostructured polytetrafluoroethylene, we were able to grow macroscopic single crystals of (pentacosane). Using high-performance Brillouin spectroscopy, we determined for the first time the complete elastic tensor of an n-alkane.

C. Fischer

Papers

Surface-induced organization of linear molecules on nanostructured polytetrafluoroethylene: Crystalline state of poly[vinylidenefluoride-trifluoroethylene]

Second-order elasticity of liquid crystals within their nematic state at high frequencies

Universal relaxation behavior of classical liquid crystals at hypersonic frequencies

Phase-transition behavior of n-alkanes on nanostructured polytetrafluorethylene films : brillouin spectroscopic and calorimetric investigations on pen tacosane

Surface-induced organization of n-alkanes on nanostructured PTFE: I. Brillouin spectroscopic investigations on pentacosane