pISSN 0374-4914 eISSN 2289-0041
• ### Research Paper 2021-05-31

#### Magnetic Properties of CoFeB Films with Step-terrace Surface Morphology

YeonJung PARK, Joonghoe DHO*

Abstract : Co60Fe20B20 (CoFeB) films was prepared on a 3° mis-cut (0001) Al2O3 substrate by using DC Sputtering, and their magnetic properties were studied. An atomic force microscopy image showed that the CoFeB film had a step-terrace surface, and the magneto-optical Kerr effect measurement suggested that magnetic hysteresis had a clear difference for in-plane direction. CoFeB films had a magnetic easy axis along the longitudinal direction of the step-terrace, and the saturation magnetic field values were about 4.3 Oe for the easy-axis direction and about 48 Oe for the hard-axis direction, which is perpendicular to the step-terrace. CoFeB films had an uniaixal magnetic anisotropy with a period of 180° within the plane. The shape magnetic anisotropy energy in the step-terrace CoFeB film was roughly 2.5 times larger than a depsition magnetic anisotropy energy in a flat surface film. The surface morphology of the step-terrace was maintained up to a thickness of 50 nm, which was about 20 times the step-height, but the effect of the shape magnetic anisotropy decreased with increasing thickness. The direction dependent magnetic hysteresis behavior could be qualitativly explained by using a modified Stoner-Wohlfarth model.

• ### Research Paper 2021-05-31

#### Deposition of Carbon Whiskers by Applying bias Voltage and Investigation of Their Field Emission Properties

Mincheol KWEON, Hong Jun BARK*

Abstract : A carbon whisker-shaped thin film, similar to a carbon tube, was fabricated, instead of conventional diamond crystal particles, by applying a bias voltage to the silicon substrate. The fabricated thin film was analyzed for shape and composition by using scanning electron microscopy and Raman spectroscopy. As the bias current was increased, the shape of the carbon whiskers tended to become thinner and longer, causing an increase in the field emission current. Additionally, an increase in the CH4 concentration and substrate temperature increased the whisker diameter. Moreover, an addition of NH3 increased the growth rate and caused the formation of sharp edges on the whiskers, resulting in a decreased operating voltage in field emission.

• ### Research Paper 2021-04-30

#### Effect of Raw Material SiO2 Powder Size on the Crystallinity of Sr3SiO5:Eu(3+/2+)(4%) Phosphor and Optical Properties of Eu(3+/2+)

Purevdulam NANKHAI, Kiwan JANG*

Abstract : We fabricated a series of Sr2.96SiO5:0.04Eu(2+/3+) phosphors by using powders of a raw-material, SiO2, with various grainsizes, and we studied the effect of grain particle size on optical properties, such as excitation and emission spectra of Eu(2+/3+) ions doped in Sr3SiO5 and the crystallinity of Sr2.96SiO5:0.04Eu(2+/3+). Some of the samples studied using x-ray diffiaction had the same crystal structure as that of the standard sample Sr3SiO5(JCPDS-260984), but the crystallinity and the optical properties of Sr2.96SiO5:0.04Eu(2+/3+) depended greatly on the size of the particles in the SiO2 powder. The studied Sr2.96SiO5:0.04Eu2+ phosphors showed the maximum emission intensity at 582 nm with a full width at half maximum of about 70 nm and had good excitation efficiencies in the 240-500 nm region. Thus, we can conclude that the combination of ultraviolet or blue LED chips with a Sr2.96SiO5:0.04Eu2+ phosphor can be used as a source of warm white light with many potential applications. Through this study, we experimentally confirmed that the fabrication of Sr2.96SiO5:0.04Eu2+ phosphors was very sensitive to the powder size of SiO2 raw material.

• ### Research Paper 2021-04-30

#### Ultrasonic Testing to Evaluate the Signal Characteristic for CFRP Composite Lamination

Yun-Taek Yeom, Hak-Joon Kim, Sung-Jin Song et al.

Abstract : CFRP (carbon fiber reinforced plastic) composites have superior chemical resistance, vibrationdamping properties, electrical insulation, dimensional safety, etc. than conventional metal materials. Also, applications of these composites are gradually being attempted in various fields, such as the automobile, shipbuilding, medical equipment, and aerospace and aviation industries, and the scope of applications is expanding. CFRP composites have properties such as imbalance and anisotropy because they are manufactured with a desired stacking order and fiber arrangement angle by using a one-way prepreg sheet. In the additive process, defects such as pores, uneven thickness, resin distribution, and micro-cracks can occur due to sliding or stacking defects and can cause the destruction of the fibers and parent materials, interfacial separation, and fracture, Thus, the characteristics for the shape of CFRP Composite lamination must be evaluate, so In this study, an evaluating of the characteristics was performed by analyzing the ultrasonic A-scan (Amplitude-scan) signal and C-scan (Contrast-scan) image for CFRP composite lamination

• ### Research Paper 2021-03-31

#### Effect of Synthesis Temperature on Luminescent Properties of Carbon dots Originated from Sucrose

Woo Tae Hong, Hyun Kyoung Yang

Abstract : Carbon dots (CDs) originating from sucrose were synthesized by using a solvothermal method. The morphological, structural and luminescent properties of those CDs were analyzed to investigate the effect of the synthesis temperature on the CDs. TEM images of the CDs showed that increasing the synthesis temperature caused an increase in the particle size and aggregation of the CDs. The FT-IR and XPS spectra of the prepared CDs indicated that an increase in the synthesis temperature eliminated the surface functionalized ligands and the defects in CDs fabricated using the solvothermal reduction. Under 400-nm excitation, the PL spectra of the CDs exhibited a blue emission band with a maximum at 477 nm. When the synthesis temperature was 220 °C, the maximum emission intensity of the CDs was the highest. When the synthesis temperature was 250 °C, the dominant emission wavelength and emission intensity decreased due to the removed of defect states in the bandgap. The results in this study, clearly show that the synthesis temperature can be used to control the morphological, structural, luminescent properties of CDs.

## Current Issue

May, 2021 | Volume 71, No. 5
• ### Research Paper 2021-05-31

#### Fabrication of Thermal Conductive Adhesive Using Ni Graphite Core-shell and Application to LED Lighting

Chang-Duk KIM*, Younjung JO, Nguyen Tam Nguyen TRUONG

Abstract : High-power light-emitting diode (LED) lighting exhibits excessive heat generation owing to the need to drive an LED chip, development of heat dissipation technology is required to resolve that problem. Until now, most of the studies on heat dissipation in LED lighting have been limited to research on heat dissipation of the chip itself and research into the manufacture of heat sinks. However, a solution in a new direction is required owing to the quantity of heat generated from dense LED chips found in high-power LED lighting or in situations where the space for the lighting is limited owing to its location. In this research, heat dissipation characteristics were improved by adding a Ni-graphite core-shell (Ni-GCS) to the thermally conductive adhesive used to bond the LED chip’s substrate to the heat sink in high-power LED lighting applications. Ni-GCS was synthesized through thermal chemical vaper deposition (thermal-CVD), and the Ni nanoparticles were confirmed are to be wrapped by a graphite layer. When high-power LED lighting using the novel thermally conductive adhesive was driven over a long period of time, improved heat dissipation characteristics were observed when the properties of the thermal changes were analyzed.

• ### Research Paper 2021-05-31

#### Synthesis of Graphite on SiC Particles by Using the Thermal-Chemical Vapor-Deposition Method with and It’s Dependence on Temperature and Time

Chang-Duk KIM*, Hyeong-Rag LEE

Abstract : Owing to its high thermal stability, mechanical and chemical stability, and good photoelectric properties, silicon carbide (SiC) is currently receiving attention as a photocatalyst for nonmetallic semiconductor materials in various applications. In this research, graphite was synthesized on the surface of SiC particles via thermal chemical vapor deposition (thermal-CVD) with the intention of increasing the utility of SiC as a photocatalyst. The excellent properties of the SiC-graphite (SCG) produced were confirmed through various analyses. Synthesis of SCG was undertaken using various synthesis temperatures (800°C, 900°C, 1000°C, and 1100°C) and synthesis times (30, 60, 90, and 120 s). The research demonstrated that graphite could be formed on the SiC surface, thus expanding the areas in which SiC and C materials can be applied.

• ### Research Paper 2021-05-31

#### Photoluminescence of Amorphous Carbon Nitride (a-C:N) thin Films Grown by Facing Target Sputtering Method

Hong Tak KIM, Hyeong-Rag LEE, Sung-Youp LEE*

Abstract : In this study, amorphous carbon nitride (a-C:N) thin films were deposited on glass substrates by using a facing target sputtering technique, and the effects of growth temperature were investigated. The deposition rate of the films gradually increased from 1.6 nm/min to 5 nm/min with increasing growth temperature. Emission peaks in the PL spectra of a-C:N films were found at 2.6 eV (green), 3.0 eV (blue), and 3.2 eV (UV). The blue and the UV emissions exhibited an inverse relationship with increasing growth temperature. The ratio of [N]/[C+N] increased from 11% to 15% with increasing to growth temperatures, and this implied an increase of C-N bonding in the films. As the growth temperature was increased, double-bonded nitrogen (N$_{d}$, =N-) and triple-bonded nitrogen (N$_{t}$, -N$<$) showed an inverse relationship, and the ratio of [N$_{t}$]/[N$_{d}$ + N$_{t}$] increased from 80% to 93%. This tendency was similar to the relationship between the blue and the UV emissions according to growth temperature. Thus, the ratio of N$_{t}$ and the intensity of UV emission are thought to be closely related, and these changes are thought to play a major role in determining the optoelectronic properties of the films.

• ### Research Paper 2021-05-31

#### Tip-Substrate Shear Interaction in Quartz Tuning Fork-Based Atomic Force Microscopy in Air

Hyoju CHOE, Dongwon KIM, Manhee LEE* et al.

Abstract : We investigate the tip-substrate interaction in shear-mode, quartz-tuning, fork-based atomic force microscopy in air. While the tip-substrate normal interaction in vacuum is usually characterized as a long-range attractive force and a short-range repulsive force, here, in shear-mode atomic force microscopy in air, we observe a negligible shear interaction until the tip abruptly experiences a viscoelastic force at a few nanometers above the sample’s surface. We show that the viscoelastic shear interaction is the result of a capillary-condensed water bridge formed in the nanosized gap between the tip and the substrate and that the shear interaction increases with decreasing tip-substrate separation until hard mechanical contact is made between the tip and the substrate. This shear interaction mediated by the capillary liquid bridge dominates over other interactions; thus, the shear force must be considered when performing shear-mode atomic force microscopy and spectroscopy and manipulation of nano-objects in air.

• ### Research Paper 2021-05-31

#### Study on the Structural and Electrical Properties of La$_{0.7}$Ca$_{0.3}$MnO$_{3}$/CaMnO$_{3}$/ La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ Heterostructures

Nguyen Thi My NHUNG, Heon-Jung KIM*

Abstract : In this study, we report the deposition of La$_{0.7}$Ca$_{0.3}$MnO$_{3}$/CaMnO$_{3}$/La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ heterostructures on (100) SrTiO$_{3}$ substrates under optimal conditions for depositions of single layers of CaMnO$_{3}$ and La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ by using the pulsed laser deposition (PLD) method. Using X-ray diffraction (XRD), atomic force microscopy (AFM), and resistivity measurements, we determined the crystallinity, morphology and electrical properties of these heterostructures. The surface of those films were smooth and uniform with small grains.

• ### Research Paper 2021-05-31

#### Magnetic Properties of CoFeB Films with Step-terrace Surface Morphology

YeonJung PARK, Joonghoe DHO*

Abstract : Co60Fe20B20 (CoFeB) films was prepared on a 3° mis-cut (0001) Al2O3 substrate by using DC Sputtering, and their magnetic properties were studied. An atomic force microscopy image showed that the CoFeB film had a step-terrace surface, and the magneto-optical Kerr effect measurement suggested that magnetic hysteresis had a clear difference for in-plane direction. CoFeB films had a magnetic easy axis along the longitudinal direction of the step-terrace, and the saturation magnetic field values were about 4.3 Oe for the easy-axis direction and about 48 Oe for the hard-axis direction, which is perpendicular to the step-terrace. CoFeB films had an uniaixal magnetic anisotropy with a period of 180° within the plane. The shape magnetic anisotropy energy in the step-terrace CoFeB film was roughly 2.5 times larger than a depsition magnetic anisotropy energy in a flat surface film. The surface morphology of the step-terrace was maintained up to a thickness of 50 nm, which was about 20 times the step-height, but the effect of the shape magnetic anisotropy decreased with increasing thickness. The direction dependent magnetic hysteresis behavior could be qualitativly explained by using a modified Stoner-Wohlfarth model.

• ### Research Paper 2021-05-31

#### Deposition of Carbon Whiskers by Applying bias Voltage and Investigation of Their Field Emission Properties

Mincheol KWEON, Hong Jun BARK*

Abstract : A carbon whisker-shaped thin film, similar to a carbon tube, was fabricated, instead of conventional diamond crystal particles, by applying a bias voltage to the silicon substrate. The fabricated thin film was analyzed for shape and composition by using scanning electron microscopy and Raman spectroscopy. As the bias current was increased, the shape of the carbon whiskers tended to become thinner and longer, causing an increase in the field emission current. Additionally, an increase in the CH4 concentration and substrate temperature increased the whisker diameter. Moreover, an addition of NH3 increased the growth rate and caused the formation of sharp edges on the whiskers, resulting in a decreased operating voltage in field emission.

• ### Research Paper 2021-05-31

#### Evaluations of Shielding Effectiveness in the Broadband Frequency Region up to 18 GHz by Using Flanged Coaxial Transmission Lines

Wongyu JANG, Baekil NAM, Minji GU et al.

Abstract : We have designed a jig that employed the flanged, coaxial transmission line through a 3D finite-element-method (FEM) simulation to measure the broadband electromagnetic (EM) shielding effectiveness (SE) in the frequency range from 0.5 GHz to 18 GHz. The flanged, coaxial transmission line comprises the ground (outer diameter: 7.00 mm) and the signal line (inner diameter: 3.04 mm). Representative specimens were prepared with metallic materials (Al, Ni, Cu sheets, \& Ni mesh) and non-metallic materials (graphene oxide and magnetic polymer composite) to evaluate the SE. We analyzed the EM properties, the reflection, absorption, and total EM SE, of the fabricated specimens. Further, the SE results acquired from the flanged, coaxial transmission line which compared with those of a rectangular waveguide by measuring the S parameters. The SE measured using the flanged, coaxial transmission line correlates well with those of the rectangular waveguides (WR-90, WR-62).

• ### Research Paper 2021-05-31

#### Characterization of a Pure CsI Crystal at Low Temperature for a Dark-Matter Search

Sedong PARK, Arshad KHAN, Hongjoo KIM*

Abstract : Scintillators are widely used as detectors to search for dark matter. In this study, we studied the scintillation properties of a pure CsI crystal to confirm that the crystal has good properties for searching for dark matter at low temperatures. To confirm if the pure CsI crystal has suitable properties for detecting dark matter, we investigated its scintillation properties by using alpha particles and gamma rays in temperature range from 300 ~ 10 K. The light yield, alpha/gamma ratio, and decay time were measured for each temperature, and it the alpha and the gamma signals could be separated by using a pulse shape discrimination. The light yield increased as the temperature decreased, and the light yields due to alpha particles and gamma rays were found to be about 80,000 photons/MeV. The decay times of alpha particles and gamma rays increased as the temperatures was decreased. Because pure CsI at low temperatures have twice the number of photoelec-trons per MeV than the CsI:Tl detector at room temperatures, we confirm that CsI has a low threshold energy at low temperatures which is an advantage when searching for low-mass dark matter.

• ### Research Paper 2021-05-31

#### Perception of Relativity and Quantum Physics by Pre-Physics Teachers and Physics Teachers

Jongwon PARK, Insun LEE*

Abstract : Based on the assumption that the teacher's perception of modern physics affects modern physics teaching, this study examined perceptions of pre-physics teachers and physics teachers about the concepts of relativity and quantum physics presented in the high school curriculum. To do this, we used the repertoire grid technique to extract four adjective pairs (difficult to understand-easy, strange-plain, interesting-boring, difficult to calculate-easy) from 29 pre-science teachers. Using this, we developed a Likert-type questionnaire and 61 pre-physics teachers and 75 physics teachers responded. The result shows that although the respondents perceived modern physics as difficult to understand, the perceptions was not so strong. The perception of strangeness is higher, indicating that it is positive for motivating students’ learning. However, recognizing that modern physics needs to be related to students’ everyday experiences, some teaching ideas for this purpose are suggested. The perception of interest was also relatively high. The perception of calculation was only investigated for quantum theory, which was perceived to be difficult, but not so high. In addition, the differences in perception between individual concepts, differences between quantum theory and relativity concepts, and differences between pre-physcis teachers and physics teachers were statistically analyzed. These results are expected to be used as basic data for teaching modern physics.

• ### Research Paper 2021-05-31

#### Analysis of the Pre-service Science Teachers' Strategies in an Inquiry Theme Finding Activity through a Change of Prior Inquiry

Bongwoo LEE*

Abstract : The purpose of this study is to analyze the strategies used by pre-service science teachers in inquiry theme finding activity through a change of prior inquiry. For this purpose, 29 pre-service science teachers participated in this study, and 94 cases were analyzed. The cases in which the theme of prior inquiry remained unchanged were classified as the use of other experimental equipment, a change in the variables (independent variable, dependent variable), and applications to different environments. The cases in which the theme of prior inquiry was changed were divided into the use of opposite perspective, application to another subject, use of prior inquiry keywords, and the use of abductive thinking. As a result of the study, the largest number of cases were found through the strategy of changing the independent variables, followed by strategies using keywords and strategies applied to other research subjects. In this paper, examples of each strategy are presented, and the implications of enhancing the ability to discover inquiry themes for pre-service science teachers and secondary school students are discussed.

## Current Issue

• ### A Numerical Calculation of the Nuclear Spin-Parity and Magnetic Moment Based on the Single-Particle Shell Model

Nguyen Ngoc DUY*, Latsamy XAYAVONG, Nguyen Kim UYEN, Vinh Nguyen Thanh PHAM, Tran Viet NHAM HAO

New Phys.: Sae Mulli 2019; 69(10): 1091-1100
https://doi.org/10.3938/NPSM.69.1091

• ### Calculation of the Stacking Fault Energy by Using the Anisotropic Next-Nearest Neighbor Ising Model

Byeong-Hyeon JEONG, Ji-Sang PARK*

New Phys.: Sae Mulli 2020; 70(8): 630-636
https://doi.org/10.3938/NPSM.70.630

• ### Research on Reactor Neutrino Event Selection by Using the Machine Learning Technique

Chang Dong SHIN, Kyung Kwang JOO*, Dong Ho MOON, Myoung Youl PAC, Junghwan GOH

New Phys.: Sae Mulli 2019; 69(8): 813-817
https://doi.org/10.3938/NPSM.69.813