• KSTLE International Journal
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• v.6 no.1
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• pp.28-32
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• 2005

The electrorheoloRical (ER) fluids are composed of a colloidal dispersion of polarizable particles in insulating oil, and it's the rheological property changes by the applied electric field. These changed are reversible and occur fast within a fewmilliseconds. The ER properties of the ER fluid such as increment of viscosity and yield stress come from the particle chain structure induced by electric fleld. When formulating the ER fluid for a speciflc application, some requirement must besatisfled, which are high yield stress under electric field, rapid response, and dispersion stability. While this characteristic makes valuable ER fluids in valious industrial applications, their lung term and quiescent application has been limited because ofproblems with particle sedimentation. In an effort to overcome sedimentation problem of ER fluids, the anhydrous ER materials of monodispersed hollow polyaniline (PANI) and adipate derivative respectively with submicron-sized suspension providing wide operating temperature range and other advantage were synthesized in a four-step procedure. The ER fluidswere characterized by FT-lR, TGA, DLS, SEM, and TEM. Stability of the suspensions was examined by an UV spectroscopy.The rheological and electrical properties of the suspension were investigated Couette-type rheometer with a high voltagegenerator, current density, and conductivity. And the behavior of ER suspensions was observed by a video camera attached toan optical microscope under 3kV/mm. The suspensions showed good ER properties, durability, and particle dispersion.

• Journal of the Korean Society for Heat Treatment
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• v.26 no.4
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• pp.165-172
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• 2013

In the present study, the microstructure and solution treatment response of Al-Zn-Mg alloys bars by thixo-extrusion was investigated. The alloy bars were solution treated at 400, 430, 460 and $490^{\circ}C$ for various times. In order to examine the microstructures and phase analysis of the samples after solution treatment, it was performed by optical and scanning electron microscopy. And, Vickers hardness and electrical conductivity was measured on the solution treated samples for each condition to investigate the solution treatment response of extruded bars during solution treatment. The results show that the optimum solution heat treatment conditions of thixo-extruded Al-Zn-Mg alloy for minimization of the grain growth and degradation promotion of the second phase is a temperature of $460^{\circ}C$ and holding time of 0.5 to 2 h.

• Journal of Korea Foundry Society
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• v.37 no.1
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• pp.14-20
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• 2017

The microstructure, electrical conductivity and hardness variation of an AZ91-5wt%Sn Mg alloy sample during a solid-solution and aging heat treatment were instigated by optical microscopy, scanning electron microscopy, X-ray diffraction and by Rockwell hardness techniques in this study. The XRD result shows that the main phases in the as-casted alloy are ${\alpha}$-Mg, $Mg_{17}Al_{12}$ and $Mg_2Sn$. From the SEM images of the AZ91-5wt%Sn Mg alloy after the solution treatment, the $Mg_{17}Al_{12}$ phases in the alloy were found to have dissolved into the matrix with an increase in the holding time during the solution treatment, but $Mg_2Sn$ phases were clearly observable. The highest peak hardness of the AZ91-5wt%Sn Mg alloy is 82HRE at an aging temperature of $200^{\circ}C$.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08b
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• pp.1425-1428
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• 2007

The amorphous IZO on flexible substrate (PC) shows similar electrical conductivity and optical transmittance with commercial ITO glass even though it was prepared at $<50\;^{\circ}C$. Moreover, it exhibits little resistance change during 5000 bending cycles, demonstrating good mechanical robustness. A green phosphorescent OLED fabricated on amorphous IZO on flexible PC shows maximum external quantum efficiency of ${\eta}_{ext}=13.7\;%$ and power efficiency of ${\eta}_p=32.7\;lm/W$, which are higher than a device fabricated on a commercial ITO on glass (${\eta}_{ext}=12.4%$ and ${\eta}_p=30.1\;lm/W$) and ITO on flexible PC (${\eta}_{ext}=8.5%$ and ${\eta}_p=14.1\;lm/W$).

• Korean Journal of Optics and Photonics
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• v.12 no.3
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• pp.230-234
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• 2001

We report a simple method for determining photovoltaic constant and conductivities of any photorefractive crytals which have no inversion symmetry by utilizing the electric field dependence of non-phase-matched second harmonic generation. New theoretical expression for the electric field dependence of Maker fringes is derived and space charge field can be determined using this from the observed change of intensity of second harmonic wave. The photovoltaic constant, dark conductivity and photoconductivity are easily deduced from an analysis of the measured relaxation behavior of space-charge field at two different light intensities. We demonstrate this method for $LiNbO_3$ at 514.5 nm.4.5 nm.

• Bulletin of the Korean Chemical Society
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• v.35 no.11
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• pp.3261-3266
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• 2014

A pellet of polycrystalline $CuGaO_2$ with a delafossite structure was prepared from $Ga_2O_3$ and CuO by high-temperature solid-state synthesis. The $CuGaO_2$ pellet was a p-type semiconductor for which the electrical conductivity, carrier density, carrier mobility and Seebeck coefficient were $5.34{\times}10^{-2}{\Omega}^{-1}cm^{-1}$, $3.5{\times}10^{20}cm^{-3}$, $9.5{\times}10^{-4}cm^2V^{-1}s^{-1}$ at room temperature, and $+360{\mu}V/K$, respectively. It also exhibited two optical transitions at about 2.7 and 3.6 eV. The photoelectrochemical properties of the $CuGaO_2$ pellet electrode were investigated in aqueous electrolyte solutions. The flat-band potential of this electrode, determined using a Mott-Schottky plot, was +0.18 V vs SCE at pH 4.8 and followed the Nernst equation with respect to pH. Under UV light illumination, a cathodic photocurrent developed, and molecular hydrogen simultaneously evolved on the surface of the electrode due to the direct reduction of water without deposition of any metal catalyst.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.953-956
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• 2003

Transparent conductive ZnO:Ga thin films were deposited on glass substrates using rf magnetron sputtering method for flat panel display. The ZnO:Ga films were preferentially oriented to c-axis (002) of on substrates. The surface morphology was smooth and had not porous whatever substrate temperature was. The electrical conductivity of the thin films were in the range of $1.6{\times}10^2{\sim}6.7{\times}10^3\;{\Omega}^{-1}cm^{-1}$ at the growth temperature from 50 to $400^{\circ}C$, whereas has a maximum at around $250^{\circ}C$. By combining of XRD and EXAFS, the crystallinity and grain size decreased with increasing substrate temperature corresponding to the reduction of the grain-boundary scattering. The optical transmittance of sputtered ZnO:Ga thin films had an improved about 86% in the UV-visible region.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.88-88
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• 2008

In this study, effect of thickness on structural, electrical and optical properties of B doped ZnO:Ga (GZOB) films was investigated. GZOB films were deposited on glass substrates by DC magnetron sputtering. The thickness range of films were from 100 nm to 600 nm to identified as increasing thickness, stress between substrate and GZOB film. The average transmittance of the films was over 80 % until 500 nm. Then a resistivity of $9.16\times10^{-4}\Omega$-cm was obtained. We presented that a GZOB film of 400 nm was optimization to obtain a high transmittance and conductivity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.45-45
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• 2008

In recent years, new materials and technology has been developed using single-walled carbon nanotubes (SWCNTs) as an alternative to indium tin oxide (ITO) to fulfil the requirements towards novel technological drive. These technologies offer products having a broad range of conductivity, excellent transparency, neutral color tone, good adhesion, abrasion resistance as well as mechanical robustness. In addition, SWCNTs can be solution processed to replace the sophisticated vacuum techniques at high temperatures. In the present work, transparent conducting films were fabricated from the purified SWCNTs. Dispersion of purified SWCNTs was accomplished in 1,2-dichlorobenzene without using surfactants or polymers following ultrasonic process. We achieved coating of nanotubes film on poly ether suiphone (PES) for an average sheet resistance ~110 ${\Omega}/{\Box}$ of optical transmittance 80% at 550 nm. Conventional spin coating method was followed to fabricate films from the purified and dispersed nanotubes solution. The results will be presented.

• Journal of Electrochemical Science and Technology
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• v.9 no.2
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• pp.118-125
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• 2018

Herein we report on the selective synthesis and direct growth of nanostructures using an aqueous chemical growth route. Specifically, Al-doped ZnO (AZO) nanoflakes (NFs) are vertically grown on indium tin oxide (ITO) coated flexible polyethylene terephthalate (PET) sheets at low temperature and ambient environment. The morphological, optical, and electrical properties of the NFs are investigated as a function of the Al content. Furthermore, these AZO-NFs are integrated into perovskite solar devices as the electron transport layer (ETL) and the fabricated devices are tested for photovoltaic performance. It was determined that the doping of AZO-NFs significantly increases the performance metrics of the solar cells, mainly by increasing the short-circuit current of the devices. The observed enhancement is primarily attributed to the improved conductivity of the doped AZO-NF, which facilitates charge separation and reduces recombination. Further, our flexible solar cells fabricated through this low temperature process demonstrate an acceptable reproducibility and stability when exposed to a mechanical bending test.