Multifunctional materials can be engineered by combining multiple chemical components, each conferring a well-defined function to the ensemble. Graphene is at the centre of an ever-growing research effort due to its combination of unique properties. Here we show that the large conformational change associated with the trans–cis photochemical isomerization of alkyl-substituted azobenzenes can be used to improve the efficiency of liquid-phase exfoliation of graphite, with the photochromic molecules acting as dispersion-stabilizing agents. We also demonstrate reversible photo-modulated current in two-terminal devices based on graphene–azobenzene composites. We assign this tuneable electrical characteristics to the intercalation of the azobenzene between adjacent graphene layers and the resulting increase in the interlayer distance on (photo)switching from the linear trans-form to the bulky cis-form of the photochromes. These findings pave the way to the development of new optically controlled memories for light-assisted programming and high-sensitive photosensors.
High fatigue resistance, bistability, and drastic property changes among isomers allow efficient modulation of the current output of organic thin-film transistors (OTFTs) to be obtained by a photogating of the charge-injection mechanism.
Here we describe a strategy to fabricate multifunctional graphene-polymer hybrid thin-film transistors (PG-TFT) whose transport properties are tunable by varying the deposition conditions of liquid-phase exfoliated graphene (LPE-G) dispersions onto a dielectric surface and via thermal annealing post-treatments. In particular, the ionization energy (IE) of the LPE-G drop-cast on SiO2 can be finely adjusted prior to polymer deposition via thermal annealing in air environment, exhibiting values gradually changing from 4.8 eV up to 5.7 eV. Such a tunable graphene's IE determines dramatically different electronic interactions between the LPE-G and the semiconducting polymer (p- or n-type) sitting on its top, leading to devices where the output current of the PG-TFT can be operated from being completely turned off up to modulable. In fact upon increasing the surface coverage of graphene nanoflakes on the SiO2 the charge transport properties within the top polymer layer are modified from being semiconducting up to truly conductive (graphite-like). Significantly, when the IE of LPE-G is outside the polymer band gap, the PG-TFT can operate as a multifunctional three terminal switch (transistor) and/or memory device featuring high number of erase-write cycles. Our PG-TFT, based on a fine energy level engineering, represents a memory device operating without the need of a dielectric layer separating a floating gate from the active channel.
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