Exploring the Capability of Cu-MoS2 Catalysts for Use in Electrocatalytic Overall Water Splitting.

Herein, we prepare MoS2 and Cu-MoS2 catalysts using the solvothermal method, a widely accepted technique for electrocatalytic overall water-splitting applications. TEM and SEM images, standard tools in materials science, provide a clear view of the morphology of Cu-MoS2. HRTEM analysis, a high-resolution imaging technique, confirms the lattice spacing, lattice plane, and crystal structure of Cu-MoS2. HAADF and corresponding color mapping and advanced imaging techniques reveal the existence of the Cu-doping, Mo, and S elements in Cu-MoS2. Notably, Cu plays a crucial role in improving the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) of the Cu-MoS2 catalyst as compared with the MoS2 catalyst. In addition, the Cu-MoS2 catalyst demonstrates significantly lower overpotential (167.7 mV and 290 mV) and Tafel slopes (121.5 mV dec-1 and 101.5 mV dec-1), standing at -10 mA cm-2 and 10 mA cm-2 for HER and OER, respectively, compared to the MoS2 catalyst. Additionally, the Cu-MoS2 catalyst displays outstanding stability for 12 h at -10 mA cm-2 of HER and 12 h at 10 mA cm-2 of OER using chronopotentiaometry. Interestingly, the Cu-MoS2‖Cu-MoS2 cell displays a lower cell potential of 1.69 V compared with the MoS2‖MoS2 cell of 1.81 V during overall water splitting. Moreover, the Cu-MoS2‖Cu-MoS2 cell shows excellent stability when using chronopotentiaometry for 18 h at 10 mA cm-2.

One-Pot Facile Synthesis of a Cluster of ZnS Low-Dimensional Nanoparticles for High-Performance Supercapacitor Electrodes.

To maximize the use of ZnS low-dimensional nanoparticles as high-performance supercapacitor electrodes, this work describes a simple one-pot synthesis method for producing a cluster of these particles. The ZnS nanoparticles fabricated in this work exhibit a cluster with unique low-dimensional (0D, 1D, and 2D) characteristics. Structural, morphological, and electrochemical investigations are all part of the thorough characterization of the produced materials. An X-ray diffraction pattern of clustered ZnS nanoparticles reflects the phase formation with highly stable cubic blende sphalerite polymorph. The confirmation of nanoparticle cluster formation featuring multiple low-dimensional nanostructures was achieved through field emission scanning electron microscopy (FE-SEM), while the internal structure was assessed using transmission electron microscopy (TEM). Systematically assessing the ZnS nanoparticles' electrochemical performance reveals their prospective qualities as supercapacitor electrode materials. The electrode assembled with this material on Ni foam demonstrates elevated specific capacitance (areal capacitance) values, reaching 716.8 F.g⁻1 (2150.4 mF.cm-2) at a current density of 3 mA.cm⁻2. Moreover, it reflects 69.1% capacitance retention with a four times increase in current density, i.e., 495.5 F.g-1 (1486.56 mF.cm-2) capacitance was archived at 12 mA.cm-2 with 100% Coulombic efficiency. Furthermore, the electrode exhibits prolonged cycling capability with 77.7% capacitance retention, as evidenced by its charge-discharge measurements sustained over 15,000 cycles at a current density of 25 mA cm⁻2.

Unraveling the importance of fabrication parameters of copper oxide-based resistive switching memory devices by machine learning techniques.

In the present study, various statistical and machine learning (ML) techniques were used to understand how device fabrication parameters affect the performance of copper oxide-based resistive switching (RS) devices. In the present case, the data was collected from copper oxide RS devices-based research articles, published between 2008 to 2022. Initially, different patterns present in the data were analyzed by statistical techniques. Then, the classification and regression tree algorithm (CART) and decision tree (DT) ML algorithms were implemented to get the device fabrication guidelines for the continuous and categorical features of copper oxide-based RS devices, respectively. In the next step, the random forest algorithm was found to be suitable for the prediction of continuous-type features as compared to a linear model and artificial neural network (ANN). Moreover, the DT algorithm predicts the performance of categorical-type features very well. The feature importance score was calculated for each continuous and categorical feature by the gradient boosting (GB) algorithm. Finally, the suggested ML guidelines were employed to fabricate the copper oxide-based RS device and demonstrated its non-volatile memory properties. The results of ML algorithms and experimental devices are in good agreement with each other, suggesting the importance of ML techniques for understanding and optimizing memory devices.

Effect of Measurement System Configuration and Operating Conditions on 2D Material-Based Gas Sensor Sensitivity.

Gas sensors applied in real-time detection of toxic gas leakage, air pollution, and respiration patterns require a reliable test platform to evaluate their characteristics, such as sensitivity and detection limits. However, securing reliable characteristics of a gas sensor is difficult, owing to the structural difference between the gas sensor measurement platform and the difference in measurement methods. This study investigates the effect of measurement conditions and system configurations on the sensitivity of two-dimensional (2D) material-based gas sensors. Herein, we developed a testbed to evaluate the response characteristics of MoS2-based gas sensors under a NO2 gas flow, which allows variations in their system configurations. Additionally, we demonstrated that the distance between the gas inlet and the sensor and gas inlet orientation influences the sensor performance. As the distance to the 2D gas sensor surface decreased from 4 to 2 mm, the sensitivity of the sensor improved to 9.20%. Furthermore, when the gas inlet orientation was perpendicular to the gas sensor surface, the sensitivity of the sensor was the maximum (4.29%). To attain the optimum operating conditions of the MoS2-based gas sensor, the effects of measurement conditions, such as gas concentration and temperature, on the sensitivity of the gas sensor were investigated.

WS2 Nanorod as a Remarkable Acetone Sensor for Monitoring Work/Public Places.

Here, we report the synthesis of the WS2 nanorods (NRs) using an eco-friendly and facile hydrothermal method for an acetone-sensing application. This study explores the acetone gas-sensing characteristics of the WS2 nanorod sensor for 5, 10, and 15 ppm concentrations at 25 °C, 50 °C, 75 °C, and 100 °C. The WS2 nanorod sensor shows the highest sensitivity of 94.5% at 100 °C for the 15 ppm acetone concentration. The WS2 nanorod sensor also reveals the outstanding selectivity of acetone compared to other gases, such as ammonia, ethanol, acetaldehyde, methanol, and xylene at 100 °C with a 15 ppm concentration. The estimated selectivity coefficient indicates that the selectivity of the WS2 nanorod acetone sensor is 7.1, 4.5, 3.7, 2.9, and 2.0 times higher than xylene, acetaldehyde, ammonia, methanol, and ethanol, respectively. In addition, the WS2 nanorod sensor also divulges remarkable stability of 98.5% during the 20 days of study. Therefore, it is concluded that the WS2 nanorod can be an excellent nanomaterial for developing acetone sensors for monitoring work/public places.

Fabrication and Development of Binder-Free Mn-Fe-S Mixed Metal Sulfide Loaded Ni-Foam as Electrode for the Asymmetric Coin Cell Supercapacitor Device.

Currently, the fast growth and advancement in technologies demands promising supercapacitors, which urgently require a distinctive electrode material with unique structures and excellent electrochemical properties. Herein, binder-free manganese iron sulfide (Mn-Fe-S) nanostructures were deposited directly onto Ni-foam through a facile one-step electrodeposition route in potentiodynamic mode. The deposition cycles were varied to investigate the effect of surface morphologies on Mn-Fe-S. The optimized deposition cycles result in a fragmented porous nanofibrous structure, which was confirmed using Field Emission Scanning Electron Microscopy (FE-SEM). X-ray photoelectron spectroscopy (XPS) confirmed the presence of Mn, Fe, and S elements. The energy dispersive X-ray spectroscopy and elemental mapping revealed a good distribution of Mn, Fe, and S elements across the Ni-foam. The electrochemical performance confirms a high areal capacitance of 795.7 mF cm-2 with a 24 µWh cm-2 energy density calculated at a 2 mA cm-2 current density for porous fragmented nanofiber Mn-Fe-S electrodes. The enhancement in capacitance is due to diffusive-controlled behavior dominating the capacitator, as shown by the charge-storage kinetics. Moreover, the assembled asymmetric coin cell device exhibited superior electrochemical performance with an acceptable cyclic performance of 78.7% for up to 95,000 consecutive cycles.

Synthesis of Mesoporous Silica Adsorbent Modified with Mercapto-Amine Groups for Selective Adsorption of Cu2+ Ion from Aqueous Solution.

In a sol-gel co-condensation, a mesoporous silica hybrid integrated with (3-mercaptopropyl)trimethoxysilane (TMPSH) was prepared and then reacted with allylamine via a post-surface functionalization approach. Approximately 15 mol% of TMSPSH was introduced into the mesoporous silica pore walls along with tetraethyl orthosilicate. The mercapto ligands in the prepared mesoporous silica pore walls were then reacted with allylamine (AM) to form the mercapto-amine-modified mesoporous silica adsorbent (MSH@MA). The MSH@MA NPs demonstrate highly selective adsorption of copper (Cu2+) ions (~190 mg/g) with a fast equilibrium adsorption time (30 min). The prepared adsorbent shows at least a five times more efficient recyclable stability. The MSH@MA NPs adsorbent is useful for selective adsorption of Cu2+ ions.

Study of solvent variation on controlled synthesis of different nanostructured NiCo2O4 thin films for supercapacitive application.

The present investigation deals with controlled synthesis of nanostructured NiCo2O4 thin films directly on stainless steel substrates by facile and economical chemical bath deposition technique, without adding a surfactant or a binder. The consequences of different compositions of solvents on morphological and electrochemical properties have been studied systematically. We used different solvent composition as Double Distilled Water (DDW), DDW:Ethanol (1:1) and DDW: N, N dimethylformamide (1:1). The films have been named as NCO-W for DDW, NCO-WE for DDW: Ethanol (1:1) solvent and NCO-WD for DDW: N, N dimethylformamide (1:1) solvent. The morphologies of NiCo2O4 thin films modify substantially with change in a solvent. NCO-W exhibited the spikes of Crossandra infundibuliformis like nanostructures. The NCO-WE favored the formation of uniformly distributed leaf-like nanostructure whereas NCO-WD showed randomly oriented nanoplates all over the surface area. The Electrochemical performance of these NiCo2O4 thin films were studied using cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy techniques. The NCO-W, NCO-WE and NCO-WD electrodes showed specific capacitance values of 271, 553 and 140 F/g respectively at the current density of 0.5 mA/cm2 and excellent capacitance retention of 90%, 91% and 80% after 2000 cycles for NCO-W, NCO-WE and NCO-WD samples respectively. This result reveals that NiCo2O4 is a prominent electrode material for supercapacitor application.

Nanocluster-Based Ultralow-Temperature Driven Oxide Gate Dielectrics for High-Performance Organic Electronic Devices.

The development of novel dielectric materials with reliable dielectric properties and low-temperature processibility is crucial to manufacturing flexible and high-performance organic thin-film transistors (OTFTs) for next-generation roll-to-roll organic electronics. Here, we investigate the solution-based fabrication of high-k aluminum oxide (Al2O3) thin films for high-performance OTFTs. Nanocluster-based Al2O3 films fabricated by highly energetic photochemical activation, which allows low-temperature processing, are compared to the conventional nitrate-based Al2O3 films. A wide array of spectroscopic and surface analyses show that ultralow-temperature photochemical activation (<60 °C) induces the decomposition of chemical impurities and causes the densification of the metal-oxide film, resulting in a highly dense high-k Al2O3 dielectric layer from Al-13 nanocluster-based solutions. The fabricated nanocluster-based Al2O3 films exhibit a low leakage current density (<10-7 A/cm2) at 2 MV/cm and high dielectric breakdown strength (>6 MV/cm). Using this dielectric layer, precisely aligned microrod-shaped 2,7-dioctyl[1]benzothieno [3,2-b][1] benzothiophene (C8-BTBT) single-crystal OTFTs were fabricated via solvent vapor annealing and photochemical patterning of the sacrificial layer.

Self-Aligned Top-Gate Metal-Oxide Thin-Film Transistors Using a Solution-Processed Polymer Gate Dielectric.

For high-speed and large-area active-matrix displays, metal-oxide thin-film transistors (TFTs) with high field-effect mobility, stability, and good uniformity are essential. Moreover, reducing the RC delay is also important to achieve high-speed operation, which is induced by the parasitic capacitance formed between the source/drain (S/D) and the gate electrodes. From this perspective, self-aligned top-gate oxide TFTs can provide advantages such as a low parasitic capacitance for high-speed displays due to minimized overlap between the S/D and the gate electrodes. Here, we demonstrate self-aligned top-gate oxide TFTs using a solution-processed indium-gallium-zinc-oxide (IGZO) channel and crosslinked poly(4-vinylphenol) (PVP) gate dielectric layers. By applying a selective Ar plasma treatment on the IGZO channel, low-resistance IGZO regions could be formed, having a sheet resistance value of ~20.6 kΩ/sq., which can act as the homojunction S/D contacts in the top-gate IGZO TFTs. The fabricated self-aligned top-gate IGZO TFTs exhibited a field-effect mobility of 3.93 cm2/Vs and on/off ratio of ~106, which are comparable to those fabricated using a bottom-gate structure. Furthermore, we also demonstrated self-aligned top-gate TFTs using electrospun indium-gallium-oxide (IGO) nanowires (NWs) as a channel layer. The IGO NW TFTs exhibited a field-effect mobility of 0.03 cm2/Vs and an on/off ratio of >105. The results demonstrate that the Ar plasma treatment for S/D contact formation and the solution-processed PVP gate dielectric can be implemented in realizing self-aligned top-gate oxide TFTs.

Locally Controlled Sensing Properties of Stretchable Pressure Sensors Enabled by Micro-Patterned Piezoresistive Device Architecture.

For wearable health monitoring systems and soft robotics, stretchable/flexible pressure sensors have continuously drawn attention owing to a wide range of potential applications such as the detection of human physiological and activity signals, and electronic skin (e-skin). Here, we demonstrated a highly stretchable pressure sensor using silver nanowires (AgNWs) and photo-patternable polyurethane acrylate (PUA). In particular, the characteristics of the pressure sensors could be moderately controlled through a micro-patterned hole structure in the PUA spacer and size-designs of the patterned hole area. With the structural-tuning strategies, adequate control of the site-specific sensitivity in the range of 47~83 kPa-1 and in the sensing range from 0.1 to 20 kPa was achieved. Moreover, stacked AgNW/PUA/AgNW (APA) structural designed pressure sensors with mixed hole sizes of 10/200 µm and spacer thickness of 800 µm exhibited high sensitivity (~171.5 kPa-1) in the pressure sensing range of 0~20 kPa, fast response (100~110 ms), and high stretchability (40%). From the results, we envision that the effective structural-tuning strategy capable of controlling the sensing properties of the APA pressure sensor would be employed in a large-area stretchable pressure sensor system, which needs site-specific sensing properties, providing monolithic implementation by simply arranging appropriate micro-patterned hole architectures.

Catalytic Metal-Accelerated Crystallization of High-Performance Solution-Processed Earth-Abundant Metal Oxide Semiconductors.

As an alternative strategy for conventional high-temperature crystallization of metal oxide (MO) channel layers, the catalytic metal-accelerated crystallization (CMAC) process using a metal seed layer is demonstrated for low-temperature crystallization of solution-processed MO semiconductors. In the CMAC process, the catalytic metal layer plays the role of seed sites for initiating and accelerating the crystallization of amorphous MO films. Generally, the solution-processed crystalline-TiO2 (c-TiO2) films required high-temperature crystallization conditions (≥500-600 °C), showing low electrical performance with a high defect density. In contrast, the suggested CMAC process could effectively lower crystallization temperature of the a-TiO2 films, enabling high-quality c-TiO2 films with well-aligned anatase grains and low-defect density. The various crystalline catalytic layers were deposited over the earth-abundant n-type amorphous titanium oxide (a-TiO2) films. Also, then, the CMAC process was performed for facile low-temperature translation of solution-processed a-TiO2 to a highly crystallized state. In particular, the Al-CMAC process using the crystalline thin-aluminum (Al) catalytic metal seed layer facilitates low-temperature (≥300 °C) crystallization of the solution-processed a-TiO2 films and the fabrication of high-performance solution-processed c-TiO2 thin-film transistors with superior field-effect mobility, good on/off switching behavior, and improved operational stability.

van der Waals Epitaxy of High-Mobility Polymorphic Structure of Mo6Te6 Nanoplates/MoTe2 Atomic Layers with Low Schottky Barrier Height.

High contact resistance between two-dimensional (2D) transition metal dichalcogenides (TMDs) and metal electrodes is a practical barrier for applications of 2D TMDs to conventional devices. A promising solution to this is polymorphic integration of 1T'-phase semimetallic and 2H-phase semiconducting TMD crystals, which can lower the Schottky barrier of the TMDs. Here, we demonstrate the van der Waals epitaxy of density-controlled single isolated 1T'-Mo6Te6 nanoplates on 2H-MoTe2 atomic layers by using metal-organic chemical vapor deposition. Importantly, in situ grown 1T'-Mo6Te6 nanoplates significantly reduce the contact resistance of the 2H-MoTe2 atomic layers, providing a record high mobility of 1139 cm2/V·s for Pd/1T'-Mo6Te6/2H-MoTe2 back-gated field-effect transistors, along with a low Schottky barrier height ( qϕb) of 8.7 meV. These results lead to the possibility of ameliorating the high contact resistance faced by other TMDs and, furthermore, offer polymorphic structures for realizing higher-mobility TMD devices.

The interplay between Zeeman splitting and spin-orbit coupling in InAs nanowires.

Coupling of the electron orbital motion and spin, i.e., spin-orbit coupling (SOC) leads to nontrivial changes in energy-level structures, giving rise to various spectroscopies and applications. The SOC in solids generates energy-band inversion or splitting under zero or weak magnetic fields, which is required for topological phases or Majorana fermions. Here, we examined the interplay between the Zeeman splitting and SOC by performing the transport spectroscopy of Landau levels (LLs) in indium arsenide nanowires under a strong magnetic field. We observed the anomalous Zeeman splitting of LLs, which depends on the quantum number of LLs as well as the electron spin. We considered that this observation was attributed to the interplay between the Zeeman splitting and the SOC. Our findings suggest an approach of generating spin-resolved chiral electron transport in nanowires.

Structural defects in a nanomesh of bulk MoS2 using an anodic aluminum oxide template for photoluminescence efficiency enhancement.

Two-dimensional (2D) materials beyond graphene have attracted considerable interest because of the zero bandgap drawbacks of graphene. Transition metal dichalcogenides (TMDs), such as MoS2 and WSe2, are the potential candidates for next 2D materials because atomically thin layers of TMDs exhibit unique and versatile electrical and optical properties. Although bulk TMDs materials have an indirect bandgap, an indirect-to-direct bandgap transition is observed in monolayers of TMDs (MoS2, WSe2, and MoSe2). Optical properties of TMD films can be improved by the introduction of structural defects. For example, large-area spatial tuning of the optical transition of bulk MoS2 films is achieved by using an anodic aluminum oxide (AAO) template to induce structural defects such as edge- and terrace-terminated defects in a nanomesh structure. Strong photoluminescence emission peaks with a band gap of 1.81 eV are observed, possibly because of radiative transition at the defect sites. This work shows that the AAO template lithography method has potential for the production of homogenous large-scale nanomesh structures for practical semiconductor processing applications in future MoS2-based electronic and optical devices.

Optical Characteristics of Double Layered Plasmonic Structure Using Nanopatterning Process.

A double layered plasmonic device based on transferring technique with polystyrene nano-beads is analyzed and demonstrated to increase the sensing characteristics of plasmonic sensor system. The double layered plasmonic devices are calculated using the three-dimensional finite-difference time-domain method for the width and thickness of the nano-hole structures. The double layered plasmonic devices with different diameters of the Au nano-hole are fabricated by transferring method with commercially available chloromethyl latex with a diameter of 0.42 µm. The optimum sensing characteristic of the proposed plasmonic device is obtained with the film and the hole thickness of 15 and 15 nm in the 246 nm wide nano-hole size. The best sensitivity of the proposed plasmonic sensor is 67.7 degree/RIU when the sensitivity of the conventional plasmonic sensor is 42.2 degree/RIU.

Electromechanical Properties and Spontaneous Response of the Current in InAsP Nanowires.

The electromechanical properties of ternary InAsP nanowires (NWs) were investigated by applying a uniaxial tensile strain in a transmission electron microscope (TEM). The electromechanical properties in our examined InAsP NWs were governed by the piezoresistive effect. We found that the electronic transport of the InAsP NWs is dominated by space-charge-limited transport, with a I ∞ V2 relation. Upon increasing the tensile strain, the electrical current in the NWs increases linearly, and the piezoresistance gradually decreases nonlinearly. By analyzing the space-charge-limited I-V curves, we show that the electromechanical response is due to a mobility that increases with strain. Finally, we use dynamical measurements to establish an upper limit on the time scale for the electromechanical response.

Short-wavelength infrared photodetector on Si employing strain-induced growth of very tall InAs nanowire arrays.

One-dimensional crystal growth enables the epitaxial integration of III-V compound semiconductors onto a silicon (Si) substrate despite significant lattice mismatch. Here, we report a short-wavelength infrared (SWIR, 1.4-3 µm) photodetector that employs InAs nanowires (NWs) grown on Si. The wafer-scale epitaxial InAs NWs form on the Si substrate without a metal catalyst or pattern assistance; thus, the growth is free of metal-atom-induced contaminations, and is also cost-effective. InAs NW arrays with an average height of 50 µm provide excellent anti-reflective and light trapping properties over a wide wavelength range. The photodetector exhibits a peak detectivity of 1.9 × 10(8) cm · Hz(1/2)/W for the SWIR band at 77 K and operates at temperatures as high as 220 K. The SWIR photodetector on the Si platform demonstrated in this study is promising for future low-cost optical sensors and Si photonics.

Structural and optical properties of the In(x)Ga(1-x)As nanowires grown on SiO2 via vapor-liquid-solid method.

We report the crystal growth of the In(x)Ga(1-x)As nanowires (NWs) on SiO2 substrate using metal organic chemical vapor deposition. Au nanoparticles which are disintegrated from thin Au film have been used as a catalyst for the vapor-liquid-solid growth. Electron microscopy characterization is performed to investigate the structural properties of the In(x)Ga(1-x)As NW. The In(x)Ga(1-x)As NW grown under an optimal condition has a single-crystal wurtzite structure without any misfit dislocation or stacking fault. Strong room temperature photoluminescence peaks are observed from In(x)Ga(1-x)As NWs passivated by GaAs. Very low light reflectance is measured at the NW surface in the wavelength range from 250 to 1200 nm. The single crystal In(x)Ga(1-x)As NWs are applicable to the various electrical and optical devices.

Structural characteristics of ternary In(x)Ga(1-x)As nanowires on Si (111) grown via Au-catalyzed VLS.

We have characterized the structural properties of the ternary In(x)Ga(1-x)As nanowires (NWs) grown on silicon (Si) substrates using metalorganic chemical vapor deposition (MOCVD). Au catalyzed vapor-liquid-solid (VLS) mode was used for the NW growth. The density of the In(x)Ga(1-x)As NW array grown under optimized condition exceeds 1 x 10(8)/cm2. X-ray diffraction (XRD) spectra confirm the In composition (x = 0.9-0.3) of the In(x)Ga(1-x)As nanowires which bandgap energy can cover the entire near-infrared (NIR) range. Massive stacking faults and twin planes were observed but no misfit dislocation was found along the NWs as confirmed by transmission electron microscopy (TEM). The energy-dispersive X-ray spectroscopy (EDS) analysis shows the gradual variation of In composition along the NW.