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Metal chalcogenides have attracted attention as potential thermoelectric materials due to their intrinsically low thermal conductivity arising from their layered structure with weak van der Waals atomic bonding. InSe, one of the post transition metal chalcogenides, also has low thermal conductivity and doping of InSe with elements such as Sn, Si, and As is known to improve the electronic transport properties. Herein, we investigated Te doping in Si-doped InSe (In0.9Si0.1Se) and report enhanced thermoelectric properties, mainly the increased Seebeck coefficient due to the increase in effective mass. Due to the increase in effective mass, the magnitude of the Seebeck coefficient systematically increased with Te doping from 234 µV/K to 405 µV/K. Eventually, the zT at 700 K was enhanced from 0.040 for the pristine sample to 0.069–0.096 for the Te-doped samples.

A new series of proton-conducting solid polymer electrolytes with different compositions, comprising polyvinylpyrrolidone (PVPK40) and polymethylmethacrylate (PMMA) as host polymers, methanesulfonic acid (MSA) as a proton-conducting salt, and alumina (Al2O3) as the nanofiller, were prepared using solution casting. High proton-conducting samples were identified and utilized for the construction of primary proton batteries. The electrical properties of the prepared electrolytes were investigated through AC impedance analysis. The highest proton conductivity (2.51 × 10−5 S/cm) was achieved at room temperature by PMMA-PVPK40-MSA-based blended polymer electrolytes (BS3). The discharge characteristics of filler-dispersed solid polymer electrolytes were better than those of other solid polymer electrolytes. The estimated energy density of the constructed proton battery using solid polymer electrolytes with blended polymers and nanofillers was 0.66 and 3.25 Wh kg−1, respectively.

A simple solution cast route was used to prepare proton conducting solid polymer electrolytes using poly(methyl methacrylate) and poly(vinylpyrrolidone) as polymer hosts and methanesulfonic acid as a proton provider. Fourier transform infrared spectra confirmed functional group interactions between polymers, blended polymers, and acid. Polymer glass transition temperature shifted with increasing acid content in the blend electrolytes provide thermal stability up to 290 °C, verified by differential scanning calorimetry and thermogravimetry analyses. Proton conductivity achieved = 1.16 × 10−4 S/cm at room temperature with an ionic transport number of 0.98. Discharge profiles verified oxidation current

Next-generation electronic and optoelectronic devices require a high-quality channel layer. Graphene is a good candidate because of its high carrier mobility and unique ambipolar transport characteristics. However, the on/off ratio and photoresponsivity of graphene are typically low. Transition metal dichalcogenides (e.g., MoSe2) are semiconductors with high photoresponsivity but lower mobility than that of graphene. Here, we propose a graphene/MoSe2 barristor with a high-k ion-gel gate dielectric. It shows a high on/off ratio (3.3 × 104) and ambipolar behavior that is controlled by an external bias. The barristor exhibits very high external quantum efficiency (EQE, 66.3%) and photoresponsivity (285.0 mA/W). We demonstrate that an electric field applied to the gate electrode substantially modulates the photocurrent of the barristor, resulting in a high gate tuning ratio (1.50 μA/V). Therefore, this barristor shows potential for use as an ambipolar transistor with a high on/off ratio and a gate-tunable photodetector with a high EQE and responsivity. An approach that enhances control over charge carrier movement in graphene-based transistors may be useful in applications such as bendable circuits and light sensors. The difference in current flow when a transistor turns from on to off plays a critical role in determining device performance. Bae Ho Park from Konkuk University in Seoul, South Korea, and colleagues report that stacking graphene on top of another two-dimensional (2D) film of molybdenum selenide can lead to larger on/off current ratios than conventional graphene transistors. Optical and electrical characterizations revealed that the interface between the 2D films created a potential barrier that blocked current flow in the device’s off state without compromising graphene’s mechanical flexibility. Using an external voltage to modulate current flow through the barrier region also allowed the stacked device to serve as a high-efficiency photodetector. we report a field-effect device with a graphene/MoSe2 channel layer and high-k ion-gel gate dielectric. The device shows a high carrier mobility (~247 cm2/V ∙ s), a high on/off ratio (3.3 × 104), and ambipolar behavior that are controlled by an applied gate voltage. The strong gating effect of the device results in higher external quantum efficiency (EQE) (66.3%), photoresponsivity (285.0 mA/W), and gate-tuning ratio (1.50 μA/V) compared to pristine devices. Therefore, our graphene/MoSe2 barristor device can be a suitable candidate for use in ambipolar transistors and gate-tunable broad-area photodetectors.

The formation of secondary phases of NiTe2 and NbTe2 in p-type Bi0.5Sb1.5Te3 thermoelectric alloys was investigated through in situ phase separation by using the melt spinning process. Adding stoichiometric Ni, Nb, and Te in a solid-state synthesis process of Bi0.5Sb1.5Te3, followed by rapid solidification by melt spinning, successfully segregated NiTe2 and NbTe2 in the Bi0.5Sb1.5Te3 matrix. Since heterointerfaces of Bi0.5Sb1.5Te3 with NiTe2 and NbTe2 form potential barriers of 0.26 and 0.08 eV, respectively, a low energy carrier filtering effect can be expected, higher Seebeck coefficients and power factors were achieved for Bi0.5Sb1.5Te3(NiTe2)0.01 (250 &mu, V/K and 3.15 mW/mK2), compared to those of Bi0.5Sb1.5Te3 (240 &mu, V/K and 2.69 mW/mK2). However, there was no power factor increase for NbTe2 segregated samples. The decrease in thermal conductivity was seen due to the possible additional phonon scattering by the phase segregations. Consequently, zT at room temperature was enhanced to 0.98 and 0.94 for Bi0.5Sb1.5Te3(NiTe2)0.01 and Bi0.5Sb1.5Te3(NbTe2)0.01, respectively, compared to 0.79 for Bi0.5Sb1.5Te3. The carrier filtering effect induced by NiTe2 segregations with an interface potential barrier of 0.26 eV effectively increased the Seebeck coefficient and power factor, thus improving the zT of p-type Bi0.5Sb1.5Te3, while the interface potential barrier of 0.08 eV of NbTe2 segregation appeared to be too small to induce an effective carrier filtering effect.

Combustible gases, such as CH4 and CO, directly or indirectly affect the human body. Thus, leakage detection of combustible gases is essential for various industrial sites and daily life. Many types of gas sensors are used to identify these combustible gases, but since gas sensors generally have low selectivity among gases, coupling issues often arise which adversely affect gas detection accuracy. To solve this problem, we built a decoupling algorithm with different gas sensors using a machine learning algorithm. Commercially available semiconductor sensors were employed to detect CH4 and CO, and then support vector machine (SVM) applied as a supervised learning algorithm for gas classification. We also introduced a pairing plot scheme to more effectively classify gas type. The proposed model classified CH4 and CO gases 100% correctly at all levels above the minimum concentration the gas sensors could detect. Consequently, SVM with pairing plot is a memory efficient and promising method for more accurate gas classification.

The aim of this study was to develop a new method, using a vibration sensor, to address the drawbacks of preexisting methods for monitoring soil ecological toxicity. A novel method was designed by inspiration from seismometers, which record signals originating from the ground motion caused by earthquake events. Similarly, the newly developed method using a vibration sensor detects the signals generated by earthworm activity, which reflects the soil ecological toxicity. To establish the new method, a stepwise approach was adopted: (1) the effects of operational conditions on the overall performance of the system were evaluated, and (2) the feasibility of the method was tested by an application study. A number of crucial factors influencing the overall performance of the method were evaluated. These were categorized based on three features: soil, tested organism, and instrumentation. The soil properties evaluated included soil type (artificial and natural), moisture content, and bulk density. In terms of the organism, the effect of the number of earthworms was investigated. Finally, with regard to instrumentation, appropriate soil chamber specifications and monitoring duration were identified. The most effective conditions for each factor were determined based on a comparative evaluation of changes in the activity levels and body weights of the earthworms. After the first step of the study, an application study was carried out to demonstrate the feasibility of the proposed method. Zinc (Zn)-contaminated soils were tested under the most efficient operational conditions identified in the preceding study. The results of the study confirm that the method is applicable to natural soils, and the best performance was achieved under soil conditions of 50–60% maximum water holding capacity and 0.95 g/cm3 bulk density. Furthermore, the optimal number of earthworms was found to be five, which corresponds 19.84 g soil per earthworm. With respect to the instrumental conditions, the most efficient specification was a cylindrical soil chamber with a diameter of 94 mm and height of 54 mm. Additionally, the most relevant monitoring duration was found to be 7 days. The results indicate that the method can shorten the testing period, reduce the soil amount and earthworm number required, and facilitate the real-time monitoring of mortality. Based on the results of the application study, we validated the proposed vibration sensor-based method for characterizing earthworm behavior in terms of its feasibility for monitoring the ecological toxicity of soil. The results indicate that dermal contact and feeding activity of earthworms decreased significantly with increasing Zn concentrations in the soil. The EC50 value of Zn calculated based on the earthworm behavior was 340.97 mg/kg. Based on the results, it is concluded that the proposed method cannot only overcome the shortcomings of traditional test methods using earthworms, but also enable real-time ecotoxicity in soil environments.

The use of organic conjugated polymers in sensors has attracted greater attention due to their application in materials technology. In the present communication, we utilized Schiff's condensation polymerization reaction for the synthesis of a novel conjugated polymer poly(tetrahexadecyl-dihydroindacenodithiophene)-alt-(p-phenylenediimine) (PIDTPD) consisting of indacenodithiophene (IDT) and p-phenylene diamine (PDA) units for use in acid vapor sensing. Conventionally, the characteristics and applications of conjugated polymers are affected by their constituents. The imine bond between the components of organic materials has received little attention compared to their active counterparts. In order to explore the practical application of conjugated polymers in sensors, we employed PIDTPD in a paper sensor and illustrated the impact of mono- and bis-protonation on the pristine material in driving a noteworthy protonation-induced color shift toward the longer wavelength region via acidochromism.

Nitrogen functionalized graphitic carbon (NGC), aside from being a distinctive support material for catalyst integration, is also intrinsically active for various electrochemical reactions especially in energy storage and conversion devices. Given the admirable conductivity and graded pore structure, the strategy of hybridizing metal oxides with NGC skeleton is reckoned to be highly compelling in the design of electrode materials. In this work, carboxy methylcellulose and melamine derived – Co3O4 NGC is used as an active electrode material for high performance asymmetric supercapacitors (ASC). The synthesized Co3O4 NGC exhibits microglobules with mesoporous network and maximum surface area of 445.3 m2 g−1 at 77 K. A solid state ASC is fabricated with activated carbon and Co3O4 NGC microglobules as negative and positive electrodes, respectively based on charge balancing theory, delivering ultra-high capacitance (128.43 F. g−1), energy density (45.66 Wh.kg−1) and power density (399.9 W.kg−1). Further, excellent capacitance retention (92.1%) over 5000 cycles confirms their long-term stability, which in turn enlightening the energy storage device progress for future generation electronics.

Lead-free (100 − x)BiFeO3–xBaTiO3 (BFBTx, x = 0, 30, 33, 40 and 50) piezoelectric thin films were deposited on platinized silicon substrates by using a pulsed laser deposition method. The BFBTx thin films has a single-phase perovskite structure with (111) preferred orientations. Atomic force microscopy images showed the dense morphology, and large piezoresponses were observed in the piezoelectric force microscope measurements. The best local piezoelectric coefficient, value of 259 pm V−1, was observed in the BFBT40 thin film. This result is one of the best values in lead-free piezoelectric thin films with a simple geometry. The BFBT40 piezoelectric thin film can be considered as a strong candidate to replace lead-based piezoelectric thin films for piezoelectric-based microelectromechanical systems.

Selectively activated inorganic synaptic devices, showing a high on/off ratio, ultrasmall dimensions, low power consumption, and short programming time, are required to emulate the functions of high-capacity and energy-efficient reconfigurable human neural systems combining information storage and processing (Li et al. Sci. Rep. 2014, 4, 4096). Here, we demonstrate that such a synaptic device is realized using a Ag/PbZr0.52Ti0.48O3 (PZT)/La0.8Sr0.2MnO3 (LSMO) ferroelectric tunnel junction (FTJ) with ultrathin PZT (thickness of ∼4 nm). Ag ion migration through the very thin FTJ enables a large on/off ratio (107) and low energy consumption (potentiation energy consumption = ∼22 aJ and depression energy consumption = ∼2.5 pJ). In addition, the simple alignment of the downward polarization in PZT selectively activates the synaptic plasticity of the FTJ and the transition from short-term plasticity to long-term potentiation.

Highly nonlinear bistable current-voltage (I–V) characteristics are necessary in order to realize high density resistive random access memory (ReRAM) devices that are compatible with cross-point stack structures. Up to now, such I–V characteristics have been achieved by introducing complex device structures consisting of selection elements (selectors) and memory elements which are connected in series. In this study, we report bipolar resistive switching (RS) behaviours of nano-crystalline BiFeO3 (BFO) nano-islands grown on Nb-doped SrTiO3 substrates, with large ON/OFF ratio of 4,420. In addition, the BFO nano-islands exhibit asymmetric I–V characteristics with high nonlinearity factor of 1,100 in a low resistance state. Such selector-free RS behaviours are enabled by the mosaic structures and pinned downward ferroelectric polarization in the BFO nano-islands. The high resistance ratio and nonlinearity factor suggest that our BFO nano-islands can be extended to an N × N array of N = 3,740 corresponding to ~107 bits. Therefore, our BFO nano-island showing both high resistance ratio and nonlinearity factor offers a simple and promising building block of high density ReRAM.

We report the impact of intrinsic defects in epitaxial BiFeO3 films on charge conduction and resistive switching of Pt/BiFeO3/SrRuO3 capacitors, although the BiFeO3 films show very similar ferroelectric domain types probed by piezoresponse force microscopy. Capacitors with p-type Bi-deficient and n-type Bi-rich BiFeO3 films exhibit switchable diode and conventional bipolar resistive switching behaviors, respectively. Both the capacitors show good retention properties with a high ON/OFF ratio of >100 in Bi-deficient films and that of >1000 in Bi-rich films. The present investigation advances considerably understanding of interface control through defect engineering of BiFeO3 thin films for non-volatile memory application.