Ferroelectricity in metal-organic frameworks: characterization and mechanisms

Ferroelectric metal–organic frameworks are emerging as an exciting field of research and have witnessed great progress in the last decade. In this contribution, we briefly discuss ferroelectricity and its means of demonstration. Three mechanisms that lead to ferroelectricity are identified and critically discussed. On the basis of the shortcomings present in the literature, we present a protocol for the study of ferroelectricity in MOF compounds.ChemE/Catalysis Engineerin

Interfacial conduction in organic ferroelectric memory diodes

Solution-processed memory diodes based on phase separated blends of ferroelectric and semiconducting polymers in the low resistance on-state operate similar to a vertical field-effect transistor at the pinch-off. Numerical simulations have shown that the performance of the diode is dominated by the conduction of charge carriers at the interface between the semiconductor and ferroelectric phases. Here, we present an unambiguous experimental demonstration of the charge injection process in the diodes. We employ a modified diode structure, wherein the electrode in contact with the semiconductor phase has been intentionally removed. Even in the absence of an electrical contact with the semiconductor phase, the diode still shows resistance switching. We provide numerical simulations that reproduce the experimentally measured I-V characteristics and therefore confirm interfacial conduction in the diodes. Furthermore, we discuss the implications of the proposed memory structure particularly in the performance of light-emitting diodes with built-in memory functionality, i.e., MEMOLEDs.Novel Aerospace Material

Spatially resolved solid-state reduction of graphene oxide thin films

Re-establishment of electrical conductivity in graphene oxide (GO), the insulating form of graphene, is (partially) accomplished by reduction through high temperature treatments in a reducing atmosphere, or using strongly reducing chemicals or electrolytic processes. The reduction methods are suited for bulk graphene oxide. Spatially resolved reduction of thin films of graphene oxide is important for a wide range of applications such as in microelectronics, where an electrolyte-free, room temperature reduction process is needed. Here, we present spatially resolved solid-state reduction of graphene oxide thin films. We demonstrate that the reduction mechanism is based on electrolysis of water that is adsorbed on the graphene oxide thin film. The reduced graphene oxide thin-films show sheet resistance of only several kOhm, with weak temperature dependence. Graphene oxide can be produced on a large scale and processed using low-cost solution casting techniques. Spatially resolved re-establishment of conductivity in GO can be used in electrically controlled water permeation or in micro- and nanoelectronic applications for instance as an anti-fuse.Novel Aerospace Material

Quantum tunnelling and charge accumulation in organic ferroelectric memory diodes

Non-volatile memories—providing the information storage functionality—are crucial circuit components. Solution-processed organic ferroelectric memory diodes are the non-volatile memory candidate for flexible electronics, as witnessed by the industrial demonstration of a 1 kbit reconfigurable memory fabricated on a plastic foil. Further progress, however, is limited owing to the lack of understanding of the device physics, which is required for the technological implementation of high-density arrays. Here we show that ferroelectric diodes operate as vertical field-effect transistors at the pinch-off. The tunnelling injection and charge accumulation are the fundamental mechanisms governing the device operation. Surprisingly, thermionic emission can be disregarded and the on-state current is not space charge limited. The proposed model explains and unifies a wide range of experiments, provides important design rules for the implementation of organic ferroelectric memory diodes and predicts an ultimate theoretical array density of up to 1012 bit cm 2.Novel Aerospace Material

Integrated circuits based on conjugated polymer monolayer

It is still a great challenge to fabricate conjugated polymer monolayer field-effect transistors (PoM-FETs) due to intricate crystallization and film formation of conjugated polymers. Here we demonstrate PoM-FETs based on a single monolayer of a conjugated polymer. The resulting PoM-FETs are highly reproducible and exhibit charge carrier mobilities reaching 3 cm2 V-1 s-1. The high performance is attributed to the strong interactions of the polymer chains present already in solution leading to pronounced edge-on packing and well-defined microstructure in the monolayer. The high reproducibility enables the integration of discrete unipolar PoM-FETs into inverters and ring oscillators. Real logic functionality has been demonstrated by constructing a 15-bit code generator in which hundreds of self-assembled PoM-FETs are addressed simultaneously. Our results provide the state-of-the-art example of integrated circuits based on a conjugated polymer monolayer, opening prospective pathways for bottom-up organic electronics.Novel Aerospace Material