bluuebunny/crossref_metadata_2025 huggingface dataset:
DC Characteristics of AlGaN/GaN HEMTs Using a Dual-Gate Structure
Authors: Hong Sejun , Hassan Sarwar Rana Abu ul , Heo Jun-Woo , Kim Hyun-Seok
Published: September 2015

Multiple techniques such as fluoride-based plasma treatment, a p-GaN or p-AlGaN gate contact, and a recessed gate structure have been employed to modulate the threshold voltage of AlGaN/GaN-based high-electron-mobility transistors (HEMTs). In this study, we present dual-gate
AlGaN/GaN HEMTs grown on a Si substrate, which effectively shift the threshold voltage in the positive direction. Experimental data show that the threshold voltage is shifted from −4.2 V in a conventional single-gate HEMT to −2.8 V in dual-gate HEMTs. It is evident that a second
gate helps improve the threshold voltage by reducing the two-dimensional electron gas density in the channel. Furthermore, the maximum drain current, maximum transconductance, and breakdown voltage values of a single-gate device are not significantly different from those of a dual-gate device.
For the fabricated single- and dual-gate devices, the values of the maximum drain current are 430 mA/mm and 428 mA/mm, respectively, whereas the values of the maximum transconductance are 83 mS/mm and 75 mS/mm, respectively.
Long-Reach Transmission Characteristics of Tunable External Cavity Laser
Authors: Oh Su Hwan , Yoon Ki-Hong , Cho Seung-Hyun , Seo Jun-Kyu
Published: September 2015

We report the transmission capability of a tunable external cavity laser (T-ECL) that utilizes a super-luminescent diode (SLD) and a polymer Bragg reflector (PBR) operating with a direct modulation of 2.5 Gb/s for a light source of a long-reach wavelength division multiplexed-passive
optical network (WDM-PON). The T-ECL successfully operated at an ambient temperature of −20 °C to 70 °C when employing a cooled SLD. A tuning range of 12-nm is achieved with a tuning power of lower than 80 mW. A side mode suppression ratio of more than 35 dB was obtained for
the whole tuning range. The linewidth of the lasing spectrum is less than 0.1 nm at 20 dB from the peak power. The transmission performance of the T-ECL, including an optical bandpass filter (OBPF), is better than that of the T-ECL excluding an OBPF for a long-reach transmission over 80 km
of single mode fiber (SMF). The power penalty of the T-ECL is less than 1.4 dB when using an OBPF for an 80-km transmission.
Fabrication of Stretchable Organic–Inorganic Hybrid Thin-Film Transistors on Polyimide Stiff-Island Structures
Authors: Jung Soon-Won , Koo Jae Bon , Park Chan Woo , Na Bock Soon , Oh Ji-Young , Lee Sang Seok
Published: September 2015

In this study, stretchable organic–inorganic hybrid thin-film transistors (TFTs) are fabricated on a polyimide (PI) stiff-island/elastomer substrate using blends of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] and poly(methyl methacrylate) (PMMA) and oxide semiconductor
In-Ga-Zn-O as the gate dielectric and semiconducting layer, respectively. Carrier mobility, Ion/Ioff ratio, and subthreshold swing (SS) values of 6.1 cm2 V−1 s−1, 107, and 0.2 V/decade, respectively,
were achieved. For the hybrid TFTs, the endurable maximum strain without degradation of electrical properties was approximately 49%. These results correspond to those obtained in the first study on fabrication of stretchable hybrid-type TFTs on elastomer substrate using an organic gate insulator
and oxide semiconducting active channel structure, thus indicating the feasibility of a promising device for stretchable electronic systems.
Highly Reflective Nonalloyed Ni/Ag/Pt Contact to Mg–Si Codoped p-GaN for Enhanced Efficiency of Light-Emitting Diodes
Authors: Oh Munsik , Kim Hyunsoo
Published: September 2015

The authors report enhanced efficiency of GaN-based light-emitting diodes (LEDs) fabricated with highly reflective nonalloyed Ni/Ag/Pt contact. The Ni/Ag/Pt contact formed on the Mg–Si codoped p-GaN produced the low specific contact resistance of 7.9×10−4
Ωcm2 under as-deposited condition, which is comparable to the reference reflector (annealed at 500 °C for 1 min in oxygen ambient). Current–voltage-temperature measurements and the secondary ion mass spectroscopy revealed that the ohmic mechanism of the nonalloyed
Ni/Ag/Pt contact is due to the more generated deep-level states associated with Mg–Si codoping, which act as the efficient hopping centers for the carrier transport at the contact/p-GaN interface. Due to the absence of interfacial reaction, the nonalloyed Ni/Ag/Pt contact showed much
higher optical reflectivity (93.4% at 450 nm) as compared to the annealed sample (57.7%), resulting in a 40.5% brighter light output power as compared to the reference LEDs.
Failure Analysis of a Nickel-Plated Electronic Connector Due to Salt-Induced Corrosion (ENGE 2014)
Authors: Lee Na-Ri , Choi Hyoung-Seuk , Choi Duck-Kyun
Published: September 2015

When electronic connectors in mobile devices are miniaturized, the thickness of plating decreases. However, this thin plating is expected to decrease the life of the connector due to problems with corrosion. In this study, salt spray aging tests were performed on miniaturized nickel-plated
stainless steel electronic connectors to observe failure mechanisms in realistic environments. The tests were performed three times using a 5% NaCl solution in an atmosphere of 45 °C; each test included several cycles where one cycle was one 24-h period consisting of 8 h of salt spray
and 16 h without salt spray. The nickel-plating layers were periodically observed by electron probe X-ray micro-analyzer, wavelength dispersive spectroscopy, and field-emission scanning electron microscopy to analyze and identify the corrosion mechanism. We found that the primary failure mode
of the nickel plating is blistering and delamination. The corrosion mechanism is typically a chain reaction of several corrosion mechanisms: pitting corrosion → stress corrosion cracking → hydrogen-induced cracking → blistering and delamination. Finally, we discuss countermeasures
to prevent corrosion of the nickel layer based on the corrosion mechanisms identified in this study.
Effects of La Incorporation in Hf Based Dielectric on Leakage Conduction and Carrier Scattering Mechanisms
Authors: You Seung-Won , Lee Dong Hwi , Nguyen Manh Cuong , Jeon Yoon Seok , Tong Duc-Tai , Bang Hyun Joon , Jeong Jae Kyoung , Choi Rino
Published: September 2015

Metal-oxide-semiconductor field effect transistors (MOSFETs) with various doses of La-incorporated in Hafnium-based dielectrics were characterized to evaluate the effect of La on dielectric and device properties. It is found that the Poole-Frenkel emission model could explain our experimental
leakage current conduction mechanism reasonably and barrier heights of localized Poole-Frenkel trap sites increase gradually with increasing La incorporation. Cryogenic measurement (from 100 K to 300 K) of MOSFETs reveals that, as the content of La incorporation in the dielectric increases,
the more increase of maximum effective mobility has been found at low temperature. It is mainly attributed to the more reduction of phonon scattering due to higher content of La atoms at the interface of dielectric and channel. Though it is relatively small, the existence of La in dielectric
reduces coulomb scattering rate as well.
Abnormal Threshold Voltage Shifts in P-Channel Low-Temperature Polycrystalline Silicon Thin Film Transistors Under Negative Bias Temperature Stress
Authors: Kim Sang Sub , Choi Pyung Ho , Baek Do Hyun , Lee Jae Hyeong , Choi Byoung Deog
Published: September 2015

In this research, we have investigated the instability of P-channel low-temperature polycrystalline silicon (poly-Si) thin-film transistors (LTPS TFTs) with double-layer SiO2/SiNX dielectrics. A negative gate bias temperature instability (NBTI) stress was
applied and a turn-around behavior phenomenon was observed in the Threshold Voltage Shift (Vth). A positive threshold voltage shift occurs in the first stage, resulting from the negative charge trapping at the SiNX/SiO2 dielectric interface being
dominant over the positive charge trapping at dielectric/Poly-Si interface. Following a stress time of 7000 s, the Vth switches to the negative voltage direction, which is “turn-around” behavior. In the second stage, the Vth moves from −1.63
V to −2 V, overwhelming the NBTI effect that results in the trapping of positive charges at the dielectric/Poly-Si interface states and generating grain-boundary trap states and oxide traps.
Optical Properties of Laser Lines and Fluorescent Spectrum in Cholesteric Liquid Crystal Laser
Authors: Jeong Mi-Yun , Chung Ki Soo , Wu J.W.
Published: September 2015

We experimentally studied the comprehensive optical properties of the laser lines and fluorescent spectrum generated by a continuous tunable cholesteric liquid crystal (CLC) laser array. We found that the laser lines generated from a CLC with a right-handed circular helix were right-handed
circular polarized and laser lines generated from a CLC with a left-handed circular helix were left-handed circular polarized. Inside the photonic band gap, the CLC structure with right-(left-) handed helicity suppressed the fluorescence generated with right (left) circular polarized light,
and instead the suppressed right (left) circular polarized light energy moved to the outside of the photonic band gap, so we can say that the fluorescence intensity outside of the photonic band gap is enhanced with right (left) handed circular polarized light. Depending on the position of
the photonic band gap, the fluorescence quantum yield value increased by up to ∼15%. These enhanced fluorescence intensities at the PBG edge will evolve into lasing at the upper lasing threshold. It is particularly interesting to see that the fluorescence intensity and shape could be controlled
by adjusting the external geometrical factor of the photonic band gaps. The lasing threshold of the CLC lasers was in the range of 1.5–5.3 μJ/pulse. For CLC laser device applications, it is necessary and essential to know the optical properties of the generated laser lines
and of the fluorescence spectrum.
Design of Circle Array Pattern for Transparent Nanomesh-Type Electrodes
Authors: Shin Seungsu , Ganorkar Shraddha , Kim Jungyoon , Kim Young-Hwan , Kim Yong Tae , Kim Seong-II
Published: September 2015

In this study, we report simulation results for the optical properties of nanomesh-type electrodes for transparent electrode. Usually, indium tin oxide (ITO) is commonly used for transparent conductor to solar cell, display, LED and other electronic modules. However, the cost is high
due to the rarity of indium. An alternative way is use of transparent nanomesh-type metal electrode for solar cell. Finite different time domain (FDTD) method was used to simulate and analyze their optical properties. Various array patterns (square, circle and circle hexagonal array) of metal
on glass (SiO2) substrates were designed and their properties of transmission and reflection were simulated by using the broad band (λ = 300 ∼ 1200 nm) plane wave source. To compare basic characteristics of each pattern, various structural parameters such as hole diameter,
pitch and metal thickness were applied. The effect of three typical metals, such as Ag, Au, and Al was also compared. In the results, we will discuss about large dip of transmission appeared at the particular wavelength region from the circle array pattern, which is design with pitch of 500
nm at the wavelength range 700 to 800 nm. The surface plasmonpolaritons (SPP) effect can be the cause of large dip and we could find a broad and high transmission from the properly designed in nanomesh-type electrodes, which was calculated as a function of wavelength.
Efficiency Enhancement of Organic Light-Emitting Devices Fabricated Using a 1,4,5,8,9,11-Hexaazatriphenylene Hexacarbonitrile Silver Electrode
Authors: Jeon Y. P. , Choi Y. H. , Kim T.W.
Published: September 2015

A 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN)/Ag/HAT-CN transparent electrode for organic light-emitting devices (OLEDs) was investigated. The current density of OLEDs was enhanced with an increase in the Ag layer thickness of a HAT-CN/Ag/HAT-CN anode. While the luminance
of the OLEDs with a HAT-CN/Ag/HAT-CN anode slightly decreased with increasing thickness of the upper HAT-CN layer, the current efficiency of the OLEDs with thicknesses for the Ag layer of 20 nm and for the upper HAT-CN layer of 100 nm was almost two times higher than that of OLEDs with an
ITO anode. Electroluminescence spectra of the OLEDs with a HAT-CN/Ag/HAT-CN anode were shifted due to the micro-cavity effect in the stacked anode, which was confirmed by the transmittance spectra.
Au-Polypyrrole Framework Nanostructures for Improved Localized Surface Plasmon Resonance Volatile Organic Compounds Gas Sensing
Authors: Lee Jae-Sung , Yoon Na-Rae , Kang Byoung-Ho , Lee Sang-Won , Gopalan Sai-Anand , Kim Sae-Wan , Lee Seung-Ha , Kwon Dae-Hyuk , Kang Shin-Won
Published: September 2015

In this paper, we propose an Au-polypyrrole (Ppy) nanorod gas sensor for the detection of volatile organic compound (VOC) gases. This gas sensor operates on the principle of localized surface plasmon resonance (LSPR). The Au-Ppy nanorods used in this experiment were synthesized using
an anodic aluminum oxide template by the electrochemical deposition method. Using field emission scanning electron microscopy, we confirmed that the Au-Ppy nanorod arrays were successfully fabricated with a uniform size. By depositing gold, the Au-Ppy nanorods exhibited both optical and LSPR
interference. The gas sensing properties of the fabricated nanorods were tested for VOCs such as acetic acid, benzene, and toluene with a short response time (∼1 min). Moreover, the proposed VOC gas sensing system was tested with three types of VOC gases over a wide concentration range
from 10 to 100 ppm. Highest sensitivity was observed for acetic acid gas, which had a linear relation with the gas concentration, indicating that the system can be used as a gas sensor.
Effects of Double Active Layer and Acetic Acid Stabilizer on the Electrical Properties of a Solution-Processed Zinc Tin Oxide Thin-Film Transistor
Authors: Shin Ji Hun , Kim Sang Jo , Ha Seung Soo , Im Yong Jin , Park Chan Hee , Yi Moonsuk
Published: September 2015

We investigated the effects of a double active layer (DAL) and acetic acid stabilizer on zinc tin oxide (ZTO) thin-film transistors (TFTs) fabricated using a solution process. The DAL was composed of two layers created by a ZTO solution doped with the same or different percentiles of
an atomic Sn concentration (30 at.%, 60 at.%). The electrical performance of the ZTO TFTs significantly was improved after we added acetic acid (AA) instead of monoethanolamine (MEA). This was accomplished by applying a type 2 DAL (bottom layer: Sn 60 at.%, top layer: Sn 30 at.%, 60/30) instead
of other types (30/30 or 60/60). It was demonstrated that AA plays a role in lowering the decomposition temperature, enhancing the metal-oxygen bridge, and decreasing hydroxyl groups in the film. In addition, the type 2 DAL structure (60/30) lowered the Ioff of the ZTO TFT
and controlled the carrier concentration in the channel. The best performances were obtained at a Sn concentration of 60 at.% in the bottom ZTO layer and 30 at.% in the top ZTO layer, with AA added as a stabilizer. The ZTO TFT exhibited an on/off ratio of 1.1×109, a saturation
mobility of 5.04 cm2/V·s, a subthreshold slope of 0.11 V/decade, and a threshold voltage of 1.6 V.
Composition Control of CuInSe2 Thin Films Using Cu/In Stacked Structure in Coulometric Controlled Electrodeposition Process
Authors: Kwon Yong Hun , Do Hyun Woo , Kim Hyoungsub , Cho Hyung Koun
Published: September 2015

Cu/In bi-metal stacked structures were prepared on Mo coated soda lime glass substrates using electrodeposition method. These metallic precursors were selenized at 550 °C for 60 min to synthesize the CuInSe2 (CIS) thin films in a thermal evaporator chamber with an Se
overpressure atmosphere. The composition ratios of CIS thin films were systematically controlled using the coulometric method of the electrodeposition, where the accumulated coulomb of In layers was varied from 1062 to 6375 mC/cm2. As a result, the stoichiometric CIS film was obtained
in the Cu/In coulomb ratio of 0.6. Highly crystallized CIS films were produced from the liquid Cu–Se phase in the Cu/In coulomb ratio of ≥ 0.6. In contrast, the crystallinity and grain size were degraded in the In-rich region. We found that the Cu/In composition ratio of CIS films
was linearly proportional to the precursor thickness determined by the coulomb ratio.
Rapidly Thermal Annealed Si-Doped In2O3 Films for Organic Photovoltaics
Authors: Lee Hye-Min , Kim Han-Ki
Published: September 2015

We report the electrical, optical, and structural properties of Si-doped In2O3 (ISO) films prepared using co-sputtering system with multi cathode guns for use in organic photovoltaics (OPVs). We investigated the effect of Si doping power on the electrical, optical,
and structural properties of ISO film that was rapidly thermally annealed at a temperature of 400 °C. Due to the high Lewis acid strength (8.096) of the Si dopant, the ISO films showed high mobility and low resistivity despite the low Si doping concentration. Low resistivity of the annealed
ISO films indicated that Si4+ acts as an effective dopant of an In2O3 matrix by substitution with the In3+ site. At a Si doping power of 50 W, ISO film showed a sheet resistance of 19.7 Ohm/square and optical transparency of 76.7%, which are acceptable
values for fabrication of OPVs. Successful operation of OPV cells fabricated on transparent ISO film indicates that ISO is a promising high mobility transparent electrode material and alternative to conventional ITO films.
Combined Effects of Pyramid-Like Structures and Antireflection Coating on Si Solar Cell Efficiency
Authors: Cho Chanseob , Oh Junghwa , Lee Byeungleul , Kim Bonghwan
Published: September 2015

We developed a novel process for synthesizing Si solar cells with improved efficiencies. The process involved the formation of pyramid-like structures on the Si substrate and the deposition and subsequent thermal annealing of an antireflection coating. The process consisted of three
main stages. First, pyramid-like structures were textured on the Si substrate by reactive ion etching and subsequently etched using a mixture of HF, HNO3, and deionized water for 300 s. Next, an antireflection coating was deposited on the substrate and was subsequently thermally
annealed in a furnace in a N2 atmosphere. After the annealing process, the minority carrier lifetime increased by approximately 40 μs. Further, because of the increase in the minority carrier lifetime and the uniform doping of the substrate, the leakage current decreased.
As a result, the efficiency of resulting solar cell increased to 17.24%, in contrast to that of the reference cell, which was only 15.89%. Thus, uniform doping and the thermal annealing of the antireflective coating improved solar cell efficiency.
A Study on the Efficiency Improvement of Dye-Sensitized Solar Cell (DSSC) by Repeated Dye Coating
Authors: Seo Young Ho , Choi Eun Chang , Hong Byungyou
Published: September 2015

Dye-sensitized solar cell (DSSC) is being extensively investigated as the next generation energy source. Despite of the attractive features like simple fabrication process and its economic efficiency, there are some problems such as low efficiency, long fabrication time and low long-term
stability. Conventionally, the dye adsorption on TiO2 photo-electrode film needs long time in the solvent with low concentration of dye to get the high efficiency. In this work, the dye coating process was considerably shortened, albeit plenty of dye was used comparing with the
conventional way. Our needs were met for the best result in our working environment and the relevant conditions to our work were obtained, which were the coating temperature of 70 °C, the dye concentration of 10 mM and the coating time of 3 min. And this coating process was successively
repeated several times to maximize the dye adsorption and to improve the cell efficiency. Therefore, the efficiency increased by 13% in the proper condition.
Enhancement of Characteristics of a Touch Sensor by Controlling the Multi-Layer Architecture of a Low-Cost Metal Mesh Pattern
Authors: Kwak Seung-Hoon , Kwak Min-Gi , Ju Byeong-Kwon , Hong Sung-Jei
Published: September 2015

In this study, the characteristics of a metal mesh touch sensor were enhanced by optimizing the multi-layer architecture of the metal mesh pattern. Low-cost metal such as an aluminum (Al) layer was mainly applied to the architectures for practical applications in touch screen panel
(TSP) industries. As well, molybdenum (Mo) was added to the architectures in order to minimize the drawbacks of Al. Three types of Mo/Al, Al/Mo and Mo/Al/Mo layers were fabricated by DC sputtering. The thickness of the Al and Mo layer was optimized at 150 and 30 nm, respectively. Low sheet
resistance below 0.27 Ω/□ was achieved with good adhesion on a glass substrate. Especially, in the case of architectures in which the Al layer was covered with an Mo layer, thermal stability and corrosion resistance was enhanced. The change in resistance of the Mo/Al/Mo architecture
was less than 0.056 even after heat-treatment at 260 °C. By using the optimized layer architecture, the mesh pattern with a 4 μm line width showed good optical transmittance (86.7%) and reflectivity (13.1%) at 550 nm, respectively. Also, a touch sensor fabricated by using the
Mo/Al/Mo mesh pattern operated well indicating that the mesh pattern is feasible in a TSP application.
Cell-Adhesive Matrices Composed of RGD Peptide-Displaying M13 Bacteriophage/Poly(lactic-co-glycolic acid) Nanofibers Beneficial to Myoblast Differentiation
Authors: Shin Yong Cheol , Lee Jong Ho , Jin Linhua , Kim Min Jeong , Kim Chuntae , Hong Suck Won , Oh Jin Woo , Han Dong-Wook
Published: September 2015

Recently, there has been considerable effort to develop suitable scaffolds for tissue engineering applications. Cell adhesion is a prerequisite for cells to survive. In nature, the extracellular matrix (ECM) plays this role. Therefore, an ideal scaffold should be structurally similar
to the natural ECM and have biocompatibility and biodegradability. In addition, the scaffold should have biofunctionality, which provides the potent ability to enhance the cellular behaviors, such as adhesion, proliferation and differentiation. This study concentrates on fabricating cell-adhesive
matrices composed of RGD peptide-displaying M13 bacteriophage (RGD-M13 phage) and poly(lactic-co-glycolic acid, PLGA) nanofibers. Long rod-shaped M13 bacteriophages are non-toxic and can express many desired proteins on their surface. A genetically engineered M13 phage was constructed
to display RGD peptides on its surface. PLGA is a biodegradable polymer with excellent biocompatibility and suitable physicochemical property for adhesive matrices. In this study, RGD-M13 phage/PLGA hybrid nanofiber matrices were fabricated by electrospinning. The physicochemical properties
of these matrices were characterized by scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and contact angle measurement. In addition, the cellular behaviors, such as the initial attachment, proliferation and differentiation, were analyzed by a CCK-8 assay and immunofluorescence
staining to evaluate the potential application of these matrices to tissue engineering scaffolds. The RGD-M13 phage/PLGA nanofiber matrices could enhance the cellular behaviors and promote the differentiation of C2C12 myoblasts. These results suggest that the RGD-M13 phage/PLGA nanofiber matrices
are beneficial to myoblast differentiation and can serve as effective tissue engineering scaffolds.
Effect of pH and Salt on Adsorption of Double-Stranded DNA on Graphene Oxide
Authors: Kim Seyeon , Park Chanoong , Gang Jongback
Published: September 2015

Graphene oxide (GO) has a large surface-to-volume ratio and hydrophobic hexagonal rings that can interact with biomolecules. Single-stranded DNA adsorbs strongly to the surface of GO via hydrophobic interactions. GO has been used in optical biosensors and biomedical platforms for the
detection of DNA, proteins, and small molecules. This study was designed to measure the adsorption of double-stranded DNA (dsDNA) onto GO according to DNA length, salt concentration, and pH of the reaction. Results showed that dsDNA molecules were adsorbed progressively as the pH changed from
6.0 to 4.0. At high pH, dsDNA adsorption was enhanced by the presence of MgCl2 rather than NaCl. Desorption of DNA from GO, with triton X-100 led to the rapid release of DNA from GO in the presence of MgCl2.
Dependence of Impedance Measurement Sensitivity of Cell Growth on Sensing Area of Circular Interdigitated Electrode
Authors: Park Jinsoo , Hwang Kyo Seon , Cho Sungbo
Published: September 2015

A circular interdigitated electrode (IDE) array for label-free and real-time impedance monitoring of cell growth was fabricated and evaluated. Both the width and spacing of fingers were 50 μm, and the exposed sensing area of the circular IDE was 1.3~3.4 mm. The electrical characteristics
of the fabricated circular IDE were modeled as an equivalent circuit, and the values of the circuit parameters extrapolated from the fitting to the measured spectra in different concentrations of NaCl or sensing areas of the circular IDE were analyzed. During cell growth, the resistance of
cells extrapolated from the fitting was increased and the maximum rate of change in the real part of the impedance was observed at frequencies of 10 to 22 kHz. The normalized real part of the impedance measured at 10 kHz during cell growth was increased more with decreasing the electrode sensing
area, albeit the number of cells to be investigated showed a corresponding increase.
Simultaneous Drug and Gene Delivery from the Biodegradable Poly(ε-caprolactone) Nanofibers for the Treatment of Liver Cancer
Authors: Che Hui-Lian , Lee Hwa Jeong , Uto Koichiro , Ebara Mitsuhiro , Kim Won Jong , Aoyagi Takao , Park In-Kyu
Published: September 2015

In this study, we present anti-cancer drug containing nanofiber-mediated gene delivery to treat liver cancer. Electro-spun nanofibers have big potential for local delivery and sustained release of therapeutic gene and drugs. We reported a temperature-responsive nanofibers mainly compounded
by branched poly(ε-caprolactone) (PCL) macro-monomers and anti-cancer drug paclitaxel. The nanofiber could be administrated into liver tumors to dramatically hinder their growth and prevent their metastasis. As a result, paclitaxel encapsulated PCL (PTX/PCL) nanofibers with diameters
of around several tens nanometers to 10 nm were successfully obtained by electro-spinning andobserved in scanning electron microscopy (SEM). Nanoparticles composed of disulfide cross-linked branched PEI (ssPEI) and anti-cancer therapeutic gene miRNA-145 were complexed based on the electrostatic
interaction and coated over the paclitaxel-loaded nanofiber. MicroRNA 145/ssPEI nanoparticles (MSNs) immobilized on the PTX/PCL nanofiber showed time-dependent sustained release of the microRNA for enhanced uptake in neighboring liver cancer cells without any noticeable cytotoxicity. From
this study we are expecting a synergistic effect on the cancer cell suppression since we have combined the drug and gene delivery. This approach uses the nanofibers and nanoparticles together for the treatment of cancer and the detailed investigation in vitro and in vivo must
be conducted for the practicality of this study. The polymer is biodegradable and the toxicity issues must be cleared by our approach.
Photodynamic Anticancer Activity of CoFe2O4 Nanoparticles Conjugated with Hematoporphyrin
Authors: Park Bong Joo , Choi Kyong-Hoon , Nam Ki Chang , Min Jeeeun , Lee Kyu-Dong , Uhm Han Sup , Choi Eun Ha , Kim Ho-Joong , Jung Jin-Seung
Published: September 2015

This work reports the synthesis and the characterization of water-soluble and biocompatible photosensitizer (PS)-conjugated magnetic nanoparticles composed of a cobalt ferrite (CoFe2O4) magnetic core coated with a biocompatible hematoporphyrin (HP) shell. The photo-functional
cobalt ferrite magnetic nanoparticles (CoFe2O4@HP) were uniform in size, stable against PS leaching, and highly efficient in the photo-generation of cytotoxic singlet oxygen under visible light. With the CoFe2O4@HP, we acquired in vitro MR
images of cancer cells (PC-3) and confirmed good biocompatibility of the CoFe2O4@HP in both normal and cancer cells. In addition, we confirmed the potential of the CoFe2O4@HP as an agent for photodynamic therapy (PDT) applications. The photodynamic
anticancer activities in 25, 50, and 100 μg/mL of CoFe2O4@HP were measured and found to exceed 99% (99.0, 99.4, and 99.5%) (p <0.002). The photodynamic anticancer activity was 81.8% (p < 0.003). From these results, we suggest that our CoFe2O4@HP
can be used safely as a type of photodynamic cancer therapy with potential as a therapeutic agent having good biocompatibility. Moreover, these photo-functional magnetic nanoparticles are highly promising for applications in versatile imaging diagnosis and as a therapy tool in biomedical engineering.
Synthesis of Imine-Bearing ZnO Nanoparticle Thin Films and Characterization of Their Structural, Morphological and Optical Properties
Authors: Kaur Narinder , Sharma Sanjeev K. , Kim Deuk Young , Sharma Hemant , Singh Narinder
Published: September 2015

We are presenting the first report on the fabrication of imine-bearing ZnO nanoparticle thin films grown on Corning glass by spin coating. The sol was prepared by dissolving imine-bearing ZnO nanoparticles in dimethylsulfoxide (DMSO). The thickness of the films was manipulated to be
125–200 nm. The X-ray diffraction (XRD) analysis showed hexagonal wurtzite structure of imine-bearing ZnO nanoparticles thin films with a (002) preferential orientation. The stretching of chemical bonds of the imine linkage and Zn–O in imine-bearing ZnO nanoparticle thin films
was confirmed by fourier transform infrared spectroscopy (FTIR). The grain size of the films increased with increasing the thickness of the films due to the number of coatings and subsequently dried at 200°C. The transmittance of imine-bearing ZnO nanoparticle thin films was observed to
be ≥94%, which was in close agreement to pure ZnO thin films in the visible region. The bandgap of imine-bearing ZnO nanoparticle thin films (3.04 eV), evaluated from Tauc’s plot, was observed to be lower than that of pure ZnO (3.21 eV), which is attributed to the interaction of the
ZnO nanoparticles with the imine receptor.
Temperature-Dependent Energy Gap Shift and Thermally Activated Transition in Multilayer CdTe/ZnTe Quantum Dots
Authors: Man Minh Tan , Lee Hong Seok
Published: September 2015

We investigated the influence of growth conditions on carrier dynamics in multilayer CdTe/ZnTe quantum dots (QDs) by monitoring the temperature dependence of the photoluminescence emission energy. The results were analyzed using the empirical Varshni and O’Donnell relations for
temperature variation of the energy gap shift. Best fit values showed that the thermally activated transition between two different states occurs due to band low-temperature quenching with values separated by 5.0–6.5 meV. The addition of stack periods in multilayer CdTe/ZnTe QDs plays
an important role in the energy gap shift, where the exciton binding energy is enhanced, and, conversely, the exciton-phonon coupling strength is suppressed with an average energy of 19.3–19.8 meV.
Dehydration of Glycerin to Acrolein Over Heteropolyacid Nano-Catalysts Supported on Silica–Alumina
Authors: Kang Tae Hun , Choi Jung Ho , Choi Jun Seon , Song In Kyu
Published: September 2015

A series of H3PW12O40 nano-catalysts supported on silica–alumina (XH3PW12O40/SA (X = 10, 15, 20, 25, and 30)) with different H3PW12O40 content (X, wt%) were prepared,
and they were applied to the dehydration of glycerin to acrolein. The effect of H3PW12O40 content on the physicochemical properties and catalytic activities of XH3PW12O40/SA nano-catalysts was investigated. Surface area and
pore volume of XH3PW12O40/SA catalysts decreased with increasing H3PW12O40 content. Formation of H3PW12O40 aggregates was observed in the catalysts with high H3PW12O40
loading. Brønsted acidity of the catalysts showed a volcano-shaped trend with respect to H3PW12O40 content. It was revealed that yield for acrolein increased with increasing Brønsted acidity of XH3PW12O40/SA catalysts.
Brønsted acidity of XH3PW12O40/SA catalysts served as a crucial factor determining the catalytic performance in the dehydration of glycerin. Among the catalysts tested, 25H3PW12O40/SA catalyst with the largest Brønsted
acidity showed the best catalytic performance.
Perpendicular Magnetic Anisotropy in Amorphous Ferromagnetic CoSiB/Pd Thin-Film Layered Structures
Authors: Jung Sol , Yim Haein
Published: September 2015

Spin transfer torque (STT) induced switching of magnetization has led to intriguing and practical possibilities for magnetic random access memory (MRAM). This form of memory, called STT-MRAM, is a strong candidate for future memory applications. This application usually requires a large
perpendicular magnetic anisotropy (PMA), large coercivity, and low saturation magnetization. Therefore, we propose an amorphous ferromagnetic CoSiB alloy and investigate CoSiB/Pd multilayer thin films, which have a large PMA, large coercivity, and low saturation magnetization. In this research,
we propose a remarkable layered structure that could be a candidate for future applications and try to address a few factors that might affect the variation of PMA, coercivity, and saturation magnetization in the CoSiB/Pd multilayers. We investigate the magnetic properties of the CoSiB/Pd
multilayers with various thicknesses of the CoSiB layer. The coercivity was obtained with a maximum of 228 Oe and a minimum value of 91 Oe in the [CoSiB 7 Å/Pd 14 Å]5 and [CoSiB 9 Å/Pd 14 Å]5 multilayers, respectively. The PMA arises from tCoSiB
= 3 Å to tCoSiB = 9 Å and disappears after tCoSiB = 9 Å.
Stability of Anomalous States of a Local Potential in Graphene
Authors: Kim S. C. , Jeong Y. H. , Eric Yang S.-R.
Published: September 2015

Graphene Landau levels have discrete energies consisting zero energy chiral states and non-zero energy states with mixed chirality. Each Landau level splits into discrete energies when a localized potential is present. A simple scaling analysis suggests that a localized potential can
act as a strong perturbation, and that it can be even more singular in graphene than in ordinary two-dimensional systems of massful electrons. Parabolic, Coulomb, and Gaussian potentials in graphene may have anomalous boundstates whose probability density has a sharp peak inside the potential
and a broad peak of size magnetic length l outside the potential. The n = 0 Landau level with zero energy has only one anomalous state while the n = ±1 Landau levels with non-zero energy have two (integer quantum number n is related to the quantized Landau
level energies). These anomalous states can provide a new magnetospectroscopic feature in impurity cyclotron resonances of graphene. In the present work we investigate quantitatively the conditions under which the anomalous states can exist. These results may provide a guide in searching for
anomalous states experimentally.
Liquid-Phase Co-Exfoliated Graphene/MoS2 Nanocomposite for Methanol Gas Sensing
Authors: Zhang Shao-Lin , Yue Hongyan , Liang Xishuang , Yang Woo-Chul
Published: September 2015

We developed an efficient method to co-exfoliate graphite and MoS2 to fabricate graphene/MoS2 nanocomposite. The size, morphology, and crystal structure of the graphene/MoS2 nanocomposite were carefully examined. The as-prepared graphene/MoS2
nanocomposite was fabricated into thin film sensor by a facile drop casting method and tested with methanol gas in various concentrations. The sensitivity, response time, and repeatability of the graphene/MoS2 nanocomposite sensor towards methanol gas were systematically investigated.
A pure MoS2− based thin film sensor was also prepared and compared with the nanocomposite sensor to better understand the synergetic effect in the sensing performance. Our research demonstrated that compositing MoS2 with graphene could overcome the shortcoming
of MoS2 as a sensor material and bring in a promising gas-sensing performance with a quicker response/recovery time and an enhanced sensitivity. Moreover, this composited material with a distinct structure and an excellent electronic property is expected to have potential application
in various fields, such as optoelectronic.
Temperature Effects on Fluorescence Intensity of Mn-Doped ZnO Quantum Dots Derived from a Sol–Gel Method
Authors: Kwon Younghoon , Kim Jongsung
Published: September 2015

Recently, various quantum dots (QDs) have been prepared and studied extensively due to their unique electrical and optical properties. Among them, ZnO has attracted much attention because it contains no heavy metals, is biocompatible, and can be easily prepared. In addition, doping
QDs with transition metals such as Mn allows for their photo-physical properties to be modified. In this study, Mn-doped ZnO QDs were synthesized by a sol–gel technique, after which the effect of temperature on their fluorescence properties was investigated. The prepared QDs were characterized
by X-ray diffraction, transmission electron microscopy, and energy dispersive X-ray spectroscopy. In addition, their photoluminescence (PL) intensities decreased linearly with temperature between 30 and 70 °C. Intensity also decreased as the amount of Mn increased. Finally, the slope of
the PL temperature dependence decreased as the amount of Mn present increased.
Surface Modification of Block Copolymer Through Sulfur Containing Plasma Treatment
Authors: Choi Sang Wook , Shin Jae Hee , Jeon Min Hwan , Mun Jeong Ho , Kim Sang Ouk , Yeom Geun Young , Kim Kyong Nam
Published: September 2015

Some of the important issues of block copolymer (BCP) as an application to the potential low cost next generation lithography are thermal stability and deformation during pattern transfer process in addition to defect density, line edge/width roughness, etc. In this study, sulfur containing
plasma treatment was used to modify the BCP and the effects of the plasma on the properties of plasma treated BCP were investigated. The polystyrene hole pattern obtained from polystyrene polystyreneblock-poly(methylmethacrylate) (PS-b-PMMA) was initially degraded when the polystyrene hole
was annealed at 190°C for 15 min. However, when the hole pattern was treated using sulfur containing plasmas using H2S or SF6 up to 2 min, possibly due to the sulfurization of the polystyrene hole surface, no change in the hole pattern was observed after the annealing
even though there is a slight change in hole shapes during the plasma treatment. The optimized plasma treated polystyrene pattern showed the superior characteristics as the mask layer by showing better thermal stability, higher chemical inertness, and higher etch selectivity during plasma
etching.
Li Storage of Calcium Niobates for Lithium Ion Batteries
Authors: Yim Haena , Yu Seung-Ho , Yoo So Yeon , Sung Yung-Eun , Choi Ji-Won
Published: September 2015

New types of niobates negative electrode were studied for using in lithium-ion batteries in order to alternate metallic lithium anodes. The potassium intercalated compound KCa2Nb3O10 and proton intercalated compound HCa2Nb3O10
were studied, and the electrochemical results showed a reversible cyclic voltammetry profile with acceptable discharge capacity. The as-prepared KCa2Nb3O10 negative electrode had a low discharge capacity caused by high overpotential, but the reversible intercalation
and deintercalation reaction of lithium ions was activated after exchanging H+ ions for intercalated K+ ions. The initial discharge capacity of HCa2Nb3O10 was 54.2 mAh/g with 92.1% of coulombic efficiency, compared with 10.4 mAh/g with
70.2% of coulombic efficiency for KCa2Nb3O10 at 1 C rate. The improved electrochemical performance of the HCa2Nb3O10 was related to the lower bonding energy between proton cation and perovskite layer, which facilitate Li+
ions intercalating into the cation site, unlike potassium cation and perovskite layer. Also, this negative material can be easily exfoliated to Ca2Nb3O10 layer by using cation exchange process. Then, obtained two-dimensional nanosheets layer, which recently
expected to be an advanced electrode material because of its flexibility, chemical stable, and thin film fabricable, can allow Li+ ions to diffuse between the each perovskite layer. Therefore, this new type layered perovskite niobates can be used not only bulk-type lithium ion batteries
but also thin film batteries as a negative material.
Disulfide-Containing Crosslinked Polyaniline Cathode for Rechargeable Battery
Authors: Lee Jeong-Min , Jung Ye-Ji , Lee A-Ran , Ha Jeong-Seon , Jo Nam-Ju
Published: September 2015

Polymer electrodes have had several advantages like being environment friendly, mechanically flexible and more inexpensive than lithium metal which is used as lithium metal oxide-based cathode. But polymer electrodes generally have had lower charge/discharge capacity. Sulfur compounds
with organothiol (–SH) or disulfide (S–S) group have advantages about high theoretical capacity but they have poor electronic conductivity. Then in this study, focusing on the enhancement of electrical performance of polymer electrode, disulfide bonds are linked to the side chain
of polyaniline (PANI) and conjugated crosslinking between polymer chains is formed. As a result, crosslinked poly(9-amino-5,8-dihydro-1H,4H-2,3,6,7-tetrathia-anthracene) (PADTTAA)-co-PANI electrodes with different ratio of ADTTAA were successfully synthesized. Elemental and compositional analysis
on the surface of the polymer sample was measured by using X-ray photoelectron spectroscopy (XPS). And the electrochemical property of disulfide-containing crosslinked PANI based cathode was investigated by confirming cyclic voltammetry and charge–discharge capacity. As the contents
of ADTTAA increased, the charge/discharge capacity increased but the conductivity and cycle life decreased.
Positive Feedback in Climate: Stabilization or Runaway, Illustrated by a Simple Experiment
Authors: Dufresne Jean-Louis , Saint-Lu Marion
Published: September 2015

The response of the various climatic processes to climate change can amplify (positive feedback) or damp (negative feedback) the initial temperature perturbation. An example of a positive feedback is the surface albedo feedback: when the surface temperature rises, part of the ice and snow melts, leading to an increase in the solar radiation absorbed by the surface and to an enhanced surface warming. Positive feedbacks can lead to instability. On Venus, for example, a positive feedback is thought to have evolved into a runaway greenhouse effect. However, positive feedbacks can exist in stable systems. This paper presents a simple representation of a positive feedback in both a stable and an unstable system. A simple experimental device based on a scale principle is introduced to illustrate the positive feedback and its stabilization or runaway regimes. Stabilization can be achieved whether the amplitude of the positive feedback declines (e.g., “saturation” of the feedback) or remains constant. The device can also be used to illustrate the existence of tipping points, which are threshold values beyond which the amplification due to feedbacks or the stability of the system suddenly changes. The physical equations of the device are established in the framework of the feedback analysis. Key features to understand why a positive feedback does not necessarily lead to a runaway effect are described. The analogy between the different components of the device and those of the climate system is established. Finally, the contribution of individual feedbacks to the total climate response is addressed.
Extreme Precipitation Indices over China in CMIP5 Models. Part I: Model Evaluation
Authors: Jiang Zhihong , Li Wei , Xu Jianjun , Li Laurent
Published: September 2015

Compared to precipitation extremes calculated from a high-resolution daily observational dataset in China during 1960–2005, simulations in 31 climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) have been quantitatively assessed using skill-score metrics. Four extreme precipitation indices, including the total precipitation (PRCPTOT), maximum consecutive dry days (CDD), precipitation intensity (SDII), and fraction of total rainfall from heavy events (R95T) are analyzed. Results show that CMIP5 models still have wet biases in western and northern China. Especially in western China, the models’ median relative error is about 120% for PRCPTOT; the 25th and 75th percentile errors are of 70% and 220%, respectively. However, there are dry biases in southeastern China, where the underestimation of PRCPTOT reach 200 mm. The performance of CMIP5 models is quite different between western and eastern China. The simulations are more reliable in the east than in the west in terms of spatial pattern and interannual variability. In the east, precipitation indices are more consistent with observations, and the spread among models is smaller. The multimodel ensemble constructed from a selection of the most skillful models shows improved behavior compared to the all-model ensemble. The wet bias in western and northern China and dry bias over southeastern China are all decreased. The median of errors for PRCPTOT has a decrease of 69% and 17% in the west and east, respectively. The good reproduction of the southwesterlies along the east coast of the Arabian Peninsula is revealed to be the main factor explaining the improvement of precipitation patterns and extreme events.
Understanding of Interdecadal Changes in Variability and Predictability of the Northern Hemisphere Summer Tropical–Extratropical Teleconnection
Authors: Lee June-Yi , Ha Kyung-Ja
Published: September 2015

Two dominant global-scale teleconnections—namely, western North Pacific–North American (WPNA) and circumglobal teleconnection (CGT)—in the Northern Hemisphere (NH) extratropics during boreal summer (June–August) have been identified as important sources for NH summer climate variability and predictability. An interdecadal shift in interannual variability and predictability of the WPNA and CGT that occurred around the late 1970s was investigated using reanalysis data and six coupled models’ retrospective forecast with a 1 May initial condition for the period 1960–79 (P1) and 1980–2005 (P2). The WPNA had a tight relationship with the decaying phase of El Niño–Southern Oscillation (ENSO) in P1, whereas it had a remarkably enhanced linkage with western North Pacific (WNP) summer monsoon rainfall in P2. The correlation coefficient between the WPNA and preceding ENSO (WNP monsoon rainfall) was reduced (increased) from −0.69 (0.1) in P1 to −0.60 (0.5) in P2. The CGT had a considerable connection with Indian summer monsoon rainfall (ISMR) in P1, whereas it had a strengthened relationship with the developing ENSO in P2. The correlation coefficient between the CGT and simultaneous ENSO (ISMR) was increased (decreased) from −0.41 (0.47) in P1 to −0.59 (0.24) in P2. Although dynamical models have difficulties in capturing the observed interdecadal changes, they are able to predict the interannual variation of the WPNA and CGT one month ahead, to some extent. The prediction skill of six models’ multimodel ensemble (MME) decreased (increased) from 0.78 (0.23) to 0.67 (0.67) for the WPNA (CGT) interannual variation. It is also noted that the spatial distribution of predictability and MME skill for 200-hPa geopotential height has been changed in relation to the changes in the WPNA and CGT.