• Journal of the Korean Vacuum Society
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• v.18 no.4
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• pp.288-295
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• 2009

We report the etch characteristics of GaAs and AlGaAs in the diffusion pump-based capacitively coupled $BCl_3$ plasma. Process variables were chamber pressure ($50{\sim}180$ mTorr), CCP power ($50{\sim}200\;W$) and $BCl_3$ gas flow rate ($2.5{\sim}10$ sccm). Surface profilometry was used for etch rate and surface roughness measurement after etching. Scanning electron microscopy was used to analyze the etched sidewall and surface morphology. Optical emission spectroscopy was used in order to characterize the emission peaks of the $BCl_3$ plasma during etching. We have achieved $0.25{\mu}m$/min of GaAs etch rate with only 5 sccm $BCl_3$ flow rate when the chamber pressure was in the range of 50{\sim}130 mTorr. The etch rates of AlGaAs were a little lower than those of GaAs at the conditions. However, the etch rates of GaAs and AlGaAs decreased significantly when the chamber pressure increased to 180 mTorr. GaAs and AlGaAs were not etched with 50 W CCP power. With $100{\sim}200\;W$ CCP power, etch rates of the materials increased over $0.3{\mu}m$/min. It was found that the etch rates of GaAs and AlGaAs were not always proportional to the increase of CCP power. We also found the interesting result that AlGaAs did not etched at 2.5 sccm $BCl_3$ flow rate at 75 mTorr and 100 W CCP power even though it was etched fast like GaAs with more $BCl_3$ gas flow rates. By contrast, GaAs was etched at ${{\sim}}0.3{\mu}m$/min at the 2.5 sccm $BCl_3$ flow rate condition. A broad molecular peak was noticed in the range of $500{\sim}700\;mm$ wavelength during the $BCl_3$ plasma etching. SEM photos showed that 10 sccm $BCl_3$ plama produced more undercutting on GaAs sidewall than 5 sccm $BCl_3$ plasma.

• Journal of Surface Science and Engineering
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• v.41 no.5
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• pp.226-231
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• 2008

Titanium and its alloy have been widely used in dental implant and orthopedic prostheses. Electrochemical characteristics of dental implant in the various simulated body fluids have been researched by using electrochemical methods. Ti-6Al-4V alloy implant was used for corrosion test in 0.9% NaCl, artificial saliva and simulated body fluids. The surface morphology was observed using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX). The electrochemical stability was investigated using potentiosat (EG&G Co, 263A). The corrosion surface was observed using scanning electron microscopy (SEM). From the results of potentiodynamic test in various solution, the current density of implant tested in SBF and AS solution was lower than that of implant tested in 0.9% NaCl solution. From the results of passive film stability test, the variation of current density at constant 250 mV showed the consistent with time in the case of implant tested in SBF and AS solution, whereas, the current density at constant 250mV in the case of implant tested in 0.9% NaCl solution showed higher compared to SBF and AS solution as time increased. From the results of cyclic potentiodynamic test, the pitting potential and |$E_{pit}\;-\;E_{corr}$| of implant tested in SBF and AS solution were higher than those of implant tested in 0.9% NaCl solution.

• Journal of Surface Science and Engineering
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• v.41 no.5
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• pp.181-188
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• 2008

A.C. impedance properties of HA/Ti compound layer coated Ti-30Ta-($3{\sim}15$)Nb alloys have been studied by electrochemical method. Ti-30Ta binary alloys contained 3, 7, 10 and 15 wt% Nb were manufactured by the vacuum furnace system. And then specimen was homogenized at $1000^{\circ}C$ for 24 hrs. The sample was cut and polished for corrosion test and coating. It was coated with HA/Ti compound layer by magnetron sputter. The non-coated and coated morphology of Ti alloy were analyzed by X-ray diffractometer (XRD), energy X-ray dispersive spectroscopy (EDX) and filed emission scanning electron microscope (FE-SEM). The corrosion behaviors were investigated using A.C. impedance test (PARSTAT 2273, USA) in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. Ti-30Ta-($3{\sim}15\;wt%$)Nb alloys showed the ${\alpha}+{\beta}$ phase, and $\beta$ phase peak was predominantly appeared in the case of increasingly Nb contents. The microstructures of Ti alloy were transformed from needle-like structure to equiaxed structure as Nb content increased. From the analysis of coating surface, HA/Ti composite surface uniformed coating layer with 750 nm thickness. The growth directions of film were (211), (112), (300) and (202) for HA/Ti composite coating on the surface after heat treatment at $550^{\circ}C$, whereas, the growth direction of film was (110) for Ti coating. The polarization resistance ($R_p$) of HA/Ti composite coated Ti-alloys were higher than those of the Ti and HA coated samples in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. Especially, corrosion resistance of Ti-Ta-Nb system increased as Nb content increased.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.3
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• pp.67-71
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• 2014

An attempt to grow high quality GaN on silicon substrate using metal organic chemical vapor deposition (MOCVD), herein GaN epitaxial layers were grown on various Si(111) substrates. Thin Platinum layer was deposited on Si(111) substrate using sputtering, followed by thermal annealing to form Pt nano-clusters which act as masking layer during dry-etched with inductively coupled plasma-reactive ion etching to generate nano-patterned Si(111) substrate. In addition, micro-patterned Si(111) substrate with circle shape was also fabricated by using conventional photo-lithography technique. GaN epitaxial layers were subsequently grown on micro-, nano-patterned and conventional Si (111) substrate under identical growth conditions for comparison. The GaN layer grown on nano-patterned Si (111) substrate shows the lowest crack density with mirror-like surface morphology. The FWHM values of XRD rocking curve measured from symmetry (002) and asymmetry (102) planes are 576 arcsec and 828 arcsec, respectively. To corroborate an enhancement of the growth quality, the FWHM value achieved from the photoluminescence spectra also shows the lowest value (46.5 meV) as compare to other grown samples.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.72-72
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• 2012

Lithium rechargeable batteries have been widely used as key power sources for portable devices for the last couple of decades. Their high energy density and power have allowed the proliferation of ever more complex portable devices such as cellular phones, laptops and PDA's. For larger scale applications, such as batteries in plug-in hybrid electric vehicles (PHEV) or power tools, higher standards of the battery, especially in term of the rate (power) capability and energy density, are required. In PHEV, the materials in the rechargeable battery must be able to charge and discharge (power capability) with sufficient speed to take advantage of regenerative braking and give the desirable power to accelerate the car. The driving mileage of the electric car is simply a function of the energy density of the batteries. Since the successful launch of recent Ni-MH (Nickel Metal Hydride)-based HEVs (Hybrid Electric Vehicles) in the market, there has been intense demand for the high power-capable Li battery with higher energy density and reduced cost to make HEV vehicles more efficient and reduce emissions. However, current Li rechargeable battery technology has to improve significantly to meet the requirements for HEV applications not to mention PHEV. In an effort to design and develop an advanced electrode material with high power and energy for Li rechargeable batteries, we approached to this in two different length scales - Atomic and Nano engineering of materials. In the atomic design of electrode materials, we have combined theoretical investigation using ab initio calculations with experimental realization. Based on fundamental understanding on Li diffusion, polaronic conduction, operating potential, electronic structure and atomic bonding nature of electrode materials by theoretical calculations, we could identify and define the problems of existing electrode materials, suggest possible strategy and experimentally improve the electrochemical property. This approach often leads to a design of completely new compounds with new crystal structures. In this seminar, I will talk about two examples of electrode material study under this approach; $LiNi_{0.5}Mn_{0.5}O_2$ based layered materials and olivine based multi-component systems. In the other scale of approach; nano engineering; the morphology of electrode materials are controlled in nano scales to explore new electrochemical properties arising from the limited length scales and nano scale electrode architecture. Power, energy and cycle stability are demonstrated to be sensitively affected by electrode architecture in nano scales. This part of story will be only given summarized in the talk.

• Polymer(Korea)
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• v.31 no.5
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• pp.399-403
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• 2007

Trans-esterification behavior of polycarbonate/poly(butylene terephthalate) (PC/PBT) blends was investigated during the melt mixing process. Rheological and fracture behaviors, and fracture morphology were also investigated as a function of PC/PBT blend ratio. Based on FT-IR and $^1H-NMR$ results, a trans-esterification reaction was confirmed to occur between PC and PBT during the melt mixing process. The melt index(MI) decreased with increased PC content, indicating the higher flow resistance of PC. The storage and loss moduli were increased by increasing the PC loading, and the PC/PBT blends were rheologically incompatible based on the Cole-Cole plot. The tensile property increased linearly with the increased PC content. However, the impact strength increased until 50 wt% of PC loading, notably around $30{\sim}40wt%$, and then was levelled off at 50 wt%. Rough ridges were formed on the impact fracture surfaces above the 40 wt% of PC content, supporting the observed higher impact strength in this range.

• Polymer(Korea)
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• v.38 no.3
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• pp.364-370
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• 2014

The retinal pigment epithelium (RPE) plays an important role in maintaining a healthy retina and the degeneration of RPE caused a number of retinal diseases. The transplantation of RPE has recently become a possible therapeutic modality for retinal degeneration. To transplant RPE cells securely, substrates are essential, and then as a substrate, we fabricated films using silk that has unique mechanical properties and biocompatibility. After the FTIR spectra, contact angle and biodegradation of silk films were confirmed, RPE cells were seeded and the influence of RPE cells on silk films was examined. We measured the cell adhesion, cell viability, morphology and specific mRNA expression by MTT assay, SEM, immunofluorescence and RT-PCR. In this study, we confirmed that attachment, proliferation and phenotype maintenance of RPE cells cultured on silk films were great, and thereby we were able to confirm the potential applications of silk films as tissue engineering carrier for regeneration of retina.

• Polymer(Korea)
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• v.35 no.4
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• pp.277-283
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• 2011

Solid dispersion is mainly used for improved dissolution of poorly water-soluble drugs. Solid dispersion of pranlukast was prepared by spray-drying with plasdone S-630. When pH of water was high, pranlukast was highly soluble in the solubility experiment of solid dispersions with varying pH. The particle size of pranlukast particles in solid dispersions was measured to be in nanometers scale based on particle size analysis. Zeta-potential analysis confirmed the negative charge of solid dispersion. SEM was used to observe the surface of solid dispersion, which confirmed spherical morphology, DSC and XRD confirmed the amorphous nature of solid dispersions. The in vitro test was carried out to find improved dissolution rate of pranlukast solid dispersion in simulated juice gastric and a controlled experiment was carried out to compare pranlukast solid dispersions with a conventional drug (Onon$^{(R)}$), These results showed the dissolution properties of pranlukast solid dispersions prepared by spray drying proper for the oral pharmaceutical formulation.

• Polymer(Korea)
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• v.38 no.1
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• pp.24-30
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• 2014

Retinal pigment epithelium (RPE) plays an important role in maintaining the visual function and the degeneration of the RPE causes several retinal degeneration disease. In order to fabricate the suitable carrier for RPE transplantation, the hybrid poly(lactide-co-glycolide) (PLGA) film with hesperidin was prepared. Hesperidin has an anti-inflammatory and antioxidant characteristics. ARPE-19 was seeded on hesperidin/PLGA film and then, cell proliferation was determined by the MTT assay, and cell adhesion and cell morphology were confirmed by SEM. Also, RT-PCR was performed to confirm the expression of the specific genes, and AEC immunohistochemical staining was performed to determine the expression of RPE65. As a result, we confirmed that attachment, proliferation and phenotype maintenance of RPE cells were more excellent on hesperidin/PLGA film than PLGA film, thereby we were able to confirm the potential applications of hesperidin/PLGA film as tissue engineering carrier for regeneration of retina.

• Polymer(Korea)
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• v.36 no.3
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• pp.287-294
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• 2012

ZnAl-LDH(layered double hydroxide) (Zn:Al=2:1 mole ratio) modified with stearic acid (SA) or oleic acid (OA) was synthesized by a coprecipitation method and compounded to SAN polymer at various contents. All the SAN composites were manufactured by a co-rotating twin-screw extruder and subsequently injection molded into several specimen. Morphology, transparency, and thermal resistance of these composites were evaluated by TEM, XRD(X-ray diffractometry), UV-Vis spectrophotometry, and thermogravimetric analysis. SAN nanocomposites containing OA-$Zn_2Al$ LDH showed better optical transmittance than SAN nanocomposites containing SA-$Zn_2Al$ LDH. All the SAN nanocomposites containing OA-$Zn_2Al$ LDH or SA-$Zn_2Al$ LDH exhibited improvement of thermal resistance at second stage of thermal oxidation. These results were explained by the fact that the interaction between organic modifier and polymer performed an important role in the property improvement of polymer nanocomposites.