bluuebunny/crossref_metadata_2025 huggingface dataset:
Human α-synemin interacts directly with vinculin and metavinculin
Authors: Sun Ning , Critchley David R. , Paulin Denise , Li Zhenlin , Robson Richard M.
Published: January 2008

Synemin is a very large, unique member of the IF (intermediate filament) protein superfamily. Association of synemin with the major IF proteins, desmin and/or vimentin, within muscle cells forms heteropolymeric IFs. We have previously identified interactions of avian synemin with α-actinin and vinculin. Avian synemin, however, is expressed as only one form, whereas human synemin is expressed as two major splice variants, namely α- and β-synemins. The larger α-synemin contains an additional 312-amino-acid insert (termed SNTIII) located near the end of the long C-terminal tail domain. Whether α- and β-synemins have different cellular functions is unclear. In the present study we show, by in vitro protein–protein interaction assays, that SNTIII interacts directly with both vinculin and metavinculin. Furthermore, SNTIII interacts with vinculin in vivo, and this association is promoted by PtdIns(4,5)P2. SNTIII also specifically co-localizes with vinculin within focal adhesions when transiently expressed in mammalian cells. In contrast, other regions of synemin show distinct localization patterns in comparison with those of SNTIII, without labelling focal adhesions. Our results indicate that α-synemin, but not β-synemin, interacts with both vinculin and metavinculin, thereby linking the heteropolymeric IFs to adhesion-type junctions, such as the costameres located within human striated muscle cells.
Analysis of apolipoprotein E nuclear localization using green fluorescent protein and biotinylation approaches
Authors: Kim Woojin S. , Elliott David A. , Kockx Maaike , Kritharides Leonard , Rye Kerry-Anne , Jans David A. , Garner Brett
Published: January 2008

Previous results indicate that apoE (apolipoprotein E) may be associated with the nucleus in specific cell types, particularly under stress conditions such as serum starvation. In addition, nuclear apoE localization in ovarian cancer was recently shown to be correlated with patient survival. In order to better understand the factors associated with apoE nuclear localization, we examined intracellular apoE trafficking using live-cell imaging of CHO (Chinese-hamster ovary) cells that constitutively expressed apoE–GFP (green fluorescent protein). In addition, we used biotinylated apoE (in a lipid-free state and as a lipidated discoidal complex) to track the uptake and potential nuclear targeting of exogenous apoE. Our results indicate that a small proportion of apoE–GFP is detected in the nucleus of living apoE–GFP-expressing CHO cells and that the level of apoE–GFP in the nucleus is increased with serum starvation. Exposure of control CHO cells to exogenous apoE–GFP did not result in nuclear apoE–GFP localization in the recipient cells. Similarly, biotinylated apoE did not reach the nucleus of control CHO cells or SK-N-SH neurons. In contrast, when biotinylated apoE was delivered to recipient cells as a lipidated apoE disc, apoE was detected in the nucleus, suggesting that the lipoprotein complex alters the intracellular degradation or trafficking of apoE. Biotinylated apoE discs containing each of the three common human apoE isoforms (E2, E3 and E4) were also tested for nuclear trafficking. All three apoE isoforms were equally detected in the nucleus. These studies provide new evidence that apoE may be targeted to the nucleus and shed light on factors that regulate this process.
Direct cardiac actions of erythropoietin (EPO): effects on cardiac contractility, BNP secretion and ischaemia/reperfusion injury
Authors: Piuhola Jarkko , Kerkelä Risto , Keenan Jacqueline I. , Hampton Mark B. , Richards A. Mark , Pemberton Chris J.
Published: January 2008

EPO (erythropoietin) has recently been shown to have protective actions upon the myocardium; however, the direct effects of EPO upon cardiac contractile and secretory functions are unknown and the signalling mechanisms are not well defined. In the present study, we provide the first evidence of direct cardiac contractile actions of EPO. In isolated perfused Sprague–Dawley rat hearts, a 30 min infusion of EPO significantly increased contractility in a dose-dependent fashion (maximal change 18±2% with 1 unit/ml EPO; P<0.005 compared with vehicle). Perfusate ET-1 (endothelin-1) increased transiently during EPO infusion, and the ETA/ETB antagonist bosentan abolished the inotropic response to EPO. BNP (B-type natriuretic peptide) secretion (28±8%; P<0.05) and nuclear transcription factor GATA-4 DNA-binding activity (51%; P<0.05) were both significantly increased by EPO and blocked by bosentan. In a model of global ischaemic injury, delivery of 1 unit/ml EPO during reperfusion significantly attenuated creatine kinase release (28±12%; P<0.05) and significantly improved contractile recovery (P<0.001), independent of ETA blockade. Apoptotic indices [assessed by TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling)/cleaved caspase-3-positive cells] were significantly decreased (P<0.01) by 1 unit/ml EPO during reperfusion alone, coincident with significantly increased phosphorylation of myocardial JAK2 (Janus kinase 2) and STAT3 (signal transducer and activator of transcription 3). Thus EPO directly enhances cardiac contractility and BNP secretion and alleviates ischemia/reperfusion injury via ET-1-dependent and -independent mechanisms respectively.
Erythropoietin in cardiovascular diseases: exploring new avenues
Authors: van der Meer Peter , van Veldhuisen Dirk J. , Januzzi James L.
Published: January 2008

Cardiovascular disease is an important burden in the Western world, with a prevalence that is increasing exponentially. Indeed, the lifetime risk of coronary artery disease at 40 years of age is 1 in 2 for men and 1 in 3 for women, and it is estimated that one-third of the population worldwide will die of cardiovascular disease, with a majority of these deaths related to MI (myocardial infarction) or the complications of MI. Recent research has suggested that EPO (erythropoietin), an endogenous erythropoietic hormone, may have pleiotropic effects well beyond the maintenance of red blood cells, and may have a cardiovascular role as well, including a potentially salutary effect on reperfusion injury. Although findings supportive of a role of EPO as a cardioprotective agent appear promising, the mechanisms behind the observed benefits remain elusive. In the present issue of Clinical Science, Piuhola and co-workers provide an interesting study that may shed light on the effects of EPO (and possibly related compounds) in the context of acute MI.
Marcus Wins Nobel Prize in Chemistry for Electron Transfer Theory
Authors: Levi Barbara Goss
Published: January 2008

Rudolf Marcus of Caltech was at a meeting of the Electrochemical Society in Toronto when he learned that the Royal Swedish Academy of Sciences had awarded him the 1992 Nobel Prize in Chemistry “for his contributions to the theory of electron transfer reactions in chemical systems.” The meeting participants were only too glad to raise their glasses to Marcus, for the fundamental theory he elucidated in the 1950s and 1960s underlies much of their work. Its applications include such diverse phenomena as photosynthesis, electrically conducting polymers, chemiluminescence and corrosion. As Marcus remarked to us, “the field continues to grow and grow.”
Video Tracks Motion of Magnetic Flux Vortices
Authors: Levi Barbara Goss
Published: January 2008

The photo Shown above is just one frame of a video that tracks the motion of magnetic flux vortices in a type-II superconductor as the temperature or magnetic field is varied. The video has received thumbs-up reviews from condensed matter viewers, many of whom have studied the behavior of such vortices, especially in the high temperature superconductors.
In High-TC Superconductors, is D-Wave the New Wave?
Authors: Levi Barbara Goss
Published: January 2008

Theorists trying to explain the mechanism for superconductivity in the copper oxide materials may not agree on much, but they all do believe it involves the coupling of electrons of opposite spin. Paths quickly diverge when it comes to the angular momentum of the pair. Is it a BCS-like swave (with l = 0)? A d-wave? Or something else? The answer is linked to the mechanism that couples the electrons. Although early experiments seemed consistent with an swave pairing, recent measurements suggest that the pairing state is at least not isotropic. If the experiments can further delineate the symmetry of the pairing state, they might help narrow the field of contending theories.
First of the Twin 10-Meter Keck Telescopes in Hawaii Starts Doing Astronomy
Authors: Schwarzschild Bertram
Published: January 2008

Near the summit of Mauna Kea, a long-dormant volcano on the island of Hawaii, the first of the two Keck Telescopes has begun doing astronomy, and construction of its identical twin, a stone's throw to the north, is well under way. The individual Keck telescopes, with effective primarymirror diameters of 10 meters, are by far the largest optical telescopes ever built. And together they will serve as an interferometer with a baseline of 95 meters.
Hulse and Taylor Win Nobel Prize for Discovering Binary Pulsar
Authors: Schwarzschild Bertram
Published: January 2008

In the summer of 1974, University of Massachusetts radioastronomer Joseph Taylor and his graduate student Russell Hulse discovered the first binary pulsar. This month in Stockholm, Hulse and Taylor are being honored with the 1993 Nobel Prize in Physics “for [this] discovery of a new type of pulsar, a discovery that has opened up new possibilities for the study of gravitation.” The importance of this new star for the investigation of gravity in the relativistic regime was clear almost from the start.
Studies on photodissociation dynamics of butadiene monoxide at 193nm
Authors: SenGupta Sumana , Indulkar Yogesh , Kumar Awadhesh , Naik Prakash D. , Bajaj Paramanand
Published: January 2008

Butadiene monoxide (BMO) undergoes the S0→S1 transition, involving the excitation of both π and n electrons to π* orbital, at 193nm. After relaxing to the ground electronic state via internal conversion, BMO molecules undergo intramolecular rearrangement and subsequently dissociate to form unexpected OH radicals, which were detected state selectively by laser-induced fluorescence technique, and the energy state distribution was measured. OH is produced vibrationally cold, OH(ν″=0,J″), with the rotational population characterized by a rotational temperature of 456±70K. The major portion (∼60%) of the available energy is partitioned into internal degrees of the photofragments, namely, vibration and rotation. A considerable portion (25%–35%) also goes to the relative translation of the products. The Λ doublet and spin-orbit ratios of OH were measured to be nearly unity, implying statistical distribution of these states and, hence, no preference for any of the Λ doublet (Λ+ and Λ−) and spin-orbit (Π3∕2 and Π1∕2) states. Formation time of the nascent OH radical was measured to be <100ns. Different products, such as crotonaldehyde and methyl vinyl ketone, were detected by gas chromatography as stable products of photodissociation. A reaction mechanism for the formation of all these photoproducts, transient and stable, is proposed. The multiple pathways by which these products can be formed have been theoretically optimized, and energies have been calculated. Absorption cross section of BMO at 193nm was measured, and quantum yield of OH generation channel was also determined.
A theoretical study of the cohesion of noble gases on graphite
Authors: Bichoutskaia Elena , Pyper Nicholas C.
Published: January 2008

The interactions of the noble gases with a graphene sheet are investigated theoretically. The short range repulsive interaction between the noble gas and each carbon atom is described using Hartree-Fock atomic densities and a local density functional theory with the exchange functional corrected for the finite range of the interaction by introducing a Rae-type correction depending on the effective number of electrons. The long range interactions are introduced as the sum of the Axilrod-Teller triple-dipole interaction plus the dipole-dipole and dipole-quadrupole dispersive attractions damped according to the theory of Jacobi and Csanak. The energy arising from the interactions between the permanent quadrupoles on the carbon atoms with the dipole they induce on the noble gas is negligible, being nonzero only on account of the atomistic structure of graphene. The mobile and delocalized nature of the graphene π electrons causes the effective number of electrons to be around 500 rather than that of 12 appropriate for a system of entirely localized interactions with individual carbon atoms. Inclusion of the Axilrod-Teller term is required to obtain reliable predictions for the binding energies and equilibrium geometries. Absorption of a noble gas atom is predicted to occur at the site above the center of a six membered ring although this is preferred over two other sites by only about 5meV. The methods presented for generating all the potentials can be applied to derive the interactions between any ion and carbon atom in the wall of a single-walled nanotube. Knowledge of these interactions is required to study the alkali halide nanocrystals encapsulated in single-walled carbon nanotubes of current interest.
Backbone and side-chain ordering in a small protein
Authors: Wei Yanjie , Nadler Walter , Hansmann Ulrich H. E.
Published: January 2008

We investigate the relation between backbone and side-chain ordering in a small protein. For this purpose, we have performed multicanonical simulations of the villin headpiece subdomain HP-36, an often used toy model in protein studies. Concepts of circular statistics are introduced to analyze side-chain fluctuations. In contrast to earlier studies on homopolypeptides [Wei et al., J. Phys. Chem. B 111, 4244 (2007)], we do not find collective effects leading to a separate transition. Rather, side-chain ordering is spread over a wide temperature range. Our results indicate a thermal hierarchy of ordering events, with side-chain ordering appearing at temperatures below the helix-coil transition but above the folding transition. We conjecture that this thermal hierarchy reflects an underlying temporal order, and that side-chain ordering facilitates the search for the correct backbone topology.
Very low transparency currents in double quantum well InGaAs semiconductor lasers with δ-doped resonant tunneling
Authors: Fekete D. , Yasin M. , Rudra A. , Kapon E.
Published: January 2008

It is demonstrated that n-type δ-doped resonant tunneling double quantum well (QW) lasers operated close to resonance exhibit an extremely low transparency current density of 14A∕cm2 per QW. This suggests that the threshold current is almost identical to that of the best reported single QW device without δ doping and yet the modal gain is almost double. The low transparency current density is mainly due to the enhanced coupling between the QWs.
Lattice-strain control of magnetoresistivity and magnetoresistive anisotropy induced by ion-beam milling in La0.65Ca0.35MnO3 films near the metal-insulator transition
Authors: Egilmez M. , Mansour A. I. , Saber M. M. , Chow K. H. , Jung J.
Published: January 2008

The lattice-disorder-induced changes in the magnetoresistivity and the magnetoresistive anisotropy of epitaxial ion-beam-milled La0.65Ca0.35MnO3 films were investigated. The results suggest that, for films less than 20nm thick, an increase of the magnetoresistivity and a reduction in the magnetoresistive anisotropy of the ion-beam-milled films are governed mostly by the point-defect-induced deformation, in contrast to the as-grown films where an increase of both the magnetoresistivity and the magnetoresistive anisotropy is determined by the epitaxial strain.
Hyper-high-sensitivity wash-free magnetoreduction assay on biomolecules using high-Tc superconducting quantum interference devices
Authors: Chieh J. J. , Yang S. Y. , Jian Z. F. , Wang W. C. , Horng H. E. , Yang H. C. , Hong Chin-Yih
Published: January 2008

In this work, we develop a platform for assaying biomolecules involving the measurement of alternating current (ac) magnetoreduction of magnetic reagent mixed with a detected sample. The magnetic reagent contains magnetic nanoparticles coated with a given kind of antibody, which associates with conjugated biomolecules. Then, the biomolecules can be quantitatively detected by measuring the ac magnetoreduction of magnetic reagent. To achieve hyper-high-sensitivity assay, a system utilizing a high-transition-temperature rf superconducting quantum interference device (SQUID) as a sensor to probe the magnetoreduction of reagent due to the association between biomolecules and magnetic nanoparticles. Examples to assay multiactive epitope, single-active epitope, and small molecules are given to demonstrate the validity of the assay platform, as well as the hyper-high sensitivity.
Electrically stable low voltage ZnO transistors with organic/inorganic nanohybrid dielectrics
Authors: Cha Sung Hoon , Oh Min Suk , Lee Kwang H. , Im Seongil , Lee Byoung H. , Sung Myung M.
Published: January 2008

We report on the fabrication of top-gate ZnO thin-film transistors (TFTs) with organic and inorganic nanohybrid dielectric layers that take superlattice form in their inside structure. The nanohybrid dielectrics were prepared by the alternate deposition of organic self-assembled monolayer and oxide monolayer on sputter-deposited ZnO channel. With a 22-nm-thin AlOx-based hybrid dielectric layer (∼130nFcm2), our ZnO TFT showed a field mobility of 0.36cm2Vs operating at 8V, while the mobility increased up to 0.66cm2Vs with a 22-nm-thin AlOx-based/TiOx-based/AlOx-based (5.5nm11nm5.5nm and ∼220nFcm2) triple hybrid layer under 2V operation. Since both ZnO-TFTs display little gate hysteresis, we conclude that our nanohybrid dielectric approach is promising to achieve a gate-stable low voltage top-gate ZnO-TFTs.
Accurate characterization of wafer bond toughness with the double cantilever specimen
Authors: Turner Kevin T. , Spearing S. Mark
Published: January 2008

The displacement loaded double cantilever test, also referred to as the “Maszara test” and the “crack opening method” by the wafer bonding community, is a common technique used to evaluate the interface toughness or surface energy of direct wafer bonds. While the specimen is widely used, there has been a persistent question as to the accuracy of the method since the actual specimen geometry differs from the ideal beam geometry assumed in the expression used for data reduction. The effect of conducting the test on whole wafer pairs, in which the arms of cantilevers are wide plates rather than slender beams, is examined in this work using finite element analysis. A model is developed to predict the equilibrium shape of the crack front and to develop a corrected expression for calculating interface toughness from crack length measurements obtained in tests conducted on whole wafer pairs. The finite element model, which is validated through comparison to experiments, demonstrates that using the traditional beam theory-based expressions for data reduction can lead to errors of up to 25%.
Spin energy enhanced by exchange interaction in a Rashba spintronic system in quantizing magnetic fields
Authors: Yang C. H. , Xu W.
Published: January 2008

Using the standard Hartree-Fock approximation on the basis of the random-phase approximation, we calculate the self-energy induced by exchange scattering due to electron-electron interaction in a spin-polarized two-dimensional electron gas (2DEG) system. Applying the exchange self-energy to a Green’s function approach, we examine how the exchange interaction affects the spin-splitting in a 2DEG with the Rashba spin-orbit interaction and Zeeman spin-splitting in the presence of quantizing magnetic fields. It is demonstrated that such a many-body interaction can lower the energy levels of the system and enhance significantly the spin-splitting around the Fermi level. We also find that the exchange-enhanced spin-splitting is achieved mainly via intra-Landau-level scattering channels and the spin energy oscillates with the magnetic fields.
Monte Carlo simulations of effective electrical conductivity in short-fiber composites
Authors: Zhang T. , Yi Y. B.
Published: January 2008

The transport properties of conductive fiber composites are strongly dependent on the interactions between the conductive contents and their overall distribution, which is associated with the percolation and conduction of the relevant fibrous network. In this study, the fibers are modeled as randomly distributed three-dimensional cylinders with each cylinder consisting of a nonconductive core covered by a permeable conductive layer. By discretizing the interconnected surfaces of individual fibers, a finite element method is applied to evaluate the equivalent electrical conductivity of the entire system. Monte Carlo simulations are performed to quantify the relationships between the conductivity and the following factors: (1) the volume fraction, (2) the solidity of fibers, (3) the thickness of the coating layer, (4) the fiber aspect ratio, and (5) the distribution of the fiber orientation angles. In comparison with the model consisting of solid fibers, it has been shown that the coated structure can attain much higher conductivity. The associated percolation properties are also estimated from the computed conductivity, and the results show good agreement with those reported in the literature. These findings can be used as guidance in designing the next generation of multiscale conductive composites.
Temperature measurement in microfluidic chips using photobleaching of a fluorescent thin film
Authors: Gui Lin , Ren Carolyn L.
Published: January 2008

A method for the whole chip temperature measurement is developed and presented here. This method includes two major contributions: (i) a specially developed measurement model illustrating the relationship between the photobleaching speed of a fluorescent dye and its temperature and (ii) an introduction of a thin polydimethylsiloxane film with rhodamine B homogeneously saturated aiming for significantly reducing fluorescent dyes’ absorption to and diffusion into polymer-made channel walls. The developed method is validated by comparing the experimentally measured temperature distribution in a microfluidic chip with the numerically predicted results.
Energy level alignment and injection barriers at spin injection contacts between La0.7Sr0.3MnO3 and organic semiconductors
Authors: Grobosch M. , Dörr K. , Gangineni R. B. , Knupfer M.
Published: January 2008

We have determined the energy level alignment at interfaces between La0.7Sr0.3MnO3 and two typical organic semiconductors, copper-phthalocyanine and α-sexithiophene. La0.7Sr0.3MnO3 thin films have been grown using pulsed laser deposition and subsequently ex situ cleaned before the organic materials have been deposited. This procedure is often applied in the fabrication of organic devices. We show that under these conditions the interfaces are free from chemical interaction and characterized by a short range interface dipole and large charge injection barriers.
In situ H2S passivation of In0.53Ga0.47As∕InP metal-oxide-semiconductor capacitors with atomic-layer deposited HfO2 gate dielectric
Authors: O’Connor E. , Long R. D. , Cherkaoui K. , Thomas K. K. , Chalvet F. , Povey I. M. , Pemble M. E. , Hurley P. K. , Brennan B. , Hughes G. , Newcomb S. B.
Published: January 2008

We have studied an in situ passivation of In0.53Ga0.47As, based on H2S exposure (50–350°C) following metal organic vapor phase epitaxy growth, prior to atomic layer deposition of HfO2 using Hf[N(CH3)2]4 and H2O precursors. X-ray photoelectron spectroscopy revealed the suppression of As oxide formation in air exposed InGaAs surfaces for all H2S exposure temperatures. Transmission electron microscopy analysis demonstrates a reduction of the interface oxide between the In0.53Ga0.47As epitaxial layer and the amorphous HfO2 resulting from the in situ H2S passivation. The capacitance-voltage and current-voltage behavior of Pd∕HfO2∕In0.53Ga0.47As∕InP structures demonstrates that the electrical characteristics of samples exposed to 50°C H2S at the end of the metal-organic vapor-phase epitaxy In0.53Ga0.47As growth are comparable to those obtained using an ex situ aqueous (NH4)2S passivation.
Enhanced annealing of the Z1∕2 defect in 4H–SiC epilayers
Authors: Storasta Liutauras , Tsuchida Hidekazu , Miyazawa Tetsuya , Ohshima Takeshi
Published: January 2008

The authors investigated the application of the carbon-implantation/annealing method for the annealing of the main lifetime limiting defect Z1∕2 in thick 4H–SiC epilayers. Examination of different implantation doses and annealing temperatures showed that finding the optimum conditions is crucial for obtaining thick layers with carrier trap concentration below 1011cm−3 in the whole 100μm epilayer. The carrier lifetime increased from less than 200ns to over 1μs at room temperature in the samples annealed with the carbon-implanted layer. The thick 4H–SiC epilayers after the application of the carbon-implantation/annealing were confirmed to be applicable for fabrication of high-voltage bipolar devices and resulted in improved conductivity modulation. Possible annealing mechanisms are discussed in detail making a comparison between annealing of as-grown material and irradiated material.
Analysis of mass transport mechanism in InGaN epitaxy on ridge shaped selective area growth GaN by metal organic chemical vapor deposition
Authors: Fang H. , Yang Z. J. , Wang Y. , Dai T. , Sang L. W. , Zhao L. B. , Yu T. J. , Zhang G. Y.
Published: January 2008

In this work, the evolution of the InGaN layer growth on the ridge shaped GaN was studied. A mass transport model was presented to simulate the epitaxy process of the InGaN layer. The model consisted of two consecutive components, gas-phase diffusion process and surface diffusion process. The mean lifetime of adatoms on epitaxial surface was associated with their reaction rate in this model. An InGaN layer on ridge shaped GaN, including (0002) and {112¯2} facets, was grown by metal organic chemical vapor deposition to confirm the mass transport model. Gradient indium content distribution and inhomogeneous thickness of the InGaN layer were observed. Simulation of the InGaN layer growth process was performed by finite difference method with the mass transport model. By analyzing the results from calculations and experiments, the origins of the InGaN layer characteristics were attributed to the two diffusion components in the growth process. Surface diffusion resulted in the inhomogeneous thickness and gas-phase diffusion chiefly led to the gradient indium content. In addition, the adatoms reaction rate on epitaxial surface determined their mean lifetime as speculated by the analysis. The demonstration of the growth process of InGaN layer offers valuable insight in obtaining high efficiency white light emitting diodes by selective area growth technology.
Atomic structures of supersaturated ZnO–Al2O3 solid solutions
Authors: Yoshioka Satoru , Oba Fumiyasu , Huang Rong , Tanaka Isao , Mizoguchi Teruyasu , Yamamoto Tomoyuki
Published: January 2008

Supersaturated ZnO–Al2O3 (>20at.% Al) thin films are grown by pulsed laser deposition technique on silica glass substrates at 600°C. They are characterized by combining x-ray diffraction, Al-K edge x-ray absorption near edge structures (XANESs), high resolution transmission electron microscope (TEM) imaging, TEM analysis, and a series of first principles calculations. The films are composed of textured wurtzite grains with c planes parallel to the substrate. The distance between c planes expands significantly when the Al concentration is greater than 10at.%. The expansion disappears after annealing the films at above 800°C. High density of dislocationlike defects is found in the as deposited film. Any segregation of Al cannot be detected either at the grain boundaries or inside the grains. The lattice expansion toward c axis and the experimental XANES can be satisfactorily explained by taking a hypothetical homologous model with the composition of (ZnO)3(Al2O3) as the local environment of Al in the supersaturated solid solution. Simplified substitutional models with Al at the Zn site in wurtzite ZnO cannot explain these experimental results. First principles calculations show that the homologous phase is energetically more favorable than the simplified substitutional models, although decomposition into ZnO and ZnAl2O4 is more favorable than the homologous phase. The local atomic structures of the supersaturated solid solution are therefore concluded to be analogous to the metastable homologous phase.
Delocalized image surface states in defect-free SiO2 hollow nanospheres
Authors: Movilla J. L. , Rajadell F. , Planelles J.
Published: January 2008

Delocalized image surface states in free-standing hollow silica nanospheres populated with one or two electrons or an exciton are theoretically predicted for a wide range of internal radii and shell thicknesses. The driving force building up these surface states is the image self-polarization potential originating from the dielectric mismatch between the nanoshell and the surrounding air. The surface states are localized in a spherical crown beyond the nanoshell border. The transition from volume to surface state will then have to overcome the spatial confining potential barrier of the nanoshell. Owing to the different spatial confining barriers of electrons and holes in the silica nanoshell, electron but no hole density can be concentrated in surface distributions. The self-polarization potential looks like a double well potential, each well located just beyond the nanoshell border, with the internal well deeper than the external one, so that an excess carrier is attracted more strongly by the inner interface. This leads the electron density of a surface state to be located mainly in the internal surface of the hollow nanosphere. The shorter the inner nanoshell radius is, the stronger the binding of the excess electron to the surface will be. The volume∕surface ground state phase diagrams of the one-electron, two-electron, and exciton systems have been calculated. All three diagrams are quite similar, thus revealing the monoelectronic character of the driving force for the transition from volume to surface states.
Interface mixing of Al∕Fe and Fe∕Al bilayer systems and the role of Ti as a stabilizing interlayer using Rutherford backscattering spectrometry and x-ray reflectometry
Authors: Priyantha W. , Chen H. , Kopczyk M. , Smith R. J. , Kayani A. , Comouth A. , Finsterbusch M. , Nachimuthu P. , McCready D.
Published: January 2008

Al ∕ Fe and Fe∕Al bilayer films with and without a Ti stabilizing interlayer at the interface have been grown on Si wafers using dc magnetron sputtering. X-ray reflectometry and Rutherford backscattering spectrometry were used to probe individual layer thicknesses and intermixing lengths. It is observed that the intermixing length is always higher when the Fe layer is on top of the Al layer. The samples with the Ti stabilizing layer, particularly when the Al layer is on top of the Fe, show that the Ti layer promotes the formation of abrupt interfaces.
Direct determination of Burgers vector sense and magnitude of elementary dislocations by synchrotron white x-ray topography
Authors: Nakamura Daisuke , Yamaguchi Satoshi , Hirose Yoshiharu , Tani Toshihiko , Takatori Kazumasa , Kajiwara Kentarou , Kimoto Tsunenobu
Published: January 2008

The x-ray topography by using highly coherent beam obtained at third-generation synchrotron facilities can provide higher spatial resolution and higher lattice-distortion sensitivity than those by former-generation facilities. Here, we report the direct determination of the Burgers vector senses and magnitudes of elementary dislocations in a high-quality silicon carbide single crystal using white x-ray section topography with a long sample-to-film distance. Our data strongly indicate that there are very weak but extraordinarily long-range elastic interactions between elementary screw dislocations. Those interactions govern dislocation-propagation behavior and the distribution of dislocations. Moreover, we found that white x-ray projection topography with a long sample-to-film distance can also be a powerful tool to effectively examine the detailed structure of elementary dislocations in single crystals.
Raman study on the effects of sintering temperature on the Jc(H) performance of MgB2 superconductor
Authors: Li W. X. , Chen R. H. , Li Y. , Zhu M. Y. , Jin H. M. , Zeng R. , Dou S. X. , Lu B.
Published: January 2008

The influence of sintering temperature on the critical transition temperature Tc and critical current density Jc for the MgB2 superconductor was investigated systematically with the observation of Raman scattering measurement and flux pinning force Fp analysis. The enhanced E2g mode in Raman spectra with increasing in situ sintering temperature shows gradual strengthening of the electron-phonon coupling in MgB2, which means that the crystals become more harmonic after higher temperature sintering. However, the crystal harmonicity is degraded for samples sintered at even higher temperature due to Mg deficiency. A possible explanation for the Jc(H) performance, which is in accordance with the Raman spectroscopy observation and Fp analysis, is the cooperation between the electron-phonon coupling in the E2g mode and the flux pinning centers, mainly originating from the lattice distortion due to the different sintering temperatures.
Near colorless all-solid-state switchable mirror based on magnesium-titanium thin film
Authors: Tajima Kazuki , Yamada Yasusei , Bao Shanhu , Okada Masahisa , Yoshimura Kazuki
Published: January 2008

Magnesium-titanium (Mg–Ti) thin film was applied to all-solid-state switchable mirror by magnetron sputtering. Mg–Ti thin film works as an anodic electrochromic material of optical switching layer of the device. For clear transparency and durability of the device, a composition of Mg–Ti thin film was optimized. Though a maximum transmittance at transparent state of the device decreased with increasing titanium content in the film, the device showed fast recovery speed to reflective state. The transmittance at a wavelength of 670nm of the device with Mg0.88Ti0.12 was reached from 0.1% (reflective state) to 36% (transparent state) within 15s by applying voltage. The reflectance was also reduced from 57% to 20% within 10s. The transparent state of the device with Mg0.88Ti0.12 thin film showed almost colorless state with a chromaticity coordinates of x=0.335 and y=0.336. In the viewpoint of transmittance and durability, the authors found that the device with Mg0.88Ti0.12 thin film was the most suitable for practical application.
Complex permittivity of a biased superlattice
Authors: Hernández-Cabrera A. , Aceituno P. , Vasko F. T.
Published: January 2008

We study the intersubband response in a superlattice subjected to a homogeneous electric field (a biased superlattice with equipopulated levels) within the tight-binding approximation. We consider the interplay between homogeneous and inhomogeneous mechanisms of broadening. We calculate the complex dielectric permittivity beyond the Born approximation for a wide spectral region, finding a low-frequency enhancement of the response. A detectable gain below the resonance is obtained for the low-doped GaAs-based biased superlattice in the terahertz spectral region. Conditions of the stimulated emission regime are discussed for metallic and dielectric waveguide structures. It is described that the appearance of a localized terahertz mode is described when a biased superlattice is placed at a vacuum-dielectric interface.
High-efficiency endothermic energy transfer in polymeric light-emitting devices based on cyclometalated Ir complexes
Authors: Liu Hong-Mei , Wang Peng-Fei , He Jian , Zheng Caijun , Zhang Xiao-Hong , Chew Siew-Ling , Lee Chun-Sing , Chang Jack , Lee Shuit-Tong
Published: January 2008

We report polymeric light-emitting diodes (PLEDs) made from pinene-substituted iridium(III) phosphorescent dopants: tris(5-(4-difluoro phenyl)-10,10-dimethyl-4-aza-tricycloundeca-2,4,6-triene) iridium (III) [Ir(F-pppy)3] and tris(5-(2,4-difluorophenyl)-10,10-dimethyl-4-aza-tricycloundeca-2,4,6-triene) iridium (III) [Ir(F2-pppy)3]. The pinene substitution introduces steric hindrance to molecular structure of the dopant that reduces triplet-triplet annihilation between dopants and consequently enhances device performance. Via endothermic energy transfer from poly(vinylcarbazole) to Ir(F-pppy)3 and Ir(F2-pppy)3, a peak electroluminescent efficiency of 32.8cd∕A or 12.3cd∕A at 12wt% Ir(F-pppy)3 or 15wt% Ir(F2-pppy)3 doped and solution-processed PLEDs have been obtained. These values represent significant improvement in performance over previously reported endothermic energy-transfer based electrophosphorescent devices.
Jump-in induced plastic yield onset of approaching microcontacts in the presence of adhesion
Authors: Kadin Y. , Kligerman Y. , Etsion I.
Published: January 2008

Approach between two deformable microbodies in the presence of adhesion is sometimes accompanied by discontinuous change of the surface profile at the narrow region near their summits (jump-in phenomenon). Previous studies of adhesive spherical contact showed that neck formation during jump-in always involves onset of local plastic yield near the edge of the contact zone. The current paper reveals that pure elastic jump-in is also feasible. The solution is based on a Lennard-Jones potential in combination with the von Mises yield criterion. The theoretical strength rather than the engineering yield strength of the material is used and the sufficient condition for jump-in induced onset of plastic yield under this extreme strength is discussed.
Formation of NaNbO3-based conductive crystal lines on glass surface by Yb fiber laser irradiation
Authors: Pang Maolin , Suzuki Ryota , Saito Makoto , Machida Ken-ichi , Hanzawa Hiromasa , Nojiri Yoshihiro , Tanase Shigeo
Published: January 2008

Na Nb O 3 -based conductive crystal lines composed of closely compacted fine particles were patterned on the 24.7Na2O–18.8Nb2O5–5Al2O3–2NiO–49.5SiO2 (mol %) glass surface by a continuous wave Yb fiber laser irradiation (λ=1078nm) using the nickel atom heat processing method. Nickel (II) ion was proved to be an efficient optical active absorbent for Yb fiber laser irradiation. Homogeneous and smooth crystal lines with a uniform width of 40μm were obtained with a laser power of 1.1W. X-ray diffraction, micro-Raman spectra, optical microscope, and impedance measurements were used to characterize the laser patterned glass. The conductivity value of the laser patterned glass was nearly two times as large as that of the glass matrix due to the formation of NaNbO3-based conductive crystal lines by Yb laser irradiation.
Measurement of semiconductor waveguide optical properties in the midinfrared wavelength range
Authors: Peter E. , Laurent S. , Sirtori C. , Carras M. , Robbo J. A. , Garcia M. , Marcadet X.
Published: January 2008

We propose a technique based on Fabry-Pérot fringes to analyze, in a broad wavelength range, the waveguide properties of semiconductor lasers in the midinfrared spectrum. This technique has been applied to strain-balanced Ga0.32In0.68As∕Al0.64In0.36As quantum cascade lasers, with a double phonon active region, in order to determine propagation losses and the effective index between 2.5 and 8μm wavelength. These results are in good agreement with the values obtained using another method.
Faceting of a quasi-two-dimensional GaAs crystal in nanoscale patterned growth
Authors: Lee S. C. , Huffaker D. L. , Brueck S. R. J.
Published: January 2008

The faceting of a quasi-two-dimensional nanoscale crystal (quasi-2D nanocrystal) grown by metal-organic vapor phase epitaxy is reported. Homoepitaxial selective growth is performed on a 200nm wide, [110]-directed stripe opening fabricated in a 30nm thick SiO2 film atop a GaAs(001) substrate. In the cross section perpendicular to the stripe opening, a selectively grown epilayer is regarded as a quasi-2D nanocrystal, which is close to a hexagonal shape symmetrically surrounded with (111)B-, (110)- and (111)A-type facets from the top as growth proceeds both vertically and laterally. The resulting faceting is interpreted on the basis of equilibrium crystal shape (ECS). The comparison of the observed crystal shape with theoretical modeling enables the measurement of the relative surface energies of the low index orientations. The ECS of a GaAs 2D crystal under the given growth conditions is proposed.
Self-sustained output power pulsations in InGaAs quantum dot ridge-waveguide lasers
Authors: Mokkapati S. , Tan H. H. , Jagadish C. , Buda M.
Published: January 2008

Self-sustained pulsations in the output power of metal-organic chemical vapor deposition grown ridge-waveguide lasers with InGaAs quantum dot active region are reported. The characteristics of the output power pulsations (range, frequency, and modulation depth) are presented. The origin of the pulsations is explained in terms of the properties of the quantum dot active region.
In situ synthesizing molecular materials between coplanar gold microgap electrodes for the fabrication of molecular devices
Authors: Liu Yaling , Ji Zhuoyu , Li Hongxiang , Hu Wenping , Zhu Daoben
Published: January 2008

In this paper, a way to integrate the synthesis of molecular materials and the fabrication of molecular devices was demonstrated by using copper tetracyanoquinodimethane (CuTCNQ). Coplanar gold microgap electrodes were prepared by photolithography or electrobeam lithography. CuTCNQ was in situ synthesized between Au gap electrodes by electrochemical deposition for the fabrication of molecular devices.
Piezoelectric nanogenerator using CdS nanowires
Authors: Lin Yi-Feng , Song Jinhui , Ding Yong , Lu Shih-Yuan , Wang Zhong Lin
Published: January 2008

Vertically grown cadmium sulfide (CdS) nanowire (NW) arrays were prepared using two different processes: hydrothermal and physical vapor deposition (PVD). The NWs obtained from the hydrothermal process were composed of alternating hexagonal wurtzite (WZ) and cubic zinc blende (ZB) phases with growth direction along WZ ⟨0001⟩ and ZB [111]. The NWs produced by PVD process are single crystalline WZ phase with growth direction along ⟨0001⟩. These vertically grown CdS NW arrays have been used to converting mechanical energy into electricity following a developed procedure [Z. L. Wang and J. Song Science 312, 242 (2006)]. The basic principle of the CdS NW nanogenerator relies on the coupled piezoelectric and semiconducting properties of CdS, and the data fully support the mechanism previously proposed for ZnO NW nanogenerators and nanopiezotronics.
“Zigzag” C60 chain arrays
Authors: Huang Han , Chen Wei , Chen Lan , Zhang Hong Liang , Wang Xue Sen , Bao Shi Ning , Wee Andrew Thye Shen
Published: January 2008

We present a low-temperature scanning tunneling microscopy investigation revealing the formation of a long range ordered α-sexithiophene (6T) monolayer nanostripe array on highly ordered pyrolytic graphite, with thiophene ring units oriented parallel to the surface. The 6T monolayer nanostripe is an effective molecular nanotemplate for the assembly of an ordered “zigzag” C60 chain array, accompanied by a slight structural modification of the underlying 6T nanostripes due to donor-acceptor intermolecular interactions between 6T and C60 molecules.
Photoluminescence from a single InGaAs epitaxial quantum rod
Authors: Sęk G. , Podemski P. , Misiewicz J. , Li L. H. , Fiore A. , Patriarche G.
Published: January 2008

Microphotoluminescence (μ-PL) experiment has been performed on a structure with InGaAs/GaAs epitaxial quantum rods (quantum dots with the aspect ratio as high as 4.1) grown by depositing short-period InAs/GaAs superlattice by molecular beam epitaxy on GaAs substrate. The exciton and biexciton emission from a single quantum rod has been detected via the excitation power dependence of the μ-PL spectra. The origin of the single rod lines has been confirmed by a rate equation model. For a number of quantum rods within the investigated ensemble, the biexciton binding energy has been determined to be in the range of 1.0–2.2meV.
Cluster related hole traps with enhanced-field-emission—the source for long term annealing in hadron irradiated Si diodes
Authors: Pintilie I. , Fretwurst E. , Lindström G.
Published: January 2008

Cluster related defects were investigated by the thermally stimulated current (TSC) method in neutron irradiated n-type Si diodes during 80°C annealing. Three hole traps labeled H (116K), H (140K), and H (152K) proved to have an electric-field-enhanced emission characteristic of Coulombic wells. Their zero field emission rates were deduced describing the TSC peaks with the three-dimensional Poole-Frenkel formalism when accounting for the electric field distribution. As acceptors in the lower half of the gap, these centers have a direct impact on the effective doping of the n-type diodes. They are revealed as causing the long term annealing effects.
Time-resolved photoluminescence of n-doped SrTiO3
Authors: Rubano A. , Paparo D. , Radović M. , Sambri A. , Granozio F. Miletto , Scotti di Uccio U. , Marrucci L.
Published: January 2008

Following the recent surge of interest in n-doped strontium titanate as a possible blue light emitter, a time-resolved photoluminescence analysis was performed on nominally pure, Nb-doped and oxygen-deficient single-crystal SrTiO3 samples. The doping effects on both the electronic states involved in the transition and the decay mechanism are respectively analyzed by comparing the spectral and dynamic features and the yields of the emission. Our time-resolved analysis, besides shedding some light on the basic recombination mechanisms acting in these materials, sets the intrinsic bandwidth limit of the proposed blue light emitting optoelectronic devices made of Ti-based perovskites heterostructures in the gigahertz range.
Resonantly photopumped lasing and its switching behavior in a photonic crystal nanolaser
Authors: Nozaki Kengo , Kita Shota , Arita Yoshiki , Baba Toshihiko
Published: January 2008

A GaInAsP photonic crystal nanolaser was operated by resonant optical pumping in which the effective cavity area was selectively excited. The laser mode intensity was markedly enhanced when the pump wavelength was tuned to a higher-order cavity mode, and room-temperature continuous-wave lasing was obtained in the fundamental mode. Furthermore, the switching behavior due to a modal wavelength shift was clearly observed, suggesting the possibility of bistable operation, and so on.
Bandgap and effective mass of epitaxial cadmium oxide
Authors: Jefferson P. H. , Hatfield S. A. , Veal T. D. , King P. D. C. , McConville C. F. , Zúñiga–Pérez J. , Muñoz–Sanjosé V.
Published: January 2008

The bandgap and band-edge effective mass of single crystal cadmium oxide, epitaxially grown by metal-organic vapor-phase epitaxy, are determined from infrared reflectivity, ultraviolet/visible absorption, and Hall effect measurements. Analysis and simulation of the optical data, including effects of band nonparabolicity, Moss-Burstein band filling and bandgap renormalization, reveal room temperature bandgap and band-edge effective mass values of 2.16±0.02eV and 0.21±0.01m0 respectively.