• Journal of the Microelectronics and Packaging Society
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• v.27 no.4
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• pp.25-37
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• 2020

In this study, hybridization of graphene oxide and metal was carried out by the functional groups containing oxygen and thermal treatment for reduction in order to enhance the electrical conductivity and magnetic properties of graphene materials. Graphene-metal hybrid materials were synthesized using the oxygen-containing functional groups (-OH, -COOH and so on) on the surface of graphene oxide by replacing them with metal ions via ion exchange method as well as thermal reduction. The metals used in this study were Fe, Ag, Ni, Zn, and Fe/Ag, and it was confirmed that metal particles of uniform size were well dispersed on the graphene surface through SEM, TEM, and EDS. All of the metal particles on the graphene surface had an oxide-crystalline structure. To check the electrical properties, sheet resistance of the rGO-metal hybrid sample was measured on the PET film made by the dip-coating, and the specific resistance was calculated by measuring the thickness of the specimen through SEM. As a result, the specific resistance was in the range of 2.14×10-5 and 3.5×10-3 ohm/cm.

• Journal of the Korean Ceramic Society
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• v.41 no.10 s.269
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• pp.728-734
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• 2004

The effect of microstructure of WC-Co substrates which have different WC grain sizes from submicron to 5 $\mu$m on the diamond-substrate adhesion strength was investigated. The substrates were pre-treated by two methods : chemical etching with Murakami's solution and subsequently with $H_2SO_4$, and thermal heat-treatment. The adhesion strength was estimated by degree of peeling after Rockwell indentation. Diamond films of 20 $\mu$m thickness deposited on the heat-treated substrates showed an excellent adhesion strength at the load of 100 kg, which ascribed to the large and elongated WC grains. However, the cutting edge of insert was deformed after heat treatment and the surface morphology of heat treated substrate strongly affected on the surface roughness of the deposited diamond films. On the contrary, the diamond film of 10 $\mu$m in thickness on the chemically etched substrates of average WC grain size over 2 $\mu$m showed good adhesion strength enough not to peel-off under a load of 60 kg. Especially, the substrate of average WC grain size over 5 $\mu$m exhibited much improved reliability of adhesion comparing with the substrate of average grain size under 2 $\mu$m. No substrate deformation was observed in this case after the chemical etching, which is more advantageous and more practical in terms of precious machining than the heat treatment case.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.4 no.2
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• pp.199-209
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• 1994

$PbTiO_3$ thin films were prepared on soda-lime-silica slide glasses, Si-wafer and sapphire substrate by the dip-coating of precursor solution. As starting materials, titanium tetra iso-propoxide and lead acetate trihydrate were used. Then acetylacetone was added to prepare stable sol. The effect of the parameters such as viscosity and composition of sol were investigated. The optical transmittance at visible range, refractive index, IR spectra were measured in varying compositions, thickness and heat treatment temperature. The crystallization of $PbTiO_3$ films were measured by using XRD and SEM. Diffusion of compositions from slide glass to thin film were investigated by using EDX, too. These sols not precipitated for 20 days. Transmittance of $PbTiO_3$ films at visible range were decreased with the increase of thickness and heat treatment temperatures, and were exhibited flat spectra. Pyrochlore type appeared in the films on slide glass and perovskite type appeared in the films on Si-wafer or sapphire at $600^{\circ}C$. Perovskite crystals transformed to $PbTi_3O_7$ phase at $800^{\circ}C$.

• Journal of the Korean Magnetics Society
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• v.15 no.2
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• pp.67-75
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• 2005

For th aim of lightweight microwave absorbers, conductive and magnetic microspheres are fabricated by plating of Co films on hollow ceramic microspheres of low density. Metal plating was carried out in a two-step electroless plating process (pre-treatment of activation and plating). Uniform coating of the film with about $2{\~}3{\cal}um$ thickness was identified by SEM. High-frequency magnetic and microwave absorbing properties were determined in the rubber composites containing the Co-coated microspheres. Due to conductive and ferromagnetic behavior of the Co thin films, high dielectric constant and magnetic loss can be obtained in the microwave frequencies. Due to those electromagnetic properties, high absorption rate (25 dB) and thin matching thickness ($2.0{\~}2.5{\cal}mm$) are predicted in the composite layers containing the metal-coated microspheres of low density (about 0.84 g/cc) for the electromagnetic radiation in microwave frequencies.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.1
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• pp.17-22
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• 2011

ZnO-based thin-film transistors (TFTs) have been fabricated and the mechanical characteristics of electric circuits, such as stress, strain, and deformation are analyzed by the finite element method (FEM). In this study, a mechanical-stability design guide for such systems is proposed; this design takes into account the stress and deformation of the bridge to estimate the stress distribution in an $SiO_2$ film with 0 to 5% stretched on 0.5-${\mu}m$-thick. The predicted buckle amplitude of $SiO_2$ bridges agrees well with experimental results within 0.5% error. The stress and strain at the contact point between bridges and a pad were measured in a previous structural analysis. These structural analysis suggest that the numerical measurement of deformation, SU-8 coating thickness for Neutral Mechanical Plane (NMP) and ITO electrode size on a dielectric layer was useful in enhancing the structural and electrical stabilities.

• Journal of Conservation Science
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• v.28 no.1
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• pp.53-62
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• 2012

The archival objects are tangible evidence related to the public service. They are unique and offer information representing the specific events, time or person. The archival objects as modern cultural heritage do not have the guideline to classify, manage and conserve them. Especially, it is difficult to apply general conservation process for burial artifacts, because there are few study example of conservation for metal archival objects and they have complex administrative value. We tried to find suitable material and application method for consolidation of copper alloy archival object. We choose three kinds of wax and acrylic resin for burial artifacts and had done comparative analysis of their characterizations following kinds and coating methods. As a result of evaluation by several surface analysis such as optical microscope, measuring film thickness, adhesive strength, contact angle and yellowing test, acrylic resin can use to archival objects of copper alloy, effectively but the method of heating after dip-coating with Wax B used before can get best effect of consolidation.

• Journal of the Microelectronics and Packaging Society
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• v.14 no.4
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• pp.37-42
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• 2007

We fabricated the polymer light emitting diodes (PLEDs) with ITO/PEDOT:PSS/PVK/PFO:MEH-PPV/LiF/Al structures. The effect of the thickness of PEDOT:PSS hole injection layer(HIL) on the electrical and optical properties of PLEDs was investigated. In addition, PVK hole transport layer(HTL) was introduced in the PLED device, and compared the properties of the PLEDS with and without PVX layer. All organic film layers were prepared by the spin coating method on the plasma treated ITO/glass substrates. As the thickness of PEDOT:PSS film layer decreased from about 80 nm to 50 nm, the luminance of PLED device increased from $220cd/m^2$에서 $450cd/m^2$. This may be ascribed to the increased transportation efficiency of the holes into the emission layer of PLED. The maximum current density and luminance were obtained fir the PLED device with PVX hole transport layer, showing that the current density and luminance were $268mA/cm^2\;and\;540cd/m^2$ at 12V, respectively. This values were improved by about 14% and 22% in current density and luminance compared with the PLED device without PVK layer.

• Bulletin of the Korean Chemical Society
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• v.32 no.1
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• pp.263-272
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• 2011

Highly luminescent and monodisperse InP quantum dots (QDs) were prepared by a non-organometallic approach in a non-coordinating solvent. Fatty acids with well-defined chain lengths as the ligand, a non coordinating solvent, and a thorough degassing process are all important factors for the formation of high quality InP QDs. By varying the molar concentration of indium to ligand, QDs of different size were prepared and their absorption and emission behaviors studied. By spin-coating a colloidal solution of InP QD onto a silicon wafer, InP QD thin films were obtained. The thickness of the thin films cured at 60 and $200^{\circ}C$ were nearly identical (approximately 860 nm), whereas at $300^{\circ}C$, the thickness of the thin film was found to be 760 nm. Different contrast regions (A, B, C) were observed in the TEM images, which were found to be unreacted precursors, InP QDs, and indium-rich phases, respectively, through EDX analysis. The optical properties of the thin films were measured at three different curing temperatures (60, 200, $300^{\circ}C$), which showed a blue shift with an increase in temperature. It was proposed that this blue shift may be due to a decrease in the core diameter of the InP QD by oxidation, as confirmed by the XPS studies. Oxidation also passivates the QD surface by reducing the amount of P dangling bonds, thereby increasing luminescence intensity. The dielectric properties of the thin films were also investigated by capacitance-voltage (C-V) measurements in a metal-insulator-semiconductor (MIS) device. At 60 and $300^{\circ}C$, negative flat band shifts (${\Delta}V_{fb}$) were observed, which were explained by the presence of P dangling bonds on the InP QD surface. At $300^{\circ}C$, clockwise hysteresis was observed due to trapping and detrapping of positive charges on the thin film, which was explained by proposing the existence of deep energy levels due to the indium-rich phases.

• Korean Journal of Optics and Photonics
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• v.10 no.3
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• pp.181-187
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• 1999

We prepared the side-chain type nonlinear optical NPP(N-(6-nitrophenyl)-(L)-prolinol) polymer films by spin coating method. Ellipsometric spectra were in situ collected by using spectroscopic phase modulated ellipsometer while the NPP polymer films were being corona poled at the temperature above glass transition. We calculated film thickness and the refractive index dispersion by modeling the spectro-ellipsometry data in transparent region. We also calculated the refractive index and the extinction coefficient of the polymer films by numerically inverting the spectro-ellipsometry data in absorbing region, while the previously determined film thickness was used. The independently determined extinction coefficient spectra from the analysis of transmission spectra were compared with those by spectro-ellipsometry and they showed an excellent agreement with each other. From the analysis of the complex refractive index change of the NPP polymer thin films induced by the corona poling, we could determine the vertical complex refractive index and the horizontal complex refractive index separately. Using the volume fraction of the vertical component f⊥, the degree of poling of poled NPP polymer films was quantitatively addressed. It is suggested that the present method can be used to quantitatively address the degree of poling in an absolute manner and to depth profile the poled fraction of thick polymer films. It will be useful to understand the structural change of polymer films and hence the poling mechanism during the poling process.

• Journal of the Korean Electrochemical Society
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• v.4 no.2
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• pp.58-64
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• 2001

YSZ ($8mol\%$ yttria-stabilized zirconia)-modified LSM $(La_{0.85}Sr_{0.15}MnO_3)$ composite cathodes were fabricated by formation of YSZ film on triple phase boundary (TPB) of LSM/YSZ/gas. The YSZ coating film greatly enlarged electrochemical reaction sites from the increase of additional TPB. The composite cathode was formed on thin YSZ electrolyte (about 30 Um thickness) supported on an anode and then I-V characterization and AC impedance analyses were performed at temperature between $700^{\circ}C\;and\;800^{\circ}C$. As results of the impedance analysis on the cell at $800^{\circ}C$ with humidified hydrogen as the fuel and air as the oxidant, R1 around the frequency of 1000 Hz represents the anode Polarization. R2 around the frequency of 100Hz indicates the cathode polarization, and R3 below the frequency of 10 Hz is the resistance of gas phase diffusion through the anode. The cell with the composite cathode produced power density of $0.55\;W/cm^2\;and\;1W/cm^2$ at air and oxygen atmosphere, respectively. The I-V curve could be divided into two parts showing distinctive behavior. At low current density region (part I) the performance decreased steeply and at high current density region (part II) the performance decreased gradually. At the part I the performance decrease was especially resulted from the large cathode polarization, while at the part H the performance decrease related to the electrolyte polarization.