• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06a
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• pp.75-87
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• 1996

This review is presented under the following headings: 1.Introduction 1.1 Brief review of the properties of AlN 1.2 Historical survey of work on ceramic and single crystal AlN 2.Thermochemical background 3.Crystal growth 4.Doping 5.Potential applications and future work The known properties of AlN which make it of interest for various are discussed briefly. The properties include chemical stability, crystal structure and lattice constants, refractive indices and other optical properties, dielectric constant, surface acoustic wave velocity and thermal conductivity. The history of work in single crystals, thin films and ceramics are outlined and the thermochemistry of AlN reviewed together with some of the relevant properties of aluminium and nitrogen; the problems encountered in growing crystals of AlN are shown to arise directly from these thermochemical relationships. Methods have been reported in the literature for growing AlN crystals from melts, solution and vapour and these methods are compared critically. It is proposed that the only practicable approach to the growth of AlN is by vapour phase methods. All vapour based procedures share the share the same problems: $.$the difficulty of preventing contamination by oxygen & carbon $.$the high bond energy of molecular nitrogen $.$the refractory nature of AlN (melting point~3073K at 100ats.) $.$the high reactivity of Al at high temperatures It is shown that the growth of epitactic layers and polycrystalline layers present additional problems: $.$chemical incompatibility of substrates $.$crystallographic mismatch of substrates $.$thermal mismatch of substrates The result of all these problems is that there is no good substrate material for the growth of AlN layers. Organometallic precursors which contain an Al-N bond have been used recently to deposit AlN layers but organometallic precursors gave the disadvantage of giving significant carbon contamination. Organometallic precursors which contain an Al-N bound have been used recently to deposit AlN layers but organometallic precursors have the disadvantage of giving significant carbon contamination. It is conclude that progress in the application of AlN to optical and electronic devices will be made only if considerable effort is devoted to the growth of larges, pure (and particularly, oxygen-free) crystals. Progress in applications of epi-layers and ceramic AlN would almost certainly be assisted also by the availability of more reliable data on the pure material. The essential features of any stategy for the growth of AlN from the vapour are outlined and discussed.

• Economic and Environmental Geology
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• v.56 no.1
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• pp.13-21
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• 2023

X-ray powder diffraction study was conducted on the bulk modulus and phase transition behavior of synthetic zeolite X under high temperature and high pressure. Water and HCO₃^- solution were used as a PTM. Sample was heated and pressurized up to 250 ℃ and 5.18 GPa. The change of unit cell volume and phase transition were observed by X-ray diffraction. The lattice constants and unit cell volume of zeolite X, gmelinite, natrolite, and smectite were calculated using the GSAS2 program to which Le Bail's whole powder pattern decomposition (WPPD) method was applied. The bulk modulus of each zeolite X and smectite were calculated using the EosFit program to which the Birch-Murnaghan equation was applied. The bulk modulus of zeolite X is 89(3) GPa in water run, and zeolite X is 92(3) GPa in HCO₃^- solution run. In both run, pressure induced hydration (PIH) occurred due to the inflow of PTM into the zeolite X framework at initial pressure. Zeolite X transited to gmelinite, natrolite, and smectite in water run. Zeolite X, however, transited to smectite in HCO₃^- solution run. Interzeolite transformation occurred in water run, and did not occur in HCO₃^- solution run, which is assumed that conflict between the environment to form zeolite and the pH of the HCO₃^- solution.

• Korean Chemical Engineering Research
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• v.61 no.3
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• pp.394-400
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• 2023

In this study, the tuning phenomena, gas storage capacity, and thermal expansion behaviors of binary (cyclopentylamine + CH₄) and (cyclopropylamine + CH₄) clathrate hydrates were investigated for the potential applications of clathrate hydrates to gas storage. To understand the tuning behaviors of binary (cyclopentylamine + CH₄) and (cyclopropylamine + CH₄) clathrate hydrates, ¹³C solid-state NMR spectroscopy was used, and the results confirmed that maximum tuning factors for the binary (cyclopentylamine + CH₄) and (cyclopropylamine + CH₄) clathrate hydrates were achieved at 0.5 mol% and 1.0 mol% of guest concentration, respectively. The gas storage capacity of binary (cyclopentylamine + CH₄) and (cyclopropylamine + CH₄) clathrate hydrates were also checked, and the results showed the CH₄ capacity of our hydrate systems was superior to that of binary (tetrahydrofuran + CH₄) and (cyclopentane + CH₄) clathrate hydrates. The synchrotron diffraction patterns of these hydrates collected at 100, 150, 200, and 250 K confirmed the formation of a cubic Fd-3m hydrate. In addition, the lattice constant of clathrate hydrates with cyclopentylamine and methane were larger than that with cyclopropylamine and methane due to the effects of molecular size and shape.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.2
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• pp.45-53
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• 2023

The growth of Si on 4H-SiC substrate has a wide range of applications as a very useful material in power semiconductors, bipolar junction transistors and optoelectronics. However, it is considerably difficult to grow very fine crystalline Si on 4H-SiC owing to the lattice mismatch of approximately 20 % between Si and 4H-SiC. In this paper, we report the growth of a Si epilayer by an Al-related nanostructure cluster grown on a 4H-SiC substrate using a mixed-source hydride vapor phase epitaxy (HVPE) method. In order to grow hexagonal Si on the 4H-SIC substrate, we observed the process in which an Al-related nanostructure cluster was first formed and an epitaxial layer was formed by absorbing Si atoms. From the FE-SEM and Raman spectrum results of the Al-related nanostructure cluster and the hexagonal Si epitaxial layer, it was considered that the hexagonal Si epitaxial layer had different characteristics from the general cubic Si structure.

• Journal of Radiation Protection and Research
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• v.48 no.4
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• pp.197-203
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• 2023

Background: The thermoluminescent dosimeter (TLD) and Monte Carlo (MC) dosimetry are carried out to determine the occupational dose for personnel in the handling of ¹²⁵I seed sources. Materials and Methods: TLDs were placed in different layers of the Alderson-Rando phantom in the thyroid, lung and also eyes and skin surface. An ¹²⁵I seed source was prepared and its activity was measured using a dose calibrator and was placed at two distances of 20 and 50 cm from the Alderson-Rando phantom. In addition, the Monte Carlo N-Particle Extended (MCNPX 2.6.0) code and a computational phantom with a lattice-based geometry were used for organ dose calculations. Results and Discussion: The comparison of TLD and MC results in the thyroid and lung is consistent. Although the relative difference of MC dosimetry to TLD for the eyes was between 4% and 13% and for the skin between 19% and 23%, because of the existence of a higher uncertainty regarding TLD positioning in the eye and skin, these inaccuracies can also be acceptable. The isodose distribution was calculated in the cross-section of the head phantom when the ¹²⁵I seed was at two distances of 20 and 50 cm and it showed that the greatest dose reduction was observed for the eyes, skin, thyroid, and lungs, respectively. The results of MC dosimetry indicated that for near the head positions (distance of 20 cm) the absorbed dose rates for the eye lens, eye and skin were 78.1±2.3, 59.0±1.8, and 10.7±0.7 µGy/mCi/hr, respectively. Furthermore, we found that a 30 cm displacement for the ¹²⁵I seed reduced the eye and skin doses by at least 3- and 2-fold, respectively. Conclusion: Using a computational phantom to monitor the dose to the sensitive organs (eye and skin) for personnel involved in the handling of ¹²⁵I seed sources can be an accurate and inexpensive method.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.4
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• pp.63-69
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• 2022

Vanadium dioxide shows a unique and interesting property of metal-insulator transition, which has attracted great attention from the viewpoints of fundamental materials science and industrial applications. In this study, the effect of Mg and W addition on the metal-insulator transition of VO₂ were investigated for the bulk materials that are prepared by spark plasma sintering. The X-ray diffraction analysis of the sintered specimens revealed that the lattice parameters barely change, and the secondary phases are present. The transition temperature of MIT appears in the range of 64.2-64.6℃, regardless of the impurity element and content. On the other hand, the addition of Mg and W alters the electrical conductivity, i.e., the electrical conductivity increases by a factor of up to 2.4 or decrease by a factor of up to 57.4 depending on the impurity type and its content. The thermal conductivity showed the values of 1.8~2.5 W/m·K below the transition temperature, and the values of 1.9~2.8 W/m·K above the transition temperature. These changes in electrical and thermal conductivities can be attributed to the combination of the change in charge carrier density, the impurities as scattering centers, and the change in microstructures.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.24 no.2
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• pp.99-104
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• 2024

In the deficiency of an exact solution yielding algorithm, approximate algorithms remain as a solely viable option to the Minimum Linear Arrangement(MinLA) problem of Binary tree. Despite repeated attempts by a number of algorithm on k = 10, only two of them have been successful in yielding the optimal solution of 3,696. This paper therefore proposes an algorithm of O(n) complexity that delivers the exact solution to the binary tree. The proposed algorithm firstly employs an In-order search method by which n = 2^k - 1 number of nodes are assigned with a distinct number. Then it reassigns the number of all nodes that occur on level 2 ≤ 𝑙 ≤ k-2, (k = 5) and 2 ≤ 𝑙 ≤ k-3, (k = 6), including that of child of leaf node. When applied to k=5,6,7, the proposed algorithm has proven Chung[14]'s S^(k)_min=2^k-1+4+S^(k-1)_min+2S^(k-2)_min conjecture and obtained a superior result. Moreover, on the contrary to existing algorithms, the proposed algorithm illustrates a detailed assignment method. Capable of expeditiously obtaining the optimal solution for the binary tree of k > 10, the proposed algorithm could replace the existing approximate algorithms.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.3
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• pp.297-303
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• 2024

In this study, KTN heterolayer thin films were fabricated by alternately stacking films of K(Ta_0.70Nb_0.30)O₃ and K(Ta_0.55Nb_0.45)O₃ synthesized using the sol-gel method. The sintering temperature and time were 750℃ and 1 hour, respectively. All specimens exhibited a polycrystalline pseudo-cubic crystal structure, with a lattice constant of approximately 0.398 nm. The average grain size was around 130~150 nm, indicating relatively uniform sizes regardless of the number of coatings. The average thickness of a single-coated film was approximately 70 nm. The phase transition temperature of the KTN heterolayer films was found to be approximately 8~12℃. Moreover, the 6-coated KTN heterolayer film displayed an excellent dielectric constant of about 11,000. As the number of coatings increased, and consequently the film thickness, the remanent polarization increased, while the coercive field decreased. The 6-coated KTN heterolayer film exhibited a remanent polarization and coercive field of 11.4 μC/cm² and 69.3 kV/cm at room temperature, respectively. ΔT showed the highest value at a temperature slightly above the Curie temperature, and for the 6-coated KTN heterolayer film, the ΔT and ΔT/ΔE were approximately 1.93 K and 0.128×10^-6 K·m/V around 40℃, respectively.

• Applied Chemistry for Engineering
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• v.25 no.5
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• pp.455-462
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• 2014

This work investigated the hydrophobic coating of silicate yellow phosphor powder in the form of divalent europium-activated strontium orthosilicate ($Sr_2SiO_4:Eu^{2+}$) by using an atmospheric pressure dielectric barrier discharge (DBD) plasma with argon as a carrier and hexamethyldisiloxane (HMDSO), toluene and n-hexane as precursors. After the plasma treatment of the phosphor powder, the lattice structure of orthosilicate was not altered, as confirmed by an X-ray diffractometer. The coated phosphor powder was characterized by scanning electron microscopy, fluorescence spectrophotometry and contact angle analysis (CAA). The CAA of the phosphor powder coated with the HMDSO precursor revealed that the water contact angle increased from $21.3^{\circ}$ to $139.5^{\circ}$ (max. $148.7^{\circ}$) and the glycerol contact angle from $55^{\circ}$ to $143.5^{\circ}$ (max. $145.3^{\circ}$) as a result of the hydrophobic coating, which indicated that hydrophobic layers were successfully formed on the phosphor powder surfaces. Further surface characterizations were performed by Fourier transform infrared spectroscopy and X-ray photoelectron spectrometry, which also evidenced the formation of hydrophobic coating layers. The phosphor coated with HMDSO exhibited a photoluminescence (PL) enhancement, but the use of toluene or n-hexane somewhat decreased the PL intensity. The results of this work suggest that the DBD plasma may be a viable method for the preparation of hydrophobic coating layer on phosphor powder.

• Korean Security Journal
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• no.40
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• pp.209-242
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• 2014

This study is to understand sure the primary crime prevention has been incidence as a social problem intended for parents through the analysis of the Crime Prevention Design (CPTED) CPTED element of recognize elements that target crime prevention strategy to effectively help students be and an object of the present invention is to provide a policy suggestion haryeoneunde proposed basic data required for orientation. To achieve the study objectives such as the core framework in this study IPA: Importance-Performance Analysis) also was selected. Subjects of study in 2010 Gyeongju Elementary parents name and were 203 first research group investigating the secondary school population of the region in 2014 to nomadic parents of 297 people sampled selection. Questionnaire that use by this study applies "Important-Performance Analysis : IPA" technique that Martilla & James(1977) presented and analyzed awareness for CPTED elements of strategy for student's crime prevention to elementary school pupil students' parentse. It was the first group, 0.886, 0.920, 0.895 and 2nd group 0.880, 0.906, 0.878 that reliability of (Cronbach' s ${\alpha}$) the importance, and believability of run chart was the first group, 0.880, 0.917, 0.878 and 2nd group, 0.735, 0.840, 0.830. Analysis of the data carried out frequency analysis, reliability analysis, Frequency analysis was performed, paired sample t-Test for the reliability analysis, and the technical statistical analysis of the data is. The analysis of lattice bars execution through the IPA, the importance of the primary parents elements of CPTED strategies are generally very high, but found that the variation depending on the components that Performance. This study, an important element of the strategy to eliminate the school building for students from inside and outside the criminal fears CPTED is a mechanical surveillance in the first group, organizational surveillance, and the second group is the region intensified I'll showed mechanically and organizational factors in the investigation, and request that the investment is urgently important element is also execution low, crime prevention personnel security higher importance than expanding the front door. The analysis result of this study expects that basic data can be used in policy direction presentation that examines closely CPTED elements of strategy for crime prevention of students and applies CPTED's component effectively at elementary school hereafter.