pISSN 0374-4914 eISSN 2289-0041
• ### Research Paper 2021-08-31

#### Mixed-Source HVPE Method for Growing Single-Crystal Hexagonal Si Microneedles

Gang Seok Lee, Kyoung Hwa Kim, Jung Hyun Park et al.

Abstract : Single-crystal hexagonal Si microneedles with an aspect ratio (length/diameter) of 195 or more were grown by using a mixed-source HVPE method at atmospheric pressure. The newly designed mixed-source HVPE method at atmospheric pressure generates a precursor gas with a high partial pressure due to the rapid reaction of Si and HCl gas at a high temperature of 1200 ◦C. At the same time, hexagonal Si microneedles are grown due to the formation of a nucleus and a seed caused by the interaction between GaCln, AlCln and SiCln gas, and it is designed as a growth mechanism that is separated from the substrate by free fall according to the grown weight. Scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), high-resolution X-ray diffraction (HR-XRD), and Raman spectra revealed a single crystal and pure hexagonal Si microneedle. As a result, the newly designed atmospheric pressure mixed-source HVPE method is expected to enable mass growth of single-crystal hexagonal Si microneedle.

• ### Research Paper 2021-08-31

#### Recognition of Preservice Physics Teachers’ Self-Understanding and Change Capacity Related to Science Education

Kwanghee Jo, Yong Jae Joung, Heekyong Kim et al.

Abstract : The purpose of this study was to investigate preservice physics teachers’ perceptions of self-understanding and change capacity related to science education. To this end, the responses of 308 students in a department of physics education at 11 universities were analyzed using a questionnaire. The questionnaire was designed to ask for the self-understanding and the change capacity related to science education. The results of the study were as follows. First, preservice physics teachers were positive in their perception of self-understanding as preservice teachers (average 3.81) and as preservice science teachers (average 3.78), the difference between them not being significant. Second, as for the change capacity, they were positive in the recognition of that as general (average 3.97), as preservice teachers (average 3.85), and as preservice science teachers (average 3.83) with significant differences in some factors. By and large, a gender difference was found. These results have great implications for improving preservice physics teachers’ professionalism and their identities as teachers.

• ### Research Paper 2021-07-30

#### Effects of Pr Concentration and Annealing Temperature on the Structural and Optical Properties of Y2O3:Pr3+Nanopowders by High-energy Ball-milling

Gi Pyo CHO, Gyeong Bok JUNG*

Abstract : Pr3+-doped Y2O3 powders were synthesized using high-energy ball milling. Their structural and photoluminescence properties were investigated as functions of the concentration of the praseodymium and the annealing temperatures. The X-ray diffraction peaks of the Y2O3:Pr3+ powders matched the standard X-ray diffraction(XRD) peaks of the cubic Y2O3 phase without impurities well. The intensity of the XRD peak increased with increasing annealing temperature, as did the photoluminescence emission intensity. These results indicate that the crystallinity of the powder improved with increasng annealing temperature. The highest PL emission intensity was observed at an annealing temperature of 1200 ◦C and Pr3+ concentration of 0.1 mol%. The PL spectra showed characteristic peaks at 618 (3P03H6), 630 (2D13H4), 644 (3P03F2), and 509 nm (3P03H5) at an excitation wavelength of 285 nm.

• ### Research Paper 2021-07-30

#### Characterization of Carbon Dots Using HEPA Filter/Fine dust Through the Solvothermal Method

Jong Won CHUNG, Hyun Kyoung YANG*

Abstract : Carbon dots were synthesized using a solvothermal method with a HEPA filter/fine dust as carbon sources. The chemical structure, particle size, surface chemical ligand, electronic structure and luminescent characteristics of the carbon dots were analyzed using transmission electron microscopy. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and photoluminescence measurements, respectively. The photoluminescence spectrum of the carbon dots showed a strong cyan fluorescence around 452 nm under 370 nm excitation. Thus, high-efficiency carbon quantum dots using discarded fine dust can be developed, and the developed quantum carbon dots may be a good candidate for potential applications in the fields of LED color rendering improvement, fingerprint detection and anti-counterfeiting.

• ### Research Paper 2021-06-30

#### Graphene/porous Silicon Solar Cells by Employing Hexagonal Boron Nitride Insulating Film

Seung Gu CHOI, Hye Rin JEON, Dong Hee SHIN*

Abstract : In this research, we successfully fabricated a (trifluoromethanesulfonyl)-amide (TFSA)-doped graphene (TFSA-GR)/porous Si (PSi) solar cell by inserting a chemical vapor deposition-hexagonal boron nitride (h-BN) insulating layer. The photovoltaic parameters of the solar cell depent greatly on the presence or the absence of the h-BN insulating layer and TFSA-GR doping. Specifically, the h-BN insulating layer prevents carrier recombination at the TFSA-GR/PSi interface, thereby improving the charge collection/separation function and, consequently, improving the efficiency. As a result, the TFSA-GR/h-BN/PSi solar cells show a maximum PCE of 12.07%. These results demonstrate that h-BN is excellent as an insulating layer in GR/Si solar cells and is promising for use in graphene/Si-based optoelectronic device application.

## Current Issue

August, 2021 | Volume 71, No. 8
• ### Research Paper 2021-08-31

#### Competition Between Spin-orbit Coupling and Hund's Coupling in $t_{2g}^5$

Ara GO*

Abstract : The effective angular momentum $j_{eff}$ efficiently describes the $t_{2g}^5$ orbitals in the presence of spin-orbit coupling. On the other hand, the $d$-orbital is spatially localized, and the local electrons have strong mutual two-body interactions, which play an important role in the metal-insulator transitions in transition-metal compounds. For a rotationally invariant $d$-orbital, the local interactions between electrons are expressed in terms of the local Coulomb interaction $U$ and Hund's coupling $J_H$. The Coulomb interaction prevents electrons from gathering at the same position, and Hund's coupling distributes the electron to maximize the spin and the orbital angular momenta. The Hund's coupling often competes against spin-orbit coupling. We explain both the competition between spin-orbit coupling and local interactions in the $t_{2g}^5$ orbital via an atomic limit description and the way in which the effects can be revealed in the electronic structure by dynamical mean-field calculation for a simplified lattice Hamiltonian.

• ### Research Paper 2021-08-31

#### A Study of the Effect of the Molarity of Mg and Ga on the Properties of ZnMgO:Ga Thin Films Deposited by Sol-gel Method

Min Sang Lee, Hyo Jin Choi, Hong Seung Kim* et al.

Abstract : In this study, we investigated the properties of ZnMgO:Ga thin films according to the concentrations of Mg and Ga. The ZnMgO:Ga thin films were deposited on a glass substrate by using a sol-gel method. As the concentrations of Mg and Ga were increased, the growth mechanism changed from a c-axis preferential orientation growth to random growth. The chemical state of O in the films was analyzed by using X-ray photoelectron spectroscopy (XPS). In particular, the variation in the oxygen ion (OI)/oxygen vacancy (OII) ratio with the additions of Mg and Ga was comparatively analyzed. As the content of the Ga precursor in the reaction source was increased, the concentration of Mg contained in the film became smaller than the content of the Mg precursor in the reaction source. Most samples showed a transmittance of 80% or more in the visible region.

• ### Research Paper 2021-08-31

#### Mixed-Source HVPE Method for Growing Single-Crystal Hexagonal Si Microneedles

Gang Seok Lee, Kyoung Hwa Kim, Jung Hyun Park et al.

Abstract : Single-crystal hexagonal Si microneedles with an aspect ratio (length/diameter) of 195 or more were grown by using a mixed-source HVPE method at atmospheric pressure. The newly designed mixed-source HVPE method at atmospheric pressure generates a precursor gas with a high partial pressure due to the rapid reaction of Si and HCl gas at a high temperature of 1200 ◦C. At the same time, hexagonal Si microneedles are grown due to the formation of a nucleus and a seed caused by the interaction between GaCln, AlCln and SiCln gas, and it is designed as a growth mechanism that is separated from the substrate by free fall according to the grown weight. Scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), high-resolution X-ray diffraction (HR-XRD), and Raman spectra revealed a single crystal and pure hexagonal Si microneedle. As a result, the newly designed atmospheric pressure mixed-source HVPE method is expected to enable mass growth of single-crystal hexagonal Si microneedle.

• ### Research Paper 2021-08-31

#### Results of the Gas Cell Development Using a fs Laser Micro-machining System

Hyunil Benjamin KIM, Kyungmin ROH, Venessa Ling Jen PHUNG et al.

Abstract : In this paper, we report the development results for a femtosecond (fs) laser machining system and a gas cell for laser wakefield acceleration research. The developed fs laser machining system consists of a mode-locked Ti:sapphire oscillator, a Ti:sapphire regenerative amplifier, a three-dimensional-moving stage, etc. The system is used to micro-machine a special-type gas cell, that will be used as a plasma source in laser-plasma acceleration research. The gas cell was designed following computational-fluid-dynamics (CFD) simulations, and the internal gas distribution in the gas cell was measured by using a Mach-Zehnder interferometer. In this paper, some of the development and research results for the laser micro-machining system and the gas cell are reported.

• ### Research Paper 2021-08-31

#### Development of Augmented Reality Experimental Materials to Visualize Standing Waves in a Resonance Tube

Jeongwoo Park*

Abstract : In this study, using augmented reality (AR), we designed an experiment that can be used to observe the pressure change of a standing wave in a resonance tube in real time. After visualizing the pressure change of the standing wave had been visualized using ESPI (electronic speckle pattern Interferometry), a physically meaningful part of it was cut and uploaded to the cloud. In a smartphone, AR was implemented by downloading the resulting image from the cloud and integrating it into a real object, a resonance tube. In this study, we proposed both a method of visualizing invisible phenomena by using AR and a method of implementing AR by transmitting information acquired through other experimental devices to a smartphone. In addition, the program, download address is provided so that anyone can use the developed program, as needed. Based on this research, it is expected that AR utilization experiments and teaching and learning materials using various peripheral experimental devices are expected to be developed in future research and their meanings interpreted.

• ### Research Paper 2021-08-31

#### Self-study on the Practice of a Teacher Educator Focusing on the Personal Epistemology of a Preservice Physics Teacher

Jaehyeok CHOI, Kwanghee JO, Yong Jae JOUNG et al.

Abstract : The purpose of this study is to understand a physics teacher educator’s practice for understanding preservice physics teachers’ personal epistemology in an undergraduate course. In this self-study, I, as a teacher educator, discussed my teaching practice for 14 senior students in a department of physics education. In the view of personal epistemology, we discussed the meaning of data from preservice teachers such as the answers on questionnaires, their journals, videos of their lesson demonstrations, and my reflective journals with three critical colleagues. As a teacher educator, 'I' expected them to change their orientations for good teaching to a student-centered lesson and to understand the implication of theoretical knowledge for being professional teachers. I found that they had difficulty in bridging theoretical knowledge and their practice; however, their personal epistemology about teaching was affected not only by my feedback but also by that of their peers. I found that the learner's individual epistemology needed to be clarified and that the process of discussion needed to be emphasized more.

• ### Research Paper 2021-08-31

#### Recognition of Preservice Physics Teachers’ Self-Understanding and Change Capacity Related to Science Education

Kwanghee Jo, Yong Jae Joung, Heekyong Kim et al.

Abstract : The purpose of this study was to investigate preservice physics teachers’ perceptions of self-understanding and change capacity related to science education. To this end, the responses of 308 students in a department of physics education at 11 universities were analyzed using a questionnaire. The questionnaire was designed to ask for the self-understanding and the change capacity related to science education. The results of the study were as follows. First, preservice physics teachers were positive in their perception of self-understanding as preservice teachers (average 3.81) and as preservice science teachers (average 3.78), the difference between them not being significant. Second, as for the change capacity, they were positive in the recognition of that as general (average 3.97), as preservice teachers (average 3.85), and as preservice science teachers (average 3.83) with significant differences in some factors. By and large, a gender difference was found. These results have great implications for improving preservice physics teachers’ professionalism and their identities as teachers.

• ### Research Paper 2021-08-31

#### Index Notation and Simplification of Tensor Expressions

Dal Ho Park*

Abstract : We discuss the pattern matching and the canonicalization as simplification strategies of tensor expressions in index notation and explain that the time required for simplification increases as the symmetry of the indices increases. The performance of simplification by using pattern matching indicates that it is not appropriate for use in practice, but the canonicalization based on the ‘Butler-Portugal’ algorithm is very efficient and so is widely used in general relativity. In this paper, in order to improve the existing simplification strategy, we introduce the concepts of index ‘kind’ to handle various indices and ‘metric state’ to solve the difficulties due to non-covariant operators. As a result, tensor expressions containing various indices and non-covariant operators are correctly simplified. In addition, we convert the implementation of the ‘Butler-Portugal’ algorithm from the GNU C language to the standard C++17 language, and as a result, we found that the asymptotic complexity of the canonicalization was greatly improved in the Windows operating system.

• ### Research Paper 2021-08-31

#### Analysis of LGP's Optical Characteristics According to Design Conditions of Large-area Flat-type LED Luminaires for High-efficiency Glare Prevention}

So Hee PARK*

Abstract : The development of high-efficiency new light sources with good characteristics is actively progressing due to the rapid growth of light source technology. Recently, the LED lighting market has been rapidly advancing to the development of convergence lighting technology utilizing various types of new functions. In this study, we tried to establish a design standard for a simple processing technique to solve the problems of slimming, cost, and differentiated technologies of fusion lighting systems with various characteristics. In addition, the scattering pattern was controlled to increase the production efficiency by minimizing the optical film and the light source, and the optical characteristics were analyzed by preparing conditions for improving the illuminance efficiency. A scattering pattern was selected to minimize glare, and light sources were arranged at the center and corners on the side of the light guide plate. As a result, the amount of light emitted to outside the light guide plate was found to have been increased by a factor of three or more. In addition, we were able to predict the effectiveness of large-area flat-type LED lighting fixtures, and to confirm that they could be used to improve the illuminance efficiency and the optical characteristics.

• ### Research Paper 2021-08-31

#### Study of the Effect of Scattering Particles on the Optical Properties of Quantum Dot-based White Light Emitting Diodes

Jung Min Kwon, Min Woo Kim, Yeong Ju Kim et al.

Abstract : The scattering effects of two scattering particles, TiO2 and SiO2, which were embedded into quantum-dot-based white light-emitting diodes (WLEDs), on the optical characteristics of those diodes were investigated. The scattering efficiency of TiO2 particles is higher than that of the SiO2 particles due to the large difference in the refractive index between TiO2 and the host matrix (hardening material) in which the yellow phosphors and the red quantum dots were located. Accordingly, the TiO2-embedded WLEDs exhibited larger changes in the color coordinates and in the correlated color temperatures, reflecting a higher color conversion efficiency. However, the luminous efficiency of the TiO2-embedded WLEDs decreased with increasing TiO2 concentration, which indicated that multiple scattering via scattering particles effectively trapped the light in the LED, resulting in a higher possibility of light loss. The color-rendering properties of WLEDs were improved by embedding scattering particles in the host matrix, which was due to the modification and the resulting flattening of the emission spectrum in the visible range.

## 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

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

Woo Tae Hong, Hyun Kyoung Yang

New Phys.: Sae Mulli 2021; 71(3): 236-241
https://doi.org/10.3938/NPSM.71.236