• Journal of Powder Materials
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• v.21 no.3
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• pp.207-214
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• 2014

In this study, nano-scale copper powders were reduction treated in a hydrogen atmosphere at the relatively high temperature of $350^{\circ}C$ in order to eliminate surface oxide layers, which are the main obstacles for fabricating a nano/ultrafine grained bulk parts from the nano-scale powders. The changes in composition and microstructure before and after the hydrogen reduction treatment were evaluated by analyzing X-ray diffraction (XRD) line profile patterns using the convolutional multiple whole profile (CMWP) procedure. In order to confirm the result from the XRD line profile analysis, transmitted electron microscope observations were performed on the specimen of the hydrogen reduction treated powders fabricated using a focused ion beam process. A quasi-statically compacted specimen from the nano-scale powders was produced and Vickers micro-hardness was measured to verify the potential of the powders as the basis for a bulk nano/ultrafine grained material. Although the bonding between particles and the growth in size of the particles occurred, crystallites retained their nano-scale size evaluated using the XRD results. The hardness results demonstrate the usefulness of the powders for a nano/ultrafine grained material, once a good consolidation of powders is achieved.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2001.11a
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• pp.35-35
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• 2001

agnesium Oxide (MgO) with a NaCI structure is well known to exhibit high secondary electron emission, excellent high temperature chemical stability, high thermal conductance and electrical insulating properties. For these reason MgO films have been widely used for a buffer layer of high $T_c$ superconducting and a protective layer for AC-plasma display panels to improve discharge characteristics and panel lifetime. Up to now MgO films have been synthesized by lE-beam evaporation, Molecular Beam Epitaxy (MBE) and Metalorganic Chemical Vapor Deposition (MOCVD), however there have been some limitations such as low film density and micro-cracks in films. Therefore magnetron sputtering process were emerged as predominant method to synthesis high density MgO films. In previous works, we designed and manufactured unbalanced magnetron source with high power density for the deposition of high quality MgO films. The magnetron discharges were sustained at the pressure of O.lmtorr with power density of $110W/\textrm{cm}^2$ and the maximum deposition rate was measured at $2.8\mu\textrm{m}/min$ for Cu films. In this study, the syntheses of MgO films were carried out by unbalanced magnetron sputtering with various $O_2$ partial pressure and specially target power densities, duty cycles and frequency using pulsed DC power supply. And also we investigated the plasma states with various $O_2$ partial pressure and pulsed DC conditions by Optical Emission Spectroscopy (OES). In order to confirm the relationships between plasma states and film properties such as microstructure and secondary electron emission coefficient were analyzed by X-Ray Diffraction(XRD), Transmission Electron Microscopy(TEM) and ${\gamma}-Focused$ Ion Beam (${\gamma}-FIB$).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.131-131
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• 2009

This paper describes the fabrication and characteristics of polycrystalline (poly) 3C-SiC microresonators with $3{\times}10^{17}{\sim}1{\times}10^{19}cm^{-3}$ in-situ N-doping concentrations. In this work, the crystallinity, carrier concentration and surface morphology of the grown thin films were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The 1.2 ${\mu}m$ thick cantilvers and the 0.4 ${\mu}m$ thick doubly-clamped beam microresonators with various lengths were implemented using in-situ doping poly 3C-SiC thin films. The characteristics of the poly 3C-SiC microresonators were evaluated using quartz and a laser vibrometer under vacuum at room temperature. The resonant frequencies of the SiC microresonators decreased with doping concentrations owing to the reduction of the Young's modulus of the poly 3C-SiC thin films. It was confirmed that the resonant frequencies of the poly 3C-SiC microresonators are controllable by adjusting the doping concentrations.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.13.2-13.2
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• 2011

뼈의 역학기능을 예측하는 인자(predictive factor) 로서 골밀도(BMD)만으로는 충분하지 않다는 최근의 임상결과는, 골밀도 이외의 새로운 뼈의 강도 및 골절리스크를 지배하는 인자의 중요성을 보여준다. 이와 같은 골역학기능에 대한 골밀도 이외의 부가적인 지배인자를 골질(bone quality)이라고 하는데, 다양한 골질관련인자(bone quality-related factor) 중 하나의 지표로서 뼈의 주성분인 생체아파타이트(BAp)의 결정학적 방향성에 주목, 대표적인 경조직 질환을 해석하였다. 파골세포결손에 의해 대리석증을 유발하는 op/op마우스는 골밀도의 변화뿐만 아니라, 골질의 유의한 변화가 있었다. 즉, 이와 같은 결과는 파골세포결손에 의한 조골세포의 활성저하의 의해 골질이 저하됨을 시사하는 결과이며, 파골세포 과잉의 의해 골다공증을 유발하는 OPG-KO마우스는 골밀도가 급격히 저하됨과 동시에, BAp배향성도 급격히 낮아졌다. 즉, 골대사회전의 상승에 따른 섬유성골(woven bone)의 형성에 의해 BAp의 결정성장이 억제되며, 그 결과 BAp배향성이 저하된다고 사료된다. 이상, 본 연구에서는 대표적인 골 질환조직을 각각의 정상골과 비교함으로써, 골양(BMD)의 변화뿐만 아니라 골질(BAp배향성)의 변화를 발견하였다. 이와 같은 변화는 골질지표로서 BAp배향성이 유효하다는 것을 강하게 시사한다. 따라서 본 연구에 의해 얻어진 견해는 경조직 질환의 병리해명에 적용 가능함과 동시에, 경조직 질환의 진단 응용이나 치료약 개발, 임플란트 개발 등 폭넓은 분야에 유용하다고 할 수 있다.

• Corrosion Science and Technology
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• v.14 no.6
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• pp.301-312
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• 2015

Corrosion of zirconium fuel cladding is known to limit the lifetime and reloading cycles of fuel in nuclear reactors. Oxide layers formed on ZIRLO4^{TM}$ cladding samples, after immersion for 300-hour and 50-day in a simulated primary water chemistry condition ($360^{\circ}C$ and 20 MPa), were analyzed by using the scanning transmission electron microscopy (STEM), in-situ transmission electron microscopy (in-situ TEM) with the focused ion beam (FIB) technique, and X-ray diffraction (XRD). Both samples (immersion for 300 hours and 50 days) revealed the presence of the ZrO sub-oxide phase at the metal/oxide interface and columnar grains developed perpendicularly to the metal/oxide interface. Voids and micro-cracks were also detected near the water/oxide interface, while relatively large lateral cracks were found just above the less advanced metal/oxide interface. Equiaxed grains were mainly observed near the water/oxide interface.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.2
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• pp.199-205
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• 2011

Stainless steel 304 and 316 plates were deposited with the multi-layered coatings of titanium film (0.1 um) and gold film (1-2 um) by an electron beam evaporation method. The XRD patterns of the stainless steel plates modified with the multi-layered coatings showed the crystalline phases of the external gold film and the stainless steel substrate. Surface microstructural morphologies of the stainless steel bipolar plates modified with multi-layered coatings were observed by AFM and FE-SEM images. The external gold films formed on the stainless steel plates showed micro structure of grains of about 100 nm diameter. The grain size of the external surface of the stainless steel plates increased with the gold film thickness. The electrical resistance and water contact angle of the stainless steel bipolar plates covered with multi-layered coatings were examined with the thickness of the external gold film.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.302-302
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• 2011

The binary chalcogenide semiconductor Bi2Se3 is at the center of intensive research on a new state of matter known as topological insulators. It has Dirac point in their band structures with robust surface states that are protected against external perturbations by strong spin-orbit coupling with broken inversion symmetry. Such unique band configurations were confirmed by recent angle-resolved photoelectron emission spectroscopy experiments with an unwanted n-type doping effect, showing a Fermi level shift of about 0.3 eV caused by atomic defects such as Se vacancies. Since the number of defects can be reduced using the molecular beam epitaxy (MBE) method. We have prepared the Bi2Se3 film on noble metal Au(111) and semiconductor Si(111) substrates by MBE method. To characterize the film, we have introduced several surface sensitive techniques including x-ray photoemission electron spectroscopy (XPS) and micro Raman spectroscopy. Also, crystallinity of the film has been confirmed by x-ray diffraction (XRD). Using home-built scanning tunneling microscope, we observed the atomic structure of quintuple layered Bi2Se3 film on Au(111).

• Journal of the Korean institute of surface engineering
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• v.39 no.5
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• pp.235-239
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• 2006

The aluminum nitride(AlN) layer on Al7075 substrate has been formed through nitrogen ion implantation process. The implantation process was performed under the conditions : 100 keV energy, total ion dose up to $2{\times}10^{18}\;ions/cm^2$. XRD analysis showed that aluminum nitride layers were formed by nitrogen implantation. The formation of Aluminum nitride enhanced surface hardness up to 265HK(0.02 N) from 150HK(0.02 N) for the unimplanted specimen. Micro-Knoop hardness test showed that wear resistance was improved about 2 times for nitrogen implanted specimens above $5\;{\times}\;10^{17}\;ions/cm^2$. The friction coefficient was measured by Ball-on-disc type wear tester and was decreased to 1/3 with increasing total nitrogen ion dose up to $1\;{\times}\;10^{18}ions/cm^2$. The enhancement of mechanical properties was observed to be closely associated with AlN formation. AES analysis showed that the maximum concentration of nitrogen increased as ion dose increased until $5\;{\times}\;10^{17}\;ions/cm^2$.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.77-77
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• 2000

Titanium oxide (TiO2) thin films have valuable properties such as a high refractive index, excellent transmittance in the visible and near-IR frequency, and high chemical stability. Therefore it is extensively used in anti-reflection coating, sensor, and photocatalysis as electrical and optical applications. Specially, TiO2 have a high dielectric constant of 180 along the c axis and 90 along the a axis, so it is highlighted in fabricating dielectric capacitors in micro electronic devices. A variety of methods have been used to produce patterned self-assembled monolayers (SAMs), including microcontact printing ($\mu$CP), UV-photolithotgraphy, e-beam lithography, scanned-probe based micro-machining, and atom-lithography. Above all, thin film fabrication on $\mu$CP modified surface is a potentially low-cost, high-throughput method, because it does not require expensive photolithographic equipment, and it produce micrometer scale patterns in thin film materials. The patterned SAMs were used as thin resists, to transfer patterns onto thin films either by chemical etching or by selective deposition. In this study, we deposited TiO2 thin films on Si (1000 substrateds using titanium (IV) isopropoxide ([Ti(O(C3H7)4)] ; TIP as a single molecular precursor at deposition temperature in the range of 300-$700^{\circ}C$ without any carrier and bubbler gas. Crack-free, highly oriented TiO2 polycrystalline thin films with anatase phase and stoichimetric ratio of Ti and O were successfully deposited on Si(100) at temperature as low as 50$0^{\circ}C$. XRD and TED data showed that below 50$0^{\circ}C$, the TiO2 thin films were dominantly grown on Si(100) surfaces in the [211] direction, whereas with increasing the deposition temperature to $700^{\circ}C$, the main films growth direction was changed to be [200]. Two distinct growth behaviors were observed from the Arhenius plots. In addition to deposition of THe TiO2 thin films on Si(100) substrates, patterning of TiO2 thin films was also performed at grown temperature in the range of 300-50$0^{\circ}C$ by MOCVD onto the Si(100) substrates of which surface was modified by organic thin film template. The organic thin film of SAm is obtained by the $\mu$CP method. Alpha-step profile and optical microscope images showed that the boundaries between SAMs areas and selectively deposited TiO2 thin film areas are very definite and sharp. Capacitance - Voltage measurements made on TiO2 films gave a dielectric constant of 29, suggesting a possibility of electronic material applications.