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>

Fast Reciprocating Probe Assembly for the KSTAR

Bak, J. G.,Lee, S. G.,KSTAR project team WILEY-VCH Verlag 2006 CONTRIBUTIONS TO PLASMA PHYSICS Vol.46 No.5

<P>A fast reciprocating probe assembly (FRPA) that can scan a distance of up to 32.5 cm with a maximum speed of 1.7 m/s was fabricated to obtain the spatial profile of basic plasma parameters in the edge region of the KSTAR plasma during a plasma discharge of 20 s. The probe driving mechanism consists of two parts; first a slow movement driven by a servo motor system and then a fast reciprocating movement actuated by a pneumatic system. A performance test of the drive system, which is remotely controlled by a PC, was carried out. The prototype of the probe head for the KSTAR FRPA was fabricated as a modular type for easy replacement. It was installed in the fast injection probe assembly (FIPA) in the Hanbit magnetic mirror device, and a radial plasma parameter profile measurement was carried out. The performance test results of the drive system and the profile measurements using the probe head are presented. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Electronic states and local structures of Cu ions in electrodeposited thin films of Cu and Cu₂O from X-ray absorption spectra

Wijesundera, R. P.,Hidaka, M.,Siripala, W.,Choi, Sun-Hee,Sung, Nark Eon,Kim, Min Gyu,Lee, Jay Min WILEY-VCH Verlag 2006 Physica status solidi. PSS. B, Basic solid state p Vol.243 No.8

<P>X-ray absorption spectra near Cu K edges have been obtained for Cu and Cu<SUB>2</SUB>O thin films potentiostatically electrodeposited in an acetate bath. The electronic states of Cu ions and the local structures around these ions are studied using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy, respectively. The inner strains in micro-size crystals of the electrodeposited Cu thin film are less than those of a commercial Cu foil. The partial electronic states of Cu ions near the Fermi level (E <SUB>F</SUB>) and the local structure around these ions show a systematic transformation from a Cu<SUB>2</SUB>O single phase (Phase I), to a Cu<SUB>2</SUB>O–Cu intermediate phase (Phase II) and a Cu single phase (Phase III) in thin films electrodeposited on titanium substrates for the deposition potential range of –100 to –900 mV. Phase II consists of independent Cu<SUB>2</SUB>O-like and Cu-like local structures, but not a Cu<SUB>2</SUB>O–Cu complex. Phase II is also characterized by a transition region from the semiconductor Cu<SUB>2</SUB>O to the metal Cu for the Cu electronic state having a p-like character near the Fermi level in the oxygen O-2p conduction band. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

QD technology and market prospects in the sectors of space exploration, biomedicine, defense, and security

Charitidis, C. A.,Golnas, A.,Chouliaras, F.,Arpatzanis, N.,Dimitriadis, C. A.,Lee, J. I.,Bakolias, C. WILEY-VCH Verlag 2008 Physica Status Solidi C Vol.5 No.12

<P>Quantum dots (QD) are a unique subset of nanomaterials characterized by their extraordinary quantum confinement behaviour. Even though the quantum dot industry is still in its infancy with revenues now reaching $10 million, it is expected to surpass $500 million in 2009. However, in order to leverage the full potential of the QD technology, new fabrication processes must be developed to attain high detectivity and high operating temperature (HOT) photodetector devices. The Quantum Dot Infrared Photodetectors (QDIPs) possess an immense potential for civilian and military applications due to the distinct characteristics stemming from their dimensionality – which provides 3D carrier confinement and the capacity for normal-incidence detection – and their amenability to bandgap engineering – which allows tailoring the peak and cutoff wavelengths according to custom needs. The QDIPs, especially when optimized to operate at higher temperatures, can become critical components in space exploration, defence and security, optical communication, quantum computing and cryptography, and medical imaging applications. Robust and reliable solutions for these fields will command a premium position in the marketplace as by responding to the societal need for secure electronic transactions, exponentially faster data processing, and higher quality diagnostic tools. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Reduction of low‐frequency noise in multilayer MoS₂ FETs using a Fermi‐level depinning layer

Kim, Yonghun,Park, Woojin,Yang, Jin Ho,Cho, Chunhum,Lee, Sang Kyung,Lee, Byoung Hun Wiley - VCH Verlag GmbH & Co. KGaA 2016 Physica Status Solidi. Rapid Research Letters Vol.10 No.8

<P>Two‐dimensional transition metal dichalcogenides (TMDCs) are potential candidate materials for future thin‐film field effect transistors (FETs). However, many aspects of this device must be optimized for practical applications. In addition, low‐frequency noise that limits the design window of electronic devices, in general, must be minimized for TMD‐based FETs. In this study, the low‐frequency noise characteristics of multilayer molybdenum disulphide (MoS<SUB>2</SUB>) FETs were investigated in detail, with two different contact structures: titanium (Ti) metal–MoS<SUB>2</SUB> channel and Ti metal–TiO<SUB>2</SUB> interlayer–MoS<SUB>2</SUB> channel. The results showed that the noise level of the device with a TiO<SUB>2</SUB> interlayer reduced by one order of magnitude compared with the device without the TiO<SUB>2</SUB> interlayer. This substantial improvement in the noise characteristics could be explained using the carrier number of fluctuation model. (© 2016 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>

New Type of Photoluminescent Iridium Complex: Novel Synthetic Route for Cationic trans-Bis(2-phenylpyridinato)iridium(III) Complex

Chin, Chong Shik,Eum, Min-Sik,Kim, Song yi,Kim, Choongil,Kang, Sung Kwon WILEY-VCH Verlag 2006 European journal of inorganic chemistry Vol.2006 No.24

<P>A new type of iridium(III) complex [trans-Ir(ppy)<SUB>2</SUB>(PPh<SUB>3</SUB>)<SUB>2</SUB>]<SUP>+</SUP> (1) has been prepared by a novel synthetic method and its structural and photoluminescent characteristics have been compared with those of the cis analogue, [cis-Ir(ppy)<SUB>2</SUB>(PPh<SUB>3</SUB>)(P(OPh)<SUB>3</SUB>)]<SUP>+</SUP> (2) which has also been newly prepared in this study. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)</P> <B>Graphic Abstract</B> <P> <img src='wiley_img/14341948-2006-2006-24-EJIC200600888-fig000.gif' alt='wiley_img/14341948-2006-2006-24-EJIC200600888-fig000'> </P>

Inter-dot spin exchange interaction in coupled II–VI semiconductor quantum dots

Lee, S.,Dobrowolska, M.,Furdyna, J. K. WILEY-VCH Verlag 2006 Physica status solidi. PSS. B, Basic solid state p Vol.243 No.4

<P>We have performed polarization selective photoluminescence (PL) experiment on a series of self-assembled quantum dots (QDs) in the form of single- and double-QD layer systems. The double layers were formed from diluted magnetic semiconductor (DMS) (either CdMnSe or CdZnMnSe) and non-DMS (either CdSe or CdZnSe) layers, separated by non-DMS ZnSe barriers. The peaks from DMS and non-DMS QD layers are clearly resolved in the PL spectra taken at zero magnetic field. When a magnetic field is applied to the double layer QD (DLQD) system, the intensities of the circularly polarized PL peaks corresponding to the non-DMS (i.e., CdSe and CdZnSe) layers exhibit significant changes, reflecting correspondingly large changes in the degrees of spin polarization of the non-DMS QDs. This enhancement of spin polarization observed in the double-layer QD structures is interpreted in terms of anti-parallel spin interaction between carriers localized in the coupled QD pairs. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

A Poly(bicyclic dimer) and a Cyclic Tetramer: Ligand Isomerism of S₂O₂ Macrocycles During the Assembly of Supramolecular Silver(I) Complexes

Lee, So Young,Seo, Joobeom,Yoon, Il,Kim, Chung-Sik,Choi, Kyu Seong,Kim, Jae Sang,Lee, Shim Sung WILEY-VCH Verlag 2006 European journal of inorganic chemistry Vol.2006 No.17

<P>Two isomeric S<SUB>2</SUB>O<SUB>2</SUB> macrocycles (L<SUP>1</SUP> and L<SUP>2</SUP>) with a 14-membered cavity have been synthesised as a model system with different binding modes. Self-assembly reactions of L<SUP>1</SUP> and L<SUP>2</SUP> with silver perchlorate afford the respective ligand-directed cyclic oligomer complexes with different shapes: a poly(bicyclic dimer) (1) and a discrete cyclic tetramer (2). The formation of these supramolecular complexes is discussed in terms of conformational discrimination of two isomeric macrocycles due to ring rigidity and interdonor distances.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)</P> <B>Graphic Abstract</B> <P> <img src='wiley_img/14341948-2006-2006-17-EJIC200600290-fig000.gif' alt='wiley_img/14341948-2006-2006-17-EJIC200600290-fig000'> </P>