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Abstract Epidermally mounted sensors using triaxial accelerometers have been previously used to monitor physiological processes with the implementation of machine learning (ML) algorithm interfaces. The findings from these previous studies have established a strong foundation for the analysis of high-resolution, intricate signals, typically through frequency domain conversion. In this study we integrate a wireless mechano-acoustic sensor with a multi-modal deep learning system for the real-time analysis of signals emitted by the laryngeal prominence area of the thyroid cartilage at frequency ranges up to 1 kHz. This interface provides real-time data visualization and communication with the ML server, creating a system that assesses severity of chronic obstructive pulmonary disease and analyzes the user’s speech patterns.

Electrochemical water splitting has received tremendous attention as an eco‐friendly approach to produce hydrogen. Noble metals and their oxides are commonly used as electrocatalysts to reduce activation energy barriers for hydrogen and oxygen evolution reactions in high‐performance electrodes, but their cost, scarcity, and limited stability hinder widespread adoption of electrochemical water splitting. Further advancements are therefore needed to reduce reliance on noble metals and improve the long‐term stability. Herein, solution‐processed 2D van der Waals (vdW) p–n heterostructures as an interfacial layer between catalysts and the electrode are introduced to enhance the catalytic performance. These heterostructures are formed by sequentially assembling electrochemically exfoliated black phosphorus and molybdenum disulfide nanosheets into electronic‐grade p‐ and n‐type semiconductor thin films, with the scalability extending across tens‐of‐centimeter scale areas. Benefiting from the charge distribution and built‐in electric field developed upon heterojunction formation, the vdW heterostructure interfacial layer increases both the catalytic activity and stability of commercial Pt/C and Ir/C catalysts compared to when these catalysts are directly loaded onto electrodes. Additionally, the vdW heterostructure also serves as a template for synthesizing nanostructured Pt and Ir catalysts through electrodeposition, further enhancing the catalytic performance in terms of mass activity and stability.

Abstract Copper iodide (CuI) has garnered considerable attention as a promising alternative to p‐type transparent conducting oxides owing to its low cation vacancy formation energy, shallow acceptor level, and readily modifiable conductivity via doping. Although sulfur (S) doping through liquid iodination has exhibited high efficacy in enhancing the conductivity with record high figure of merit (FOM) of 630 00 MΩ−1, solution‐processed S‐doped CuI (CuI:S) for low‐cost large area fabrication has yet to be explored. Here, a highly conducting CuI:S thin‐film for p‐type transparent conducting electrode (TCE) is reported using low temperature solution‐processing with thiourea derivatives. The optimization of thiourea dopant is determined through a comprehensive acid‐base study, considering the effects of steric hindrance. The modification of active groups of thioureas facilitated a varying carrier concentration range of 9 × 1018–2.52 × 1020 cm−3 and conductivities of 4.4–390.7 S cm−1. Consequently, N‐ethylthiourea‐doped CuI:S exhibited a FOM value of 7 600 MΩ−1, which is the highest value among solution‐processed p‐type TCEs to date. Moreover, the formulation of CuI:S solution for highly conductive p‐type TCEs can be extended to CuI:S inks, facilitating high‐throughput solution‐processes such as inkjet printing and spray coating.

Abstract The water solubility of molecules is one of the most important properties in various chemical and medical research fields. Recently, machine learning-based methods for predicting molecular properties, including water solubility, have been extensively studied due to the advantage of effectively reducing computational costs. Although machine learning-based methods have made significant advances in predictive performance, the existing methods were still lacking in interpreting the predicted results. Therefore, we propose a novel multi-order graph attention network (MoGAT) for water solubility prediction to improve the predictive performance and interpret the predicted results. We extracted graph embeddings in every node embedding layer to consider the information of diverse neighboring orders and merged them by attention mechanism to generate a final graph embedding. MoGAT can provide the atomic-specific importance scores of a molecule that indicate which atoms significantly influence the prediction so that it can interpret the predicted results chemically. It also improves prediction performance because the graph representations of all neighboring orders, which contain diverse range of information, are employed for the final prediction. Through extensive experiments, we demonstrated that MoGAT showed better performance than the state-of-the-art methods, and the predicted results were consistent with well-known chemical knowledge.

Abstract Two-dimensional (2D) black phosphorus (BP), or phosphorene, has recently emerged as a promising 2D semiconductor because of its p-type charge transport behavior and near-infrared photoresponsivity. However, the application of BP in practical electronic and optoelectronic devices is hindered by challenges in producing high-quality BP films over large areas. In this manuscript, we present a facile solution-based process to create wafer-scale BP films for fabrication of p-channel field-effect transistors that are responsive to near infrared light. Few-layer BP nanosheets are first exfoliated from the bulk crystal via electrochemical intercalation of cationic molecules and then vacuum-filtered through an anodic aluminum oxide membrane. The resulting BP film can be transferred onto an SiO2-coated silicon substrate, thereby allowing for realization of field-effect transistors after electrode deposition and thermal annealing. The transistor array exhibits spatial uniformity in electrical performance with an average hole mobility of ~0.002 cm2 V−1 s−1 and on/off ratio of 130. Furthermore, gate-induced modulation of the BP channel allows for enhancement in the photoresponsivity for 1550-nm light illumination up to 24 mA W−1, which benefits the application of the phototransistor array for near infrared imaging.

Abstract Inkjet printing is a cost-effective and scalable way to assemble colloidal materials into desired patterns in a vacuum- and lithography-free manner. Two-dimensional (2D) nanosheets are a promising material category for printed electronics because of their compatibility with solution processing for stable ink formulations as well as a wide range of electronic types from metal, semiconductor to insulator. Furthermore, their dangling bond-free surface enables atomically thin, electronically-active thin films with van der Waals contacts which significantly reduce the junction resistance. Here, we demonstrate all inkjet-printed thin-film transistors consisting of electrochemically exfoliated graphene, MoS2, and HfO2 as metallic electrodes, a semiconducting channel, and a high-k dielectric layer, respectively. In particular, the HfO2 dielectric layer is prepared via two-step; electrochemical exfoliation of semiconducting HfS2 followed by a thermal oxidation process to overcome the incompatibility of electrochemical exfoliation with insulating crystals. Consequently, all inkjet-printed 2D nanosheets with various electronic types enable high-performance, thin-film transistors which demonstrate field-effect mobilities and current on/off ratios of ~10 cm2 V−1 s−1 and >105, respectively, at low operating voltage.

Abstract Platinum diselenide (PtSe2) has shown great potential as a candidate two‐dimensional (2D) material for broadband photodetectors and electrocatalysts because of its unique properties compared to conventional 2D transition metal dichalcogenides. Synthesis of 2D PtSe2 with controlled layer number is critical for engineering the electronic behavior to be semiconducting or semimetallic for targeted applications. Electrochemical exfoliation has been investigated as a promising approach for mass‐producing in a cost‐effective manner, but obtaining high‐quality films with control over electronic properties remains difficult. Here, we demonstrate wafer‐scale 2D PtSe2 films with pre‐determined electronic types based on a facile solution‐based strategy. Semiconducting or semimetallic PtSe2 nanosheets with large lateral sizes are produced via electrochemically driven molecular intercalation, followed by centrifugation‐based thickness sorting. Finally, gate‐tunable broadband visible and near‐infrared photodetector arrays are realized based on semiconducting PtSe2 nanosheet films, while semimetallic films are used to create catalytic electrodes for overall water splitting with long‐term stability.

Artificial sensory systems have emerged as pivotal technologies to bridge the gap between the virtual and real-world, replicating human senses to interact intelligently with external stimuli. To practically apply artificial sensory systems in the real-world, it is essential to mass-produce nanomaterials with ensured sensitivity and selectivity, purify them for desired functions, and integrate them into large-area sensory devices through assembly techniques. A comprehensive understanding of each process parameter from material processing to device assembly is crucial for achieving a high-performing artificial sensory system. This review provides a technological framework for fabricating high-performance artificial sensory systems, covering material processing to device integrations. We introduce recent approaches for dispersing and purifying various nanomaterials including 0D, 1D, and 2D nanomaterials. We then highlight advanced coating and printing techniques of the solution-processed nanomaterials based on representative three methods including (i) evaporation-based assembly, (ii) assisted assembly, and (iii) direct patterning. We explore the application and performances of these solution-processed materials and printing methods in fabricating sensory devices mimicking five human senses including vision, olfaction, gustation, hearing, and tactile perception. Finally, we suggest an outlook for possible future research directions to solve the remaining challenges of the artificial sensory systems such as ambient stability, device consistency, and integration with AI-based software.

Abstract Ferroelectric two dimensional (2D) materials hold great potential to develop modern miniaturized electronic and memory devices. 2D ferroelectrics exhibiting spontaneous polarization in the out‐of‐plane direction have been extensively investigated to date, but the loss of their polarization during device operation has been problematic. Although 2D materials with in‐plane ferroelectric behavior are more stable against depolarization and thus promising for memory and logic applications, experimental realization of in‐plane 2D ferroelectric devices is still scarce. Here, we demonstrate in‐plane ferroelectric field effect transistors (FETs) based on a van der Waals heterojunction (vdWHJ), which can perform multibit memory and logic operations. Tin monosulfide (SnS), a 2D material with in‐plane ferroelectricity, is partially stacked on top of a semiconducting molybdenum disulfide (MoS2) on a silicon dioxide (SiO2)‐coated silicon substrate to fabricate vdWHJ FETs in back‐gate configuration. Switching of the in‐plane polarization direction in the SnS channel modulates the contact barriers at the electrode/SnS and SnS/MoS2 interfaces, thereby creating high resistance states and low resistance states (LRS). The device exhibits a logic transfer characteristic with a high drain current on/off ratio (>106) in LRS and non‐volatile memory performance with excellent retention characteristics (extrapolated retention time > 10 years). With exquisite tuning of the channel resistance by SnS polarization and gate bias, we realize multiple states with distinct current levels for multibit memory and logic operations suitable for programmable logic‐in‐memory applications.

Abstract We demonstrated highly transparent and flexible polytetrafluoroethylene (PTFE) passivation for the MoS2/Ag nanowire (Ag NW) electrodes used in thin film heaters (TFHs). The electrical, optical, and mechanical properties of PTFE coated MoS2/Ag NW electrode were compared to the bare MoS2/Ag NW electrode to demonstrate effective passivation of the sputtered PTFE films before and after the 85 °C–85% temperature-relative humidity environment test. In addition, we investigated the performances of TFHs with PTFE/MoS2/Ag NW as a function of PTFE thickness from 50 to 200 nm. The saturation temperature (87.3 °C) of TFHs with PTFE/MoS2/Ag NW electrode is higher than that (61.3 °C) of TFHs with bare MoS2/Ag NW, even after the 85 °C–85% temperature-relative humidity environment test, due to effective passivation of the PTFE layer. This indicates that transparent PTFE film prepared by sputtering process provides effective thin film passivation for the two-dimensional (2D) MoS2 and Ag NW hybrid electrode against harsh environment condition.

Two-dimensional molybdenum disulfide (MoS2) nanosheets have emerged as a promising material for transparent, flexible micro-supercapacitors, but their use in electrodes is hindered by their poor electrical conductivity and cycling stability because of restacking. In this paper, we report a novel electrode architecture to exploit electrochemical activity of MoS2 nanosheets. Electrochemically exfoliated MoS2 dispersion was spin coated on mesh-like silver networks encapsulated with a flexible conducting film exhibiting a pseudocapacitive behavior. MoS2 nanosheets were electrochemically active over the whole electrode surface and the conductive layer provided a pathway to transport electrons between the MoS2 and the electrolyte. As the result, the composite electrode achieved a large areal capacitance (89.44 mF cm−2 at 6 mA cm−2) and high energy and power densities (12.42 µWh cm−2 and P = 6043 µW cm−2 at 6 mA cm−2) in a symmetric cell configuration with 3 M KOH solution while exhibiting a high optical transmittance of ~80%. Because the system was stable against mechanical bending and charge/discharge cycles, a flexible micro-supercapacitor that can power electronics at different bending states was realized.

Abstract Metal nanoparticles (MeNPs) have been used in various industrial applications, owing to their unique physical and chemical properties different from the bulk counterparts. However, the natural oxidation of MeNPs is an imminent hindrance to their widespread applications despite much research efforts to prevent it. Here, a rational approach for non‐oxidized bare MeNPs in air, which requires no additional surface passivation treatment is reported. The direct synthetic route uses the [Gd2C]2+ · 2e− electride as an exceptional electron‐donating agent to reduce diverse metal precursors in alcoholic solvents. All synthesized bare Cu, Ag, and Sn nanoparticles are ultra‐stable in ambient air, exhibiting no trace of metal oxides even on their outermost atomic layer. This unique resistance to oxidation is ascribed to the accumulation of excess electrons on the surface of bare MeNPs, which originates from the spontaneous transfer of anionic electrons from the electride during the nanoparticle growth process. This approach provides not only a revolutionary scheme to obtain MeNPs with non‐passivated and non‐oxidized surfaces, but also fundamental knowledge about metal oxidation.

Nanostructuring of Pt nanocatalysts increases the surface‐to‐volume ratio, thus enabling efficient usage of Pt for hydrogen evolution reaction (HER). Direct electrochemical reduction of Pt on the electrode can produce nanostructured Pt catalysts, which has been time‐consuming for the conventional colloidal synthesis. However, carbon‐based growth templates commonly used to create Pt nanoparticles offer limited control over morphologies and HER performance. Herein, a facile electrochemical synthesis of Pt nanoflowers (NFs) with well‐defined petals is presented. Semiconducting MoS2 nanosheets are solution processed into a film on a carbon paper (CP) to synthesize Pt NFs upon reduction of Pt precursor. The Pt NFs show higher HER activities than spherical or spiky Pt nanoparticles because of their larger active surface area and enable faster release of hydrogen bubbles during HER. By generating sulfur vacancies and MoOx on the MoS2 template using a reactive ion etching, the areal density and spatial uniformity of Pt NFs can be greatly enhanced and a mass activity can be achieved more than 10 times as high as that of the conventional Pt/C electrode. Multiple electrodes with nearly similar electrochemical properties can be repeatedly produced by using a single precursor solution, which highlights the cost‐efficiency and scalability of our synthesis strategy.

Abstract In this research, dispersion of a new type of one-dimensional inorganic material Nb2Se9, composed of van der Waals bonds, in aqueous solution for bio-application study were studied. To disperse Nb2Se9, which exhibits hydrophobic properties in water, experiments were carried out using a block copolymer (poloxamer) as a dispersant. It was confirmed that PPO, the hydrophobic portion of Poloxamer, was adsorbed onto the surface of Nb2Se9, and PEO, the hydrophilic portion, induced steric hinderance to disperse Nb2Se9 to a size of 10 nm or less. To confirm the adaptability of muscle cells C2C12 to the dispersed Nb2Se9 using poloxamer 188 as dispersant, a MTT assay and a live/dead assay were performed, demonstrating improvement in the viability and proliferation of C2C12 cells.

Abstract The recent advancements in multivalued logic gates represent a rapid paradigm shift in semiconductor technology toward a new era of hyper Moore's law. Particularly, the significant evolution of materials is guiding multivalued logic systems toward a breakthrough gradually, whereby they are transcending the limits of conventional binary logic systems in terms of all the essential figures of merit, i.e., power dissipation, operating speed, circuit complexity, and, of course, the level of the integration. In this review, recent advances in the field of multivalued logic gates based on emerging materials to provide a comprehensive guideline for possible future research directions are reviewed. First, an overview of the design criteria and figures of merit for multivalued logic gates is presented, and then advancements in various emerging nanostructured materials—ranging from 0D quantum dots to multidimensional heterostructures—are summarized and these materials in terms of device design criteria are assessed. The current technological challenges and prospects of multivalued logic devices are also addressed and major research trends are elucidated.

The placement of nanomaterials at predefined locations is a key requirement for their integration in nanoelectronic devices. Here, the authors devise a method allowing placement of solution-based nanomaterials by using structured graphene layers as deposition sites with the aid of an electric field.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Donor–acceptor-type organic semiconductor molecules are of great interest for potential organic field-effect transistor applications with ambipolar characteristics and non-volatile memory applications. Here, we synthesized an organic semiconductor, PDPPT-TT, and directly utilized it in both field-effect transistor and non-volatile memory applications. As-synthesized PDPPT-TT was simply spin-coated on a substrate for the device fabrications. The PDPPT-TT based field-effect transistor showed ambipolar electrical transfer characteristics. Furthermore, a gold nanoparticle-embedded dielectric layer was used as a charge trapping layer for the non-volatile memory device applications. The non-volatile memory device showed clear memory window formation as applied gate voltage increases, and electrical stability was evaluated by performing retention and cycling tests. In summary, we demonstrate that a donor–acceptor-type organic semiconductor molecule shows great potential for ambipolar field-effect transistors and non-volatile memory device applications as an important class of materials.

In this paper, we propose a solvent-free device fabrication method using a melt-blown (MB) fiber to minimize potential chemical and thermal damages to transition-metal-dichalcogenides (TMDCs)-based semiconductor channel. The fabrication process is composed of three steps; (1) MB fibers alignment as a shadow mask, (2) metal deposition, and (3) lifting-up MB fibers. The resulting WSe2-based p-type metal-oxide-semiconductor (PMOS) device shows an ON/OFF current ratio of ~2 × 105 (ON current of ~−40 µA) and a remarkable linear hole mobility of ~205 cm2/V·s at a drain voltage of −0.1 V. These results can be a strong evidence supporting that this MB fiber-assisted device fabrication can effectively suppress materials damage by minimizing chemical and thermal exposures. Followed by an MoS2-based n-type MOS (NMOS) device demonstration, a complementary MOS (CMOS) inverter circuit application was successfully implemented, consisted of an MoS2 NMOS and a WSe2 PMOS as a load and a driver transistor, respectively. This MB fiber-based device fabrication can be a promising method for future electronics based on chemically reactive or thermally vulnerable materials.