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With the emergence of environmental, biomedical, and medical monitoring technologies, development of flexible and lightweight sensors is ongoing. This work presents a flexible lightweight bilayer (BL) film (polycarbonate/polycrystalline layer of crystalline (BEDT-TTF)xBr(H2O)y salts [BEDT-TTF = bis (ethylendithio)tetrathiafulvalene]) as a promising material for humidity sensing which may be applied in a number of monitoring scenarios. X-ray structural characterization revealed the presence of three different crystal types in the crystalline layer of the BL film, i.e., [phase I, [(BEDT-TTF)5(Br4(H5O2))]; phase II, [(BEDT-TTF)2Br(H2O)3]; and crystals of neutral BEDT-TTF compound], showing that phase I is highly sensitive to humidity. The humidity testing of the BL film showed that it is capable of monitoring relative humidity (RH) levels from 15 up to 90% with a well-defined and reproducible electrical signal. Electrical resistance measurements revealed that the crystalline conducting layer can absorb moisture reaching equilibrium at constant RH as reflected in a stable relative resistance response. The structural response of the BL film to variations of RH clearly demonstrated that crystallite interlayer spacing (d) of phase I is strongly affected, exhibiting a reversible metal–nonmetal transition, while phase II was insensitive to humidity. An overview of mechanical and humidity sensing properties of the developed BL film corroborates that it can be used as flexible hygrometer as well as moisture sensing units on the board of low-cost electronic sensing devices.

Correction for ‘Metal-functionalized covalent organic frameworks as precursors of supercapacitive porous N-doped graphene’ by Jorge Romero et al., J. Mater. Chem. A, 2017, 5, 4343–4351

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The isolation of 2D-materials is already a success for graphene, graphene oxide, boron nitride and a few clays or metal chalcogenides, however despite the fact that some of them show very interesting physical properties, they lack useful functionalities. Metal-Organic Frameworks (MOFs) are multifunctional materials showing a wide range of physical and chemical properties that can be structurally designed by suitable selection of their building-blocks. This strategy may allow the production of layers with a variety of useful electronic and molecular recognition functionalities. Herein we isolate 2D-MOF flakes with areas of hundreds of square microns and an excellent control of the molecular thickness (from single up to ca. 50 layers). The samples exhibit such good photoluminescence and mechanical properties as to allow free-standing characterization of few layers' flakes.

© 2015 American Chemical Society. Thin films of organic semiconductors have been widely studied at different length scales for improving the electrical response of devices based on them. Hitherto, a lot of knowledge has been gained about how molecular packing, morphology, grain boundaries, and defects affect the charge transport in organic thin film transistors. However, little is known about the impact of an electric field on the organic semiconductor microstructure and the consequent effect on the device performances. To fill this gap, we investigated the evolution of the structure of pentacene thin film transistors during device operation by in situ real time X-ray diffraction measurements and theoretical calculations. We observed for the first time the occurrence of a reversible structural strain taking place during the bias application mainly due to reorientation at the terrace edges of monolayer islands under the effect of electrical field. Strain exhibits the same trend of the threshold voltage hinting to the existence of a direct correlation between the phenomenon of bias stress and the structural modification.

The applications of organic semiconductors in complex circuitry such as printed CMOS-like logic circuits demand miniaturization of the active structures to the submicrometric and nanoscale level while enhancing or at least preserving the charge transport properties upon processing. Here, we addressed this issue by using a wet lithographic technique, which exploits and enhances the molecular order in polymers by spatial confinement, to fabricate ambipolar organic field effect transistors and inverter circuits based on nanostructured single component ambipolar polymeric semiconductor. In our devices, the current flows through a precisely defined array of nanostripes made of a highly ordered diketopyrrolopyrrole-benzothiadiazole copolymer with high charge carrier mobility (1.45 cm2 V-1 s-1 for electrons and 0.70 cm2 V-1 s-1 for holes). Finally, we demonstrated the functionality of the ambipolar nanostripe transistors by assembling them into an inverter circuit that exhibits a gain (105) comparable to inverters based on single crystal semiconductors.