Remanent polarization of evaporated films of vinylidene fluoride oligomers

Abstract

A remanent polarization of 130Ϯ3 mC/m 2 , large among the values reported for organic materials, and rectangular D -E hysteresis curves were realized in synthesized vinylidene fluoride ͑VDF͒ oligomer ͓CF 3 (CH 2 CF 2 ) 17 I͔ 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.

Vinylidene fluoride telomers for piezoelectric devices

“…at 123 K under a vacuum of 10 À5 Pa to ensure that the VDF telomers were in a ferroelectric state (form I) and that the axis of the molecular chain was oriented parallel to the substrate. 8,9 The thickness of the VDF telomer and the Al electrodes was controlled at 300 and 50 nm, respectively. Stacks of Al/VDF telomer/Al acted as the capacitor, and the charge was proportional to the stress applied to the film.…”

“…Among organic ferroelectrics, CF 3 (VDF) 17 I possesses a relatively high remanent polarization. 9 Furthermore, previous experiments on CF 3 (VDF) 13.4 C 2 H 5 revealed that the piezoelectric coefficient of VDF telomers was greater than that of oligo(VDF-co-TrFE) copolymers, and a thinner and more uniform film could be obtained. 6,7 The objective of this study was to design various VDF-based telomers, such as C n F 2n+1 (VDF) p -(C 2 H 4 ) x -X (where n¼4 or 6; p¼6-23; x¼0, 1 and X¼H or I), and to alter the crystallinity, ferroelectric and piezoelectrical properties by controlling the number of VDF units and end groups.…”

Coplanar switching of polarization in thin films of vinylidene fluoride oligomers

“…The obtained value of E c of about 0.6 MV/m (supplementary material, Sec. IV) 28 is two to three orders of magnitude lower than the previously reported values for VDF oligomers (100-200 MV/m), 21 and at least an order of magnitude lower than the lowest coercive field reported for the PVDF-TrFE nanostructures (of order 10 MV/m). 31 The coercive field value obtained from analysis of the PFM images is in good agreement with the macroscopic currentvoltage measurements (Fig.…”

“…In our case, molecular chains are oriented nearly normal to the substrate and thus each molecular chain has a smaller interaction cross-sectional area at the interface (substrate) than the in-plane oriented molecular chains. This provides a relatively large degree of freedom for the dipole rotation (less steric hindrance 21 ) resulting in the low coercive field value.…”

“…16,17 VDF-oligomers, which contain a finite number of the VDF units, represent an ideal opportunity to investigate their ferroelectric properties as a function of molecular arrangements controlled by fabrication conditions. 18,19 Previously, VDF-oligomer films with molecular chains aligned parallel to the substrate have been extensively characterized by macroscopic electrical, [20][21][22] structural, 18,23,24 and local probe-based methods. 14,23,25 In this article, using high-resolution piezoresponse force microscopy (PFM), we have investigated the switching characteristics of the highly crystalline VDF-oligomer thin films with molecular chains oriented normal to the substrate.…”