Showing papers in "Electronic Materials Letters in 2021"

Colorimetric Sensors for Toxic and Hazardous Gas Detection: A Review

Abstract: Since the industries are vastly rising, the threat of toxic and hazardous substance to human beings and demands of the accurate sensor is increasing. Colorimetric sensors that detect substances by measuring the absorbance or fluorescence spectra shift are one of the most emerging strategies these days. However, conventional colorimetric gas sensors are limited to specific application due to the limitation of detecting only liquid phase substances. For practical applications of the colorimetric sensors, it is necessary to detect low concentrations of toxic and hazardous substances in gaseous media. Besides, operation with low power consumption and excellent selectivity and sensitivity should be considered for Internet of Things (IoT) application. In this paper, various efforts on the investigation of several materials, including dyes, polymers, metal–organic complexes, and metal oxides as active sensor elements of the colorimetric gas sensors for IoT application are summarized. This paper also reviews various kinds of colorimetric gas sensor that exhibit great sensing properties to toxic and hazardous gases and introduce a brief overview of the challenges of colorimetric gas sensors as a candidate for future IoT gas sensor technology.

Transparent Electrode Techniques for Semitransparent and Tandem Perovskite Solar Cells

Abstract: Inorganic–organic halide perovskite solar cells have attracted significant attention to the photovoltaic community considering their high-efficiency, tunable bandgap, low-cost, and easy fabrication. Perovskite solar cells are especially an attractive top cell partner for tandem applications with silicon bottom cells and other solar cell types with lower bandgap absorbers. For such tandem applications, semitransparent perovskite solar cell techniques with high near-infrared transparency become important, since the incident light needs to efficiently reach the bottom cell. This review article will summarize the status and progress of perovskite-based tandem solar cells development, while focusing on the transparent electrode approaches and techniques. Future directions and challenges of transparent electrodes for semitransparent and tandem perovskite-based photovoltaics will also be discussed.

Additive Effects of Copper and Alkali Metal Halides into Methylammonium Lead Iodide Perovskite Solar Cells

Abstract: Fabrication and characterization of methylammonium lead iodide perovskite solar cells incorporated with formamidinium iodide, copper halides, alkali metal halides and decaphenylcyclopentasilane were performed. Addition of CuCl and KI at 2% into the perovskite layer offered compact morphologies and crystal orientation in the perovskite layer, improving short circuit current densities, series resistance and open-circuit voltages related to conversion efficiencies. The stabilities of conversion efficiencies were improved for the perovskite layer incorporated with 2% CuCl and 2% NaI. The stabilities depended on the state of the surface morphologies and crystal orientation while suppressing decomposition reaction in the perovskite layer. The photovoltaic mechanisms were associated with promotion of carrier generation and diffusion in the crystalline layer. The electronic correlation was based on the charge transfer between 5p orbital of I ion and 3d orbital of Cu ion near valence band, promoting the carrier generation and diffusion related to the short circuit current densities.

Combined Experimental and DFT-TDDFT Characterization Studies of Crystalline Mesoporous-Assembled [ZrO2]NPs and [DPPP + Gly/ZrO2]C Nanocomposite Thin Film

Abstract: [(Z)-2-((1,3-bis(diphenyl phosphaneyl) propylidene) amino) acetic acid/Zirconium oxide nanoparticles] composites thin film [DPPP + Gly/ZrO2]C is synthesized by utilizing physical vapor deposition (PVD) with a speed rate of 2000 rpm/30 s. The optimization of the samples was performed using density functional theory (DFT) by DMol3 and Cambridge Serial Total Energy Package (CASTEP) program. The [DPPP + Gly/ZrO2]C nanocomposite thin film is examined by different techniques including scanning electron microscope (SEM), X-ray diffraction (XRD), proton nuclear magnetic resonance (1HNMR), and Fourier transform infrared (FT-IR). The [DPPP + Gly/ZrO2]C nanocomposite thin film with the thickness (150 ± 5 nm) is fabricated at optimization conditions. The optical constants (refractive index, $$n\left(\lambda \right)$$ , extinction coefficient, $$k\left(\lambda \right)$$ , dielectric constants ( $${\epsilon }_{1}\left(\lambda \right)$$ and $${\epsilon }_{2}\left(\lambda \right)$$ ) and optical conductivity ( $${\sigma }_{1}\left(\lambda \right)$$ and $${\sigma }_{2}\left(\lambda \right)$$ )) for [DPPP + Gly/ZrO2]C nanocomposite thin film are computed and compared by using experiment and CATSTEP methods. The optical properties of simulated FTIR, XRD, and CATSTEP of the considered fiber nanocomposites are in somewhat compatible with the experimental study. The nano nanocomposite thin films present a promising result to be a good candidate for optoelectronics and solar cell applications.

Toward Understanding the Adsorption And Inhibition Mechanism of Cu-MBTA Passivation Film on Copper Surface: A Combined Experimental and DFT Investigation

Abstract: The adsorption and passivation reactions of 5-methyl benzotriazole (MBTA) with different copper samples (as received, citric acid treated and citric acid and KIO4 treated) were studied. The experiments were characterized by contact angle measurement, potentiodynamic polarization curve, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. The results showed that the adsorption behavior of MBTA on different treated surfaces was different and MBTA was preferentially adsorbed on the surface of citric acid treated copper. Based on the density functional theory, quantum chemical descriptors such as the frontier molecular orbital energies EHOMO, ELUMO and the energy gap between them, molecular electrostatic potential, and Fukui function had been calculated and discussed. The adsorption mechanism of MBTA and copper surface was further revealed, which had positive significance for the corrosion inhibition of copper surface in copper interconnection CMP.

Morphological and Electrical Properties of β-Ga2O3/4H-SiC Heterojunction Diodes

Abstract: s-Ga2O3/4H-SiC heterojunction diodes were fabricated by depositing β-Ga2O3 thin films on 4H-SiC substrates using radio frequency sputtering. X-ray diffraction (XRD) analysis revealed increased reflectivity of β-Ga2O3 ( $$\overline{4 }$$ 02), ( $$\overline{2 }$$ 02) and ( $$\overline{6 }$$ 03) crystal planes with optimized sputtering power. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were performed to confirm grain size and distribution. The Hall mobility (30.16 cm2/V $$\bullet$$ s) and carrier concentration (3.14 $$\times$$ 1014 cm–3) showed with large and homogeneous grain distribution thin films. For these thin films, mobility and carrier concentration value could improve up to 9% and 55%. The effect of these electrical characteristics was ascribed to reduction of the grain boundary scattering. The I–V characteristics along with Hall measurement of the heterojunction diode suggest that the improvement in the threshold voltage and current density is caused by a substantial enhancement in charge carrier mobility.

Self-Supported Phosphorus-Doped Vertically Aligned Graphene Arrays Integrated with FeCoNiP Nanoparticles as Bifunctional Electrocatalysts for Water-Splitting Over a Wide pH Range

Abstract: Self-supported non-noble metal based bifunctional electrocatalysts with high catalytic activity and long-term stability in a wide pH range are highly essential for the production of hydrogen and oxygen, remains a great challenge. Herein, a bifunctional electrocatalyst is synthesized via electroless plating of FeCoNiP nanoparticles on self-supported phosphorus-doped vertically aligned graphene arrays (FeCoNiP/P-VG). FeCoNiP/P-VG exhibits an exceptionally high catalytic activity for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in a wide pH range, with an overpotential of 81 and 141 mV for HER, and 240 and 409 mV for OER, in 1.0 M KOH and 0.5 M H2SO4 respectively, at current density of 10 mA. It also performs quite low Tafel slope value of 40 mV·dec−1 for HER and 69 mV·dec−1 for OER in 1.0 M KOH. More importantly, it shows prominent stability in acidic and alkaline electrolytes. This study may open a new avenue for the design and fabrication of self-supported bifunctional electrocatalysts for water splitting.

Effect of ALD- and PEALD- Grown Al2O3 Gate Insulators on Electrical and Stability Properties for a-IGZO Thin-Film Transistor

Abstract: This study investigated the electrical and stability characteristics of Al2O3 as a gate insulator, which was deposited by various atomic layer deposition methods in top-gate staggered amorphous InGaZnO (a-IGZO) thin film transistors. A trimethylaluminum precursor was used as an Al source, and H2O gas (H2O device) and O2 plasma with a long plasma time (O2 LP device) and a short plasma time (O2 SP device) were used as oxidants. The initial electrical characteristics, including the hysteresis, on–off current ratio, and subthreshold swing, were superior in the H2O device compared to the O2 LP and O2 SP devices. In the positive bias stress (PBS) results, the degradation characteristics showed a tendency similar to the transfer properties. However, under the negative bias illumination stress (NBIS), the stability of the H2O device was significantly reduced compared to the O2 LP and O2 SP devices. In this paper, the mechanism of instability, which has opposite results in terms of the PBS and NBIS for the three devices, was identified using capacitance–voltage, three-terminal charge pumping as electrical analysis techniques and secondary ion mass spectroscopy (SIMS) as a physical analysis technique. It was confirmed that the surface oxidation of a-IGZO deteriorates the interfacial properties, causing the transfer characteristics to degrade. The carbon of the Al2O3 film identified via SIMS analysis acts as a trap layer, causing deterioration in the PBS. Alternatively, in the NBIS, it was observed that the carbon acts as a capture site for photo-excited holes, thereby promoting device stability.

Confined Growth of High-quality Single-Crystal MAPbBr3 by Inverse Temperature Crystallization for Photovoltaic Applications

Abstract: Organic–inorganic hybrid halide perovskite solar cells are promising for next-generation thin-film solar cells, demonstrating power conversion efficiency exceeding 25% In particular, single-crystal perovskite materials are estimated to possess superior optoelectronic properties that can further enhance the efficiency However, fabricating thin single-crystal perovskite for a light-absorber layer remains challenging In this study, a 40-µm-thick single-crystalline MAPbBr3 perovskite is fabricated by inverse temperature crystallization (ITC) with a selective seed-transfer technique By using a separate seed growth process and a seed-transfer process, a 1623-mm2-large single domain high-quality single-crystalline MAPbBr3 perovskite can be grown without additional nucleation The grown single-crystal MAPbBr3 exhibits a low surface roughness of 051 nm and low trap density of 761 × 108 cm−3 We also fabricate solar cells with single-crystalline MAPbBr3 using a glass substrate coated with SnO2 and indium-tin-oxide thin films The single-crystal MAPbBr3-based solar cells demonstrate a power conversion efficiency of 431%

Large-Dimensional Organic Semiconductor Crystals with Poly(butyl acrylate) Polymer for Solution-Processed Organic Thin Film Transistors

Abstract: Despite solution processed organic semiconductors have attracted much research attention, the randomized crystallization and large prevalence of grain boundary remain as a challenge to realize high performance organic electronic applications. In this work, we report the incorporation of poly(butyl acrylate) polymer additive with organic semiconductors with the mediation of a solvent vapor annealing method in order to modify the nucleation and crystal growth process. As 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was experimented as a benchmark semiconductor, we demonstrated that the TIPS pentacene/poly(butyl acrylate) mixture exhibits rigidly aligned crystals, large grain width and improved areal coverage. In particular, thin film morphological characterization indicated a substantial reduction in misorientation angle by approximately two orders of magnitude as well as a 5-fold enlargement of grain width. A grain boundary model is proposed as a theoretic basis to understand the connection between grain width and hole mobility. Bottom-gate, top-contact thin film transistors based on TIPS pentacene/poly(butyl acrylate) blends demonstrated enhanced hole mobility of up to 0.11 cm2/Vs.

Implementation of In–Ga–Zn–O Thin-Film Transistors with Vertical Channel Structures Designed with Atomic-Layer Deposition and Silicon Spacer Steps

Abstract: Vertical channel thin film transistors (VTFTs) using silicon (Si) spacer steps and In–Ga–Zn–O (IGZO) active channels were demonstrated. The Si spacer step was strategically introduced from the viewpoint of a new structural design to secure the surface quality of the back-channel region of the nanoscale IGZO VTFTs. The vertical sidewalls of the Si spacer were patterned via plasma etching technique using CF4/O2 gas mixtures with controlled process conditions. The atomic layer deposition (ALD) was found to be one of the most important process parameters to obtain promising device operations of the fabricated IGZO VTFTs. The device parameters of drain current on/off ratio, carrier mobility at linear region, and subthresholde swing for the IGZO VTFT with a channel length of 250 nm were obtained to be 6.9 × 107, 3.21 cm2/Vs, and 460 mV/dec, respectively. The fabricated VTFT also showed negligible variations in threshold voltage against the gate bias stresses of ± 1 MV/cm for 104 s. The introduction of Si spacer steps and the IGZO channels prepared by conformal ALD could be presented as effective methodologies for implementing highly-functional nanoscale IGZO VTFTs.

Development of a Highly Flexible Composite Electrode Comprised of Ti3C2-Based MXene Nanosheets and Ag Nanoparticles

Abstract: To fabricate electrodes for use in flexible electronic devices with improved resistance to the mechanical stresses induced by repeated bending, we developed a highly flexible and conductive composite comprised of Ti3C2-based MXene nanosheets and Ag nanoparticles. Specifically, we synthesized Ti3C2-based MXene nanosheets and added them as a second filler to an Ag dispersion to fabricate Ag–MXene composite paste. Although the synthesized MXene nanosheets are somewhat less electrically conductive than pure Ag nanoparticles, the conductivity of the pattern formed by printing this composite paste was comparable to that of pure Ag nanoparticle-based electrode. Moreover, resistance in the resulting electrode remained fairly constant despite repeated bending employing a curvature radius of 2 mm. We attribute this to the presence of the MXene nanosheets, whose homogeneously distributed hydroxyl or oxygen terminate surface functional groups prevented or delayed the propagation of cracks inside the printed pattern despite repeated bending.

Enhanced capacity retention based silicon nanosheets electrode by CMC coating for lithium-ion batteries

Abstract: Si nanosheets (SiNS) as two dimensional Si nanomaterials are promising candidates for anodes of lithium ion batteries (LIBs) by their large surface area and excellent mechanical durability. In this study, we fabricated polymeric binder (carboxymethyl cellulose, CMC) coated SiNS electrodes using a spin-coating process and characterized the electrochemical properties. The CMS coated SiNS electrodes were homogeneously covered with a CMC polymer layer and showed the improved capacity retention with maintaining over 90% of initial capacity after several cycles. The result of electrochemical impedance spectroscopy indicates that the CMC layer provide the chemical stability of Si surface and suppress the continuous growth of the SEI layer. Furthermore, CMC coated layer on SiNS provide improved mechanical stability that maintains the adhesion of SiNS to the current collector during the discharge–charge cycles.

Characteristics of Copper Nitride Nanolayer Used in 3D Cu Bonding Interconnects

Abstract: Cu–Cu bonding is a key process in fine pitch Cu interconnect in 3-dimenssional Si integration. Despite the excellent electrical property and pattern ability of Cu material, the Cu–Cu bonding process is affected by the high bonding temperature and easy oxidation. Thus, the ability to protect the copper surface in a reactive air environment is very important in Cu–Cu bonding, especially for die–to–wafer Cu bonding applications. We studied Cu–Cu bonding using a copper nitride nanolayer as an antioxidant passivation layer and investigated the stability of the copper nitride nanolayer over 7 days and its decomposition capability across temperatures of up to 400 °C. We found that the copper nitride (Cu4N) nanolayer formed by two-step Ar/N2 plasma treatment protected the copper surface from further oxidation in the air, and that the energy required for thermal decomposition of the copper nitride nanolayer in this study was about 29.6 kJ/mol. It can be seen that the bonding temperature of Cu–Cu bonding can be sufficiently lowered by using a low–temperature decomposition property of copper nitride.

Effects of Se Doping on Thermoelectric Properties of Tetrahedrite Cu 12 Sb 4 S 13−z Se z

Abstract: Tetrahedrite Cu12Sb4S13 is composed of abundant non-toxic components and has attracted attention as a promising thermoelectric material with low thermal conductivity at intermediate temperatures. The carrier concentration can be optimized by doping (substituting), thereby maximizing its power factor and reducing its thermal conductivity. In this study, Cu12Sb4S13−zSez (z = 0.1–0.4) compounds were synthesized using mechanical alloying and hot pressing. Our objective was to maintain a high power factor through Se doping and to reduce the lattice thermal conductivity through additional phonon scattering. X-ray diffraction analysis revealed that the lattice constant increased with an increase in Se substitution for the S sites, and all the specimens appeared as a single tetrahedrite phase. As the Se doping level increased, the carrier (hole) concentration decreased while the mobility increased. The Hall and Seebeck coefficients were both positive, indicating that Se-doped tetrahedrites exhibit p-type conduction. As the Se substitution increased, the electrical conductivity decreased, but the Seebeck coefficient increased. In addition, Se doping lowered both, the electronic and lattice thermal conductivities, which resulted in decreased thermal conductivity. A maximum dimensionless figure of merit (ZT) of 0.87 was obtained at 723 K for Cu12Sb4S12.8Se0.2 with a high power factor of 0.96 mW m−1 K−2 and a low thermal conductivity of 0.77 W m−1 K−1.

Charge Transport and Thermoelectric Properties of Ge-Doped Famatinites Cu3Sb1−yGeyS4

Abstract: Ge-doped famatinites Cu3Sb1−yGeyS4 (0 ≤ y ≤ 0.1) were prepared by mechanical alloying and hot pressing. The phase transition, microstructure, charge transport properties and thermoelectric properties were examined in accordance with the Ge content. The famatinites were maintained as a single phase with a tetragonal structure at temperatures below their melting point without secondary phases. The melting points of Cu3SbS4 and Cu3Sb0.92Ge0.08S4 were 817 and 819 K, respectively. The hot-pressed specimens exhibited high relative densities of 98.3–99.5%. The a-axis and c-axis were decreased from 0.5386 to 0.5378 nm and from 1.0744 to 1.0719 nm, respectively, by doping Sb sites with Ge. Both intrinsic and Ge-doped famatinites exhibited positive Hall and Seebeck coefficients. The carrier concentration and mobility of Cu3SbS4 were 2.2 × 1018 cm−3 and 1.6 cm2 V−1 s−1, but those of Ge-doped specimens increased to (0.4–3.3) × 1019 cm−3 and 29–71 cm2V−1 s−1, respectively. Cu3SbS4 exhibited non-degenerate semiconductor characteristics and demonstrated a dimensionless figure of merit, ZT, of 0.1 at 623 K owing to a power factor of 0.14 m Wm−1 K−2 and a thermal conductivity of 0.62 Wm−1 K−1. However, the Ge-doped specimens exhibited degenerate semiconductor behaviors, and Cu3Sb0.92Ge0.08S4 exhibited the highest ZT of 0.55 at 623 K owing to a power factor of 0.64 m W m−1 K−2 and a thermal conductivity of 0.72 Wm−1 K−1.

Ag-Deposited Porous Silicon as a SERS-Active Substrate for the Sensitive Detection of Catecholamine Neurotransmitters

Abstract: The sensitive detection of various neurotransmitters is very useful in diagnosing diseases related to the dysfunction of the neurotransmitter system. Surface-enhanced Raman scattering (SERS) is one of the best methods for bio-analyte detection as it provides a molecular fingerprint at a trace concentration level. In this study, Ag-deposited porous silicon (Ag@pSi) was fabricated as a SERS-active substrate via metal-assisted chemical etching and electroless plating methods. Dopamine (DA) and norepinephrine (NE) neurotransmitters were tested as probing analytes. The Ag@pSi substrate demonstrated the sensitive detection of the neurotransmitters (DA and NE) over the wide concentration range (from 10‒6 to 10‒10 M), with a good linearity between the intensity of specific Raman peak and the log-scale concentration. The Ag@pSi substrate also distinguished the individual analytes in a mixture of DA and NE at 10‒8 M, confirming the efficacy of the developed SERS substrate for the selective detection of neurotransmitters.

Electronic Band Transitions in γ-Ge3N4

Abstract: Electronic band structure in germanium nitride having spinel structure, γ-Ge3N4, was examined using two spectroscopic techniques, cathodoluminescence and synchrotron-based photoluminescence. The sample purity was confirmed by x-ray diffraction and Raman analyses. The spectroscopic measurements provided first experimental evidence of a large free exciton binding energy De≈0.30 eV and direct interband transitions in this material. The band gap energy Eg = 3.65 ± 0.05 eV measured with a higher precision was in agreement with that previously obtained via XES/XANES method. The screened hybrid functional Heyd–Scuseria–Ernzerhof (HSE06) calculations of the electronic structure supported the experimental results. Based on the experimental data and theoretical calculations, the limiting efficiency of the excitation conversion to light was estimated and compared with that of w-GaN, which is the basic material of commercial light emitting diodes. The high conversion efficiency, very high hardness and rigidity combined with a thermal stability in air up to ~ 700 °C reveal the potential of γ-Ge3N4 for robust and efficient photonic emitters.

Chlorine‐Based High Density Plasma Etching of α-Ga2O3 Epitaxy Layer

Abstract: High density plasma etching of α-Ga2O3 epitaxy layer was performed in chlorine-based (Cl2/Ar and BCl3/Ar) inductively coupled plasmas (ICPs) and the effect of plasma composition, ICP source power and rf chuck power on the etch rate and surface morphology has been studied. The α-Ga2O3 etch rate increased as Cl2 or BCl3 content in the gas mixture and ICP source power increased, and Cl2/Ar ICP discharges produced higher etch rates than BCl3/Ar discharges under the conditions examined. Increasing rf chuck power was found to increase the α-Ga2O3 etch rate and to improve surface morphology of the etched field. The highest etch rates of ~ 612 A/min and ~ 603 A/min were obtained in 13Cl2/2Ar and 13BCl3/2Ar ICP discharges under a moderate source power (500 W) and rf chuck power (250 W) condition, respectively. Anisotropic pattern transfer with a vertical sidewall was performed into the α-Ga2O3 layer using a 10Cl2/5Ar ICP discharge.

Dependence of the Generation Behavior of Charged Nanoparticles and Ag Film Growth on Sputtering Power during DC Magnetron Sputtering

Abstract: Effects of sputtering power on the deposition rate and microstructure, crystallinity, and electrical properties of Ag films during direct current (DC) magnetron sputtering are investigated. Thin films (~ 100 nm) are deposited at sputtering powers of 10, 20, 50, 100, 200 and 300 W and analyzed by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and a four-point probe. The film deposited at a sputtering power of 10 W has the lowest growth rate, but the highest crystalline quality, with the lowest full width at half maximum (FWHM) and the lowest resistivity. The film deposited at a sputtering power of 200 W has the highest growth rate, and the second best crystalline quality in view of FWHM and resistivity. The film deposited at a sputtering power of 50 W has the moderate growth rate, and the worst crystalline quality in view of FWHM and resistivity. High-resolution TEM observations reveal that films deposited at sputtering powers of 10 and 200 W have far fewer defects, such as grain boundaries, dislocations and stacking faults than those deposited at a sputtering power of 50 W. Such deposition behavior could be explained by sputtering power, which affected the generation of the charged nanoparticles. And the high quality of films could be obtained at a high deposition rate, in which charge plays an important role.

Improving Dielectric Properties in Novel P(VDF-HFP)/V2AlC MAX/Montmorillonite Composite Films via Interfacial Electric-Leakage Depressing Strategy

Abstract: Dielectric constants of polymer/conductor composites are often high, owing to strong interface interaction in those composites. They can be used for dielectric energy storage, but they usually have high dielectric loss and conductivity. In order to reduce the dielectric loss and conductivity in poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP))/V2AlC MAX composites, in this study, we explored the novel P(VDF-HFP)/V2AlC MAX/montmorillonite (MMT) ternary composites. Compared with binary composites, the ternary composites showed the mildly reduced dielectric constant, significantly decreased dielectric loss and conductivity. Using highly-conductive V2AlC MAX filler aimed at taking advantage of the polymer/MAX interface polarization to increase the dielectric response of composites. Employing well-insulating MMT filler aimed at reducing the interface electric leakage conduction. At 1 kHz, the outstanding ternary composite with 2 wt% MMT and 20 wt% MAX could exhibit a high dielectric constant of ca. 27 and low dielectric loss of ca. 0.21. This work might offer a new research idea for the construction of high-performance composite dielectric films containing modern MAX ceramic fillers.

Fabrication of h-BN Filled Epoxy-Based Thermally Conductive Adhesive Tapes Containing Cyclic Carbonate-Terminated Oligomers

Abstract: Thermally conductive (TC) adhesive tapes consisting of adhesives and TC fillers are widely used as thermal interface materials because of their tack properties for temporary fixation and high peel strength for permanent bond. However, the trade-off between peel strength and thermal conductivity with increasing filler loading impedes the manufacture of high-performance TC tapes. Therefore, a technique to realize high thermal conductivity of TC adhesives with lower filler loading is crucial. In this study, epoxy-based adhesives (EAs) was used to fabricate TC adhesive tapes. To secure high peel strength of EAs, a cyclic carbonate-terminated oligomer (CCO) was synthesized and employed as a component. The simultaneous reactions between epoxy resin, CCO and curing agent were analyzed using FTIR spectroscopy. Thanks to tack, the partially cured EAs could be used to fabricate tapes which were temporarily fixed and then permanently bonded via complete curing. Next, EAs and h-BN fillers were admixed to produce TC adhesive tapes. Because h-BN fillers were partially aligned to the in-plane direction by bar-coating, the in-plane thermal conductivity of the TC-1 adhesive containing only 20 wt% h-BN fillers was as high as 2.73 W/m K, which was slightly lower than that (2.97 W/m⋅K) of the TC-4 adhesive containing 35 wt% h-BN fillers. In addition, the peel strength of the TC-1 adhesive tape reached 2307 (± 64) gf/in.

High-Performance Liquid Chromatography for Determining a Mixture of Nonsteroidal Anti-inflammatory Drugs

Abstract: Nonsteroidal anti-inflammatory drugs (NSAIDs), which block the activity of cyclooxygenase (COX) isoenzymes and inhibit the synthesis of prostaglandin, have been used for pain relief. For the enhancement of the potency or the decrease of side-effects, NSAIDs are normally prescribed as a mixture with other chemical components including caffeine and proton pump inhibitor. Here, we developed a method to separate a mixture of three NSAIDs, such as aspirin, paracetamol, and naproxen, using reverse-phase high-performance liquid chromatography (RP-HPLC). An isocratic mobile phase consisting of acidic water and acetonitrile was selected to run at a low flow rate, such as 0.8 mL/min. The mixture of three NSAIDs was injected at a low volume into a C18 column having 150 mm in length and characterized using a UV detector at 230 nm. We identified three peaks in the chromatogram indicating three compounds. The elution time of the peaks was less than 10 min. The method proposed here can be used for identification of the combination of NSAIDs.

Thermoelectric Properties of Te-doped In0.9Si0.1Se with Enhanced Effective Mass

Abstract: 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.

Thermally Enhanced Boron Nitride Nanotube/reduced Graphene Oxide Paper and Their Application

Abstract: We demonstrated the thermally robust reduced graphene oxide (rGO)/boron nitride nanotube (BNNT) papers and their application in electromagnetic interference shielding. In order to overcome the thermal durability shortcomings of electromagnetic wave shielding paper based on rGO nanomaterial, rGO/BNNT electromagnetic interference (EMI) shielding paper having excellent thermal durability could be manufactured using BNNT nanomaterials having excellent chemical and thermal stability at high temperature. With the addition of a little BNNT, the durability against temperature can be increased by more than two times while there is little reduction in EMI performance.

Characterization of Silver Nanowire Flexible Transparent Electrode with Grid Pattern Formed via Thermocompression

Abstract: In this study, we present a new and simple method that utilizes post-processing such as thermal treatment and mechanical compression to manufacture a grid patterned silver nanowire (AgNW) flexible transparent electrode with low sheet resistance, high transmittance, and high flexibility. The effects of thermal treatment and mechanical compression on the structural, optical, and electrical properties of AgNW deposited by bar coating have been analyzed as a function of temperature and pressure. It was discovered that there is a critical thermal treatment temperature (Tc) that determined the abrupt change—decreasing, then rapidly increasing—in the sheet resistance of AgNW. When additional pressure was applied during thermal treatment, Tc was lowered. The cohesion between AgNW wires was improved by thermal treatment below Tc, and further strengthened when pressure was applied simultaneously with heat. However, when thermal treatment was performed above Tc, the unique wire structure of AgNW collapsed. It has also been found that heat treatment and mechanical compression improve the flexibility of AgNW.

Structural, Magnetic and Dielectric Properties of Perovskite (Tb 0.874 Mn 0.106 )Mn 1-x Ni x O 3-δ

Abstract: (Tb0.874Mn0.106)Mn1−xNixO3−δ (0.0 ≤ x ≤ 0.20) solid solutions have been synthesized by solid state method. They all crystallize in orthorhombic Pnma space group with perovskite structure at room temperature. The unit cell volume decreases with an increase of Ni in (Tb0.874Mn0.106)Mn0.80Ni0.20O3−δ. The samples show two magnetic orderings. The temperature dependent dielectric constant shows an abnormal step like increase for all the solid solutions. The dielectric constants decrease with an increase in frequency. The activation energies calculated from dielectric loss are related to the oxygen vacancies in the samples.

Tungsten Oxide-Modified ITO Electrode for Electrochromic Window Based on Reversible Metal Electrodeposition

Abstract: Reversible metal electrodeposition (RME) windows are a promising material for electrochromic windows and electronic display applications. However, the lifetime of RME devices is a major drawback in the preparation of commercial and practical devices. In this study, we propose a new strategy to prolong the stability and improve the efficiency of RME devices. By using tungsten oxide, a well-known electrochromic material, to modify the surface of a transparent conductive electrode, superior, stable, and highly effective devices were prepared successfully. By applying a low potential of − 0.8 V to 0.5 V, the RME device can quickly switch between a bleached state and colored state with different colors changing from transparent to black and deep blue. The performance improvement of the RME device can be explained by the simultaneous reduction of tungsten oxide and metal ion deposition in the conductive substrate under an applied potential. Furthermore, the lifetime of the device increased significantly (over 1500 cycles) owing to the shielding role of tungsten oxide film in the acid medium, which is an indispensable component of reversible electrochromic devices. Recently, reversible metal electrochromic (RME) windows are promising electrochromic device (ECD) due to simple process, low cost, and fast response. However, the main drawback of RME devices is their instability caused by the erosion of conductive electrode in an electrolyte-acidic medium. Therefore, developing stable, effective, and noble-metal-free RME devices is a tough challenge in the development of ECDs. In this study, a well-known electrochromic material, tungsten oxide (WO3), was successfully employed to modify the surface of a transparent conductive electrode (TCE)-the indispensable part for ECDs, which plays an important role as a shield of TCE electrode. ECD fabricated using WO3 modified TCE had an extremely prolonged lifetime (over 1500 cycles) compared with ECD prepared by using bare TCE. The efficiency of ECD also increased significantly owing to the electrochromic performance of WO3 that took place simultaneously with reversible metal deposition in the redox process. Therefore, WO3 modified conductive electrodes are a great candidate for enhancing the performance of ECD.

Charging Compensation Layer on Polyimide for Enhanced Device Stability in Flexible Technology

Abstract: In this paper, we propose a structure that prevents the charging effects that occur in devices fabricated on polyimide (PI) substrates. In general, when fabricating a device on a PI substrate, an inorganic barrier layer is first deposited to prevent penetration of oxygen and moisture. In this study, we confirmed that fluorine ions were induced from PI by bias stress and proposed a SiOCH/SiO2 double layer as a barrier to prevent charging. Then, Al/PI/SiO2/Al and Al/ PI/SiOCH/SiO2/Al metal–insulator–metal capacitors were manufactured. The capacitor characteristics before and after application of bias stress were verified through current–voltage (I–V) and capacitance–voltage (C–V), which are electrical characterization methods, and secondary ion mass spectrometry (SIMS), which is a physical analysis method. As the voltage increased, the capacitance and current of the Al/PI/SiO2/Al capacitor varied, but those of the Al/PI/SiOCH/SiO2/Al device did not change. Finally, SIMS analysis confirmed that the PI-derived fluorine ions replaced the Si–CH3 bonds within the SiOCH film with Si–F bonds, thereby preventing capacitance and current fluctuations.