Ex) Article Title, Author, Keywords
pISSN 0374-4914
eISSN 2289-0041
pISSN 0374-4914
eISSN 2289-0041
Ex) Article Title, Author, Keywords
Abstract : Potassium silicate solution (PSS) added with Y3Al5O12:Ce3+(YAG:Ce3+) phosphors was synthesized by using a solid-state reaction method. The crystal structure, morphology, and luminescence properties of the phosphors were measured for various PSS concentrations. The X-ray diffraction pattern of the phosphors shows that the addition of PSS promotes the formation of a garnet structure at lower temperature than commercial YAG phosphors. FE-SEM images show that the addition of PSS promotes the growth of particle size and aggregation. With the addition of 10 wt.% of PSS, the PL spectra show that the emission intensity at 533 nm is 20% higher than the normal phosphor. In determining the performance of PSS-added YAG:Ce3+ phosphors, white LEDs were fabricated by combining blue LEDs and phosphors. The phosphor exhibited lower color temperature because of the enhancement of yellow emission. Result shows that PSS can be applied as a flux, which decreases the synthesis temperature of YAG phosphors.
Abstract : For this qualitative study, we conducted an in-depth analysis of unexpected situations that occur in sixth-grade electric circuit lessons in a South Korean elementary school, the causes of these situations, and factors affecting the teacher’s responses. We performed a detailed observation of electric circuit lessons taught by an experienced teacher and carried out pre-lesson and post-lesson interviews. The causes of unexpected situations were found to be students’ neglect of electrical components, poor quality electrical components, images in the textbook, and real-life examples and analogies used by the teacher. The situations considered unexpected by the teacher included an electric circuit that did not light up, incorrect experimental results, and student questions regarding the teacher’s real-life examples. The teacher handled these unexpected situations by explaining that electrical components are consumables, giving real-life examples, providing opportunities for inquiry, and limiting textbook use. These responses originated from the teacher’s belief that science teaching should be student-centered and inquiry-based, and needs to emphasize the relationship between science and real-life experience. The study offers implications for science education in general and the teaching of electric circuits, which presents significant difficulties for elementary school teachers.
Abstract : This paper proposes two methods for calculating current flow through an electric bulb, which is a nonlinear electric device: the graphical method and the optimal auxiliary function method. The currents flowing through an electric bulb of 2.5 V − 0.3 A with room temperature resistance R0 = 1.3 Ω according to the terminal voltages of it are calculated via the methods and are compared with the measured currents. Compared with the measured currents, the currents calculated via the graphical method have error rates below 5.95%, and the currents calculated via the optimal auxiliary function method have error rates below 2.44% in the operating region of the electric bulb. These low error rates demonstrate the validity and practicality of the two methods.
Abstract : Light scattering by small particles enables the characterization of their size, density, and refractive index. For example, a collimated laser beam can be used to detect micrometer-scale particles, such as fine dusts in air or microplastics in water, by measuring the intensity of the light scattered by them. However, millimeter-size laser beams cannot be used to detect particles smaller than 1 μm because the size of these particles is comparable to the wavelength of the laser beam, resulting in low light scattering. In this study, we demonstrated the measurement of light scattering by small particles with diameters of hundreds of nanometers by using a home-built laser microscope. We used two identical objective lenses to achieve optimized light illumination and collection in the measurements. The signal-to-noise ratio was minimized by achieving balanced detection with the lock-in amplifiers. Single particles were clearly revealed in the scanning scattering-intensity map. We expect that our proposed method will be useful for detecting and characterizing nanoscale particles in environment-monitoring systems.
Abstract : A solid-phase synthesis mechanism of CuAlO2 was studied, and a method for suppressing the secondary phases of CuO and CuAl2O4 during synthesis was developed. The p-type electrical characteristics according to the Mg addition amount were analyzed. Results showed that during heating, Cu2O was changed to CuO with high mobility and reactivity formed on the Al2O3 surface. The CuO-Al2O3 interface induced a diffusion reaction depending on the temperature. During heat treatment, Cu loss occurred in the upper and lower layers and CuO phase was observed in the middle layer. This non-uniformity caused Cu loss in the entire sample. After Cu loss was compensated, a single CuAlO2 phase was obtained. CuAlO2 and CuAl(1-x)Mg(x)O2 showed p-type conductivity. The residual amount of CuO and CuAl2O4 phases increased with the Mg doping amount and affected the decrease in hole mobility.
Abstract : A theoretical model, based on the density functional theory, has been proposed to study the electrostatic adsorption of uniformly charged soft (penetrating inside each other) and hard spherical ions, where the charge is uniformly smeared on the surface and uniformly smeared inside a sphere. The proposed model explains the layering phenomenon arising from the packing effect of hard spherical ions regardless of the charge distribution of ions, and the results are comparable to Monte Carlo simulation data for the soft and hard spherical ions. The strong cross-correlation between the hard sphere contribution and Coulomb interaction appears at strongly surface-associated ion and depends on the size of ions, whereas the hard sphere contribution plays an important role in ionic adsorption at low charged ion. The charge distribution of ions strongly influence the local charge and particle densities; the sphere distribution, where the charge is uniformly smeared on the surface, shows higher particle density than the shell distribution, where the charge is uniformly smeared inside a sphere.
Abstract : Carbon dots, which are carbon nanomaterials with a size below 10 nm, have easy luminescence modification, environmental friendliness, good photo-stability, low price, and hydrophilic properties. Considering that the characteristics of carbon dots can be modified by synthesis and their conditions, the synthesis of carbon dots has been performed for various methods. In this study, the carbon dots derived from whey protein were synthesized through hydrothermal decomposition. The carbon dots have a particle size of 10 nm and amorphous structure. In addition, the carbon dots have hydrophilic characteristics and various organic bonding among carbon, nitrogen, and oxygen atoms. The PL spectra of carbon dots showed that the dominant excitation and emission wavelengths of carbon dots were 275 and 420 nm, respectively. The Fe3+ ion sensing application of the carbon dots performed by mixing Fe3+ solution and carbon dot solution showed a 36% decrease in luminescence intensity, whereas the luminescence wavelength was not changed. Based on these results, the carbon dots derived from whey protein can be applied as the luminescent sensor for Fe3+ ions and hemoglobin detection.
Abstract : Potassium silicate solution (PSS) added with Y3Al5O12:Ce3+(YAG:Ce3+) phosphors was synthesized by using a solid-state reaction method. The crystal structure, morphology, and luminescence properties of the phosphors were measured for various PSS concentrations. The X-ray diffraction pattern of the phosphors shows that the addition of PSS promotes the formation of a garnet structure at lower temperature than commercial YAG phosphors. FE-SEM images show that the addition of PSS promotes the growth of particle size and aggregation. With the addition of 10 wt.% of PSS, the PL spectra show that the emission intensity at 533 nm is 20% higher than the normal phosphor. In determining the performance of PSS-added YAG:Ce3+ phosphors, white LEDs were fabricated by combining blue LEDs and phosphors. The phosphor exhibited lower color temperature because of the enhancement of yellow emission. Result shows that PSS can be applied as a flux, which decreases the synthesis temperature of YAG phosphors.
Abstract : A high resolution is essential for nano-imaging and micro-patterning; thus, a highly refractive material is necessary. The refractive index of general optical glass with respect to visible light is about 1.5, and even made with a high refractive index, it is less than 2.0. Therefore, obtaining a materialwith a sufficiently high refractive index is limited only by the optical material itself. In this study, the light transmission phenomenon of visible light in the nano-sized metal array structure was analyzed by 3D simulation. The refractive index of the metal array medium was calculated in accordance with the geometric size of the sub-wavelength metal material and the refractive index of the domain space. The refractive index of the medium was higher as the diameter and spacing between the cylindrical nano-sized metals were smaller, and there was no significant change in the refractive index was observed when the diameter was more than 30 nm. With respect to the 500-nm incident light wavelength the refractive index of the metal medium increased with the increase of the refractive index of the domain space.
Abstract : Vanadium dioxide (VO2) films were prepared on the n-GaN layer at 600 °C and oxygen partial pressure of 10–20 mTorr using pulsed laser deposition. The VO2 films displayed flat surfaces with a roughness of 1.9–2.1 nm, and they were hetero-epitaxy ones with the (200) orientation on n-GaN (0002). With the increase of the temperature, the resistance of the samples exhibited metal-insulator transition behaviors with a resistance change of ~104 times at TMI of ~350~K. Current–voltage characteristics indicated that VO2/n-GaN heterojunctions correspond to semiconductor/semiconductor junctions displaying a rectification ratio of ~100 below TMI, whereas they were metal/semiconductor junctions with a rectification ratio of 3–4 above TMI. When UV light was illuminated, VO2/n-GaN heterostructures clearly showed the photovoltaic effect and photocurrent switching behavior. The VO2/n-GaN heterostructure made at10 mTorr had a potential barrier of ~1.07 eV, which was estimated from capacitance–voltage measurement. This study shows that the metal-insulator transition behavior can modify the interfacial properties of the VO2/n-GaN heterostructure.
Abstract : Brownmillerite transition metal oxides are materials with alternating layers of transition metal–oxygen octahedral (MO6) and transition metal–oxygen tetrahedral (MO4), which have attracted considerable attention because of their various physical properties, for example, ion conductors, catalysts, synaptic device properties, metal-insulator transition, and multiferroicity. In particular, we can easily control the structure of the SrFeO2.5 thin film through pulsed laser epitaxy conditions and heat treatment. In this paper, we will discuss the fabrication and properties of SrFeO2.5 thin films deposited using pulsed laser epitaxy. The developmental trend of SrFeO2.5 thin-film devices based on topotactic phase transition and the behavior of atoms will be examined to promote oxygen diffusion during the topotactic phase transition. Furthermore, the room-temperature ferroelectric and ferromagnetic phenomena utilizing the low-dimensional tetrahedral network within the brownmillerite structure will be discussed.
Abstract : We investigated the passivation method of the laser-cut surface of a Si wafer. Wet and dry passivation processes were performed through dip-coating and plasma-enhanced chemical vapor deposition (PECVD), respectively. Dip-coating method of the laser-cut surface of the Si wafer with the Nafion solution reduced the passivation characteristics because the Nafion solution penetrated toward the center of the Si wafer surface. In the PECVD-based dry process, the SiNx thin film was well deposited on the laser-cut surface of the Si wafer, and the passivation performance was improved. The minority carrier lifetime was improved with increasing SiNx thin film thickness from 20 to 60 nm, owing to the increase in the number of dangling Si–H bonds of the cut surface of the Si wafer. The minority carrier lifetime mapping via photoluminescence measurement confirmed that the laser-cut surface of the Si wafer was well passivated. In addition, the minority carrier lifetime was rapidly increased at the laser-cut area of the Si wafer coated with a 50 nm-thick SiNx thin film.
Abstract : This study aimed to analyze the content of the photoelectric effect presented in introductory physics textbooks. Extracting the contents related to the photoelectric effect presented in six introductory physics textbooks widely used in Korea, the characteristics of the composition of the photoelectric effect contents were evaluated. Results show that the contents of the photoelectric effect in introductory physics textbooks differed depending on the textbook. In addition, based on the history of science related to the photoelectric effect, several textbooks did not include the history of science in the acceptance of the theory of the photoelectric effect. The photoelectric effect principle was primarily explained using the photon model, and the explanation based on the classical viewpoint, that is, the wave theory, was presented only in some textbooks. Moreover, several differences in the definition of photons and the quantum interpretation of experimental results were observed among textbooks. Furthermore, the implications for introductory physics education were discussed on the basis of the results of this study.
Abstract : For this qualitative study, we conducted an in-depth analysis of unexpected situations that occur in sixth-grade electric circuit lessons in a South Korean elementary school, the causes of these situations, and factors affecting the teacher’s responses. We performed a detailed observation of electric circuit lessons taught by an experienced teacher and carried out pre-lesson and post-lesson interviews. The causes of unexpected situations were found to be students’ neglect of electrical components, poor quality electrical components, images in the textbook, and real-life examples and analogies used by the teacher. The situations considered unexpected by the teacher included an electric circuit that did not light up, incorrect experimental results, and student questions regarding the teacher’s real-life examples. The teacher handled these unexpected situations by explaining that electrical components are consumables, giving real-life examples, providing opportunities for inquiry, and limiting textbook use. These responses originated from the teacher’s belief that science teaching should be student-centered and inquiry-based, and needs to emphasize the relationship between science and real-life experience. The study offers implications for science education in general and the teaching of electric circuits, which presents significant difficulties for elementary school teachers.
Abstract : Not many modern physics-related activities can be practiced in high school physics classes. Michelson interferometer experiments played an important role in the development of the theory of relativity. Furthermore, the principle of the Michelson interferometer has recently been used in the observation of gravitational waves, and thus, it can stimulate physics students' curiosity and interest in physics, and also allow them to experience the usefulness of physics. Commercial Michelson interferometer is expensive, having numerous optical components, and requires precise manipulation. The purpose of this study was to devise a low-cost Michelson interferometer experiment set that can be easily applied in high school physics classes. We devised a Michelson interferometer experiment set using convex mirrors, slide glass, and a 5 mW laser pointer and applied it to the performance assessment of high school students taking physics class as an elective. Student responses were examined to evaluate the effect of the experiment on the attitude toward physics laboratory.
Abstract : This study analyzed the changes in students’ misconceptions and thoughts about electrical circuits in PDEODE inquiry activities using PhET simulation. Consequently, some students had typical misconceptions about electric circuits and unique misconceptions depending on the student. The definition of current and voltage, direction of current, magnitude of the current at each point in an electric circuit, and voltage between the two points were easily transformed into scientific concepts by immediately confirming falsification cases with PhET simulations. However, the misconception of the electric current consumption model and related factors that affect the brightness of a light bulb did not change into a scientific concept even after several exploration activities. In addition, the students kept the idea that current is consumed by the bulb and developed incorrect mathematical formulas or ad hoc ideas to explain the results of virtual experiments related to the brightness of the bulb.
Abstract : In this study, we review the present status and possibility of teaching quantum physics in schools. We review the trends of research in teaching quantum physics to schoolchildren and analyze the content and representation of children’s trade books. The main contents of quantum physics in children’s trade books are categorized by atom and its structure, energy quantization, duality of light and matter, measurement and uncertainty, and entanglement and quantum technology. The quantum physics representation tools in children’s trade books are categorized by direct explanation, modeling/visualization, storytelling/historical description, and technology/everyday life.
Abstract : Hitting time in random walks on graphs is a substantial quantity for classical and quantum studies on Markov chains. The connection between random walks and electric networks has been recognized for a long time. Recently, the expression of hitting time was introduced in terms of effective resistance and total conductance. This expression has been used as a key element for the proof of quadratic speedup for finding marked vertices by quantum walks. However, to the best of our knowledge, no explicit derivation of the expression has been reported yet. This study provides a rigorous derivation of the expression, which facilitates a deep understanding of quantum walks.
Abstract : The various properties of the ground and excited electronic states of 4-{[(1,3, 4 - thiadiazol-2-yl- 5-amine) sulfanyl]methyl}- benzo[h] chromen -2(H)-one (THASMEBCH) were theoretically simulated utilizing density functional theory (DFT) and B3LYP in a 6-31 G (d,p) basis set. Bond lengths and angles were determined using DFT methods. Electronic properties, such as electronic energy, ionization potential, absolute softness, electrophilic index, electron affinity, absolute chemical hardness, and molecular electrostatic potential were studied. UV-visible, Raman, and IR spectra were evaluated by theoretical quantum computations. 1H and 13C Nuclear magnetic resonance (NMR) were reduced by GIAO method. On the basis of CIS, ZINDO, and TD-DFT theories, the Mullikan atomic charge was described for optimization.
Abstract : An Nd:YVO4 crystal with a thickness of 1 mm was longitudinally pumped with a laser diode with an output of 1 W and a wavelength of 808 nm. The thermal lens of the Nd:YVO4 crystal was measured using He-Ne laser, and the focal length was 76 cm. The focal length of the thermal lens in the case of lasing was measured from the resonator mode image size, and the measured result was 85 cm. It was approximately 12% longer than the focal length without lasing. M2 of a CW laser with a wavelength of 1064 nm was obtained by measuring the mode radius change as a function of propagation distance. M2 was also measured by measuring a beam parameter product. The two results were compared, which were consistent with each other within approximately 7.8%. Pointing stability, which is an important characteristic for laser applications, was also measured. When the resonator length was 5 cm, Δθx was 11 μrad and Δθy was 13 μrad.
YeonJung PARK, Joonghoe DHO*
New Phys.: Sae Mulli 2021; 71(5): 450-456
https://doi.org/10.3938/NPSM.71.450
Jongwon PARK, Insun LEE*
New Phys.: Sae Mulli 2021; 71(5): 476-489
https://doi.org/10.3938/NPSM.71.476
Chang-Duk KIM*, Younjung JO, Nguyen Tam Nguyen TRUONG
New Phys.: Sae Mulli 2021; 71(5): 422-426
https://doi.org/10.3938/NPSM.71.422
pISSN 0374-4914
