• Applied Chemistry for Engineering
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• v.23 no.4
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• pp.377-382
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• 2012

CdS thin films have been widely used as a buffer layer of CIGS semiconductor solar cells to reduce the lattice mismatch between transparent electrode and absorber layer. In order to prepare the CdS films with high transparency and low resistivity, they were deposited by varying Cd concentration with the constant S concentration in the solution using chemical bath deposition method. They were analyzed in terms of structural, optical and electrical properties of CdS films according to the $[S^{2-}]/[Cd^{2+}]$ ratio. In the case of Cd concentration higher than S concectration, CdS thin films were formed mainly by cluster- by-cluster formation due to the homogeneous reaction between Cd and S in the solution. Therefore the grain size increased and the transmittance decreased. On the other hand, in the case of Cd concentration lower than S concentration, CdS films were formed by heterogeneous reaction on the substrate rather than in the solution. The CdS films have the grains with the uniform circular shape of a few hundreds ${\AA}$. As the Cd concentration increased in the solution, the $[S^{2-}]/[Cd^{2+}]$ ratio decreased and the resistivity decreased by the increase in the carrier concentration due to the formation S vacancy by the excess Cd.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.102-102
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• 2018

Electronic industry had required the finer size and the higher performance of the device. Therefore, 3-D die stacking technology such as TSV (through silicon via) and micro-bump had been used. Moreover, by the development of the 3-D die stacking technology, 3-D structure such as chip to chip (c2c) and chip to wafer (c2w) had become practicable. These technologies led to the appearance of HBM (high bandwidth memory). HBM was type of the memory, which is composed of several stacked layers of the memory chips. Each memory chips were connected by TSV and micro-bump. Thus, HBM had lower RC delay and higher performance of data processing than the conventional memory. Moreover, due to the development of the IT industry such as, AI (artificial intelligence), IOT (internet of things), and VR (virtual reality), the lower pitch size and the higher density were required to micro-electronics. Particularly, to obtain the fine pitch, some of the method such as copper pillar, nickel diffusion barrier, and tin-silver or tin-silver-copper based bump had been utillized. TCB (thermal compression bonding) and reflow process (thermal aging) were conventional method to bond between tin-silver or tin-silver-copper caps in the temperature range of 200 to 300 degrees. However, because of tin overflow which caused by higher operating temperature than melting point of Tin ($232^{\circ}C$), there would be the danger of bump bridge failure in fine-pitch bonding. Furthermore, regulating the phase of IMC (intermetallic compound) which was located between nickel diffusion barrier and bump, had a lot of problems. For example, an excess of kirkendall void which provides site of brittle fracture occurs at IMC layer after reflow process. The essential solution to reduce the difficulty of bump bonding process is copper to copper direct bonding below $300^{\circ}C$. In this study, in order to improve the problem of bump bonding process, copper to copper direct bonding was performed below $300^{\circ}C$. The driving force of bonding was the self-annealing properties of electrodeposited Cu with high defect density. The self-annealing property originated in high defect density and non-equilibrium grain boundaries at the triple junction. The electrodeposited Cu at high current density and low bath temperature was fabricated by electroplating on copper deposited silicon wafer. The copper-copper bonding experiments was conducted using thermal pressing machine. The condition of investigation such as thermal parameter and pressure parameter were varied to acquire proper bonded specimens. The bonded interface was characterized by SEM (scanning electron microscope) and OM (optical microscope). The density of grain boundary and defects were examined by TEM (transmission electron microscopy).

• Analytical Science and Technology
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• v.23 no.2
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• pp.138-146
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• 2010

The Korean Ministry of the Environment revised a few sections of the regulations in the Law of indoor air quality management for the reinforcement or adjustment of the regulation criteria standard for releasing pollutants from building materials. Especially, in case of sealant, the contents covering liquid building materials, excess standards and testing methods have been added simultaneously in this revision, As a result it is impossible to compare original standards with revised standards directly. For this reason, this study reviewed revised test method of sealant pollutant emission rates in terms of impact and validity in comparison with the original test method. Through this study, the basic properties of revised pollutant emission control standards was assessed. Especially in sealant, since each product has a wide deviation of time required for complete drying, it is proved that there are a large number of products that are not hardened completely in test time. The result of our experiments on the revised test methods showed that this revised test methods yield emission rates that are two and half times less than those of the original testing method. To apply the revised test method of sealant to all the sealant products, It is necessary to extend the test period or improve specimen to fit the test method for quickly drying sealant products.

• Applied Chemistry for Engineering
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• v.1 no.1
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• pp.83-90
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• 1990

The semiconducting $(Pb_1\;_xSn_x)_1$ $_yTe_y$, one of the low - temperature thermoelectric materials, has been prepared and its chemical composition and nonstoichiometry has been analyzed. The content of Pb in the specimens was determined by the complexometric back - titration method with EDTA and Pb(II) standard solutions. Te - content was analyzed with the redox titration method. The electrical conductivity and the thermoelectric power have also been measured by the DC 4 - probe and the heat-pulse technique, respectively. All of the specimens showed a nonstoichiometric behavior in their chemical compositions (Te excess), thus gave rise to a p - type semiconducting property, and the nonstoichoimetry became bigger as the Sn - content increased. The thermoelectric power vs. temperature results have been analyzed upon the basis of the Fermi level vs. temperature profiles in the saturation regime. The specimen of x=0.1 evolved a transition from p - to n - type property at about 670K, which has been explained by the fact that the mobility of electrons is bigger than that of holes in the temperature range of the intrinsic regime.

• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.3
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• pp.304-311
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• 2014

In this study, to apply hydrogen energy to ship engine and to generate effective hydrogen production, we investigated the effects of high temperature $H_2SO_4$ feed rate and cooling water rate to pump parts with fixed frequency needed to reciprocate motion and a simulation was conducted at each condition. In the fixed frequency and cooling water inlet flow rate of 0.5 Hz and 3.9 kg/s, we changed the high temperature $H_2SO_4$ flow rate to 47.46 kg/s (it is 105 % of 45.2 kg/s), 49.72 kg/s (110 %), and 51.98 kg/s (115 %). Also, at 0.5 Hz and 45.2 kg/s of frequency and high temperature $H_2SO_4$ flow, the thermal hydraulic analysis was performed at the condition of 95 % (3.705 kg/s), 90 % (3.51 kg/s), and 85 % (3.315 kg/s). In overall simulation cases, the physical properties of materials are more influential to the temperature increase in the pump part rather than the changes on the feed rate of high temperature $H_2SO_4$ and cooling water. A continuous operation of pump was also capable even if the excess feed of high temperature $H_2SO_4$ of about 15 % or the less feed of cooling water of about 15 % were performed, respectively. When the increasing feed of high temperature $H_2SO_4$ of up to 5 %, 10 %, and 15 % were compared with base flow (45.2 kg/s), the deviation of time period rose to a certain temperature and ranged from 0 to 4.5 s in the same position (same material). In case of cooling water, the deviation of time period rose to a certain temperature and ranged from 0 to 5.9 s according to the decreasing feed changes of cooling water at 5 %, 10 %, and 15 % compared to a base flow (3.9 kg/s). Finally, the additional researches related to the two different materials (Teflon and STS for Pitch and End-plate), which are concerned about the effects of temperature changes to the parts contacting different materials, are needed, and we have a plan to conduct a follow-up study.

• Korean Journal of Materials Research
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• v.20 no.10
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• pp.518-523
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• 2010

In this study, partially stabilized zirconia was synthesized using a chemical $Y_2O_3$ stabilizer and hydrothermal method. First, $YCl_3-6H_2O$ and $ZrCl_2O-8H_2O$ was dissolved in distilled water. Y-TZP (a $Y_2O_3$-doped toughened zirconia polycrystalline precursor) was also prepared by conventional co-precipitates in the presence of an excess amount of $NH_4OH$ solution under a fixed pH of 12. The Y-TZP precursors were filtered and repeatedly washed with distilled water to remove $Cl^-$ ions. $ZrO_2$-Xmol%$Y_2O_3$ powder was synthesized by a hydrothermal method using Teflon Vessels at $180^{\circ}C$ for 6 h of optimized condition. The powder added with the Xmol%- $Y_2O_3$ (X = 0,1,3,5 mol%) stabilizer of the $ZrO_2$ was synthesized. The crystal phase, particle size, and morphologies were analyzed. Rectangular specimens of $33mm{\times}8mm{\times}3$ mm for three-point bend tests were used in the mechanical properties evaluation. A teragonal phase was observed in the samples, which contains more than 3 mol% $Y_2O_3$. The $3Y-ZrO_2$ agglomerated particle size was measured at $7.01{\mu}m$. The agglomerated particle was clearly observed in the sample of 5 mol % $Y_2O_3-ZrO_2$, and and the agglomerated particle size was measured at 16.4 um. However, a 20 nm particle was specifically observed by FE-SEM in the sample of 3 mol% $Y_2O_3-ZrO_2$. The highest bending fracture strength was measured as 321.3 MPa in sample of 3 mol% $Y_2O_3-ZrO_2$.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.183-184
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• 2013

Two main MBE growth techniques have been used: plasma-assisted MBE (PA-MBE), which utilizes a rf plasma to supply active nitrogen, and ammonia MBE, in which nitrogen is supplied by pyrolysis of NH3 on the sample surface during growth. PA-MBE is typically performed under metal-rich growth conditions, which results in the formation of gallium droplets on the sample surface and a narrow range of conditions for optimal growth. In contrast, high-quality GaN films can be grown by ammonia MBE under an excess nitrogen flux, which in principle should result in improved device uniformity due to the elimination of droplets and wider range of stable growth conditions. A drawback of ammonia MBE, on the other hand, is a serious memory effect of NH3 condensed on the cryo-panels and the vicinity of heaters, which ruins the control of critical growth stages, i.e. the native oxide desorption and the surface reconstruction, and the accurate control of V/III ratio, especially in the initial stage of seed layer growth. In this paper, we demonstrate that the reliable and reproducible growth of GaN on Si (110) substrates is successfully achieved by combining two MBE growth technologies using rf plasma and ammonia and setting a proper growth protocol. Samples were grown in a MBE system equipped with both a nitrogen rf plasma source (SVT) and an ammonia source. The ammonia gas purity was ＞99.9999% and further purified by using a getter filter. The custom-made injector designed to focus the ammonia flux onto the substrate was used for the gas delivery, while aluminum and gallium were provided via conventional effusion cells. The growth sequence to minimize the residual ammonia and subsequent memory effects is the following: (1) Native oxides are desorbed at $750^{\circ}C$ (Fig. (a) for [$1^-10$] and [001] azimuth) (2) 40 nm thick AlN is first grown using nitrogen rf plasma source at $900^{\circ}C$ nder the optimized condition to maintain the layer by layer growth of AlN buffer layer and slightly Al-rich condition. (Fig. (b)) (3) After switching to ammonia source, GaN growth is initiated with different V/III ratio and temperature conditions. A streaky RHEED pattern with an appearance of a weak ($2{\times}2$) reconstruction characteristic of Ga-polarity is observed all along the growth of subsequent GaN layer under optimized conditions. (Fig. (c)) The structural properties as well as dislocation densities as a function of growth conditions have been investigated using symmetrical and asymmetrical x-ray rocking curves. The electrical characteristics as a function of buffer and GaN layer growth conditions as well as the growth sequence will be also discussed. Figure: (a) RHEED pattern after oxide desorption (b) after 40 nm thick AlN growth using nitrogen rf plasma source and (c) after 600 nm thick GaN growth using ammonia source for (upper) [110] and (lower) [001] azimuth.

• Journal of the Korean Magnetics Society
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• v.27 no.3
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• pp.87-91
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• 2017

Carbon-encapsulated Ni and metal Ni nanoparticles were synthesized by levitational gas condensation (LGC). Methane ($CH_4$) gas was used to coat the surface of the Ni nanoparticles. The Ni particles had a core diameter of 10 nm, and were covered by 2~3 nm thin carbon layers with multi-shells structure.The low magnetization comparing with the Ni nanoparticles without carbon-shell results in the coexistence of nonmagnetic carbon and a large surface spin percentage with disordered magnetization orientation for the nanoparticles. Biginelli reactions in the presence of L-proline and Ni and carbon encapsulated Ni nanoparticles were carried out to change the ratio between stereoisomers. The obtained S-enantiomers for 3,4-dihydropyrimidine (DHPM) using catalysts of Ni, and Ni@C was an excess of about ${\Delta}{\sim}7.4%$ and ${\Delta}{\sim}19.6%$, respectively. The nanopowders were fully recovered using magnet to reuse as a catalyst. The Ni@C was shown at same yield to formation of 3,4-DHPM, though it was recycled for catalyst in the reaction.

• Korean Journal of Materials Research
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• v.11 no.3
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• pp.178-184
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• 2001

Transparent and highly oriented KLN thin films have been grown by an rf- magnetron sputtering deposition method. A homogeneous and stable KLN target was prepared by calcine and sintering process. For KLN target, stoichiometry and composition excess with K of 30% and 60%, and Li of 15% and 30% respectively, was prepared. The targets were sintered at low temperature to prevent vaporization of K and Li. KLN thin films were fabricated by rf-magnetron sputtering method using those targets. In this experiment, using the target of composition excessed with K of 60% and Li of 30%, single phase KLN thin film was produced. KLN thin film has excellent crystallinity and highly c-axis oriented on Corning 1737 substrate. Transmittance of thin film in visible range was 90%, absorption edge is 333 nm and refractive index at 632.8 nm was 1.93.

• Korean Journal of Materials Research
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• v.12 no.9
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• pp.706-711
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• 2002

High-pure tantalum powder was fabricated through Na reduction process and has been produced by using $K_2$TaF$_{7}$, and KCI, KF for raw material and diluent, respectively. A raw material and diluent were charged at the hestalloy bomb by the weight rate of 1:2, 1:1, 1:0.5 and 1:0.25 each other, investigated properties of morphology, chemical composition and yield and particle size after reduced. Ta metal has been achieved by reduction of $K_2$$TaF_{7}$ 500g with 1% sodium in excess of stoichiometric amount in the charge at a reduction temperature of $850^{\circ}C$ for 3hours. According to amount of the diluent, a formation of the powder doesn't have an effect. The diluent prevented the temperature rising caused from the heat of reaction and it maintained the speed of reducing reaction. But in the mixture ratio of raw material and diluent in the 1 : 2 and 1 : 0.25, an oxide and partially not reacted K were detected. As the amount of diluent increased, the size of tantalum powder decreased. According as raw material and the mixture ratio of diluent change from 1:0.25 to 1:2, the size is decreased from 5$\mu\textrm{m}$ to 1$\mu\textrm{m}$, and a particle size distribution which is below 325 mesh in fined powder increases from 71% to 83%. In the case of average size of Tantalum powder which is the mixture ratio (1:0.5), we would get the Ta powder with grain size about 3$\mu\textrm{m}$, which come close to the average size (2~4$\mu\textrm{m}$) of tantalum powder which is used commonly in the present is Ta powder about 3$\mu\textrm{m}$.