상변태2 : 비정질 실리콘 박막의 저온 결정화에 미치는 전기장의 영향

최덕균 대한금속재료학회 ( 구 대한금속학회 ) 1999 대한금속학회 추계학술대회 개요집 Vol.1999 No.-

Non-linear behavior of multilayer ceramic capacitors with a new equivalent circuit under AC-fields

최덕균,Hyeon-Pyo Jeon,Eun-Sang Na,김상우 한양대학교 세라믹연구소 2007 Journal of Ceramic Processing Research Vol.8 No.4

The electrical properties were investigated to understand better the non-linear behavior of multilayer ceramic capacitors (MLCCs). The electrical properties of the capacitors with a new equivalent circuit were simulated by a Sawyer-Tower circuit system under a high AC-field using B2 spice software, the simulated results were then compared with the experimental results. The experimental Q-V curves showed the non-linearity of ferroelectricity in the applied AC-fields. The predicted Q-V curves using B2 spice software under various AC-fields also showed the non-linearity of ferroelectricity in high AC-fields. As a result, the nonlinear dielectricity of the MLCCs was successfully simulated by the new circuit model.

$Si_3N_4$ 결합 SiC 내화재료에 있어서 생성된 $Si_3N_4$의 미구조 변화

최덕균,이준근 한국세라믹학회 1982 한국세라믹학회지 Vol.19 No.2

This paper deals with the $Si_3N_4$-bonded SiC refractory in terms of its microstructure development during nitridation. When mixture of SiC grains and fine Si power is fired under nitrogen atmosphere, an interlocking network of $Si_3N_4$ whiskers is formed by nitridation of Si. It is found that the strength of $Si_3N_4$-bonded SiC refractory is soley due to the physical nature of this interlocking whiskers. At the initial stage of nitridation, $Si_3N_4$ whisker forms in very thin and long shape and, with further nitridation, it becomes thicker with diameters up to 0.35$\mu\textrm{m}$. It is found that the mechanical strength of $Si_3N_4$-bonded SiC refractory depends on the degree of nitridation and the development of microstructure.

꿀풀과 식물 정유의 주성분인 Thymol의 미백활성에 관한 연구

최덕균,박찬익,이선미,백정인 대한본초학회 2019 大韓本草學會誌 Vol.34 No.4

Objectives : Thymol (2-isopropyl-5-methylphenol), a natural monoterpenoid phenol, is one of the major odorant constituents found in natural essential oils of various herbal plants, such as Thymus quinquecostatus and Thymus vulgaris. Multiple biological activities of thymol, including antioxidative, antimicrobial, and anti-inflammatory effects, have been reported in numerous in vitro studies, and recently it was suggested that thymol may could inhibit oxidization of L-dihydroxyphenylalanine (L-DOPA) to dopaquinone required in melanogenesis pathway, as an antioxidant. Methods : MTT assay was performed to test the cytotoxic effect of thymol in B16F10 cells. Inhibitory effect of thymol to tyrosinase activities were examined using both mushroom tyrosinase and intracellular tyrosinase. Expression level of tyrosinase in B16F10 cells were investigated by western blot analysis. Results : The cell viability was decreased by thymol treatment in dose-dependant manner, leading significant cytotoxicity in 500 and 1000 μM thymol-treated groups. In the alpha-melanocyte stimulating hormone (α-MSH) -induced melanogenesis, administration of thymol significantly decreased extracellular (secreted) melanin content in dose-dependent manner. Cellular tyrosinase activity assay and western blot analysis of intracellular tyrosinase showed that thymol has a strong anti-melanogenic effect by inhibition of tyrosinase activity and by decreasing expression of tyrosinase that contribute to melanin synthesis in the B1610 cells. Conclusions : As the first functional study that prove anti-melanogenic effect of thymol and its underlying mechanism in the living cells, our study suggests the applicability of fragrance as the functional materials of cosmetics or health supplement, not as just an additive.

GaAs/Si Heteroepitaxy 구조에서 GaAs의 초기 핵생성에 관한 이론적 고찰

최덕균 한국결정성장학회 1991 韓國結晶成長學會誌 Vol.1 No.1

GaAs를 Si 웨이퍼에 성장시킬 때 초기단계의 핵생성에 대하여 computer simulation을 통해 이론적으로 고찰하였다. 기존의 핵생성이론과는 달리 초기의 미세한 핵의 경우 핵을 구성하는 ledge와 ledge간의 상호작용은 핵의 크기 및 모양에 의하여 결정되는 ledge간의 거리에 따라 변화함을 알 수 있었다. 따라서 여러 형태의 핵에 대하여 분석하여 본 결과 다층의 피라미드 형태로 GaAs 핵이 생성될 때 가장 낮은 excess에너지가 요구되었고 이와 같은 결과는 이러한 형태가 필연적으로 포함하게 되는 에너지가 낮은 Ga(111) facet 때문인 것으로 밝혀졌다. 그러므로 GaAs/Si에서 가장 문제가 되고 있는 전위결함도 초기의 핵생성에 크게 기인함을 알 수 있다. Early stage of GaAs nucleation on Si substrate was theoretically studied by computer simulation. Compared to the constant ledge interaction energy in conventional nucleation theory, functional behavior of ledge-ledge interaction resulted in small size clusters depending on the cluster size and shape. Among various kinds of clusters, the multilayer pyramidal shape GaAs cluster requires smallest excess free energy due to the formation of Ga(111) facet planes. There this result suggests that the defects involved in GaAs/Si are originated from the early stage nucleation.

Crystallization behavior of FALC processed a-Si at various electric field intensities

최덕균,김영배,강선미,정용재,김상진 한양대학교 세라믹연구소 2004 Journal of Ceramic Processing Research Vol.5 No.1

The effect of various electric field intensities on a Cu-field aided lateral crystallization (FALC) process of amorphous silicon(a-Si) films has been studied. The electric field intensity investigated in this study ranged from 15 V/cm to 180 V/cm. The intensity of the Raman spectral peak from the polycrystalline silicon (c-Si) increased monotonically with the electric field intensity during thermal annealing at a temperature of 450oC. The degree of crystallization calculated from the intensity of the Raman peak increased as well and resulted in 82% at the highest electric field of 180 V/cm. The crystallization velocity obtained from the sample at 180 V/cm was about 50 times larger than that from the sample at 15 V/cm. Consequently, it was verified that both the degree of crystallization and crystallization velocity depend strongly on the electric field intensities in FALC process

The effect on photosynthesis and osmotic regulation in Beta vulgaris L. var. Flavescens DC. by salt stress

최덕균,황정숙,최성철,임성환,김종국,추연식 한국생태학회 2016 Journal of Ecology and Environment Vol.39 No.1

This study was to investigate the effect of salt stress on physiological characteristics such as plant growth, photosynthesis, solutes related to osmoregulation of Beta vulgaris. A significant increase of dry weight was observed in 50 mM and 100 mM NaCl. The contents of Chl a, b and carotenoid were lower in NaCl treatments than the control. On 14 day after NaCl treatment, photosynthetic rate (PN), the transpiration rate (E) and stomatal conductance of CO2 (gs) were reduced by NaCl treatment. On 28 day after NaCl treatment, the significant reduction in gs and E was shown in NaCl 200 mM. However, PN and water use efficiency (WUE) in all NaCl treatments showed higher value than that of control. Total ion contents (TIC) and osmolality were higher than the control. On 14 day after treatment, the contents of proline (Pro) increased significantly in 200 mM and 300 mM NaCl concentration compared with control, whereas on 28 day in all treatments it was lower than that of the control. The contents of glycine betaine (GB) increased with the increase of NaCl concentration. The contents of Na+, Cl-, GB, osmolality and TIC increased with the increase of NaCl concentrations. These results suggested that under severe NaCl stress conditions, NaCl treatment did not induce photochemical inhibition on fluorescence in the leaves of B. vulgaris, but the reduction of chlorophyll contents was related in a decrease in leaf production. Furthermore, increased GB as well as Na+ and Cl- contents resulted in a increase of osmolality, which can help to overcome NaCl stress.

(Ba,Sr)TiO₃박막과 산화물 전극간의 계면제어와 그에 따른 특성변화

최덕균,박경웅,오세훈 국립경상대학교 공과대학 부설 첨단소재연구소 1998 尖端素材 Vol.8 No.-

기존의 산화물 전극인 RuO₂의 문제점인 BST와의 구조적 불일치를 perovskite 구조를 갖는 CSR전극의 적용을 통해 해결하고 더 나아가 BST와 조성적인 일치까지 이룰 수 있는 BSR이라는 새로운 전극물질을 이용하여 그에 따른 전기적 특성변화를 고찰하였다. CSR박막의 격자상수는 Ca, Sr의 양을 조절함으로써 3.83-3.94Å까지 변화시킬 수 있으며 BST와 완벽한 격자 정합을 이룰 수 있었다. 그리고 이러한 구조적 특성의 장점은 계면영역에서의 비정질 층의 감소 뿐만 아니라 결정성의 향상으로 나타났다. BSR전극위에 증착된 BST는 거의 epitaxial하게 성막됨을 HREM를 통해 관찰하였으며 이러한 현상은 self-graded interface에 의해 가능한 것으로 생각되어진다. 이러한 BSR 전극위에 증착된 BST는 유전상수 500 이상, 누설전류 8×10(-8)A/㎠이하 값을 나타내었다. 또한 누설전류는 구조적인 면에서 많은 영향을 받고 유전상수는 박막의 화학적, 조성적인 면에 많은 영향을 받음이 관찰되었다. The electrical properties of BST thin films on the structurally identical CSR electrode and on the chemically and structurally similar BSR electrode were investigated in relation with the interfaces. Lattice parameter of CSR films can be varied by controlling the Ca/Sr ratios from 3.83 to 3.94Å, so that the perfect lattice match with BST films can be obtained. Such structural match of CSR film with dielectric film resulted in improved crystallinity of interfacial layer, and the significant reduction of the undesirable layer in the interface region as a result. Further improvement in interfacial structure was achieved for the BST thin film on BSR electrode and was confirmed by HREM. It is thought that epitaxial growth of BST/BSR structure is associated with the self-graded interface. BST thin films deposited on (Ba0.51Sr0.49) RuO₃ electrode exhibited high dielectric constant(>500) and low leakage current density(<8×10(-8)A/cm₂). It turned out that the dielectric constant of BST thin films was more dependent on the chemical composition of the BSR and the leakage current was pore influenced by the structural campatibility with the electrodes.

RF Magnetron Sputtering법으로 $BaTiO_3$ 박막 증착시 $O_2/Ar$비가 박막의 특성에 미치는 영향

안재민,최덕균,김영호 한국세라믹학회 1994 한국세라믹학회지 Vol.31 No.8

Structural and electrical properties of BaTiO3 thin films deposited on Pt/SiO2/Si substrates by RF magnetron sputtering method have been investigated. Crystallization behavior and electrical properties were studied for the films deposited under various sputtering gas compositions (Ar+O2 gas mixture) and substrate temperatures. All the films deposited above 50$0^{\circ}C$ were all crystallized and their preferred orientation changed from (001) to (111) with the addition of oxygen gas. The dielectric constant of films deposited in pure argon was about 110 and showed little dependence on the substrate temperature. But that was increased as the ratio of O2/Ar increased and its substrate temperature dependence was discernible. The highest dielectric constant reached to 550. In addition, the films deposited in mixed gas showed stable dielectric properties against the frequency and temperature.

Sputtering법에 의한 $BaTiO_3$ 박막의 상형성에 관한 연구

안재민,최덕균,김영호 한국세라믹학회 1993 한국세라믹학회지 Vol.30 No.8

BaTiO3 sputtering targets of 3 inch diameter were prepared by sintering the CIP (Cold Isotatic Pressing) compacts at 136$0^{\circ}C$ for 3hrs. The apparent density and grain size were 97% and 30${\mu}{\textrm}{m}$, respectively. After BaTiO3 films were deposited on Si and Pt/Ti/SiO2/Si substrates using these targets, films were annealed at various conditions and the crystallization behavior, reaction with the substrate and the electrical properties were investigated. The films on both substrates required 5~20hrs furnace annealing for crystallization at the temperatures from $600^{\circ}C$ to 80$0^{\circ}C$. For the films on Si substrate, interaction between the film and the substrate was suppressed upt o $700^{\circ}C$ for 10 hrs and the relative dielectric constant was 30. As the annelaing temperature and time were increased, the relative dielectric constants of the films decreased due to the formation of silicate phases through the reaction with the substrate. For the BaTiO3 films on Pt/Ti/SiO2/Si substrate, the reaction with the substrate was further reduced when the annealing condition was identical to that for Si substrate, but the reaction between the layers in Pt electrode took place above $700^{\circ}C$. When the films were annealed at $600^{\circ}C$ where the stability of Pt electrode was sustained, relative dielectric constant was increased to 110 since the reaction with substrate was effectively reduced even for a longer annealing time and the crystallization was enhanced.