Impact of a Diverse Combination of Metal Oxide Gas Sensors on Machine Learning-Based Gas Recognition in Mixed Gases

A challenge for chemiresistive-type gas sensors distinguishing mixture gases is that for highly accurate recognition, massive data processing acquired from various types of sensor configurations must be considered. The impact of data processing is indeed ineffective and time-consuming. Herein, we systemically investigate the effect of the selectivity for a target gas on the prediction accuracy of gas concentration via machine learning based on a support vector machine model. The selectivity factor S(X) of a gas sensor for a target gas “X” is introduced to reveal the correlation between the prediction accuracy and selectivity of gas sensors. The presented work suggests that (i) the strong correlation between the selectivity factor and prediction accuracy has a proportional relationship, (ii) the enhancement of the prediction accuracy of an elemental sensor with a low sensitivity factor can be attained by a complementary combination of the other sensor with a high selectivity factor, and (iii) it can also be boosted by combining the sensor having even a low selectivity factor

Proton Conducting Perhydropolysilazane-Derived Gate Dielectric for Solution-Processed Metal Oxide-Based Thin-Film Transistors

Perhydropolysilazane (PHPS), an inorganic polymer composed of Si–N and Si–H, has attracted much attention as a precursor for gate dielectrics of thin-film transistors (TFTs) due to its facile processing even at a relatively low temperature. However, an in-depth understanding of the tunable dielectric behavior of PHPS-derived dielectrics and their effects on TFT device performance is still lacking. In this study, the PHPS-derived dielectric films formed at different annealing temperatures have been used as the gate dielectric layer for solution-processed indium zinc oxide (IZO) TFTs. Notably, the IZO TFTs fabricated on PHPS annealed at 350 °C exhibit mobility as high as 118 cm2 V–1 s–1, which is about 50 times the IZO TFTs made on typical SiO2 dielectrics. The outstanding electrical performance is possible because of the exceptional capacitance of PHPS-derived dielectric caused by the limited hydrolysis reaction of PHPS at a low processing temperature (<400 °C). According to our analysis, the exceptional dielectric behavior is originated from the electric double layer formed by mobile of protons in the low temperature-annealed PHPS dielectrics. Furthermore, proton conduction through the PHPS dielectric occurs through a three-dimensional pathway by a hopping mechanism, which allows uniform polarization of the dielectric even at room temperature, leading to amplified performance of the IZO TFTs

High Durability and Waterproofing rGO/SWCNT-Fabric-Based Multifunctional Sensors for Human-Motion Detection

Wearable strain–pressure sensors for detecting electrical signals generated by human activities are being widely investigated because of their diverse potential applications, from observing human motion to health monitoring. In this study, we fabricated reduced graphene oxide (rGO)/single-wall carbon nanotube (SWCNT) hybrid fabric-based strain–pressure sensors using a simple solution process. The structural and chemical properties of the rGO/SWCNT fabrics were characterized using scanning electron microscopy (SEM), Raman, and X-ray photoelectron spectroscopy (XPS). Complex networks containing rGO and SWCNTs were homogeneously formed on the cotton fabric. The sensing performance of the devices was evaluated by measuring the effects of bending strain and pressure. When the CNT content was increased, the change in relative resistance decreased, while durability was significantly improved. The rGO/SWCNT (0.04 wt %) fabric sensor showed particularly high mechanical stability and flexibility during 100 000 bending tests at the extremely small bending radius of 3.5 mm (11.6% bending strain). Moreover, the rGO/SWCNT fabric device exhibited excellent water resistant properties after 10 washing tests due to its hydrophobic nature. Finally, we demonstrated a fabric-sensor-based motion glove and confirmed its practical applicability

Data_Sheet_1_Synthesis of Mo2C and W2C Nanoparticle Electrocatalysts for the Efficient Hydrogen Evolution Reaction in Alkali and Acid Electrolytes.docx

The synthesis of low cost, high efficacy, and durable hydrogen evolution electrocatalysts from the non-noble metal group is a major challenge. Herein, we establish a simple and inexpensive chemical reduction method for producing molybdenum carbide (Mo2C) and tungsten carbide (W2C) nanoparticles that are efficient electrocatalysts in alkali and acid electrolytes for hydrogen evolution reactions (HER). Mo2C exhibits outstanding electrocatalytic behavior with an overpotential of −134 mV in acid medium and of −116 mV in alkaline medium, while W2C nanoparticles require an overpotential of −173 mV in acidic medium and −130 mV in alkaline medium to attain a current density of 10 mA cm−2. The observed results prove the capability of high- and low-pH active electrocatalysts of Mo2C and W2C nanoparticles to be efficient systems for hydrogen production through HER water electrolysis.</p

Multilayered MoS₂ Sphere-Based Triboelectric–Flexoelectric Nanogenerators as Self-Powered Mechanical Sensors for Human Motion Detection

High-performance, wearable, and self-powered mechanical sensors for human health monitoring, motion detection systems, and human–machine interfaces are attracting attention owing to the increased interest in green energy. Piezoelectric and triboelectric effects are being exploited to develop various types of self-powered mechanical sensors; however, unresolved issues such as complicated processes and limitations in material selection and practical applications remain. A type of effective self-powered mechanical sensor based on the hybrid triboelectric–flexoelectric effect of multilayered MoS2 hollow spheres is reported herein. This triboelectric–flexoelectric mechanical sensor (TFMS) exhibits superior sensing characteristics, including wide-range pressure detection and superior stability, owing to the remarkable hybrid triboelectric–flexoelectric effect of optimized MoS2 hollow spheres under stress. In addition, the operating mechanism of the fabricated TFMS is discussed based on the size and number of the multilayered MoS2 spheres using finite element method (FEM) simulations of the effective stress under pressure changes. Furthermore, the effective operation of the sensor in detecting various human physiological motions from the wrist pulse to walking/running is demonstrated. These results are expected to promote the development of advanced mechanical sensors for applications such as next-generation prostheses and human–machine interfaces

Performance Improvement of Quantum Dot-Light-Emitting Diodes Enabled by an Alloyed ZnMgO Nanoparticle Electron Transport Layer

Since the introduction of inorganic ZnO, typically in the form of nanoparticles (NPs), as an electron transport layer (ETL) material, the device performance of electrically driven colloidal quantum dot-light-emitting diodes (QLEDs), in particular, with either Cd-based II–VI or non-Cd-based III–V (e.g., InP) quantum dot (QD) visible-emitters, has been rapidly improved. In the present work, three Zn1–xMgxO (x = 0, 0.05, 0.1) NPs that possess different electronic energy levels are applied as ETLs of solution-processed, multilayered I–III–VI type QLEDs that consist of a Cu–In–S, Cu–In–Ga–S, or Zn–Cu–In–S QD emitting layer (EML) plus a common organic hole transport layer of poly­(9-vinlycarbazole). The luminance and efficiency of those QLEDs are found to be strongly dependent on the type of ZnMgO NP ETL, resulting in the substantial improvements by means of alloyed ZnMgO ETL versus pure ZnO one. Ultraviolet photoelectron and absorption spectroscopic measurements on a series of ZnMgO NP films reveal that their conduction band minimum (CBM) levels are systematically closer to the vacuum level with increasing Mg content. Therefore, such beneficial effects of alloyed NPs on QLED performance are primarily ascribed to the reduced electron injection barrier between ETL and QD EML that is enabled by the upshift of their CBM levels

3D-Stacked Carbon Composites Employing Networked Electrical Intra-Pathways for Direct-Printable, Extremely Stretchable Conductors

The newly designed materials for stretchable conductors meeting the demands for both electrical and mechanical stability upon morphological elongation have recently been of paramount interest in the applications of stretchable, wearable electronics. To date, carbon nanotube-elastomeric polymer mixtures have been mainly developed; however, the method of preparing such CNT–polymer mixtures as stretchable conductors has been limited to an ionic liquid-mediated approach. In this study, we suggest a simple wet-chemical method for producing newly designed, three-dimensionally stacked carbon composite materials that facilitate the stable morphological elongation up to a strain of 300% with normalized conductivity variation of only 0.34 under a strain of 300%. Through a comparative study with other control samples, it is demonstrated that the intraconnected electrical pathways in hierarchically structured composite materials enable the generation of highly stretchable conductors. Their direct patternability is also evaluated by printing on demand using a programmable disperser without the use of prepatterned masks

AC-Impedance Spectroscopic Analysis on the Charge Transport in CVD-Grown Graphene Devices with Chemically Modified Substrates

A comprehensive study for the effect of interfacial buffer layers on the electrical transport behavior in CVD-grown graphene based devices has been performed by ac-impedance spectroscopy (IS) analysis. We examine the effects of the trap charges at graphene/SiO₂ interface on the total capacitance by introducing self-assembled monolayers (SAMs). Furthermore, the charge transports in the polycrystalline graphene are characterized through the temperature-dependent IS measurement, which can be explained by the potential barrier model. The frequency-dependent conduction reveals that the conductivity of graphene is related with the mobility, which is limited by the scattering caused by charged adsorbates on SiO₂ surface

Direct Determination of Field Emission across the Heterojunctions in a ZnO/Graphene Thin-Film Barristor

Graphene barristors are a novel type of electronic switching device with excellent performance, which surpass the low on–off ratios that limit the operation of conventional graphene transistors. In barristors, a gate bias is used to vary graphene’s Fermi level, which in turn controls the height and resistance of a Schottky barrier at a graphene/semiconductor heterojunction. Here we demonstrate that the switching characteristic of a thin-film ZnO/graphene device with simple geometry results from tunneling current across the Schottky barriers formed at the ZnO/graphene heterojunctions. Direct characterization of the current–voltage−temperature relationship of the heterojunctions by ac-impedance spectroscopy reveals that this relationship is controlled predominantly by field emission, unlike most graphene barristors in which thermionic emission is observed. This governing mechanism makes the device unique among graphene barristors, while also having the advantages of simple fabrication and outstanding performance