bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical and optical properties of lanthanum-modified lead zirconate titanate thin films by radio-frequency magnetron sputtering
Authors: Leng W. J. , Yang C. R. , Ji H. , Zhang J. H. , Tang J. L. , Chen H. W. , Gao L. F.
Published: November 2006

( Pb , La ) ( Zr , Ti ) O 3 (PLZT) thin films were grown on Pt∕Ti∕SiO2∕Si and fused quartz substrates by radio-frequency magnetron sputtering at 650°C. X-ray diffraction analysis shows that the PLZT films are polycrystalline with (100)-preferential orientation. The Al/PLZT/Pt capacitors have been fabricated and show good ferroelectric properties with the remanent polarization of 24.3μC∕cm2 and coercive field of 142kV∕cm. The leakage current density is only about 0.86×10−7A∕cm2 at 200kV∕cm. The energy gap Eg of the films is estimated to be about 3.54eV by optical transmittance measurements. Their fundamental optical constants are obtained by a Filmetrics F20 reflectance spectrometer (F20). These results show that the PLZT ferroelectric thin films are promising materials for optoelectronic devices.
Hydrogenation-assisted nanocrystallization of amorphous silicon by radio-frequency plasma-enhanced chemical vapor deposition
Authors: Hashemi P. , Abdi Y. , Mohajerzadeh S. , Derakhshandeh J. , Khajooeizadeh A. , Robertson M. D. , Thompson R. D. , MacLachlan J. M.
Published: November 2006

The effects of plasma-enhanced hydrogenation on the crystallization of pure, electron-beam evaporated amorphous silicon (a-Si) at temperatures as low as 300°C were investigated. Successive steps of hydrogenation in the plasma-enhanced chemical vapor deposition chamber, and in situ annealing in a N2 ambient environment were applied to the a-Si samples over a range of low temperatures and plasma powers. At specific plasma-power densities, nanocrystalline silicon layers with an average grain size of less than 10nm were formed where their size, distribution, and porosity could be varied by altering the plasma power and hydrogenation temperature. The surface morphology and the nanocrystalline quality of the samples were characterized using scanning electron microscopy, dark-field transmission electron microscopy, and electron diffraction. In addition, by plasma-enhanced oxidation at a temperature of 250°C, a thin layer of oxide was grown and its physical, structural, and electrical characteristics were investigated.
Increasing the electrical conductivity of poly(vinylidene fluoride) by KrF excimer laser irradiation
Authors: Ji Yaling , Jiang Yijian
Published: November 2006

This letter describes the increase in electrical conductivity of poly(vinylidene fluoride) induced by excimer laser irradiation with λ=248nm. The electrical conductivity was found to increase from 10−13to10−4Ω−1cm−1. As a result, experiments produced a transition in the property of the material from an insulator to a conductor. Optimal conditions for laser irradiation were determined in terms of the laser energy density, the repetition frequency, and the total number of laser shots. This letter also discusses the micromechanics of increasing conductivity in the light of Raman spectroscopy and x-ray photoelectron spectroscopy.
Organic single-crystal complementary inverter
Authors: Briseno Alejandro L. , Tseng Ricky J. , Li Sheng-Han , Chu Chih-Wei , Yang Yang , Falcao Eduardo H. L. , Wudl Fred , Ling Mang-Mang , Chen Hong Zheng , Bao Zhenan , Meng Hong , Kloc Christian
Published: November 2006

The authors demonstrate the operation of an organic single-crystal complementary circuit in the form of a simple inverter. The device is constructed from a high mobility p-type organic single-crystal transistor of tetramethylpentacene (TMPC) and a n-type single-crystal transistor of N,N′-di[2,4-difluorophenyl]-3,4,9,10-perylenetetracarboxylic diimide (PTCDI). Field-effect mobilities of up to 1.0cm2∕Vs are reported for TMPC devices, while a mobility of 0.006cm2∕Vs is reported for a n-type PTCDI single-crystal device. Considering that organic single-crystal inverters have not yet been explored, they are representative of potential candidates for use in high-performance complementary circuits.
Structural and magnetic stabilities of cubic and orthorhombic phases of CeMnNi4
Authors: Murugan P. , Singh Abhishek Kumar , Das G. P. , Kawazoe Yoshiyuki
Published: November 2006

First-principles density functional calculations have been carried out on cubic and orthorhombic phases of CeMnNi4, in order to understand their structural and magnetic stabilities. The calculations show the orthorhombic phase to be energetically favorable as compared to the cubic phase reported experimentally by Singh et al. [Appl. Phys. Lett. 88, 022506 (2005)]. Ferromagnetic state turns out to be more stable for both cubic and orthorhombic phases, the latter having lower total magnetic moment. The moment is mainly localized on Mn atoms, and their alignment is mediated via the indirect exchange interaction. Half-metallic nature as proposed experimentally is elusive for the pure compound which shows metallic behavior.
Magnetic shape memory in Ni2MnGa as influenced by applied stress
Authors: Callaway J. D. , Sehitoglu H. , Hamilton R. F. , Aslantas K. , Miller N. , Maier H. J. , Chumlyakov Y.
Published: November 2006

The authors report on the stress-strain and strain-temperature behaviors of a Ni2MnGa alloy. Depending on the applied stress during cooling from austenite, different levels of transformation strain were observed culminating in the formation of a single variant of martensite and transformation strain of 4%. The results underscore an optimum stress level that maximizes shape memory strains. At higher stress levels, plasticity curtails the level of transformation strain and the concomitant magnetic shape memory strains. Similarly, the results uncover an optimum bias stress to maximize magnetic induced shape memory, producing strains exceeding 5% with reversible strains of 3%.
Ground state monoclinic (Mb) phase in (110)c BiFeO3 epitaxial thin films
Authors: Xu Guangyong , Li Jiefang , Viehland D.
Published: November 2006

The lattice structure of (110)-oriented BiFeO3 epitaxial thin layers has been identified by synchrotron x-ray diffraction. By using (221) and (221¯) peaks in the (HHL) zone, a ground state monoclinic Mb phase has been observed with lattice parameters of (β;am∕√2andcm)=(89.35°;3.985and3.888Å). These results demonstrate a change in phase stability from rhombohedral in bulk single crystals, to monoclinic in epitaxial thin films with two domain states whose polarization is slightly tilted away from [110] towards [111].
Observation of leakage sites in a hafnium silicon oxynitride gate dielectric of a metal-oxide-semiconductor field-effect transistor device by electron-beam-induced current
Authors: Chen J. , Sekiguchi T. , Fukata N. , Takase M. , Chikyow T. , Yamabe K. , Hasunuma R. , Akasaka Y. , Inumiya S. , Nara Y. , Yamada K.
Published: November 2006

Leakage sites in hafnium silicon oxynitride gate dielectrics of metal-oxide-semiconductor field-effect transistors were directly identified by means of electron-beam-induced current (EBIC) technique. Leakage sites were observed as bright spots mostly on the periphery of gate. With the gate bias increasing, the EBIC current of bright spots increased exponentially, but the number of bright spots did not increase.
Microfluidic dye laser intracavity absorption
Authors: Galas J. C. , Peroz C. , Kou Q. , Chen Y.
Published: November 2006

The authors report absorption measurements on low concentration analytes using a microfluidic dye laser. The laser cavity is made of two gold mirrors coated on the end faces of two optical fibers inserted in a chip. Rhodamine 6G dye molecules dissolved in ethanol are used for laser amplification and absorption measurements are done with methylene blue dye solutions. When optically pumped with a frequency doubled Nd:YAG laser at 532nm wavelength, the device shows a laser output emission at 565nm and a high sensitivity of the lasing output to the losses in the cavity, in good agreement with the results of numerical calculations.
Room temperature tunable detection of subterahertz radiation by plasma waves in nanometer InGaAs transistors
Authors: Teppe F. , Orlov M. , El Fatimy A. , Tiberj A. , Knap W. , Torres J. , Gavrilenko V. , Shchepetov A. , Roelens Y. , Bollaert S.
Published: November 2006

The authors report on the demonstration of room temperature, tunable terahertz detection obtained by 50nm gate length AlGaAs∕InGaAs high electron mobility transistors (HEMTs). They show that the physical mechanism of the detection is related to the plasma waves excited in the transistor channel and that the increasing of the drain current leads to the transformation of the broadband detection to the resonant and tunable one. They also show that the cap layer regions significantly affect the plasma oscillation spectrum in HEMTs by decreasing the resonant plasma frequencies.
Free energy for protein folding from nonequilibrium simulations using the Jarzynski equality
Authors: West Daniel K. , Olmsted Peter D. , Paci Emanuele
Published: November 2006

The equilibrium free energy difference between two long-lived molecular species or “conformational states” of a protein (or any other molecule) can in principle be estimated by measuring the work needed to shuttle the system between them, independent of the irreversibility of the process. This is the meaning of the Jarzynski equality (JE), which we test in this paper by performing simulations that unfold a protein by pulling two atoms apart. Pulling is performed fast relative to the relaxation time of the molecule and is thus far from equilibrium. Choosing a simple protein model for which we can independently compute its equilibrium properties, we show that the free energy can be exactly and effectively estimated from nonequilibrium simulations. To do so, one must carefully and correctly determine the ensemble of states that are pulled, which is more important the farther from equilibrium one performs simulations; this highlights a potential problem in using the JE to extract the free energy from forced unfolding experiments. The results presented here also demonstrate that the free energy difference between the native and denatured states of a protein measured in solution is not always equal to the free energy profile that can be estimated from forced unfolding simulations (or experiments) using the JE.
Ultrafast two-dimensional NMR spectroscopy using constant acquisition gradients
Authors: Shrot Yoav , Frydman Lucio
Published: November 2006

Multidimensional NMR spectroscopy plays an important role in the characterization of molecular structure and dynamics. A new methodology for acquiring this kind of spectra has been recently demonstrated, endowed with the potential to compress arbitrary multidimensional NMR acquisitions into a single scan. This “ultrafast” nD acquisition protocol is based on a spatiotemporal encoding of the indirect-domain spin evolution, followed by a repetitive decoding and reencoding of the information thus stored employing a train of alternating-sign gradients. Such train of switching gradients extending throughout the course of the data acquisition may pose extreme demands on a magnetic resonance system, particularly when dealing with nonshielded gradients, strong eddy currents, or rapidly relaxing spin systems. Limits to the in vivo applicability of such fast-switching scheme may also arise due to gradient-induced perineural stimulation. The present study describes a new approach to ultrafast nD NMR that reduces the number of gradient switchings during the acquisition period to zero, leading in essence to a constant-gradient acquisition scheme. This approach operates on the basis of a novel spatiotemporal encoding including discrete, temporally overlapping, frequency-shifted pulses. Principles and examples of this new approach are given; sensitivity limitations and signal-enhancing prospects of such constant-gradient acquisitions are also discussed and exemplified.
Slow dynamics in a primitive tetrahedral network model
Authors: De Michele Cristiano , Tartaglia Piero , Sciortino Francesco
Published: November 2006

We report extensive Monte Carlo and event-driven molecular dynamics simulations of the fluid and liquid phase of a primitive model for silica recently introduced by Ford et al. [J. Chem. Phys. 121, 8415 (2004)]. We evaluate the isodiffusivity lines in the temperature-density plane to provide an indication of the shape of the glass transition line. Except for large densities, arrest is driven by the onset of the tetrahedral bonding pattern and the resulting dynamics is strong in Angell’s classification scheme [J. Non-Cryst. Solids 131–133, 13 (1991)]. We compare structural and dynamic properties with corresponding results of two recently studied primitive models of network forming liquids—a primitive model for water and an angular-constraint-free model of four-coordinated particles—to pin down the role of the geometric constraints associated with bonding. Eventually we discuss the similarities between “glass” formation in network forming liquids and “gel” formation in colloidal dispersions of patchy particles.
The limits of Navier-Stokes theory and kinetic extensions for describing small-scale gaseous hydrodynamics
Authors: Hadjiconstantinou Nicolas G.
Published: November 2006

This paper reviews basic results and recent developments in the field of small-scale gaseous hydrodynamics which has received significant attention in connection with small-scale science and technology. We focus on the modeling challenges arising from the breakdown of the Navier-Stokes description, observed when characteristic lengthscales become of the order of, or smaller than, the molecular mean free path. We discuss both theoretical results and numerical methods development. Examples of the former include the limit of applicability of the Navier-Stokes constitutive laws, the concept of second-order slip and the appropriate form of such a model, and how to reconcile experimental measurements of slipping flows with theory. We also review a number of recently developed theoretical descriptions of canonical nanoscale flows of engineering interest. On the simulation front, we review recent progress in characterizing the accuracy of the prevalent Boltzmann simulation method known as direct simulation Monte Carlo. We also present recent variance reduction ideas which address the prohibitive cost associated with the statistical sampling of macroscopic properties in low-speed flows.
The escape of a particle from a driven harmonic potential to an attractive surface
Authors: Tshiprut Z. , Klafter J. , Urbakh M.
Published: November 2006

We investigate theoretically the dynamics of a colloidal particle, trapped by optical tweezers, which gradually approaches an attractive surface with a constant velocity until it escapes the trap and jumps to the surface. We find that the height of the energy barrier in such a colloid-surface system follows the scaling ΔE∝(z0(t)−const)3∕2 when the trap approaches the surface, z0(t) being the trap surface distance. Using this scaling we derive equations for the probability density function of the jump lengths, for the velocity dependence of its mean and most probable values, and for the variance. These can be used to extract the parameters of the particle-surface interaction from experimental data.
Radiation effects in water ice: A near-edge x-ray absorption fine structure study
Authors: Laffon C. , Lacombe S. , Bournel F. , Parent Ph.
Published: November 2006

The changes in the structure and composition of vapor-deposited ice films irradiated at 20K with soft x-ray photons (3–900eV) and their subsequent evolution with temperatures between 20 and 150K have been investigated by near-edge x-ray absorption fine structure spectroscopy (NEXAFS) at the oxygen K edge. We observe the hydroxyl OH, the atomic oxygen O, and the hydroperoxyl HO2 radicals, as well as the oxygen O2 and hydrogen peroxide H2O2 molecules in irradiated porous amorphous solid water (p-ASW) and crystalline (Icryst) ice films. The evolution of their concentrations with the temperature indicates that HO2, O2, and H2O2 result from a simple step reaction fuelled by OH, where O2 is a product of HO2 and HO2 a product of H2O2. The local order of ice is also modified, whatever the initial structure is. The crystalline ice Icryst becomes amorphous. The high-density amorphous phase (Iah) of ice is observed after irradiation of the p-ASW film, whose initial structure is the normal low-density form of the amorphous ice (Ial). The phase Iah is thus peculiar to irradiated ice and does not exist in the as-deposited ice films. A new “very high density” amorphous phase—we call Iavh—is obtained after warming at 50K the irradiated p-ASW ice. This phase is stable up to 90K and partially transforms into crystalline ice at 150K.
Reversible creation and annihilation of a local leakage path in HfO2∕GeOx stacked gate dielectrics: A direct observation by ultrahigh vacuum conducting atomic force microscopy
Authors: Yamamura K. , Kita K. , Toriumi A. , Kyuno K.
Published: November 2006

By direct observation using ultrahigh vacuum conducting atomic force microscopy, it is found that a local leakage path in HfO2∕GeOx stacks created by an electrical stress with a positive tip bias annihilates after applying a reverse tip bias. The creation and annihilation of these paths are repeatable without noticeable degradation. The fact that these paths annihilate by a very small reverse bias suggests that this behavior is caused by local reduction and oxidation in the HfO2 layer.
Absorption spectra of trilayer rhombohedral graphite
Authors: Lu Chi-Lang , Lin Hong-Chang , Hwang Chi-Chuan , Wang Jei , Lin Min-Fa , Chang Cheng-Peng
Published: November 2006

Absorption spectra of trilayer rhombohedral graphite are studied with the tight-binding model. The interlayer interactions cause a tiny energy gap and band-edge states in electronic structures. The band-edge states exhibit logarithmic divergences and discontinuities in the density of states. The frequencies of the absorption peaks correspond to the vertical transition energies of the band-edge states. Optical spectra of trilayer simple hexagonal and orthorhombic graphites are also investigated. The stacking effects on the density of states and absorption spectra are presented and discussed in detail.
Silicon-based photonic crystal nanocavity light emitters
Authors: Makarova Maria , Vuckovic Jelena , Sanda Hiroyuki , Nishi Yoshio
Published: November 2006

The authors have demonstrated an up to sevenfold enhancement of photoluminescence from silicon-rich silicon nitride film due to a single photonic crystal cavity. The enhancement is partially attributed to the Purcell effect [Purcell, Phys. Rev. 69, 681 (1946)], which is predicted to be up to 35-fold by finite difference time-domain calculations for emitters spectrally and spatially aligned with the electric field. Experimentally measured cavity quality factors vary in the range of 200–300, showing excellent agreement with calculations. The emission peak can be tuned to any wavelength in the 600–800nm range.
Dispersion and transitions of dipolar plasmon modes in graded plasmonic waveguides
Authors: Xiao J. J. , Yakubo K. , Yu K. W.
Published: November 2006

Coupled plasmon modes are studied in graded plasmonic waveguides, which are periodic chains of metallic nanoparticles embedded in a host with gradually varying refractive indices. The authors identify three types of localized modes called “light,” “heavy,” and “light-heavy” plasmonic gradons outside the passband, according to various localizations. The authors also demonstrate different transitions among extended and localized modes when the interparticle separation d is smaller than a critical dc, whereas the three types of localized modes occur for d>dc, with no extended modes. The transitions can be explained with phase diagrams constructed for the lossless metallic systems.
Angle dependence of two-wave mixing efficiency in photorefractive multiple quantum wells
Authors: Gramlich Michael , Balasubramanian Sunder , Yu Ping
Published: November 2006

The authors have investigated how two-wave mixing efficiency changes as a function of angle tuning while crossing over from the Raman-Nath diffraction to the Bragg diffraction in AlGaAs∕GaAs photorefractive multiple quantum wells (PRQWs). They have shown that by changing the inclination angle of the PRQW, the apparent thickness of the PRQW (as seen by the mixing beams) can become larger than the grating fringe spacing. This moves the wave mixing from Raman-Nath diffraction to Bragg diffraction and causes an enhancement in the mixing efficiency at smaller fringe spacing.
Process integration of microtubes for fluidic applications
Authors: Thurmer Dominic J. , Deneke Christoph , Mei Yongfeng , Schmidt Oliver G.
Published: November 2006

Three-dimensional InGaAs∕GaAs microtubes are integrated by photolithography into a microfluidic device. The integration process, made possible due to advances in fabricating long, homogeneous rolled-up microtubes, is described in detail. Liquid filling and emptying of individual microtubes, and the final microfluidic device are investigated by video microscopy. The authors find an agreement for their channels with the Washburn equation [Phys. Rev. 17, 273 (1921)] for filling using a modified capillary pressure fit to experimental conditions. Emptying of a vacuum pumped microfluidic device also qualitatively agrees with theory. The results suggest rolled-up micro- and nanotubes as possible systems to provide fully integrative fluid analysis on a chip.
Depletion-mode GaAs metal-oxide-semiconductor field-effect transistor with HfO2 dielectric and germanium interfacial passivation layer
Authors: Kim Hyoung-Sub , Ok Injo , Zhang Manhong , Lee T. , Zhu F. , Yu L. , Lee Jack C. , Koveshnikov S. , Tsai W. , Tokranov V. , Yakimov M. , Oktyabrsky S.
Published: November 2006

The authors present depletion-mode n-channel GaAs metal-oxide-semiconductor field-effect transistor (MOSFET) with a TaN gate electrode, a thin HfO2 gate dielectric, and a thin germanium (Ge) interfacial passivation layer (IPL). Depletion-mode MOSFET on the molecular-beam epitaxy-grown n-type GaAs layer with an equivalent oxide thickness of 17Å exhibits excellent transistor output characteristics such as a maximum transconductance of 176mS∕mm and a maximum effective electron mobility of 970cm2∕Vs. MOSFET shows a surface accumulation channel conduction above flatband condition, indicating that a high quality interface can be achieved using a Ge IPL on GaAs substrate.
Piezoelectric diaphragm as a high performance biosensor platform
Authors: Xin Yang , Li Zhimin , Odum LeVar , Cheng Z.-Y. , Xu Zhuo
Published: November 2006

The design of a piezoelectric diaphragm as a dual-functional biosensor platform, bending and thickness modes, is reported. The diaphragm using bending mode exhibits a higher sensitivity than the state-of-the-art microcantilevers, while the diaphragm using thickness mode has a much higher sensitivity than the bending mode. It was experimentally found that for the bending mode the diaphragm in liquid exhibits the same Q value as the diaphragm in air, while for the thickness mode the diaphragm in liquid exhibits a much smaller Q value. That is, the bending mode is the better candidate for developing high performance sensor platforms employed in liquid.
Fast and highly anisotropic thermal transport through vertically aligned carbon nanotube arrays
Authors: Ivanov Ilia , Puretzky Alexander , Eres Gyula , Wang Hsin , Pan Zhengwei , Cui Hongtao , Jin Rongying , Howe Jane , Geohegan David B.
Published: November 2006

This letter reports on fast and highly anisotropic thermal transport through millimeter-tall, vertically aligned carbon nanotube arrays (VANTAs) synthesized by chemical vapor deposition on Si substrates. Thermal diffusivity measurements were performed for both longitudinal and transverse to the nanotube alignment direction, with longitudinal values as large as 2.1±0.2cm2∕s and anisotropy ratios as large as 72. Longitudinal thermal conductivities of 15.3±1.8W∕(mK) for porous 8±1vol% VANTAs in air and 5.5±0.7W∕(mK) for epoxy-infiltrated VANTAs already exceed those of phase-changing thermal interface materials used in microelectronics. Data suggest that further improvements are possible through optimization of density and defects in the arrays.
Enhancing sensitivity of a whispering gallery mode biosensor by subwavelength confinement
Authors: Gaathon O. , Culic-Viskota J. , Mihnev M. , Teraoka I. , Arnold S.
Published: November 2006

The authors demonstrate enhanced sensitivity of a spherical whispering gallery mode biosensor (WGMB) by confining orbiting light near the surface using a subwavelength (sub-λ) high refractive index layer on a fluorine doped silica microsphere (radius R∼200μm). Their experiments at a free space wavelength λ∼1310nm show that the frequency shift sensitivity by changing the external refractive index is increased by more than 700% by adding a 340nm thick polystyrene layer. This advance is expected to move the WGMB well into the lead as the most sensitive method for unlabeled biosensing.
Dynamics of graphite flake on a liquid
Authors: Miura K. , Tsuda D. , Kaneta Y. , Harada R. , Ishikawa M. , Sasaki N.
Published: November 2006

One-directional motion, where graphite flakes are driven by a nanotip on an octamethylcyclotetrasiloxane (OMCTS) liquid surface, is presented. A transition from quasiperiodic to chaotic motions occurs in the dynamics of a graphite flake when its velocity is increased. The dynamics of graphite flakes pulled by the nanotip on an OMCTS liquid surface can be treated as that of a nanobody on a liquid.
The freezing transition of a hard sphere fluid subject to the Percus-Yevick approximation
Authors: Dong H. , Evans G. T.
Published: November 2006

A classical density functional theory is applied to the calculation of the fluid-solid transition for hard spheres, using the Percus-Yevick (PY) direct correlation function. Three algebraic conditions are established for the coexistence densities and the Lindemann parameter. The terms neglected in the present analysis are small and the present theory, in our eyes, is essentially an exact solution given the PY approximation. No fluid-solid transition is found for the bcc lattice, whereas for expanded fcc lattices, the agreement with previous density functional theory-based theories is good.
Efficiency of assembling of nanowires in suspension by ac electric fields
Authors: Fan D. L. , Zhu F. Q. , Cammarata R. C. , Chien C. L.
Published: November 2006

The authors report a versatile and efficient method for assembling nanowires in suspension into scaffolds using ac electric fields. The electric field and its gradient aligns and transports, respectively, the nanowires into scaffolds according to the electric field distributions. The assembling efficiency strongly depends on the frequency of the applied ac voltages and varies as square of the voltage. The assembly morphology is highly influenced by the frequency regardless of applied voltages.
Synthesis and thermoelectric properties of KyCo4Sb12
Authors: Pei Y. Z. , Chen L. D. , Zhang W. , Shi X. , Bai S. Q. , Zhao X. Y. , Mei Z. G. , Li X. Y.
Published: November 2006

Polycrystalline K-filled CoSb3 are synthesized successfully. The uplimit for K filling is at least 0.45, being higher than those of either alkaline-earth (AE) or rare-earth (RE) metals but being in consistent with our earlier theoretical prediction. The measured transport properties (300–800K) show that K filling does not lower thermal conductivity much in comparison with AE or RE filling due to the relatively low mass of K atom. However, it improves electrical conductivity, retains large Seebeck coefficient, and leads to a reasonably good thermoelectric performance for the filled skutterudites. The maximum figure of merit ZT reaches 1 at 800K for K0.38Co4Sb12.
Effect of twin boundaries on electrical transport in a Ni–Mn–Ga single crystal
Authors: Srivastava Vijay Kumar , Chatterjee Ratnamala , O’Handley R. C.
Published: November 2006

Detailed electrical resistivity measurements for different twin configurations and crystallographic directions on Ni49Mn29Ga22 Heusler alloy are presented. Important results of these measurements are (i) the resistivity of the crystal is not related to the number of twin boundaries present (as previously reported) but instead depends upon the local environment of the atoms (c‖ long direction or c⊥ long direction) in the crystal. The crystallographic anisotropy of the resistivity is appreciable ρc‖I>ρc⊥I. (ii) Intermartensitic transition temperature is strongly affected by the twin configuration and suppressed for the twinned state as compared to the single-variant states.
Molecular beam epitaxy grown template for subsequent atomic layer deposition of high κ dielectrics
Authors: Lee K. Y. , Lee W. C. , Lee Y. J. , Huang M. L. , Chang C. H. , Wu T. B. , Hong M. , Kwo J.
Published: November 2006

Molecular beam epitaxy (MBE) grown high κ dielectrics of Al2O3 and HfO2 are employed as templates to suppress effectively the oxide/Si interfacial layer formation during the subsequent atomic layer deposition (ALD) growth. The absence of the interfacial layer was confirmed using x-ray photoelectron spectroscopy and high resolution transmission electron microscopy. Two composite films consisting of ALDAl2O3(1.9nm)∕MBEAl2O3(1.4nm) and ALDAl2O3(3.0nm)∕MBEHfO2(2.0nm) showed overall κ values of 9.1 and 11.5, equivalent oxide thicknesses of 1.41 and 1.7nm, Dit of 2.2×1011 and 2×1011cm−2eV−1, and leakage current densities of 2.4×10−2A∕cm2 at Vfb−1V and 1.1×10−4A∕cm2 at Vfb+1V, respectively. The attainment of high dielectric constant suggests that there is no low κ capacitor in series near the oxide/Si interface.
Effect of electromigration-induced back stress gradient on nanoindentation marker movement in SnAgCu solder joints
Authors: Xu Luhua , Pang John H. L. , Tu K. N.
Published: November 2006

The electromigration-induced back stress in Pb-free SnAgCu solder was studied by an area array of nanoindentation markers on the cross section of a solder joint. The marker movements driven by combined electron wind force and electromigration-induced back stress gradient were measured at different locations. The back stress gradient was determined from the observation of marker motion using the proposed model. With the applied current density of 104A∕cm2 at 125°C, the stress gradient near the anode is 97kPa∕μm.
A
-site disorder induced collapse of charge-ordered state and phase separated phase in manganites
Authors: Wang K. F. , Yuan F. , Dong S. , Li D. , Zhang Z. D. , Ren Z. F. , Liu J.-M.
Published: November 2006

The effects of A-site cational size mismatch (A-site disorder) on the stability of charge-ordered states and phase separated phase in a series of manganites with constant A-site ionic average radii ⟨rA⟩=1.18Å but different A-site ionic size mismatches σ2 are experimentally investigated. It is revealed that the charge/orbital ordered antiferromagnetic ground state becomes destabilized and eventually collapses into coexisting of the predominant ferromagnetic metal (FMM) state and short-range charge/orbital ordered state with increasing σ2, resulting in enhanced colossal magnetoresistance. However, further increasing A-site disorder will suppress the FMM state and seem to favor a cluster-glass insulating state due to the severe electronic localization.
Directional edge-emitting UV random laser diodes
Authors: Leong Eunice S. P. , Yu S. F. , Lau S. P.
Published: November 2006

The authors have achieved directional coherent random lasing from p-GaN∕i-ZnO–SiO2 nanocomposite/n-ZnO heterojunction diodes. This is due to the use of relatively low refractive indexed carrier injection layers (i.e., cladding layers) and relatively high refractive indexed intrinsic layer with stripes of ZnO clusters (i.e., core layer) that allows the transverse confinement of in-plane closed-loop random cavities. Hence, directional lasing emission can be observed from the edge of the diodes. However, the choice of highly concentrated ZnO clusters, which is supposed to enhance the transverse confinement and optical gain, is not preferred for the fabrication of intrinsic layer. This is because the influence of corrugation effect (i.e., strong surface scattering) supersedes the transverse optical confinement of the diodes.
Electron spin coherence in n-doped CdTe∕CdMgTe quantum wells
Authors: Bratschitsch R. , Chen Z. , Cundiff S. T. , Zhukov E. A. , Yakovlev D. R. , Bayer M. , Karczewski G. , Wojtowicz T. , Kossut J.
Published: November 2006

The spin coherence of a two-dimensional electron gas (2DEG) at different densities in CdTe∕Cd0.85Mg0.15Te quantum wells has been examined by the time-resolved Kerr rotation technique using resonant excitation of either trions or excitons. The formation of negatively charged trions, either excited resonantly or via exciton states, causes strong spin polarization of the 2DEG. This effect leads to a long lasting exponential decay in the nanosecond regime. Spin dephasing times T2* of the 2DEG measured as a function of electron density up to 2.4×1011cm−2 show a nonmonotonic behavior with a maximum at 8×1010cm−2.
High accuracy optical characterization of anisotropic liquids by merging standard techniques
Authors: Tkachenko V. , Abbate G. , Marino A. , Vita F. , Giocondo M. , Mazzulla A. , De Stefano L.
Published: November 2006

The design and fabrication of active and passive hybrid photonic devices, with tunable optical properties, based on liquid crystals require a very accurate knowledge of their anisotropic refractive indices up to 100ppm in the wavelength region of interest. At this aim, the authors have integrated two standard optical techniques commonly used in liquid crystals characterization, the variable angle spectroscopic ellipsometry and the half leaky guided mode spectroscopy, exploiting their best performances and overcoming their limits. The dispersion curves of nematic liquid crystal E7 have been estimated in the 450–1700nm wavelength interval with both precision and accuracy of 10−4.
Size-dependent phase transition memory switching behavior and low writing currents in GeTe nanowires
Authors: Lee Se-Ho , Ko Dong-Kyun , Jung Yeonwoong , Agarwal Ritesh
Published: November 2006

Synthesis and device characteristics of highly scalable GeTe nanowire-based phase transition memory are reported. The authors have demonstrated reversible phase transition memory switching behavior in GeTe nanowires, and obtained critical device parameters, such as write and erase currents, threshold voltage, and programming curves. The diameter dependence of memory switching behavior in GeTe nanowires was studied and a systematic reduction of writing currents with decreasing diameter was observed, with currents as low as 0.42mA for a 28nm nanowire. Results show that nanowires are very promising for scalable memory applications and for studying size-dependent phase transition mechanisms at the nanoscale.
Terahertz birefringence of liquid crystal polymers
Authors: Rutz F. , Hasek T. , Koch M. , Richter H. , Ewert U.
Published: November 2006

The authors present terahertz time-domain spectroscopy (TDS) measurements on injection molded liquid crystalline polymers (LCPs). Pure LCP yields a strong birefringence of Δn=0.2. They find that the direction of the optical axis varies within the injection molded sample. By terahertz (polarization) imaging domains of certain directions of the optical axis could be observed. These strongly depend on the mold geometry. Since the alignment of particles and rodlike polymer molecules tend to follow the melt flow during injection molding, terahertz TDS can be used to analyze injection molded LCP parts and control the process performance.
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monitoring in ambient air by communication band laser diode based difference frequency generation in a quasi-phase-matched LiNbO3 waveguide
Authors: Yanagawa Tsutomu , Tadanaga Osamu , Magari Katsuaki , Nishida Yoshiki , Miyazawa Hiroshi , Asobe Masaki , Suzuki Hiroyuki
Published: November 2006

Methane in ambient air is detected by difference frequency generation in a direct-bonded quasi-phase-matched LiNbO3 ridge waveguide using near infrared communication band laser diodes as pump and signal sources. Absorption lines for the Q branch in the 3.3μm ν3 band are measured by using a Hanst configuration multipass cell with a 107m path length. The authors detect 35ppb CH4 in 2kPa ambient air with a single wavelength scan of a signal external cavity laser diode by suppressing various spectroscopic fringes and stabilizing the pump laser diode oscillation mode with a fiber Bragg grating.
Polymorphism and metastable phenomena in liquid tin under pressure
Authors: Di Cicco Andrea , Trapananti Angela , Principi Emiliano , De Panfilis Simone , Filipponi Adriano
Published: November 2006

Polymorphism of substances under high pressures is observed and used to obtain materials with new physical properties. Here the authors present experimental results revealing phase transitions and structure of liquid tin at high pressure under metastable conditions using x-ray absorption spectroscopy and x-ray diffraction. They show that there is an abrupt change in the undercooling limit of liquid Sn above 2GPa, where nucleation takes place into the Sn-III metastable solid phase. The liquid local structure is found to be composed of tetrahedral and close-packed configurations. The latter are found to dominate at high pressure favoring crystallization to the Sn-III metastable solid phase.
Nanobumps on silicon created with polystyrene spheres and 248 or 308nm laser pulses
Authors: Piparia Reema , Rothe Erhard W. , Baird R. J.
Published: November 2006

Huang et al. [Appl. Phys. Lett. 86, 161911 (2005)] formed arrays of nanobumps on a silicon substrate. They applied a 248nm laser pulse to a surface monolayer of 1-μm-diameter polystyrene spheres. The authors first replicated their experiment with 248nm light. But when 308nm pulses were applied instead, the nanobumps had a different shape and composition. At 248nm, much of the laser light is absorbed in the polystyrene, which serves to quickly distort, melt, and ablate the sphere. At 308nm, very little light is absorbed. The nanobumps from 248nm radiation are organic polymers, while those formed with 308nm pulses are silicon based.
Numerical simulation of biomagnetic fluid downstream an eccentric stenotic orifice
Authors: Khashan Saud A. , Haik Yousef
Published: November 2006

Biomagnetic fluid dynamics is the study of the interaction of biological fluids with an applied steady magnetic field. The composition of the biological fluid is considered nonconducting; however, it has magnetic moment. The magnetic moment of the biological fluid can be enhanced by tagging superparamagnetic particles. Several biomedical applications recently developed utilize the magnetic labeling of cellular components. In this paper, the biomagnetic fluid downstream an eccentric stenotic orifice is considered. An external magnetic field is applied at different locations down stream the stenotic orifice. It is found that based on the location of the magnetic field, the reattachment point downstream the stenotic orifice changes; it is also found that the shear stress will be affected based on the magnetic field location. Major changes in the flow pattern have been also observed based on the magnetic field strength.
A detailed analysis of vibrational excitations in x-ray photoelectron spectra of adsorbed small hydrocarbons
Authors: Steinrück H.-P. , Fuhrmann T. , Papp C. , Tränkenschuh B. , Denecke R.
Published: November 2006

The vibrational fine structure of x-ray photoelectron (XP) spectra of a number of different small hydrocarbon molecules and reaction intermediates adsorbed on Pt(111) and Ni(111) has been investigated in detail. The data for methyl, methylidyne, acetylene, and ethylene can consistently be analyzed within the linear coupling model. The S factor, i.e., the intensity ratio of the first vibrationally excited to the adiabatic transition, is obtained to be 0.17±0.02 per C–H bond; for the deuterated species a value of 0.23±0.02 is obtained. Therefore, the vibrational fine structure can be used for fingerprinting in the analysis of XP spectra and for identifying unknown reaction intermediates. From the data, Δr, the change of the minimum in the potential energy curve upon core ionization, is calculated within the linear coupling model using a first order correction. For all adsorbates, including the deuterated ones, a value of Δr=0.060±0.004Å is obtained. Furthermore, from the binding energy of the adiabatic peak and from the energy of the vibrational excitation in the ionic final state some information on the adsorbate/substrate bond and the adsorption site can be derived.
Why alkali metals preferably bind on structural defects of carbon nanotubes: A theoretical study by first principles
Authors: Mpourmpakis Giannis , Froudakis George
Published: November 2006

By using ab initio calculations we investigated the interaction of alkali metal atoms and alkali metal cations with perfect and defective carbon nanotubes. Our results show that the alkali metals prefer to interact with the pentagons and heptagons that appear on the defective site of the carbon nanotube rather than with the hexagons. The alkali metals remain always positively charged not depending on their charge state (neutral, cation) or the different carbon ring that they interact with. The molecular orbital energy level splitting from a defect creation on the carbon nanotube along with the localization of charge-electron density on the defect, results in binding the alkali metals more efficient. More interestingly, metallic sodium appears to bind very weak on the nanotube compared to the rest of alkali metals. The Na anomaly is attributed to the fact that unlike the K case, sodium’s inner p shell falls energetically lower than carbon nanotube’s p molecular orbitals. As a result, the Na p shell is practically excluded from any binding energy contribution. In the alkali metal cation case the electronegativity trend is followed.
Reduction and solution of the chemical master equation using time scale separation and finite state projection
Authors: Peleš Slaven , Munsky Brian , Khammash Mustafa
Published: November 2006

The dynamics of chemical reaction networks often takes place on widely differing time scales—from the order of nanoseconds to the order of several days. This is particularly true for gene regulatory networks, which are modeled by chemical kinetics. Multiple time scales in mathematical models often lead to serious computational difficulties, such as numerical stiffness in the case of differential equations or excessively redundant Monte Carlo simulations in the case of stochastic processes. We present a model reduction method for study of stochastic chemical kinetic systems that takes advantage of multiple time scales. The method applies to finite projections of the chemical master equation and allows for effective time scale separation of the system dynamics. We implement this method in a novel numerical algorithm that exploits the time scale separation to achieve model order reductions while enabling error checking and control. We illustrate the efficiency of our method in several examples motivated by recent developments in gene regulatory networks.
In situ determination of interface dipole energy in organic light emitting diodes with iridium interfacial layer using synchrotron radiation photoemission spectroscopy
Authors: Kim Soo Young , Lee Jong-Lam
Published: November 2006

The interface dipole energies between 4,4′-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl and Ir interfacial layers with different thicknesses (2 and 20nm) coated on indium tin oxides (ITOs) were measured in situ using synchrotron radiation photoemission spectroscopy. In 20nm Ir coated ITO, the work function increment of 0.15eV due to O2 plasma treatment was accompanied by an increase of interface dipole energy. In 2nm Ir coated ITO, no change in the interface dipole energy was found. Thus, the work function increase (0.45eV) in the 2nm Ir by O2 plasma treatment reduced the hole injection barrier by about 0.45eV.
Experimental confirmation of backscattering enhancement induced by a photonic jet
Authors: Heifetz Alexander , Huang Kevin , Sahakian Alan V. , Li Xu , Taflove Allen , Backman Vadim
Published: November 2006

The authors report experimental confirmation of backscattering enhancement induced by a photonic jet emerging from a dielectric sphere, a phenomenon recently predicted by theoretical solutions of Maxwell’s equations. To permit relatively straightforward laboratory measurements at microwave frequencies rather than visible light, they appropriately scaled the original conceptual dimensions of the dielectric microsphere and its adjacent perturbing nanoparticle (located within the microsphere’s photonic jet). Their experiments verified the existence of enhanced position-dependent backscattering perturbations by the adjacent particle. Their measured backscattering perturbations agreed well with prior theory and with additional finite-difference time-domain computational models of the complete microwave test geometry.
Real time observation of domain reversal in cerium-doped Sr0.61Ba0.39Nb2O6 single crystal fibers
Authors: Huang C. , Bhalla A. , Guo R.
Published: November 2006

Domain configuration is of significant importance in utilizing ferroelectric single crystals such as strontium barium niobate (SBN) to design optoelectronic and nonlinear optical devices. This letter reports the real time observation of domain reversal in cerium doped SBN crystal fibers by electro-optic imaging microscopy. The SBN single crystal fibers studied were grown using the laser heated pedestal growth technique. The dynamic polarization switching behavior of SBN crystal fibers can be described as an antiparallel domain nucleation at low electric fields after a dormant period and a sideways growth of domain walls at higher electric field. These two different mechanisms result in the asymmetric current curve of domain switching dynamics.
Enhancement of field emission of aligned carbon nanotubes by thermal oxidation
Authors: Zeng Baoqing , Xiong Guangyong , Chen Shuo , Wang W. Z. , Wang D. Z. , Ren Z. F.
Published: November 2006

To improve the field emission current density of aligned carbon nanotubes grown by thermal chemical vapor deposition, postgrowth thermal annealing was conducted at 850°C for 1h in vacuum plus at 465°C for 2h in air. It was found that the highest field emission current density significantly improved by a factor of 4 (from 19to79mA∕cm2), which is due to the substantial increase of the emitting area of the carbon nanotubes after annealing. This result is important for applications of using carbon nanotubes as high current electron sources, microwave devices, flat panel displays, etc.
Optical transitions of Cu2O nanocrystals in SiO2 fabricated by ion implantation and two-step annealing
Authors: Amekura H. , Umeda N. , Takeda Y. , Kishimoto N.
Published: November 2006

Nanocrystals (NCs) of cuprous oxide (Cu2O), cupric oxide (CuO), and copper metal (Cu) are fabricated in silica glasses (SiO2) by implantation of 60keV Cu− ions at different annealing conditions. At room temperature, Cu2O NCs show two sharp absorption peaks at 2.58 and 2.71eV due to autoionized exciton states, and Cu NCs show a broad peak at ∼2.2eV due to the surface plasmon resonance (SPR). With decreasing temperature down to 2.8K, the peaks of Cu2O NCs become much narrower, while the SPR peak of Cu NCs keeps almost the same peak width.