The ongoing miniaturization of electronic devices has boosted the development of new post-silicon two-dimensional (2D) semiconductors, such as transition metal dichalcogenides, one of the most prominent materials being molybdenum disulfide (MoS2). A major obstacle for the industrial production of MoS2-based devices lies in the growth techniques. These must ensure the reliable fabrication of MoS2 with tailored 2D properties to allow for the typical direct bandgap of 1.9 eV, while maintaining large-area growth and device compatibility. In this work, we used a versatile and industrially scalable MoS2 growth method based on ionized jet deposition and annealing at 250 °C, through which a 3D stable and scalable material exhibiting excellent electronic and optical properties of 2D MoS2 is synthesized. The thickness-related limit, i.e., the desired optical and electronic properties being limited to 2D single/few-layered MoS2, was overcome in the thin film through the formation of encapsulated highly crystalline 2D MoS2 nanosheets exhibiting a bandgap of 1.9 eV and sharp optical emission. The newly synthesized 2D-in-3D MoS2 structure will facilitate device compatibility of 2D materials and confer superior optoelectronic device function.
Manufacturing molecule-based functional elements directly at device interfaces is a frontier in bottom-up materials engineering. A longstanding challenge in the field is the covalent stabilization of pre-assembled molecular architectures to afford nanodevice components. Here, we employ the controlled supramolecular self-assembly of anthracene derivatives on a hexagonal boron nitride sheet, to generate nanographene wires through photo-crosslinking and thermal annealing. Specifically, we demonstrate µm-long nanowires with an average width of 200 nm, electrical conductivities of 106 S m−1 and breakdown current densities of 1011 A m−2. Joint experiments and simulations reveal that hierarchical self-assembly promotes their formation and functional properties. Our approach demonstrates the feasibility of combined bottom-up supramolecular templating and top-down manufacturing protocols for graphene nanomaterials and interconnects, towards integrated carbon nanodevices.
Most electrical sensor and biosensor elements require reliable transducing elements to convert small potential changes into easy to read out current signals. Offering inherent signal magnification and being operable in many relevant environments field‐effect transistors (FETs) are the element of choice in many cases. In particular, using electrolyte gating, numerous sensors and biosensors have been realized in aqueous environments. Over the past years, electrolyte‐gated FETs have been fabricated using a variety of semiconducting materials, including graphene, ZnO, as well as conjugated molecules and polymers. Above all, using conducting polymers top‐performing devices have been achieved. Herein, an approach to use a transition metal dichalcogenide (TMDC)‐based monolayer device as a transducing element is presented. Using MoS2 monolayers, it is shown that such electrolyte‐gated devices may be regarded as very promising transducing elements for sensor and biosensor applications, enabled by their high sensitivity for environmental changes and the possibility of using the naturally occurring sulfur vacancies as grafting points of biorecognition layers. Furthermore, the behavior of such a device under prolonged operation in a dilute biologically relevant electrolyte such as phosphate buffered saline solution (PBS) is reported.
The rapid evolution of artificial intelligence-well established at the software level-is pushing the development of devices able to integrate-at the hardware level-the learning capability of biological nervous systems. [1][2][3] In order to reproduce the functionalities of biological neural networks-based on neurons interconnected through synapses [4] -these systems are mimicked in the form of artificial neural networks (ANNs). Neuromorphic devices serve as building blocks for ANNs, by operating as artificial neurons or synapses. Since the signal transfer across the biological synapse is modulated by ion dynamics, a biomimetic artificial synapse would therefore benefit from imitating this behavior.This approach has previously been explored and reported in literature, employing mainly transistor-based architectures. There, the conductivity is mediated by ionic doping of the transistor channel. [5,6] While these devices display a variety of neuromorphic functionalities, their architecture is based on three-terminal devices. This approach not only impedes dense integration into ANNs-in the form of crossbar arrays [7] -but also breaks with the biomimetic principle, as the synapse is inherently two-terminal. Thus, an equally twoterminal synaptic device would be preferable and various concepts have been presented in literature. These devices are based on metallic filament formation, [8][9][10] phase change, [11,12] spin state, [13,14] ferroelectric effects, [15,16] redox chemistry, [17] or biomembranes. [18,19] In this work, we propose to add another mechanism-inspired by the ion-based operating principle of the biological synapse-by revisiting a concept for a wholly different category of device. Although not for neuromorphic applications, controlling the electronic properties of a two-terminal device through dynamic polarization of ions has previously been employed in light-emitting electrochemical cells (LECs). [20,21] In such a device, a single layer, based on an organic mixed ionic-electronic conductor-mixed with a salt-is sandwiched between two electrodes. Upon applying a bias, the salt dissociates and ions drift toward the electrodes, resulting in the formation of electric double layers at the electrode interfaces. [22][23][24][25] This allows for improved carrier injection without the need of additional injection or transport layers and upon balanced Neuromorphic devices are likely to be the next evolution of computing, allowing to implement machine learning within hardware components. In biological neural systems, learning and signal processing are achieved by communication between neurons through time-dependent ion flux in the synapses. Integrating such ion-mediated operating principles in neuromorphic devices can deliver an energy efficient and powerful technology. Here a device known as a light-emitting electrochemical cell is revisited and modified, exploiting its ability to modulate current through ion accumulation/depletion at the electrodes and turn it into an organic synaptic diode. This two-terminal de...
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