• Electronic Materials Letters
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• 제14권6호
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• pp.700-711
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• 2018

CdS synthesized by the chemical bath method at $70^{\circ}C$, has been used as an electron transport layer in the planar structure of the perovskite solar cells. A two-step spin process produced a mixed halide perovskite of $CH_3NH_3PbI_{3-x}Cl_x$ and a mixture of $PbCl_2$ and $PbI_2$ was deposited on CdS, followed by a sub-sequential reaction with MAI ($CH_3NH_3I$). The added $PbCl_2$ to $PbI_2$ in the first spin-step affected the structure, orientation, and shape of lead halides, which varied depending on the content of Cl. A small amount of Cl enhanced the surface morphology and the preferred orientation of $PbI_2$, which led to large and uniform grains of perovskite thin films. In contrast, the high content of Cl produces a new phase PbICl in addition to $PbI_2$, which leads to the small and highly uniform grains of perovskites. An improved surface coverage of perovskite films with the large and uniform grains maximized the performance of perovskite solar cells at 0.1 molar ratio of $PbCl_2$ to $PbI_2$. The depth profiling of elements in both lead halide films and mixed halide perovskite films were measured by Rutherford backscattering spectroscopy, revealing the distribution of chlorine along with the thickness, and providing the basis for the mechanism for enhanced preferred orientation of lead halide and the microstructure of perovskites.

• 천문학회보
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• 제46권1호
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• pp.45.2-46
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• 2021

The Hayabusa 2 mission target asteroid (162173) Ryugu is a near-Earth, carbonaceous (C-type) asteroid. Before the arrival, this asteroid is expected to be covered with mm- to cm- sized grains through the thermal infrared observations [1]. These grains are widely understood to be formed by past impacts with other celestial bodies and fractures induced by thermal fatigue [2]. However, the close-up images by the MASCOT lander showed lumpy boulders but no abundant fine grains [3]. Morota et al. suggested that there would be submillimeter particles on the top of these boulders but not resolved by Hayabusa 2's onboard instruments [4]. Hence, we conducted polarimetry of Ryugu to investigate microscopic grain sizes on its surface. Polarimetry is a powerful tool to estimate physical properties such as albedo and grain size. Especially, it is known that the maximum polarization degree (Pmax) and the geometric albedo (pV) show an empirical relationship depending on surface grain sizes [5]. We observed Ryugu from UT 2020 November 30 to December 10 at large phase angles (ranging from 78.5 to 89.7 degrees) to derive Pmax. We modified TRIPOL (Triple Range Imager and POLarimeter, [6]) to attach to the 1.8-m telescope at the Bohyunsan Optical Astronomy Observatory (BOAO). With this instrument, we observed the asteroid and determined linear polarization degrees at the Rc-band filter. We obtained sufficient data sets from 7 nights at this observatory to determine the Pmax value, and collaborated with other observatories in Japan (i.e., Hokkaido University, Higashi-Hiroshima, and Nishi-Harima) to acquire linear polarization degrees of the asteroid from total 24 nights observations with large phase angle coverage (From 28 to 104 degrees). The observational results have been published in Kuroda et al. (2021) [7]. We thus found the dominance of submillimeter particles on the surface of Ryugu from the comparison with other meteorite samples from the campaign observation. In this presentation, we report our activity to modify the TRIPOL for the 1.8-m telescope and the polarimetric performance. We also examine the rotational variability of the polarization degree using the TRIPOL data.

• 한국가구학회지
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• 제20권1호
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• pp.82-94
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• 2009

In this study, I suggest dyed-Glued laminated woods by using birch woods which are relatively cheaper than others. Since the dyed-Glued laminated woods which have the various colors to satisfy people's tastes and the dignified grains in the old woods enable us to product freely, these can provide us with stability of supply through replacing rare materials. The making wooden furniture designed with dyed-Glued laminated woods has these following characteristics. (1) This method which uses various colored woods can fulfill consumers' tastes through dyeing wooden plates, instead of using domestic woods which have limited colors-white, yellow and black. (2) Gathering wooden plates made by setting them into various frames enables us to get in large quantities of the materials with good grains, which we can only take from old woods. (3) Producing culture products using various colors and grains has enabled us to satisfy consumers and to create pro-environmental pieces. In conclusion, this study can be an alternative idea to forest resources which have been decreasing, and be an application method of using cheaper birch woods as well. Gathering and dyeing wooden plates might bring about the economic effect and be of much help to the expansion as furniture materials as well as interior ones.

• 한국세라믹학회지
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• 제39권3호
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• pp.217-221
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• 2002

Si and ${\alpha}-Si_3N_4$ powder mixtures added with 3 wt% $Y_2O_3$ were reacted under 5 MPa nitrogen pressure. The reaction products contained ${\alpha}-Si_3N_4$ particles with elongated shapes. Length and width of the elongated grains were the maximum when the starting powder mixture of 50 wt% Si - 47 wt% ${\alpha}-Si_3N_4$ and 3 wt% $Y_2O_3$ was used. Aspect ratio of the elongated grains were between 4.4 and 5. When the starting powder mixture contained 70 wt% Si, large particles with irregular shapes appeared. Meanwhile, the reaction did not proceed when the starting powder mixture contained 30 wt% Si and less. The SHS product was easy to crush and the elongated particles obtained from the starting powder mixtures of 40 wt% Si - 57 wt% ${\alpha}-Si_3N_4$ - 3 wt% $Y_2O_3$ and 50 wt% Si - 47 wt% ${\alpha}-Si_3N_4$ - 3 wt% $Y_2O_3$ were good candidates for the seeds.

• 한국안광학회지
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• 제5권1호
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• pp.55-59
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• 2000

본 연구에서는 ${\beta}$-SiC, ${\alpha}$-SiC, $Al_2O_3$, $Y_2O_3$ 분말들을 출발원료로 사용하여 일축 가압 소결 및 열처리함으로서 길게 자란 탄화규소입가들이 균일하게 분포된 자기강화 미세구조를 갖는 안경렌즈 절삭용 재료를 제조하였다. 주사전자 현미경을 통해 미세구조를 관찰하였다. 가압 소결과 열처리 동안에 탄화규소의 ${\beta}{\rightarrow}{\alpha}$ 상변태에 기인하여 길게 자란 ${\alpha}$-SiC 입자들이 형성되었고, 이로 인해 파괴인성이 증가하였다. 신소재의 대표적인 경도와 파괴인성은 각각 13.3 GPa과 $4.8MPa{\cdot}m^{1/2}$이었다.

• 천문학회보
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• 제43권1호
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• pp.73.1-73.1
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• 2018

We investigated shock history of three achondrite meteorites: NWA 3117, a howardite from asteroid Vesta, NWA 2727, a breccia from the Moon, and NWA 856, a shergottite from Mars. Shock histories were evaluated from deformation of plagioclase feldspars. Feldspar grains were classified based on observations in cross-polarized light as undulatory, mosaic, mosaic-recrystallized or maskelynite. This sequence represents increasing deformation of original feldspar crystals. Undulatory crystals have wavy extinction, mosaic crystals have patchy extinction, and mosaic-recrystallized grains appear as if they were originally coarse-grained and have recrystallized to mosaics of small equant crystals. Maskelynite grains are isotropic, indicating transformation to glass. Based on feldspar deformation, the degrees of impact processing are NWA 856 > NWA 3117 > NWA 2727. The high deformation of NWA 856 is expected because this sample is from Mars, which is a large parent body and requires a powerful impact to accelerate a rock to escape velocity. In contrast, the parent body of NWA 3117 (Vesta) is smaller than that of NWA 2727 (the Moon), yet NWA 3117 appears more highly deformed than NWA 2727. One possible explanation is that NWA 2727 is from a relatively young part of the Moon, which has not been exposed to impacts as long as the surface of Vesta.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.32.1-32.1
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• 2018

Novel soft magnetic materials can be achieved by altering material properties such as morphology, composition, crystallinity, and grain size of soft magnetic alloys. Especially, magnetic properties (i.e., saturation magnetization, coarcivity) of soft magnetics are significantly affected by grain boundaries which act as a control of magnetic domain wall movement. Thus, we herein develop a two-step electroless plating method to control morphology and grain size of FeCo films for excellent magnetic properties. Accordingly, the chemical composition to control the degree of polarization of FeCo alloys was altered by electroless deposition parameters; for example, electrolyte concentration and temperature. The grain size and crystallinity of FeCo alloys was dramatically affected by the reaction temperature because the grain growth mechanism dominantly occurs at $90^{\circ}C$ where as the neucleation only happens at $50^{\circ}C$. By simply controlling the temperature, the micron-sized FeCo grains embedded FeCo film was synthesized where the large grains allow high magnetization originated from larger magnetic domain with low corecivity and the nano-sized grains allow excellent soft magnetic properties due to the magnetic correlation length.

• 한국세라믹학회지
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• 제36권4호
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• pp.432-443
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• 1999

The self-toughened Si3N4 ceramics where needle-like coarse ${\beta}$-Si3N4 grains were dispersed within fine-grain-ed matrix were prepared via hot-prssing at 1730$^{\circ}C$ for 2 h using 5 vol% ${\beta}$-Si3N4 whiskers as a seed. In this study the microstructures and mechanical properties of self-toughened Si3N4 ceramics were investigated. The flexural strength of self-toughened Si3N4 ceramics was increased from 600-800 MPa of the Si3N4 monolith to 830-1025 MPa. The KIC was also increased from 4.0-5.0MPa$.$m1/2 of the Si3N4 monolith to 5.8-6.5MPa$.$m1/2$.$The needle-like coarse Si3N4 grains in self-toughened ceramics were considered to induce various toughening mechanisms including the crack deflection pull-out and bridging and to contribute to KIC improvement. In ad-dition to toughening mechanisms the KIC improvement was considered to be partially indebted also to the orien-tation of large ${\beta}$-Si3N4 grains and to the promoting effect of ${\beta}$-Si3N4 whiskers on the ${\alpha}$ to ${\beta}$ transtion.

• Journal of Magnetics
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• 제8권4호
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• pp.146-148
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• 2003

Multilayered films of Co/Pd have been studied as a candidate material for a high density perpendicular recording medium due to higher anisotropy energy. However, high exchange coupling among grains results in large transition noise. To reduce the exchange coupling and grain size, addition of 3rd elements and physical separation of grains have been attempted. In the present paper, effects of sputtering pressure, Co sublayer thickness and Pd underlayer thickness on magnetic properties and microstructures were studied. It was found that by increasing sputtering pressure from 5 mTorr to 25 mTorr, Ms decreased to one half and coercivity increased more than 5000 Oe. The increase of the coercivity is associated with physical separation of grains by high pressure sputtering. Ms per volume of Co for Co/Pd multilayered film deposited at 25 mTorr shows continuous decrease with increasing Co sublayer thickness. This was related to void formation and intermixing of Co/Pd interface. Also, effect of Pd underlayer thickness on magnetic properties will be discussed.

• 한국자기학회지
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• 제5권5호
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• pp.416-420
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• 1995

An attempt has been made to investigate the mechanism of magnetic alignment in the magnets produced by upset forging the $Pr_{20}Fe_{74}B_{4}Cu_{2}$ cast bulk alloy. Upset forging of the cast alloy was carried out for 20 sec to an 80 % thickness reduction (strain rate : $4{$\times}10^{-2}s^{-1}$) in an open die configuration at varying temperatures in the range $600^{\circ}-900^{\circ}C$. It has been found that the upset forging process at temperatures above $800^{\circ}C$ can achieve a magnetic alignment to a great extent from copper-containing Pr-Fe- B-type cast ingot. The growth manner of the ferromagnetic $Pr_{2}Fe_{14}B$ matrix grain in Pr-Fe-B-type alloys was studied by examining the morphology change of the matrix grain in sintered body, and it was found that the matrix grains grew in anisotropic manner such that the grain grew more rapidly along the a- or b-axis than along the c-axis. This anisotropic grain growth led to the plate-like shape of the matrix grain. The magnetic alignment during the upset forging was attributed to grain boundary gliding of the plate-like grains, and the geometry of the grains in the cast ingot and the presence of a large amount of the praseodymium-rich grain boundary phase were thought to play a key role in the achievement of magnetic alignment.