npsm 새물리 New Physics : Sae Mulli

pISSN 0374-4914 eISSN 2289-0041
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  • Research Paper 2020-10-30

    Far-infrared spectroscopic study on MAPbI$_3$ and MAPbBr$_3$

    Jaeseung LIM, Sangheon PARK, Yu-Seong SEO et al.

    Abstract : MAPbX$_3$, is an organic-inorganic perovskite material system which can be applied in various areas such as magneto-optical data storage, solar cells, lasers, LEDs, etc. MAPbI$_3$ and MAPbBr$_3$ are known to undergo a cubic-to-tetragonal transition at temperatures of about 327 K and 220 K and a tetragonal-to-orthorhombic transition at about 150 K and 145 K, respectively. The transmittance spectra of pallet samples are measured in the far-infrared (FIR) region at various temperatures from room temperature to 80 K by using a Fourier transform infrared (FTIR) spectroscopy-type Bruker Vertex 80v spectrometer. The absorption coefficients are obtained and fitted by using the Drude-Lorentz model to obtain other optical constants including the electric permittivity, optical conductivity, and extinction coefficient. Then, the optical conductivity is fitted to obtain the position and damping coefficient of the longitudinal optical (LO) and the transverse optical (TO) phonons for the sample materials, which are used to calculate the electron-phonon coupling constants, polaron mass, and polaron radii.

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  • Research Paper 2020-10-30

    Interactive Simulation of the Motions of a Linear Mass-Spring Chain with VPython

    Chang-Bae KIM*, Dong Ryeol LEE, Hee-Sang KIM et al.

    Abstract : A computer program written in the VPython language on the Glow Script platform is developed with a view to aiding the study of vibrations and the waves. It simulates the forced motions of coupled oscillators of arbitrarily large number. Understanding the harmonic oscillations of physical systems underlies the core curriculum of college physics. It normally starts with the simple harmonic oscillation of a single oscillator and, afterwards, adds damping and external harmonic forcing. More than one coupled oscillators are, then, introduced and they give ways for understanding waves in continuous media as the number of oscillators becomes large. The reported product visualizes the motions of coupled oscillators and enhance the comprehension of such concepts as the normal modes of vibration and stationary waves.

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  • Research Paper 2020-09-29

    Projection Photolithography for Microscale Patterning and 2D Field-effect Transistor Demonstration

    So Jeong SHIN, Hyun Seok LEE*

    Abstract : In this paper, we introduce a method to realize microscale patterning at arbitrary positions via a projector-based photolithography technique even without a hard photomask. For applying this technique to micro/nano device fabrications, we equip an optical microscope with a digital micromirror device module and a UV light source with a 405-nm wavelength. A bilayer photoresist (PR) and a lift-off processes are used for fabricating versatile micropatterns implemented by using this equipment, where the PMGI (polymethylglutarimide) PR and the AZ 5214 PR used for the bilayer allow the construction of undercut structures for a post-lift-off process. Through process optimization, we realize a line pattern width of $\sim$ 560 nm without a side-wall effect, nearly approaching the theoretical optical diffraction limits of the given optics. Using the optimization process, we demonstrated field-effect-transistors with a channel length of a few $\mu$m for randomly oriented triangular-MoS$_{2}$ monolayers synthesized by using chemical vapor deposition. Our demonstration visualizes that the projection photolithography technique partially replaces an expensive electron-beam lithography for microdevice fabrication at a laboratory level.

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  • Research Paper 2020-09-29

    Growth Mechanism and Characterization of AlN Microspheres by HVPE Method

    Kyoung Hwa KIM, Jung Hyun PARK, Hyung Soo AHN* et al.

    Abstract : An AlN microsphere was grown by using a mixed-source hydride vapor phase epitaxy (HVPE) method a reactor and combining the source with the growth regions and a graphite boat prefilled with the mixed source (Ga+Al) in the source region. The custom-designed reactor was designed to minimize reactions between quartz and AlCl vapor species and to reduce the response distance for synthesis for neighboring source and growth zones at a high source-zone temperature of 1150$^{\circ}$C. Field-emission scanning electron microscopy (FE;SEM), electron-energy dispersive spectroscopy (EDS), and field-emission transmission electron microscopy (FE;TEM) were used in order to investigate the characteristics of the AlN microsphere. We discuss the role of Ga in the mixed source in the AlN microsphere growth process and the results of an investigation of the growth mechanism of the AlN microsphere.

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  • Research Paper 2020-08-31

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

    Byeong-Hyeon JEONG, Ji-Sang PARK*

    Abstract : A stacking fault is a type of extended defect formed in a material. It is known to prohibit the transport of charges in semiconductor materials and promote the recombination of charges; therefore, the performance of electronic devices can be suppressed. For investigating of the stability of stacking faults, first-principles calculations are widely performed, which can be also described using an anisotropic next-nearest-neighbor Ising model (ANNNI) and can be constructed using the total energy of polytypes obtained from the first-principles calculations. In this study, we constructed the ANNNI model for diamond Si and zinc-blende CdTe, ZnS, and GaAs. Our models consider the interactions between two and three layers, resulting in a lower error than the models using only two-layer interactions. The predicted stacking fault energy was similar to that from the first-principles calculations, indicating that the stacking fault energy can be obtained using the ANNNI model.

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Current Issue

    October, 2020 | Volume 70, No. 10
  • Research Paper 2020-10-30

    Far-infrared spectroscopic study on MAPbI$_3$ and MAPbBr$_3$

    Jaeseung LIM, Sangheon PARK, Yu-Seong SEO et al.

    Abstract : MAPbX$_3$, is an organic-inorganic perovskite material system which can be applied in various areas such as magneto-optical data storage, solar cells, lasers, LEDs, etc. MAPbI$_3$ and MAPbBr$_3$ are known to undergo a cubic-to-tetragonal transition at temperatures of about 327 K and 220 K and a tetragonal-to-orthorhombic transition at about 150 K and 145 K, respectively. The transmittance spectra of pallet samples are measured in the far-infrared (FIR) region at various temperatures from room temperature to 80 K by using a Fourier transform infrared (FTIR) spectroscopy-type Bruker Vertex 80v spectrometer. The absorption coefficients are obtained and fitted by using the Drude-Lorentz model to obtain other optical constants including the electric permittivity, optical conductivity, and extinction coefficient. Then, the optical conductivity is fitted to obtain the position and damping coefficient of the longitudinal optical (LO) and the transverse optical (TO) phonons for the sample materials, which are used to calculate the electron-phonon coupling constants, polaron mass, and polaron radii.

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  • Research Paper 2020-10-30

    Comparison of the Giant Magnetoresistances and Planar Hall Resistances for Multilayera Based on the Antiferromagnet IrMn for use in Magnetic Sensors

    Se-Hoon NOH, Sang-Su PARK, Sang-Suk LEE*

    Abstract : The sensitivities of giant magnetoresistance (GMR) and planar Hall resistance (PHR) from different classes of magnetic multilayers were compared for biosensing applications. The magnetoresistance ratio (MR), exchange coupling field ($H_{\text{ex}}$), coercivity ($H_{\text{c}}$), interlayer coupling field ($H_{\text{int}}$), and magnetic sensitivity (MS) were measured, and in each sample, the thickness of the nonmagnetic Cu layer was varied to control magnetic exchange interactions and other magnetic characteristics to ensure that the MR and the PHR were more sensitive to the magnetic field. In each case, we found that the sensitivities of the MR and the PHR with respect to the magnetic field were greatly enhanced as the thickness of the Cu layer was increased, thus suggesting a way to engineer highly sensitive MR and PHV devices for use in biosensors.

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  • Research Paper 2020-10-30

    Effect of Etch Depth and Etch Angle of Etched LEDs on the Light Extraction Efficiency

    Kee Young KWON*, Jang Geun KI

    Abstract : The effects of electrode absorption in a TIP (truncated inverted pyramid) LED (light-emitting diode) and of the etch depth and the etch angle of an etched LED on the light extraction efficiency have been studied. TIP LED may have a 100\% light extraction efficiency if no loss occurs in the medium, but when absorption occurs at the electrode, the light extraction efficiency decreases rapidly and is highest when the height of the active region is located at the center of the two electrodes. In the case of the etched LED, when the etch depth exceeds 36% of the chip thickness, the effect of increasing the light escape cone becomes dominant. If the light absorption coefficient of the chip material is zero, the light extraction efficiency approaches 100% when the etch angle exceeds 20 degrees. Even for a loss of $\alpha$ = 5 [cm$^{-1}$] inside the chip, the effect of increasing the light escape cone becomes dominant when the etch angle exceeds 20 degrees.

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  • Research Paper 2020-10-30

    Discussion on the $J^{PC}=0^{--}$ Tetraquark of $u$ and $d$ Quarks within the QCD sum rule

    Hee-Jung LEE*

    Abstract : Using the QCD sum rule including the contributions from the instanton and the operator product expansion up to the dimension 10 operators of $O(\alpha_{s})$, we discuss the tetraquark state with the quantum numbers $J^{PC}=0^{--}$ consisting of a scalar diaquark and a pesudoscalar diquark of $u$ and $d$ quarks. From the QCD sum rule analysis, we found that the above tetraquark state of $J^{PC}=0^{--}$ would not exist for masses below 2 GeV. This result is similar to the result from a previous study\cite{5} in which the QCD sum rule without the contribution from the instanton was applied to analyze the tetraquark state with $u$ and $s$ quarks that had the same structure of the tetraquark state as in this work.

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  • Research Paper 2020-10-30

    Optimization of Pinhole Collimator According to Magnification Imaging for Radiation Disaster Monitoring: Monte Carlo Simulation

    Jong-Hun WON, Dong-Hee HAN, Seung-Jae LEE et al.

    Abstract : A gamma camera system using a pinhole collimator is used to locate a large area such as that of a radiation disaster. However, the existing pinhole collimators have difficulty in determining the correct position because the rotation radius and the magnification are fixed. The purpose of this study was to use Monte Carlo simulations to optimize the pinhole collimator of a gamma camera with magnification images for radiation monitoring. The sensitivity and the resolution were simulated for various the hole diameters and channel heights. This allowed the optimal design variables for each magnification were optimized between 3.5 and 4.5 mm for magnifications from 1.0 to 3.0. The simulation results allowed us to determine the optimal values of the hole diameter and the channel height, which was be 4 mm and 4 mm, respectively. These results demonstrated that the pinhole collimator designed in this study can be utilized to create a disaster radiation-monitoring system.

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  • Research Paper 2020-10-30

    Performance Evaluation of a Diverging Collimator in a Small Gamma Camera by Hole Type and Arrangement

    Dong-Hee HAN, Jong-Hun WON, Cheol-Ha BAEK*

    Abstract : For overcoming the drawbacks of pinhole collimators, which are used to detect a wide field of view, compact diverging collimators using metal-based precision machining have recently been drawing attention in the 3D printer field. Thus, we evaluated the performances of diverging collimators among the square, circular and hexagonal holes, as well as the arrangements of the GAGG crystals. The GATE code and the STL file were used, as was a $^{99m}$Tc point source. The total area and the height of the collimator were set at 25.8 × 25.8 $mm^2$ and 15 mm respectively. While the spatial resolution for all holes was relatively constant within a low error, the sensitivity for the square holes was 37.3% better than that for circular boles and 52.2% better than that for hexagonal holes, Similar results were obtained when the source was moved to the X-axis. Also, if the arrangement of crystals matched the type of the holes in the collimator, the spatial resolution was slightly better, confirming that the higher the degree of matching the hole, the better the performance.

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  • Research Paper 2020-10-30

    Students' Understanding of the Ontological and Epistemological Meanings of Physics Equations

    Minchul KIM, Yongwook CHEONG, Jinwoong SONG*

    Abstract : A physics equation is a mathematical symbol of the relationship between physics concepts. Although the interactions between physics and mathematics are diverse, in the context of physics teaching and learning, the mathematical aspect tends to be overemphasized. Therefore, in this study, the characteristics of science gifted students' understanding of the ontological and the epistemological meanings of physics equations were analyzed. In semantic classification according to ontological categories, students were relatively correct in classifying the state relationship, but not the interaction and causal relationship. In the classification according to the epistemological category, students were relatively correct in the classification of the empirical law, but not in the classification of a principle. In particular, the students tended to classify a physical equation corresponding to a principle as an the empirical law. Educational implications related to these findings are discussed.

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  • Research Paper 2020-10-30

    Observation of Interference Colors due to Photoelasticity Without Polarizer

    Yu CHEN, Hyejung KWAK, Pyung Kang JUNG et al.

    Abstract : The interference colors caused by the birefringence of a photoelastic material were examined for alignments that can be seen without a polarizer. When light enters a transparent plate with photoelasticity at an incident angle, reflected or refracted light is partially polarized, and this process serves as a polarizing plate. Because the refracted light is divided into ordinary light and extraordinary light, that is, linear polarization components perpendicular to each other, the polarization direction is changed while passing through the medium. Because the refractive index varies with the wavelength of light according to the dispersion relation, the degree of change in the polarization depends on the color. This interference color can be measured without a polarizer. In this study, we tried to explore various configurations in which interference color occurs without a polarizer.

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  • Research Paper 2020-10-30

    Interactive Simulation of the Motions of a Linear Mass-Spring Chain with VPython

    Chang-Bae KIM*, Dong Ryeol LEE, Hee-Sang KIM et al.

    Abstract : A computer program written in the VPython language on the Glow Script platform is developed with a view to aiding the study of vibrations and the waves. It simulates the forced motions of coupled oscillators of arbitrarily large number. Understanding the harmonic oscillations of physical systems underlies the core curriculum of college physics. It normally starts with the simple harmonic oscillation of a single oscillator and, afterwards, adds damping and external harmonic forcing. More than one coupled oscillators are, then, introduced and they give ways for understanding waves in continuous media as the number of oscillators becomes large. The reported product visualizes the motions of coupled oscillators and enhance the comprehension of such concepts as the normal modes of vibration and stationary waves.

    Show More  
  • Research Paper 2020-10-30

    Analytic Solutions for Vibrating Strings with Varying Mass Density

    Won Sik L'YI

    Abstract : In general, the analytic solutions of one-dimensional wave equations with position-dependent mass densities cannot be found. In this study, we solve the wave equations of strings for the cases of linearly or exponentially changing mass densities. When the mass density changes linearly, the solution can be written in terms of the Bessel function $J_{1/3}$ and the Neunmann function $N_{1/3}.$ For large position $x,$ the spatial form of the wave changes as $1/\sqrt[4]{x},$ and the spatial oscillation is narrowed with the length which is proportional to $1/\sqrt{x}.$ When the mass density changes exponentially, the solution can be written in terms of the Bessel function and the Neunmann function with an imaginary order. As $x\to -\infty,$ the solutions reduce to sine and cosine functions. However, as $x\to \infty,$ two types of solutions exist, one increasing rapidly, and the other decaying rapidly. For a string of finite length both solutions are possible, but when a string stretches to $x\to\infty,$ the divergent solution is not allowed, and the string has fixed nodes.

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  • Research Paper 2020-10-30

    Graphical Illustration of the Learning Process in Simple Neural Networks

    Xue-Mei CUI, Donghyeon GIM, Seung Kee HAN*

    Abstract : Recently, artificial neural networks (ANNs) have been utilized for various tasks, including image classification, speech recognition, and machine translation, and for medical diagnosis. For practical applications, we use neural networks composed of a very large number of neurons, but we do not have much information on how to fix the number of hidden layers or the number of neurons in a layer. In this paper, a graphical illustration of neural learning in simple neural networks of a multilayer perceptron (MLP) is presented. In the case of XOR-like problems, the learning process corresponds to finding a line or surface that separates several states into two groups in a higher dimensional space. Here, we illustrate graphically how the bipartition problem depends on the number of neurons in a layer, we also address the meaning of adding a layer in the network. We expect that this intuitive graphical understanding of increasing the number of neurons or layers in simple neural networks will be useful in constructing neural networks for practical problems.

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  • Research Paper 2020-10-30

    Properties of Systolic Blood Pressure and Systolic time of Arterial Pulse Waveform According to Thermal Effect of the Upper body by Using the Shoulder Heat Therapy

    Min-Ju LEE, So-Youn LEE, Sang-Suk LEE*

    Abstract : Thermal therapy has been widely used to increase the immunity of the human body. The physical parameters in blood pressure and systolic time were investigated according to the effect of shoulder heat treatment. There were almost no changes in body temperature and oxygen saturation after two subjects in their 20s with different blood pressures were almost the same as those before SHT. The pulse rate, heart rate, and diastolic blood pressure (DBP) were all lower after SHT. In particular, the systolic blood pressure (SBP) had decreased by an average of 4 mmHg from an average of 128 mmHg for Subject-1 and by an average of 7 mmHg from an average of 102 mmHg for Subject-2. The systolic time (S.time) after SHT was increased by an average of 35 ms for Subject-1 and 19 ms for Subject-2. These results suggest that the thermal effect is a measure of positive changes in the body for the regular use of the SHT.

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  • Research Paper 2020-10-30

    Development of a Depth Measurement with Two Types of Scintillators

    Cheol-Ha BAEK, Seung-Jae LEE*

    Abstract : We have developed a detector that uses two types of scintillators and s photo sensor to measure the depth of interaction. A different type of scintillator was used for each layer, and light generated by interacting with the scintillator was collected using a photo sensor. The energy spectrum of the designed detector was obtained using a DETECT2000 simulation, and the performance of the designed detector was verified through preliminary experiments. As a scintillator, a lutetium oxyorthosilicate (LSO) or a Gadolinium Aluminium Gallium Garnet (GAGG) scintillator was used, and a silicon photomultiplier (SiPM) was used as the photo sensor. In the simulation, the scintillator array was composed of two layers, and a light yield corresponding to gamma ray interactions was generated in each scintillator pixel to obtain a signal to measure the energy spectrum. In the preliminary experiment, the energy spectrum was measured using a single-pixel scintillator, and the result was the photoelectric peak of the GAGG scintillator in the high-energy channel and that of the LSO scintillator in the low-energy channel as in the simulation. Because different photoelectric peaks are formed in the energy spectrum, the positions where the gamma rays and the scintillator interact can be measured, thereby improving the spatial resolution through measurement of the interaction depth.

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Current Issue

October, 2020
Vol.70 No.10

pISSN 0374-4914
eISSN 2289-0041

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pISSN 0374-4914
eISSN 2289-0041