npsm 새물리 New Physics : Sae Mulli

pISSN 0374-4914 eISSN 2289-0041
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  • 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.

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  • Research Paper 2021-06-30

    The Characteristics of the Process of Pursuing Universality in Einstein’s Research Papers

    Eunye LEE, Hongbin KIM*, Gyoungho LEE

    Abstract : In general, science has the characteristics of pursuing universal truths or laws, and science education emphasizes teaching the nature of science. In this study, the characteristics of the process of pursuing universality, which is one facet of the nature of science, were investigated in three representative papers of Albert Einstein: general relativity, special relativity and photoelectric effect. The three research papers were found to show the following common characteristics of the process of pursuing universality: First, the pursuit of universality begins with an inconvenience caused by defects or a contradiction in the existing knowledge of physics. Second, the content of universality includes the frame-independent laws of physics, the frame-independent physical quantities (invariants), and the object-independent laws of physics. Third, the method of pursuing universality includes pointing out specific defects in existing knowledge of physics, accepting principles and concepts that should be universally respected, and making new arguments as universal ones that everyone will naturally accept.

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  • 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.

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  • 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.

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  • 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.

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Current Issue

    June, 2021 | Volume 71, No. 6
  • Research Paper 2021-06-30

    The Phase and Morphology of Hydrothermally Synthesized Nanostructured Nickel/nickel Hydroxides and Their Supercapacitor Application

    Seung-yong EOM, Jinjoo JUNG*,Do-Hyung KIM

    Abstract : Urchin-like nanostructured nickel/nickel hydroxides (NNHO) were successfully synthesized by using the hydrothermal method, and the phase and the morphology of the nanostructured nickel/nickel hydroxide were controlled by using different synthesis temperatures. The diameter of the nanostructured NNHO synthesized at a relatively high temperature wes bigger than that of the samples synthesized at low temperature, which could be explained by using Ostwald ripening. The phase of the as-synthesized nanostructure was composed of crystalline metallic nickel on the inside and amorphous nickel hydroxide on the surface. To compare the electrochemical properties, the as-synthesized samples are converted to nickel oxide (NO) by annealing at different temperatures. The as-synthesized NNHO showed the highest specific capacitance, as well as easy electrolyte accessibility, because NNHO had not only an easily accessible nanostructure but also the synergistic effect of crystalline nickel and amorphous nickel hydroxide. The present work can contribute to the synthesis of nanostructured NNHO and to the applications of supercapacitors using heterostructure materials.

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  • 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.

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  • Research Paper 2021-06-30

    The Characteristics of the Process of Pursuing Universality in Einstein’s Research Papers

    Eunye LEE, Hongbin KIM*, Gyoungho LEE

    Abstract : In general, science has the characteristics of pursuing universal truths or laws, and science education emphasizes teaching the nature of science. In this study, the characteristics of the process of pursuing universality, which is one facet of the nature of science, were investigated in three representative papers of Albert Einstein: general relativity, special relativity and photoelectric effect. The three research papers were found to show the following common characteristics of the process of pursuing universality: First, the pursuit of universality begins with an inconvenience caused by defects or a contradiction in the existing knowledge of physics. Second, the content of universality includes the frame-independent laws of physics, the frame-independent physical quantities (invariants), and the object-independent laws of physics. Third, the method of pursuing universality includes pointing out specific defects in existing knowledge of physics, accepting principles and concepts that should be universally respected, and making new arguments as universal ones that everyone will naturally accept.

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  • Research Paper 2021-06-30

    Analysis of the Possibility of Achieving the Purpose of Newton's Second law Experiment Presented in the 2015 Revised Curriculum Physics I Textbooks

    Sangwoo HA, Minchul KIM*

    Abstract : This study was conducted to determine if Newton’s second law experiment presented in the 2015 revised curriculum physicsⅠ textbooks can achieve the purpose of the experiment. For this purpose, Newton’s second law experiments presented in eight kinds of physicsⅠ textbooks were classified based on the method used to apply a force to an object, and experiments were performed to obtain real data. As a result of the study, all textbooks will have difficulty in deriving the desired goal from the textbook when the currently presented method is used. Specifically, in the experiment using elastic force, a specific method for constant external force needs to be proposed. In addition, in the experiment using the gravity of weight, it seems to be necessary to consider the error from the frictional force. In conclusion, we need to carefully examine if the experiments in the textbook can achieve their purposes. In particular, performing experiments involving Newton’s second law is difficult; therefore, it is necessary to consider what is the best way to deal with Newton’s second law experiment in a textbook.

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  • 2021-06-30

    Fiber-optic Interferometer Using Chirped Fiber Bragg Gratings in the Reference arm

    Seung Seok LEE, Eun Seo CHOI*

    Abstract : In this paper, we describe the characteristics of interferometry using a chirped fiber Bragg grating as the reference arm of a fiber-optic interferometer and propose a method to improve the maximum measurement displacement. This fiber-optic interferometer generated a symmetrically chirped interference signal due to the group delay given by the dispersion characteristics. The position information of the reflector at the sample arm could be restored through a signal processing technique for extracting the envelope from the interference signal. Interfering signals were measured while increasing the displacement of the reflector at the sample arm at intervals of 500 $\mu$m from 0 to 6.5 mm. From the measured interference signal, the displacement information of the reflector at the sample arm could be restored with a resolution of 100 $\mu$m. The proposed technique was able to overcome the measurement limitations of the existing spectrometer-based dispersive interferometer, and the proposed method can provide improved depth information in various optical measurements and optical imaging applications based on interferometers.

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  • Research Paper 2021-06-30

    Noncritically Phase Matched Second Harmonic Generation and Wedged face Third Harmonic Generation of Q-switched Nd:YVO4 Laser Radiation

    Dongil JANG, Byung-Jun PARK, Seong-Yeon LEE et al.

    Abstract : We report on the noncritical phase matching of second harmonic generation and wedged-face third-harmonic generation in lithium triborate (LBO) caused by the 1064-nm nanosecond pulses from Q-switched Nd:YVO4 laser. Phase matching is required to obtain efficient harmonic generation by manipulating the phase difference between the nonlinear waves created at different positions along the nonlinear crystal. Because second harmonic generation through noncritical phase matching it does not induce a walk-off between the 532-nm and 1064-nm beams, is advantageous, especially for third-harmonic generation. We could obtain 532-nm light at 2.83 W from 1064-nm light at the 5.84 W, corresponding to a maximum second-harmonic conversion efficiency of 48%. The wedge for third-harmonic generation in LBO was incorporated in order to compensate for the walk-off between the propagations of the the 1064-nm and the 532-nm beams. Light at 355 nm up to an average power of 1.70 W could be generated, with a maximum third-harmonic conversion efficiency of 29%.

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  • Research Paper 2021-06-30

    Relationship Between the First Formant of a Vowel and Classical Singing Strategy with Ascending Pitch

    Seong-Ryong Ryu*

    Abstract : Sound from a person’s vocal cords is resonated through the vocal track. The spectrum of synthesized voices was analyzed for the /e/ vowels of male and female voices as the pitch goes up by using the singing synthesizer Madde. Vowel turn over is needed to maintain the vocal track shape of a given vowel at the intersection of the first formant F1 and 2f0 of a male voice, and F1 should track f0 when the female pitch reaches the normal F1 location. The weighted average of the harmonics contained in the F1 bandwidth was calculated and then used to explain the passive opening and closing of a vowel at the intersection of F1/2f0. The ratio of the first formant intensity relative to the total intensity of a voice was calculated, and the effect of changes in the ratio on the pharyngeal resonance in vocal vocalization and the migration of sensation of the sound were explained.

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Current Issue

June, 2021
Vol.71 No.6

pISSN 0374-4914
eISSN 2289-0041

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pISSN 0374-4914
eISSN 2289-0041