Solution-Processed Field-Effect Transistors Based on Dihexylquaterthiophene Films with Performances Exceeding Those of Vacuum-Sublimed Films

Solution-processable oligothiophenes are model systems for charge transport and fabrication of organic field-effect transistors (OFET) . Herein we report a structure vs function relationship study focused on the electrical characteristics of solution-processed dihexylquaterthiophene (DH4T)-based OFET. We show that by combining the tailoring of all interfaces in the bottom-contact bottom-gate transistor, via chemisorption of ad hoc molecules on electrodes and dielectric, with suitable choice of the film preparation conditions (including solvent type, concentration, volume, and deposition method), it is possible to fabricate devices exhibiting field-effect mobilities exceeding those of vacuum-processed DH4T transistors. In particular, the evaporation rate of the solvent, the processing temperature, as well as the concentration of the semiconducting material were found to hold a paramount importance in driving the self-assembly toward the formation of highly ordered and low-dimensional supramolecular architectures, confirming the kinetically governed nature of the self-assembly process. Among the various architectures, hundreds-of-micrometers long and thin DH4T crystallites exhibited enhanced charge transport

A Multifunctional Polymer-Graphene Thin-Film Transistor with Tunable Transport Regimes

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 <i>via</i> 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 <i>via</i> 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 (<i>p</i>- or <i>n</i>-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

Supramolecular Self-Assembly in a Sub-micrometer Electrodic Cavity: Fabrication of Heat-Reversible π‑Gel Memristor

The use of biomimetic approaches toward the production of nonsolid yet functional architectures holds potential for the emergence of novel device concepts. Gels, in particular those obtained via self-assembly of π-conjugated molecules, are dynamic materials possessing unique (opto)­electronic properties. Their adaptive nature imparts unprecedented responsivity to various stimuli. Hitherto, a viable device platform to electrically probe in situ a sol–gel transition is still lacking. Here we describe the fabrication of a sub-micrometer electrodic cavity, which enables low-voltage electrical operation of π-gels. Thanks to the in situ supramolecular self-assembly of the π-gelator occurring within the cavity, we conceived a novel gel-based memristor whose sol–gel transition is reversible and can be controlled via heating and dc bias. This work opens perspectives toward the fabrication of a novel generation of nonsolid multiresponsive devices

Electrochemical Functionalization of Graphene at the Nanoscale with Self-Assembling Diazonium Salts

We describe a fast and versatile method to functionalize high-quality graphene with organic molecules by exploiting the synergistic effect of supramolecular and covalent chemistry. With this goal, we designed and synthesized molecules comprising a long aliphatic chain and an aryl diazonium salt. Thanks to the long chain, these molecules physisorb from solution onto CVD graphene or bulk graphite, self-assembling in an ordered monolayer. The sample is successively transferred into an aqueous electrolyte, to block any reorganization or desorption of the monolayer. An electrochemical impulse is used to transform the diazonium group into a radical capable of grafting covalently to the substrate and transforming the physisorption into a covalent chemisorption. During covalent grafting in water, the molecules retain the ordered packing formed upon self-assembly. Our two-step approach is characterized by the independent control over the processes of immobilization of molecules on the substrate and their covalent tethering, enabling fast (<i>t</i> < 10 s) covalent functionalization of graphene. This strategy is highly versatile and works with many carbon-based materials including graphene deposited on silicon, plastic, and quartz as well as highly oriented pyrolytic graphite

Coherent Coupling of WS₂ Monolayers with Metallic Photonic Nanostructures at Room Temperature

Room temperature strong coupling of WS₂ monolayer exciton transitions to metallic Fabry–Pérot and plasmonic optical cavities is demonstrated. A Rabi splitting of 101 meV is observed for the Fabry–Pérot cavity. The enhanced magnitude and visibility of WS₂ monolayer strong coupling is attributed to the larger absorption coefficient, the narrower line width of the <i>A</i> exciton transition, and greater spin–orbit coupling. For WS₂ coupled to plasmonic arrays, the Rabi splitting still reaches 60 meV despite the less favorable coupling conditions, and displays interesting photoluminescence features. The unambiguous signature of WS₂ monolayer strong coupling in easily fabricated metallic resonators at room temperature suggests many possibilities for combining light–matter hybridization with spin and valleytronics