bluuebunny/crossref_metadata_2025 huggingface dataset:
Carrier Transport Properties of Bilayer Graphene Obtained via Hall Measurements
Authors: Jeon Hyojin , Park Bae Ho , Jang Moongyu
Published: September 2015

The electron transport characteristics of bilayer graphene were investigated in terms of changes in the temperature from 2 to 300 K. The purpose of this study was a confirming the reported values5 of the carrier density and the mobility for using a ballistic quantum transport
experiment. The mechanical exfoliation method was adopted to get the best quality of bilayer graphene and the number of layers of graphene was identified by the Raman spectra. Our bilayer graphene was a slightly n-doped state with the neutrality point at Vg =−7.5 V.
Hall measurements provided an accurate means to evaluate the carrier density and the mobility. In magnetic field of −9 to 9 T, clear Shubnikov-de Haas oscillations were measured in bilayer graphene, indicating the presence of a clear electron quantum transport mechanism. The mobility
and the carrier density of the bilayer graphene at 2 K were measured to be 9,400 cm2/V · s and 3×1011 cm−2, respectively.
Investigation of Switching Phenomenon in Metal-Tantalum Oxide Interface
Authors: Yawar Abbas , Park Mi Ra , Hu Quanli , Song Woo Jin , Yoon Tae-Sik , Choi Young Jin , Kang Chi Jung
Published: September 2015

To investigate the nature of the switching phenomenon at the metal-tantalum oxide interface, we fabricated a memory device in which a tantalum oxide amorphous layer acted as a switching medium. Different metals were deposited on top of the tantalum oxide layer to ensure that they will
react with some of the oxygen contents already present in the amorphous layer of the tantalum oxide. This will cause the formation of metal oxide (MOx) at the interface. Two devices with Ti and Cu as the top electrodes were fabricated for this purpose. Both devices showed
bipolar switching characteristics. The SET and RESET voltages for the Ti top electrode device were ∼+1.7 V and ∼−2 V, respectively, whereas the SET and RESET voltages for the Cu top electrode device were ∼+0.9 V and ∼−0.9 V, respectively. In the high-resistance
state (HRS) conduction, the mechanisms involved in the devices with Ti and Cu top electrodes were space-charge limited conduction (SCLC) and ohmic, respectively. On the other hand, in the low-resistance state (LRS), the Ti top electrode device undergoes SCLC at a high voltage and ohmic conduction
at a low voltage, and the Cu top electrode again undergoes ohmic conduction. From the consecutive sweep cycles, it was observed that the SET voltage gradually decreased with the sweeps for the Cu top electrode device, whereas for the Ti top electrode device, the set voltage did not vary with
the sweeps.
Design and Analysis of CMOS-Compatible III–V Compound Electron–Hole Bilayer Tunneling Field-Effect Transistor for Ultra-Low-Power Applications
Authors: Kim Sung Yoon , Seo Jae Hwa , Yoon Young Jun , Lee Ho-Young , Lee Seong Min , Cho Seongjae , Kang In Man
Published: September 2015

In this work, we design and analyze complementarymetal-oxide-semiconductor (CMOS)-compatible III–V compound electron–hole bilayer (EHB) tunneling field-effect transistors (TFETs) by using two-dimensional (2D) technology computer-aided design (TCAD) simulations. A recently
proposed EHB TFET exploits a bias-induced band-to-band tunneling (BTBT) across the electron–hole bilayer by an electric field from the top and bottom gates. This is in contrast to conventional planar p+−p−−n TFETs, which utilize
BTBT across the source-to-channel junction.We applied III–V compound semiconductor materials to the EHB TFETs in order to enhance the current drivability and switching performance. Devices based on various compound semiconductor materials have been designed and analyzed in terms of their
primary DC characteristics. In addition, the operational principles were validated by close examination of the electron concentrations and energy-band diagrams under various operation conditions. The simulation results of the optimally designed In0.53Ga0.47As EHB TFET
show outstanding performance, with an on-state current (Ion) of 249.5 μA/μm, subthreshold swing (S) of 11.4 mV/dec, and threshold voltage (Vth) of 50mV at VDS = 0.5 V. Based on the DC-optimized InGaAs EHB TFET,
the CMOS inverter circuit was simulated in views of static and dynamic behaviors of the p-channel device with exchanges between top and bottom gates or between source and drain electrodes maintaining the device structure.
Impedance Characterization of the Degradation of Insulating Layer Patterned on Interdigitated Microelectrode
Authors: Lee Gihyun , Kim Sohee , Cho Sungbo
Published: September 2015

Life-time and functionality of planar microelectrode-based devices are determined by not only the corrosion-resistance of the electrode, but also the durability of the insulation layer coated on the transmission lines. Degradation of the insulating layer exposed to a humid environment
or solution may cause leakage current or signal loss, and a decrease in measurement sensitivity. In this study, degradation of SU-8, an epoxy-based negative photoresist and insulating material, patterned on Au interdigitated microelectrode (IDE) for long-term (>30 days) immersion in an
electrolyte at 37 °C was investigated by electrical impedance spectroscopy and theoretical equivalent circuit modeling. From the experiment and simulation results, it was found that the degradation level of the insulating layer of the IDE electrode can be characterized by monitoring the
resistance of the insulating layer among the circuit parameters of the designed equivalent circuit modeling.
Effects of Magnetic Domain Walls on the Anisotropic Magnetoresistance in NiFe Nanowires
Authors: Nam Chunghee
Published: September 2015

We show that a type of magnetic domain walls (DWs) can be monitored by anisotropic magnetoresistance (AMR) measurements due to a specific DW volume depending on the DW type in NiFe magnetic wires. A circular DW injection pad is used to generate DWs at a low magnetic field, resulting
in reliable DW introduction into magnetic wires. DW pinning is induced by a change of DW energy at an asymmetric single notch. The injection of DW from the circular pad and its pinning at the notch is observed by using AMR and magnetic force microscope (MFM) measurements. A four-point probe
AMR measurement allows us to distinguish the DW type in the switching process because DWs are pinned at the single notch, where voltage probes are closely placed around the notch. Two types of AMR behavior are observed in the AMR measurements, which is owing to a change of DW structures. MFM
images and micromagnetic simulations are consistent with the AMR results.
Highly Oriented Carbon Nanotube Sheets for Rechargeable Lithium Oxygen Battery Electrodes
Authors: Ryu Seongwoo , Kim Byung Gon , Choi Jang Wook , Lee Haeshin
Published: September 2015

Lithium oxygen batteries are one of the next generation rechargeable batteries. High energy density of lithium oxygen batteries have been considered as a very attractive power option for electric vehicles and many other electronic devices. However, they still faced substantial challenges
such as short cycle life, large voltage hysteresis, low gravimetric and volumetric power. Here we developed a highly aligned CNT structured sheet for favorable lithium oxygen cathode electrodes. We fabricated highly oriented CNT sheets by rolling vertically aligned CNT arrays. Highly oriented
CNT sheets provide excellent electrical conductivity with favorable mesoporous structure for cathode electrode. As a result, the CNT sheet performed maximum discharging capacity of 1810 mA/gc. We found that electrical conductivity and pore distribution plays important rolls for improving performance
in lithium oxygen batteries. This study suggests new strategies of designing highly efficient porous carbon electrodes for lithium oxygen batteries.
Resistive Switching Characteristics of Atomic-Layer-Deposited Y2O3 Insulators with Deposition Temperature
Authors: Jung Yong Chan , Seong Sejong , Lee Taehoon , Park In-Sung , Ahn Jinho
Published: September 2015

Resistive switching characteristics of insulating Y2O3 films grown by an atomic layer deposition technique have been investigated with their growth temperature range of 250 °C to 350 °C. Ru/Y2O3/Ru resistors reveal the bi-stable unipolar
resistive switching behaviors. Resistive switching behaviors are related to the chemical bonding states of Y2O3 insulating films. As the insulating film growth temperature increases, Y2O3 film becomes much stoichiometric and little contaminated with
impurities. Moreover, the resistance ratio high resistance state to low resistance state increases at growth temperature over 300 °C.
Electrical Properties and Reliability Analysis of Solution-Processed Indium Tin Zinc Oxide Thin Film Transistors with O2-Plasma Treatment
Authors: Ko Sun Wook , Kim Soon Kon , Kim Jong Min , Cho Jae Hee , Park Hyoung Sun , Choi Byoung Deog
Published: September 2015

In this paper, we report the effects of O2-plasma treatment on the reliability and electrical properties of indium tin zinc oxide (ITZO) films. Excellent electrical properties, including a saturation mobility (μsat) of ∼20.2 cm2/V ·
s, a threshold voltage (VTH) of ∼−6.8 V, a sub-threshold swing (S.S) of ∼0.956 V/decade, and an on/off current ratio (ION/OFF) of ∼105 can be found with a molarity of 0.4 M and ratio of In:Zn:Sn = 2:1:2. Following O2-plasma
treatment, it was confirmed that the electrical properties of the ITZO films are improved when compared to the untreated films. The devices showed a decreased S.S of ∼0.51 V/decade, while the VTH and ION/OFF tended to increase. To determine the reliability
of a-ITZO TFTs, we analyzed the electrical characteristics according to gate bias stress, VG, stress = 10 V for 4000 s. Improved reliability was confirmed when compared with the variation in threshold voltage prior to O2-plasma treatment, most likely
stemming from a smooth surface on the active layer as a result of O2-plasma treatment. We were able to obtain a solution a-ITZO film transmittance of 92% in the visible light region (400∼700 nm). These results show that a-ITZO TFTs fabricated via solution process with optimized
molar ratio exhibit good electrical properties. a-ITZO films fabricated via spin-coating are a visible alternative to those fabricated via high-cost sputtering methods, and are applicable in flexible and transparent electronics.
Monodispersepoly[BMA-co-(COPS-I)] Particles by Soap-Free Emulsion Copolymerization and Its Optical Properties as Photonic Crystals
Authors: Lee Ki Chang , Choo Hun Seung
Published: September 2015

In order to study the surfactant-free emulsion copolymerization of benzyl methacrylate (BMA) with sodium 1-allyloxy-2-hydroxypropane sulfonate (COPS-I) and the resulting optical properties, a series of experiments was carried out at various reaction conditions such as the changes of
BMA concentration, COPS-I concentration, BMA concentration under a fixed COPS-I amount, initiator and divinyl benzene (DVB) concentration. All the latices showed highly monodispersed spherical particles in the size range of 144∼435 nm and the respective shiny structural colors from their
colloidal photonic crystals. It is found that the changes in such polymerization factors greatly affect the number of particles and particle diameter, polymerization rate, molecular weight, zeta-potential, and refractive indices. The increase of number of particles led to the increased rate
of polymerization and zeta-potential of the latices, on the other hand, to the decreased molecular weight. Refractive indices and the reflectivity increased with COPS-I concentration, on the other hand, and decreased with DVB concentration. Especially, refractive indices of the resulting poly[BMA-co-(COPS-I)]
colloidal photonic crystals showed much higher values of 1.65∼2.21 than that of polystyrene, due to the formation of core–shell shaped morphology. Monodisperse and high refractive index of poly[BMA-co-(COPS-I)] particles prepared in this work could be used for the study in photonic
crystals and electrophoretic display.
Gapped Surface Plasmon Polariton Waveguide Device Based on a Liquid Crystal
Authors: Lee Dong Hun , Lee Myung-Hyun
Published: September 2015

We propose a gapped surface plasmon polariton waveguide (G-SPPW) device based on a liquid crystal (LC) at a wavelength of 1.55 μm. The G-SPPW device is composed of an input 2.0-μm-wide and 5.0-μm-long insulator-metal-insulator waveguide (IMI-W), an 8-μm-long
gap, and an output 2.0-μm-wide and 25.0-μm-long IMI-W. The LC is used for the gap and the 5.15-μm-thick upper and lower dielectric layers. The input surface plasmon polaritons (SPPs) propagate and jump over the gap in the G-SPPW with a coupling loss of less than
∼0.68 dB. The propagation and coupling losses of the 38-μm-long G-SPPW device are varied in the range of ∼0.5268 dB to ∼2.6716 dB and ∼0.1446 dB to ∼0.6784 dB, respectively, with LC tilt angles (1, 2) = 0° ∼ 90° at a fixed
90° twist angle. The normalized transmission of the G-SPPW device is also varied in the range from −3.351 dB to −0.6714 dB with 1, 2 = 0° ∼ 90° at a fixed 90° twist angle. The output SPP characteristics of the G-SPPW device can be properly
controlled by the orientation of the LC molecules. The proposed G-SPPW device shows potential for new active plasmonic device applications.
Detection of Matrix Elements and Trace Impurities in Cu(In, Ga)Se2 Photovoltaic Absorbers Using Surface Analytical Techniques
Authors: Kim Min Jung , Lee Jihye , Kim Seon Hee , Kim Haidong , Lee Kang-Bong , Lee Yeonhee
Published: September 2015

Chalcopyrite Cu(In,Ga)Se2 (CIGS) thin films are well known as the next-generation solar cell materials notable for their high absorption coefficient for solar radiation, suitable band gap, and ability for deposition on flexible substrate materials, allowing the production
of highly flexible and lightweight solar panels. To improve solar cell performances, a quantitative and depth-resolved elemental analysis of photovoltaic thin films is much needed. In this study, Cu(In,Ga)Se2 thin films were prepared on molybdenum back contacts deposited on soda-lime
glass substrates via three-stage evaporation. Surface analyses via AES and SIMS were used to characterize the CIGS thin films and compare their depth profiles. We determined the average concentration of the matrix elements, Cu, In, Ga, and Se, using ICP-AES, XRF, and EPMA. We also obtained
depth profiling results using TOF-SIMS, magnetic sector SIMS and AES, and APT, a sub-nanometer resolution characterization technique that enables three-dimensional elemental mapping. The SIMS technique, with its high detection limit and ability to obtain the profiles of elements in parallel,
is a powerful tool for monitoring trace elements in CIGS thin films. To identify impurities in a CIGS layer, the distribution of trace elements was also observed according to depth by SIMS and APT.
Effects of Doping Ratio of Cobalt and Iron on the Structure and Optical Properties of Bi3.25La0.75FexCo1–xTi2O12 (x = 0, 0.25, 0.5, 0.75, 1)
Authors: Song Myoung Geun , Han Jun Young , Bark Chung Wung
Published: September 2015

The wide band gap of complex oxides is one of the major obstacles limiting their use in photovoltaic cells. To identify an effective route for tailoring the band gap of complex oxides, this study examined the effects of cobalt and iron doping on lanthanum-modified Bi4Ti3O12-based
oxides synthesized using a solid reaction. The structural and optical properties were analyzed by X-ray diffraction and ultraviolet-visible absorption spectroscopy. As a result, the optimal iron to cobalt doping ratio in bismuth titanate powder resulted in an ∼1.8 eV decrease in the optical
band gap. This new route to reduce the optical bandgap can be adapted to the synthesis of other complex oxides.
Electrostatic Discharge Characteristics of InGaN/GaN Light-Emitting Diodes with Si-Doped Graded Superlattice
Authors: Lee Kwanjae , Lee Cheul-Ro , Kim Jin Soo , Lee Jin Hong , Lim Kee Young , Leem Jae-Young
Published: September 2015

We report the influences of a Si-doped graded superlattice (SiGSL) on the electrostatic discharge (ESD) characteristics of an InGaN/GaN light-emitting diode (LED). For comparison, a conventional InGaN/GaN LED (C-LED) was also investigated. The luminous efficacy for the SiGSL-LED was
2.68 times stronger than that for the C-LED at the injection current of 20 mA. The resistances estimated from current–voltage (I–V) characteristic curves were 16.5 and 8.8 Ω for the C-LED and SiGSL-LED, respectively. After the ESD treatment at the voltages of 4000 and
6000 V, there was no significant change in the I–V curves for the SiGSL-LED. Also, there was small variation in the I–V characteristics for the SiGSL-LED at the ESD voltage of 8000 V. However, the I–V curves for the C-LED were drastically degraded with
increasing ESD voltage. While the light emission was not observed at the injection current of 20 mA from the C-LED sample after the ESD treatment, the emission spectra for the SiGSL-LED sample were clearly measured with the output powers of 10.47, 9.66, and 7.27 mW for the ESD voltages of
4000, 6000, and 8000 V respectively.
Improved Photo-Induced Stability in Amorphous Metal-Oxide Based TFTs for Transparent Displays
Authors: Koo Sang-Mo , Ha Tae-Jun
Published: September 2015

In this paper, we investigate the origin of photo-induced instability in amorphous metal-oxide based thin-film transistors (oxide-TFTs) by exploring threshold voltage (Vth) shift in transfer characteristics. The combination of photo irradiation and prolonged gate bias
stress enhanced the shift in Vth in amorphous hafnium-indium-zinc-oxide (a-HfIZO) TFTs. Such results stem from the extended trapped charges at the localized defect states related to oxygen vacancy which play a role in a screening effect on the electric field induced by gate
voltage. We also demonstrate the chemically clean interface in oxide-TFTs by employing oxygen annealing which reduces the density of trap states, thereby resulting in improved photo-induced stability. We believe that this work stimulates the research society of transparent electronics by providing
a promising approach to suppress photo-induced instability in metal-oxide TFTs.
Effects of Chlorine Ions on the Dissolution Mechanism of Cu Thin Film in Phosphoric Acid Based Solution
Authors: Seo Bo-Hyun , Kim Byoung O. , Seo Jong Hyun
Published: September 2015

The dissolution mechanisms of Cu thin film were studied with a focus on the effect of chlorine ion concentrations in mixture solutions of phosphoric and nitric acid. The dissolution behaviors of Cu thin film were investigated by using potentio-dynamic curves and impedance spectroscopy
with varying chlorine ion concentrations. The copper dissolution rate decreased and as a result of this change, CuClx salt films formed on the Cu surface in the presence of chlorine ions in the mixture solution. Such behavior was interpreted as being competitive adsorption
between chlorine and nitrate ions on the copper surface. The passive oxide film on the Cu surface was further investigated in detail using X-ray photoelectron spectroscopy in both the absence and presence of differing chlorine ion concentrations.
Electrical and Optical Properties of Green Polymer Light Emitting Diodes with Various Structures of Au Nanoparticles
Authors: Park Byung Min , Kim Gi Ppeum , Mun Sae Chan , Chang Ho Jung
Published: September 2015

The green polymer light emitting diodes (PLEDs) were fabricated using the solution precursor synthesis method. To improve the device’s electrical and optical properties, gold (Au) nanoparticles (NPs) were added to the hole injection layer (HIL) with poly(3,4-ethylene-dioxythiophene):
poly(styrenesulfolnate) (PEDOT:PSS) organic material. The green PLED devices with a structure of glass/ITO/PEDOT:PSS+Au NPs/PVK:Ir(ppy)3/TPBi/LiF/Al were prepared by conventional spin-coating and thermal evaporation methods. Various concentrations of Au NPs were doped to the HILs
to optimize the device’s light emitting characteristic. The effects of Au NPs concentrations on the properties of PLEDs were investigated. The doping concentrations of Au NPs were changed ranging from 0.0 to 1.0 vol%. At the optimized Au NPs concentration of 0.5 vol%, we also studied
the effects of various film layers with and without Au NPs on the properties of PLEDs. The maximum luminance and external quantum efficiency of the devices were found to be 20430 cd/m2 and 7.49%, respectively.
Synthesis and Electroluminescent Property of New Orange Iridium Compounds for Flexible White Organic Light Emitting Diodes
Authors: Lee Ho Won , Jeong Hyunjin , Kim Young Kwan , Ha Yunkyoung
Published: September 2015

Recently, white organic light-emitting diodes (OLEDs) have aroused considerable attention because they have the potential of next-generation flexible displays and white illuminated applications. White OLED applications are particularly heading to the industry but they have still many
problems both materials and manufacturing. Therefore, we proposed that the new iridium compounds of orange emitters could be demonstrated and also applied to flexible white OLEDs for verification of potential. First, we demonstrated the chemical properties of new orange iridium compounds.
Secondly, conventional two kinds of white phosphorescent OLEDs were fabricated by following devices; indium-tin oxide coated glass substrate/4,4-bis[N-(napthyl)-N-phenylamino]biphenyl/N,N- dicarbazolyl-3,5-benzene doped with blue and new iridium compounds for orange
emitting 8 wt%/1,3,5-tris[N-phenylbenzimidazole-2-yl]benzene/lithium quinolate/aluminum. In addition, we fabricated white OLEDs using these emitters to verify the potential on flexible substrate. Therefore, this work could be proposed that white light applications can be applied and
could be extended to additional research on flexible applications.
Synthesis and Luminescent Properties of Gd2MoO6:Eu3+
Authors: Kwon Sook Hyun , Moon Byung Kee , Jeong Jung Hyun , Yang Hyun Kyoung , Kim Jung Hwan
Published: September 2015

A series of 6 mol% Eu3+ doped Gd2MoO6 samples were prepared by using the sol–gel method. The X-ray diffraction patterns of the samples confirmed their monoclinic structure after they were annealed at 1300 °C, and a scanning electron microscope
image revealed closely packed particles. The excitation spectra showed that the intensity of the excitation band decreased and the charge transfer band shifted from 370 to 350 nm with decreasing sintering temperature. The emission spectra are dominated by the hypersensitive forced electron
dipolar transition 5D0 → 7F2 at 612 nm. The as synthesized phosphor can be used as a red phosphor in white light emitting diodes.
The Electrochemical Behavior of Mo–Ta Alloy in Phosphoric Acid Solution for TFT-LCD Application
Authors: Lee Sang-Hyuk , Kim Byoung O. , Seo Jong Hyun
Published: September 2015

Molybdenum–tantalum alloy thin film is a suitable material for the higher corrosion resistance and low resistivity for gate and data metal lines. In this study, Mo–Ta alloy thin films were prepared by using a DC magnetron co-sputtering system on a glass substrate. An abrupt
increase in the etching rates of low Mo–Ta alloys was observed. From the observed impedance analysis, the defect densities in the MoTa oxide films increased from 5.4×1021 (cm−3) to 8.02×1021 (cm−3) up to the 6 at% of
tantalum level; and above the 6 at% of tantalum level, the defect densities decreased. This electrochemical behavior is explained by the mechanical instability of the MoTa oxide film.
Fabrication of a Dopamine Sensor Based on Carboxyl Quantum Dots
Authors: Zhao Fei , Kim Jongsung
Published: September 2015

A quantum dot (QD)-based optical biosensor was developed to detect the activity of dopamine (DA) via the quenching of QD fluorescence intensity. In this study, we examined the fluorescence quenching of DA-conjugated quantum dots (DA@QDs) at various solution pH values. The fluorescence
intensity of the QDs is quenched by electronic energy transfer from the QDs to the o-quinone group of dopamine oxide. The degree of fluorescence quenching was dependent on DA concentration. The influence of the external environment pH factor on fluorescence quenching was investigated.
The results showed that the degree of fluorescence quenching of DA@QDs was highest in a slightly alkaline solution-pH of approximately 9. Fluorescence enhancement with increased pH appears to be due to electronic energy transfer, which is related to an increased degree of dopamine-o-quinone
oxidation. The fluorescence quenching of QDs by DA is of considerable interest due to its potential for the direct detection of the DA in vivo via a simple procedure with a very low limit of detection.
Stimulated Osteogenic Differentiation of Human Mesenchymal Stem Cells by Reduced Graphene Oxide
Authors: Jin Linhua , Lee Jong Ho , Jin Oh Seong , Shin Yong Cheol , Kim Min Jeong , Hong Suck Won , Lee Mi Hee , Park Jong-Chul , Han Dong-Wook
Published: September 2015

Osteoprogenitor cells play a significant role in the growth or repair of bones, and have great potential as cell sources for regenerative medicine and bone tissue engineering, but control of their specific differentiation into bone cells remains a challenge. Graphene-based nanomaterials
are attractive candidates for biomedical applications as substrates for stem cell (SC) differentiation, scaffolds in tissue engineering, and components of implant devices owing to their biocompatible, transferable and implantable properties. This study examined the enhanced osteogenic differentiation
of human mesenchymal stem cells (hMSCs) by reduced graphene oxide (rGO) nanoparticles (NPs), and rGO NPs was prepared by reducing graphene oxide (GO) with a hydrazine treatment followed by annealing in argon and hydrogen. The cytotoxicity profile of each particle was examined using a water-soluble
tetrazolium-8 (WST-8) assay. At different time-points, a WST-8 assay, alkaline phosphatase (ALP) activity assay and alizarin red S (ARS) staining were used to determine the effects of rGO NPs on proliferation, differentiation and mineralization, respectively. The results suggest that graphene-based
materials have potential as a platform for stem cells culture and biomedicalapplications.
Fabrication and Characterization of Graphene-Based Electrochemical Sensors for Glucose Measurement
Authors: Park Minjeong , Choi Hyonkwang , Park Yunjae , Lee Wookyoung , Lee Jewon , Jeon Minhyon
Published: September 2015

Glucose in the blood is generally measured by electrochemical method using glucose oxidase (GOx) which acts as enzymes and reduced graphene oxide (rGO) composite. The rGO, which has low dispersibility, reduces the sensing capability of sensors. In order to solve this problem, the rGO
electrodes with the addition of polyvinylpyrrolidone (PVP) have been reported. However, rGO with low electrical conductivity and mobility is not compatible to the electrochemical system. In this study, graphene with excellent electrical properties was added to PVP protected rGO. The rGO was
synthesized using a Hummer and Offeman's method. Graphene was synthesized using chemical vapor deposition (CVD) with a Cu catalyst. Platinum (Pt) electrodes, Ag/AgCl, and PVP protected rGO were used as working electrode, reference electrode, and counter electrode, respectively. Surface morphology
and structural properties of graphene were analyzed using atomic force microscopy (AFM), Raman spectroscopy, and Fourier transform infrared spectroscopy (FT-IR). Cyclic voltametry (CV) and I-V probe station were used to analyze the performance of the electrodes. Glucose concentration
was systematically varied and the reduction current was monitored using I-V probe station.
Synthesis and Properties of Cellulose-Functionalized POSS-SiO2/TiO2 Hybrid Composites
Authors: Hong Gwang-Wook , Ramesh Sivalingam , Kim Joo-Hyung , Kim Hyeon-Ju , Lee Ho-Saeng
Published: September 2015

The mechanical, thermal, optical, electrical and morphological properties of cellulose, an excellent natural biomaterial, can be improved by organic-inorganic hybrid composite methods. Based on the pristine properties of cellulose, the preparation of cellulose-metal oxide hybrid nanocomposites
using a dispersion process of nanoparticles into the cellulose host matrix by traditionalmethods, has limitations. Recently, the functionalized cellulose-polymer-basedmaterials were considered to be an important class of high-performance materials, providing the synthesis of various functional
hybrid nanocomposites using a sol-gel method. Transparent cellulose-POSS-amine-silica/titania hybrids were prepared by an in-situ sol-gel process in the presence of γ-aminopropyltrimethoxylsilane (γ-APTES). The methodology involves the formation of covalent
bonding between the cellulose- POSS amine and SiO2/TiO2 hybrid nanocomposite material. An analysis of the synthesized hybrid material by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, differential thermal calorimetry, scanning
electron microscopy, and transmission electron microscopy indicated that the silica/titania nanoparticles were bonded covalently and dispersed uniformly into the cellulose-POSS amine matrix. In addition, biological properties of the cellulose-POSSsilica/titania hybrid material were examined
using an antimicrobial test against pathogenic bacteria, such as Bacillus cereus (F481072) and E.coli (ATCC35150) for the bacterial effect.
Production of Light Olefins Through Catalytic Cracking of C5 Raffinate Over Surface-Modified ZSM-5 Catalyst
Authors: Lee Joongwon , Park Seungwon , Hong Ung Gi , Jun Jin Oh , Song In Kyu
Published: September 2015

Surface modification of phosphorous-containing porous ZSM-5 catalyst (P/C-ZSM5-Sil.(X)) was carried out by a chemical liquid deposition (CLD) method using tetraethyl orthosilicate (TEOS) as a silylation agent. Different amount of TEOS (X = 5, 10, 20, and 30 wt%) was introduced
into P/C-ZSM5il.(X) catalysts for surface modification. The catalysts were used for the production of light olefins (ethylene and propylene) through catalytic cracking of C5 raffinate. It was found that external surface acidity of P/C-ZSM5-Sil.(X) catalysts significantly
decreased with increasing TEOS content. In the catalytic reaction, both conversion of C5 raffinate and yield for light olefins showed volcano-shaped curves with respect to TEOS content. Among the catalysts tested, P/C-ZSM5- Sil.(20) catalyst exhibited the best catalytic performance
in terms of conversion of C5 raffinate and yield for light olefins. Thus, an optimal TEOS content was required for CLD treatment to maximize light olefin production in the catalytic cracking of C5 raffinate over P/C-ZSM5-Sil.(X) catalysts.
Direct Dehydrogenation of n-Butane Over Pt/Sn/Zn/γ-Al2O3 Nano-Catalyst: Effect of Zn Content
Authors: Seo Hyun , Lee Jong Kwon , Hong Ung Gi , Park Gle , Yoo Yeonshick , Lee Jinsuk , Chang Hosik , Song In Kyu
Published: September 2015

A series of Pt/Sn/XZn/γ-Al2O3 nano-catalysts with different Zn content (X = 0, 0.25, 0.5, 0.75, and 1.0 wt%) were prepared by a sequential impregnation method. They were applied to the direct dehydrogenation of n-butane to n-butene
and 1,3-butadiene. The effect of zinc content of Pt/Sn/XZn/γ-Al2O3 nano-catalysts on their physicochemical properties and catalytic activities in the direct dehydrogenation of n-butane was investigated. The catalytic performance of Pt/Sn/XZn/γ-Al2O3
nano-catalysts strongly depended on zinc content. Among the catalysts tested, Pt/Sn/0.5Zn/γ-Al2O3 nano-catalyst showed the best catalytic performance in terms of yield for total dehydrogenation products (TDP, n-butene and 1,3-butadiene). TPR (temperature-programmed
reduction) and H2-chemisorption experiments were carried out to measure metal-support interaction and Pt surface area of the catalysts. Experimental results revealed that metal-support interaction and Pt surface area of the catalysts were closely related to the catalytic performance.
Yield for TDP increased with increasing metal-support interaction and Pt surface area of the catalysts.
Fabrication and Electrical Characteristics of Graphite/Carbon Nanotube/Polyvinyl Butyral Composite Film via Tape-Casting and Heat-Treatment
Authors: Kim Min-Young , Choi Seung-Woo , Boo Seong Jae , Lee Jong-Ho , Noh Hee Sook , Kim Ho-Sung
Published: September 2015

Composite stacking films, which can be applied as the bipolar plates of redox flow batteries, were fabricated via a tape-casting process that used slurry of graphite, CNT, and resin materials. The slurry was made of 25~45 wt% conductive filler (graphite, CNT) and 55~75 wt% polyvinyl
butyral (PVB) binder solution (binder, dispersant, plasticizer, and solvent). The sheet thickness of the composite films was controlled to 70~150 μm, and composite films of about 1 mm in thickness were also fabricated by stacking and laminating the sheet film, including the conductive
filler of above 85 wt%. The effects of the shape and physical properties of the graphite were investigated with regard to the dispersion behavior and flow of the slurry on the carrier film of the tape-casting device. As a result, the acicular graphite showed a good dispersion property with
the resin of the PVB binder, as compared to spherical graphite. The composite film with acicular graphite showed a lower resistivity than that of a film with spherical graphite. Furthermore, the effects of adding a small amount of CNT and the heat-treatment to the composite stacking film were
also studied. Finally, the composite film showed an electrical characteristic of below 50 mΩ·cm and a high bending strength of above 20 MPa.
Synthesis of Dimethyl Carbonate from Ethylene Carbonate and Methanol Over Nano-Catalysts Supported on CeO2–MgO
Authors: Jun Jin Oh , Lee Joongwon , Kang Ki Hyuk , Song In Kyu
Published: September 2015

A series of CeO2(X)–MgO(1−X) (X = 0, 0.25, 0.5, 0.75, and 1.0) nano-catalysts were prepared by a co-precipitation method for use in the synthesis of dimethyl carbonate from ethylene carbonate and methanol. Among the CeO2(X)–MgO(1−X)
catalysts, CeO2(0.25)–MgO(0.75) nano-catalyst showed the best catalytic performance. Alkali and alkaline earth metal oxides (MO = Li2O, K2O, Cs2O, SrO, and BaO) were then supported on CeO2(0.25)–MgO(0.75) by an incipient wetness
impregnation method with an aim of improving the catalytic performance of CeO2(0.25)–MgO(0.75). Basicity of the catalysts was determined by CO2-TPD experiments in order to elucidate the effect of basicity on the catalytic performance. The correlation between catalytic
performance and basicity showed that basicity played an important role in the reaction. Yield for dimethyl carbonate increased with increasing basicity of the catalysts. Among the catalysts tested, Li2O/CeO2(0.25)–MgO(0.75) nano-catalyst with the largest basicity
showed the best catalytic performance in the synthesis of dimethyl carbonate.
Application of Si and SiO2 Etching Mechanisms in CF4/C4F8/Ar Inductively Coupled Plasmas for Nanoscale Patterns
Authors: Lee Junmyung , Efremov Alexander , Yeom Geun Young , Lim Nomin , Kwon Kwang-Ho
Published: September 2015

An investigation of the etching characteristics and mechanism for both Si and SiO2 in CF4/C4F8/Ar inductively coupled plasmas under a constant gas pressure (4 mTorr), total gas flow rate (40 sccm), input power (800 W), and bias power (150
W) was performed. It was found that the variations in the CF4/C4F8 mixing ratio in the range of 0–50% at a constant Ar fraction of 50% resulted in slightly non-monotonic Si and SiO2 etching rates in CF4-rich plasmas and greatly decreasing
etching rates in C4F8-rich plasmas. The zero-dimensional plasma model, Langmuir probe diagnostics, and optical emission spectroscopy provided information regarding the formation-decay kinetics for the plasma active species, along with their densities and fluxes. The model-based
analysis of the etching kinetics indicated that the non-monotonic etching rates were caused not by the similar behavior of the fluorine atom density but rather by the opposite changes of the fluorine atom flux and ion energy flux. It was also determined that the great decrease in both the
Si and SiO2 etching rates during the transition from the CF4/Ar to C4F8/Ar gas system was due to the deposition of the fluorocarbon polymer film.
A New Anthracene Derivative Containing t-Butyl Group for Solution Process Organic Light-Emitting Diodes
Authors: Lee Jaehyun , Kim Seungho , Kim Jee-Hwan , Park Jongwook
Published: September 2015

4-(10-(3′,5′-diphenylbiphenyl-4-yl)anthracen-9-yl)-N,N-diphenylaniline [TATa] and a new anthracene derivative of 4-(2 or 3-tert-butyl-10-(3′,5′-diphenylbiphenyl-4-yl)anthracen-9-yl)-N,N-diphenylaniline [T-TATa] isomer by introduced
t-butyl group were synthesized. OLED devices of TATa and T-TATa were fabricated by solution process. Its physical properties such as optical, electrochemical, and electroluminescent properties were also investigated. Two compounds were used as emitting layer (EML) in OLED device: ITO/PEDOT
(40 nm)/synthesized materials (60 nm)/TPBi (20 nm)/LiF (1 nm)/Al (200 nm). The luminance efficiency of the synthesized compounds at 10 mA/cm2 were measured 0.85 cd/A for TATa and 1.49 cd/A for T-TATa, respectively. Moreover, the power efficiency of T-TATa is 1.08 lm/W. Its value
is almost two times higher than 0.56 lm/W of TATa. As a result, more improved efficiency was shown with the device in a compound including t-butyl group to TATa core part, when the deivces were prepared by solution process.
Synthesis and Electroluminescence Property of New Hexaphenyl Benzene Derivatives Including Emitting Core for OLED
Authors: Shin Hwangyu , Kang Hyeonmi , Kim Jong-Hyung , Wang Yun-Fan , Kim Seungho , Kay Kwang-Yol , Park Jongwook
Published: September 2015

Three new emitting compounds of 5P-2TPA, 5P-2An and 5P-2Py for OLED based on hexaphenyl benzene moiety were synthesized. Physical properties were systematically examined by the change of the substitution groups of the synthesized materials. Photoluminescence (PL) spectrum of the synthesized
materials showed maximum emitting wavelengths of about 437∼488 nm in solution state and 457∼516 nm in film state, indicating blue emission color. OLED devices were fabricated by the synthesized compounds using vacuum deposition process as an emitting layer. Device structure was ITO/2-TNATA
60 nm/NPB 15 nm/EML 35 nm/TPBi 20 nm/LiF 1 nm/Al 200 nm. External quantum efficiencies and CIE values of 5P-2TPA, 5P-2An and 5P-2Py were 3.34, 1.06 and 2.06% and (0.14, 0.12), (0.23, 0.45) and (0.24, 0.45), respectively. The three compounds exhibited thermal stablility with high Td
of 426 °C, 449 °C and 467 °C.
Improved Performance of Red Phosphorescent Organic Light Emitting Diodes Using Partial Mixed Host System
Authors: Sun Yong , Lee Ho Won , Lee Song Eun , Yang Hyung Jin , Yoo Han Kyu , Hwang Kyo Min , Kim Chan Woo , Yoon Seung Soo , Kim Young Kwan
Published: September 2015

Phosphorescent organic light-emitting diodes (PHOLEDs) have shown a heterojunction system that is a bulk heterojunctioned emitting layer (EML). In our work, we have demonstrated an improvement in efficiency with a partial mixed host system in an EML. A mixed host system, which is mixed
with a host material and an electron transporting material, was used on the red PHOLEDs. In general, the recombination zone is located at the electron transporting layer (ETL) side in typical PHOLEDs due to excessive accumulation at the interface. However, this study proposed the removal of
interfaces through the advantage of a mixed host system and a mixed layer between EML and ETL sides to increase the electron mobility of the experiments. Detailed optical and electrical analysis of these phenomena, were demonstrated.
Preparation and Characterization of Palmitoyl Grafted Cellulose Nano Absorbent for the Efficient Adsorption of Pyrene from Aqueous Solution
Authors: Jadhav Arvind H. , Mai Xuan Thang , Appiah-Ntiamoah Richard , Lee Hanyeong , Momade Francis W. Y. , Seo Jeong Gil , Kim Hern
Published: September 2015

Palmitoyl grafted modified cellulose were prepared by simple chemical grafting method and applied as nano adsorbent for removal of pyrene from aqueous solution. The chemical properties and morphology of prepared nano-adsorbent were characterized by FT-IR, XRD, SEM, EDX, TGA, and contact
angle. Results showed that palmitoyl successfully grafted on the surface of cellulose and possess effective organic functional groups for the adsorption of pyrene from aqueous solution. The adsorption performance of modified cellulose was significantly improved toward pyrene in aqueous solution.
It is worthy to note that 0.25 g of palmitoyl grafted cellulose (PMC) removed 92% pyrene compared to unmodified cellulose which adsorbed 36% pyrene from 1.65 ppm aqueous solution of pyrene in very short contact time at room temperature. Results showed that, presence of various organic functional
groups from palmitoyl chains grafted on cellulose backbone affected to pyrene removal. After completion of adsorption phenomenon nano-adsorbent can be removed by simply filtration process and reused several times. The adsorption capacity was studied under different experimental conditions
and their effects on adsorption such as temperature, pH, and contact time were also studied. The kinetics and isotherms of material were also determined.
Preparation and Characterization of Electro-Spun Fabricated Ag–TiO2 Composite Nanofibers and Its Enhanced Photo-Catalytic Activity for the Degradation of Congo Red
Authors: Jadhav Arvind H. , Zhang Hongliang , Agyemang Frank O. , Hiremath Vishwanath , Lee Kyuyoung , Chandradass Jeyaseelan , Seo Jeong Gil , Kim Hern
Published: September 2015

Electro-spun fabricated TiO2 nanofibers were prepared by simple electro-spinning method, in subsequent step silver (Ag) was deposited using precipitation method and obtained Ag-TiO2 composite nanofibers. The properties and morphology of these prepared composite
nanofibers were characterized by XRD, SEM, EDX, and TGA. The prepared electro-spun composite nanofibers were applied as catalyst for the photodegradation of Congo-red under immited solar light in aqueous solution. Result reveals that, Ag loaded TiO2 composite nanofibers were effectively
increased photodegradation of Congo red compared with pure TiO2 nanofibers in analogous condition. As a result, 92.0% decomposition of Congo red was obtained by using 5 wt% of Ag loaded TiO2 composite nanofibers at room temperature in short reaction time using 300 W of
solar light. In addition, photodegradation of Congo red was also studied under different experimental conditions such as amount of Ag loaded in TiO2 nanofibers and contact time. Moreover, we also studied sintering effect on TiO2 nanofibers and their consequent effect
on photodegradation reaction. After completion of reaction, the nanofibers can be easily separated by filtration process and reused several times without significant loss of activity. Overall study reveals that, Ag–TiO2 composite nanofibers were strongly enhanced the surface
activity for the photo catalytic degradation of Congo red under ambient condition.
Synthesis of Ba2SiO4:Eu2+ by a Hybrid Process and Its Luminescent Properties
Authors: Park Jung Hye , Ahn Wonsik , Kim Young Jin
Published: September 2015

Ba2SiO4:Eu2+ powders were prepared using a sol–gel-combustion (hybrid) process with tetraethyl orthosilicate (TEOS) and colloidal silica (C-SiO2) as Si sources. The effects of the silicon sources and preparation conditions on phase formation
and luminescent properties were investigated. The B2S:Eu2+ powders synthesized with TEOS were composed of the irregular particles, whereas C-SiO2 was more conducive to uniform particle distribution for the Ba2SiO4:Eu2+ powders,
leading to the enhancement of the emission intensity. The photoluminescence spectra of the synthesized powders exhibited broad excitation bands spanning 250 to 450 nm, and strong green-emission bands, whose intensities and positions were heavily dependent on the concentration of Eu2+
and Sr2+ substituted for Ba2+ in Ba2SiO4.
Improving Performance of Dye-Sensitized Solar Cell by Multi-Emission Effect of Phosphors
Authors: Kim Young Moon , Kim Chang Seob , Choi Hyung Wook
Published: September 2015

Generally, the N-719 dye, used in dye-sensitized solar cells (DSSCs), only absorbs visible light in the wavelength range from 400 to 700 nm. Consequently, most of the ultraviolet and infrared rays from the sun are not utilized by this dye. However, ultraviolet and infrared rays can
be converted to visible light by upconversion luminescence. Such visible light can then be reabsorbed by the dye, allowing for a larger range of solar irradiation to be utilized in DSSCs. Phosphor (ZnGa2O4, Y2O3:Er3+), acting as a luminescence
medium, was added to the TiO2 electrode of DSSCs, and owing to the effect of upconversion, it increased their photocurrent density and efficiency. Phosphor (ZnGa2O4, Y2O3:Er3+) co-doped TiO2 electrode cells showed
better performance than phosphorfree cells. In fact, the highest efficiency observed for a DSSC containing five phosphor layers was 7.03% with a short-circuit current density (Jsc) of 15.62 mA/cm2, an open circuit voltage (Voc) of 0.661 V, and
a fill factor (FF) of 68.17%.
Effect of Cu Alloying on S Poisoning of Ni Surfaces and Nanoparticle Morphologies Using Ab-Initio Thermodynamics Calculations
Authors: Kim Ji-Su , Kim Byung-Kook , Kim Yeong-Cheol
Published: September 2015

We investigated the effect of Cu alloying on S poisoning of Ni surfaces and nanoparticle morphologies using ab-initio thermodynamics calculations. Based on the Cu segregation energy and the S adsorption energy, the surface energy and nanoparticle morphology of pure Ni, pure Cu, and
NiCu alloys were evaluated as functions of the chemical potential of S and the surface orientations of (100), (110), and (111). The constructed nanoparticle morphology was varied as a function of chemical potential of S. We find that the Cu added to Ni for NiCu alloys is strongly segregated
into the top surface, and increases the S tolerance of the NiCu nanoparticles.
Effect of Inductively Coupled Plasma on the Structural and Electrical Properties of Ti-Doped ITO Films Formed by IPVD
Authors: Hong Chan-Hwa , Shin Jae-Heon , Park Nae-Man , Kim Kyung-Hyun , Kim Bo-Sul , Song Chang-Woo , Yang Ji-Woong , Seo Woo-Hyung , Ju Byeong-Kwon , Cheong Woo-Seok
Published: September 2015

In this study, we investigated Ti-doped ITO films formed through ionized physical vapor deposition (IPVD) using inductively coupled plasma (ICP). Ti-doped ITO thin films showed an enhanced mobility with ICP power; owing to the improved crystallinity, and the sheet resistance of the
Ti-doped ITO (30 nm) largely decreased from 295.1 to 134.5 ohm/sq, even during at room temperature. Therefore, IPVD technology offers a useful tool for transparent electrodes with a large area window-unified touch-screen panel.
Effect of the Addition of CeO2 to Iron Phosphate Glass for Catalytic Applications
Authors: Chung Jae-Yeop , Kim Jong-Hwan , Choi Su-Yeon , Ryu Bong-Ki
Published: September 2015

We investigated the effect of CeO2 content on the catalytic behavior and chemical properties of the (100?x)(80P2O5–20Fe2O3)–xCeO2 (x = 0, 4, 8, 12, 16, 20 and 24 wt%) glass system. Using thermogravimetric
analysis, we confirmed that the catalytic activity increased until a CeO2 content of 16 wt%, beyond which, it decreased. The reasons for the change in the catalytic properties of the glass samples were determined using Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron
spectroscopy (XPS), and density analyses. It was confirmed using the FT-IR and XPS-O1s spectra that CeO2 acts as a network modifier in iron phosphate glass. When the CeO2 content is above 16 wt%, the number of non-bridging oxygen atoms decreases with increasing CeO2
content. For these reasons, the catalytic properties decrease when the CeO2 content is more than16 wt%. From the dissolution rate measurements, it can be observed that cerium-iron phosphate has a high water resistance. Also, as we expected, it can be confirmed that the chemical
durability is improved with increasing CeO2 content.