Large-area atomic-smooth polyvinylidene fluoride Langmuir-Blodgett film exhibiting significantly improved ferroelectric and piezoelectric responses  

具有显著提高的铁电与压电响应、大面积原子级平整的PVDF Langmuir-Blodgett膜

作　　者：Shan He Mengfan Guo Zhenkang Dan Shun Lan Weibin Ren Le Zhou Yue Wang Yuhan Liang Yunpeng Zheng Jiayu Pan Yang Shen 何珊;郭梦帆;但振康;蓝顺;任伟斌;周乐;王玥;梁宇晗;郑云鹏;潘家雨;沈洋(State Key Laboratory of New Ceramics and Fine Processing,School of Materials Science and Engineering,Tsinghua University,Beijing 100084,China)

机构地区：[1]State Key Laboratory of New Ceramics and Fine Processing,School of Materials Science and Engineering,Tsinghua University,Beijing 100084,China

出　　处：《Science Bulletin》2021年第11期1080-1090,M0003,共12页科学通报（英文版）

基　　金：supported by the National Natural Science Foundation of China(51625202);the National Key Research&Development Program of China(2017YFB0701603)。

摘　　要：Large roughness and structure disorder in ferroelectric ultrathin Langmuir-Blodgett(LB)film results in severe space scatter in electrical,ferroelectric and piezoelectric characteristics,thus limiting the nanoscale research and reliability of nano-devices.However,no effective method aiming at large-area uniform organic ferroelectric LB film has ever been reported to date.Herein,we present a facile hot-pressing strategy to prepare relatively large-area poly(vinylidene fluoride)(PVDF)LB film with ultra-smooth surface root mean square(RMS)roughness is 0.3 nm in a 30μm×30μm area comparable to that of metal substrate,which maximized the potential of LB technique to control thickness distribution.More importantly,compared with traditionally annealed LB film,the hot-pressed LB film manifests significantly improved structure uniformity,less fluctuation in ferroelectric characteristics and higher dielectric and piezoelectric responses,owing to the uniform dipole orientation and higher crystalline quality.Besides,different surface charge relaxation behaviors are investigated and the underlying mechanisms are explained in the light of the interplay of surface charge and polarization charge in the case of nanoscale non-uniform switching.We believe that our work not only presents a novel strategy to endow PVDF LB film with unprecedented reliability and improved performance as a competitive candidate for future ferroelectric tunnel junctions(FTJs)and nano electro mechanical systems(NEMS),but also reveals an attracting coupling effect between the surface potential distribution and nanoscale non-uniform switching behavior,which is crucial for the understanding of local transport characterization modulated by band structure,bit signal stability for data-storage application and the related surface charge research,such as charge gradient microscopy(CGM)based on the collection of surface charge on the biased ferroelectric domains.在新兴的柔性和可穿戴电子设备中,有机铁电超薄膜发挥着至关重要的作用.然而,传统方法制备的铁电性聚偏氟乙烯(PVDF)超薄膜具有较大的表面粗糙度和结构不均匀性,极大地限制了其应用与相关科学研究.本文提出了一种将Langmuir-Blodgett(LB)技术和热压法结合制备PVDF薄膜的方法,该方法简便高效,制备的薄膜具有大面积的原子级光滑表面,且膜厚可精确控制至A级别.同时,由于更均匀的偶极取向和更高的晶体质量,该超薄膜表现出高度均匀的铁电翻转特性和增强的介电和压电响应.这种方法使PVDF LB膜具有前所未有的可靠性和更优异的性能,十分有望未来应用于铁电隧道结(FTJs)和纳米机电系统(NEMS).我们进一步研究了PVDF LB薄膜的表面电荷弛豫行为,揭示了表面电势分布与纳米尺度非均匀极化翻转行为之间的耦合关系.

关 键 词：Poly(vinylidene fluoride)(PVDF) Langmuir-Blodgett film Roughness FERROELECTRIC PIEZORESPONSE Charge relaxation 

分 类 号：TB383.2[一般工业技术—材料科学与工程] TQ325.4[化学工程—合成树脂塑料工业]