Measurement of the flexoelectric response in ferroelectric and relaxor polymer thin films

Poddar, Shashi; Ducharme, Stephen

doi:10.1063/1.4829622

Cited by 53 publications

(28 citation statements)

References 31 publications

(48 reference statements)

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“…Next, the nanopillars were coated with 45 monolayers of a P(VDF-TrFE-CFE) terpolymer capping layer through LB deposition. The terpolymer capping layer, which has high dielectric constant, little remnant polarization and negligible pyroelectric response compared with P(VDFTrFE) copolymer, [42][43][44] was chosen to prevent short-circuit and to share less voltage drop across the multilayer capacitor during the DC poling process (see ESI †). The terpolymer-coated nanopillar sample was then covered with a 100 nm thick aluminum top electrode by thermal evaporation through a shadow mask.…”

Section: Fabrication Of Nanopillar Array and Capacitorsmentioning

confidence: 99%

Ferroelectric polymer nanopillar arrays on flexible substrates by reverse nanoimprint lithography

Song

Foreman

et al. 2016

J. Mater. Chem. C

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aWith the increasing interest in deploying ferroelectric polymer in flexible electronics and electromechanics, high-throughput and low-cost fabrication of 3D ferroelectric polymer nanostructures on flexible substrates can be a significant basis for future research and applications. Here, we report that large arrays of ferroelectric polymer nanopillars can be prepared directly on soft, flexible substrates by using low-cost polydimethylsiloxane (PDMS) soft-mold reverse nanoimprint lithography at 135 1C and at pressures as low as 3 bar. The nanopillar arrays were highly uniform over large areas of at least 200 Â 200 mm and had good crystallinity with nearly optimum (110) orientation. Furthermore, the method leaves little or no residual polymer layer, fully isolating the nanopillars to avoid cross-talk and, obviating the need for additional etching processes that arises with conventional low-contrast nanoimprinting. The ferroelectric properties of individual nanopillars were probed by piezoresponse force microscopy, which showed that they exhibited switchable and bi-stable polarization. In addition, the polarization hysteresis loops probed by pyroelectric measurements of the entire array showed that the nanopillar capacitor arrays had good ferroelectric switching characteristics, over areas of at least 1 mm Â 1 mm. IntroductionFerroelectric polymer nanostructures are of great interest due to their potential use in a wide range of applications, such as organic electronics, 1,2 electro-mechanics, 3,4 nonvolatile memories, [5][6][7][8] and solid-state energy storage, harvesting and conversion. [9][10][11][12] With the increasing application of ferroelectric polymers in the area of flexible electronics, [13][14][15][16] high-throughput and low-cost fabrication of uniform ferroelectric polymer nanostructures with good ferroelectric properties over large areas on flexible substrates will be a significant basis for flexible electronics applications. Previous studies of ferroelectric polymers, like polyvinylidene-co-trifluoroethylene, P(VDF-TrFE), report results from conventional nanoimprint lithography (NIL) with highcost rigid molds at high pressures ranging from 20 bar to 120 bar and 130 to 150 1C to produce ferroelectric nanostructures on hard substrates. 5,7,[17][18][19][20][21] Application of conventional NIL to produce nanostructured films on flexible substrates has a number of drawbacks, such as mechanical and thermal deformation of the substrates, 22,23 poor adhesion, 24 and incompatibility with high temperatures. 25,26 These drawbacks lead to low throughput and poor pattern uniformity in large arrays. 27,28 In addition, the conventional nanoimprint procedure usually requires an additional etching process to remove a residual polymer layer left between the imprinted structures. 29,30 This extra etching process may also be incompatible with flexible substrates due to their poor etching resistance. 31 Previous research on reverse nanoimprinting, where the material is first coated onto rigid mold and then transferred ...

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Section: Fabrication Of Nanopillar Array and Capacitorsmentioning

confidence: 99%

Ferroelectric polymer nanopillar arrays on flexible substrates by reverse nanoimprint lithography

Song

Foreman

et al. 2016

J. Mater. Chem. C

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“…[4][5][6] In liquid crystals, 7 upon application of a strain gradient, the ordering of the large bulky molecules is strongly dependent on the shape anisotropy of the molecular species. In the case of polymers, [8][9][10][11] and elastomers, 12 the ordering of the polymer chains depends on the size and rigidity of the side groups and cross-linked functional groups. While in inorganic amorphous materials, 13 a distortion in the random network of local bonding units renders the system polar.…”

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confidence: 99%

“…The flexoelectric current I was measured using the lock-in amplifier at the oscillation frequency f and the flexoelectric coefficient was extracted from the slope of polarization P ¼ 1/(2pfA) and the strain gradient 11 where L ¼ 30 mm is the length of the bottom electrode.…”

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“…The films of the polyethylene were also fabricated by LB method at a target pressure of 15 mN/m. 11 The films were transferred onto the substrate by the horizontal Schaefer's method. 35 Silicon dioxide thin films were made using an rf magnetron sputtering system at 2 Â 10 À3 Torr argon pressure.…”

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“…The details of solution preparation method are discussed in greater detail in previous reports. 11,34 The thin films of terpolymer were fabricated using a Langmuir-Blodgett (LB) deposition trough (NIMA 622) at a target pressure of 10 mN/m. The films of the polyethylene were also fabricated by LB method at a target pressure of 15 mN/m.…”

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Finite-size scaling of flexoelectricity in Langmuir-Blodgett polymer thin films

Poddar

Foreman

Adenwalla

et al. 2016

Applied Physics Letters

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The flexoelectric effect, which is a linear coupling between a strain gradient and electrical polarization, is a fundamental electromechanical property of all materials with potential for use in nanoscale devices, where strain gradients can be quite large. We report a study of the dependence of the flexoelectric response on thickness in ultrathin films of polar and non-polar polymers. The measurements of the flexoelectric response in non-polar polyethylene and the polar relaxor polymer polyvinylidene-co-trifluoroethylene-co-chlorofluoroethylene were made using a bent cantilever method and corrected for the contribution from the electrode oxide. The results show that the value of the flexoelectric coefficient increases with decreasing thickness, by up to a factor of 70 compared to the bulk value, reaching such enhanced values in films of only 10 nm thickness. These results are consistent with a model accounting for interfacial contributions, and underline how large electromechanical coupling can be produced at the nanoscale. The results also distinguish the surface flexoelectric response from that coming from the volume.

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Thermally Induced Flexo‐Type Effects in Nanopatterned Multiferroic Layers

Cai

Antohe

Nysten

et al. 2020

Adv Funct Materials

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The difficulty to generate and control large strain gradients in materials hinders the investigation and application of flexoelectricity and flexomagnetism. This work demonstrates that thermal expansion can be used to induce very large non‐uniform strains at the nanoscale, resulting in giant strain gradients at moderate temperatures. This is demonstrated in a nanopatterned multiferroic hybrid layer consisting of a regular array of ferromagnetic metallic nanocylinders embedded in a ferroelectric polymer matrix. The thermally‐induced strain gradients can fully depolarize the ferroelectric component, and modify the magnetization of the ferromagnetic component via flexoelectric and flexomagnetic effects, respectively. Finite‐element analysis provides a quantitative view on thermal expansion‐induced strains and strain gradients supporting the experimental findings. This work shows that nanoscale thermal strain engineering provides an additional degree of freedom to control electrical polarization and magnetization, which paves the way for the design and operation of novel functional devices and nanostructures.

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Measurement of the flexoelectric response in ferroelectric and relaxor polymer thin films

Cited by 53 publications

References 31 publications

Ferroelectric polymer nanopillar arrays on flexible substrates by reverse nanoimprint lithography

Ferroelectric polymer nanopillar arrays on flexible substrates by reverse nanoimprint lithography

Finite-size scaling of flexoelectricity in Langmuir-Blodgett polymer thin films

Thermally Induced Flexo‐Type Effects in Nanopatterned Multiferroic Layers

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