• Journal of Welding and Joining
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• v.28 no.3
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• pp.92-98
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• 2010

Ferritic stainless steels, which have relatively small thermal expansion coefficient and excellent corrosion resistance, are increasingly being used in vehicle manufacturing, in order to increase the lifetime of exhaust manifold parts. But, there are limits on use because of the problem related to cosmetic resistance, corrosions of condensation and high temperature salt etc. So, Aluminum-coated stainless steel instead of ferritic stainless steel are utilized in these parts due to the improved properties. In this investigation, Al-8wt% Si alloy coated 409L ferritic stainless steel was used as the base metal during Gas Tungsten Arc(GTA) welding. The effects of coated layer on the microstructure and hardness were investigated. Full penetration was obtained, when the welding current was higher than 90A and the welding speed was lower than 0.52m/min. Grain size was the largest in fusion zone and decreased from near HAZ to base metal. As welding speed increased, grain size of fusion zone decreased, and there was no big change in HAZ. Hardness had a peak value in the fusion zone and decreased from the bond line to the base metal. The highest hardness in the fusion zone resulted from the fine re-precipitation of the coarse TiN and Ti(C, N) existed in the base metal during melting and solidification process and the presence of fine $Al_2O_3$ and $SiO_2$ formed by the migration of the elements, Al and Si, from the melted coating layer into the fusion zone.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.2
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• pp.55-60
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• 2022

In this study, a heat treatment experiment was conducted to select a new melt composition that can easily control the unintentionally doped nitrogen (N-UID) without degrading the SiC single crystal quality during TSSG process. The experiment was carried out for about 2 hours at a temperature of 1900℃ under Ar atmosphere. The used melt composition is based on either Si-Ti 10 at% or Si-Cr 30 at%, and also Co or Sc transition metals, which are effective for carbon solubility, were added at 3 at%, respectively. After the experiment, the crucible was cross-sectionally cut, and evaluated the Si-C reaction layer on the crucible-melt interface. As a result, with Sc addition, Si-C reaction layers uniformly occurred with a Si-infiltrated layer (~550 ㎛) and a SiC interlayer (~23 ㎛). This result represented that the addition of Sc is an effective transition metal with high carbon solubility and can feed carbon sources into the melt homogeneously. In addition, Sc is well known to have low reactivity energy with nitrogen compared to other transition metals. Therefore, we expect that both growth rate and Nitrogen UID can be controlled by Si-Sc based melt in the TSSG process.

• Advances in Energy Research
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• v.5 no.3
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• pp.219-226
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• 2017

Electrochemical double layer capacitors (EDLCs) have received a tremendous interest due to their suitability for diverse applications. They have been fabricated using different carbon based electrodes including activated carbons, single walled/multi walled carbon nano tubes. But, graphite which is one of the natural resources in Sri Lanka has not been given a considerable attention towards using for EDLCs though it is a famous carbon material. On the other hand, EDLCs are well reported with various liquid electrolytes which are associated with numerous drawbacks. Gel polymer electrolytes (GPE) are well known alternative for liquid electrolytes. In this paper, it is reported about an EDLC fabricated with a nano composite polyethylene oxide based GPE and two Sri Lankan graphite based electrodes. The composition of the GPE was [{(10PEO: $NaClO_4$) molar ratio}: 75wt.% PC] : 5 wt.% $TiO_2$. GPE was prepared using the solvent casting method. Two graphite electrodes were prepared by mixing 85% graphite and 15% polyvinylidenefluoride (PVdF) in acetone and casting n fluorine doped tin oxide glass plates. GPE film was sandwiched in between the two graphite electrodes. A non faradaic charge discharge mechanism was observed from the Cyclic Voltammetry study. GPE was stable in the potential windows from (-0.8 V-0.8 V) to (-1.5 V-1.5 V). By increasing the width of the potential window, single electrode specific capacity increased. Impedance plots confirmed the capacitive behavior at low frequency region. Galvanostatic charge discharge test yielded an average discharge capacity of $0.60Fg^{-1}$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.4013-4018
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• 2014

A 0.45 $cm^2$ DSSC device with a glass/FTO/blocking layer/$TiO_2$/N719(dye)/electrolyte/50 nm-Pt/50 nm-Au/FTO/glass was prepared to examine the stability of the Au/Pt bilayered counter electrode (CE) with electrolyte and the energy conversion efficiency (ECE) of dye-sensitized solar cells (DSSCs). For comparison, a 100 nm-thick Pt only CE DSSC was also prepared using the same method. The photovoltaic properties, such as the short circuit current density ($J_{sc}$), open circuit voltage ($V_{oc}$), fill factor (FF), and ECE, were checked using a solar simulator and potentiostat with time after assembling the DSSC. The microstructure of the Au/Pt bilayer was examined by optical microscopy after 0~25 minutes. The ECE of the Pt only CE-employed DSSC was 4.60 %, which did not show time dependence. On the other hand, for the Au/Pt CE DSSC, the ECEs after 0, 5 and 15 minutes were 5.28 %, 3.64 % and 2.09 %, respectively. The corrosion areas of the Au/Pt CE determined by optical microscopy after 0, 5, and 25 minutes were 0, 21.92 and 34.06 %. These results confirmed that the ECE and catalytic activity of Au/Pt CE decreased drastically with time. Therefore, a Au/Pt CE-employed DSSC may be superior to the Pt only CE-employed one immediately after integration of the device, but it would degrade drastically with time.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.90.1-90.1
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• 2010

Due to the rapidly diminishing energy sources and higher energy production cost, the interest in dye-sensitized solar cells (DSSCs) has been increasing dramatically in recent years. A typical DSSC is constructed of wide band gap semiconductor electrode such as $TiO_2$ or ZnO that are anchored by light-harvesting sensitizer dyes and surrounded by a liquid electrolyte with a iodide ion/triiodide ion redox couple. DSSCs based on one-dimensional nano-structures, such as ZnO nanorods, have been recently attracting increasing attention due to their excellent electrical conductivity, high optical transmittance, diverse and abundant configurations, direct band gap, absence of toxicity, large exiton binding energy, etc. However, solar-to-electrical conversion performances of DSSCs composed of ZnO n-type photo electrode compared with that of $TiO_2$ are not satisfactory. An important reason for the low photovoltaic performance is the dissolution of $Zn^{2+}$ by the adsorption of acidic dye followed by the formation of agglomerates with dye molecules which could block the I-diffusion pathway into the dye molecule on the ZnO surface. In this paper, we prepared the DSSC with the ZnO electrode using the chemical bath deposition (CBD) method under low temperature condition (< $100^{\circ}C$). It was demonstrated that the ZnO seed layers played an important role on the formation of the ZnO nanostructures using CBD. To achieve truly low-temperature growth of the ZnO nanostructures on the substrates, a two-step method was developed and optimized in the present work. Firstly, ZnO seed layer was prepared on the FTO substrate through the spin-coating method. Secondly, the deposited ZnO seed substrate was immersed into an aqueous solution of 0.25M zinc nitrate hexahydrate and 0.25M hexamethylenetetramine at $90^{\circ}C$ for hydrothermal reaction several times.

• Journal of Korean Society on Water Environment
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• v.28 no.1
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• pp.115-120
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• 2012

Different colloidal particles generally co-exist in the water and wastewater. Thus, there needs to identify practical electrokinetic characteristics of the particles, comparing with the case when each colloidal material is independently distributed. In this study, changes of overall zeta potential was examined through mixed dispersions of $TiO_{2}$ and $MnO_{2}$. The mixing ratios were classified into 3-type in order to distinguish the effects of the proportions of each particle from those of total concentration in colloidal suspensions. The types are single colloidal dispersions of $TiO_{2}$ and $MnO_{2}$ (1:0, 0:1), mixed dispersions at different ratios (0.75:0.25, 0.5:0.5, 0.25:0.75), and a mixed dispersion with doubled concentration (1:1), respectively. It showed that the overall variation of zeta potential as a function of pH was intensified in a colloidal dispersion with the ratio of 1:1. It was concerned that the double action of ion would contribute to this result. On the one hand, the zeta potentials of each colloidal dispersion commonly decreased at the state of strong acid and base under the influence of compression of the electric double layer. The changing patterns were also considered through calculating total interaction energy between colloidal particles based on DLVO theory and measuring turbidity of the colloidal dispersions.

• The Korean Journal of Ceramics
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• v.6 no.1
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• pp.64-67
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• 2000

Reactively sputtered $Pb(Zr,Ti)O_3$(PZT) films on $IrO_2$and Ir were evaluated with particular consideration on interface properties. The $IrO_2$and Ir were previously annealed at $650^{\circ}C$ in $O_2$or $N_2$atmosphere, respectively. There was no appreciable roughening in the interface of the $PZT/IrO_2$respective to that of the PZT/Ir; the rms roughness of $IrO_2$and Ir was about 3nm and 10nm, respectively. The ferroelectric properties of the $PZT/IrO_2$were found to be better than that of the PZT/Ir; however, the leakage current of the $PZT/IrO_2$was slightly larger than that of the PZT/Ir. The $PZT/IrO_2$thin films did not exhibit any fatigue up to $10^{11}$ cycles; the $P^*\;_r-P^r$ value decreased only from 16.6 to 14$\mu$C/$\textrm{cm}^2$ until $10^{12}$ polarization reversals. On the other hand, although thin $IrO_2$layer was formed between PZT and Ir, the PZT/Ir thin films began to undergo fatigue after $10^9$ polarization reversals.

• JSTS:Journal of Semiconductor Technology and Science
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• v.8 no.1
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• pp.66-79
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• 2008

Several oxides have recently been reported to have resistance-switching characteristics for nonvolatile memory (NVM) applications. Both binary and ternary oxides demonstrated great potential as resistive-switching memory elements. However, the switching mechanisms have not yet been clearly understood, and the uniformity and reproducibility of devices have not been sufficient for gigabit-NVM applications. The primary requirements for oxides in memory applications are scalability, fast switching speed, good memory retention, a reasonable resistive window, and constant working voltage. In this paper, we discuss several materials that are resistive-switching elements and also focus on their switching mechanisms. We evaluated non-stoichiometric polycrystalline oxides ($Nb_2O_5$, and $ZrO_x$) and subsequently the resistive switching of $Cu_xO$ and heavily Cu-doped $MoO_x$ film for their compatibility with modem transistor-process cycles. Single-crystalline Nb-doped $SrTiO_3$ (NbSTO) was also investigated, and we found a Pt/single-crystal NbSTO Schottky junction had excellent memory characteristics. Epitaxial NbSTO film was grown on an Si substrate using conducting TiN as a buffer layer to introduce single-crystal NbSTO into the CMOS process and preserve its excellent electrical characteristics.

• Bulletin of the Korean Chemical Society
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• v.35 no.10
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• pp.3052-3058
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• 2014

In this article, we have designed and synthesized a novel donor-${\pi}$-acceptor (D-${\pi}$-A) type porphyrin-based sensitizer (denoted UI-5), in which a carboxyl anchoring group and a 9,9-dimethyl fluorene were introduced at the meso-positions of porphyrin ring via phenylethynyl and ethynyl bridging units, respectively. Long alkoxy chains in ortho-positions of the phenyls were supposed to reduce the degree of dye aggregation, which tends to affect electron injection yield in a photovoltaic cell. The cyclic voltammetry was employed to determine the band gap of UI-5 to be 1.41 eV based on the HOMO and LUMO energy levels, which were estimated by the onset oxidation and reduction potentials. The incident monochromatic photon-to-current conversion efficiency of the UI-5 DSSC assembled with double-layer (20 nm-sized $TiO_2$/400 nm-sized $TiO_2$) film electrodes appeared lower upon overall ranges of the excitation wavelengths, but exhibited a higher value over the NIR ranges (${\lambda}$ = 650-700 nm) compared to the common reference sensitizer N719. The UI-5-sensitized cell yielded a relatively poor device performance with an overall conversion efficiency of 0.74% with a short circuit photocurrent density of $3.05mA/cm^2$, an open circuit voltage of 0.54 mV and a fill factor of 0.44 under the standard global air mass (AM 1.5) solar conditions. However, our report about the synthesis and the photovoltaic characteristics of a porphyrin-based sensitizer in a D-${\pi}$-A structure demonstrated a significant complex relationship between the sensitizer structure and the cell performance.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.504-504
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• 2011

최근 디지털 프린팅 기술의 핵심기술로 떠오르고 있는 잉크젯 프린팅 기술은 최근 기존의 문서인쇄 뿐 아니라, 직물 인쇄, 태양전지 등의 다양한 반도체 소자 제조에 널리 활용되고 있으며, 점차 그 응용 분야를 넓혀가고 있다. 특히 thermal 방식의 잉크젯 피린팅 기술은 etching, thin film process, lithography등의 반도체 공정 기술을 이용하여 제작할 수 있기 때문에, 현재 잉크젯 프린팅 기술은 대부분 thermal 방식을 체택하고 있다. 이러한 thermal 잉크젯 프린팅 방법에서는 잉크를 토출시키기 위하여, 전기적 에너지를 열에너지로 전환하는 전자저항막층이 필수적으로 필요하게 되는데, 이러한 전자저항막층은 수백도가 넘는 고온 및 잉크와 접촉으로 인한 부식 및 산화 문제가 발생할 수 있는 열악한 환경에서 사용되므로, Ta, SiN과 같은 보호층을 필수적으로 필요로 한다. 그러나 최근 잉크젯 프린터의 고해상도 고속화, 대면적 인쇄성 등과 같은 다양한 요구 증가에 따라, 잉크젯 프린터의 저전력 구동이 이슈로 떠올라 열효율에 방해가 되는 보호층을 제거할 필요성이 제기되고 있다. 지금까지는 Poly-Si, $HfB_2$, TiN, TaAl, TaN _0.8 등의 물질들이 잉크젯 프린터용 전자저항막 물질로 연구되거나 실제로 사용되어져 왔으나, 이러한 물질들을 보호층을 제거하는 경우 쉽게 산화되거나, 부식되는 문제점을 가지고 있다. 따라서, 기존 전자저항막의 기능을 만족시키면서, 산화나 부식에 대한 강한 내성을 가져 보호층을 제거하더라도 안정적으로 구동이 가능한 하이브리드 기능성(히터 + 보호층)을 가지는 잉크젯 프린터용 전자저항막 물질의 개발이 시급한 실정이다. 본 연구에서는 자기조립특성을 가져 정밀제어가 가능한 원자층증착법(Atomic Layer Deposition)을 이용하여 원자/나노 단위의 미세 구조 컨트롤을 통해 내열 내산화 내부식성 저온도저항계수를 동시에 가지는 다기능성 전자저항막을 설계 및 개발하고자 하였다. 전자저항막 개발을 위하여 우수한 내부식 내산화성을 가지고 결정립 크기에 따른 온도저항계수 조절이 가능한 platinum group metal들과 전기 저항 및 내열성 향상을 위한 물질의 복합구조막을 원자증증착법으로 증착하였다. 또한, 전자저항막 증착시 미세구조와 공정 변수가 내부식성, 내산화성, 그리고 온도저항계수에 미치는 영향을 체계적으로 연구하여, proto-type의 inkjet printhead를 구현하였다.