• Journal of the Korean Society for Precision Engineering
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• v.31 no.6
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• pp.513-519
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• 2014

For depth machining in die and mold, Electrical Discharge Machining (EDM) is used generally. To make deep hole and deep shape efficiently, cemented carbide endmill for depth machining is necessary. For this purpose, cemented carbide endmill was designed using design of experiment (DOE). To improve cutting performance, endmill was coated with multilayer surface treatment, TiAlCrSiN and TiAlCrN, for higher wear resistance. In order to evaluate the endmill, Transverse Rupture Strength (TRS) test was tried for investigating the relationship between surface treatment and strength in endmill body. Scratch test was also used for measuring adhesion force of each surface treatment. To evaluate hardness of surface treatment, Atomic Force Microscope (AFM) analysis was carried out. Wear test was executed for characteristics of each surface treatment in high temperature. Consequently, TiAlCrSiN was superior to the TiAlCrN coating in case of high temperature environment such as cutting.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.5
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• pp.196-201
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• 2014

We investigated defects and surface polarity in AlN and GaN by using wet chemical etching. Therefore, the effectiveness and reliability of estimating the single crystals by defect selective etching in NaOH/KOH eutectic alloy have been successfully demonstrated. High-quality AlN and GaN single crystals were etched in molten NaOH/KOH eutectic alloy. The etching characteristics and surface morphologies were carried out by scanning electron microscope (SEM) and atomic force microscope (AFM). The etch rates of AlN and GaN surface were calculated by etching depth as a function of etching time. As a result, two-types of etch pits with different sizes were revealed on AlN and GaN surface, respectively. Etching produced hexagonal pits on the metal-face (Al, Ga) (0001) plane, while hexagonal hillocks formed on the N-face. On etching rate calibration, it was found that N-face had approximately 109 and 15 times higher etch rate than the metal-face of AlN and GaN, respectively. The size of etch pits increased with an increase of the etching time and they tend to merge together with a neighbouring etch pits. Also, the chemical mechanism of each etching process was discussed. It was found that hydroxide ion ($OH^-$) and the dangling bond of nitrogen play an important role in the selective etching of the metal-face and N-face.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.5
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• pp.262-267
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• 2009

Superhydrophobic $TiO_2$ thin films were successfully fabricated on a glass substrate by wet process. Layer-by-layer (LBL) deposition and liquid phase deposition (LPD) methods were used to fabricate the thin films of micro-nano complex structure with a high roughness. To fabricate superhydrophobic $TiO_2$ thin films, the (PAH/PAA) thin films were assembled on a glass substrate by LBL method and then $TiO_2$ nanoparticles were deposited on the surface of (PAH/PAA) thin film by LPD method, Subsequently, hydrophobic treatment using fluoroalkyltrimethoxysilane (FAS) was carried out on the surface of prepared $TiO_2$ thin films. The $TiO_2$ thin film fabricated with 45 minutes immersion time on $(PAH/PAA)_{10}$ showed the RMS roughness of 65.6nm, water contact angel of $155^{\circ}$ and high transmittance of above 80% (>650nm in wavelength) after the hydrophobic treatment. The Surface morphologies, optical properties and contact angel of prepared thin films with different experimental conditions were measured by field emission scanning electron microscope (FE-SEM), atomic force microscope (AFM), UV-Vis spectrophotometer and contact angle meter.

• Applied Chemistry for Engineering
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• v.18 no.4
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• pp.356-360
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• 2007

Recently, dye sensitized solar cells (DSSCs) composed of nanoporous $TiO_2$, light-sensitive dyes, electrolytes, and counter electrode have been received much attention. Nanostructured particles with higher surface area for the higher adsorption of Ru (II) dye are required to increase the quantity of light absorption. Also, it has been reported that the key factor to achieve high energy conversion efficiency in the photoelectrode of DSSC is the heat treatment of $TiO_2$ paste with acid addition. In this work, we investigated the influence of acid treatment of $TiO_2$ solar cell on the photovoltaic performance of DSSC. The working electrodes fabricated in this work were characterized by X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), field emission scanning electron microscope (FE-SEM), and atomic force microscope (AFM). In addition, the influence of nanostructured photoelectrode fabricated with the acid-treated paste on the energy conversion efficiency was investigated on the basis of photocurrent-potential curves. It was found that the influence of acid-treated paste on the photovoltaic efficiency was significant.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.5
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• pp.227-231
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• 2010

Super hydrophilic $TiO_2$ thin films with photocatalytic property were successfully fabricated on a glass substrate by liquid phase deposition (LPD). The $TiO_2$ thin film formed nano particles on a surface at $70^{\circ}C$. As an immersion time in $TiF_4$ solution increased, the thickness of thin films gradually increased. $TiO_2$ thin film showed a water contact angel of below ca. $5^{\circ}$ and the transmittance of ca. 75~90 % in visible range. In addition, $TiO_2$ thin film showed the photocatalytic property to decompose methyl orange solution by the illumination of UV light. The surface morphologies, optical properties and contact angel of prepared thin films with a different immersion time were measured by field emission scanning electron microscope (FE-SEM), atomic force microscope (AFM), UV-Vis spectrophotometer and contact angle meter.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2000.11a
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• pp.3-4
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• 2000

Many researchers are interested in the synthesis and characterization of carbon nitride and diamond-like carbon (DLq because they show excellent mechanical properties such as low friction and high wear resistance and excellent electrical properties such as controllable electical resistivity and good field electron emission. We have deposited amorphous carbon nitride (a-C:N) thin films and DLC thin films by shielded arc ion plating (SAIP) and evaluated the structural and tribological properties. The application of appropriate negative bias on substrates is effective to increase the film hardness and wear resistance. This paper reports on the deposition and tribological OLC films in relation to the substrate bias voltage (Vs). films are compared with those of the OLC films. A high purity sintered graphite target was mounted on a cathode as a carbon source. Nitrogen or argon was introduced into a deposition chamber through each mass flow controller. After the initiation of an arc plasma at 60 A and 1 Pa, the target surface was heated and evaporated by the plasma. Carbon atoms and clusters evaporated from the target were ionized partially and reacted with activated nitrogen species, and a carbon nitride film was deposited onto a Si (100) substrate when we used nitrogen as a reactant gas. The surface of the growing film also reacted with activated nitrogen species. Carbon macropartic1es (0.1 -100 maicro-m) evaporated from the target at the same time were not ionized and did not react fully with nitrogen species. These macroparticles interfered with the formation of the carbon nitride film. Therefore we set a shielding plate made of stainless steel between the target and the substrate to trap the macropartic1es. This shielding method is very effective to prepare smooth a-CN films. We, therefore, call this method "shielded arc ion plating (SAIP)". For the deposition of DLC films we used argon instead of nitrogen. Films of about 150 nm in thickness were deposited onto Si substrates. Their structures, chemical compositions and chemical bonding states were analyzed by using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and infrared spectroscopy. Hardness of the films was measured with a nanointender interfaced with an atomic force microscope (AFM). A Berkovich-type diamond tip whose radius was less than 100 nm was used for the measurement. A force-displacement curve of each film was measured at a peak load force of 250 maicro-N. Load, hold and unload times for each indentation were 2.5, 0 and 2.5 s, respectively. Hardness of each film was determined from five force-displacement curves. Wear resistance of the films was analyzed as follows. First, each film surface was scanned with the diamond tip at a constant load force of 20 maicro-N. The tip scanning was repeated 30 times in a 1 urn-square region with 512 lines at a scanning rate of 2 um/ s. After this tip-scanning, the film surface was observed in the AFM mode at a constant force of 5 maicro-N with the same Berkovich-type tip. The hardness of a-CN films was less dependent on Vs. The hardness of the film deposited at Vs=O V in a nitrogen plasma was about 10 GPa and almost similar to that of Si. It slightly increased to 12 - 15 GPa when a bias voltage of -100 - -500 V was applied to the substrate with showing its maximum at Vs=-300 V. The film deposited at Vs=O V was least wear resistant which was consistent with its lowest hardness. The biased films became more wear resistant. Particularly the film deposited at Vs=-300 V showed remarkable wear resistance. Its wear depth was too shallow to be measured with AFM. On the other hand, the DLC film, deposited at Vs=-l00 V in an argon plasma, whose hardness was 35 GPa was obviously worn under the same wear test conditions. The a-C:N films show higher wear resistance than DLC films and are useful for wear resistant coatings on various mechanical and electronic parts.nic parts.

• Korean Chemical Engineering Research
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• v.43 no.4
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• pp.495-502
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• 2005

Copper was plated on the tungsten substrate by use of a direct copper electroless plating. The optimum deposition conditions were found to be with a concentration of $CuSO_4$ 7.615 g/L, EDTA of 10.258 g/L, and glyoxylic acid of 7 g/L, respectively. The solution temperature was maintained at $60^{\circ}C$. The pH was varied from 11.0 to 12.8. After the deposition, the properties of the copper film were investigated with X-ray diffractometer (XRD), Field emission secondary electron microscope (FESEM), Atomic force microscope (AFM), X-ray photoelectron spectroscope (XPS), and Rutherford backscattering spectroscope (RBS). The best deposition condition was founded to be the solution pH of 11.8. In the case of 10 min deposition at the pH of 11.8, the grain shape was spherical, Cu phase was pure without impurity peak ($Cu_2O$ peak), and the surface root mean square roughness was about 11 nm. The thickness of the film turned out to be 140 nm after deposition for 12 min and the deposition rate was found to be about 12 nm/min. Increase in pH induced a formation of $Cu_2O$ phase with a long rectangular grain shape. The pH control seems to play an important role for the orientation of Cu in electroless deposition. The deposited copper concentration was 99 atomic percent according to RBS. The resulting Cu/W film yielded a good adhesive strength, because Cu/W alloy forms during electroless deposition.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.3
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• pp.97-100
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• 2008

Polar and non-polar GaN was grown by the HVPE on various substrates and influence of polarity has been investigated. The $10\;{\mu}m$ thickness GaN were grown by HVPE is along A-plane ($11{\bar{2}}0$), C-plane (0001) and M-Plane ($10{\bar{1}}0$) sapphire substrate respectively. Surface properties were observed by optical microscope and atomic force microscopy. High resolution X-ray diffraction (HR-XRD) confirms the wurtzite structure. The donor band exciton peak located at ${\sim}3.4\;eV$ and also located yellow luminescence peak at 2.2 eV. The polarity of the GaN film has a strong influence on the morphology and the optical properties.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.411-411
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• 2012

Over the recent years, surface enhanced Raman spectroscopy (SERS) has dramatically grown as a label-free detecting technique with the high level of selectivity and sensitivity. Conventional SERS-active nanostructured layers have been deposited or patterned on rigid substrates such as silicon wafers and glass slides. Such devices fabricated on a flexible platform may offer additional functionalities and potential applications. For example, flexible SERS-active substrates can be integrated into microfluidic diagnostic devices with round-shaped micro-channel, which has large surface area compared to the area of flat SERS-active substrates so that we may anticipate high sensitivity in a conformable device form. We demonstrate fabrication of flexible SERS-active nanostructured substrates based on soft-lithography for simple, low-cost processing. The SERS-active nanostructured substrates are fabricated using conventional Si fabrication process and inkjet printing methods. A Si mold is patterned by photolithography with an average height of 700 nm and an average pitch of 200 nm. Polydimethylsiloxane (PDMS), a mixture of Sylgard 184 elastomer and curing agnet (wt/wt = 10:1), is poured onto the mold that is coated with trichlorosilane for separating the PDMS easily from the mold. Then, the nano-pattern is transferred to the thin PDMS substrates. The soft lithographic methods enable the SERS-active nanostructured substrates to be repeatedly replicated. Silver layer is physically deposited on the PDMS. Then, gold nanoparticle (AuNP) inks are applied on the nanostructured PDMS using inkjet printer (Dimatix DMP 2831) to deposit AuNPs on the substrates. The characteristics of SERS-active substrates are measured; topology is provided by atomic force microscope (AFM, Park Systems XE-100) and Raman spectra are collected by Raman spectroscopy (Horiba LabRAM ARAMIS Spectrometer). We anticipate that the results may open up various possibilities of applying flexible platform to highly sensitive Raman detection.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.96-96
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• 2009

투명전도막은 FPD의 전자부품에서 전극으로 널리 사용되고 있으며 현재 대부분의 투명전도막으로는 ITO가 사용되고 있다. 하지만, ITO에 사용되는 In은 희유금속으로 지속적인 사용량 증가로 가격의 급등과 더불어 수급 불안정으로 인해 In을 대체하고자 하는 연구가 집중적으로 이루어지고 있다. 그러나 $In_2O_3$를 대체한 ZnO계 등은 비저항이 높아 대체 적용이 가능하지 못하고 있다. 이에 In의 양을 줄이면서 상대적으로 저가이면서 광학적 특성이 우수한 ZnO을 첨가하여 기존의 ITO에 상응하는 전기전도도와 광투과율을 얻을 수 있는 새로운 3성분계 TCO 에 대한 연구가 활발히 이루어지고 있다. 따라서, 본 연구그룹은 $In_2O_3$을 기본 조성으로 하는 $In_2O_3-ZnO-SnO_2$계를 선정하여 IZTO target을 제조 후 RF magnetron sputtering 방법으로 투명전도막을 제작하였다. 본 연구에서는 RF 파워와 동작압력, 동작시간 그리고 열처리온도의 증착 조건에 따른 IZTO 박막의 특성을 평가하였다. 박막의 특성 및 표면 미세구조를 관찰하기 위해 AFM(Atomic Force Microscope)을 이용하였으며, XRD(X-ray diffraction)을 이용하여 결정성을 분석하였고, 4 point-prove, Hall effect measurement와 UV/Visible spectrometer를 통해 전기적, 광학적 특성을 평가하였다.