Search

Poly(vinylidene fluoride-trifluoroethylene) is a ferroelectric copolymer. It is considered a promising candidate for sensors, nonvolatile memory applications, and energy harvesting. However, imprint, a phenomenon associated with ferroelectric polarization, changes reversibly the material properties over time. In particular, imprint results in an increase of the ferroelectric polarization switching time and the coercive field, as well as in the decay of the remanent polarization and the permittivity. We present a concept to explain imprint and present experimental evidence supporting this concept. In this concept, an internal electric field arises as a consequence of the interaction between ferroelectric dipoles and relaxational dipoles present in the crystalline and the amorphous phase, respectively. We use an extended Weiss mean field approach and show that this internal field results in the experimentally observed imprint. In addition, we show that the imprint can be largely suppressed by increasing the copolymer's crystallinity. [ABSTRACT FROM AUTHOR]

The wettability and adhesion of biological surfaces often depend on their periodically arranged hybrid micro–nano array structures. Various fabrication processes are designed to mimic biomimetic micro–nano array surfaces. This review summarizes the types of micro–nano array structures and analyzes fabrication methods based on top‐down and bottom‐up construction, including templating, etching, self‐assembly, and electrospinning/electrospraying. This review focuses on the shape reconfiguration of surface micro–nano array structures under physical stimuli, as well as the changes in material surface properties during the reconfiguration process. In addition, the applications of biomimetic micro–nano array composite surfaces in the fields of droplet transport, adhesion properties, sensors, and soft robotics are also discussed, and the current challenges and prospects in this field are identified. [ABSTRACT FROM AUTHOR]

The last few decades have witnessed the rapid development of electronic computers relying on von Neumann architecture. However, due to the spatial separation of the memory unit from the computing processor, continuous data movements between them result in intensive time and energy consumptions, which unfortunately hinder the further development of modern computers. Inspired by biological brain, the in situ computing of memristor architectures, which has long been considered to hold unprecedented potential to solve the von Neumann bottleneck, provides an alternative network paradigm for the next-generation electronics. Among the materials for designing memristors, i.e., nonvolatile memories with multistate tunable resistances, ferroelectric polymers have drawn much research interest due to intrinsic analog switching property and excellent flexibility. In this review, recent advances on artificial synapses based on solution-processed ferroelectric polymers are discussed. The relationship between materials' properties, structural design, switching mechanisms, and systematic applications is revealed. We first introduce the commonly used ferroelectric polymers. Afterward, device structures and the switching mechanisms underlying ferroelectric synapse are discussed. The current applications of organic ferroelectric synapses in advanced neuromorphic systems are also summarized. Eventually, the remaining challenges and some strategies to eliminate non-ideality of synaptic devices are analyzed. [ABSTRACT FROM AUTHOR]

Development of unconventional computing architectures, including neuromorphic computing, relies heavily on novel devices with properly engineered properties. This requires exploration of new functional materials and their designed interfaces. Ferroelectric memories including two‐terminal ferroelectric tunnel junctions and three‐terminal ferroelectric field‐effect transistors have shown promising performances in recent years as analog, multibit memory components with ultralow power consumption. However, for ferroelectric memory technology to become a mainstream technology, CMOS integration of these components is of major importance. For further diversifying their application to edge computing and smart sensing industry, a vast unchartered territory of low‐temperature processable and CMOS back‐end‐of‐line (BEOL) compatible materials needs to be researched. In recent years, doped HfO2‐based memory devices and in‐memory computing architectures have gathered huge momentum as one of the "beyond von Neumann" computing alternatives. In comparison, molecular ferroelectric‐based systems are still in their early exploratory phase. This review discusses the potential for doped HfO2 and molecular ferroelectrics as CMOS BEOL and flexible and wearable platform compatible neuromorphic devices and circuits and the challenges that need to be overcome for turning the opportunities to a technological reality. [ABSTRACT FROM AUTHOR]

Since the discovery of piezoelectricity in poly(vinylidene fluoride) (PVDF) 50 years ago, ferroelectric polymers have established their own areas for research and applications due to their unique properties in comparison to single crystals and inorganics. PVDF is a semicrystalline polymer that can crystallize into five different polymorphs. Among them, the polar β-phase is the most interesting one for electroactive properties because it has the highest dipolar moment and the highest piezoelectric response. In the early days, the β-PVDF was typically produced by melt processing, limiting its form to free-standing films. The rapid development of flexible electronics, however, highly requires β-PVDF fabricated from solutions under mild conditions. The objective of this perspective is to summarize the effective methods to produce β-PVDF from solution, to present the approaches for enhancing the electroactive properties through morphological controls, and to discuss the applications of PVDF-based ferroelectric polymers in flexible electronics. In addition, current challenges that may impede the further development of this field are pointed out. [ABSTRACT FROM AUTHOR]

With the rapid development of wearable and flexible electronics, energy harvesting from the environment has attracted much attention. As one representative piezoelectric polymer, poly(vinylidene fluoride‐trifluoroethylene) [P(VDF‐TrFE)] is an expected candidate for mechanical energy harvesting and self‐powered mechanical sensors due to its flexibility and moderate piezoelectricity. However, low crystallinity and electroactivity limit its electric performance. Controllable modulation of microstructure and crystallization is one feasible measure to enhance piezoelectric property. Here the piezoelectric properties of epitaxial P(VDF‐TrFE) films which are fabricated via removable polytetrafluoroethylene template method are reported. Piezoelectric measurement between 50 and 800 Hz presents an averaged d33 coefficient of −40.7 pC N−1 for epitaxial film, ≈61% enhancement to that of non‐epitaxial one. Transverse piezoelectric experiment indicated that epitaxy process enhanced open‐circuit voltage and short‐circuit current outputs. Simple piezoelectric energy harvesters are prepared by depositing both epitaxial and nonepitaxial films on flexible polyimide substrates. Epitaxial film shows a maximum generated power density of 0.118 µW cm−2 and energy conversion efficiency of 0.81%, both of which are much larger than those from nonepitaxial film (0.047 µW cm−2 and 0.30%). Piezoelectric films are used to monitor bending, punching, twisting and finger tapping operations, where epitaxial film exhibited larger open‐circuit voltage responses than nonepitaxial one. [ABSTRACT FROM AUTHOR]

Developing new memory concepts and devices has been one of the most productive fields of research for the past decade. There is a need for a nonvolatile memory technology based on resistance switching. An ideal memory element is a bistable rectifying diode that enables realization of a simple crossbar memory array with highest areal bit density. Ferroelectrics have been suggested to code digital information due to their intrinsic and stable binary electronic polarization. However, realization of a ferroelectric bistable rectifying diode is challenging since ferroelectricity and electrical conductivity are mutually exclusive and cannot coexist in a single compound. As a solution, lateral ferroelectric-semiconductor heterostructures have been suggested for the realization of ferroelectric diodes. Bistable rectifying diodes and their respective nonvolatile crossbar memory arrays based on ferroelectric-semiconductor lateral heterostructures have been successfully demonstrated with organic ferroelectrics and organic semiconductors. The present review focuses on the resistance switching in ferroelectric-semiconductor heterostructure rectifying diodes based on polymers and discusses the latest developments over the last decade. [ABSTRACT FROM AUTHOR]

Enzyme catalysis has been studied for over a century. How it actually occurs has not been visualized until recently. By combining in crystallo reaction and X-ray difraction analysis of reaction intermediates, we have obtained unprecedented atomic details of the DNA synthesis process. Contrary to the established theory that enzyme-substrate complexes and transition states have identical atomic composition and catalysis occurs by the two-metal-ion mechanism, we have discovered that an additional divalent cation has to be captured en route to product formation. Unlike the canonical two metal ions, which are coordinated by DNA polymerases, this third metal ion is free of enzyme coordination. Its location between the α- and β-phosphates of dNTP suggests that the third metal ion may drive the phosphoryltransfer from the leaving group opposite to the 3'-OH nucleophile. Experimental data indicate that binding of the third metal ion may be the rate-limiting step in DNA synthesis and the free energy associated with the metal-ion binding can overcome the activation barrier to the DNA synthesis reaction. [ABSTRACT FROM AUTHOR]

In recent years human–machine interaction has become increasingly important in industrial applications and daily life. Proximity sensors are expected to become an important part of such systems. The mechanisms of these sensors are usually based on ultrasound, capacitance, triboelectric effect, optical imaging or semiconducting devices. The fabrication and sensing performance of solution‐based organic transistor proximity sensors is reported. To enhance electrical performance, nanogroove templates are introduced to guide the oriented growth of organic semiconducting layer. The templates are realized by friction‐transferring polytetrafluoroethylene thin layers onto SiO2/Si substrates. An extended gate structure for proximity sensing is designed, in which one end of a silver wire is electrically connected with the gate of the transistor and the other end serves as the sensing end. Proximity sensing is characterized by bringing various charged stimuli close to the sensor and recording the resulting change in drain current. The sensor showed good repeatability during the approach and withdrawal of a stimulus. A maximum current response of 2.2 μA between distances of 3 mm and 53 mm and distance sensitivity of 2.5 nA mm‐1 at a distance of 13 mm are obtained when a charged polytetrafluoroethylene rod is moved up and down above the sensing end. [ABSTRACT FROM AUTHOR]