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Despite the remarkable thermal properties of graphene, the heat transport along the z-axis is intrinsically limited by the van der Waals interactions, leading to thermal anisotropy in multilayered graphene (or graphite) and its composites. Herein, we report a graphene foam (GF) with three-dimensional (3D) pore structure-based metal composites with excellent isotropic thermal conductivity and fast heat transfer performance. The 3D periodic structure of the GF–copper composites composed of high-quality multilayer graphene and copper was formed via a chemical vapor deposition (CVD) and a spark plasma sintering (SPS) process. The high-quality graphene layers in GF were well-bonded to copper, forming a clear interface without voids in the consolidated composites. Owing to the uniform 3D interconnection of graphene layer in the GF, in spite of less than 1 vol% carbon in the copper matrix, the GF–copper composites showed high isotropic thermal conductivity, which was higher by about 11 and 6% for in-plane and through-plane, respectively, than those of the bulk copper (∼400 W m−1 K−1). The superior performance of the 3D graphene-based metal–carbon composites offers remarkable opportunities in thermal management for advanced electronic and optoelectronic devices requiring high power density and efficiency.

With the increase in electrification, the demand for the functionality and features of electric vehicles (EVs) is increasing, and accordingly, the required weight of copper (Cu) is increasing. Additionally, Cu usage increase as the wiring/functions of autonomous vehicles (AVs) increase. Therefore, limited energy efficiency due to the high mass density of Cu electrical cables has become a challenging issue to be overcome. With this trend, carbon-metal core-shell wire is an attractive lightweight material. It remains a challenge to further improve the properties of previously reported carbon-metal core-shell wire. Here, we report CNTF-Cu-Gr wires obtained by introducing graphene into Cu electroplated on CNTFs. Electroplated Cu was coated with graphene via chemical vapor deposition, which also provided synergetic effects, enabling better thermal and electrical properties. These CNTF-Cu-Gr wires exhibit excellent overall performance in terms of mechanical, electrical, and thermal properties and are lightweight. We expect that these dual core-shell wires will be used in practical applications in the near future.

Two-dimensional transition metal dichalcogenide semiconductors are very promising candidates for future electronic applications with low power consumption due to a low leakage current and high on-off current ratio. In this study, we suggest a complementary circuit consisting of ambipolar WSe2 and n-MoS2 field-effect transistors (FETs), which demonstrate dual functions of a frequency doubler and single inversion AND (SAND) logic gate. In order to reduce the power consumption, a high-quality thin h-BN single crystal is used as a gate dielectric that leads to a low operating voltage of less than 5 V. By combining the low operating voltage with a low operating current in the complementary circuit, a low power consumption of 300 nW (a minimum of 10 pW) has been achieved, which is a significant improvement compared to the tens of μW consumed by a graphene channel. The complementary circuit shows the effective frequency doubling of the input with a dynamic range from 20 to 100 Hz. Furthermore, this circuit satisfies all the truth tables of a SAND logic gate that can be used as a universal logic gate like NAND. Considering that the NAND logic gate generally consists of four transistors, it is significantly advantageous to implement the equivalent circuit SAND logic gate with only two FETs. Our results open up possibilities for analog- and logic-circuit applications based on low-dimensional semiconductors.

Doping is an effective method for controlling the electrical properties and work function of graphene which can improve the power conversion efficiency of graphene-based Schottky junction solar cells (SJSCs). However, in previous approaches, the stability of chemical doping decreased over time due to the decomposition of dopants on the surface of graphene under ambient conditions. Here, we report an efficient and strong p-doping by simple sandwich doping on both the top and bottom surfaces of graphene. We confirmed that the work function of sandwich-doped graphene increased by 0.61 eV and its sheet resistance decreased by 305.8 Ω/sq, compared to those of the pristine graphene. Therefore, the graphene-silicon SJSCs that used sandwich-doped graphene had a power conversion efficiency of 10.02%, which was 334% higher than that (2.998%) of SJSCs that used pristine graphene. The sandwich-doped graphene-based silicon SJSCs had excellent long-term stability over 45 days without additional encapsulation.

We investigated the Young’s modulus and Poisson’s ratio of Green River oil shale at elevated temperatures under triaxial conditions using an X-ray computed tomography (CT) scanner for in situ imagi...

Transition metal dichalcogenides (TMDs) have attracted significant interest as one of the key materials in future electronics such as logic devices, optoelectrical devices, and wearable electronics. However, a complicated synthesis method and multistep processes for device fabrication pose major hurdles for their practical applications. Here, we introduce a direct and rapid method for layer-selective synthesis of MoS2 and WS2 structures in wafer-scale using a pulsed laser annealing system (λ = 1.06 μm, pulse duration ∼100 ps) in ambient conditions. The precursor layer of each TMD, which has at least 3 orders of magnitude higher absorption coefficient than those of neighboring layers, rigorously absorbed the incoming energy of the laser pulse and rapidly pyrolyzed in a few nanoseconds, enabling the generation of a MoS2 or WS2 layer without damaging the adjacent layers of SiO2 or polymer substrate. Through experimental and theoretical studies, we establish the underlying principles of selective synthesis and optimize the laser annealing conditions, such as laser wavelength, output power, and scribing speed, under ambient condition. As a result, individual homostructures of patterned MoS2 and WS2 layers were directly synthesized on a 4 in. wafer. Moreover, a consecutive synthesis of the second layer on top of the first synthesized layer realized a vertically stacked WS2/MoS2 heterojunction structure, which can be treated as a cornerstone of electronic devices. As a proof of concept, we demonstrated the behavior of a MoS2-based field-effect transistor, a skin-attachable motion sensor, and a MoS2/WS2-based heterojunction diode in this study. The ultrafast and selective synthesis of the TMDs suggests an approach to the large-area/mass production of functional heterostructure-based electronics.

Direct-patterned Cu-based conductive electrodes were printed through electrohydodynamic (EHD) jet printing via cone-jet mode. The introduction of a capping agent in the synthesis of the Cu ink limited excessive conductivity, which enabled the pristine Cu ink to achieve the various printing modes of EHD jet printing: dripping, micro-dripping, cone-jet, and multi-jet. We also obtained optimal printing conditions by adjusting the viscosity by adding poly(ethylene oxide) (PEO) to the pristine Cu inks, resulting in well-defined printing patterns. The optimized PEO content in the ink was determined to be ∼10 wt%, which gave us a stable cone-jet mode and well-defined Cu/PEO composite electrode lines with sharp edges. We utilized the Cu/PEO composite electrode lines as source and drain and a triisopropylsilylethynyl (TIPS)–pentacene/PS blend as the active layer for bottom-gate bottom-contact organic field-effect transistors (OFETs). The resulting devices exhibited an average field-effect mobility (μFET), threshold voltage (Vth), and on/off current ratio (Ion/Ioff) of 0.253 cm2/V, 0.253 V, and ∼106, respectively.

While perovskite solar cells (PSCs) have emerged as promising low-cost solar power generators, most reported high-performance PSCs employ electron transport layers (ETLs, mainly TiO2) treated at hi...

Until now, a specifically designed functional molecular species has been recognized as an absolute necessity for realizing the diode’s behavior in molecular electronic junctions. Here, we suggest a facile approach for the implementation of a tailored diode in a molecular junction based on non-functionalized alkyl and conjugated molecular monolayers. A two-dimensional semiconductor (MoS2 and WSe2) is used as a rectifying designer at the alkyl or conjugated molecule/Au interface. From the adjustment of band alignment at molecules/two-dimensional semiconductor interface that can activate different transport pathways depending on the voltage polarity, the rectifying characteristics can be implemented and controlled. The rectification ratio could be widely tuned from 1.24 to 1.83 × 104 by changing the molecular species and type and the number of layers of the two-dimensional semiconductors in the heterostructure molecular junction. Our work sets a design rule for implementing tailored-diode function in a molecular heterojunction structure with non-functionalized molecular systems., Molecular electronics holds promise for device miniaturization yet can only be realized by choosing specially designed molecular species to date. Here, Shin et al. show tunable rectifying characteristics in a molecular heterojunction with non-functionalized molecules and two-dimensional semiconductors.

Polarization-sensitive photodetection has attracted considerable attention as an emerging technology for future optoelectronic applications such as three-dimensional (3D) imaging, quantum optics, and encryption. However, traditional photodetectors based on Si or III-V InGaAs semiconductors cannot directly detect polarized light without additional optical components. Herein, we demonstrate a self-powered linear-polarization-sensitive near-infrared (NIR) photodetector using a two-dimensional WSe2/ReSe2 van der Waals heterostructure. The WSe2/ReSe2 heterojunction photodiode with semivertical geometry exhibits excellent performance: an ideality factor of 1.67, a broad spectral photoresponse of 405-980 nm with a significant photovoltaic effect, outstanding linearity with a linear dynamic range wider than 100 dB, and rapid photoswitching behavior with a cutoff frequency up to 100 kHz. Strongly polarized excitonic transitions around the band edge in ReSe2 lead to significant 980 nm NIR linear-polarization-dependent photocurrent. This linear polarization sensitivity remains stable even after exposure to air for longer than five months. Furthermore, by leveraging the NIR (980 nm)-selective linear polarization detection of this photodiode under photovoltaic operation, we demonstrate digital incoherent holographic 3D imaging. Accepted version

Photophysical and photochemical properties of graphene quantum dots (GQDs) strongly depend on their morphological and chemical features. However, systematic and uniform manipulation of the chemical structures of GQDs remains challenging due to the difficulty in simultaneous control of competitive reactions, i.e., growth and doping, and the complicated post-purification processes. Here, we report an efficient and scalable production of chemically tailored N-doped GQDs (NGs) with high uniformity and crystallinity via a simple one-step solvent catalytic reaction for the thermolytic self-assembly of molecular precursors. We find that the graphitization of N-containing precursors during the formation of NGs can be modulated by intermolecular interaction with solvent molecules, the mechanism of wh ich is evidenced by theoretical calculations and various spectroscopic analyses. Given with the excellent visible-light photoresponse and photocatalytic activity of NGs, it is expected that the proposed approach will promote the practical utilization of GQDs for various applications in the near future., Photophysical and photochemical features of graphene quantum dots (GQDs) strongly depend on their chemical nature that remains challenging to be controlled in a systematic and uniform manner. Here the authors report an efficient solvent-catalyst-aided growth of chemically tailored N-doped GQDs.

We developed a new and efficient sulfur-tolerant catalyst for application as a solid oxide electrolysis cell (SOEC) cathode designed with in situ exsolved CoNi alloy nanoparticles anchored on a Ruddlesden–Popper (R.P.) support of La1.2Sr0.8Co0.4Mn0.6O4 and evaluated its catalytic activity for CO2 electrolysis to CO under a CO2 gas stream containing H2S species. This catalyst was prepared by in situ annealing of a perovskite derivative (La0.6Sr0.4Co0.5Ni0.2Mn0.3O3) in a 20% H2/N2 gas at 800 °C. The catalyst exhibited good reversibility of structural transitions during reduction and re-oxidation processes. A high current density of 703 mA cm−2 was achieved at 1.3 V and 850 °C with a maximum faradaic efficiency of 97.8%. In situ grown CoNi alloy nanoparticles and the high oxygen vacancy content in the R.P. support were responsible for its high catalytic activity and efficiency. Importantly, no sign of performance degradation was observed in galvanostatic tests over a period of 90 h operation under H2S-containing CO2 gas conditions. Moreover, the catalyst showed no noticeable structural changes even after exposure to 100 ppm H2S/N2, indicating that the catalyst developed in this study is highly active for CO2 electrolysis with a high tolerance against sulfur-poisoning species. Therefore, this Ruddlesden–Popper material with in situ exsolved CoNi alloy nanoparticles should be a promising cathode catalyst for practical application to H2S-containing CO2 gas streams that are effluents of power stations or steel making plants.

With the significance of heat management, recently, high thermal conducting polymers have attracted attention as promising polymeric matrix materials in miniaturized and flexible devices. Porphyrin-based reactive metallomesogens (PorV-x; x = -2H, -Ni, -Cu, and -Zn) were newly designed and synthesized for the fabrication of thermal conducting polymers. Self-assembled and subsequently polymerized PorV-x films exhibited excellent mechanical, chemical, and thermal stability. The thermal conducting properties of PorV-x films can be adjusted as desired by controlling the molecular planarity through metal core substitution. From the results of systematic experiments, it was realized that a deep understanding of the correlation between the supramolecular packing structure and thermal properties is essential for the precise control of the heat dissipating performance in advanced heat managing materials.

Here, we studied the triboelectric properties of structurally controlled laser-induced graphene (LIG) to clarify the key factors for improving the energy harvesting performance. With a facile defocusing method, the LIG morphology was modulated in porous LIG, in short carbon fiber combined LIG (SF-LIG) and in long carbon fiber-dominant LIG (LF-LIG). Through correlation analysis of the triboelectrification characteristic according to the material properties of LIG, it was found that asymmetric defects as well as the graphitic-N configuration within the fibrous LIG structure can significantly improve the triboelectric effectiveness by supplying trap sites and lowering the work function, respectively. The vertically aligned fibrous structure also increases the structural contact area, contributing to the improvement in the charge transfer efficiency. As a result, it was demonstrated that the long carbon fiber structure of LF-LIG can improve the performance by 130 times (512 mW m−2) compared with porous LIG-based triboelectric nanogenerators (TENGs) (3.9 mW m−2). As a feasible application, all LIG-based flexible triboelectric touch sensors are fabricated, which are composed of LF-LIG active matrices (4 × 4) and LIG electrodes through a one-step laser writing process. The demonstrated touch sensor independently addressed each pixel for tracking the location of the human touch, showing self-powering capabilities. This work presents a facile strategy for surface morphology modification of LIGs and investigates their triboelectric charging effect, which might promote the development of practical flexible TENGs for wearable electronic devices.

Since its development, polyurethane foam (PUF) has been widely used as an insulator, including in the marine industry. Liquefied natural gas (LNG) carriers have the highest market share in the LNG-related shipbuilding industry. PUF is used as an insulator in membrane-type cargo containment systems (CCSs) as one of the most important components of LNG carriers. Because PUF is subjected to constant load and deformation when used in insulation for LNG CCSs and is exposed to the cryogenics of the seawater environment for extended times, it is essential to evaluate the mechanical behavior of PUF in such environments. In this study, to investigate the effects of applying an initial strain and of immersion in various media on the mechanical properties of PUF, compression tests were carried out at ambient and cryogenic temperature using a universal testing machine. The mechanical behavior of PUF after deformation recovery upon subjection to various initial strain levels was estimated experimentally. In addition, the microstructure of the PUF specimen prior to testing was analyzed to investigate the effects of the initial strain level and immersion in different media on the mechanical behavior of PUF.

Wearable technology offers new ways to be more proactive about our health and surroundings in real time. For next-generation wearable systems, robust storage and recording media are required to monitor and process the essential electrical signals generated under various unpredictable strain conditions. Here, we report the first fibriform organic transistor memory integrated on a thin and flexible metal wire. A capillary tube coating system allows the formation of a thin and nanograined organic ferroelectric film on the wire. The uniform morphology imparts excellent switching stability (∼100 cycles), quasi-permanent retention (over 5 × 104 s), and low-voltage operation (below 5 V) to the fiber-shaped memory devices. When sewn in a stretchable textile fabric, the memory fiber achieves long retention time of more than 104 s with negligible degradation of memory window even under a constant diagonal strain of 100% that exhibits reliable data storage under tough environments. These results illustrate the possibility of the practical, wearable fiber memory for recording electronic signals in smart garment applications.

The electro-mechanical reliability of the metal layer on flexible substrates under repetitive mechanical deformations should be guaranteed for real commercialization of flexible electronics. The mechanical and electrical properties of metal films are closely related to their microstructure, which can be changed by thermal annealing during the fabrication process. This study investigates the reliability of an annealed Cu film on flexible substrates using tensile and bending fatigue tests, comparing it with a non-annealed sample. For the tensile test, the annealed Cu film exhibits a superior stretchability due to microstructure change including large grains. For the fatigue test, however, the annealed sample reliability decreases due to the acceleration of fatigue damage formation induced by the repetitive bending deformation. This study can provide useful information for designing of highly reliable flexible electronics.

For the construction of well-defined hierarchical superstructures of pristine [60]fullerene (C60) arrays, pyrene-based molecular tweezers (PT) were used as host molecules for catching and arranging C60 guest molecules. The formation of host-guest complexes was systematically studied in solution as well as in the solid state. Two-dimensional proton nuclear magnetic resonance spectroscopic studies revealed that PT-host and C60-guest complexes were closely related to the molecular self-assembly of PT. Ultraviolet and fluorescence spectroscopic titrations indicated the formation of stable 1:1 and 2:1 (PT/C60) complexes. From the nonlinear curve-fitting analysis, equilibrium constants for the 1:1 (log K1) and 2:1 (log K2) complexes were estimated to be 4.96 and 5.01, respectively. X-ray diffraction results combined with transmission electron microscopy observations clearly exhibited the construction of well-defined layered superstructures of the PT-host and C60-guest complexes. From electron mobility measurements, it was demonstrated that the well-defined hierarchical hybrid nanostructure incorporating a C60 array exhibited a high electron mobility of 1.7 × 10-2 cm2 V-1 s-1. This study can provide a guideline for the hierarchical hybrid nanostructures of host-guest complex and its applications.

A simple, cost-effective, and one-step procedure for fabrication of gold-nanoparticle-transition metal oxide (Au-TMO) thin films with tuned optical and structural properties is described. In this approach, a homogeneous mixed precursor solution was used to fabricate Au-MoO3 and Au-WO3 thin films via a spray pyrolysis technique. The in-situ grown Au nanoparticles in the host matrices exhibited a characteristic surface plasmon resonance absorption in the visible-NIR region with peak positions at λmax ≈ 600 nm, ≈550 nm, and ≈575 nm for Au-MoO3, Au-a-WO3 (amorphous), and Au-h-WO3 (hexagonal) films, respectively. The structural and morphological characterization measurements confirmed that the high purity in-situ grown Au nanoparticles were 10–100 nm in size, and individual particles were embedded into the host matrices. These films were applied as plasmon-induced photoelectric conversion devices with ITO/NiOx/Au-WO3/Ag structures as a prototype device. The device exhibited a short-circuit current of 0.1 mA with an open-circuit voltage of ∼1.4 V under one-sun illumination. Our one-step fabrication approach is highly promising for fabricating other Au-TMOs thin films with tuned optical properties on a large area and can be applied for various optoelectronic applications.

Stretchable organic light-emitting diodes are ubiquitous in the rapidly developing wearable display technology. However, low efficiency and poor mechanical stability inhibit their commercial applications owing to the restrictions generated by strain. Here, we demonstrate the exceptional performance of a transparent (molybdenum-trioxide/gold/molybdenum-trioxide) electrode for buckled, twistable, and geometrically stretchable organic light-emitting diodes under 2-dimensional random area strain with invariant color coordinates. The devices are fabricated on a thin optical-adhesive/elastomer with a small mechanical bending strain and water-proofed by optical-adhesive encapsulation in a sandwiched structure. The heat dissipation mechanism of the thin optical-adhesive substrate, thin elastomer-based devices or silicon dioxide nanoparticles reduces triplet-triplet annihilation, providing consistent performance at high exciton density, compared with thick elastomer and a glass substrate. The performance is enhanced by the nanoparticles in the optical-adhesive for light out-coupling and improved heat dissipation. A high current efficiency of ~82.4 cd/A and an external quantum efficiency of ~22.3% are achieved with minimum efficiency roll-off., A transparent twistable and stretchable MoO3/Au/MoO3 electrode is demonstrated by Choi et al. for organic light-emitting diodes. The device fabricated on thin elastomer shows enhanced EQE with minimum efficiency roll-off owing to the improved charge injection and heat dissipation from the substrate.

Transition metal dichalcogenides (TMDs) possess great potential for use in gas sensing applications because, in contrast to conventional metal oxides, they have unique semiconducting properties with band gaps that can be tuned by adjusting thickness and composition. However, one issue is that their recovery time at room temperature is too long for them to be used practically in sustainable sensing applications. We found that incorporating Se atoms weaken interactions with gas molecules compared to when S atoms are used alone, therefore, the responsivity, as well as the recovery properties, of MoSxSe2-x sensors were significantly enhanced by increasing the ratio of Se to S. Herein, we demonstrate high-performance gas sensors that are based on reduced graphene oxide (rGO) fibers coated with MoSxSe2-x, the fabricated sensor could efficiently refresh its surface to allow fast, complete recovery at room temperature. Furthermore, it was shown that the porosity of rGO fibers with their large surface-to-volume ratio leads to enhanced sensing at room temperature.

Summary The critical gas saturation in permeable sands was studied as a function of depletion rate and the presence of an aqueous phase as the major experimental variables. Voidage-replacement ratios (VRR = injected volume/produced volume) less than 1 were used to obtain pressure depletion with active water injection. Three different live crude oils were considered. Two of the oils are viscous Alaskan crudes with dead-oil viscosities of 87.7 and 600 cp, whereas the third is a light crude oil with a dead-oil viscosity of 9.1 cp. The critical gas saturation for all tests ranged from 4 to 16%. These values for critical gas saturation are consistent with the finding that the gas phase displayed characteristics similar to those of a foamy oil. For a given oil and depletion rate, the critical gas saturation was somewhat larger for VRR = 0 than it was for VRR = 0.7. The oil recovery correlates with the critical gas saturation (i.e., for a given VRR, tests exhibit greater oil recovery when the critical gas saturation is elevated). For the conditions tested, there was not a strong correlation of critical gas saturation over more than two orders of magnitude of the rate of pressure depletion, for a given VRR. Such behavior might be consistent with theoretical studies reported elsewhere that suggest that the critical gas saturation is independent of the pressure-depletion rate when the rate of depletion is small.

Since its discovery, the existence of graphene, a 2D extract of graphite, has been in the spotlight in the field of optoelectrical physics. Suspended graphene is potentially an ideal structure for utilizing intrinsic properties of the graphene by reducing the hindrance due to interaction with substrate. Here, an autonomous fabrication of suspended graphene is proposed where it only requires a single transfer which yields multiple arrays of micron-scale suspended graphenes all at once. Large area graphene sheets transferred onto a substrate of array-patterned 3D-electrodes easily tear into pieces due to the strain gradients induced by the step heights of the electrode patterns, and each torn graphene piece takes its position between individual electroplated Cu-microgap electrode pairs. With the absence of long-range scattering from randomly charged impurities in the substrate and the correspondingly enhanced carrier mobility of suspended graphene, our novel structure is demonstrated for the application of a visible light-emitting device. It is observed that the electrically driven thermal emission spectra spans the blue side of the visible band, which corresponds to a temperature of above 3000 K. The facile access to mass production of suspended graphene can bridge the current 2D materials research to the wide field of electronics and optoelectronics.

Amorphous KNbO3 (KN) films were grown on a TiN/SiO2/Si substrate to synthesize a KN memristor as a potential artificial synapse. The Pt/KN/TiN memristor exhibited typical and reliable bipolar switching behavior with multiple resistance levels. It also showed the transmission properties of a biological synapse, with a good conductance modulation linearity. Moreover, the KN memristor can emulate various biological synaptic plasticity characteristics including short-term plasticity, long-term plasticity, spike-rate dependent plasticity, paired-pulse facilitation, and post-tetanic potentiation by controlling the number and rate of the potentiation spike. Spike-timing-dependent plasticity (STDP), which is an essential property of biological synapses, is also realized in the KN memristor. The synaptic plasticity of the KN memristor can be explained by oxygen vacancy movement and oxygen vacancy filaments. The metaplasticity of biological synapses was also implemented in the KN memristor, including the metaplasti...

The present study investigated thermal and mechanical characteristics of irradiated polyurethane foams (PUFs) according to the irradiation does under various temperature conditions, including low/cryogenic temperatures. Fourier transform infrared analysis was performed to obtain information on the PUF molecular structure. In addition, Macro- and microstructural investigations were carried out to determine the relationship between thermal and mechanical characteristics and irradiation dose. The test results were quantitatively presented, and it was found that the irradiated PUF has potential for application in industrial structures.

In this study, we developed reduced graphene oxide (rGO)-incorporated porous agarose (Ar-rGO) composites that were prepared via a "one-pot" sol-gel method involving a mixing and vacuum freeze-drying process. These composites represent an easy-to-use adsorbent for organic contaminant removal. Ar-rGOs can efficiently adsorb organic molecules, especially aromatic organic compounds from wastewater, because of the synergistic effect between the agarose bundles, which function as a water absorption site, and the rGO sheets, which function as active sites for pollutant binding. The pore structures and morphology of the Ar-rGO composites varied according to the added rGO, resulting in effective water infiltration into the composites. The main adsorption mechanism of the aromatic organic compounds onto Ar-rGOs involved π-π interactions with the rGO sheets. The surface interaction was more effective for adsorbing/desorbing the aromatic pollutants than the electrostatic interaction via the O-containing functional groups. In addition, we confirmed that Ar-rGO is highly stable over the entire pH range (1-13) because of the presence of the rGO sheets.

Herein, we achieved, air-stable low-temperature processed PSC (L-PSC) using alkali-metal modified ZnO ETLs. Using a simple chemical alkali-metal modification method, the surface defects of the ZnO were effectively passivated. As a result, the interfacial decomposition reactions were suppressed, while raising the Fermi energy level and enhancing electron mobility. The improved interfacial charge transfer and internal electric field in the developed L-PSC using K modified ZnO (ZnO-K) exhibited an improved power conversion efficiency (PCE) of 19.90% with negligible hysteresis, while a pristine ZnO based L-PSC exhibited a PCE of 16.10% with significant hysteresis. The ZnO-K based L-PSC also exhibited remarkably higher long-term air-storage stability (91% retention after 800 h) than pristine ZnO based L-PSCs (36% retention after 800 h) due to the suppressed decomposition reactions. The PCE and air stability of our L-PSC with the modified ZnO are among the highest reported for PSCs processed at ≤150 °C.

With the growth of nanoelectronics, the importance of thermal management in device packaging and the improvement of high-current-carrying interconnects/wires for avoiding the premature failure of devices have been emphasized. The heat and electrical transport properties of the bulk may not be valid in the characterization of a material at the nanometer level, because the phenomena that occur at the interfaces and grain boundaries become dominant. The failure mechanism of bulk metal interconnects has been understood in the context of electromigration; however, in nanoscale materials, the effect of the heat dissipation that occurs at the nanointerfaces may play an important role. Here, we report the preparation of continuous carbon nanotube (CNT)–Cu composite fibers that possess Cu nanofibrillar structures with a high current-carrying capacity. Various-shaped CNT–Cu microfibers with different Cu grain morphologies were produced via Cu electroplating on continuous CNT fibers. Cu fibril structures were embedded in the voids inside the CNT fiber during the early stage of electrodeposition. The temperature-dependent and magnetic field-dependent electrical properties and the ampacity of the produced CNT–Cu microfibers were measured, and the failure mechanism of the fiber was discussed. The interconnection of Cu nanograins on the surface of the individual CNTs contributed to the enhancement in the charge-carrying ability of the fiber. The effective ampacity of the Cu nanofibrils was estimated to be ~1 × 107 A/cm2, which is approximately 50 times larger than the ampacity measured for a bulk Cu microwire. Nanoscale metal fibrils increase the maximum current a spun carbon nanotube fiber can carry before failing, researchers in South Korea demonstrate. Ensuring that components don’t overheat is a crucial consideration when designing electronic devices. High electrical currents can heat and thus damage the wires, or interconnects, that link different parts of the circuit. This is particularly important in nanoelectronics, where the interconnects are narrow. Sang Hyun Lee from the Korea Institute of Science and Technology, Jeonbuk, and colleagues addressed this problem by embedding copper fibrils within continuous carbon nanotube fiber. They compared various fibril shapes to systematically study the electrical and thermal properties at the interface between the copper and the carbon nanotube. The maximum current their composite fibers could tolerate before damage occurred was fifty times higher than for conventional copper microwires. The copper nanofibrils are formed at the void inside the long continuous carbon nanotube (CNT) fiber by electroplating. Electrical conduction through the composite fiber was dominated by the nanofibrils even though their cross-sectional area is much smaller than that of CNTs. The nanofibrils could carry a very high current density due to their bamboo-like structure and the thermal dissipation through CNTs.

This paper reports the variation in the optical and geometrical properties of individual organic layers to be used for thermally damaged top-emission organic light-emitting diodes (TEOLEDs). The copper deposited on the back of TEOLEDs is employed as a thermal facilitator, and a certain thermal damage occurs to the organic layers and devices. The phosphorescent host material 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) is rapidly damaged to a significant extent owing to the low glass transition temperature (Tg), which also changes its optical and geometrical surface properties. Although the optical properties of the hole transport layer, N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) were changed slightly, the surface morphology was changed significantly. Despite having a higher Tg, the exciton blocking layer, tris(4-carbazoyl-9-ylphenyl)amine (TCTA), shows notable variations in optical properties and surface morphology due to heat exposure. Surprisingly, the electroluminescence spectra and micro-cavity are affected by increasing temperature without any considerable changes in device performance. Hence, this study reveals that besides Tg, the surface morphologies and thicknesses of the organic layers are also important factors in the annealing process and play a vital role in causing thermal damage to TEOLEDs.

A bi-layer interconnect with La0.8Sr0.2MnO3 and La0.4Sr0.6Ti0.6Mn0.4O3 (LSM/LSTM) is applied to anode-supported button cells and flat-tubular cells. Using a button cell, SEM images and gas permeation tests confirm that the bi-layer possesses a dense microstructure. The area specific resistance (ASR) of the LSM/LSTM remains nearly constant under oxidizing/reducing atmospheres with varying gas concentrations. For comparison, an LSM/LST with the same thickness is prepared; an increase in the ASR is observed as the concentration of H2 feed to the LST side decreases. The difference in the ASR of LSM/LST can be explained by exposure to a relatively high oxygen partial pressure and partial destruction of the interfacial LST layer region where oxygen diffuses from the LSM layer. Flat-tubular cells with the LSM/LSTM bi-layer interconnect achieve a maximum power density (MPD) of 463 mW cm−2 using humidified H2 fuel and air at 800 °C. With decreasing H2 concentration in the fuel, the polarization resistance increases rather than the ohmic resistance, implying that the LSM/LSTM interconnect provides stable conduction property. In comparison with the conventional LSM/LST interconnect cell, it shows improved stability and performance as the concentration of H2 in the fuel decreases.

The thermal-conducting support is highly desirable for endothermic and exothermic reactions as long as highly dispersed active sites can be maintained. The core-shell Al@Al2O3 supports with different aluminum (Al) contents were prepared from Al particle by controlling the reaction time during hydrothermal surface oxidation and applied as a support to the supported Ru catalysts for preferential CO oxidation in H2 (PROX). The prepared catalysts were characterized by N2-physisorption, X-ray diffraction, CO chemisorption, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), in situ diffuse reflectance infrared Fourier transform spectroscopy after CO adsorption (CO-DRIFTS), and temperature-programmed desorption of ammonia (NH3-TPD) and ethanol (ethanol-TPD). The catalytic activity was dependent on the Al content in the Al@Al2O3 support. The most active Ru/Al@γ-Al2O3 catalyst oxidized CO selectively in H2 over a wide reaction temperature. The surface property of the outermost exterior alumina layer in the Al@γ-Al2O3 support, determined with ethanol TPD, was beneficial for formation of Ru nanoparticles with weak adsorption of CO, probed with CO-DRIFTS, results in the high catalytic performance for PROX.

The further development of unconventional resources is anticipated to increase the intensity of hydraulic fracturing operations. Injecting water-based fracturing fluids into shale formations, especially shales producing gas, may have adverse impacts of water blocking, scale formation, and water-sensitive clay minerals. Accordingly, nonaqueous candidates such as carbon dioxide ( CO 2 ) need to be explored to avoid injection of millions of gallons of water and to increase the effectiveness of stimulation jobs. This study investigates fracturing behavior accompanying supercritical carbon dioxide (sc- CO 2 ) injection compared to water. A High Pressure High Temperature (HPHT) triaxial cell was utilized to conduct shale breakdown experiments under reservoir-like conditions. Furthermore, the experimental setup allows continuous monitoring of in situ details using X-ray Computed Tomography (CT). Here, CT images were utilized for the first time to investigate and confirm the breakdown pressure using Fast Iterative Digital Volume Correlation (FIDVC) that permits visualization of in situ deformation and strain. One inch diameter Green River shale samples were fractured under triaxial stress conditions. Results demonstrated a roughly 2 to 3 times greater breakdown pressure for sc- CO 2 compared to water for the samples studied. Compressive infiltration stress might explain such behavior, and mineralogy is believed to be a major contributor to such differences between injectants. Under isotropic horizontal stresses, sc- CO 2 induces fractures propagating almost independent of bedding planes. This is a promising finding for probable larger stimulated volume achieved by sc- CO 2 . CT imaging to monitor fracture propagation demonstrated excellent performance in detecting fracture propagation. We anticipate this technique to help significantly when monitoring fracture propagation mechanisms for laboratory samples with slow pressurization as well as studies of slip on pre-existing fractures.

The controllability of switching conductive filaments is one of the central issues in the development of reliable metal-oxide resistive memory because the random dynamic nature and formation of the filaments pose an obstacle to desirable switching performance. Here, we introduce a simple and novel approach to control and form a single silicon nanocrystal (Si-NC) filament for use in SiOx memory devices. The filament is formed with a confined vertical nanoscale gap by using a well-defined single vertical truncated conical nanopore (StcNP) structure. The physical dimensions of the Si-NC filaments such as number, size, and length, which have a significant influence on the switching properties, can be simply engineered by the breakdown of an Au wire through different StcNP structures. In particular, we demonstrate that the designed SiOx memory junction with a StcNP of pore depth of ∼75 nm and a bottom diameter of ∼10 nm exhibited a switching speed of up to 6 ns for both set and reset process, significantly fas...

The effect of alumina crystalline phases on CO and CO2 methanation was investigated using alumina-supported Ni catalysts. Various crystalline phases, such as α-Al2O3, θ-Al2O3, δ-Al2O3, η-Al2O3, γ-Al2O3, and κ-Al2O3, were utilized to prepare alumina-supported Ni catalysts via wet impregnation. N2 physisorption, H2 chemisorption, temperature-programmed reduction with H2, CO2 chemisorption, temperature-programmed desorption of CO2, and X-ray diffraction were employed to characterize the catalysts. The Ni/θ-Al2O3 catalyst showed the highest activity during both CO and CO2 methanation at low temperatures. CO methanation catalytic activity appeared to be related to the number of Ni surface-active sites, as determined by H2-chemisorption. During CO2 methanation, Ni dispersion and the CO2 adsorption site were found to influence catalytic activity. Selective CO methanation in the presence of excess CO2 was performed over Ni/γ-Al2O3 and Ni/δ-Al2O3; these substrates proved more active for CO methanation than for CO2 methanation.

An efficient oxidation catalyst was developed to increase the combustion efficiency of unreacted CO, H2, and CH4 in flue gas of solid oxide fuel cell (SOFC) stack. Amorphous Cu-Mn oxide catalyst (CuMnLa/Alumina) showed high catalytic activity, but significant degradation occurred due to phase transition to spinel structure at high temperatures (T > 650°C). La0.8Sr0.2Mn0.67Cu0.33O3 perovskite (LSMC(p)) supported CuO or Mn2O3 exhibited improved thermal stability than CuMnLa/Alumina catalyst. Especially in case of 50Mn/LSMC(p), after the catalyst was exposed to 800°C for 24 h, T50 of CO, H2 and CH4 was achieved at 170, 230 and 600°C, respectively. This result is much lower than that of CuMnLa/Alumina, which was exposed to the same condition. The high combustion efficiency is due to retention of the Cu2+-Mn3+ redox couple, and supply of lattice oxygen from LSMC(p), especially at high temperature. This article is protected by copyright. All rights reserved.

We studied a polycrystalline p-type WSe2 semiconductor for thermoelectric applications. The polycrystalline WSe2 nanocompound was prepared via a thermal reaction process of tungsten and selenium elements and it was sintered to produce a bulk structure using spark plasma sintering equipment. The resulting bulk specimen showed different morphological aspects, in which we observed irregularly-shaped grains along the direction perpendicular to the sintering pressing direction (i.e., along transversal direction) while finding thin layers along the parallel direction (i.e., along longitudinal direction). The specimen recorded a significantly low longitudinal thermal conductivity possibly because longitudinal phonon transport should be hindered due to the thin layers. Electron transport along the longitudinal direction might not be greatly interrupted by the morphological characteristics because the specimen recorded high carrier mobility along the direction resulting in lower electrical resistivity than that of a single crystalline equivalent. The specimen also showed moderate carrier concentration, which led to a plausible Seebeck coefficient. Since the specimen exhibited the significantly low thermal conductivity with the electrical properties, it recorded a higher figure of merit than the equivalent, which is the highest thermoelectric performance for p-type WSe2 in bulk phase ever developed.

A memristor architecture based on metal-oxide materials would have great promise in achieving exceptional energy efficiency and higher scalability in next-generation electronic memory systems. Here, we propose a facile method for fabricating selector-less memristor arrays using an engineered nanoporous Ta2O5–x architecture. The device was fabricated in the form of crossbar arrays, and it functions as a switchable rectifier with a self-embedded nonlinear switching behavior and ultralow power consumption (∼2.7 × 10–6 W), which results in effective suppression of crosstalk interference. In addition, we determined that the essential switching elements, such as the programming power, the sneak current, the nonlinearity value, and the device-to-device uniformity, could be enhanced by in-depth structural engineering of the pores in the Ta2O5–x layer. Our results, on the basis of the structural engineering of metal-oxide materials, could provide an attractive approach for fabricating simple and cost-efficient mem...

CO and CO2 methanation was investigated over Ni catalysts supported on different supports such as γ-Al2O3, SiO2, TiO2, CeO2, and ZrO2. Among them, Ni/CeO2 was determined to be the most active for CO and CO2 methanation. These catalytic activities increased with increasing surface area of CeO2. To increase the specific catalytic activity for CO and CO2 methanation, various Ni-CeO2 catalysts with different Ni contents were prepared using co-precipitation method. The optimum Ni content was determined for both reactions. The prepared catalysts were characterized with inductively coupled plasma-atomic emission spectroscopy, N2 physisorption, temperature-programmed reduction, temperature-programmed desorption, and X-ray diffraction. The high Ni dispersion and strong CO2 adsorption appeared to be responsible for the high catalytic activity for CO and CO2 methanation. This Ni-CeO2 can be applied to the low-temperature CO and CO2 methanation reactor to achieve high single-pass conversions of CO and CO2.

Copper is widely used because it is inexpensive, abundant, and highly conductive. However, most copper used in industrial coating processes is in the form of circular powder, which is problematic for large area, high conductive coatings. In this work, 2D single-crystalline Cu nanoplates (Cu NPLs) were synthesized and a systematic study on coating with large-scale Cu NPLs using a Meyer-rod coating process was performed. The rheological behaviors of the Cu solution with various concentrations, surface tensions, and speeds were analyzed using Ca and Re numbers to optimize coating conditions. In addition, the effect of intensive pulse light (IPL) to sinter the coper film within a 1 s timeframe was also investigated in order to be able to produce an electrode in the shortest possible time which is applicable to industry. Finally, the Meyer-rod coated electrode was utilized in an electrochemical luminescence (ECL) device.

As the technology of flexible electronics has remarkably advanced, the long-term reliability of flexible devices has attracted much attention, as it is an important factor for such devices in reaching real commercial viability. To guarantee the bending fatigue lifetime, the exact evaluation of bending strain and the change in electrical resistance is required. In this study, we investigated the bending strains of Cu thin films on flexible polyimide substrates with different thicknesses using monolayer and bilayer bending models and monitored the electrical resistance of the metal electrode during a bending fatigue test. For a thin metal electrode, the bending strain and fatigue lifetime were similar regardless of substrate thickness, but for a thick metal film, the fatigue lifetime was changed by different bending strains in the metal electrode according to substrate thickness. To obtain the exact bending strain distribution, we conducted a finite-element simulation and compared the bending strains of thin and thick metal structures. For thick metal electrodes, the real bending strain obtained from a bilayer model or simulation showed values much different from those from a simple monolayer model. This study can provide useful guidelines for developing highly reliable flexible electronics.

Organic electronics demand new platforms that can make integrated circuits and undergo mass production while maintaining diverse functions with high performance. The field-effect transistor has great potential to be a multifunctional device capable of sensing, data processing, data storage, and display. Currently, transistor-based devices cannot be considered intrinsic multifunctional devices because all installed functions are mutually coupled. Such incompatibilities are a crucial barrier to developing an all-in-one multifunctional device capable of driving each function individually. In this study, we focus on the decoupling of electric switching and data storage functions in an organic ferroelectric memory transistor. To overcome the incompatibility of each function, the high permittivity needed for electrical switching and the ferroelectricity needed for data storage become compatible by restricting the motion of poly(vinylidene fluoride-trifluoroethylene) via photocrosslinking with bis-perfluorobenzoazide. The two-in-one device consisting of a photocrosslinked ferroelectric layer exhibits reversible and individual dual-functional operation as a typical transistor with nonvolatile memory. Moreover, a p-MOS depletion load inverter composed of the two transistors with different threshold voltages is also demonstrated by simply changing only one of the threshold voltages by polarization switching. We believe that the two-in-one device will be considered a potential component of integrated organic logic circuits, including memory, in the future.

An all-organic composite system was introduced as an active component for organic resistive memory applications. The active layer was prepared by mixing a highly polar plastic-crystalline organic molecule (succinonitrile, SN) into an insulating polymer (poly(methyl methacrylate), PMMA). As increasing concentrations of SN from 0 to 3.0 wt % were added to solutions of different concentrations of PMMA, we observed distinguishable microscopic surface structures on blended films of SN and PMMA at certain concentrations after the spin-casting process. The structures were organic dormant volcanos composed of micron-scale PMMA craters and disk type SN lava. Atomic force microscopy (AFM), cross-sectional transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray spectrometer (EDX) analysis showed that these structures were located in the middle of the film. Self-assembly of the plastic-crystalline molecules resulted in the phase separation of the SN:PMMA mixture during solvent evaporation. The organic craters remained at the surface after the spin-casting process, indicative of the formation of an all-organic composite film. Because one organic crater contains one SN disk, our system has a coplanar monolayer disk composite system, indicative of the simplest composite type of organic memory system. Current-voltage (I-V) characteristics of the composite films with organic craters revealed that our all-organic composite system showed unipolar type resistive switching behavior. From logarithmic I-V characteristics, we found that the current flow was governed by space charge limited current (SCLC). From these results, we believe that a plastic-crystalline molecule-polymer composite system is one of the most reliable ways to develop organic composite systems as potential candidates for the active components of organic resistive memory applications.

In this report, we demonstrate that moisture/O2 in ambient air is the major issue for the photovoltaic performance degradation and severe photocurrent hysteresis of non-encapsulated planar-perovskite solar cells. Consequently, this leads to difficulty in determining the real power conversion efficiency (PCE). Upon longer storage time, the evidence of a small amount of iodine in the hole transport layer (HTL) led to hindering the charge transport from the HTL to the anode, thus resulting in the decrease of short-circuit current density and fill factor. Meanwhile, the transient chronoamperometry result suggests that the increase of hysteresis with storage time is ascribed to the changes of activation energy. It is further supported by X-ray photoelectron spectroscopy depth profile analysis, which revealed that penetration of moisture/O2 caused the shifts of iodine distribution within the perovskite layer after aging time of >72 h. Remarkably, effective moisture/O2 passivation can be achieved by combination of polyimide and UV-cured polymer as a novel encapsulation process, which exhibited an impressive stabilized PCE of above 14% (retained 97% of its initial efficiency) and simultaneously maintained the hysteresis up to ∼1000 h.

We demonstrate the possibility of irradiating sol–gel ZnO with an electron beam (EB-ZnO) to modify sol–gel ZnO, and EB-ZnO is explored as a cathode interfacial layer for inverted polymer solar cells. We investigate the effect of EB-ZnO on the surface, optical and electric properties of sol–gel ZnO films through morphology, chemical composition, optical band gap shift, various defect excitations (photoluminescence) and work function measurement. Oxygen vacancies and the formation of nitrogen on the surface of EB-ZnO films contribute to the formation of n-type degenerated EB-ZnO films. The electric properties of EB-ZnO strongly depend on the adsorbed dose, and EB-ZnO with a suitable dose of 100 kGy improved the power conversion efficiency of inverted polymer solar cells based on PTB7-Th: PC71BM from 8.05% for non-treated sol–gel ZnO to 9.36% for EB-ZnO with an enhanced fill factor.

A new monolithic solid oxide fuel cell (SOFC) design stacked with flatten tubes of unit cells without using metallic interconnector plate is introduced and evaluated in this study. The anode support is manufactured in a flat tubular shape with fuel channel inside and air gas channel on the cathode surface. This design allows all-ceramic stack to provide flow channels and electrical connection between unit cells without needing metal plates. This structure not only greatly reduces the production cost of SOFC stack, but also fundamentally avoids chromium poisoning originated from a metal plate, thereby improving stack stability. The fuel channel was created in the extrusion process by using the outlet shape of mold. The air channel was created by grinding the surface of pre-sintered support. The anode functional layer and electrolyte were dip-coated on the support. The cathode layer and ceramic interconnector were then spray coated. The maximum power density and total resistance of unit cell with an active area of 30 cm2 at 800 °C were 498 mW/cm2 and 0.67 Ωcm2, respectively. A 5-cell stack was assembled with ceramic components only without metal plates. Its maximum power output at 750 °C was 46 W with degradation rate of 0.69%/kh during severe operation condition for more than 1000 h, proving that such all-ceramic stack is a strong candidate as novel SOFC stack design.

A highly stable electrode material of Ruddlesden–Popper structure, La1.2Sr0.8Mn0.4Fe0.6O4 (RPLSMF), is prepared from La0.6Sr0.4Mn0.2Fe0.8O3 (LSMF) perovskite by in situ annealing in flowing H2 at the operation temperature of solid oxide fuel cells. The crystallinity, morphology, and oxidation states of each element and electrochemical properties of RPLSMF are characterized. Doping Mn into the B-site of RPLSMF improves the phase stability of the structure in H2 to prevent formation of La2O3. The XPS results also suggest that improved phase stability promotes formation of Fe2+/3+ pairs that facilitate fuel oxidation by redox coupling. Additionally, during phase transition to RPLSMF, metallic Fe nanoparticles form, which enlarge H2 chemisorption and oxidation sites. Consequently, RPLSMF exhibits outstanding and stable electrochemical activity with a maximum power density of 0.72 W cm−2 at 1073 K when used as an anode material in LSGM electrolyte-supported cells. As the phase transition between the RPLSMF and LSMF is reversible under a redox environment, RPLSMF/GDC is applied as an electrode in the symmetrical cell of RPLSMF-GDC/LSGM/LSMF-GDC. It exhibits a substantial power density of 0.64 W cm−2 with a total polarization resistance of 0.51 Ω cm2.

Recently, research on micro-electronic and optoelectronic devices has been rapidly increasing. Parts and products related to these devices are becoming smaller and more integrated within circuits. As a result, the heat generated in devices has increased greatly. When excess heat is generated, important properties are affected such as efficiency and lifetime and, in severe cases, this can result in the failure of devices. Therefore, efficient cooling is required and it becomes necessary to study the heat dissipation properties of device materials. Research on heat-dissipating materials with high thermal conductivities and large surface areas, and which can transfer heat rapidly to facilitate progressive heat-release, is being actively pursued. In this study, a porous copper with reduced graphene oxide (pCu-rGO) heterostructure was fabricated by thermal annealing using Cu powder and GO. The thermal properties were then investigated and the results indicated that the pCu-rGO heterostructure exhibits a higher thermal conductivity than porous Cu. In addition, the thermal resistance of the sample was measured by applying it as a heat sink of a light emitting diode (LED). The result was 18.33% lower than that of bulk Cu. Also, when an overcurrent of 750 mA was applied for 144 hours, the luminance of bulk Cu decreased from 100% to 86.07%. On the other hand, the pCu-rGO showed that the luminance was maintained at 95.64%. Therefore, it is expected to resolve the existing problem of heat generation in electronic and optical devices.