Controllable Preparation,Structure And Properties Of Oriented P(VDF-TrFE) Ferroelectric Thin Films

Poly(vinylidene fluoride-trifluoroethylene)(P(VDF-TrFE))is one of the most popular polymer ferroelectric materials,and its crystallization behavior directly determines the final ferroelectric properties of the material.P(VDF-TrFE)films after melt recrystallization normally form flat-on lamellae whose molecular chain is perpendicular to the substrate without ferroelectric properties,thus the processing temperature is limited below melting point.To explore the method which can produce edge-on lamellae with molecular chain parallel to the substrate is highly desirable.Here we employ three kinds of substrates and successfully control the molecular orientation.The effect of melting temperature on the crystallization and ferroelectric properties of P(VDF-TrFE)after melt crystallization spin-coated on single-layer graphene substrate was studied.The results show that P(VDF-TrFE)forms rod-like crystals which take an edge-on orientation,and the crystal length becomes larger and wider with the enhancing of melting temperature.Piezoresponse force microscopy(PFM)results show that melting temperature does not affect the coercive voltage of P(VDF-TrFE),but has a great influence on the d33 value which presents the quality of ferroelectric properties.The highest d33 value of P(VDF-TrFE)was obtained when the melting temperature is 150 ?.The effect of crystallization temperature on the structure and properties of P(VDF-TrFE)was also explored.The length of edge-on rod-like lamellae changes slightly and irregularly with crystallization temperature.The coercive voltage and d33 value of P(VDF-TrFE)are both dependent on crystallization temperature.When the crystallization temperature is 128 ?,the ferroelectric performance of P(VDF-TrFE)films is the highest which is because the highest crystallinity was obtained when isothermal crystallizing at the fastest crystallization temperature.The vacuum-evaporated carbon on the surface of P(VDF-TrFE)thin film can also fix the molecular chain parallel to the film surface.Such strong fixing effect can be retained when melting temperature is enhanced to 250 ?showing good ferroelectric performance in the MFM devices.This provides a simple and cheap technology to produce ferroelectric devices of P(VDF-TrFE)with wide processing temperature window.