• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.81-81
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• 2011

Sol-gel spin-coating법을 이용하여 ZnO 박막을 증착하였다. Sol 전구체 용액을 Si(100) 기판에 증착하고 전열처리(pre-heat treatment)하여 gel 상태의 ZnO 박막을 형성시킨 후 다른 속도로 냉각시켰다. Atomic force microscopy (AFM), X-ray diffraction (XRD), Raman, photoluminescence (PL)을 이용하여 냉각속도가 ZnO 박막의 구조적 및 광학적 특성에 미치는 영향을 분석하였다. 느린 속도($5^{\circ}C$/min)로 냉각시킨 ZnO 박막은 나노섬유질구조(nano-fibrous structure)를 나타내었고, 상온에서 바로 냉각시킨 ZnO 박막은 매우 매끄러운 표면(mirror-like surface)을 나타내었다. ZnO (100), ZnO (002), ZnO (101) 방향을 나타내는 회절피크가 관찰되었고, 냉각속도에 따른 ZnO 박막의 배향성을 알아보기 위하여 texture coefficient (TC)를 계산해 보았다. 상온에서 바로 냉각시킨 ZnO 박막(TC(002)=76.3%)이 느린 속도로 냉각시킨 박막(TC(002)=45.2%)보다 (002) 방향으로의 배향성이 우세하게 나타났으며, 잔류응력도 작았다. 뿐만 아니라 PL을 이용한 광학적 특성평가에서도 상온에서 바로 냉각시킨 ZnO 박막에서 더 강한 강도와 좁은 반치폭(full-width at halt-maximum)을 갖는 near-band-edge emission (NBE) 피크가 관찰되었다. 후열처리에 따른 구조적 및 광학적 특성 변화 또한 연구하였다.

• Advances in nano research
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• v.4 no.1
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• pp.1-14
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• 2016

Superparamagnetic iron oxide nanoparticles (Nps), composed of magnetite, $Fe_3O_4$, or maghemite, ${\gamma}-Fe_2O_3$, core and biocompatible polymer shell, such as dextran or chitozan, have recently found wide applications in magnetic resonance imaging, contrast enhancement and hyperthermia therapy. For different diagnostic and therapeutic applications, current attempt is focusing on the synthesis and biomedical applications of various ferrite Nps, such as $CoFe_2O_4$ and $MnFe_2O_4$, differing from iron oxide Nps in charge, surface chemistry and magnetic properties. This study is focused on the synthesis of manganese ferrite, $MnFe_2O_4$, Nps by most commonly used chemical way pursuing better control of their size, purity and magnetic properties. Co-precipitation syntheses were performed using aqueous alkaline solutions of Mn(II) and Fe(III) salts and NaOH within a wide pH range using various hydrothermal treatment regimes. Different additives, such as citric acid, cysteine, glicine, polyetylene glycol, triethanolamine, chitosan, etc., were tested on purpose to obtain good yield of pure phase and monodispersed Nps with average size of ${\leq}20nm$. Transmission electron microscopy (TEM), X-ray diffraction, energy dispersive X-ray spectroscopy (EDX), $M\ddot{o}ssbauer$ spectroscopy down to cryogenic temperatures, magnetic measurements and inductively coupled plasma mass spectrometry were employed in this study.

• Journal of the Korean Magnetics Society
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• v.21 no.5
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• pp.185-192
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• 2011

The technique of producing thin film plays a crucial role in modern science and technology as well as in industrial purposes. Numerous efforts have been made to get high quality thin film through surface treatment of materials. PVD (Physical Vapor Deposition) and CVD (Chemical Vapor Deposition) are two of the most popular deposition techniques used in both scientific study and industrial use. It is well known that the film deposited by PVD and CVD commonly possesses a columnar microstructure which affects many film properties. In recent years, various types of deposition sources which feature high material uses and excellent film properties have been developed. Electromagnetic levitation source appeared as an alternative deposition source to realize high deposition rate for industrial use. Complex film structures such as nano multilayer and multi-components have been prepared to achieve better film properties. Glancing angle deposition (GLAD) has also been developed as a technique to engineer the columnar structure of thin films on the micro- and nanoscale. In this paper, the trends and major issues of thin film technology based on PVD and CVD have been discussed together with the prospect of thin film technology.

• Fashion & Textile Research Journal
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• v.21 no.3
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• pp.363-369
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• 2019

This study developed electroconductive textiles by coating polypyrrole to PET nonwoven-based Polyvinyl Alcohol (PVA) nanoweb made by electrospinning and applying the developed electrotextiles as ECG Electrodes. To find the optimum coating conditions for high electrical conductivity, the ratios of 2.6-Naphthalenedisulfonic acid with Disodium Salt (NDS) vs Ammonium Persulfate (APS) as an oxidant and a doping agent in the solution were changed from 3:7 to 7:3; the immersion time of the specimen in the solution was 1 hour. PVA nanowebs coated with polypyrrole under various conditions were filmed with FE-SEM. FT-IR analysis was also performed to examine the presence of polypyrrole nanoparticles in the PVA nanoweb. The electrical resistance of the treated specimens were measured with a Multimeter. Consequently, the PVA Nano Web was undamaged even after heat treatment that allowed for coating. Uniform polypyrrole nanoparticles then formed on the surface of the PVA nanoweb after coating. The measured electrical resistance was shown to be at least $12K{\Omega}/{\Box }$ from a maximum of $3,456K{\Omega}/{\Box }$. The proper amount of NDS content had a positive effect on the conductivity improvement of electroconductive textiles; in addition, the highest electrical conductivity was achieved with a ratio of 3:7 between NDS and APS.

• Applied Chemistry for Engineering
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• v.22 no.2
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• pp.185-189
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• 2011

In this work, nano-sized M-ferrites (M=Co, Ni, Cu, Zn) for the decomposition of carbon dioxide were synthesized by the chemical co-precipitation. From the thermogravimetric analysis, it was clear that the maximum weight loss of each sample took place below $350^{\circ}C$. High temperature calcination resulted in more systematic crystallines, smaller specific surface area and larger particle size. An analysis by FTIR in the range of $375{\sim}406cm^{-1}$ revealed the presence of chelates at the octahedral site, which implies the formation of spinel structure in the ferrites. The current work showed that a $500^{\circ}C$ is the optimum heat treatment temperature of metal ferrites for $CO_2$ decomposition reaction.

• Advances in nano research
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• v.13 no.1
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• pp.87-96
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• 2022

Drug self-delivery systems can easily realize combination drug therapy and avoid carrier-induced toxicity and immunogenicity because they do not need non-therapeutic carrier materials. So, designing appropriate drug self-delivery systems for specific diseases can settle most of the problems existing in traditional drug delivery systems. Retinal pigment epithelium is very important for the homeostasis of retina. However, it is vulnerable to oxidative damage and difficult to repair. Worse still, the antioxidants can hardly reach the retina by non-invasive administration routes due to the ocular barriers. Herein, the targeted group (folic acid) and antioxidant (melatonin) have been grafted on the surface of ZnO quantum dots to fabricate a new kind of drug self-delivery systems as a protectant via eyedrops. In this study, the negative nanoparticles with size ranging in 4~6 nm were successfully synthesized. They could easily and precisely deliver drugs to retinal pigment epithelium via eyedrops. And they realized acid degradation to controlled release of melatonin and zinc in retinal pigment epithelium cells. Consequently, the structure of retinal pigment epithelium cells were stabilized according to the expression of ZO-1 and β-catenin. Moreover, the antioxidant capacity of retinal pigment epithelium were enhanced both in health mice and photic injury mice. Therefore, such new drug self-delivery systems have great potential both in prevention and treatment of oxidative damage induced retinal diseases.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1B
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• pp.91-96
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• 2009

Layered double hydroxide is synthesized and used in the arsenate adsorption experiments. The shapes of two materials analyzed by TEM showed that unheated material is amorphous in shape, micro-sized while heat treated material showed more crystallized in shape and nano-sized. X-ray diffraction showed this result more obvious. $N_2$ adsorption-desorption results showed that the materials are mesoporous and the specific surface area of the heated material is more than two times larger than the unheated material. Adsorption of As(V) is expected to be more in the heated material than the unheated material. Kinetic test of arsenate adsorption showed very fast reaction. The reactivity of Fe with As(V) might be the main factor for this result. The reaction kinetic of the heated and the unheated materials were similar and even the adsorption isotherms showed similar results for both materials. Both materials are found to be useful in remediation of soil and groundwater polluted by waste mine tailings consist of high concentration of As(V).

• Journal of the Korean institute of surface engineering
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• v.46 no.2
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• pp.68-74
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• 2013

For the coating of diamond films on WC-Co tools, a buffer interlayer is needed because Co catalyzes diamond into graphite. W and Ti were chosen as candidate interlayer materials to prevent the diffusion of Co during diamond deposition. W or Ti interlayer of $1{\mu}m$ thickness was deposited on WC-Co substrate under Ar in a DC magnetron sputter. After seeding treatment of the interlayer-deposited specimens in an ultrasonic bath containing nanometer diamond powders, $2{\mu}m$ thick nanocrystalline diamond (NCD) films were deposited at $600^{\circ}C$ over the metal layers in a 2.45 GHz microwave plasma CVD system. The cross-sectional morphology of films was observed by FESEM. X-ray diffraction and visual Raman spectroscopy were used to confirm the NCD crystal structure. Micro hardness was measured by nano-indenter. The coefficient of friction (COF) was measured by tribology test using ball on disk method. After tribology test, wear tracks were examined by optical microscope and alpha step profiler. Rockwell C indentation test was performed to characterize the adhesion between films and substrate. Ti and W were found good interlayer materials to act as Co diffusion barriers and diamond nucleation layers. The COFs on NCD films with W or Ti interlayer were measured as less than 0.1 whereas that on bare WC-Co was 0.6~1.0. However, W interlayer exhibited better results than Ti in terms of the adhesion to WC-Co substrate and to NCD film. This result is believed to be due to smaller difference in the coefficients of thermal expansion of the related films in the case of W interlayer than Ti one. By varying the thickness of W interlayer as 1, 2, and $4{\mu}m$ with a fixed $2{\mu}m$ thick NCD film, no difference in COF and wear behavior but a significant change in adhesion was observed. It was shown that the thicker the interlayer, the stronger the adhesion. It is suggested that thicker W interlayer is more effective in relieving the residual stress of NCD film during cooling after deposition and results in stronger adhesion.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.4
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• pp.705-713
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• 2016

For the soft ground construction, the factors not considered in the design stage occurs in the construction stage so that they cause the increase of the construction cost due to the structural stability and the design change. The subject of the study is the construction section of the industrial complex access road made in the Ochang region of Chungcheongbuk-do. The study is concerned with selecting the soft ground handling method such as the replacement method using rock debris and the surcharge reflecting the service load as the soft ground handling measure and analyzing the effect of reducing the construction cost with the stability of structures and the reduction of the construction period. The soft ground in the study section consists of sandy and cohesive soil and is 2.4m to 5.5m deep. It is distributed unevenly between the 1.5m to 5.9m stratums under the ground surface. Settlement is not serious, but the future uneven settlement and difference are expected so that the future settlement behavior is estimated by analyzing the site measurement results after the soft ground treatment. Moreover, in consideration of the regional characteristics and economic efficiency, soil with good quality is replaced with rock debris as the replacement material so that 29% of the construction cost is reduced due to the increase of stability and the reduction of duration. If the estimation of the dispersion of the pore water pressure within the dam body and the change of the underground water level and the relation of the actually measured soft ground with consolidation is studied further on the basis of the study, it is expected that the behavior of the soft ground will be correctly estimated in various site conditions.

• Journal of the Korean Ceramic Society
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• v.39 no.6
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• pp.550-557
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• 2002

TiO$_2$ particles coated on fly ash composites for use in photocatalyst were synthesized by the precipitation dropping method and heated at $700^{\circ}C$ for 2 h. The pH of reaction solution, the addition rate of NH$_4$HCO$_3$, the stirring speed, the reaction temperature and the concentration of TiC1$_4$ had a pronounced effect on the nature of precipitated TiO$_2$ particles on the surface off fly ash and the crystal structure of precipitated TiO$_2$ particles. At an addition rate of NH$_4$HCO$_3$; 1.0 ml/min, the pH of the reaction solution; 6, the stirring speed; 1,000 rpm and the reaction temperature; 8$0^{\circ}C$, about 10 nm of TiO$_2$ particle size and homogeneous precipitated layer on the surface of a fly ash was achieved. On the contrary, at an addition rate of NH$_4$HCO$_3$; 0.3,0.5 ml/min, the pH of the reaction solution; 2 and 11, the stirring speed; 300~500 rpm and the reaction temperature; lower than 5$0^{\circ}C$:, Inhomogeneous precipitated layer was developed on a fly ash. TiO$_2$ particles with anatase phase was formed as-dried precipitation at the low concentration of Tic14, the high addition rate of NH$_4$HCO$_3$ and the high reaction temperature, the crystalline fraction of anatase increased with raising heat-treatment temperature and rutile phase began to formation at 80$0^{\circ}C$. The crystal size of TiO$_2$ particles increased with raising the heat-treatment temperature, the crystal size was showed about 21 m at $700^{\circ}C$. Anatase type of TiO$_2$ coated on the fly ash heated at $700^{\circ}C$ for 2 h showed 1.25 g/cm$^3$of particle density, 82.8% of strength and 69.5 Lab of whiteness and can be used as a photocatalyst.