Ex) Article Title, Author, Keywords
pISSN 0374-4914
eISSN 2289-0041
pISSN 0374-4914
eISSN 2289-0041
Ex) Article Title, Author, Keywords
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.
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.
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.
Abstract : For Ce(Fe$_{0.4}$Co$_{0.6}$)$_{2}$ and CeFe$_{2}$ compounds, we obtained Fe/Co $3d$ and Ce $4f$ spectra by using photoelectron spectroscopy. With the Anderson impurity Hamiltonian, we analyzed theoretically the Ce $4f$ spectra of two compounds. Not only a bulk contribution but also a surface contribution to the Ce $4f$ spectrum is needed to explain the experimental Ce $4f$ spectrum, For the Ce(Fe$_{0.4}$Co$_{0.6}$)$_{2}$ compound, we obtained a theoretical bulk $4f$ spectrum by using a bare $f$ electron binding energy, $\epsilon_{f}^ B $, to be 0.90 eV and the average hybridization between a $f$ and conduction electrons, $\Delta_{av}^B$, to be 47.6 meV. From the theoretical results of the Ce(Fe$_{0.4}$Co$_{0.6}$)$_{2}$ compound, the number of $4f$ electrons, $n_{f}^B$, is 0.88 and the Kondo temperature, $T_{K}$, is 261K. For the CeCo$_{2}$ compound, we obtained a theoretical bulk $4f$ spectrum, $n_{f}^B$=0.80 and $T_{K}$=691K with $\epsilon_{f}^ B $=0.90 eV and $\Delta_{av}^B$=61.5 meV.
Abstract : In this study, we derived an approximate analytic function for the off-axis magnetic field of a finite-length solenoid by using the magnetic vector potential of a circular current loop. We verified that the derived analytic function reduced to a well-known magnetic field formula on the vertical axis of the solenoid and also inferred the magnetic field on the horizontal axis of the solenoid. Furthermore, we investigated the magnetic field at arbitrary points satisfying the approximate conditions through a simulation performed using Wolfram Mathematica.
Abstract : We address hydrogen exodiffusion of hydrogenated amorphous silicon thin films by using thermal desorption spectroscopy. Amorphous silicon has a disordered atomic structure and consists of dangling bonds, which work as electronically active defects. These defects can be passivated by hydrogen, and the material is called hydrogenated amorphous silicon.~Hydrogen exodiffusion provides information on Si-H bonding and the microstructure of the material.~In this work, we fabricated a series of hydrogenated amorphous silicon thin films of different thicknesses and analyzed the Si-H bonding and the microstructure of the films by using hydrogen exodiffusion. In particular, we observed that the 10-nm thin film showed porous microstructure because the film was still in island/channeling stage of film deposition at initial moments, which is premature for uniform film growth. A complementary analysis using Fourier-transform infrared spectroscopy gave consistent results.
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.
Abstract : Nuclear magnetic resonance (NMR) spectroscopy is currently widely used in modern chemistry and biology as a standard characterizing tool, especially for structural information on molecules or proteins. On the other hand, in condensed matter physics, NMR, taking advantage of the fact that a nuclear moment is extremely sensitive to the surrounding electrons has been developed into a sophisticated, independent local probe to investigate the static and the dynamic properties of interacting electrons in diverse materials. While the use of the NMR technique in condensed matter physics is much richer and more complex than in other disciplines, finding an appropriate introductory reference written for condensed matter NMR is not easy. The purpose of this review is to provide a practical quick reference for condensed matter NMR to researchers or beginners in this field. For this, I tried to introduce a concise description of the important concepts and principles of condensed matter NMR which minimizing or omitting complex theoretical background material.
Abstract : Nuclear magnetic resonance data of $^{27}$Al in an yttrium aluminum garnet (YAG: Y$_3$Al$_5$O$_{12}$) single crystal co-doped with V$_2$O$_5$(0.7\%) and Cr$_2$O$_3$(0.2\%) are obtained using a Fourier transform NMR spectrometer within the temperature range between 180 K ~ 410 K. The line width of the $^{27}$Al nucleus resonance line decreases with as temperature increases due to motional narrowing. The chemical shift of $^{27}$Al NMR spectra decreases as temperature increases for YAG crystal. The spin-lattice relaxation times $T_1$ of $^{27}$Al nucleus were computed as a function of temperature. The $T_1$ of $^{27}$Al nucleus in YAG single crystal increases as temperature increases. The calculated activation energy for the $^{27}$Al nucleus in YAG: V, Cr single crystal is $E_{a} = 58 \pm 3$ meV.
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.
Abstract : The use of supercapacitors in a battery system could be a solution to eliminate the need for short-term frequent replacement of batteries and to reduce size, resources and maintenance fees during frequency regulation (F/R) of a power grid. Furthermore, the electrochemical properties of graphene are different from those of commercial active carbon and still need additional verification in order to be applied to large-scale electrodes. In this study, we used spray-dry processed 3D crumpled graphene in order to improve energy density, which is directly connected to both the performance and the inhibition of electrode active-material restacking. We evaluated the charge/discharge electro chemical performance of graphene electrodes under various process conditions for the purpose of designing a proper electrode composition and electrolyte. As a result, the power density of graphene electrodes could be maintained between 17 kW/kg and 26 kW/kg by decreasing the binder content from 10 wt% to 5 wt%. In addition, the electrical capacity per volume was increased to 500% by using a 2-roll press, and the power density was confirmed to have been improved by more than 370% when SBPBF4 was used instead of TEABF4. Finally, we suggest an efficient process for the manufacture of large-scale electrodes. This process will allow entire of the capacitance and the electrochemical stability of a graphene supercapacitor.
Abstract : A high-efficiency grating antenna and a multimode interference beam splitter using a silicon-nitride waveguide have been studied for an optical phased array with an operating wavelength of 1550 nm. A waveguide grating antenna with patterned top cladding and a 1x2 multimode interference beam splitter with a tapered waveguide are considered. The optimized waveguide grating antenna and the multimode interference beam splitter offer above 70% directionality and 98% high single-mode transmission, respectively. These results indicate the possibility of using silicon nitride as a waveguide for a high-efficiency optical phased array.
Abstract : The Laplace and the Fourier transforms are famous integral transform methods in mathematical physics for solving differential equations. However, most undergraduate textbooks on differential equations only contain a few chapters covering Laplace and Fourier transforms, begin with their definitions as improper integrals on a half line, $(0,\infty)$, or on an entire line, $(-\infty,\infty)$, respectively, proceed with their properties, and then apply them to solve differential equations. Many students just follow these procedures while wondering how those integral transform methods arise naturally for physically reasonable situations. This present article presents new perspectives on derive the general definitions of the Laplace and the Fourier transforms and presents examples in physics to help students discover the Laplace and the Fourier transforms on various domains, in contrast to only a half line and a whole line in most textbooks.
Abstract : The purpose of this study was to analyze the physics-education-related articles published in the academic journals of “New Physics: Sae Mulli” in the early 2000s and recently, and to explore the characteristics of the changes and the trends in the field of physics education research. The analysis targeted 40 articles published from 2000 to 2002 and 113 papers published from 2017 to 2019. The result of the analysis showed that physics education research has tended to increase over the past 20 years, and that its weight has gradually increased in the journal. In the early 2000s, development research, which suggested experimental tools, for mechanics, for middle school students, was the most representative case. On the other hand, in recent years, the school level of participants has risen, based on pedagogical factors and learner responses. A tendency to turn to research using social science methods was noted. In addition, the participation targets, physics contents, and research methods have been diversified. Based on these results, we discuss some approaches and suggestions for improving the quality of physics education.
Abstract : We have numerically evaluated the position space and momentum space information entropy of the isospectral Modified Hylleraas plus exponential Rosen Morse potential and established that each level can be re-arranged as a function of the deformation parameter. The information densities of this potential have been graphically demonstrated and their properties thoroughly analyzed. An asymmetric shape dependence on the values of quantum number $(n, l)$ is observed for the position space information densities. The characteristic features of the information entropy in position and momentum space have been analyzed, and the lower bound of the sum of the entropies, expressed by using the Bialynicki-Birula and Mycielski inequality is satisfied. Compared to undeformed potential exhibiting squeezing phenomena in momentum space only the information entropy squeezing has been realized for position space, as well as momentum space, as a function of the deformation parameter with the choice of the same set of parameters. Interestingly, squeezed coherent states are obtained for the isospectral Eckart potential.
Abstract : A light guide plate (LGP) applied to an edge-type backlight unit is combined with a plastic optical fiber (POF) optical system, and a scattering pattern is applied at the bottom of the LGP. Then, the luminous effect of the LGP on the light emitted from the light source is analyzed. The proposed side-emitting system is bent to surround the edge of the LGP, and the light-emitting diodes (LED) are combined at the end of a POF. Computer simulations are performed to realize indirect light by controlling the light from the light-emitting holes in the cladding of the POF. In this paper, the illuminance produced inside the LGP due to the light-emitting grooves of the side-emitting system and the uniformity of the brightness of the upper portion are analyzed to confirm the efficiency of the side-emitting system coupled with the LGP. In addition, to establish the criteria for the LGP processing condition combined with the side-emitting system, we optimize the control conditions of the light-emitting holes in the cladding and the conditions of the scattering pattern at the LGP bottom to improve the optical characteristics of the LGP. Thus, the low-efficiency problem can be addressed from an optical perspective.
Abstract : In this research, the optimum phase control condition was analyzed by calculating the change in the nonlinear refractive index induced in a ytterbium-doped optical fiber by using 980-nm pump light. Simulations were performed to obtain the characteristic of the refractive index change while varying the optical power of the pump light and the length of the optical fiber. By investigating this characteristic, we were able to determine the optimal optical fiber length at a specific pump light power and calculate the amount of phase change. As a result of the simulation on the 10-cm-long ytterbium-doped optical fiber, the pump light power required to induce the $\pi$ rad phase change of the 1330-nm signal light was calculated to be 8.5 mW. The pump light power applied to induce a $\pi$ rad phase change in the fiber optic Michelson interferometer experiment was 9.5 mW, which was very similar to the simulation result. Thus, we confirmed that the phase control required by the phase-shifting interferometer could be sufficiently achieved by using a low pump-light power and an optical fiber of several tens of cm in length.
Abstract : Metallic nanoslits are useful for optical devices with strong light-matter interactions based on electric-field enhancements. The periodic array of metallic nanoslits with subwavelength pitch is promising because of the enhanced light transmission resulting in a high signal-to-noise ratio in the transmitted light signal. Here, we discuss the effective medium analysis of a periodic subwavelength nanoslit array composed of noble metals, that should be useful for the design of a nanoslit array. We calculate the optical transmission spectrum of a metallic nanoslit array for P-polarized incident light in the near infrared region by using full-wave numerical simulations; then, we analyze the transmission spectrum and its resonant light transmission by using an effective medium theory. The results show that the resonant transmission, which depends on the shape of the metallic nanostructures, can be analyzed in terms of changes in the effective permittivity and permeability, thereby it facilitating the efficient derivation of the design parameters of nanoslits for near infrared optical devices.
Abstract : We propose the fiber-optic reflection filter that can optically change the spectral bandwidths by using ytterbium-doped fiber Bragg gratings (Yb-FBGs). When 980-nm pump light is applied to the ytterbium-doped special optical fiber, the refractive index of the optical fiber core changes, and the central wavelength of fiber gratings shifts. To use this feature, we fabricated Yb-FBGs with lengths of 10 mm and 20 mm, and we measured the spectra for various applied current values of the pumping light. We implemented a fiber-optic reflection filter by using two Yb-FBG’s and measured its filter characteristics. The central wavelength of the 10-mm Yb-FBG was fixed by using a pump, and a variable light output was applied to the 20-mm Yb-FBG by using the other pump. Changes in the center wavelength and the bandwidth of the spectrum for the reflection filter according to the applied current of the other pump were observed. As a result of the measurement, the change rates of the center wavelength and the half width of the filter were about 0.60 pm/mA and about 0.05 pm/mA, respectively.~Development of various light sources and sensors may be possible by using the characteristics of a reflective filter capable of optically fine spectrum control.
Heungsoon IM, Hong-Seok KIM, Nam-Hee KIM, Yong-Joo DOH*
New Phys.: Sae Mulli 2018; 68(10): 1041-1047
https://doi.org/10.3938/NPSM.68.1041
Gukhyung IHM*
New Phys.: Sae Mulli 2018; 68(10): 1048-1051
https://doi.org/10.3938/NPSM.68.1048
Kyoung Hwa KIM, Ji-Hoon AHN, Hyung Soo AHN*, Min YANG, Sam Nyung YI, Injun JEON, Chae Ryong CHO, Hunsoo JEON, Jae Hak LEE, Hyo Suk LEE, Suck-Whan KIM†
New Phys.: Sae Mulli 2018; 68(10): 1052-1058
https://doi.org/10.3938/NPSM.68.1052
pISSN 0374-4914
