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>

Magnetotransport of lateral Py/Pt/Py spin valve device

Han, Giju,Chang, Joonyeon,Eom, Jonghwa,Kim, Hyungjun,Kim, Young Keun,Han, Suk-Hee WILEY-VCH Verlag 2007 Physica Status Solidi. B Vol.244 No.12

<P>Spin injection and accumulation have been investigated for Py/Pt/Py lateral spin valves with various channel length. Clear spin valve effects were found at antiparallel magnetic configuration of two ferromagnetic electrodes. The observation of memory effect suggests the spin valve effect observed in Pt channel is resulted from effective spin injection and detection. The magnitude of spin valve signal decreases as the channel length increases. The measurement yields that spin diffusion length and spin injection polarization of Pt channel is 120 nm and 18% at 5K. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Nanocomposite of SWNTs and SnO₂ fabricated by soldering process for ammonia gas sensor application

Duc Hoa, Nguyen,Van Quy, Nguyen,Suk Cho, You,Kim, Dojin WILEY-VCH Verlag 2007 Physica status solidi. PSS. A, Applications and ma Vol.204 No.6

<P>We introduce a simple method to fabricate an ammonia gas sensor with a nanocomposite of single-walled carbon nanotubes (SWNTs) and SnO<SUB>2</SUB>. The nanocomposite showed a semiconducting property. With exposure to ammonia gas, the electrical resistance of the nanocomposite sensor increases rapidly. It was found that the sensor can detect the concentration of NH<SUB>3</SUB> down to the 10 ppm level at room temperature. The sensor exhibited a fast response time of less than 100 s and good sensing response and recovery. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Inverse giant magnetoresistance due to spin-dependent bulk scattering in Fe_1–xCr_x/Cu/Co

Thi, Ngoc Anh Nguyen,Thi, Hoang Yen Nguyen,Yi, Hyunjung,Joo, Sung-Jung,Shin, Kyung-Ho WILEY-VCH Verlag 2007 Physica status solidi. PSS. A, Applications and ma Vol.204 No.12

<P>Inverse giant magnetoresistance (IGMR) can be observed in multilayers with alternating two ferromagnetic layers F1 and F2 possessing opposite spin scattering asymmetries. We report here the observation of inverse current-in-plane giant magnetoresistance (CIP-IGMR) in Fe<SUB>1–x</SUB>Cr<SUB>x</SUB>/Cu/Co spin-valve systems with varying Cr concentration and FeCr-layer thickness. The highest magnitude of IGMR, –0.45%, has been achieved in the sample doped with 35 at.% Cr. It is shown that the proper substitution of Cr for Fe can alter spin-dependent scattering in the Fe layer, causing the inversion of the bulk spin scattering asymmetry coefficient therefore resulting in CIP-IGMR. The GMR has a dominant contribution to the observed inverse MR, rather than the anisotropic magnetoresistance (AMR) component. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Different nanostructure cathode catalysts application for direct methanol fuel cell

Dipti, Sharmin Sultana,Chung, Uoo-Chang,Kim, Jong-Pil,Chung, Won-Sub WILEY-VCH Verlag 2007 Physica status solidi. PSS. A, Applications and ma Vol.204 No.12

<P>Direct methanol fuel cell (DMFC) belongs to the same family of energy conversion device and the application of new hydrogen storage nanomaterials such as carbon nanotube (CNTs) supported catalysts is being addressed in an increasing industrial approach. In this present study, multiwall carbon nanotube supported Pt and Pt-Ni nanoparticles were prepared as cathode catalysts for direct methanol fuel cell application. Transmission electron microscopy and X-ray diffraction analyses indicated the formation of well-dispersed Pt and Pt-Ni nanoparticles having sizes of around 2 ∼ 4 nm on carbon nanotube. Furthermore, the electrochemical characterization by the cyclic voltammetry (CV) demonstrated that these catalysts have higher catalytic activity and the methanol oxidation reaction of the Pt-Ni/CNTs is respectively almost similar and slightly higher than Pt/CNTs electrocatalysts. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Magnetic properties of Mn-doped Bi₂Te₃ and Sb₂Te₃

Choi, Jeongyong,Choi, Sungyoul,Choi, Jiyoun,Park, Yongsup,Park, Hyun-Min,Lee, Hee-Woong,Woo, Byung-Chul,Cho, Sunglae WILEY-VCH Verlag 2004 Physica status solidi. PSS. B, Basic solid state p Vol.241 No.7

<P>We have fabricated Mn-doped Bi<SUB>2</SUB>Te<SUB>3</SUB> and Sb<SUB>2</SUB>Te<SUB>3</SUB> single crystals by the vertical gradient solidification method. The compositions and crystal structures of Bi<SUB>2−x</SUB>Mn<SUB>x</SUB>Te<SUB>3</SUB> and Sb<SUB>2−x</SUB>Mn<SUB>x</SUB>Te<SUB>3</SUB> were determined using Electron Probe Micro-Analyzer (EPMA) and powder X-ray diffraction (XRD) patterns, respectively. Both crystal structures were rhombohedral with smaller lattice constants because of the smaller atomic radius of Mn than those of Bi and Sb. Based on the magnetization measurements, Mn-doped Bi<SUB>2</SUB>Te<SUB>3</SUB> and Sb<SUB>2</SUB>Te<SUB>3</SUB> compounds have ferromagnetic ordering at T<SUB>C</SUB> = 10 and 17 K, respectively. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Influence of film thickness on the electrical and magnetic properties of Co–Fe–Al–O films

Phan, M. H.,Tuan, L. A.,Ha, N. D.,Phan, T. L.,Kim, C. G.,Kim, C. O.,Yu, S. C. WILEY-VCH Verlag 2007 Physica Status Solidi C Vol.4 No.12

<P>Influence of film thickness (t) on the electrical and magnetic properties of Co–Fe–Al–O films has been systematically investigated via means of vibrating sample magnetometry (VSM), permeability spectra and magneto-optical Kerr effect (MOKE). It is found that the electrical resistivity (ρ) decreases as the film thickness increases; ρ = 412.5 µΩcm for the t = 600 nm sample decreases to ρ = 368.2 µΩcm for the t = 1200 nm sample. The coercive force, measured along the easy-axis direction, decreases as the film thickness increases. Interestingly, along the hard-axis magnetization direction, the magnetic hysteresis loop is reversed and the coercive force is negative for the t = 600 and 800 nm samples. However, this peculiar feature disappears as t reaches 1200 nm, which is probably attributed to the microstructural change with respect to changes of film thickness. At a frequency of 1GHz, the hard-axis effective permeability decreases from 1252 to 1000 as the film thickness increases from 600 to 1200 nm, respectively. The VSM and MOKE results reveal an increase in magnetic anisotropy in the near-surface region of the film. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Rare earth doped CaSO₄ luminescence phosphors for applications in novel displays – new recipes

Lakshmanan, Arunachalam,Kim, Seon-Bae,Kum, Byung Gon,Jang, Hyun Myung,Kang, Bong Koo WILEY-VCH Verlag 2006 Physica status solidi. PSS. A, Applications and ma Vol.203 No.3

<P>New Recipes for rare earth doped CaSO<SUB>4</SUB> luminescence phosphors which give high photoluminescence efficiency combined with high thermal stability desired for noval display applications are described. The influence of cooling rate, thermal treatments and water washing as well as crystal size and morphology on the luminescence efficiency are described. While a modified co-precipitation technique was found best suited for preparing thermostimulated luminescence phosphors required for radiation dosimetry, those made by solid state diffusion reactions at high temperatures were found best suited to achieve the high photoluminescence efficiency required for lighting and display applications. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Experimental observation of the electric coupling effect in split ring resonators and the prevention

Lam, V. D.,Kim, J. B.,Lee, S. J.,Wang, D. F.,Lee, Y. P. WILEY-VCH Verlag 2007 Physica status solidi. PSS. A, Applications and ma Vol.204 No.12

<P>We studied experimentally the transmission properties of arrays of split-ring resonators (SRRs) for different electromagnetic polarizations in the microwave-frequency regime. It is known that, besides the electric response through the cut-wire like, another electric coupling to the magnetic resonance of the SRR appears when the incident electric field is parallel to the gap-bearing sides of the SRR. The resonance frequency of this effect is very close to the magnetic resonance. This might degrade or even destroy the left-handed properties of the material when the SRRs are combined with the wires. To avoid this effect we have changed the structure of SRRs from an asymmetric one with a single gap to a symmetric one with two gaps. The results are also compared with the previous studies. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Amplification of magnetic fields by supernova-driven turbulence

Kim, J.,Balsara, D. S. WILEY-VCH Verlag 2006 Astronomische Nachrichten Vol.327 No.5

<P>Observations of μG magnetic fields in radio galaxies at cosmological epochs as early as around z = 2 have shortened the available time for dynamo action. This fact suggests that the mean-field dynamo mechanism in a global galactic scale either is too slow to amplify a seed field generated by the Biermann battery effect to the level of the observed field strength at z ∼ 2 or needs much stronger seed fields of an order of 10<SUP>–10</SUP> G. A “contamination” picture that amplified magnetic fields in smaller objects, such as stars or AGNs, within a relatively shorter timescale spread out through supernova ejecta, stellar winds, and AGN jets to nearby environments is gaining momentum. In line with this picture, we demonstrate, through three-dimensional numerical experiments, that magnetic fields can be amplified by supernova-driven turbulence with two orders of magnitude smaller e-folding timescale than that of the mean-field dynamo mechanism. Therefore, supernova-driven turbulence may play an important role in amplifying small-scale B -fields in any astrophysical systems that have harbored massive stars. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>