bluuebunny/crossref_metadata_2025 huggingface dataset:
Charge separation and transport behavior of a two-dimensional charge sheet at organic donor-acceptor heterointerfaces
Authors: Sakanoue Tomo , Irie Toru , Adachi Chihaya
Published: June 2009

Charge separation and transport behavior were investigated at an organic heterolayered interface consisting of a 4,4′,4″-tris[3-methylphenyl(phenyl)amino] triphenylamine (m-MTDATA) organic donor and a hexadecafluoro-copper-phthalocyanine (F16CuPc) organic acceptor. A two-dimensional charge sheet of electron-hole pairs was induced due to the formation of charge-transfer complexes at the heterointerface. The induced charges could be separated by application of an electric field perpendicular to the heterointerface. The charge-separation behavior was independent of the work function of the contact electrodes but was strongly dependent on the energy-level alignment between the highest occupied molecular orbital of the donor molecules and the lowest unoccupied molecular orbital of the acceptor molecules. This enabled the preparation of an organic light-emitting diode without injecting holes from the anode. The charge-transport behavior along the heterointerface was also investigated by fabricating laterally arranged contact electrodes. The F16CuPc/m-MTDATA heterointerface exhibited high conductivity of 0.001 S/cm, which is seven orders of magnitude higher than that of a single-layer F16CuPc or m-MTDATA film. In situ electrical measurements during formation of the heterointerface enabled the effective thickness of the charge sheet to be determined as being accumulated within 2–3 nm, which corresponds to the bilayer of both F16CuPc and m-MTDATA.
Theoretical and experimental approach to characteristic magnetic measurement data of polymer bonded soft magnetic composites
Authors: Anhalt M. , Weidenfeller B.
Published: June 2009

Soft magnetic composites consisting of an organic binder and FeCoV particles have been produced and examined afterward regarding the dependence of magnetic field H at polarization J on filler content C. In general, the applied magnetic field to achieve a certain value of polarization is proportional to the inverse filler content, following H∼1∕C, and the polarization is directly proportional to the filler content, following J∼C. With use of the evaluated material data and the inner demagnetization factor Ni a model for calculating the permeability of soft magnetic composites has been derived. As input values the permeability of the soft magnetic particles μ, the filler content C, and the geometric demagnetization factor of the particles Np are used. The elaborated approach shows an excellent agreement with experimental permeability data of the FeCoV composites.
Magnetic properties of Al-doped Zn0.95Co0.05O films: Experiment and theory
Authors: Belghazi Y. , Stoeffler D. , Colis S. , Schmerber G. , Ulhaq-Bouillet C. , Rehspringer J. L. , Berrada A. , Aubriet H. , Petersen J. , Becker C. , Ruch D. , Dinia A.
Published: June 2009

Al-doped ZnCoO films were grown by sol-gel process onto SiO2 and Si(100) substrates. Structural analysis shows that all samples have the hexagonal würtzite structure with a slight preferential orientation along the c-axis. The insertion of Al and Co into the ZnO matrix has been experimentally evidenced by UV-visible spectroscopy and transmission electron microscopy. This is further supported by x-ray photoelectron spectroscopy which indicated that all Co is under ionic form and that the samples contain no metallic clusters. The creation of free carriers by Al doping was confirmed by Hall effect and resistance measurements. Although a weak ferromagnetism is observed in all films, no clear influence of Al doping on the magnetic properties is evidenced which is in agreement with electronic structure calculations. The calculations show clearly that there is almost no overlap between the Al and the Co states, suggesting no change in the magnetic properties of ZnCoO with the Al doping. The only major role of Al is to change the conduction type of ZnCoO from p to n type.
Counting statistics of tunneling through a single molecule: Effect of distortion and displacement of vibrational potential surface
Authors: Dong Bing , Fan H. Y. , Lei X. L. , Horing N. J. M.
Published: June 2009

We analyze the effects of a distortion of the nuclear potential of a molecular quantum dot (QD) as well as a shift in its equilibrium position on nonequilibrium-vibration-assisted tunneling through the QD with a single level (εd) coupled to the vibrational mode. For this purpose, we derive an explicit analytical expression for the Franck–Condon (FC) factor for a displaced-distorted oscillator surface of the molecule and establish rate equations in the joint electron-phonon representation to examine the current-voltage characteristics and zero-frequency shot noise and skewness as well. Our numerical analysis shows that the distortion has two important effects. The first one is that it breaks the symmetry between the excitation spectra of the charge states, leading to asymmetric tunneling properties with respect to εd>0 and εd<0. Second, distortion (frequency change in the oscillator) significantly changes the voltage-activated cascaded transition mechanism and consequently gives rise to a different nonequilibrium vibrational distribution from that of the case without distortion. Taken in conjunction with strongly modified FC factors due to distortion, this results in some new transport features: the appearance of strong negative differential conductance even for a single-level QD with symmetric tunnel couplings, a giant Fano factor even for a molecule with an extremely weak electron-phonon interaction, and enhanced skewness that can have a large negative value under certain conditions.
Transport properties of MgO magnetic tunnel junctions
Authors: Dimitrov D. V. , Gao Zheng , Wang Xiaobin , Jung Wonjoon , Lou Xiaohua , Heinonen Olle
Published: June 2009

We have studied transport properties of nanopillars with high-quality MgO tunnel barriers and with a range of MgO barrier thickness, and compared the bias-voltage dependence of tunneling magnetoresistance, differential conductivity, and resistance in parallel and antiparallel states with theoretical models. The differential conductance in the antiparallel state suggests that the dominant scattering mechanism for this state is inelastic scattering that mixes propagating Δ5 states in the electrode with evanescent Δ1 states in the MgO barrier. In addition, we observed in large populations of parts with both low- and high-voltage bias transport anomalies in the parallel state. Finally, in the junctions studied here, we observed a much weaker decrease in the tunneling magnetoresistance with bias voltage than reported in previous studies.
Influence of lattice parameters on the resonance frequencies of a cut-wire-pair medium
Authors: Lam V. D. , Tung N. T. , Cho M. H. , Park J. W. , Rhee J. Y. , Lee Y. P.
Published: June 2009

We studied both theoretically and experimentally the influence of the lattice constant on the resonance frequencies of cut-wire-pair structures, which are essential components in assembling left-handed materials. These structures were designed and fabricated, and the transmission spectra were measured in the microwave-frequency regime. Numerical simulation was performed using the transfer-matrix method. All the numerical results were in good agreement with the experimental data. It was found that the lattice parameters of the cut-wire-pair structure provide sensitive effects on the electric resonance, especially, in the propagation k and the electric field E directions, while the magnetic resonance frequency is nearly unchanged, except for its bandwidth and depth. In addition, we also studied the effect of dielectric layer thickness on the resonance frequencies of the cut-wire-pair structure. These sensitive changes in the electric resonance might have remarkable effects on the effective plasma frequency and therefore on the left-handed behavior of combined structures consisting of cut-wire pairs and continuous wires.
Sensing of atomized liquids through field effects of polarization and ionization induced by nanostructures
Authors: Hou Zhongyu , Cai Bingchu , Liu Hai
Published: June 2009

The mechanism and instrumentation of an atomized liquid sensing system is presented, characterizing the dynamic polarization and ionization processes of liquid droplets in an electric field converged by one dimensional nanostructures. The microarchitecture implementing the mechanism is realized by microlithography technology. It is shown that the current amplitude is a function of both droplets’ flow rate and its chemistry; thus, one of them can be differentiated when the other is a constant. Further, the current-time spectrum responding to the vaporization and diffusion processes can enhance the differentiability. The methodology can be applied to atomized liquid sensing or liquid chemistry differentiation.
Theory of long-lived nuclear spin states in solution nuclear magnetic resonance. II. Singlet spin locking
Authors: Pileio Giuseppe , Levitt Malcolm H.
Published: June 2009

In a previous paper [M. Carravetta and M. H. Levitt, J. Chem. Phys. 122, 214505 (2005)], we presented the theory of long-lived nuclear spin singlet states in low magnetic field. In this paper, we consider the spin locking of long-lived singlet states in high magnetic field by the application of resonant radio frequency irradiation. We present theoretical results for unmodulated irradiation, including approximate analytical expressions for the singlet decay rate constants. We show the results of numerical simulations, which indicate that modulated radio frequency fields may be used to achieve broadband spin locking of singlet states but only in the case of a small difference in Larmor frequencies between the members of the spin pair.
Orientation dynamics in multiwalled carbon nanotube dispersions under shear flow
Authors: Pujari Saswati , Rahatekar Sameer S. , Gilman Jeffrey W. , Koziol Krzysztof K. , Windle Alan H. , Burghardt Wesley R.
Published: June 2009

We report studies of the orientation state of multiwalled carbon nanotubes (MWNTs) dispersions in steady and transient shear flows. Uncured epoxy was used as a viscous Newtonian suspending medium and samples were prepared from “aligned” MWNTs using methods previously reported [S. S. Rahatekar et al., J. Rheol. 50, 599 (2006)]. Orientation measurements were performed in both the flow-gradient (1-2) and flow-vorticity (1-3) plane of simple shear flow using in situ x-ray scattering techniques. Steady state measurements in the 1-2 plane indicate that the MWNT orientation is shear rate dependent, with the MWNTs orienting closer to the flow direction at higher shear rates. During steady shear, anisotropy was measured to be higher in the 1-2 plane than in the 1-3 plane, demonstrating that the nanotube orientation state is not unaxially symmetric in shear. It is hypothesized that the steady state MWNT orientation is governed primarily by a rate-dependent state of nanotube aggregation/disaggregation, which was separately characterized by optical microscopy of the same samples under shear. High flux synchrotron radiation allowed for time-resolved structural studies in transient flows. A partial relaxation of flow-induced anisotropy was observed following flow cessation, despite the very small rotational diffusivity estimated for these nanotubes. Long transients are observed in step-down experiments, as the orientation state changes in response to the slow tube aggregation process.
Observation of rarefactive ion acoustic solitary waves in dusty plasma containing negative ions
Authors: Adhikary Nirab Chandra , Deka Manoj Kumar , Bailung Heremba
Published: June 2009

The propagation characteristics of rarefactive ion acoustic solitary waves in dusty plasma containing negative ions has been observed experimentally. It was found that, in the present dusty plasma condition, applied rarefactive (negative) voltage pulse cannot break into rarefactive solitons until a sufficient concentration of negative ions is introduced into the dusty plasma. The velocity of rarefactive solitary wave in multicomponent plasma with negative ions is greater than that in the presence of negatively charged dust. The velocity and width of the solitary waves are measured and compared with numerical results of the Korteweg–de Vries Burgers equation.
In the eye of the beholder: Inhomogeneous distribution of high-resolution shapes within the random-walk ensemble
Authors: Müller Christian L. , Sbalzarini Ivo F. , van Gunsteren Wilfred F. , Žagrović Bojan , Hünenberger Philippe H.
Published: June 2009

The concept of high-resolution shapes (also referred to as folds or states, depending on the context) of a polymer chain plays a central role in polymer science, structural biology, bioinformatics, and biopolymer dynamics. However, although the idea of shape is intuitively very useful, there is no unambiguous mathematical definition for this concept. In the present work, the distributions of high-resolution shapes within the ideal random-walk ensembles with N=3,…,6 beads (or up to N=10 for some properties) are investigated using a systematic (grid-based) approach based on a simple working definition of shapes relying on the root-mean-square atomic positional deviation as a metric (i.e., to define the distance between pairs of structures) and a single cutoff criterion for the shape assignment. Although the random-walk ensemble appears to represent the paramount of homogeneity and randomness, this analysis reveals that the distribution of shapes within this ensemble, i.e., in the total absence of interatomic interactions characteristic of a specific polymer (beyond the generic connectivity constraint), is significantly inhomogeneous. In particular, a specific (densest) shape occurs with a local probability that is 1.28, 1.79, 2.94, and 10.05 times (N=3,…,6) higher than the corresponding average over all possible shapes (these results can tentatively be extrapolated to a factor as large as about 1028 for N=100). The qualitative results of this analysis lead to a few rather counterintuitive suggestions, namely, that, e.g., (i) a fold classification analysis applied to the random-walk ensemble would lead to the identification of random-walk “folds;” (ii) a clustering analysis applied to the random-walk ensemble would also lead to the identification random-walk “states” and associated relative free energies; and (iii) a random-walk ensemble of polymer chains could lead to well-defined diffraction patterns in hypothetical fiber or crystal diffraction experiments. The inhomogeneous nature of the shape probability distribution identified here for random walks may represent a significant underlying baseline effect in the analysis of real polymer chain ensembles (i.e., in the presence of specific interatomic interactions). As a consequence, a part of what is called a polymer shape may actually reside just “in the eye of the beholder” rather than in the nature of the interactions between the constituting atoms, and the corresponding observation-related bias should be taken into account when drawing conclusions from shape analyses as applied to real structural ensembles.
Sphere-forming diblock copolymers in slit confinement: A dynamic density functional theory study
Authors: Tan Hongge , Song Qinggong , Niu Xiaohui , Wang Ziyu , Gao Wenfang , Yan Dadong
Published: June 2009

With mean-field dynamic density functional theory, we study the morphologies of sphere-forming diblock copolymers confined between two homogeneous surfaces. The effects of the film thickness and the surface field strength on the phase behavior of sphere-forming copolymer film are investigated. The morphologies deviating from the bulk sphere-forming structure are revealed, including cylinders oriented perpendicular to the surface, cylinders oriented parallel to the surface, perforated lamellae and lamellae by varying the film thickness, and surface field strength. We also construct the phase diagram of surface reconstruction, in which some interesting phase transitions are presented. Besides, we compare the present phase diagram with the relevant phase diagram of cylinder-forming block copolymer film.
Corrected direct force balance method for atomic force microscopy lateral force calibration
Authors: Asay David B. , Hsiao Erik , Kim Seong H.
Published: June 2009

This paper reports corrections and improvements of the previously reported direct force balance method (DFBM) developed for lateral calibration of atomic force microscopy. The DFBM method employs the lateral force signal obtained during a force-distance measurement on a sloped surface and relates this signal to the applied load and the slope of the surface to determine the lateral calibration factor. In the original publication [Rev. Sci. Instrum. 77, 043903 (2006)], the tip-substrate contact was assumed to be pinned at the point of contact, i.e., no slip along the slope. In control experiments, the tip was found to slide along the slope during force-distance curve measurement. This paper presents the correct force balance for lateral force calibration.
Thin film nanocalorimeter for heat capacity measurements of 30 nm films
Authors: Queen D. R. , Hellman F.
Published: June 2009

A silicon nitride membrane-based nanocalorimeter is described for measuring the heat capacity of 30 nm films from 300 mK to 800 K and in high magnetic fields with absolute accuracy ∼2%. The addenda heat capacity of the nanocalorimeter is less than 2×10−7 J/K at room temperature and 2×10−10 J/K at 2.3 K. This is more than ten times smaller than any existing calorimeter suitable for measuring thin films over this wide temperature range. The heat capacities of thin Cu and Au films are reported and agree with bulk values. The thermal conductivity of the thin low stress silicon nitride is substantially smaller than thicker membranes while the specific heat is enhanced below 20 K. Design of the nanocalorimeter will be discussed along with fabrication details and calibration results.
A search for lowest energy structures of ZnS quantum dots: Genetic algorithm tight-binding study
Authors: Pal Sougata , Sharma Rahul , Goswami Biplab , Sarkar Pranab , Bhattacharyya S. P.
Published: June 2009

The lowest energy structures of ZnS quantum dots of different sizes have been determined by an unbiased search using genetic algorithm (GA) coupled with the density-functional tight-binding method. The GA search converges to a rather new ringlike configurations of ZnS quantum dots. We have studied the structural, electronic, and optical properties of these ringlike clusters and compared these properties with those of other reported structures of ZnS quantum dots, namely, hollow, zinc-blende, wurtzite, and rocksalt structures.
Method of determining the exciton diffusion length using optical interference effect in Schottky diode
Authors: Banerjee Suman , Parhi Anukul Prasad , Iyer S. Sundar Kumar , Kumar Satyendra
Published: June 2009

A general model of calculating the short circuit photocurrent and exciton diffusion length from Schottky diode is given here using optical interference method. This method of estimating the exciton diffusion length can be very useful for those materials that do not give photoluminescence. It also serves as an accurate and simple method to determine the exciton diffusion length, which is an important material property to design devices such as organic solar cells. Our model is verified with the spectral response of indium tin oxide (ITO)/copper phthalocyanine (CuPc)/Al and ITO/CuPc/Ag Schottky diodes.
Time-resolved characterization of external-cavity quantum-cascade lasers
Authors: Hinkov Borislav , Yang Quankui , Fuchs Frank , Bronner Wolfgang , Köhler Klaus , Wagner Joachim
Published: June 2009

We report on the temporal and spectral evolution of the lasing spectrum of an external-cavity quantum-cascade (QC) laser operated in pulsed mode. Time-resolved lasing spectra, recorded on nanosecond time scale, revealed that after turn-on of the 100 ns current pulse multiple-mode lasing starts at the gain maximum of the QC laser controlled by the cavity formed by the chip facets. Depending on the spectral tuning after a time delay of 15–35 ns, the QC laser couples to the external cavity as seen from a change in lasing wavelength to that defined by the external grating as wavelength selective element.
Static and dynamic analysis of a four-tube piezoelectric actuator
Authors: Ma Yuting , Feng Zhihua , Pan Chengliang , Kong Fanrang
Published: June 2009

Piezoelectric tubes with film electrodes on their outer and inner surfaces can be used to compose multitube actuators. The actuator of four piezoelectric tubes can substitute the traditional single-tube actuator with quartered electrodes which has been widely used in scanning probe microscopy and piezoelectric motors. In this article, the static deflection, static bending moment, resonant frequency, and dynamic deflection of the four-tube actuator are all studied in detail. The comparison between this actuator and the traditional single-tube actuator is also done and the results show that the four-tube actuator has better performances under certain conditions. The experiment results of a prototype actuator testified the validation of the analysis.
Growth rate enhancement by nitrogen in diamond chemical vapor deposition—a catalytic effect
Authors: Dunst S. , Sternschulte H. , Schreck M.
Published: June 2009

The diamond growth rate enhancement factor A([N2],[CH4]) of nitrogen has been measured in situ by laser reflection interferometry using thin reflecting iridium interlayers on on-axis and off-axis single crystals. “A” shows a characteristic linear decrease with the methyl radical concentration in the gas phase. The resulting local maximum in the growth rate curve yields conditions for which growth is accelerated when the methane concentration is decreased. In a model that fits the measurements quantitatively nitrogen catalyzes growth and competes with the hydrocarbon growth species for adsorption sites. The data allow excluding of several alternative models for nitrogen induced growth rate enhancement.
Surface-emitting quantum cascade lasers with metallic photonic-crystal resonators
Authors: Xu Gangyi , Moreau Virginie , Chassagneux Yannick , Bousseksou Adel , Colombelli Raffaele , Patriarche G. , Beaudoin G. , Sagnes I.
Published: June 2009

Surface emitting photonic-crystal quantum cascade lasers operating at λ≈7.3 μm are demonstrated. The photonic crystal resonator is written solely on the top metallization layer. The mismatch between the modes supported by metallized and nonmetallized regions yields enough optical feedback to achieve laser action. The devices exhibit single-mode emission with a side mode suppression ratio of ≈20 dB, the wavelength is lithographically tunable across a range of almost 70 cm−1, and the radiation is emitted from the surface. The maximum operating temperature is 220 K. The divergence of the output beam, which is doughnut-shaped, is approximately 9°.
A scale-bridging method for nanoparticulate polymer nanocomposites and their nondilute concentration effect
Authors: Yang Seunghwa , Cho Maenghyo
Published: June 2009

Due to the enhanced interaction among constituents and the resultant effect of particle size on the elastic modulus, nanocomposites with volume fractions higher than 12% show critical nondilute concentrations. In order to describe nondilute concentrations and the effect of particle size, a multi-inclusion model was adopted and a method was developed to transfer nanoscale physical information to a continuum-based analytical model. The accuracy and applicability of the present scale-bridging method at dilute and nondilute concentrations were verified by comparing results of the present method with those of molecular dynamics and finite element analysis.
Exact surface plasmon dispersion relations in a linear-metal-nonlinear dielectric structure of arbitrary nonlinearity
Authors: Yin Haiping , Xu C. , Hui P. M.
Published: June 2009

Exact analytic expression for obtaining the surface plasmon (SP) dispersion relations in a system consisting of a thin metallic film sandwiched between a linear dielectric and a nonlinear dielectric of arbitrary nonlinearity is derived, based on a generalized first integral approach. The changes in SP dispersion relations on film thicknesses and nonlinearity are studied by model calculations. The thick-film limit generalizes previous results on metal/Kerr-type nonlinear interface to arbitrary nonlinearity. An analytic expression is obtained for the limiting SP frequency at large wave vectors with previous result recovered as a special case.
Self-diffusion of a sphere in an effective medium of rods
Authors: Cichocki Bogdan , Ekiel-Jeżewska Maria L.
Published: June 2009

Self-diffusion of a sphere in a network of rods is analyzed theoretically. Hydrodynamic interactions are taken into account according to the model of Dhont et al. [J. Chem. Phys. 122, 044905 (2005); Dhont et al., J. Chem. Phys.124, 044907 (2006); Dhont et al., J. Chem. Phys.126, 214501 (2007)] based on the Debye–Bueche–Brinkman equation. The hydrodynamic screening length of the effective medium is assumed to be much larger than the sphere radius and the rod thickness. The self-diffusion coefficient, given by Dhont et al. in terms of four-dimensional integrals, is in this work expressed in terms of a single integral only and therefore evaluated numerically with a high precision. Moreover, simple expressions for the self-diffusion coefficient are derived and shown to be independent of the rod length. They can be useful for experimental verification of the model.
Resonantly probing micropillar cavity modes by photocurrent spectroscopy
Authors: Kistner C. , Reitzenstein S. , Schneider C. , Höfling S. , Forchel A.
Published: June 2009

We demonstrate electrical readout of high quality quantum dot micropillars by means of photocurrent (PC) spectroscopy under resonant excitation. Applying this technique enables a high spectral resolution mapping of the optical mode spectrum of the micropillar revealing quality factors of up to 11 000 for a 3 μm diameter device. PC spectroscopy also shows that the contacted micropillars can act as light sensors with highly wavelength selective and photon sensitive detection capabilities down to 20 nW incident power. Moreover, bias voltage dependent PC studies provide an effective tool to study the competition between carrier tunneling out of the quantum dots and the radiative recombination.
Modeling single-particle energy levels and resonance currents in a coherent electronic quantum dot mixer
Authors: Payette C. , Partoens B. , Yu G. , Gupta J. A. , Austing D. G. , Nair S. V. , Amaha S. , Tarucha S.
Published: June 2009

We present model calculations based on a coherent tunneling picture, which reproduce well both the single-particle energy level position and the resonant current strength at two typical anticrossings, one involving two levels and the other three levels in a coherent mixer composed of two weakly coupled vertical quantum dots. An essential ingredient is the inclusion of higher degree terms to account for deviations from an ideal elliptical parabolic confining potential in realistic dots. We also calculate density plots of the mixed states for the modified potential.
Enhancement of responsivity in solar-blind β-Ga2O3 photodiodes with a Au Schottky contact fabricated on single crystal substrates by annealing
Authors: Suzuki Rikiya , Nakagomi Shinji , Kokubun Yoshihiro , Arai Naoki , Ohira Shigeo
Published: June 2009

We fabricated β-Ga2O3 photodiodes with a Au Schottky contact on a single crystal substrate and investigated the effect of postannealing on the electrical and optical properties of the photodiodes. The ideality factor improved to near unity by annealing at temperatures above 200 °C; however, the reverse leakage current remained nearly unchanged. The responsivity in the wavelength region below 260 nm was enhanced dramatically by a factor of more than 102 after annealing at 400 °C resulting in maximum responsivity of 103 A/W, accompanied with a contrast ratio of about six orders of magnitude between the responsivities at 240 and 350 nm.
Horizontal position analysis of single acceptors in Si nanoscale field-effect transistors
Authors: Khalafalla M. A. H. , Ono Y. , Nishiguchi K. , Fujiwara A.
Published: June 2009

The authors performed conductance measurements to identify the horizontal position of single boron acceptors in silicon-on-insulator nanoscale field-effect transistors at a temperature of 6 K. The horizontal position, i.e., how far the acceptor is from the source or drain terminal, is qualitatively obtained, and it is shown, on the level of single dopants, that the acceptor near the source significantly affects the subthreshold nature of the transistor.
Role of microconvection induced by Brownian motion of nanoparticles in the enhanced thermal conductivity of stable nanofluids
Authors: Shima P. D. , Philip John , Raj Baldev
Published: June 2009

We investigate the role of microconvection induced by Brownian motion of nanoparticles on thermal conductivity enhancement in stable nanofluids containing nanoparticles of average diameters 2.8–9.5 nm. Nanofluids with a fixed particle loading of 5.5 vol. %, the effective thermal conductivity (k/kf) increases from 1.05 to 1.25 with increasing particle diameter. Upon increasing the aspect ratio of the linear chains in nanofluids, very large enhancement of thermal conductivity is observed. These findings confirm that microconvection is not the key mechanism responsible for thermal conductivity enhancements in nanofluids whereas aggregation has a more prominent role.
Controlling the conductance and noise of driven carbon-based Fabry–Pérot devices
Authors: Foa Torres Luis E. F. , Cuniberti Gianaurelio
Published: June 2009

We report on ac transport through carbon nanotube Fabry–Pérot devices. We show that tuning the intensity of the ac gating induces an alternation of suppression and partial revival of the conductance interference pattern. For frequencies matching integer multiples of the level spacing of the system Δ, the conductance remains irresponsive to the external field. In contrast, the noise in the low bias voltage limit behaves as in the static case only when the frequency matches an even multiple of the level spacing, thereby highlighting its phase sensitivity in a manifestation of the wagon-wheel effect in the quantum domain.
Blue phosphorescent organic light-emitting device with double emitting layer
Authors: Lee Jiun-Haw , Huang Chih-Lun , Hsiao Chih-Hung , Leung Man-Kit , Yang Chih-Chiang , Chao Chun-Chieh
Published: June 2009

In this paper, we demonstrated a blue phosphorescent organic light-emitting device (OLED) with a higher current-efficiency and a lower driving-voltage using conventional iridium(III)bis[4,6-(di-fluorophenyl)-pyridinato-N,C2′] picolinate (FIrpic) doped in the double emitting layer (DEML), which consists of a hole- and an electron-transporting material, N,N′-dicarbazolyl-3,5-benzene (mCP) and 2,2′-bis[5-phenyl-2-(1,3,4)oxadazolyl]biphenyl (OXD), respectively. Compared to OLEDs with only single mCP- and OXD-EML, current-efficiency of the optimized DEML-OLED increases by 30.82% and 141.37%, combining with a voltage reduction of 0.34 and 0.59 V at 50 mA/cm2, which comes from the better charge balance in DEML.
Fermi edge singularity observed in GaN/AlGaN heterointerfaces
Authors: Akopian N. , Vardi A. , Bahir G. , Garber V. , Ehrenfreund E. , Gershoni D. , Poblenz C. , Elsass C. R. , Smorchkova I. P. , Speck J. S.
Published: June 2009

We observe sharp spectral lines, at energies which are higher than the bulk GaN band gap, in the photoluminescence and photoluminescence excitation spectra of GaN/AlGaN heterointerfaces grown by molecular beam epitaxy. The spectra and their temperature dependence are in accord with the Fermi edge singularity expected for two dimensional electron gas systems. The associated localized hole energy in the AlGaN interface side was extracted directly from the spectra.
Optical properties of well-crystallized and size-tuned ZnO quantum dots
Authors: Suzuki Keigo , Kondo Hiroyuki , Inoguchi Masashi , Tanaka Nobuhiko , Kageyama Keisuke , Takagi Hiroshi
Published: June 2009

Well-crystallized and size-tuned ZnO quantum dots (QDs) were prepared by pulsed laser ablation and following size classification using a differential mobility analyzer. Photoluminescence (PL) spectra of the ZnO QDs showed predominant ultraviolet (UV) emission. The finely size-tuned ZnO QDs allowed us to precisely evaluate the quantum confinement effect, i.e., the size-driven color-tunable behavior in the UV emission range. The faint green luminescence found in the PL spectra and the low Stokes shifts of several tens meV demonstrated that the present QDs are almost free from defects. These features are quite favorable for use in future optoelectronic devices.
Magnetocaloric effect in preferentially textured Mn50Ni40In10 melt spun ribbons
Authors: Hernando B. , Sánchez Llamazares J. L. , Prida V. M. , Baldomir D. , Serantes D. , Ilyn M. , González J.
Published: June 2009

Inverse and direct magnetocaloric properties were evaluated in preferentially textured Mn50Ni40In10 ribbons applying the magnetic field H∥ along the ribbon length and perpendicular H⊥ to the ribbon plane (ΔH=30 kOe). Maximum magnetic entropy change, hysteretic losses, and refrigerant capacity were not significantly affected by crystallographic texture. Refrigeration capacity around structural transition is strongly reduced by the large hysteretic losses associated to the metamagnetic field-induced reverse martensitic transformation and narrower working temperature range making the interval around the magnetic transition more efficient for a refrigerant cycle (RCstruct=71 J kg−1 versus RCstructeff≈60 J kg−1, and RCmagn=89–86 J kg−1, for H∥ and H⊥, respectively).
Tailoring the hole concentration in superlattices based on nitride alloys
Authors: Zheng Qing-Hong , Yin Yi-An , Zhu Li-Hong , Huang Jin , Li Xiao-Ying , Liu Bao-Lin
Published: June 2009

By introducing Mg-doped InGaN/AlGaN strained-layer superlattice (SL) as p-type layer, the performance of p-type Ohmic contact is improved as compared with AlGaN/GaN and InGaN/GaN SLs. InGaN/AlGaN SL yields higher hole concentration due to larger oscillation of the valence band edge and smaller activation energy. The calculated average hole concentration in InGaN/AlGaN SL shows a twofold increase compared to that in AlGaN/GaN SL at the same Mg-doped level. The measured sheet hole density for ten periods of InGaN/AlGaN SL is as high as 4.4×1014 cm−2. Finally, Ni/Au contacts on Mg-doped InGaN/AlGaN SL with specific contact resistance of 7.3×10−5 Ω cm2 are realized.
Metal organic chemical vapor deposition of crack-free GaN-based light emitting diodes on Si (111) using a thin Al2O3 interlayer
Authors: Fenwick William E. , Melton Andrew , Xu Tianming , Li Nola , Summers Christopher , Jamil Muhammad , Ferguson Ian T.
Published: June 2009

Crack-free GaN light emitting diodes (LEDs) have been grown by metal organic chemical vapor deposition on Si(111) substrates using an atomic layer deposition-grown Al2O3 interlayer. Devices on Si show a longer emission wavelength compared to those on sapphire. This is attributed to tensile strain in the layers on Si, which may increase indium incorporation. Internal quantum efficiency is similar on both substrates. Luminescence intensity versus current density measurements show higher efficiency for the LEDs on Si relative to sapphire at high drive currents. These results show comparable performance characteristics for GaN-based devices on Si and sapphire substrates.
Electronic properties of nanocrystalline LaNiO3 and La0.5Sr0.5CoO3 conductive films grown on silicon substrates determined by infrared to ultraviolet reflectance spectra
Authors: Hu Z. G. , Li W. W. , Li Y. W. , Zhu M. , Zhu Z. Q. , Chu J. H.
Published: June 2009

Electronic band structures of nanostructured LaNiO3 (LNO) and La0.5Sr0.5CoO3 (LSCO) films have been investigated by near-normal incident optical reflectance at room temperature. Dielectric constants of the conductive films in the photon energy range of 0.47–6.5 eV have been extracted with the Drude–Lorentz function. It is found that four interband electronic transitions can be uniquely assigned for the perovskite-type metallic oxides. Moreover, optical conductivity is approximately varied from 100 to 450 Ω−1 cm−1 and shows a different variation trend for the LNO and LSCO layers. The discrepancy could be ascribed to diverse electronic structure, grain size, and crystalline formation.
Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight
Authors: Guter Wolfgang , Schöne Jan , Philipps Simon P. , Steiner Marc , Siefer Gerald , Wekkeli Alexander , Welser Elke , Oliva Eduard , Bett Andreas W. , Dimroth Frank
Published: June 2009

A metamorphic Ga0.35In0.65P/Ga0.83In0.17As/Ge triple-junction solar cell is shown to provide current-matching of all three subcells and thus composes a device structure with virtually ideal band gap combination. We demonstrate that the key for the realization of this device is the improvement of material quality of the lattice-mismatched layers as well as the development of a highly relaxed Ga1−yInyAs buffer structure between the Ge substrate and the middle cell. This allows the metamorphic growth with low dislocation densities below 106 cm−2. The performance of the approach has been demonstrated by a conversion efficiency of 41.1% at 454 suns (454 kW/m2, AM1.5d ASTM G173–03).
Adiabatic ionization potential of acetic acid and torsional dynamics of its cation
Authors: Zielke Philipp , Forysinski Piotr W. , Luckhaus David , Signorell Ruth
Published: June 2009

Pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy and supersonic cooling are used to investigate the CH3 torsional dynamics of the acetic acid cation and to determine an accurate value for the first adiabatic ionization potential of acetic acid (IP=85 912±5 cm−1), which has been the subject of debates for more than 40 yr. A doubling of the torsional barrier upon ionization is due to a significant shortening of the C–C bond and reduces the tunneling efficiency by an order of magnitude.
Carefully timed radio pulses sustain quantum phase
Authors: Day Charles
Published: June 2009

After subtle modifications, a technique borrowed from nuclear magnetic resonance can suppress the bane of quantum information processing: decoherence.
Balloon-borne telescope resolves cosmic far-IR background into starburst galaxies
Authors: Schwarzschild Bertram
Published: June 2009

Their distribution of redshifts manifests the falling cosmic rate of star formation since its heyday some two billion years after the Big Bang.
Meteor trails track upper atmospheric winds
Authors: Wilson Mark
Published: June 2009

An old technique gets a makeover using radar that combines high power and interferometry.
Resonant radio waves rotate tokamak plasma
Authors: Day Charles
Published: June 2009

An experiment at MIT’s Alcator tokamak has demonstrated a technique that could make fusion plasma easier to confine.
US photovoltaics industry may be too small for Obama’s big solar energy plans
Authors: Kramer David
Published: June 2009

But a government-industry consortium might provide a boost for US PV manufacturers.
Marburger calls for a new academic field of study in ‘the science of science policy’
Authors: Kramer David
Published: June 2009

Science adviser to George W. Bush says researchers, models, and decision tools could bring more rationality to science budgets and policies.
Probing stars with optical and near-IR interferometry
Authors: Brummelaar Theo ten , Creech-Eakman Michelle , Monnier John
Published: June 2009

New high-resolution data and images, derived from the light gathered by separated telescopes, are revealing that stars are not always as they seem.
Plasticity and toughness in bone
Authors: Ritchie Robert O. , Buehler Markus J. , Hansma Paul
Published: June 2009

Our bones are full of microscopic cracks, but the hierarchical character of the bones’ structure—from molecular to macroscopic scales—makes them remarkably resistant to fracture.
Rogue waves
Authors: Garett Chris , Gemmrich Johannes
Published: June 2009

Rich and challenging physics lies behind the gigantic ocean waves that seem to appear without warning to damage ships or sweep people off rocky shores.
Auralization of spaces
Authors: Vorländer Michael
Published: June 2009

Being able to determine and re-create what a room sounds like is useful not only in concert halls and opera houses but also in classrooms, houses, and virtual reality.
Face Classification in Schizophrenia: Evidence for a Sensitivity to Distinctiveness
Authors: Johnston Robert A , Tomlinson Eleanor , Jones Chris , Weaden Alan
Published: June 2009

The face-processing skills of people with schizophrenia were compared with those of a group of unimpaired individuals. Participants were asked to make speeded face-classification decisions to faces previously rated as being typical or distinctive. The schizophrenic group responded more slowly than the unimpaired group; however, both groups demonstrated the customary sensitivity to the distinctiveness of the face stimuli. Face-classification latencies made to typical faces were shorter than those made to distinctive faces. The implication of this finding with the schizophrenic group is discussed with reference to accounts of face-processing deficits attributed to these individuals.
Contrasting response mechanisms to root-zone salinity in three co-occurring Mediterranean woody evergreens: a physiological and biochemical study
Authors: Tattini Massimiliano , Traversi Maria Laura , Castelli Silvana , Biricolti Stefano , Guidi Lucia , Massai Rossano
Published: June 2009

The present study investigated the extent to which physiological and biochemical traits varied because of root-zone salinity in three Mediterranean evergreens differing greatly in their strategies of salt allocation at an organismal level: the ‘salt-excluders’, Olea europaea L. and Phillyrea latifolia L. (both Oleaceae), and Pistacia lentiscus L., which, instead, largely uses Na+ and Cl− for osmotic adjustment. Both Oleaceae spp. underwent severe leaf dehydration and reduced net photosynthesis and whole-plant growth to a significantly greater degree than did P. lentiscus. Osmotic adjustment in Oleaceae mostly resulted from soluble carbohydrates, which, in turn, likely feedback regulated net photosynthesis. Salt stress reduced the actual efficiency of PSII photochemistry (ΦPSII) and enhanced the concentration of de-epoxided violaxanthin-cycle pigments in O. europaea and P. latifolia. Phenylpropanoid metabolism was upregulated by salt stress to a markedly greater degree in O. europaea and P. latifolia than in P. lentiscus. In contrast, species-specific variations in leaf lipid peroxidation were not observed in response to salinity stress. The results suggest that the species-specific ability to manage the allocation of potentially toxic ions out of sensitive leaf organs, other than affecting physiological responses, largely determined the extent to which leaf biochemistry, mostly aimed to counter salt-induced oxidative damage, varied in response to salinity stress.
The S. pombe mitotic regulator Cut12 promotes spindle pole body activation and integration into the nuclear envelope
Authors: Tallada Victor A. , Tanaka Kenji , Yanagida Mitsuhiro , Hagan Iain M.
Published: June 2009

The fission yeast spindle pole body (SPB) comprises a cytoplasmic structure that is separated from an ill-defined nuclear component by the nuclear envelope. Upon mitotic commitment, the nuclear envelope separating these domains disperses as the two SPBs integrate into a hole that forms in the nuclear envelope. The SPB component Cut12 is linked to cell cycle control, as dominant cut12.s11 mutations suppress the mitotic commitment defect of cdc25.22 cells and elevated Cdc25 levels suppress the monopolar spindle phenotype of cut12.1 loss of function mutations. We show that the cut12.1 monopolar phenotype arises from a failure to activate and integrate the new SPB into the nuclear envelope. The activation of the old SPB was frequently delayed, and its integration into the nuclear envelope was defective, resulting in leakage of the nucleoplasm into the cytoplasm through large gaps in the nuclear envelope. We propose that these activation/integration defects arise from a local deficiency in mitosis-promoting factor activation at the new SPB.
GNL3L stabilizes the TRF1 complex and promotes mitotic transition
Authors: Zhu Qubo , Meng Lingjun , Hsu Joseph K. , Lin Tao , Teishima Jun , Tsai Robert Y.L.
Published: June 2009

Telomeric repeat binding factor 1 (TRF1) is a component of the multiprotein complex “shelterin,” which organizes the telomere into a high-order structure. TRF1 knockout embryos suffer from severe growth defects without apparent telomere dysfunction, suggesting an obligatory role for TRF1 in cell cycle control. To date, the mechanism regulating the mitotic increase in TRF1 protein expression and its function in mitosis remains unclear. Here, we identify guanine nucleotide-binding protein-like 3 (GNL3L), a GTP-binding protein most similar to nucleostemin, as a novel TRF1-interacting protein in vivo. GNL3L binds TRF1 in the nucleoplasm and is capable of promoting the homodimerization and telomeric association of TRF1, preventing promyelocytic leukemia body recruitment of telomere-bound TRF1, and stabilizing TRF1 protein by inhibiting its ubiquitylation and binding to FBX4, an E3 ubiquitin ligase for TRF1. Most importantly, the TRF1 protein-stabilizing activity of GNL3L mediates the mitotic increase of TRF1 protein and promotes the metaphase-to-anaphase transition. This work reveals novel aspects of TRF1 modulation by GNL3L.
Bub1 regulates chromosome segregation in a kinetochore-independent manner
Authors: Klebig Christiane , Korinth Dirk , Meraldi Patrick
Published: June 2009

The kinetochore-bound protein kinase Bub1 performs two crucial functions during mitosis: it is essential for spindle checkpoint signaling and for correct chromosome alignment. Interestingly, Bub1 mutations are found in cancer tissues and cancer cell lines. Using an isogenic RNA interference complementation system in transformed HeLa cells and untransformed RPE1 cells, we investigate the effect of structural Bub1 mutants on chromosome segregation. We demonstrate that Bub1 regulates mitosis through the same mechanisms in both cell lines, suggesting a common regulatory network. Surprisingly, Bub1 can regulate chromosome segregation in a kinetochore-independent manner, albeit at lower efficiency. Its kinase activity is crucial for chromosome alignment but plays only a minor role in spindle checkpoint signaling. We also identify a novel conserved motif within Bub1 (amino acids 458–476) that is essential for spindle checkpoint signaling but does not regulate chromosome alignment, and we show that several cancer-related Bub1 mutants impair chromosome segregation, suggesting a possible link to tumorigenesis.