bluuebunny/crossref_metadata_2025 huggingface dataset:
Protective effects of polyphenolic compounds on oxidative stress-induced cytotoxicity in PC12 cells
Authors: Crispo James A.G. , Ansell Dominique R. , Piche Matthew , Eibl Joseph K. , Khaper Neelam , Ross Gregory M. , Tai T.C.
Published: May 2010

To investigate the beneficial properties associated with polyphenols, we screened 12 polyphenols for their ability to increase the viability of PC12 cells subjected to oxidative stress via CoCl2 and H2O2. Cell viability data demonstrate that 50 µmol/L methyl gallate and 50 µmol/L fisetin significantly increase viability of H2O2-stressed cells. Further, viability data suggest that 100 µmol/L epigallocatechin gallate (EGCG) increases basal viability, but has no rescue effect on cells stressed with CoCl2 or H2O2. Analysis of intracellular reactive oxygen species (ROS) shows that EGCG, methyl gallate, and gallic acid are effective in reducing CoCl2-derived ROS, and that methyl gallate is effective in attenuating H2O2-derived ROS. Examination of nitric oxide concentrations shows that methyl gallate significantly increases nitric oxide, both in nonstressed and H2O2-stressed cells, whereas EGCG results are consistent with the scavenging of nitric oxide under nonstressed and stressed conditions. Furthermore, analysis of total glutathione levels reveals that EGCG, methyl gallate, and gallic acid pretreatments with and without H2O2 stress have the ability to significantly alter glutathione metabolism. These findings suggest that EGCG, methyl gallate, and gallic acid may have potential therapeutic properties.
Water-soluble compounds in the herbal preparation Abana inhibit lipid biosynthesis and enhance cholesterol efflux in HepG2cells
Authors: Vidyashankar Satyakumar , Godavarthi Ashok , Varma R. Sandeep , Nandakumar Krishna S.
Published: May 2010

Higher concentrations of circulating lipids (cholesterol and triglycerides) and their decreased catabolism pose a major risk in the development of atherosclerosis and coronary heart disease (CHD). Although statins are widely used for treatment of hyperlipidemia, side effects associated with their use have prompted the search for a safer alternative for treating hyperlipidemia. The present study investigated the effect of water-soluble compounds in Abana (WSCA), a polyherbal drug formulation traditionally used in India for the treatment of hyperlipidemia, on lipid metabolism in HepG2cells. WSCA reduced cholesterol and triglyceride content in the cells and their supernatant. WSCA inhibited the incorporation of [2-14C]acetate into cellular cholesterol and fatty acids, suggesting the inhibition of lipid synthesis. In addition, WSCA inhibited HMG-CoA reductase, a key metabolic enzyme involved in the biosynthesis of cholesterol. WSCA also increased cholesterol and fatty acid secretion into the cell supernatant, suggesting the enhanced removal of cholesterol and fatty acids. Furthermore, WSCA showed decreased linoleic acid (18:2) and arachidonic acid (20:4) content in HepG2cells. The present study is the first to show that WSCA simultaneously inhibited cellular cholesterol biosynthesis and increased cholesterol secretion into the cell supernatant in HepG2cells.
PRESCRIBING MEAN CURVATURE ON 𝔹n
Authors: ABDELHEDI WAEL , CHTIOUI HICHEM
Published: May 2010

In this paper, we consider the problem of multiplicity of conformal metrics that are equivalent to the Euclidean metric, with zero scalar curvature and prescribed mean curvature on the boundary of the ball 𝔹n, n ≥ 4. Under the assumption that the order of flatness at critical points of the prescribed mean curvature function H(x) is β∈(n-2, n-1), we establish some Morse inequalities at infinity, which give a lower bound on the number of solutions to the above problem, in terms of the total contribution of its critical points at infinity to the difference of topology between the level sets of the associated Euler–Lagrange functional. As a by-product of our arguments, we derive a new existence result through an Euler–Hopf type formula.
MINIMALITY, HARMONICITY AND CR GEOMETRY FOR REEB VECTOR FIELDS
Authors: PERRONE DOMENICO
Published: May 2010

Let (M, g) be a Riemannian manifold and T1 M its unit tangent sphere bundle. Minimality and harmonicity of unit vector fields have been extensively studied by considering on T1M the Sasaki metric [Formula: see text]. This metric, and other well-known Riemannian metrics on T1 M, are particular examples of Riemannian natural metrics. In this paper we equip T1 M with a Riemannian natural metric [Formula: see text] and in particular with a natural contact metric structure. Then, we study the minimality for Reeb vector fields of contact metric manifolds and of quasi-umbilical hypersurfaces of a Kähler manifold. Several explicit examples are given. In particular, the Reeb vector field ξ of a K-contact manifold is minimal for any [Formula: see text] that belongs to a family depending on two parameters of metrics of the Kaluza–Klein type. Next, we show that the Reeb vector field ξ of a K-contact manifold defines a harmonic map [Formula: see text] for any Riemannian natural metric [Formula: see text]. Besides this, if the Reeb vector ξ of an almost contact metric manifold is a CR map then the induced almost CR structure on M is strictly pseudoconvex and ξ is a pseudo-Hermitian map; if in addition ξ is geodesic then [Formula: see text] is a harmonic map. Moreover, the Reeb vector field ξ of a contact metric manifold is a CR map iff ξ is Killing and [Formula: see text] is a special metric of the Kaluza–Klein type. Finally, in the final section, we obtain that there is a family of strictly pseudoconvex CR structures on T1S2n+1 depending on one parameter, for which a Hopf vector field ξ determines a pseudo-harmonic map (in the sense of Barletta–Dragomir–Urakawa [8]) from S2n+1 to T1S2n+1.
HOMOTOPY GROUPS OF MODULI SPACES OF STABLE QUIVER REPRESENTATIONS
Authors: WILKIN GRAEME
Published: May 2010

The purpose of this paper is to describe a method for computing homotopy groups of the space of α-stable representations of a quiver with fixed dimension vector and stability parameter α. The main result is that the homotopy groups of this space are trivial up to a certain dimension, which depends on the quiver, the choice of dimension vector, and the choice of parameter. As a corollary we also compute low dimensional homotopy groups of the moduli space of α-stable representations of the quiver with fixed dimension vector, and apply the theory to the space of non-degenerate polygons in three-dimensional Euclidean space.
DIGITAL CONTROL AS SOURCE OF CHAOTIC BEHAVIOR
Authors: CSERNÁK GÁBOR , STÉPÁN GÁBOR
Published: May 2010

In the present paper, we introduce and analyze a mechanical system, in which the digital implementation of a linear control loop may lead to chaotic behavior. The amplitude of such oscillations is usually very small, this is why these are called micro-chaotic vibrations. As a consequence of the digital effects, i.e. the sampling, the processing delay and the round-off error, the behavior of the system can be described by a piecewise linear map, the micro-chaos map. We examine a 2D version of the micro-chaos map and prove that the map is chaotic.
FROM FIRST LYAPUNOV COEFFICIENTS TO MAXIMAL CANARDS
Authors: KUEHN CHRISTIAN
Published: May 2010

Hopf bifurcations in fast–slow systems of ordinary differential equations can be associated with a surprisingly rapid growth of periodic orbits. This process is referred to as canard explosion. The key step in locating a canard explosion is to calculate the location of a special trajectory, called a maximal canard, in parameter space. A first-order asymptotic expansion of this location was found by Krupa and Szmolyan [2001a, 2001b, 2001c] in the framework of a "canard point"-normal-form for systems with one fast and one slow variable. We show how to compute the coefficients in this expansion using the first Lyapunov coefficient at the Hopf bifurcation thereby avoiding the use of this normal form. Our results connect the theory of canard explosions with existing numerical software, enabling easier calculations of where canard explosions occur.
FAST LIGHT ENHANCEMENT BY BIDIRECTIONAL PUMPING IN ERBIUM-DOPED FIBERS
Authors: EZQUERRO J. M. , HERNÁNDEZ G. , NOMBELA M. , CALDERÓN OSCAR G. , MELLE SONIA
Published: May 2010

We analyze the effect of pump configuration on the propagation velocity of an amplitude-modulated 1536 nm signal propagating through an ultra-highly doped erbium fiber amplifier. The nonlinear effects arising from the high value of the doping level lead to a strong variation of the pump power and signal gain along the fiber. We found that bidirectional pumping presents larger advancements than co-propagating and counter-propagating configurations. Numerical simulations allow us to explain the phenomenon in terms of the gain profile uniformity.
PROGRESS ON THE FABRICATION OF ON-CHIP, INTEGRATED CHALCOGENIDE GLASS (CHG)-BASED SENSORS
Authors: RICHARDSON K. , PETIT L. , CARLIE N. , ZDYRKO B. , LUZINOV I. , HU J. , AGARWAL A. , KIMERLING L. , ANDERSON T. , RICHARDSON M.
Published: May 2010

In this paper, we review ongoing progress in the development of novel on-chip, low loss planar molecular sensors that address the emerging need in the field of biochemical sensing. Chalcogenide glasses were identified as the material of choice for sensing due to their wide infrared transparency window. We report the details of manufacturing processes used to realize novel high-index-contrast, compact micro-disk resonators. Our findings demonstrate that our device can operate in dual modalities, for detection of the infrared optical absorption of a binding event using cavity enhanced spectroscopy, or sensing refractive index change due to surface molecular binding and extracting micro-structural evolution information via cavity enhanced refractometry.
INTERSUBBAND OPTICAL ABSORPTION COEFFICIENTS AND REFRACTIVE INDEX CHANGES OF AN ELLIPSOIDAL FINITE POTENTIAL QUANTUM DOT
Authors: REZAEI G. , VAHDANI M. R. K. , BARATI M.
Published: May 2010

Intersubband optical absorption coefficient and refractive index changes of a weakly prolate ellipsoidal quantum dot, using the compact-density matrix formalism and iterative method, are investigated. In this regard, the linear and nonlinear intersubband optical absorption coefficient and refractive index changes of a GaAs / Al x Ga 1-x As ellipsoidal quantum dot, as functions of the dot radius, ellipticity constant, stoichiometric ratio and incident light intensity are calculated. The results indicate that absorption coefficient and refractive index changes strongly depend on the light intensity, size and geometry of the dot and structure parameters such as aluminium concentration in GaAs / Al x Ga 1-x As structures.
SPECTRAL FEATURES OF THE ALTERNATING CLUSTER PROCESS
Authors: GRÜNEIS FERDINAND
Published: May 2010

The alternating cluster process is a Poisson process the rate of which is modulated by an underlying two-state process. We derive the power spectral density of the alternating cluster process; besides random noise we obtain excess noise due to the impact of modulation.
ANALYSIS OF LEAN MANUFACTURING FRAMEWORKS
Authors: ANAND G. , KODALI RAMBABU
Published: May 2010

In recent years, the applications of Lean Manufacturing (LM) in different types of industries are growing rapidly. Some of the organizations have reported huge benefits, while many industries have not obtained the desired results. One of the reasons for this can be attributed to improper understanding of LM by both the management and employees of an organization. Researchers worldwide have attempted to solve this issue by proposing various frameworks. A literature review on frameworks of LM revealed around 30 frameworks. A comparative analysis carried out on these frameworks has shown that these frameworks suffer from various shortcomings. Hence in this paper, an attempt has been made to propose a new conceptual framework for LM, which will resolve some of these limitations. The proposed framework utilizes 65 LM elements, which are categorized according to the decision levels and the role of internal stakeholders in an organization. According to the authors' knowledge, there is no LM framework in the literature, which is as comprehensive as the proposed one and which provides a complete integration of these elements into a coherent whole. However, the proposed framework is conceptual and needs to be validated.
THE DEVELOPMENT OF HETEROGENEOUS OBJECT DESIGN FOR RAPID PROTOTYPING
Authors: LIN RONG-SHINE , YANG Y. C. , HSU B. X.
Published: May 2010

Rapid Prototype (RP) manufacturing has been widely used in many industries, including prototype fabrication, product assembly testing, mechanism interference testing, and rapid tooling. Researchers have been focusing on the RP applications for functional part fabrication in recent years. One of the most challenging research topics in RP is Rapid Prototype fabrication, particularly with graded material objects. Graded material means that the material's composition is changed according to the area of the object. The graded material object model includes the typical part geometric information and the heterogeneous material information that forms a more complicated object model. This research developed a heterogeneous object model, which was implemented on a software program. Results show that the heterogeneous model contains material grading information as well as geometry information. Two examples are included for the material composition distribution at the end of this paper.
CLASSICAL TENSORS AND QUANTUM ENTANGLEMENT I: PURE STATES
Authors: ANIELLO P. , CLEMENTE-GALLARDO J. , MARMO G. , VOLKERT G. F.
Published: May 2010

The geometrical description of a Hilbert space associated with a quantum system considers a Hermitian tensor to describe the scalar inner product of vectors which are now described by vector fields. The real part of this tensor represents a flat Riemannian metric tensor while the imaginary part represents a symplectic two-form. The immersion of classical manifolds in the complex projective space associated with the Hilbert space allows to pull-back tensor fields related to previous ones, via the immersion map. This makes available, on these selected manifolds of states, methods of usual Riemannian and symplectic geometry. Here, we consider these pulled-back tensor fields when the immersed submanifold contains separable states or entangled states. Geometrical tensors are shown to encode some properties of these states. These results are not unrelated with criteria already available in the literature. We explicitly deal with some of these relations.
COMPOSITION ALGEBRAS AND THE TWO FACES OF G2
Authors: BOYA LUIS J. , CAMPOAMOR-STURSBERG RUTWIG
Published: May 2010

We consider composition and division algebras over the real numbers: We note two rôles for the group G2: as automorphism group of the octonions and as the isotropy group of a generic three-form in seven dimensions. We show why they are equivalent, by means of a regular metric. We express in some diagrams the relation between some pertinent groups, most of them related to the octonions. Some applications to physics are also discussed.
LOCAL TRACE FORMULAE AND SCALING ASYMPTOTICS IN TOEPLITZ QUANTIZATION
Authors: PAOLETTI ROBERTO
Published: May 2010

A trace formula for Toeplitz operators was proved by Boutet de Monvel and Guillemin in the setting of general Toeplitz structures. Here, we give a local version of this result for a class of Toeplitz operators related to continuous groups of symmetries on quantizable compact symplectic manifolds. The local trace formula involves certain scaling asymptotics along the clean fixed locus of the Hamiltonian flow of the symbol, reminiscent of the scaling asymptotics of the equivariant components of the Szegö kernel along the diagonal.
Nitrogen-Related Recombination Center in GaAsN Grown by Chemical Beam Epitaxy
Authors: Bouzazi Boussairi , Suzuki Hidetoshi , Kojima Nobuaki , Ohshita Yoshio , Yamaguchi Masafumi
Published: May 2010

A nitrogen-related deep electron trap, at approximately 0.33 eV below the conduction band minimum of GaAsN grown by chemical beam epitaxy, is confirmed to act as a recombination center. The level is found to be responsible for the reverse bias current in the depletion region of n-type GaAsN schottky junction and N+-GaAs/p-GaAsN heterojunction, where the current is due mainly to electrons. This result is obtained by correlating the thermal activation energy of the reverse bias current and the activation energy of electron traps, investigated in the two structures by deep level transient spectroscopy.
Comparison of Nanocrystalline TiO2 Films Prepared on Unheated Substrates Using Single- and Dual-Cathode DC Unbalanced Magnetron Sputtering Systems
Authors: Witit-Anun Nirun , Kasemanankul Prasertsak , Chaiyakun Surasing , Pokaipisit Artorn , Limsuwan Pichet
Published: May 2010

Titanium dioxide (TiO2) films were deposited on unheated Si(100) wafers by single- and dual-cathode dc unbalanced magnetron sputtering. Each cathode was specially designed with a high magnetic field strength. The effect of the radial distance from the center of the coating cathode on the film structures was investigated. For the substrate placed at the center of the coating cathode, it was found that the TiO2 films deposited by dual-cathode sputtering exhibit rutile with higher crystallinity than films deposited by single-cathode sputtering. At various radial distance from the center to 6 cm to the left and light of the center, mixed phases of rutile and anatase were observed on TiO2 films deposited using both single- and dual-cathode sputtering systems. Furthermore, in the case of using dual-cathode, crystalline TiO2 films were obtained for a longer range to the left of the center than to the right owing to the higher magnetic field strength.
Low Temperature Dielectric Relaxations in ZnO Varistor
Authors: Tsonos Christos , Kanapitsas Athanasios , Triantis Dimos , Anastasiadis Cimon , Stavrakas Ilias , Pissis Polycarpos
Published: May 2010

The main purpose of this work is to study the behaviour of ZnO varistor by means of dielectric relaxation spectroscopy at the low temperature range. The complex frequency spectrum of dielectric losses has been studied in detail and analysed carefully by fitting of a sum of Havriliak–Negami expression. Three relaxation processes are studied here, exhibiting a very strong Cole–Davidson behaviour. The faster relaxation process shows an unusual thermal behaviour. Initially, its relaxation time increases as the temperature rises but later it becomes thermally activated. The transition temperature of thermal behaviour of this process was found very close to the characteristic value of 0.4θD=160 K, where θD is the Debye temperature of ZnO. The de-activation energy of this process has been estimated by using the Arrhenius type relation to be 78 meV, a value very close to the higher longitudinal optical (LO) phonon energy in ZnO, 72 meV. This is a strong indication that the predicted Holstein transition between large to small-polaron motion should be observed in ZnO. The two remaining relaxations are electronic processes, the slower one is associated with the doubly ionised zinc interstitial Zni
••, while the other should be related to defects induced by the dopants, or of complexes of intrinsic native defect with dopant impurities.
Crystal Structures and Electric Properties of (1-x)BiFeO3–xBiCoO3 Thin Films Prepared by Chemical Solution Deposition
Authors: Nakamura Yoshitaka , Kawai Masanori , Azuma Masaki , Shimakawa Yuichi
Published: May 2010

The crystal structures and electric properties of epitaxial (1-x)BiFeO3–xBiCoO3 thin films with x = 0–0.30 prepared by chemical solution deposition on SrTiO3(001) and SrRuO3(001)/SrTiO3(001) substrates were investigated. The crystal structures changed from rhombohedral to tetragonal at x = 0.15–0.2. Saturated ferroelectric polarizations were observed for films with x = 0–0.10, and films with x = 0.15–0.20 did not show polarization reversal. The piezoelectric constant d
33 initially increased with increasing Co content and showed a maximum value of 80 pm/V at x = 0.05.
Diffraction Efficiency Improvement in Liquid Crystal Blazed Gratings with Spatially Distributed Hybrid Orientation Domains
Authors: Honma Michinori , Akagawa Yoshikazu , Ogasawara Masanori , Nose Toshiaki
Published: May 2010

Diffraction properties of liquid crystal (LC) blazed gratings consisting of spatially distributed hybrid orientation domains were investigated. First, the dependence of diffraction efficiency on cell parameters was clarified; wider grating periods and high blaze levels ensure higher diffraction efficiency. Next, enhancement of the diffraction efficiency of the LC blazed grating was attempted by introducing additional microrubbing patterns. The applicability of the additional pattern for eliminating the disclination was confirmed. It has been revealed that the diffraction efficiency is successfully improved by eliminating the disclination regardless of grating period. The improvement becomes significant for shorter grating periods.
Photovoltaic Properties of Bulk Heterojunction Organic Solar Cell Composed of Coumarin 6 Dye as Light Harvester and Donor Material
Authors: Ismail Yasser A. M. , Soga Tetsuo , Jimbo Takashi
Published: May 2010

The behavior and properties of coumarin 6 (C6) dye as a light harvester and, at the same time, a donor material in combination with a fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) acceptor molecule in a new bulk heterojunction (BHJ) solar cell were demonstrated for the first time. The C6:PCBM combination represented a good example of a BHJ blend containing a charge transfer complex (CTC). The formation of a BHJ by blending C6 dye as a donor with PCBM as an acceptor, therefore achieving efficient charge separation and transport throughout the C6:PCBM blend, was verified through the symbatic behavior of the corresponding solar cell. The formation of a CTC in the C6:PCBM blend was indicated from the redshift of the C6 absorption peak after blending with PCBM and verified through the variation in the redshift of the C6 peak with the variation of the C6:PCBM blend composition and, also, through Fourier transform infrared spectroscopy, which revealed additional infrared absorption peaks in the C6:PCBM blend not related to either C6 or PCBM. The formation of a CTC in the C6:PCBM BHJ solar cell assisted in improving the photocurrent and device performance parameters through ultrafast charge separation occurring within the CTC in the blend.
Switching Time Reduction for Electrostatic Torsional Micromirrors Using Input Shaping
Authors: Eun Youngkee , Jeong Bongwon , Kim Jongbaeg
Published: May 2010

We have demonstrated switching time reduction for microfabricated, vertical comb-based electrostatic torsional micromirror actuators by suppressing residual vibration using pre-shaped command inputs. The step input is pre-shaped by pulse–impulse convolution method, one of the impulse shaping filters. The micromirror actuators tested in experiment are made of single-crystal silicon and driven by vertical comb sets in torsional direction. Before shaping the input signal, the measured 2% settling time is 25 ms with percent overshoot of 58% for a step voltage input to induce the angular motion in micromirror actuator. The improved settling time is observed to be 8 ms with 5.8% overshoot when the pre-shaped input is applied. The input-shaping technique is applied to two types of microactuators with different dynamic characteristics in order to verify its feasibility on various systems, and it is experimentally shown that the pre-shaped input command successfully suppresses the residual vibration for both highly underdamped microactuators.
An Intensity Modulator for Terahertz Electromagnetic Waves Utilizing Two-Dimensional Plasmon Resonance in a Dual-Grating-Gate High-Electron-Mobility Transistor
Authors: Nishimura Takuya , Magome Nobuhiro , Otsuji Taiichi
Published: May 2010

We propose an intensity modulator utilizing two-dimensional plasmons (2DPs) in a dual-grating-gate high-electron-mobility transistor. The device primarily functions as a plasmon-resonant emitter in which the seeds ofnon-radiativelongitudinal modes of 2DPs are efficiently converted intoradiativetransverse modes of terahertz (THz) electromagnetic waves. In this work, we numerically study the behavior of the mode conversion between 2DPs and THz electromagnetic waves as a function of the 2DP dispersion. The finite difference time domain analysis demonstrates that the coupling of THz electromagnetic waves and 2DPs changes with the electron drift velocity and with the sheet electron density in 2DPs. The analysis also reveals that the intensity of transmitted waves can be modulated over a wide THz range with an extinction ratio beyond 60% by optimizing the sheet electron density and the drift velocity under nominal area-factor condition (ratio of the 2DP area over the total active channel area) up to 0.6.
Heralded Single Photon Source-Based Decoy-State Quantum Key Distribution with Dual Detectors
Authors: Feng Yu , Lee Seounghun , Kim Semin , Kim Seunghwan , Kim Kyonghon
Published: May 2010

In practical quantum key distribution (QKD) systems, the heralded single photon source (HSPS) based on parametric down-conversion (PDC) has attracted significant attentions from many researchers because its various advantages compared to the weak coherent source. We propose a heralded single photon source-based decoy-state QKD with dual detectors and demonstrate in a theoretical simulation that this method improves the performance of QKD system. The secure key generation rate is increased significantly with our proposal both in thermal and Poisson distributions of photons. The secure key rate produced by our scheme is higher than the state of the art key rate of current high-speed QKD system. The decoy-state QKD system using the heralded single photon source with dual detectors can be an important alternative for the present practical QKD systems.
Effects of Facet Orientation on Relative Stability between Zinc Blende and Wurtzite Structures in Group III–V Nanowires
Authors: Yamashita Tomoki , Akiyama Toru , Nakamura Kohji , Ito Tomonori
Published: May 2010

The relative stability between the wurtzite and zinc blende structures in InP, GaP, and GaAs nanowires with {111}/{1100} facets and those with {110}/{1120} facets is systematically investigated using our empirical interatomic potential calculations in conjunction with first-principles calculations. Moreover, we discuss chemical trends in the structural stability of InP, GaP, and GaAs nanowires. Our calculations clarify that the wurtzite structure is stabilized over the entire diameter range for nanowires with {111}/{1100} facets. In contrast, for nanowires consisting of {110}/{1120} facets, the crystal structure of nanowires depends on the nanowire diameter and the ionicity of semiconductors. This is because the surface energy difference between the {111} and {1100} surfaces is large compared with that between the {110} and {1120} surfaces. The calculated results imply that the stability of nanowire side facets is an important factor determining the crystal structure.
Structure and Expansion Characteristics of Laser Ablation Tin Plasma into a Vacuum
Authors: Zhu Qiushi , Yamada Junzaburo , Kishi Nozomu , Hosokai Tomonao , Watanabe Masato , Okino Akitoshi , Horioka Kazuhiko , Hotta Eiki
Published: May 2010

The internal structure and expansion characteristics of a laser ablation tin plasma into a vacuum have been investigated. A Q-switched Nd:YAG laser with the power density of 1011 W/cm2 at the focal spot on the tin bulk target was employed to create the ablation plasma. The ion velocity distribution calculated from the time-of-flight measurements displays a multimodal structure; shifted-Maxwell–Boltzmann fitting indicates ions with multiple charge states exist in the ablation plume, and the temperature of the Knudsen layer was estimated to be ∼4.0×105 and ∼8.3×105 K for the laser energy of 77 and 129 mJ, respectively. Particle acceleration mechanisms were discussed according to the time resolved, two-dimensional images of the Sn I and Sn II plasma plume. The unstable adiabatic expansion with the formation of Knudsen layer was found dominates the expansion behavior of Sn I, and the Knudsen layer temperature was calculated to be 6.68×105 K according to the front edge velocity of the Sn I plume.
Optical Investigation of Deep Ultraviolet Degradation of Pellicles
Authors: Cheon Hyuknyeong , Choi Hyungseok , Oh Hye-Keun , An Ilsin
Published: May 2010

As optical lithography goes deep into the ultraviolet (UV) range for higher resolution, high-energy photons cause many problems that are associated with the photomask (PM). Upon repeated deep-UV exposure, unwanted crystals or layers can form on the PM surface following the photoreaction of surrounding contaminants. Moreover, the pellicle that is a part of the PM can react with deep UV, although it is designed to show high transparency and radiation durability. Our pellicle showed an initial reduction in thickness and then an increase in absorption after extended exposure to the 193 nm line of an ArF excimer laser. Both phenomena were responsible for the transmission loss of a pellicle. Particularly, the transmission loss caused by the thickness reduction was related to the interference effect. Lithography simulation showed that the reduced transmission by the pellicle led to the critical dimension variation. Moreover, a non-uniform reduction of thickness near the edge of the exposed area suggested that the apodization effect might occur near the edge of patterns.
Synthesis of Copper Nano-Ink in Alcohol Media
Authors: Kim Nam-Soo , Hwang Se-Yeon , Kim Eun-Young , Han Kenneth N.
Published: May 2010

Copper nano-ink has been synthesized in various kinds of alcohol with carbon chain of 1 through 5 using a direct reduction by hydrazine. The solubility of copper nitrate was best with methanol and decreased dramatically when the chain length increased. The nano-ink prepared using copper in alcohol was then compared with those prepared in distilled water under the same conditions. The results have shown that methanol is a better medium than water in that oxidation of copper in alcohol was minimized and the size of nano-particles was much smaller than those prepared in water under similar conditions.
Dye-Doped Polymer Dispersed Liquid Crystal Films for Flexible Displays
Authors: Yang Kee-Jeong , Lee Seung-Chul , Choi Byeong-Dae
Published: May 2010

Red, green, and blue dyes were doped to polymer dispersed liquid crystal (PDLC) films for flexible display applications. Dichroic dye-doped liquid crystal droplets had a bipolar configuration. The E7–DG6071–dye composition showed better chromaticity data than other compositions. The small-particle-size red-dye-doped PDLC film showed good color differences. To improve the color difference, the dye particle size has to be small, and the bead milling process can make dye particles small. In this system, the bigger the liquid crystal droplet size, the higher the PDLC film driving voltage (V
on), except in the LC–DG6071–red dye composition. This is the reason that the splay deformation increase is greater than the droplet size increase. In the electro-optic characteristics of dye-doped PDLC film, the TL205–DG6071–red dye composition had the lowest V
on and the TL205–DG7052–red dye had the highest contrast ratio.
Improvements of Indium Tin Oxide Film Deposited on Poly(ethylene terephthalate) Substrates by Plasma-Polymerized Hydrogenated Silicon–Carbon–Oxide Buffer Layer
Authors: Lan Yin Feng , Chang Hui Rou , He Ju Liang
Published: May 2010

A plasma-polymerized hydrogenated silicon–carbon–oxide (Si–C–O:H) buffer layer was interlaid for improving durability of indium tin oxide (ITO) films on poly(ethylene terephthalate) (PET) substrates. It was demonstrated that this buffer layer efficiently improves the durability of specimens under static and dynamic mechanical bending. Experimental results show that the Si–C–O:H buffer layer only negligibly affects the optical transmission and electrical resistivity of coated specimens. The static bending test revealed that the critical radius of curvature (R
c) is 16.0 mm while it is 22.1 mm for the ITO-coated PET with and without buffer layer. The dynamic bending test at curvature radius of 17.7 mm showed that the ITO-coated PET specimen with buffer layer can tolerate more than 2000 cycles, whereas it is less than 200 cycles without buffer layer. The Si–C–O:H buffer layer can significantly reduce the stress in ITO films during bending and therefore improve the bending durability of ITO films.
Synthesis of Binary Complex Colloidal Particles by Using Polyelectrolyte Multilayer-Coated Particles as Templates
Authors: Koo Hye Young , Lee Ha-Jin , Kim Jun Kyung , Choi Won San
Published: May 2010

We report a feasible fabrication of binary complex particles based on polyelectrolyte multilayer-coated particles (PEMPs). Binary complex particles were synthesized by combination of large organic and small inorganic nanoparticles. The PEMPs were prepared by alternating adsorption of two kinds of polyelectrolytes with opposite charges onto colloidal particles. In this structure, polyelectrolytes act as a matrix to bind precursor for metal nanoparticles. Following reduction and hydrolysis of the PEMPs could generate bimetallic complexes onto PEMPs. We found that size and composition of the bimetallic complexes depend on the amount of gold precursor added to the suspension of the PEMPs.
Assembly of Acircular SnO2 Rod Using Optical Tweezers and Laser Curing of Metal Nanoparticles
Authors: Nam Chanhyuk , Hong Daehie , Chung Jaeik , Chung Jaewon , Hwang Insung , Lee Jongheun , Ko Seunghwan , Grigoropoulos Costas P.
Published: May 2010

Acicular tin dioxide (SnO2) rods (1–2 µm in diameter, 5–20 µm long) were assembled and fused on the patterned gold electrode by an optical tweezer. In addition, the electrical contact between the assembled SnO2 rod and the gold electrode was improved by laser curing of gold nanoparticles and the subsequent sintering in the oven. Here, the nanoparticles covered the entire area of the assembled SnO2 rod by evaporating a droplet of nanoparticle solution dripped on the assembled SnO2 rod. Subsequently, nanoparticles near the contact area between the rod and electrode were locally cured by direct heating with a focused infrared laser beam, which induced desorption of the surface monolayer. Therefore, the cured gold nanoparticles could be sintered after the non-laser irradiated nanoparticles were cleaned by the initial solvent application. Without sintering of the nanoparticles, the resistance of the assembled SnO2 rod was measured over several MΩ. After the nanoparticle sintering it could be reduced to a few hundred kΩ, which was in agreement with the resistance of the assembled SnO2 rod.
Characteristics of Silicon Oxynitride Barrier Films Grown on Poly(ethylene naphthalate) by Ion-Beam-Assisted Deposition
Authors: Lee Do Kyung , Shin Han Jae , Sohn Sang Ho
Published: May 2010

For the application of transparent barriers to water vapor permeation for plastic substrates, we have prepared silicon oxynitride thin films on a poly(ethylene naphthalate) substrate at room temperature by the ion-beam-assisted electron beam evaporation method and investigated their characteristics with respect to N2 flow rate in the ion source. The experimental results reveal that when N2 flow rate increases, the nitrogen concentration and Si–N bonding in SiO
x
N
y
films increase owing to the assisted N2 ion incorporations during the film deposition process. Also, with increasing N2 flow rate, the surface roughness and optical transmittance of the barrier film decrease, whereas refractive index and film density increase. It is confirmed that the water vapor transmission rate of our barrier films decreases with the incorporation of N2 ions into the films, being strongly dependent on surface roughness and film density.
Stretchable Low Resistance Thick Silver Electrode on Poly(dimethylsiloxane) Compliant Elastomeric Substrate
Authors: Jeong Jaewook , Kim Sangwoo , Cho Junhee , Kim Donghyun , Hong Yongtaek
Published: May 2010

In this paper, we demonstrated a stretchable, low resistive thick silver electrode directly deposited on a roughened poly(dimethylsiloxane) (PDMS) substrate and analyzed its surface crack evolution under the tensile stress. Improvement in the stretching property of the electrode was explained by analyzing changes in the stress distribution when the surface roughness is introduced on the PDMS substrate. It was found that the roughened surface plays two important roles of releasing the film stress of the thick electrode during the relatively long deposition process and uniformly distributing the highly stressed spots in the electrode, which can be easily damaged under the tensile strain.
Influence of Electrode Position and Electrostatic Forces on the Generation of Meniscus in Dielectric Ink
Authors: Rahman Ahsan , Ali Adnan , Rahman Khalid , Kim Hyung-Chan , Doh Yang-Hoi , Kim Dong-Soo , Choi Kyung-Hyun
Published: May 2010

This paper analyzes and reports the influence of electrodes positioning on dielectric ink for the formation of stable meniscus in the electrostatic inkjet head, experimentally. To introduce the electrostatic inkjet head for the fabrication of different printed devices, it is important to know the best position of electrode in the inkjet head for the optimal electrification of the ink. The paper also examines electrode position and electrically driven liquid handling operations. From experiments, it has been deduced that the head performs best when the electrode position is at orifice in dielectric ink. For better understanding and evaluation of this phenomenon, simulations were also performed. The finite element model of the head with dielectric fluid has been developed to analyze the behavior under electric field. And to optimize the analysis, the research is also supported by the statistical techniques. Furthermore, the meniscus shape and response on applied voltage is studied and analyzed. Paper also elaborates and addresses issues like the meniscus generation using dielectric ink and ejections at low voltage with stability problems.
Nanoparticle Selective Laser Processing for a Flexible Display Fabrication
Authors: Ko Seung Hwan , Pan Heng , Lee Daeho , Grigoropoulos Costas P. , Park Hee K.
Published: May 2010

To demonstrate a first step for a novel fabrication method of a flexible display, nanomaterial based laser processing schemes to demonstrate organic light emitting diode (OLED) pixel transfer and organic field effect transistor (OFET) fabrication on a polymer substrate without using any conventional vacuum or photolithography processes were developed. The unique properties of nanomaterials allow laser induced forward transfer of organic light emitting material at low laser energy while maintaining good fluorescence and also allow high resolution transistor electrode patterning at plastic compatible low temperature. These novel processes enable an environmentally friendly and cost effective process as well as a low temperature manufacturing sequence to realize inexpensive, large area, flexible electronics on polymer substrates.
Influence of Ball Spacer Size and Density on Liquid Crystal Margin of In-Plane Switching Panel Fabricated by the Inkjet Process
Authors: Cho Hang Sup , Kwon Dhang , Lee Myoung Ho , Kang Dong Woo , Kim Bong Chul , Yu Sang Jeon
Published: May 2010

In this paper, we investigated the influence of ball spacer size and density on liquid crystal (LC) margin of in-plane switching (IPS) panel fabricated by the inkjet process. In the case of using 3.0 µm ball spacer alone, LC margin is decreased rapidly with increasing the ball spacer density. Also, the good condition is not achieved, even though we adjust the ball spacer density for the several conditions. However, it is possible to get LC margin of 8.7% and the push strength of 6.0 kgf by mixing ball spacers of 2.75 µm and 3.0 µm. In condition with 100 number/mm2 of 3.0 µm, we achieved higher LC margin without the decrease of the push strength by increasing the ball spacer of 2.75 µm.
Noble Logic for Preventing Scratch on Roll-to-Roll Printed Layers in Noncontacting Transportation
Authors: Lee Changwoo , Kang Hyunkyoo , Kim Hojoon , Shin Keehyun
Published: May 2010

The use of roll-to-roll (R2R) printed electronics is a relatively new method of mass producing flexible electronic devices while keeping production costs down. The geometrical qualities of a printed pattern, such as surface roughness and uniformity, could deteriorate. Moreover, the geometric qualities of a printed layer affect the functional qualities of a printed electronic device directly. Therefore, the functional qualities (conductivity and mobility) of a multilayer electronic device could deteriorate in the presence of a scratch defect on the printed layer. In general, a scratch on a printed pattern on a flexible substrate is induced by contact between the rolls and printed pattern in R2R printing systems. To prevent such contact, one of the best solutions is to use an air flotation unit. However, a scratch defect could be induced even though an air flotation process is used to minimize contact, because the flotation height of a moving web is affected by web tension. In this paper, we discuss an analytical model of an air-floated moving substrate. For the noncontacting transfer of a moving web without a scratch defect, a mathematical tension model has been developed by considering an induced strain due to aerodynamic forces and verified by numerical and experimental studies. Additionally, the correlation between the flotation height of an air-floated moving web and speed compensation used to control the tension are investigated. The analysis shows that tension fluctuations can cause the substrate to touch the air-flotation subsystem, which is installed to prevent contact, resulting in defects such as scratches on the printed layer. On the basis of the proposed model, a logic is developed to minimize scratch defects on R2R printed layers in noncontacting transportation. Through a guideline based on this logic, the scratched area density on R2R printed layers can be reduced by approximately 70%.
Electrohydrodynamic Spray Deposition of ZnO Nanoparticles
Authors: Choi Kyung Hyun , Khan Saleem , Dang Hyun Woo , Doh Yang Hoi , Hong Sung Jei
Published: May 2010

This paper presents the electrospray deposition of solution-based ZnO nanoparticles. Transparent thin film transistors in active matrix displays have become the most interested research area. Electrospray assures direct deposition by eliminating etching steps required after deposition by other techniques. Uniform layers of minimum thickness 87 nm on glass and 356 nm on polyimide using electrospray experiment is achieved. Contact angle analyzer has been used for finding properties like wetting energy, spreading coefficient and work of adhesion of the ink on glass and polyimide substrates. All experiments were performed in ambient conditions.
Nickel Line Patterning Using Silicon Supersonic Micronozzle Integrated with a Nanoparticle Deposition System
Authors: Jung Kyubong , Song Woojin , Chun Doo-Man , Kim Yang-Hee , Yeo Jun-Cheol , Kim Min-Saeng , Ahn Sung-Hoon , Lee Caroline Sunyong
Published: May 2010

In this study, 3-µm- and 20-nm nickel powders were deposited on Si substrates to pattern a metal line using a nanoparticle deposition system (NPDS) at room temperature. The stand-off distance (SoD), the distance between the substrate and the end of nozzle, was varied from 300 to 1000 µm to determine its effect on deposition properties. A Ni line was successfully formed on the Si substrate. When 3-µm Ni powders were used, the thickness of the deposited layer on the Si substrate was measured to be 5.4 µm, and its width was 176.4 µm at a SoD of 300 µm. In contrast, the deposited average thickness at a SoD of 500 µm was 1.1 µm, with a width of 190.6 µm. Moreover, the deposited thickness was measured to be 6.4 µm using 20-nm Ni powders at a SoD of 300 µm. Thus, it was found that the deposited thickness decreased as SoD increased, indicating an inversely proportional relationship. For deposition behavior, depending on the size of powders, it was found that 20-nm Ni powders resulted in a thicker deposition than did 3-µm Ni powders, as momentum transfer between carrier gas and powders is inversely proportional to the powder size. Thus, as the powder size decreased, its spray velocity increased; hence, it is more effective to use nano powders for Ni line patterning. Surface resistivity of the deposited Ni line was 1.83 ×10-7 Ω·m using 20-nm powders and 1.61 ×10-7 Ω·m using 3-µm powders. These values are close to the standard resistivity value for bulk Ni, which is 6.9 ×10-8 Ω·m, making NPDS a promising technique for metal line-fabrication equipment.
A Study of Hybrid Drying Process to Improve Drying Speed and Electrical Conductivity for Roll-to-Roll Printing
Authors: Park Jiyong , Rhee Sehun
Published: May 2010

In this study, we present a new drying method for the roll–roll printing process that improves drying speed and electric conductivity. Generally, hot air is used for drying. However, drying using hot air requires a long time despite the high electrical conductivity obtained in the final specimen. To overcome this problem, we developed a drying process that integrates hot air drying and infrared (IR). First, different drying methods (hot air drying and IR drying) were analyzed by analyzing the specimens obtained after drying of a poly(ethylene terephthalate) (PET) substrate printed with silver ink. After determining and analyzing the outcomes obtained used these two methods individually, the two methods were combined to create a drying process with optimal performance. And focusing on trapped solvent, the drying sequence was analyzed. In addition, micromechanism analysis was performed to investigate the various drying conditions.
Copper–Holmium Alloy Film for Reliable Interconnects
Authors: Lin Chon-Hsin , Leau Wen-Kuan , Wu Cheng-Hui
Published: May 2010

We fabricate reliable interconnects via advanced barrierless metallization by cosputtering a pure copper (Cu) film with small amounts of holmium nitride (HoN
x
) on a silicon (Si) substrate. No noticeable interaction occurs between the resulting Cu(HoN
x
) film and the substrate even after heating at 660 °C for 1 h. The resistivity of the alloy film, which remains stable after five cycles of heating at 600 °C (total: 2.5 h), is high under the as-deposited condition, but decreases to ∼3.0 µΩ cm after annealing. The leakage current of the alloy film is three times lower than that of the pure Cu film. The correlation between the leakage current and the time-dependent dielectric breakdown (TDDB) lifetime reveals that the alloy film has a TDDB lifetime of >10 years. Furthermore, the alloy film adheres better to the Si substrate than does the pure Cu film. Our alloy film thus has improved features that are desirable for a reliable interconnect.
Evolution of Microstructures in Nanocrystalline VN Barrier Leading to Failure in Cu/VN/SiO2/Si Systems
Authors: Takeyama Mayumi B. , Itoi Takaomi , Noya Atsushi
Published: May 2010

We have investigated the evolution of microstructures in a nanocrystalline VN barrier of ∼10 nm thickness to clarify the failure mechanism in a Cu/VN/SiO2/Si system owing to high-temperature annealing. Transmission electron microscopy observation reveals that the as-deposited VN barrier shows a uniform layer with a columnar structure composed of grains no larger than 10 nm in size. A negligible change in the morphology of the VN barrier is evident even after annealing at 600 °C for 1 h. Annealing at 800 °C brings about noticeable growth of VN grains in the lateral direction without any solid-phase reaction at each interface, resulting in a failure of the VN barrier owing to local discontinuity of the layer. This result is also consistent with the result obtained by Auger electron spectroscopy. It is revealed that the thin VN barrier fails after annealing at 800 °C for 1 h owing to the loss of the continuity in the lateral direction without chemical reaction and intermixing at barrier interfaces.