Visualization and control of morphology and functionality of ferroelectric polymer nano-lamellae

Abstract

Ferroelectric polymers have attracted great interest due to their potential usage in a wide range of applications, such as nonvolatile memories devices, energy transducers, and wearable sensors. Such polymeric materials are especially desirable due to their increased flexibility, easy of processing, toxicity, and chemical stability. However, ferroelectric polymers often exhibit poor ferroelectric properties compared to their ceramic counterparts. Well-aligned nanostructures potentially have enhanced materials properties. We demonstrate an approach for fabricating oriented poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] thin films with enhanced ferroelectric properties by preparing the film on a nanostructured patterned substrate via spin coating. Prior to that, the crystalline morphologies and ferroelectric properties of films in flat Si wafers under different processing conditions were optimized and characterized using scanning probe microscopy (SPM). Afterwards, the behavior and functionality of P(VDF-TrFE) films on patterned substrate was investigated. The hypothetic mechanism of alignment was explored by comparing the crystalline arrangement in different fabrication conditions and periodicity of patterns. Dipole and chain orientation in film were evaluated through structural characterization and SPM-based methods. As a result, bidirectional alignment of P(VDF-TrFE) lamellae on patterned substrate was obtained when the size of lamellae is comparable with the period of pattern. The degree of alignment showed a decreasing trend with the increase of period. Moreover, the preferential orientation of ferroelectric lamellae results in ordered molecular chain, which provides excellent ferroelectric properties with low coercive field and high in-plane remnant polarization. We envision the integration of such aligned ferroelectric polymer with cheaper, flexible electronic devices.