The charge transport in molecular systems is governed by a series of carrier-molecule quantum interactions, which result in a broad set of chemical and physical phenomena. The precise control of such phenomena is one of the main challenges toward the development of novel device concepts. In molecular systems, direct tunneling across 1−10 nm barriers and activated hopping over longer distances have been described as the main charge transport mechanisms. The continuous transition from one mechanism to the other, by increasing the transport distance, has mainly been reported for molecular chains covalently bonded to the electrodes. In elementary molecular junctions, like those formed by physisorbed organic semiconductor thin films, such transition remains unclear. Here, we report the first experimental evidence for sequential, long-range coherent tunneling across physisorbed ensembles by investigating the charge transport in copper phthalocyanine layers (5−60 nm thick films). Like observed for chemisorbed molecules, our junction exhibits a gradual transition from coherent tunneling to activated transport in the 10−22 nm thickness range. The present work contributes to connect the quantum transport to diffusive-related phenomena in such an elementary organic system.

The effective utilization of vertical organic transistors in high current density applications demands further reduction of channel length (given by the thickness of the organic semiconducting layer and typically reported in the 100 nm range) along with the optimization of the source electrode structure. Here we present a viable solution by applying rolled-up metallic nanomembranes as the drain-electrode (which enables the incorporation of few nanometer-thick semiconductor layers) and by lithographically patterning the source-electrode. Our vertical organic transistors operate at ultra-low voltages and demonstrate high current densities (~0.5 A cm−2) that are found to depend directly on the number of source edges, provided the source perforation gap is wider than 250 nm. We anticipate that further optimization of device structure can yield higher current densities (~10 A cm−2). The use of rolled-up drain-electrode also enables sensing of humidity and light which highlights the potential of these devices to advance next-generation sensing technologies.

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According to the forecast of Allied Market Research, the flexible electronics market is projected to reach $42.48 billion by 2027. It is estimated to revolutionize the lighting technology, power integration displays, and health monitoring systems. The popularity of flexible electronics is mainly due to the unique benefits of organic materials and devices that offer cost-effectiveness, low-temperature processability, mechanical softness, and shape adaptability, [5][6][7] which are difficult to obtain with traditional, complementary-metal-oxide-semiconductor (CMOS)-based rigid systems. [8] Over the past two decades, research interest in flexible electronic systems has grown exponentially, driven by the requirements of interface softness and shape adaptability for electronics used in Internet-of-Things (IoT), [9] human-machine interfaces, [10] and advanced healthcare. [11] Although significant progress has been made in academia, the practical application of flexible electronics in the industry is limited. Presently, thin-film photovoltaics and flexible displays mainly contribute to the flexible electronics market, with a noticeable presence held by radio frequency identification (RFID) tags and medical X-ray imagers. [12] Indeed, much of the success of present flexible electronic systems rely on the performance and reliability of thin-film The development of flexible and conformable devices, whose performance can be maintained while being continuously deformed, provides a significant step toward the realization of next-generation wearable and e-textile applications. Organic field-effect transistors (OFETs) are particularly interesting for flexible and lightweight products, because of their low-temperature solution processability, and the mechanical flexibility of organic materials that endows OFETs the natural compatibility with plastic and biodegradable substrates. Here, an in-depth review of two competing flexible OFET technologies, planar and vertical OFETs (POFETs and VOFETs, respectively) is provided. The electrical, mechanical, and physical properties of POFETs and VOFETs are critically discussed, with a focus on four pivotal applications (integrated logic circuits, light-emitting devices, memories, and sensors). It is pointed out that the flexible function of the relatively newer VOFET technology, along with its perspective on advancing the applicability of flexible POFETs, has not been reviewed so far, and the direct comparison regarding the performance of POFET-and VOFET-based flexible applications is most likely absent. With discussions spanning printed and wearable electronics, materials science, biotechnology, and environmental monitoring, this contribution is a clear stimulus to researchers working in these fields to engage toward the plentiful possibilities that POFETs and VOFETs offer to flexible electronics.

Freestanding, edge-supported silicon nanomembranes are defined by selective underetching of patterned silicon-on-insulator substrates. The membranes are afterward introduced into a molecular beam epitaxy chamber and overgrown with InAs, resulting in the formation of InAs islands on flat areas and at the top of the Si nanomembranes. A detailed analysis of sample morphology, island structure, and strain is carried out. Scanning electron microscopy shows that the membrane stays intact during overgrowth. Atomic force microscopy reveals a lower island density on top of the freestanding membranes, denoting a modified wetting or diffusivity in these areas. An observed bending of the membrane indicates a strain transfer from the InAs islands to the compliant substrate. X-ray diffraction and finite-element modeling indicate a nonuniform strain state of the island ensemble grown on the freestanding membrane. A simulation of the bending of the nanomembranes indicates that the islands at the center of the freestanding area are highly strained, whereas islands on the border tend to be fully relaxed. Finally, continuum elasticity calculations suggest that for a sufficiently thin membrane InAs could transfer enough strain to the membrane to allow coherent epitaxial growth, something not possible on bulk substrates.

The controllable transfer of a single electron in devices (SEDs) is one of the viable trends for a new generation of technology. However, novel applications demand innovative strategies to fabricate and evaluate SEDs. Here, we report a hybrid organic/inorganic SED that combines an ensemble of physisorbed, semiconducting molecular layers (SMLs) and Au nanoclusters embedded in the transport channel by in situ, field-induced metal migration. The SED is fabricated using an integrative platform based on rolled-up nanomembranes (rNMs) to connect ultrathin SMLs from the top, forming large-area tunnel junctions. The combination of high electric fields (1−4 MV/cm), electrode point contacts, low temperatures (10 K), and ultrathin molecular layers (<10 nm) lead to field-induced migration of Au electrode nanoparticles inward the SML of the junction channel. This phenomenon can be either observed in the as-prepared rNM junctions or intentionally induced by the application of high electric fields (>1 MV/cm). The propelled electrode particles become trapped in the soft molecular material, acting as Coulomb islands positioned in between a double-barrier tunnel junction. As a result, the hybrid organic/inorganic rNM junctions present single-charge effects, namely Coulomb blockade and Coulomb staircase. Such an in situ, field-induced metal migration process opens possibilities to create novel and complex SEDs by using different molecular materials. From another perspective, the reported metal diffusion in such nanoscale junctions deserves attention as it can occasionally mask moleculedependent responses.

Organic electrochemical transistors (OECTs) are technologically relevant devices presenting high susceptibility to physical stimulus, chemical functionalization, and shape changes—jointly to versatility and low production costs. The OECT capability of liquid‐gating addresses both electrochemical sensing and signal amplification within a single integrated device unit. However, given the organic semiconductor time‐consuming doping process and their usual low field‐effect mobility, OECTs are frequently considered low‐end category devices. Toward high‐performance OECTs, microtubular electrochemical devices based on strain‐engineering are presented here by taking advantage of the exclusive shape features of self‐curled nanomembranes. Such novel OECTs outperform the state‐of‐the‐art organic liquid‐gated transistors, reaching lower operating voltage, improved ion doping, and a signal amplification with a >104 intrinsic gain. The multipurpose OECT concept is validated with different electrolytes and distinct nanometer‐thick molecular films, namely, phthalocyanine and thiophene derivatives. The OECTs are also applied as transducers to detect a biomarker related to neurological diseases, the neurotransmitter dopamine. The self‐curled OECTs update the premises of electrochemical energy conversion in liquid‐gated transistors, yielding a substantial performance improvement and new chemical sensing capabilities within picoliter sampling volumes.

Nanomembranes (NMs) are freestanding structures with few-nanometer thickness and lateral dimensions up to the microscale. In nanoelectronics, NMs have been used to promote reliable electrical contacts with distinct nanomaterials, such as molecules, quantum dots, and nanowires, as well as to support the comprehension of the condensed matter down to the nanoscale. Here, we propose a tunable device architecture that is capable of deterministically changing both the contact geometry and the current injection in nanoscale electronic junctions. The device is based on a hybrid arrangement that joins metallic NMs and molecular ensembles, resulting in a versatile, mechanically compliant element. Such a feature allows the devices to accommodate a mechanical stimulus applied over the top electrodes, enlarging the junctions' active area without compromising the molecules. A model derived from the Hertzian mechanics is employed to correlate the contact dynamics with the electronic transport in these novel devices denominated as variable-area transport junctions (VATJs). As a proof of concept, we propose a direct application of the VATJs as compression gauges envisioning the development of hypersensitive pressure pixels. Regarding sensitivity (∼480 kPa −1 ), the VATJ-based transducers constitute a breakthrough in nanoelectronics, with the prospect of carrying its sister-field of molecular electronics out of the laboratory via integrative, hybrid organic/inorganic nanotechnology.