This work investigated the effects of different conductive agents on the electrochemical properties of anodes. SiOx possesses high theoretical capacity and shows excellent cycle performance; however, the low initial coulombic efficiency and poor electrical conductivity limit its applications in real batteries. In this study, electrodes were fabricated using two different conductive agents, and the resulting physical and electrochemical properties were analyzed. SEM observations confirmed the formation of a CNT conductive network throughout the electrodes, while the electrical conductivity contributed to the electrode was confirmed by impedance measurements. Thus, the electrode fabricated with the CNT conductive agent showed greater capacity and superior cycle performance than did the electrode fabricated using the DB conductive agent.
Advances in laser technology have enabled ultra-high-speed ultra-precise processing, thus expanding potential applications to the semiconductor, medical, and photovoltaic industries. In particular, laser scribing technology has been applied to the production of shingled solar modules. In this work, we analyze the effect of laser scribing conditions, e.g., scribing depth, on the characteristics of the resulting divided solar cells. When the scribing depth was greater than 100 ㎛, the solar cells were well separated. In addition, the desired scribing depths were reached in fewer scans when the laser spot overlap was 100%. The efficiency of the divided cells decreased due to the high series resistance at scribing depths of less than 100 ㎛. However, at scribing depths of approximately 100 ㎛, the series resistance was low and efficiency reduction was minimized.
Single-crystal diamond obtained by chemical vapor deposition (CVD) exhibits great potential for use in next-generation power devices. Low defect density is required for the use of such power devices in high-power operations; however, plastic deformation and lattice strain increase the dislocation density during diamond growth by CVD. Therefore, characterization of the dislocations in CVD diamond is essential to ensure the growth of high-quality diamond. In this work, we analyze the characteristics of the dislocations in CVD diamond through synchrotron white beam X-ray topography. In estimate, many threading edge dislocations and five mixed dislocations were identified over the whole surface.
In this study, photoluminescence (PL) analysis was performed to evaluate the optical properties of commercial ZnO substrates. Particular attention was paid to the bound exciton (BX) luminescence, which is usually the strongest emission intensity of commercial substrates. At 15 K, PL analysis revealed that the BX peak due to donor-type impurities (donor-bound-exciton; DX) dominated, while two-electron satellite (TES) emission, donor-accepter pair (DAP) emission, and LO-phonon replica emission were also observed. The impurity concentration of the ZnO substrate was determined to be 1015 to 1016/cm3 by examination of the temperature variation of DAP, while the half width and intensity change of the luminescence revealed that the temperature change of BX can be interpreted almost the same as the analysis of free-exciton emission.
This report constitutes the first demonstration in Korea of single-crystal lateral gallium oxide (Ga2O3) as a metal-oxide-semiconductor field-effect-transistor (MOSFET), with a breakdown voltage in excess of 480 V. A Si-doped channel layer was grown on a Fe-doped semi-insulating β-Ga2O3 (010) substrate by molecular beam epitaxy. The single-crystal substrate was grown by the edge-defined film-fed growth method and wafered to a size of 10×15 mm2. Although we fabricated several types of power devices using the same process, we only report the characterization of a finger-type MOSFET with a gate length (Lg) of 2 μm and a gate-drain spacing (Lgd) of 5 μm. The MOSFET showed a favorable drain current modulation according to the gate voltage swing. A complete drain current pinch-off feature was also obtained for Vgs<-6 V, and the three-terminal off-state breakdown voltage was over 482 V in a Lgd＝5 μm device measured in Fluorinert ambient at Vgs＝-10 V. A low drain leakage current of 4.7 nA at the off-state led to a high on/off drain current ratio of approximately 5.3×105. These device characteristics indicate the promising potential of Ga2O3-based electrical devices for next-generation high-power device applications, such as electrical autonomous vehicles, railroads, photovoltaics, renewable energy, and industry.
A flat-type piezoelectric ceramic ultrasonic transmitter was successfully fabricated for application in acoustic devices with cone-free diaphragms. The transmitter, possessing a center frequency of 40.6 kHz, exhibited a higher displacement characteristic for a multilayer type compared with a single layer type. Surface roughness treatment of an Al elastic diaphragm influenced a slight increase (1.1 dB) in the sound pressure level (SPL) at 10 Vrms due to the enlarged surface area. The fabricated multilayer piezoelectric ceramic ultrasonic transmitter showed increasing SPL with increasing input voltage, with a maximum SPL of approximately 123.6 dB at 10 Vrms. This implies a doubly increased SPL density of 3.6 dB/mm3, superior to that of a commercial open-type transmitter with a cone.
In this study, a high-temperature vulcanizing (HTV) method was used to achieve a shore a hardness of 70. The basic base was composed of 60% silicon gum (GUM) which is a high-viscosity polymer, 30% fumed silica (FS), and 5% of plasticizer. The GUM and FS were mixed well with less than 1% silane to improve rubber strength. Expanded vermiculite was added as a filler at 10%, 15%, and 20%. The curing conditions were 170℃ for 10 min and a molding method was applied. We report herein, the results of inorganic analysis and flame-retardant and tracking tests on the expanded vermiculite. The flame retardance and tracking test outcomes for a shore a hardness of 70 were found to be optimal when the expanded vermiculite content was 10%.
In this study, we fabricated plate-type shunt resistors with thermal stability by parallelly connecting metal alloy plates with positive temperature coefficient of resistance (TCR) and carbon nanotube (CNT) plates with negative TCR. The metal alloy plates, which were prepared by alloying Cu and Mn with a composition of 91 wt% of Cu and 9 wt% of Mn, showed around 800 ppm/℃ of TCR, and the CNT plates prepared from the CNT solution by using the vacuum filtration method showed around -800 ppm/℃ of TCR. The shunt resistor that was fabricated by stacking metal alloy plates and CNT plates in this work showed about 46.93 ppm/℃ of TCR. Therefore, we conclude that a shunt resistor with low TCR can be realized by simply adjusting the TCR of the metal alloy only, because the TCR of the CNT plate has an identical value.
We fabricated a printed Ag:CNT film as a liquid sensor for the detection of HNS (hazardous and noxious substances) in seawater. The paste required for printing was prepared using Ag powder, MWCNTs (multi-walled carbon nanotubes), and an organic binder. The heat treatment process for binder removal was optimized. In order to confirm that the sensor was operational, the resistance change characteristics in brine (3.5%) and methanol (99.8%) were assessed at 20℃. EDL (electrical double layer) formation and redox reactivity were confirmed as the most important reactions affect each electrical property of sensor in brine and methanol. From these results, it was determined that printed Ag:CNT film can be applied as a sensor to detect HNS in seawater.
Pure BiFeO3 (BFO) and (Eu, V) co-doped Bi0.9Eu0.1Fe0.975V0.025O3+δ (BEFVO) thin films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by chemical solution deposition. The effects of co-doping were observed by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy (SEM). The electrical properties of the BEFVO thin film were improved as compared to those of the pure BFO thin film. The remnant polarization (2Pr) of the BEFVO thin film was approximately 26 μC/cm2 at a maximum electric field of 1,190 kV/cm with a frequency of 1 kHz. The leakage current density of the co-doped BEFVO thin film (4.81×10-5 A/cm2 at 100 kV/cm) was two orders of magnitude lower than of that of the pure BFO thin film.
In this work, the magnetic arc reduction phenomena encountered in AC relay contacts were analyzed. To this end, arc duration, instantaneous voltage, and current changes due to changes in the magnetic field were observed. The arc generated at the contact point was affected by the magnitude of the applied magnetic field; the voltage and current waveforms rapidly intersected, resulting in a decrease in arc duration and arc energy. Furthermore, the orientation of the N pole of the magnetic field was found to play a role in the effectiveness of potential arc prevention.
This work presents the response characteristics of a ZnO varistor to conductive EMP. An E1 pulse, standardized to MIL-STD-188-125-1, was applied to the varistors wherein the residual current and response times were measured with the applied E1 pulse current. Additionally, the response time was measured according to the length of the connection path. Consequently, the amplitude of the residual voltage through the ZnO varistors was increased with increasing amplitude of the applied E1 pulse current. As the length of the connection path increased, the operating response time and residual peak voltage also increased. These results indicate that the response characteristics of ZnO varistors can be applied to basic data to support the use of varistors as a protective measure against conductive EMP.
A solvent free, highly concentrated silica-acryl monomer hybrid sol was synthesized using aqueous colloidal silica as a precursor. The effects of the silica particle size, type of surface treatment agent employed, and silica content on the formation of the hybrid sol were systematically studied. The optical and physical properties of the coating solution prepared using the hybrid sol were also characterized. The viscosity of the hybrid sol tended to decrease as the particle size of the silica and the molecular weight of the surface treatment agent increased. The PET substrate coated with MPTMS-Mix (mixture, 70 wt%) solution showed the highest surface hardness (6 H) and low surface roughness (Ra= 0.044 μm), which could be attributed to an increase in packing density caused by the infiltration of small particles into the pores formed between larger particles.
Black phosphorus (BP) is a potential candidate for an anode in lithium ion batteries due to its high theoretical capacity and the large interlayer spacing in the monolayered phosphorene form, allowing for lithium intercalation/ deintercalation. In this study, large-scale exfoliation of bulk BP was accomplished using a solution of NaOH and N-methyl-2-pyrrolidone (NMP), yielding phosphorene, which can be assembled into nanoflakes using electrophoretic deposition (EPD). Through the systematic addition of NaOH and subsequent sonication, BP nanoflakes were obtained in high yields by EPD, allowing for the integration of these nanoflakes into an anode in the film state. Anodes with a charge/discharge capacity of 172 mAh/g at a rate of 200 mA/g were obtained, which are promising for battery applications through various post-film treatments.
The use of military lithium batteries in this field accelerates the generation of internal pressure because the active materials, lithium and the electrolyte, react to form sulfur dioxide gas. This also reduces the amount of electrolyte. In this condition, batteries can ‘vent’ or ‘explode’ especially when completely discharged. Such venting and explosion can be regarded as a safety accident, as toxic gases and shrapnel are ejected from the batteries which can harm the user. A DTaQ was carried out in 2017 as a quality problem solution project to solve this safety issue. A protection circuit was thereby developed, which included a micro controller unit (MCU) which can stop battery usage when in an over-discharging state by sensing its low-voltage condition. In 2018, this concept was expanded to lithium batteries for the remote controlled ammunition system. This paper reports results of the improved performance.
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