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pISSN : 1225-1429 / eISSN : 2234-5078

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2022, Vol.32, No.2

  • 1.

    Low temperature growth of Ga2O3 thin films on Si substrates by MOCVD and their electrical characteristics

    Jungbok Lee , Ahn Nam Jun , Hyung Soo Ahn and 2 other persons | 2022, 32(2) | pp.45~50 | number of Cited : 0
    Abstract PDF
    Ga2O3 thin films were grown on n-type Si substrates at various growth temperatures of 500, 550, 600, 650 and 700°C. The Ga2O3 thin films grown at 500°C and 550°C were characterized as featureless flat surface. Grown at highertemperatures (600, 650, and 700°C) showed very rough surface morphology. To figure out the annealing effect on the thin films grown at relatively low temperatures (500, 550, 600, 650 and 700°C), the Ga2O3 films were thermally treated at 900°C for 10 minutes. Crystal structure of the Ga2O3 f ilms g rown a t 500 and 550°C were changed from amorphous to polycrystallinestructure with flat surface. Ga2O3 film grown at 550°C was chosen for the fabrication of a Schottky barrier diode (SBD). Electrical properties of the SBDs depend on the thermal treatment were evaluated. A MSM type photodetector wasmade on the low temperature grown Ga2O3 thin film. The photocurrent for the illumination of 266 nm wavelength showed 5.32 times higher than dark current at the operating voltage of 10 V.
  • 2.

    Sintering prevention of Ag by the addition of 2-dimensional nanosheet

    Lee Sang Eun , Hee Jung Park | 2022, 32(2) | pp.51~54 | number of Cited : 0
    Abstract PDF
    The physical properties of the noble metal current-collector used for fuel cells are greatly influenced by the material porosity. Therefore, increasing the porosity of the material studies has attracted much attention. One of the most representative strategies is to use porosity additives in sintering materials. The conventional porosity additive had a threedimensional structure of a spherical powder. In this study, porosity additive with 2-dimensional (2D) nanosheet was used todecrease the sintering density of Ag current-collector and its effect was confirmed. As a 2D layered structure material, 1 nm-thick RuO2 nanosheets were used as porosity additives.
  • 3.

    Study on the characteristics of transition metals for TSSG process of SiC single crystal

    leeseungjune , Yong-Jae Yoo , Seong-Min Jeong and 3 other persons | 2022, 32(2) | pp.55~60 | number of Cited : 0
    Abstract PDF
    In this study, a heat treatment experiment was conducted to select a new melt composition that can easily control the unintentionally doped nitrogen (N-UID) without degrading the SiC single crystal quality during TSSG process. The experiment was carried out for about 2 hours at a temperature of 1900°C under Ar atmosphere. The used melt composition is based on either Si-Ti 10 at% or Si-Cr 30 at%, and also Co or Sc transition metals, which are effective for carbon solubility, were added at 3 at%, respectively. After the experiment, the crucible was cross-sectionally cut, and evaluated the Si-C reaction layer on the crucible-melt interface. As a result, with Sc addition, Si-C reaction layers uniformly occurred with a Si-infiltrated layer (~550 µm) and a SiC interlayer (~23 µm). This result represented that the addition of Sc is an effective transition metal with high carbon solubility and can feed carbon sources into the melt homogeneously. In addition, Sc is well known to have low reactivity energy with nitrogen compared to other transition metals. Therefore, we expect that both growth rate and Nitrogen UID can be controlled by Si-Sc based melt in the TSSG process.
  • 4.

    A study on the synthesis of a cathode active material precursor from a waste lithium secondary battery

    Boram Kim , Dae-Weon Kim , Tae-heon Kim and 5 other persons | 2022, 32(2) | pp.61~67 | number of Cited : 0
    Abstract PDF
    A metal salt solution was prepared from valuable metals (Ni, Co, Mn) recovered from a scrap of waste lithium secondary batteries, and an NCM811 precursor was synthesized from the solution. The effect on precursor formation accordingto reaction time was confirmed by SEM, PSA, and ICP analysis. Based on the analysis results, the electrochemical properties of the synthesized NCM811 precursor and the commercial NCM811 precursor were investigated. The Galvano charge-discharge cycle, rate performance, and Cycle performance were compared, and as a result, there was no significant difference from commercial precursors.
  • 5.

    Mechanism of change in compressive strength of geopolymers by immersion method

    kimhakmin , KIM, YOOTAEK | 2022, 32(2) | pp.68~76 | number of Cited : 0
    Abstract PDF
    This study was performed to investigate the mechanism of the change in compressive strength of autoclave cured geopolymers. Specimens were immerged in distilled water, 2M, 8M, and 14M alkaline solutions for 3, 7, and 21 days. Thechange in the specimens immersed in a short period of time was not significant, but the compressive strength of the specimens immersed in the distilled water and 8M alkali solution) for 21 days increased more than twice as much asbefore immersion because of additional geopolymerization. However, compressive strength decreased due to the alkaline aggregate reaction when alkaline solution was supplied more than a certain level of concentration. Therefore, immersing thespecimens for more than 21 days in the distilled water or 8M alkaline solution would be desirable for the improvement of compressive strength of autoclave cured specimens.
  • 6.

    Synthesis of Ni-MWCNT by pulsed laser ablation and its water splitting properties

    KYOUNG-WON CHO , Chae Hui Ra , Jeong Ho Ryu | 2022, 32(2) | pp.77~82 | number of Cited : 0
    Abstract PDF
    Recently, research on the development of low-cost/high-efficiency water electrolysis catalysts to replace noble metal catalysts is being actively conducted. Since overvoltage reduces the overall efficiency of the water splitting device,lowering the overvoltage of the oxygen evolution reaction (OER) is the most important task in order to generate hydrogen more efficiently. Currently, noble metal catalysts show excellent characteristics in OER performance, but they areexperiencing great difficulties in commercialization due to their high price and efficiency limitations due to low reactivity. In this study, a water electrolysis catalyst Ni-MWCNT was prepared by successfully doping Ni into the MWCNTs structure through the pulsed laser ablation in liquid (PLAL) process. High resolution-transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS) were performed for the structure and chemical composition of the synthesized Ni-MWCNT. Catalytic oxygen evolution reaction evaluation was performed by linear sweep voltammetry (LSV) overvoltage characteristics, Tafel slope, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and Chronoamperometry (CA) was used for measurement.