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Emerging freestanding membrane technologies, especially using inorganic thermoelectric materials, demonstrate the potential for advanced thermoelectric platforms. However, using rare and toxic elements during material processing must be circumvented. Herein, we present a scalable method for synthesizing highly crystalline CuS membranes for thermoelectric applications. By sulfurizing crystalline Cu, we produce a highly percolated and easily transferable network of submicron CuS rods. The CuS membrane effectively separates thermal and electrical properties to achieve a power factor of 0.50 mW m−1 K−2 and thermal conductivity of 0.37 W m−1 K−1 at 650 K (estimated value). This yields a record‐high dimensionless figure‐of‐merit of 0.91 at 650 K (estimated value) for covellite. Moreover, integrating 12 CuS devices into a module resulted in a power generation of ~4 μW at ΔT of 40 K despite using a straightforward configuration with only p‐type CuS. Furthermore, based on the temperature‐dependent electrical characteristics of CuS, we develop a wearable temperature sensor with antibacterial properties. [ABSTRACT FROM AUTHOR]

The pursuit of sub‐1‐nm field‐effect transistor (FET) channels within 3D semiconducting crystals faces challenges due to diminished gate electrostatics and increased charge carrier scattering. 2D semiconductors, exemplified by transition metal dichalcogenides, provide a promising alternative. However, the non‐idealities, such as excess low‐frequency noise (LFN) in 2D FETs, present substantial hurdles to their realization and commercialization. In this study, ideal LFN characteristics in monolayer MoS2 FETs are attained by engineering the metal‐2D semiconductor contact and the subgap density of states (DOS). By probing non‐ideal contact resistance effects using CuS and Au electrodes, it is uncovered that excess contact noise in the high drain current (ID) region can be substantially reduced by forming a van der Waals junction with CuS electrodes. Furthermore, thermal annealing effectively mitigates sulfur vacancy‐induced subgap density of states (DOS), diminishing excess noise in the low ID region. Through meticulous optimization of metal‐2D semiconductor contacts and subgap DOS, alignment of 1/f noise with the pure carrier number fluctuation model is achieved, ultimately achieving the sought‐after ideal LFN behavior in monolayer MoS2 FETs. This study underscores the necessity of refining excess noise, heralding improved performance and reliability of 2D electronic devices. [ABSTRACT FROM AUTHOR]

The increasing demand for miniature, flexible electronic devices have fueled the need for compact and high‐performing energy storage solutions. Microsupercapacitors (mSCs) with reduced dimension and novel electrode design have gained prominence. This concept paper summarizes and views the recent advancements in mSCs with a focus on 3D graphene electrodes and their novel electrode design to increase energy performance of the devices. Especially, we focus on these 3D graphene structures fabricated using a laser‐scribing method which offer an efficient, cost‐effective approach for enhanced mSC performance. Further, this work delves into the vital link between the electrical field effect and geometrically engineered interdigitated electrodes, which is pivotal for maximizing the ion transport and mSC energy storage performance. The insights presented here are promising for meeting the power requirements of future miniature electronics. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) vertical van der Waals heterostructures (vdWHs) show great potential across various applications. However, synthesizing large-scale structures poses challenges owing to the intricate growth parameters, forming unexpected hybrid film structures. Thus, precision in synthesis and thorough structural analysis are essential aspects. In this study, we successfully synthesized large-scale structured 2D transition metal dichalcogenides (TMDs) via chemical vapor deposition using metal oxide (WO3 and MoO3) thin films and a diluted H2S precursor, individual MoS2, WS2 films and various MoS2/WS2 hybrid films (Type I: MoxW1−xS2 alloy; Type II: MoS2/WS2 vdWH; Type III: MoS2 dots/WS2). Structural analyses, including optical microscopy, Raman spectroscopy, transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy, and cross-sectional imaging revealed that the A1g and E2g modes of WS2 and MoS2 were sensitive to structural variations, enabling hybrid structure differentiation. Type II showed minimal changes in the MoS2′s A1g mode, while Types I and III exhibited a ~2.8 cm−1 blue shift. Furthermore, the A1g mode of WS2 in Type I displayed a 1.4 cm−1 red shift. These variations agreed with the TEM-observed microstructural features, demonstrating strain effects on the MoS2–WS2 interfaces. Our study provides insights into the structural features of diverse hybrid TMD materials, facilitating their differentiation through Raman spectroscopy. [ABSTRACT FROM AUTHOR]

In plane micro‐supercapacitors that are miniaturized energy storage components have attracted significant attention due to their high power densities for various ubiquitous and sustainable device systems as well as their facile integration on various flexible/wearable platform. To implement the micro‐supercapacitors in various practical applications that can accompany solid state or gel electrolyte and flexible substrates, ions must be readily transported to electrodes for achieving high power densities. Herein, we show large enhancement in electrochemical properties of flexible, in‐plane micro‐supercapacitor using sharp‐edged interdigitated electrode design, which was simply fabricated through direct laser scribing method. The sharp‐edged electrodes allowed strong electric field to be induced at the corners of the electrode fingers which led to the greater accumulation of ions near the surface of electrode, significantly enhancing the energy storage performance of micro‐supercapacitors. The electric field‐enhanced in‐plane micro‐supercapacitor showed the volumetric energy density of 1.52 Wh L−1 and the excellent cyclability with capacitive retention of 95.4% after 20 000 cycles. We further showed various practicability of our sharp‐edged design in micro‐supercapacitors by showing circuit applicability, mechanical stability, and air stability. These results present an important pathway for designing electrodes in various energy storage devices. [ABSTRACT FROM AUTHOR]

Two–dimensional materials have the potential to be applied in flexible and transparent electronics. In this study, single-layer MoS2 field-effect transistors (FETs) with Au/Ti–graphene heteroelectrodes were fabricated to examine the effect of the electrodes on the electrical properties of the MoS2 FETs. The contact barrier potential was tuned using an electric field. Asymmetrical gate behavior was observed owing to the difference between the MoS2 FETs, specifically between the MoS2 FETs with Au/Ti electrodes and those with graphene electrodes. The contact barrier of the MoS2 FETs with Au/Ti electrodes did not change with the electric field. However, the contact barrier at the MoS2–graphene interface could be modulated. The MoS2 FETs with Au/Ti–graphene electrodes exhibited enhanced on/off ratios (~102 times) and electron mobility (~2.5 times) compared to the MoS2 FETs with Au/Ti electrodes. These results could improve the understanding of desirable contact formation for high-performance MoS2 FETs and provide a facile route for viable electronic applications. [ABSTRACT FROM AUTHOR]

This work features a thin, flexible thermoelectric membrane in a multifunctional wearable device, highlighting its advanced energy harvesting capabilities. [ABSTRACT FROM AUTHOR]

Van der Waals (vdW) heterostructures based on two-dimensional (2D) transition metal dichalcogenides (TMDCs), particularly WS2/MoS2 heterostructures with type-II band alignments, are considered as ideal candidates for future functional optoelectronic applications owing to their efficient exciton dissociation and fast charge transfers. These physical properties of vdW heterostructures are mainly influenced by the interlayer coupling occurring at the interface. However, a comprehensive understanding of the interlayer coupling in vdW heterostructures is still lacking. Here, we present a detailed analysis of the low-frequency (LF) Raman modes, which are sensitive to interlayer coupling, in bilayers of MoS2, WS2, and WS2/MoS2 heterostructures directly grown using chemical vapor deposition to avoid undesirable interfacial contamination and stacking mismatch effects between the monolayers. We clearly observe two distinguishable LF Raman modes, the interlayer in-plane shear and out-of-plane layer-breathing modes, which are dependent on the twisting angles and interface quality between the monolayers, in all the 2D bilayered structures, including the vdW heterostructure. In contrast, LF modes are not observed in the MoS2 and WS2 monolayers. These results indicate that our directly grown 2D bilayered TMDCs with a favorable stacking configuration and high-quality interface can induce strong interlayer couplings, leading to LF Raman modes. [ABSTRACT FROM AUTHOR]

Flexible electronics and optoelectronics based on monolayered, semiconducting transition metal dichalcogenides (TMDCs) channel have recently received attention as the 2D structure possess superior mechanical, optical, and electrical properties. However, there is a lack of understanding of strain‐dependent electrical and photoelectrical properties in the electrode‐TMDC channel system. Here, two‐terminal flexible device is fabricated and strain‐engineered contact barrier modulation between monolayer MoS2 channel and Au electrode is shown. It is found experimentally through in situ strain electrical and kelvin probe force microscope measurements that tensile strain lowers the contact energy barriers between MoS2 and Au, in which the changes in the contact barriers is attributed to the strain‐induced increase of the electron affinity in MoS2 monolayer. Furthermore, the strain‐induced barrier modulation is also shown to affect photoresponse behaviors in a MoS2 flexible photodetectors through bending of energy bands that affect photogenerated carrier transport and electron‐hole recombination. These findings present important pathway toward designing flexible devices based on 2D TMDCs. [ABSTRACT FROM AUTHOR]

The implications of graphene for tunneling diodes have attracted great attention due to the excellent electrical properties of graphene. Most graphene-based tunneling diodes have been fabricated with a vertical structure. They are limited by a complicated fabrication process. Herein, we present a lateral-structured graphene tunneling diode with asymmetric geometry. The asymmetric geometry induces strong electric field enhancement leading electronic band bending. Therefore, the asymmetry of the graphene tunneling is improved as much as 2.5 times. The lateral device structure opens up possibilities to apply graphene tunneling diodes in future electronic circuits. [ABSTRACT FROM AUTHOR]

Traditional synthetic routes for transition metal sulfides typically involve solution and thermal-based processes to exploit their favorable pseudo-capacitive properties. However, there is a practical need to develop alternative processes to fabricate metal sulfide electrodes because of the time-consuming processes (＞12 h), additional heat-treatment to active reactants, relatively high post-heat-treatment temperature (200–400 °C) and non-scalable nature of existing synthetic routes. Herein, utilizing a solution-based sulfur precursor, one-dimensional single-crystalline Cu2S nanostructures have been successfully prepared via a solution-based direct synthesis process within 10 min at room temperature without the need for thermal treatment steps. The fabricated electrode exhibits a capacitance of 750 mF cm−2 at a current density of 2 mA cm−2. Moreover, the rate capacitance is maintained at about 82.3% as the current density is increased to 40 mA cm−2, and the capacity retains 90.5% of the initial value after 20 000 cycles. Importantly, as this method involves a solution-based formulation it is compatible with roll-to-roll processes, which is promising for mass and scalable production of the electrodes. The synthetic method ensures a facile and efficient approach to fabricating scalable one-dimensional single crystalline Cu2S nanostructures, highlighting the uniqueness of the solution-based sulfur activation method. [ABSTRACT FROM AUTHOR]

Chemical doping is one of the most effective methods to tune the electrochemical properties of graphene. We report a simple and relatively low-temperature process for the fabrication of boron doped graphene by using a spin-on dopant (SOD) method. SOD-treated graphene was successfully doped with boron atoms at a temperature lower than 600 °C. The fabricated boron doped graphene exhibits a specific capacitance of 4 mF cm−2, as well as a high-rate performance of 91.9% at 200 mV s−1 as an electrode material for pseudocapacitors. It also shows excellent oxygen reduction activity and durability with a current retention of 91.4% and methanol-tolerance properties. These features are beneficial for catalyst applications in the oxygen reduction reaction due to well-engineered boron sites with high electrical conductivity and many active sites for electrochemical reactions. [ABSTRACT FROM AUTHOR]

Functionalization of transition metal dichalcogenides has been studied with the aim of tuning their electrical and optical properties, but structural information during functionalization and its reversibility have not been elucidated. We report a simple and effective method for hydrogenation of monolayer MoSe2 using hydrogen plasma treatment. The covalent bonding of hydrogen to MoSe2 was confirmed by X-ray photoelectron spectroscopy, and the degree of hydrogenation was modulated from 32% to 80% by increasing the plasma treatment time from 5 to 40 s. Transmission electron microscopy confirmed a 1.5% reduction in the lattice constant of hydrogenated MoSe2 without structural damages or defects; crystal structures of hydrogenated MoSe2 and as-prepared MoSe2 were identical. Photoluminescence (PL) investigation of hydrogenated MoSe2 showed charge transfer from hydrogen to MoSe2. Furthermore, reversible desorption of hydrogen from hydrogenated MoSe2 was achieved by heat treatment. The optical and electrical properties of as-prepared and hydrogenated MoSe2 samples were compared. The PL peak of hydrogenated MoSe2 returned to the as-prepared one after heat treatment at 500 °C. Furthermore, the electron mobility of MoSe2 decreased from 29 to 9 cm2 V−1 s−1 after hydrogenation and was restored to 27 cm2 V−1 s−1 upon heat treatment at 500 °C. This reversible hydrogen adsorption and desorption lends control over the optical and electrical properties of monolayer MoSe2 and contributes to the hydrogen functionalization of monolayer transition metal dichalcogenides and other two-dimensional materials. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (h-BN) isgaining significant attentionas a two-dimensional dielectric material, along with graphene andother such materials. Herein, we demonstrate the growth of highlycrystalline, single-layer h-BN on Pt foil through a low-pressure chemicalvapor deposition method that allowed h-BN to be grown over a widearea (8 × 25 mm2). An electrochemical bubbling-basedmethod was used to transfer the grown h-BN layer from the Pt foilonto an arbitrary substrate. This allowed the Pt foil, which was notconsumed during the process, to be recycled repeatedly. The UV–visibleabsorption spectrum of the single-layer h-BN suggested an opticalband gap of 6.06 eV, while a high-resolution transmission electronmicroscopy image of the same showed the presence of distinct hexagonalarrays of B and N atoms, which were indicative of the highly crystallinenature and single-atom thickness of the h-BN layer. This method ofgrowing single-layer h-BN over large areas was also compatible withuse of a sapphire substrate. [ABSTRACT FROM AUTHOR]

To effectively improve the energy density and reduce the self-discharging rate of micro-supercapacitors, an advanced strategy is required. In this study, we developed a hydroquinone (HQ)-based polymer-gel electrolyte (HQ-gel) for micro-supercapacitors. The introduced HQ redox mediators (HQ-RMs) in the gel electrolyte composites underwent additional Faradaic redox reactions and synergistically increased the overall energy density of the micro-supercapacitors. Moreover, the HQ-RMs in the gel electrolyte weakened the self-discharging behavior by providing a strong binding attachment of charged ions on the porous graphitized carbon electrodes after the redox reactions. The micro-supercapacitors with HQ gel (HQ-MSCs) showed excellent energy storage performance, including a high energy volumetric capacitance of 255 mF cm−3 at a current of 1 µA, which is 2.7 times higher than the micro-supercapacitors based on bare-gel electrolyte composites without HQ-RMs (b-MSCs). The HQ-MSCs showed comparatively low self-discharging behavior with an open circuit potential drop of 37% compared to the b-MSCs with an open circuit potential drop of 60% after 2000 s. The assembled HQ-MSCs exhibited high mechanical flexibility over the applied external tensile and compressive strains. Additionally, the HQ-MSCs show the adequate circuit compatibility within series and parallel connections and the good cycling performance of capacitance retention of 95% after 3000 cycles. [ABSTRACT FROM AUTHOR]

The excellent physical and chemical properties of carbon nanomaterials render them suitable for application in gas sensors. However, the synthesis of carbon nanomaterials using high-temperature furnaces is time consuming and expensive. In this study, we synthesize a carbon nanomaterial using local laser-scribing on a substrate coated with a Cu-embedded polyimide (PI) thin film to reduce the processing time and cost. Spin coating using a Cu-embedded PI solution is performed to deposit a Cu-embedded PI thin film (Cu@PI) on a quartz substrate, followed by the application of a pulsed laser for carbonization. In contrast to a pristine PI solution-based PI thin film, the laser absorption of the Cu-embedded PI thin film based on Cu@PI improved. The laser-scribed carbon nanomaterial synthesized using Cu@PI exhibits a three-dimensional structure that facilitates gas molecule absorption, and when it is exposed to NO2 and NH3, its electrical resistance changes by −0.79% and +0.33%, respectively. [ABSTRACT FROM AUTHOR]

Carbon nanomaterials have attracted significant research attention as core materials in various industrial sectors owing to their excellent physicochemical properties. However, because the preparation of carbon materials is generally accompanied by high-temperature heat treatment, it has disadvantages in terms of cost and process. In this study, highly sensitive carbon nanomaterials were synthesized using a local laser scribing method from a copper-embedded polyacrylonitrile (CuPAN) composite film with a short processing time and low cost. The spin-coated CuPAN was converted into a carbonization precursor through stabilization and then patterned into a carbon nanomaterial of the desired shape using a pulsed laser. In particular, the stabilization process was essential in laser-induced carbonization, and the addition of copper promoted this effect as a catalyst. The synthesized material had a porous 3D structure that was easy to detect gas, and the resistance responses were detected as −2.41 and +0.97% by exposure to NO2 and NH3, respectively. In addition, the fabricated gas sensor consists of carbon materials and quartz with excellent thermal stability; therefore, it is expected to operate as a gas sensor even in extreme environments. [ABSTRACT FROM AUTHOR]

Hydrogen gas (H2) is being intensively proposed as a next-generation clean energy owing to the depletion of fossil fuels. Electrochemical water splitting is one of the most promising processes for hydrogen production. Furthermore, many efforts focusing on electrochemical water splitting have been made to develop low-cost, electrochemically active, and stable catalysts for efficient hydrogen production. MoS2 has emerged as an attractive material for developing catalysts for the hydrogen evolution reaction (HER). Hence, in this study, we design hierarchically ordinated two-dimensional (2D) MoS2 nanosheets on three-dimensional (3D) reduced graphene oxide (rGO) (H-2D/3D-MoS2-rGO) aerogel structures as a new class of electrocatalysts for the HER. We use the one-pot hydrothermal synthesis route for developing high-performance electroactive materials for the HER. The as-prepared H-2D/3D-MoS2-rGO contains a unique 3D hierarchical structure providing large surface areas owing to the 3D porous networks of rGO and more active sites owing to the many edge sites in the MoS2 nanosheets. In addition, the H-2D/3D-MoS2-rGO structure exhibits remarkable electrochemical properties during the HER. It shows a lower overpotential than pure MoS2 and excellent electrochemical stability owing to the large number of active sites (highly exposed edge sites) and high electrical conductivity from the rGO structure. [ABSTRACT FROM AUTHOR]