Electrical transport properties of a single wall carbon nanotube network

Hwang, J. S.,Kim, H. T.,Kim, H. K.,Son, M. H.,Hwang, S. W.,Ahn, D. WILEY-VCH Verlag 2009 Physica Status Solidi. B Vol.246 No.4

<P>A single wall carbon nanotube (SWCNT) network is fabricated and its electronic transport properties are investigated. It shows a typical p-type field-effect-transistor (FET) behavior and nonlinearities in the source current-source bias characteristics. The network also exhibits incomplete turn-off and a small mobility. These characteristics are explained by the fact that the network is a mixture of metallic and semiconducting SWCNTs connecting with one another. Various cross junctions such as SWCNT (semiconducting)-SWCNT (semiconducting), SWCNT (semiconducting)-SWCNT (metallic) are the source of nonlinearities and the small mobility. Incomplete turn-off can be explained by the parallel conduction paths consisting of metallic SWCNTs which are insensitive to the gate bias. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Novel carbonyl iron/polystyrene (CI/PS) composites synthesized via solvent casting and their magnetorheology

Lee, Mi Ah,Fang, Fei Fei,Choi, Hyoung Jin Wiley - VCH Verlag GmbH & Co. KGaA 2007 Physica Status Solidi. A Vol.204 No.12

<P>As a magnetic material, carbonyl iron (CI) has been extensively used for magnetorheological (MR) fluids. However, MR fluids based on CI particles possess severe shortcomings of sedimentation and uniform dispersion due to the density difference between CI particles and carrier liquid. To overcome these problems, we prepared CI/polystyrene (PS) composites via a solvent casting method. The density of the synthesized CI/PS particles was much lower than that of the pristine CI particles. We further dispersed the composite particles in lubricant oil and investigated their MR properties using a rotational rheometer in parallel plate geometry with the magneto-rheological device. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Effect of electrode pattern on light emission distribution in InGaN/GaN light emitting diode

Hwang, Sungmin,Yoon, Joosun,Shim, Jongin,Yoo, Kyungyul WILEY-VCH Verlag 2008 Physica status solidi. PSS. C, Current topics in s Vol.5 No.6

<P>The effect of geometrical electrode pattern on the blue InGaN/GaN multi-quantum well (MQW) light emitting diode (LED) devices is investigated both theoretically and experimentally. A 3-dimensional circuit model of an LED is constructed and then the corresponding circuit parameters are extracted. Circuit parameters of an LED consist of the resistances of the metallic film and epitaxial layer, and intrinsic diodes representing the light-emitting active region. Both the transmission line model (TLM) and current-voltage (I-V) characteristics of LED are employed to extract circuit parameters experimentally. These circuit parameters are then applied to the circuit model to generate light emission patterns in a top-surface emitting-type LED. Experiment results verify that the emitting light distribution from fabricated LED coincides reasonably well with the theoretical results. This makes it possible to design an LED theoretically and predict its actual properties. The LED structure proposed using the model is shown to exhibit not only good light uniformity, but also higher light output power and lower voltage drop. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Application of ellipsometry in immersion lithography

Jeong, H.,Cheon, H.,Kyoung, J.,Oh, H.,An*, I. Wiley - VCH Verlag GmbH & Co. KGaA 2008 Physica Status Solidi C Vol.5 No.5

<P>Optical lithography with an ArF excimer laser (193 nm) can produce sub 100nm patterns. Without the reduction of wavelength, further increase in resolution is expected by employing an immersion technique in which a liquid medium is filled between the objective lens and underlying photoresist. In this case, resolution can be enhanced through the increase of numerical aperture. However, in order for immersion lithography to be successful, many problems associated with the liquid environment need to be solved. One of the serious problems is the interaction between liquid and photoresist. Liquid may penetrate into the photoresist and cause leaching problem. This in turn modifies the physical and chemical properties of the photoresist. Thus, it is important to monitor the modification of the photoresist by immersion liquid. In this work, spectroscopic ellipsometry and imaging ellipsometry are used to investigate the absorption of liquid by photoresist as well as top coat which is used to prevent water penetration into underlying photoresist. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Left invariant metrics and curvatures on simply connected three-dimensional Lie groups

Ha, Ku Yong,Lee, Jong Bum WILEY-VCH Verlag 2009 Mathematische Nachrichten Vol.282 No.6

<P>For each simply connected three-dimensional Lie group we determine the automorphism group, classify the left invariant Riemannian metrics up to automorphism, and study the extent to which curvature can be altered by a change of metric. Thereby we obtain the principal Ricci curvatures, the scalar curvature and the sectional curvatures as functions of left invariant metrics on the three-dimensional Lie groups. Our results improve a bit of Milnor's results of [7] in the three-dimensional case, and Kowalski and Nik&n.vacute;cević's results [6, Theorems 3.1 and 4.1] (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

The role of a conductive CaRuO₃ bottom electrode for ferroelectric BaTiO₃ films on a Si substrate

Paik, Hanjong,Hong, Jongin,Jang, Yong-oon,Park, Yun Chang,Lee, Jeong Yong,Song, Hanwook,No, Kwangsoo WILEY-VCH Verlag 2009 Physica status solidi. PSS. A, Applications and ma Vol.206 No.7

<P>A capacitor of Pt/BaTiO<SUB>3</SUB>/CaRuO<SUB>3</SUB> (Pt/BTO/CRO) was successfully prepared on a Si substrate by using radio-frequency (RF) magnetron sputtering. The preferentially (110)-oriented CRO bottom electrode enabled us to obtain highly oriented BTO thin film on the Si substrate. Local epitaxy between BTO and CRO was clearly confirmed by high resolution transmission electron microscopy (HRTEM) and fast Fourier transformation (FFT) analysis. The clear interface between CRO and BTO without any Si diffusion and silicate formation was determined by Auger electron spectroscopy (AES). The polarization value (2P<SUB>r</SUB>) of 6 μC/cm<SUP>2</SUP>, the coercive field (2|E<SUB>c</SUB>|) of 61 kV/cm and the stable current density of 1 × 10<SUP>–8</SUP> A/cm<SUP>2</SUP> around 2100 kV/cm electric field were obtained. Its tunability on CRO was reached up to 0.52 with a loss tangent less than 0.09 at room temperature. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Ratiometric Fluorescence Sensing of Fluoride Ions by an Asymmetric Bidentate Receptor Containing a Boronic Acid and Imidazolium Group

Xu, Zhaochao,Kim, Sook Kyung,Han, Su Jung,Lee, Chongmok,Kociok-Kohn, Gabriele,James, Tony D.,Yoon, Juyoung WILEY-VCH Verlag 2009 EUROPEAN JOURNAL OF ORGANIC CHEMISTRY Vol.2009 No.18

<P>The synthesis of the first examples of anion receptors that utilize boron–fluoride interactions and (C–H)<SUP>+</SUP>···F<SUP>–</SUP>-type ionic hydrogen-bond interactions in the binding of F ions is reported herein. o-, m-, and p-Phenylboronic acids were linked to naphthoimidazolium through a methylene group. On the basis of fluorescence and <SUP>19</SUP>F NMR studies, we have confirmed that the addition of fluoride to a boron center occurs prior to the formation of (C–H)<SUP>+</SUP>···F<SUP>–</SUP>-type ionic hydrogen bond with the imidazolium moiety. More importantly, these investigations have demonstrated that only the receptor bearing the ortho-directed boron and imidazolium exhibits enhanced fluoride binding. The increased binding ability of the asymmetric bidentate receptor of ortho-boronic acid and imidazolium towards F<SUP>–</SUP> enables it to sense fluoride ions in a 95:5 CH<SUB>3</SUB>CN/HEPES aqueous solution. The fluorescence responses to different anions were also explored; the ortho-boron-imidazolium receptor displayed ratiometric fluorescence changes and a high selectivity towards fluoride ions over other anions (Cl<SUP>–</SUP>, Br<SUP>–</SUP>, CH<SUB>3</SUB>CO<SUB>2</SUB><SUP>–</SUP>, HSO<SUB>4</SUB><SUP>–</SUP>, and H<SUB>2</SUB>PO<SUB>4</SUB><SUP>–</SUP>).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)</P> <B>Graphic Abstract</B> <P>An asymmetric bidentate receptor containing boronic acid and an imidazolium group can recognize F<SUP>–</SUP>, as evidenced by ratiometric fluorescence responses in aqueous solution. <img src='wiley_img/1434193X-2009-2009-18-EJOC200900120-fig000.gif' alt='wiley_img/1434193X-2009-2009-18-EJOC200900120-fig000'> </P>

TEM study of the structural similarity between NaCl and rhombohedral phase of Te-based ternary chalcogenide materials

Sun, Changwoo,Lee, Jeongyong,Kim, Yongtae WILEY-VCH Verlag 2009 Physica status solidi. PSS. A, Applications and ma Vol.206 No.1

<P>Comparing the phase-change behaviour of Ge–Bi–Te (GBT) to that of Ge–Sb–Te (GST), we have tried to verify a general relationship between a metastable NaCl and a stable rhombohedral structure that is easily incurred by stretching the cube along the body diagonal. High-resolution transmission electron microscopy (TEM) images show that the NaCl as well as the rhombohedral GBT and GST structures are observed along specific directions. From the TEM images, we suggest an atomic model and a phase transition mechanism by lattice distortion. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Effects of external magnetic field on magnetic properties and surface morphology of electrodeposited CoFeNi alloys

Kim, Hyun Kyung,Chun, Dong Won,Han, Jun Hyun,Kim, Kwang Bum,Jeung, Won Young WILEY-VCH Verlag 2007 Physica status solidi. PSS. A, Applications and ma Vol.204 No.12

<P>The magnetic properties and surface morphology of CoFeNi alloy films electrodeposited under external magnetic field were investigated. It was observed that crystallographic anisotropy in CoFeNi films was induced due to the preferential orientation of applied magnetic field. In addition, the CoFeNi alloy films showed excellent magnetic property (low H<SUB>c</SUB>), which is considered that not only the smaller grain size of the films, but also more uniform surface of the films than that deposited in absence of applied magnetic field. These observed phenomena could be explained with magneto-hydrodynamic (MHD) convection of charged ions at the interface of electrode and electrolyte induced by Lorentz force. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Local Hall effect in a hybrid InSb cross junction

Kim, W. Y.,Chang, J. Y.,Han, S. H.,Chang, S. G.,Lee, W. Y. WILEY-VCH Verlag 2004 Physica status solidi. A, Applied research Vol.201 No.8

<P>We present the local Hall effect in a hybrid Hall device incorporating a micron-scaled InSb semiconductor cross junction and a single microstructured ferromagnetic element. A clear hysteresis loop was found to appear in the output signal for the cross junction with a ferromagnetic element due to the strong perpen- dicular component of the magnetic fringe field emanating from the edge of the ferromagnet. We demon- strate that the local fringe field from the ferromagnetic element inducing a Hall voltage improves the Hall sensitivity (4.5 Ω/Oe). (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>