• Title/Summary/Keyword: Optical properties

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A Growth and Characterization of CsPbBr3 Thin Film Grown by Thermal Chemical Vapor Deposition (열화학기상증착법을 이용한 CsPbBr3 박막 성장 및 특성 연구)

  • Ga Eun Kim;Min Jin Kim;Hyesu Ryu;Sang Hyun Lee
    • Journal of the Microelectronics and Packaging Society
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    • v.30 no.2
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    • pp.71-75
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    • 2023
  • In this study, inorganic perovskite films with different compositions were grown by thermal chemical vapor deposition depending on the substrate and their optical properties were compared. Inorganic perovskite crystals were grown on SiO2/Si and c-Al2O3 substrates using CsBr and PbBr2, respectively, under the same growth conditions. Cs4PbBr6-CsPbBr3 crystallites were grown on the SiO2 with polycrystalline structure, while a CsPbBr3 (100) dominant thin film was formed on the c-Al2O3 substrate with single crystal structure. From the photoluminescence measurement, CsPbBr3 showed typical green emission centered at 534 nm with a full width at half maximum (FWHM) of about 91 meV. The Cs4PbBr6-CsPbBr3 mixed structure exhibits blue-shifted emission at 523 nm with a narrow FWHM of 63 meV and a fast decay time of 6.88 ns. These results are expected to be useful for application in photoelectric devices such as displays, solar cells, and light sensors based on inorganic metal perovskites.

Rendezvous Mission to Apophis: IV. Investigation of the internal structure - A lesson from an analogical asteroid Itokawa

  • Jin, Sunho;Kim, Yaeji;Jo, Hangbin;Yang, Hongu;Kwon, Yuna G.;Ishiguro, Masateru;Jeong, Minsup;Moon, Hong-Kyu;Choi, Young-Jun;Kim, Myung-Jin
    • The Bulletin of The Korean Astronomical Society
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    • v.46 no.2
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    • pp.58.1-59
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    • 2021
  • Exploration of asteroids' internal structure is essential for understanding their evolutional history. It also provides a fundamental information about the history of coalescence and collision of the solar system. Among several models of the internal structures, the rubble-pile model, confirmed by the near-Earth asteroid (25143) Itokawa by Hayabusa mission [1], is now widely regarded as the most common to asteroids with size ranging from 200 m to 10 km [2]. On the contrary, monolithic and core-mantle structures are also possible for small asteroids [3]. It is, however, still challenging to look through the interior of a target object using remote-sensing devices. In this presentation, we introduce our ongoing research conducted at Seoul National and propose an idea to infer the internal structure of Apophis using available instruments. Itokawa's research provides an important benchmark for Apophis exploration because both asteroids have similar size and composition [4][5]. We have conducted research on Itokawa's evolution in terms of collision and space weathering. Space weathering is the surface alteration process caused by solar wind implantation and micrometeorite bombardment [6]. Meanwhile, resurfacing via a collision acts as a counter-process of space weathering by exposing fresh materials under the matured layer and lower the overall degree of space weathering. Therefore, the balance of these two processes determine the space weathering degrees of the asteroid. We focus on the impact evidence on the boulder surface and found that space weathering progresses in only 100-10,000 years and modifies the surface optical properties (Jin & Ishiguro, KAS 2020 Fall Meeting). It is important to note that the timescale is significantly shorter than the Itokawa's age, suggesting that the asteroid can be totally processed by space weathering. Accordingly, our result triggers a further discussion about why Itokawa indicates a moderately fresh spectrum (Sq-type denotes less matured than S-type). For example, Itokawa's smooth terrains show a weaker degree of space weathering than other S-type asteroids [7]. We conjecture that the global seismic shaking caused by collisions with >1 mm-sized interplanetary dust particles induces granular convection, which hinders the progression of space weathering [8]. Note that the efficiency of seismic wave propagation is strongly dependent on the internal structure of the asteroid. Finally, we consider possible approaches to investigate Apophis's internal structure. The first idea is studying the space weathering age, as conducted for Itokawa. If Apophis indicates a younger age, the internal structure would have more voids [9]. In addition, the 2029 close encounter with Earth provides a rare natural opportunity to witness the contrast between before and after the event. If the asteroid exhibits a slight change in shape and space weathering degree, one can determine the physical structure of the internal materials (e.g., rubble-pile monolithic, thick or thin regolith layer, the cohesion of the materials). We will also consider a possible science using a seismometer.

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Effects of Substrate Temperature on Figure of Merit of Transparent Conducting GZO Thin Films (기판온도가 GZO 투명전도막의 재료평가지수에 미치는 영향 )

  • Hyun-Ho Shin;Yang-Hee Joung;Seong-Jun Kang
    • The Journal of the Korea institute of electronic communication sciences
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    • v.18 no.5
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    • pp.797-802
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    • 2023
  • We prepared GZO (Ga2O3 : 5 wt %, ZnO : 95 wt %) thin film on glass substrate according to the substrate temperature using the pulsed laser deposition method and investigated electrical and optical properties of the thin film. Through the XRD measurements, their were confirmed that all GZO thin films grew preferentially in c-axis and the GZO thin film deposited at 300℃ showed the best crystallinity with a FWHM of 0.38°. As the substrate temperature increased from 150 to 300℃, the resistivity of GZO thin film tend to decrease, while the average transmittance in the visible light region was not significantly affected. The figure of merit of the GZO thin film deposited at 300℃ was 2.05×104-1·cm-1, which was the best value, the resistivity and the average transmittance in the visible light region were 3.72 × 10-4 Ω·cm and 87.71 %, respectively. In this study, it was found that GZO thin film is very promising material for transparent conducting thin film.

Influences of luting cement shade on the color of various translucent monolithic zirconia and lithium disilicate ceramics for veneer restorations

  • Ghada Alrabeah;Nawaf Alamro;Atif Alghamdi;Ahmed Almslam;Meshari Azaaqi
    • The Journal of Advanced Prosthodontics
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    • v.15 no.5
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    • pp.238-247
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    • 2023
  • PURPOSE. The purpose of this study was to assess the effect of resin cement shade on the color of different novel ultratranslucent monolithic zirconia and lithium disilicate veneer materials. MATERIALS AND METHODS. For a total of 40 specimens, flat cylindrical discs with a 9-mm diameter and 0.5-mm thickness were created using CAD/CAM technology. The specimens were divided into five groups according to their material (n = 8) (e.max, Prettau, Aidite, Shofu and Dima) using A1 shade. Resin discs with the same diameter and shade as the specimens served as tooth-colored substructures. Three shades (neutral, light and warm) of resin cement try-in pastes (Variolink Esthetic LC) were used as the luting cement material. The color of each material group was measured before and after cementation using the three cement shades, and the CIE L*a*b* coordinates were obtained with a spectrophotometer. Values for the translucency parameter (TP) and color change delta E (E) before (baseline) and after cementation of each specimen were determined. To compare differences among the material groups within each shade of cement and among various shades of cement within each material, the data were analyzed using one-way ANOVA and post hoc testing. RESULTS. Color coordinates L*, a* and b* significantly changed after the application of try-in pastes relative to baseline values, with a noticeable decrease in lightness (L*) (P < .05). A significant color change (ΔE) was observed in all tested materials after cementation, with ΔE values exceeding 3.3 (P < .05). Although TP changed after cementation for most materials tested, these changes were not statistically significant (P > .05). Shofu and Dima ceramics showed the lowest TP values, while Aidite and Prettau showed the highest TP values. For e.max, translucency decreased after cementation with neutral and warm shades, and it significantly increased after cementation with a light shade. CONCLUSION. The shade of cement significantly altered the final color of the ceramic veneer material to a level above the threshold at which the clinical perception of color change occurred (> 3.3). The TP was not influenced by the cement shade. The translucency levels of the novel ultratranslucent multilayer monolithic zirconia ceramics Aidite and Prettau were higher than that of the lithium disilicate e.max material.

New Yellow Aromatic Imine Derivatives Based on Organic Semiconductor Compounds for Image Sensor Color Filters (이미지 센서 컬러 필터용 유기반도체 화합물 기반의 신규 황색 아로마틱 이민 유도체)

  • Sunwoo Park;Joo Hwan Kim;Sangwook Park;Godi Mahendra;Jaehyun Lee;Jongwook Park
    • Applied Chemistry for Engineering
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    • v.34 no.6
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    • pp.590-595
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    • 2023
  • Novel aromatic imine derivatives with yellow were designed and synthesized for their potential application in color filters for image sensors. The synthesized compounds possessed chemical structures using aromatic imine groups. This innovative material was evaluated thoroughly, considering its optical and thermal properties under conditions similar to commercial device manufacturing processes. Following a rigorous performance evaluation, it was found that (E)-3-methyl-4-((3-methyl-5-oxo-1-phenyl-1H-pyrazol-4(5H)-ylidene)methyl)-1-phenyl-1H-pyrazol-5(4H)-one, abbreviated as MOPMPO, exhibited an impressive solubility of 0.5 wt% in propylene glycol monomethyl ether acetate, predominantly utilized as the solvent in the industry. Furthermore, MOPMPO showed exceptional performance as a color filter material for image sensors, having a high decomposition temperature of 290 ℃. These data unequivocally establish MOPMPO as a viable yellow dye additive for coloring materials in image sensor applications.

Development of Solution-based Carbon Nanotube and Silver Nanowire Coating Technology using Silk Printing Technique (실크 스크린 프린팅 기법을 적용한 용액 기반의 탄소나노튜브와 은 나노 와이어 코팅 기술 개발)

  • Moojin Kim
    • Journal of Industrial Convergence
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    • v.21 no.9
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    • pp.33-39
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    • 2023
  • Nano-sized materials can be coated on various substrates, and since this material is transparent and conductive, it can be used as a transparent electrode for electronic devices or an electrode for power supply. In this study, CNT and Ag nanowires were repeatedly coated using the silk screen technique, and samples formed up to 5 times were fabricated, and their optical and electrical properties were measured and analyzed. It was confirmed that marks were formed on the surface of the silkscreen-coated sample according to the coating direction, and the trend of transmittance and surface resistance according to the number of times of coating was investigated. As the number of coatings increased, transmittance and surface resistance tended to decrease. In particular, in the case of transmittance, the range of change was large in the samples coated 2 and 5 times. These changes were confirmed by the Ag nanowire coating. In addition, starting from 700 nm, the previous wavelength region increased according to the wavelength, while the above showed a tendency to decrease. The surface resistance was lowered from 9Ω/cm2 when coating once to 0.856Ω/cm2 when coating five times. It was found that the resistance value was affected by Ag similarly to the permeability. In the future, it is necessary to realize a desired transparent electrode through Ag concentration and coating of Ag nanowires with other methods and fusion with highly transparent CNT to apply to electronic devices.

Adsorption Behaviors of Amphiphilic AuNPs at the Interface between Diverse organic Solvents and Water (다양한 유기용매와 물 경계면에서의 양친매성 금나노입자의 흡착 거동)

  • Yeon-Su Lim;Yeong-min Lee;Kyo-Chan Koo;Hee-Young Lee
    • Journal of Adhesion and Interface
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    • v.25 no.1
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    • pp.157-161
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    • 2024
  • Amphiphilic gold nanoparticles, synthesized by the simultaneous binding of hydrophilic and hydrophobic ligands on their surfaces, find diverse applications in energy, bio, optical, electronic technologies, and various other fields. Particularly, these amphiphilic gold nanoparticles possess both hydrophilic and hydrophobic characteristics, enabling them to activate interface at the interface of immiscible fluids and form organized structures. The surface properties of gold nanoparticles play a crucial role in influencing the behaviors of amphiphilic gold nanoparticles at the interface of two fluids. Therefore, this study investigated the adsorption behaviors of gold nanoparticles at the organic solvent-water interface based on the surface characteristics of amphiphilic gold nanoparticles and the type of organic solvents. It was observed that the amount of adsorbed gold nanoparticles at the interface increased with the length of hydrocarbon chains in hydrophobic ligands and increased with shorter hydrocarbon chains in the organic solvent. Furthermore, using the Langmuir isotherm model, the study confirmed the formation of a monolayer by amphiphilic gold nanoparticles and obtained significant thermodynamic parameters simultaneously.

Effect of Ethanol Fractionation of Lignin on the Physicochemical Properties of Lignin-Based Polyurethane Film

  • Sungwook WON;Junsik BANG;Sang-Woo PARK;Jungkyu KIM;Minjung JUNG;Seungoh JUNG;Heecheol YUN;Hwanmyeong YEO;In-Gyu CHOI;Hyo Won KWAK
    • Journal of the Korean Wood Science and Technology
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    • v.52 no.3
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    • pp.221-233
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    • 2024
  • Lignin, a prominent constituent of woody biomass, is abundant in nature, cost-effective, and contains various functional groups, including hydroxyl groups. Owing to these characteristics, they have the potential to replace petroleum-based polyols in the polyurethane industry, offering a solution to environmental problems linked to resource depletion and CO2 emissions. However, the structural complexity and low reactivity of lignin present challenges for its direct application in polyurethane materials. In this study, Kraft lignin (KL), a representative technical lignin, was fractionated with ethanol, an eco-friendly solvent, and mixed with conventional polyols in varying proportions to produce polyurethane films. The results of ethanol fractionation showed that the polydispersity of ethanol-soluble lignin (ESL) decreased from 3.71 to 2.72 and the hydroxyl content of ESL increased from 4.20 mmol/g to 5.49 mmol/g. Consequently, the polyurethane prepared by adding ESL was superior to the KL-based film, exhibiting improved miscibility with petrochemical-based polyols and reactivity with isocyanate groups. Consequently, the films using ESL as the polyol exhibited reduced shrinkage and a more uniform structure. Optical microscope and scanning electron microscope observations confirmed that lignin aggregation was lower in polyurethane with ESL than in that with KL. When the hydrophobicity of the samples was measured using the water contact angle, the addition of ESL resulted in higher hydrophobicity. In addition, as the amount of ESL added increased, an increase of 7.4% in the residual char was observed, and a 4.04% increase in Tmax the thermal stability of the produced polyurethane was effectively improved.

Highly Doped Nano-crystal Embedded Polymorphous Silicon Thin Film Deposited by Using Neutral Beam Assisted CVD at Room Temperature

  • Jang, Jin-Nyeong;Lee, Dong-Hyeok;So, Hyeon-Uk;Hong, Mun-Pyo
    • Proceedings of the Korean Vacuum Society Conference
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    • 2012.08a
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    • pp.154-155
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    • 2012
  • The promise of nano-crystalites (nc) as a technological material, for applications including display backplane, and solar cells, may ultimately depend on tailoring their behavior through doping and crystallinity. Impurities can strongly modify electronic and optical properties of bulk and nc semiconductors. Highly doped dopant also effect structural properties (both grain size, crystal fraction) of nc-Si thin film. As discussed in several literatures, P atoms or radicals have the tendency to reside on the surface of nc. The P-radical segregation on the nano-grain surfaces that called self-purification may reduce the possibility of new nucleation because of the five-coordination of P. In addition, the P doping levels of ${\sim}2{\times}10^{21}\;at/cm^3$ is the solubility limitation of P in Si; the solubility of nc thin film should be smaller. Therefore, the non-activated P tends to segregate on the grain boundaries and the surface of nc. These mechanisms could prevent new nucleation on the existing grain surface. Therefore, most researches shown that highly doped nc-thin film by using conventional PECVD deposition system tended to have low crystallinity, where the formation energy of nucleation should be higher than the nc surface in the intrinsic materials. If the deposition technology that can make highly doped and simultaneously highly crystallized nc at low temperature, it can lead processes of next generation flexible devices. Recently, we are developing a novel CVD technology with a neutral particle beam (NPB) source, named as neutral beam assisted CVD (NBaCVD), which controls the energy of incident neutral particles in the range of 1~300eV in order to enhance the atomic activation and crystalline of thin films at low temperatures. During the formation of the nc-/pm-Si thin films by the NBaCVD with various process conditions, NPB energy directly controlled by the reflector bias and effectively increased crystal fraction (~80%) by uniformly distributed nc grains with 3~10 nm size. In the case of phosphorous doped Si thin films, the doping efficiency also increased as increasing the reflector bias (i.e. increasing NPB energy). At 330V of reflector bias, activation energy of the doped nc-Si thin film reduced as low as 0.001 eV. This means dopants are fully occupied as substitutional site, even though the Si thin film has nano-sized grain structure. And activated dopant concentration is recorded as high as up to 1020 #/$cm^3$ at very low process temperature (< $80^{\circ}C$) process without any post annealing. Theoretical solubility for the higher dopant concentration in Si thin film for order of 1020 #/$cm^3$ can be done only high temperature process or post annealing over $650^{\circ}C$. In general, as decreasing the grain size, the dopant binding energy increases as ratio of 1 of diameter of grain and the dopant hardly be activated. The highly doped nc-Si thin film by low-temperature NBaCVD process had smaller average grain size under 10 nm (measured by GIWAXS, GISAXS and TEM analysis), but achieved very higher activation of phosphorous dopant; NB energy sufficiently transports its energy to doping and crystallization even though without supplying additional thermal energy. TEM image shows that incubation layer does not formed between nc-Si film and SiO2 under later and highly crystallized nc-Si film is constructed with uniformly distributed nano-grains in polymorphous tissues. The nucleation should be start at the first layer on the SiO2 later, but it hardly growth to be cone-shaped micro-size grains. The nc-grain evenly embedded pm-Si thin film can be formatted by competition of the nucleation and the crystal growing, which depend on the NPB energies. In the evaluation of the light soaking degradation of photoconductivity, while conventional intrinsic and n-type doped a-Si thin films appeared typical degradation of photoconductivity, all of the nc-Si thin films processed by the NBaCVD show only a few % of degradation of it. From FTIR and RAMAN spectra, the energetic hydrogen NB atoms passivate nano-grain boundaries during the NBaCVD process because of the high diffusivity and chemical potential of hydrogen atoms.

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Development of environmentally friendly inorganic fluorescent pigments, A3V5O14 (A = K and Rb) and Cs2V4O11: Crystal structure, optical and color properties (친환경 무기 형광 안료 A3V5O14 (A = K and Rb) and Cs2V4O11 개발: 결정구조, 광학적 특성 및 착색 특성)

  • Jeong, Gyu Jin;Kim, Jin Ho;Lee, Younki;Hwang, Jonghee;Toda, Kenji;Bae, Byoungseo;Kim, Sun Woog
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.30 no.2
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    • pp.47-54
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    • 2020
  • To develop the bright-vivid red- and yellow-inorganic fluorescent pigments with high luminescence properties, A3V5O14 (A = K and Rb) and Cs2V4O11 inorganic pigments were synthesized by a water assisted solid state reaction (WASSR) method and a conventional solid state reaction method. Although impurity peaks corresponding to the AVO3 and AV3O8 (A = K, Rb, and Cs) were observed in all samples prepared, the trigonal structure A3V5O14 (A = K and Rb) and orthorhombic structure Cs2V4O11 were successfully obtained as a main phase. These inorganic pigments showed the broad absorption band (under 550 nm) originated from CT transitions of VO4 polyhedron, and the strong broad red- and green-emission bands due to 3T21A1 and 3T11A1 transitions of the [VO4]3- group. The A3V5O14 (A = K and Rb) and Cs2V4O11 pigments showed a bright-vivid red- and yellow-body color, where the a* values of the A3V5O14 (A = K and Rb) were +35.5 and +45.9, respectively, and b* value of Cs2V4O11 pigments was +50.3. The L* values of the A3V5O14 (A = K and Rb) and Cs2V4O11 inorganic pigments were over +45. These results indicate that the A3V5O14 (A = K and Rb) and Cs2V4O11 inorganic pigments could be an attractive candidate as a bright-vivid red- and yellow inorganic pigments.