The Research Of Molecular Ferroelectric Thin Film And Its Device

Rochelle salt(potassium sodium tartrate tetrahydrate,[KNaC4H4O6](4H2O))was discovered as the first ferroelectric crystal by Valasek in 1920,a great deal of effort has been put into the exploration of ferroelectric materials.Fifteen years later,Busch and Scherrer discovered KH2PO4,whose relative dielectric constant is about 30.Very soon,the first non-hydrogen-bonded ferroelectric BaTiO3 belonging to the perovskite family was discovered in the early 1940s,indicating the blossom of the ferroelectrics.Ferroelectric materials show potential applications in photovoltaics,data storage,electro-optic modulation,piezoelectrics,photo-acoustic modulation,etc.Their ferroelectric performance and application limits were then improved dramatically.In recent decades,the traditional ceramic ferroelectrics such as Pb(ZrTi)O3(PZT),Bi0.5Na0.5TiO3(BNT),Bi4Ti3O12(BTO)have exposed their limitations,like large energy gap,poor conductivity,high film production costs.At the same time,there is no doubt that molecular-based ferroelectric materials would bring new hope.Compared with traditional metal oxide ferroelectrics,molecular-based ferroelectric materials have novel structural features such as chain structure,host-guest inclusion or ion type.Their ferroelectricity and semiconductor properties are relatively independent,which make it easier to engineering the energy gap,conductivity,dielectric properties according to different application requirements,without sacrificing their ferroelectric performance.The production of traditional ferroelectric ceramics often involves high temperature sintering,sputtering,pulsed laser deposition and other physical methods,which affect their application potential in modern devices.While on the other hand,molecular ferroelectrics can be synthesized with solution method,hydrothermal method or other chemical techniques,with low cost,simple processing and easy to achieve large-scale production.At the same time,high-quality thin-film of molecular ferroelectrics can be easily prepared by solution-based method,which would be greatly benefit the thin film devices or flexible electronics.In 2004,the discovery of graphene opened the avenue of two-dimensional materials.Ever since then two-dimensional materials with unique physical,chemical,mechanical properties has attracted great attention over the world.They have been found mainly iin the following categories:1,hexagonal structured represented by graphene and h-BN.2,a three-atomed layer crystal represented by a transition metal sulfur compound(MoS2,WS2,etc.)in which a metal atomic layer is sandwiched between adjacent sulfur atom layers.3,metal oxide(MnO2,WoO3)and bimetallic hydroxide(Mg6Al2(OH)16).While some other two-dimensional layered material has also been reported,such as phosphoric acid(Phosphorene),transition metal carbon/nitrogen compounds(MXenes)and so on.The excellent performance of these two-dimensional materials in the energy storage,optoelectronics,catalyst and other areas have shown promising application potential.At the same time,today,in the rapid development of two-dimensional materials,ferroelectric materials and two-dimensional hybrid appears to be interesting.The combination of ferroelectricity and excellent properties of two-dimensional materials has been foreseen as a potential candidate for next generation electronic devices,optoelectronic devices and so on.In this work,based on the study of molecular ferroelectrics and two-dimensional material hybrid structure/devices,based on different molecular ferroelectrics and two-dimensional materials,we explored their applications and fundamental properties.This dissertation consists of three parts:Part 1:Preparation and characterization of molecular ferroelectric thin films.Part 2:Preparation and characterization of two-dimensional materials.Part 3:Preliminary exploration of molecular ferroelectric and two-dimensional hybrid devices.