• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.10 no.2
• /
• pp.79-83
• /
• 2011

Magnetic seal uses a magnetic fluid to seal a gap between a rotating shaft and housing. It is distinguished from other kinds of seals from the fact that solid contact does not occur in the seal. This implies that it is free from solid rubbing thus dustless and provides a clean circumstance. That is the reason why the magnetic seal is used exclusively for most of vacuum chambers in semiconductor process where dustless clean circumstance is critical. A magnetic seal has been developed of which design parameters are determined based on published data, and an air pressure test has been done to examine its sealing capability. Effects of some design parameters have been studied through FEM analysis. The results show some notable aspects of design parameters and provide suggestions for developing the seals. Regarding the sealing capacity of the magnetic seal the factor to match the theoretical value with the actual one was found to be 0.4~0.7, which means still there is some discrepancy between theory and actual.

• Journal of the Korean Vacuum Society
• /
• v.12 no.4
• /
• pp.269-274
• /
• 2003

The electrical, optical and structural properties of ZnNiO thin _ films deposited on Si substrates using rf-magnetron sputtering method have been investigated before and after the thermal annealing processes. The crystallinity of the ZnNiO thin film become degraded with increasing the Ni contents. This is mainly because the lattice of the thin film was expanded due to the oxygen-deficient conditions. Concerning the electrical properties of the thin film, the carrier concentration increases ($6.81\times10^{14}\textrm{cm}^{-2}$) and Hall mobility decreases (36.3 $\textrm{cm}^2$/Vㆍs) with higher doping concentration of Ni. However, the carrier concentration and Hall mobility became low ($1.10\times10^{14}\textrm{cm}^2$ and high (209.6 $\textrm{cm}^2$/Vㆍs), respectively, after the thermal annealing process at $1000 ^{\circ}C$. We also observed a strong luminescene center peaking at 546 nm in photoluminescence spectra, which was caused by a deep level center in the ZnO band gap with oxygen deficient ZnNiO structure.

• Journal of the Korean Chemical Society
• /
• v.59 no.5
• /
• pp.397-406
• /
• 2015

ZnO, II-VI group inorganic compound semi-conductor, has been receiving much attention due to its wide applications in various fields. Since the ZnO has 3.37 eV of a wide band gap and 60 meV of big excitation binding energy, it is well-known material for various uses such the optical property, a semi-conductor, magnetism, antibiosis, photocatalyst, etc. When applied in the field of photocatalyst, many research studies have been actively conducted regarding magnetic materials and the core-shell structure to take on the need of recycling used materials. In this paper, magnetic core-shell ZnFe₂O₄@SiO₂ nanoparticles (NPs) have been successfully synthesized through three steps. In order to analyze the structural characteristics of the synthesized substances, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR) were used. The spinel structure of ZnFe₂O₄ and the wurtzite structure of ZnO were confirmed by XRD, and ZnO production rate was confirmed through the analysis of different concentrations of the precursors. The surface change of the synthesized materials was confirmed by SEM. The formation of SiO₂ layer and the synthesis of ZnFe₂O₄@ZnO@SiO₂ NPs were finally verified through the bond of Fe-O, Zn-O and Si-O-Si by FT-IR. The magnetic property of the synthesized materials was analyzed through the vibrating sample magnetometer (VSM). The increase and decrease in the magnetism were respectively confirmed by the results of the formed ZnO and SiO₂ layer. The photocatalysis effect of the synthesized ZnFe₂O₄ @ZnO@SiO₂ NPs was experimented in a black box (dark room) using methylene blue (MB) under UV irradiation.

• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 1996.06b
• /
• pp.259-279
• /
• 1996

최근 정보·전자산업의 발전으로 고 신뢰성 전자재료에 대한 수요가 증대되고 있으며 이러한 첨단산업의 기반의 될 신소재 중 전자세라믹스가 차지하는 비중이 그 대부분을 차지하고 있으며 이에 대한 수요와 기대가 점점 커지고 있다. 이러한 전자세라믹스는 유전재료, 자성재료, 압전재료, 도전성 재료 등으로 나뉘게 된다. 어떠한 분류에 들어가든 그 조성은 금속의 산화물 형태가 일반적이며 미세한 분말의 성형체를 소결(sintering) 함으로써 최종제품으로 완성된다. 이러한 전잣라믹스가 최근 요구되는 고 신뢰성, 고 밀도화를 달성하기 위해선 원료 분말 제조단계부터 제어가 필요하다. 원료분말의 균일·균질성과 그 입도는 소결특성 뿐만아니라 전기적 특성에도 큰 영향을 미치기 때문이다. 세라믹스의 분말제조 방법 중 일반적으로 사용되는 방법으로는 고상 산화물을 혼합하여 하소(calcination)한 후 분쇄하는 '고상합성법'과 금속의 염 또는 alkoxide 용액을 이용하여 화학적으로 제조하는 '습식 화학적 합성법'이 있다. 고상합성법은 합성온도가 높고 기계적 분쇄와 혼합에 의존하므로 균일·균질성이 떨어지고 분말크기를 1㎛ 이하로 만들기 힘들다. 반면에 습식화학적 합성법은 기계적인 분쇄와 혼합에선 얻을 수 없는 원자 혹은 분자단위의 균일한 혼합과 submicron 이하의 미세한 분말을 얻을 수 있다. 따라서 이러한 습식 화학적 합성으로 얻은 분말을 사용하면 미세한 입자의 특성으로 인해 소결온도를 낮출 수 있으며 균일한 미세구조와 균질한 조성을 갖게되어 기계적·전기적 물성증진도 가져올 수 있게 된다. 습식 화학적 분말합성법은 전술하였듯이 alkoxide의 가수분해를 이용하는 sol-gel 법과 금속의 염(salt) 용액을 이용하여, 화학적으로 화합물 침전을 얻거나 또는 공침전물(coprecipitate) 형태의 분말을 얻는, 침전법으로 나뉠 수 있다. 침전법의 근본원리는 pH 및 pCO3 등에 따른 이온종의 용해도 차이를 이용하는 것으로써 각 이온종에 따른 solubility product(ksp)를 이용하여 설명된다. 본 연구에서는 침전법을 사용한 Ba-, Pb-계 전자세라믹스의 분말합성에 대한 이론적 고찰과 공정개발 및 실험을 통한 물성증진 효과에 대해 알아보았다. 본 실험상의 전자세라믹스 조성은 강유전체, 세라믹반도체, 압효과에 대해 알아보았다. 본 실험상의 전자세라믹스 조성은 강유전체, 세라믹 반도체, 압전재료로 널리 사용되는 BaTiO3, PZT(PbZrO3-PbTiO3)와 수직 자기기록매체로 큰 가능성이 있으며 hard ferrite로 널리쓰이는 Ba-feerite(BaFe12O19)로써 수산화물 형태의 침전에 대한 기구(mechanism)와 물성에 대해 살펴보았다. 이러한 침전법에 의한 분말합성 과정에는 소결체의 물성에 영향을 미치는 pH 조절제나 원료에서 혼입될 수 있는 Na+, K+, Cl-, SO4- 등의 제거(washing 혹은 filtering)가 필수적이다. 그러나 침전법에서 얻게 되는 분말은 매우 미세하여 colloid를 형성하게 되며, 이러한 colloid 상태의 미세한 침전입자가 filtering media에 끼이게 되어 견고하면서도 상당한 부피를 가지는 filter cake을 형성하기 때문에 filtering에 많은 시간과 다량의 filtering agent (본 실험의 경우엔 증류수)가 필요하게 된다. 따라서 이러한 문제점을 해결하기 위하여 colloid 상태의 침전물을 얼렸다 녹이는 freezing process를 개발, 적용하여 그 원리 및 효과, 그로인한 분말형태를 관찰하여 보았다.

• Journal of the Microelectronics and Packaging Society
• /
• v.6 no.1
• /
• pp.81-89
• /
• 1999

The fabrication process for miniaturizing the Electronic Article Surveillance (EAS) sensor was studied using micromachining technique. Two types of sensor structure, free standing membrane type and diving beard type, were proposed and researched for establishing the fabrication process. The membrane type structure was easy to change the sensor shape but had the limitation for miniaturizing, because the size of the sensor depends on the silicon substrate thickness. The diving board type structure has the advantage of miniaturization and of free motion. Since the elastic modulus is not trio high, SiN film is expected to be adequate for the supporting membrane of magnetic sensor. The selectivity of $H_2O_2$for sputtered W with respect to Fe-B-Si, which was studded for magnetic sensor materials, was high enough to be removed after using as a protection layer. Therefore, the diving board type process using the silicon nitride film for the supporter of the sensor material and the sputtered W for protection layer is expected to be useful fur miniaturizing the Electronic Article Surveillance (EAS) sensor.

• Korean Journal of Materials Research
• /
• v.13 no.11
• /
• pp.737-741
• /
• 2003

Polycrystalline $Ti_{l-x}$ $Co_{x}$ $O_2$thin films on $SiO_2$ (200 nm)/Si (100) substrates were prepared using liquid-delivery metalorganic chemical vapor deposition. Microstructures and ferromagnetic properties were investigated as a function of doped Co concentration. Ferromagnetic behaviors of polycrystalline films were observed at room temperature, and the magnetic and structural properties strongly depended on the Co distribution, which varied widely with doped Co concentration. The annealed $Ti_{l-x}$ $Co_{x}$ $O_2$thin films with $x\leq$0.05 showed a homogeneous structure without any clusters, and pure ferromagnetic properties of thin films are only attributed to the X$l-x_{l-x}$ $Co_{x}$X$O_2$phases. On the other hand, in case of thin films above x = 0.05, Co-rich clusters formed in a homogeneous $Ti_{l-x}$ $Co_{x}$ $O_2$phase, and the overall ferromagnetic (FM) properties depended on both FMTCO and FMCo. Co-rich clusters with about 10-150 nm size decreased the value of Mr (the remanent magnetization) and increased the saturation magnetic field.

• Journal of the Korean Vacuum Society
• /
• v.21 no.5
• /
• pp.258-263
• /
• 2012

Fe-diluted Si alloys grown on p-type Si (100) substrates by pulsed-laser deposition method were studied for structural, electrical, and magnetic properties. The X-ray diffraction patterns for these alloy samples showed a few of peaks with cubic structures such as FeSi, $Fe_3Si$, and $Fe_4Si$. The Fe-composition in alloys are confirmed as Fe atomic percent about 1.25~6.49 % from energy dispersive spectroscopy measurement. The resistivity as a function of the reciprocal temperature was indicated an exponential increase with two activation energies of 5.21 and 7.79 meV. The maximum value of the magnetization at 10 K was about 100 emu/cc, and the ferromagnetism was also observed until 350 K from total magnetization as a function of temperature with applied magnetic field of 3,000 Oe.

• Journal of the Korean Magnetics Society
• /
• v.6 no.5
• /
• pp.298-304
• /
• 1996

We have manufactured FMR spectrometer over wide range(2-35 GHz). In order to test FMR spectrometer, res¬onance absorption has been measured of the standard sample DPPH. The Q vaules of absorption line are 189-1096. As a result, We noticed that FMR spectrometer has been manufactured well. FMR studies of MgFez04 single crystal have been performed at S, J, K-band. The resonance lines have been observed for the each orientation of (100) plane at 300 K. The values of the magnetic anisotropy constant $K_{1}$ and the spectroscopic spli tting g valule have been calculated from the ferromagnetic resonance curve, $-2.9{\times}10^{4}erg/cm^{3}$, 2.02 at 23.89 GHz, $-2.2{\times}10^{4}erg/cm^{3}$, 1.89 at 5.3 GHz and $-2.8{\times}10^{4}erg/cm^{3}$, 2.01 at 3.6 GHz.

• Korean Journal of Materials Research
• /
• v.14 no.4
• /
• pp.235-238
• /
• 2004

The LT-MBE (low temperature molecular beam epitaxy) allows to dope GaAs with Mn over its solubility limit. A 75 urn thick GaMnAs layers are grown on a low temperature grown LT-GaAs buffer layer at a substrate temperature of $260^{\circ}C$ by varying Mn contents ranged from 0.03 to 0.05. The typical growth rate for GaMnAs layer is fixed at 0.97 $\mu\textrm{m}$/h and the V/III ratio is varied from 25 to 34. The electrical and magnetic properties are investigated by Hall effect and superconducting quantum interference device(SQUID) measurements, respectively. Double crystal X-ray diffraction(DCXRD) is also performed to investigate the crystallinity of GaMnAs layers. The $T_{c}$ of the $Ga_{l-x}$ /$Mn_{x}$ As films grown by LT-MBE are enhanced from 38 K to 65 K as x increases from 0.03 into 0.05 whereas the $T_{c}$ becomes lower to 45 K when the V/III ratio increases up to 34 at the same composition of x=0.05. This means that the ferromagnetic exchange coupling between Mn-ion and a hole is affected by the growth condition of the enhanced V/III ratio in which the excess-As and As-antisite defects may be easily incorporated into GaMnAs layer.

• Journal of the Korean Magnetics Society
• /
• v.21 no.3
• /
• pp.88-92
• /
• 2011

We grew $Zn_{0.4}Fe_{2.6}O_4$ thin films using Pulsed Laser Deposition and studied their crystal structure and magnetical characteristics as a function of growth temperature ($T_g$). For the film with $T_g=300^{\circ}C$, X-ray reflections from ${\alpha}-Fe_2O_3$ and ZnO were observed. However, when $T_g$ was increased from 300 to $500^{\circ}C$, crystal structure of inverse spinel was stabilized with the crystal orientation of $Zn_{0.4}Fe_{2.6}O_4(111)/Al_2O_3(0001)$ without any detection of ${\alpha}-Fe_2O_3$ and ZnO phases. The surface morphology shows flattening behavior with increasing $T_g$ from 300 to $500^{\circ}C$. These observations indicate that Zn is substituted into tetrahedron A-site of the inverse-spinel $Fe_3O_4$. M-H curves exhibit clear ferromagnetism for the sample with $T_g=500^{\circ}C$ whereas no ferromagnetism is observed for the film with $T_g=300^{\circ}C$.