bluuebunny/crossref_metadata_2025 huggingface dataset:
Transition from quasistatic to ferromagnetic resonance regime in giant magnetoimpedance
Authors: Barandiarán J. M. , García-Arribas A. , de Cos D.
Published: June 2006

Detailed measurements of giant magnetoimpedance (GMI) in an amorphous ribbon and a magnetic/nonmagnetic multilayer are presented for frequencies up to 3GHz. Through this frequency range, the transition from quasistatic to dynamic regime of GMI can be clearly distinguished, due to the appearance of the ferromagnetic resonance (FMR). The unambiguous experimental evidence presented mediates between conflicting interpretations of GMI: the ones that assume the existence of FMR even for low frequencies and the ones that consider that it is irrelevant. The frequency at which the transition takes place is shown to be related with the width of the resonance, which is substantially different for both samples. It is concluded that the large increase of permeability caused by the ferromagnetic resonance can be advantageous for GMI-based devices only for samples with a small, very well-defined perpendicular anisotropy.
Experimental measurement of the principal isentrope for aluminum 6061-T6 to 240GPa
Authors: Davis Jean-Paul
Published: June 2006

Using a magnetic pressure drive, an absolute measurement of stress and density along the principal compression isentrope is obtained for solid aluminum to 240GPa. Reduction of the free-surface velocity data relies on a backward integration technique, with approximate accounting for unknown systematic errors in experimental timing. Maximum experimental uncertainties are ±4.7% in stress and ±1.4% in density, small enough to distinguish between different equation-of-state (EOS) models. The result agrees well with a tabular EOS that uses an empirical universal zero-temperature isotherm.
The thickness dependence of ferroelectric and magnetic properties in epitaxial BiFeO3 thin films
Authors: Jiang Q. , Qiu J. H.
Published: June 2006

In the framework of a general Landau free energy function, which is used in conventional ferroelectrics, we investigate the ferroelectric and magnetic properties of multiferroic epitaxial BiFeO3 thin films. It is shown that the properties of BiFeO3 thin films, such as lattice parameter, polarization, and magnetization, etc., are functions of misfit strains. The film thickness dependence of epitaxial strains due to relaxation by misfit dislocations during film deposition is incorporated into the model by using an effective substrate lattice parameter. Therefore, the thickness dependence of ferroelectric and magnetic properties in BiFeO3 epitaxial thin films is well explained.
Material-dependent high-frequency current fluctuations of cathodic vacuum arcs: Evidence for the ecton cutoff of the fractal model
Authors: Anders André , Oks Efim
Published: June 2006

Current fluctuations of cathodic arcs were recorded with high analog bandwidth (up to 1GHz) and fast digital sampling (up to 5Gsamples∕s). The power spectral density of the arc current was determined by fast Fourier transform clearly showing material dependent, nonlinear features in the frequency domain. These features can be associated with the nonlinear impedance of the conducting channel between cathode and anode, driven by the explosive nature of electron emission and plasma formation. The characteristic times of less than 100ns can be associated with individual explosive processes, “ectons,” and therefore represent the short-time physical cutoff for the fractal model of cathodic arcs.
Magnetization curves for tetragonal martensites: Experiments and modeling
Authors: Chernenko Volodymyr A. , Zagorodnyuk Sergei P. , L’vov Victor A. , O’Handley Robert C. , Kono Yukio
Published: June 2006

In the absence of twin boundary motion, the magnetization curves of tetragonal martensites depend on the relative orientation of crystal axes, the shape anisotropy, and the applied field. Two tetragonal martensites with the lattice parameters ratio c∕a<1 (easy axis) and c∕a>1 (easy plane) exist in Ni–Mn–Ga alloys. The magnetization curves of rods and plates of both types of martensite, chosen for their immobile twin boundaries, have been measured at room temperature. The M(H) curves are well described by a theory including magnetocrystalline anisotropy and magnetostatic energy. The results can indicate the variant distribution in each of the samples.
Modeling and characterization of organic thin film transistors for circuit design
Authors: Fadlallah M. , Benzarti W. , Billiot G. , Eccleston W. , Barclay D.
Published: June 2006

In this paper, we develop a device model of an organic thin film transistor for a circuit design, more specifically, for organic radio frequency identification applications. This model is based on variable range hopping theory, i.e., a carrier may either hop over a small distance with a high activation energy or hop over a long distance with a low activation energy. The model takes into account all the operating regimes in direct current and transient mode; the transistor symmetry is also considered. The model has been developed using a physical basis where the model parameters can easily be extracted and it improves convergence in circuit simulations. It is also suitable for computer aided design applications.
Effect of Mn+ ion implantation on the Raman spectra of ZnO
Authors: Zhong Hongmei , Wang Jinbing , Chen Xiaoshuang , Li Zhifeng , Xu Wenlan , Lu Wei
Published: June 2006

Raman measurements have been performed on ZnO bulk materials implanted with 220keV Mn+ ions with various doses from 1015to1017cm2. The results reveal two modes at about 230 and 523cm−1, respectively, which are not observed in unimplanted ZnO. One mode at 230cm−1 is assigned to the acoustic-phonon branch at the zone boundary. Another mode at 523cm−1 is attributed to Zn-related vibration due to Mn incorporation. By using a real-space recursion method, the theoretical calculation indicates that the Zn-related mode originates from the vibration of the Zn atom surrounded with the first nearest neighbor of Mn atoms, where the local Zn-related structures are formed by Mn atoms replacing partially the O atoms in the ZnO crystal lattice.
Passively Q-switched laser operation of Nd:LaB3O6 cleavage microchip
Authors: Chen Y. J. , Gong X. H. , Lin Y. F. , Tan Q. G. , Luo Z. D. , Huang Y. D.
Published: June 2006

Pumped by a Ti:sapphire laser, a passively Q-switched laser oscillation from an unprocessed Nd:LaB3O6 cleavage microchip with a Cr4+:YAG saturable absorber has been demonstrated. The influence of the transmission of the output coupler on the pulse width and repetition rate at various absorbed pump powers has been investigated. A pulse with 2.8μJ energy, 2.2ns duration, and 29kHz repetition rate at 1060nm was obtained at the absorbed pump power of 1.25W and output coupler transmission of 3.2%, which results in 1.25kW peak power. The polarization and spectral properties of laser radiation were measured.
Three-dimensional continuous modeling of beam-electron cloud interaction: Comparison with analytic models and predictions for the present and future circular machines
Authors: Ghalam A. Z. , Katsouleas T. , Decyk V. K. , Huang C. K. , Mori W. B. , Rumolo G. , Benedetto E. , Zimmermann F.
Published: June 2006

Long-term beam-electron cloud interaction is modeled with a three-dimensional parallel continuous model originally developed for plasma wakefield acceleration modeling. The simulation results are compared with the two-macroparticle model for strong head-tail instability. The two-macroparticle model captures some of the instability features of the beam; however, this model is too simple to accurately describe the complex nature of the beam-cloud interaction. The effects of dipole magnets on the horizontal and vertical beam size are discussed. The dipole magnets have stabilizing effect and reduce the beam spot size growth especially in the horizontal plane. The code is then used to model and make predictions for the beam dynamics in the presence of an electron cloud for several present and future circular machines around the world.
X-ray scattering study of hydrogen implantation in silicon
Authors: Sousbie Nicolas , Capello Luciana , Eymery Joël , Rieutord François , Lagahe Chrystelle
Published: June 2006

The effect of hydrogen implantation in silicon single crystals is studied using high-resolution x-ray scattering. Large strains normal to the sample surface are evidenced after implantation. A simple and direct procedure to extract the strain profile from the scattering data is described. A comparison between different crystallographic orientation of the implanted silicon surface is then presented, namely, for ⟨100⟩, ⟨110⟩, and ⟨111⟩ orientations, showing a dependence that can be related to bond orientation. Effect of annealing on the stressed structure is finally described.
Microwave properties of Ba0.5Sr0.5TiO3 thin film coplanar phase shifters
Authors: Suherman P. M. , Jackson T. J. , Tse Y. Y. , Jones I. P. , Chakalova R. I. , Lancaster M. J. , Porch A.
Published: June 2006

Coplanar waveguide transmission lines have been used to show that the temperature dependent properties of Ba0.5Sr0.5TiO3 thin films used for microwave phase shifters in the frequency range 45MHz–50GHz are correlated strongly with the microstructure of the films. The highest tunability and figure of merit of the phase shifters were obtained for films with the narrowest ferroelectric-paraelectric phase transition range, lowest mosaic spread, and widest columnar microstructure. The study also showed that the operating temperature plays an important role in achieving the optimum phase shift for microwave applications.
Stress induced monoclinic phase in epitaxial BaTiO3 on MgO
Authors: Misirlioglu I. B. , Alpay S. P. , He Feizhou , Wells B. O.
Published: June 2006

We present a detailed strain analysis of epitaxial ferroelectric films taking into account multiple sources of strain, including the lattice mismatch between the film and the substrate, thermal strains due to differences in the thermal expansion coefficients of the film and the substrate, and relaxation by the formation of interfacial dislocations. The lattice parameters of the film are calculated using a thermodynamic formalism coupled with the strain analysis. The theoretical model shows that epitaxial (001) BaTiO3 films on (001) MgO are expected to display successive phase transformations with decreasing temperatures that are different than the bulk. This is verified experimentally for 50nm thick (001) BaTiO3 films grown on (001) MgO substrates at 720°C using pulsed laser deposition. A synchrotron x-ray diffraction study displays two slope changes in the temperature dependence of the out-of-plane lattice constant. This indicates that two phase transformations exist in the film as a function of temperature with transition temperatures and lattice constants that are consistent with the theoretically predicted phases. Theoretical results show that the first transformation at around 270°C corresponds to a paraelectric-ferroelectric transition. The ferroelectric phase has an orthogonal symmetry (Amm2) with in-plane polarization components. The transformation at around −20°C is an Amm2↔Pm transition between two ferroelectric phases. The ferroelectric Pm phase is monoclinic compared to the rhombohedral R3m phase in bulk.
Fluorine in preamorphized Si: Point defect engineering and control of dopant diffusion
Authors: Impellizzeri G. , Mirabella S. , Priolo F. , Napolitani E. , Carnera A.
Published: June 2006

While it is known that F modifies dopant diffusion in crystalline Si, the physical mechanisms behind this process are still unclear. In this work we report experimental studies about the F control of the point defect density in preamorphized Si layers. These studies put the basis for the understanding of the F behavior and for the realization of ultra-shallow junctions. We first investigated the F incorporation process during the solid phase epitaxy (SPE) of amorphous Si layers. We elucidated the role of the SPE temperature on the F incorporation and suggested a new route towards a F profile engineering. Moreover, we explained the role of F in modifying the point defect population (self-interstitials, Is, and vacancies, Vs), employing B and Sb spike layers as markers for Is and Vs, respectively. We clearly showed that F decreases the B diffusion while enhances the Sb one, pointing out the capacity to induce an Is undersaturation or a Vs supersaturation. These data rule out the hypothesis of a chemical bonding between F and the dopants. Such F ability in modifying the Is/Vs density resulted to be a transient effect, because strictly correlated with the presence of F in the Si samples, which decreases with the annealing time. In addition, we evidenced that even if F is spatially separated from B, i.e., localized between shallow-implanted B and the end-of-range (EOR) region, it still suppresses the enhancement of B diffusivity, due to the EOR defects dissolution. These studies, besides improving the current understanding of the physical mechanisms by which F influences the dopant diffusion in Si, could be helpful for the realization of ultra-shallow junctions for the future metal-oxide-semiconductor devices.
Effect of sulfurization conditions and post-deposition annealing treatment on structural and electrical properties of silver sulfide films
Authors: Kundu Manisha , Terabe Kazuya , Hasegawa Tsuyoshi , Aono Masakazu
Published: June 2006

We examined the structural and electrical properties of silver sulfide films as a function of the sulfurization time of 70-nm-thick Ag films. Variations in the sulfurization time caused variations in the Ag∕S atomic percentage ratio of the silver sulfide films, and as-grown films with various compositions, such as S-rich (Ag∕S=1.59), stoichiometric (Ag∕S=2), and Ag-rich (Ag∕S=2.16) films were formed. Amongst the various as-grown films, Ag ions existed in the most polarizable environment in the Ag-rich films. All the films existed in the acanthite α-phase, and the sulfurization conditions did not cause any drastic change in the preferred orientation of this phase. The resistivity of these films strongly depended on the Ag∕S ratio. While the resistivity of stoichiometric or S-rich films was about 107–108Ωcm, excess Ag of the Ag-rich film caused a decrease in the resistivity by four orders of magnitude. The Ag∕S ratio also played a significant role in our observation of the change in resistance within the films from high- to low-resistance state and vice versa with the reversal of the bias polarity of the film. Distinct switching of the resistance was observed only for the Ag-rich film. We also examined the effects of post-deposition annealing (PDA) of various films at 190°C. PDA caused the formation of Ag-rich films (Ag∕S=2.12–2.17) in all cases, and Ag ions existed in a more polarizable environment in all the films as compared with stoichiometric film. All the annealed films contained mixed acanthite α-phase and argentite β-phase. Furthermore, all the films had low resistivities of about 0.01–0.02Ωcm, which indicated that the coexisting metallic argentite β-phase of the films significantly improved the conductivity of the films as compared to the as-grown film with similar Ag∕S ratio. Clear switching behavior of the resistance could be observed within all the annealed films, thereby indicating that excess Ag in the silver sulfide films is a requirement for observation of such a phenomenon.
Optimal temperature distribution in a three dimensional triple-layered skin structure with embedded vasculature
Authors: Dai Weizhong , Bejan Adrian , Tang Xingui , Zhang Le , Nassar Raja
Published: June 2006

In recent years there has been interest in research related to hyperthermia combined with radiation and cytotoxic drugs to enhance the killing of tumors. When heating the tumor tissue, the crucial problem is keeping the temperature of the normal tissue surrounding the tumor below a certain threshold so as not to cause damage to the tissue. Hence, in order to control the process, it is important to obtain a temperature field of the entire treatment region. Recently, we have developed a numerical method for obtaining an optimal temperature distribution in a triple-layered skin structure. In this article, we extend our study to a triple-layered skin structure embedded with multilevel blood vessels, and develop a numerical method for obtaining an optimal temperature distribution.
Large Faraday effect in a short wavelength range for disordered zinc ferrite thin films
Authors: Tanaka Katsuhisa , Nakashima Seisuke , Fujita Koji , Hirao Kazuyuki
Published: June 2006

We have prepared a zinc ferrite (ZnF2O4) thin film 85nm thick deposited on a silica glass substrate by using a radio frequency sputtering method. Faraday effect measurements have been carried out not only for as-deposited but also for annealed thin films. The thin film annealed at 300°C as well as the as-deposited thin film exhibit a large Faraday rotation angle at a wavelength of around 390nm. In particular, the thin film annealed at 300°C manifests the largest Faraday effect among the present thin films; the rotation angle of 1.65°∕μm is attained at a wavelength of 386nm. The thin films 1.08μm thick exhibit a large magnetization at room temperature, and the dependence of the magnetization on the external magnetic field is suggestive of a ferrimagnetic behavior.
Wetting-induced electrorheological effect
Authors: Shen Cai , Wen Weijia , Yang Shihe , Sheng Ping
Published: June 2006

We demonstrate the role of particle-fluid wetting in inducing the electrorheological (ER) effect. Nanoparticles of barium titanyl oxalate coated with urea (BTRU) were suspended in either silicone oil or hydrocarbon oil. In the former, a high yield stress of more than 250kPa can be attained at an electric field of 5kV∕mm, while for the latter no measurable ER effect can be obtained. The two suspensions exhibit completely different appearances. Whereas the silicone oil suspension has the consistency of light cream, in the case of hydrocarbon oil with the same solid concentration the appearance is that of a lumpy paste. This clear visual distinction is attributed to the wetting characteristic between the solid BTRU particles and the suspending oil. We found that by adding a controlled, small amount of surfactant additive to the hydrocarbon oil suspension (oleic acid), the consistency can change drastically to resemble that of the silicone oil suspension, with a yield stress of 260kPa attained at an electric field of 3kV∕mm. We give a simple physical picture of wetting-induced giant electrorheological effect.
Hexagonal zinc sulfide nanocrystals coated by esters with a well-defined exciton feature
Authors: Song Shuqing , Gao Qiuming
Published: June 2006

Hexagonal zinc sulfide nanocrystals (ZnS NCs) were prepared under mild solvothermal condition at 170°C with the polymer ester used as ligand for their stability and effective passivation. Well-defined absorption peaks with the largest blueshift of 89nm were observed for the ZnS NCs based on the ultraviolet-visible (UV-vis) absorption spectra analyses compared with that of the bulk one, which are in correspondence with the apparent quantum confinement effects. Well excited states were obtained from UV-vis absorption and photoluminescent excitation (PLE) spectra for the ZnS NCs. PL emission spectra showed dominant band-edge luminescence.
Direct observation of Barkhausen effect in strip-patterned ferromagnetic Co∕Pd multilayer films
Authors: Choe Sug-Bong , Kim Dong-Hyun , Ryu Kwang-Su , Lee Hae-Seung , Shin Sung-Chul
Published: June 2006

The one-dimensional Barkhausen effect was observed in lithographically defined magnetic strips of Co∕Pd multilayer films. The magnetic domain expanded stepwise with a constant speed between pinning sites. Both the wall propagation and the pinning were characterized by the thermal activation process based on their exponential dependency on the strength of the applied magnetic field. The Barkhausen volume was determined to be 1.7×10−13cm3, which was several orders larger than the activation volume of the wall propagation, 6.5×10−18cm3.
Computation of methodology-independent ionic solvation free energies from molecular simulations. II. The hydration free energy of the sodium cation
Authors: Kastenholz Mika A. , Hünenberger Philippe H.
Published: June 2006

The raw ionic solvation free energies computed from atomistic (explicit-solvent) simulations are extremely sensitive to the boundary conditions (finite or periodic system, system shape, and size) and treatment of electrostatic interactions (Coulombic, lattice sum, or cutoff based) used during these simulations. In the present article, it is shown that correction terms can be derived for the effect of (A) an incorrect solvent polarization around the ion due to the use of an approximate (not strictly Coulombic) electrostatic scheme; (B) the finite size or artificial periodicity of the simulated system; (C) an improper summation scheme to evaluate the potential at the ion site and the possible presence of a liquid-vacuum interface in the simulated system. Taking the hydration free energy of the sodium cation as a test case, it is shown that the raw solvation free energies obtained using seven different types of boundary conditions and electrostatic schemes commonly used in explicit-solvent simulations (for a total of 72 simulations differing in the corresponding simulation parameters) can be corrected so as to obtain a consistent value for this quantity.
Calculation of the direct tunneling current in a metal-oxide-semiconductor structure with one-side open boundary
Authors: Nadimi E. , Radehaus C. , Nakhmedov E. P. , Wieczorek K.
Published: June 2006

The leakage current through the oxide of an n-channel metal-oxide-semiconductor (MOS) structure with an open boundary on one side is numerically computed by applying a one-dimensional Schrödinger-Poisson self-consistent solver. By embedding the n-channel MOS structure in a well, which prevents the penetration of particles into the metallic gate, the potential profile, the bounded energy levels, and the spatial distribution of electrons in the quantized levels are calculated in the inversion regime. Penetration of electrons into the metallic gate with an open boundary results in a broadening of the discrete bound states at the interface of the substrate with the oxide, transforming the bounded energy levels to the quasibound states. Starting from the continuity equation, a qualitative formula for the current in terms of the electron lifetime in the quasibound states is derived. Based on the determination of the energy level width corresponding to the wave functions, we suggest a method to compute the lifetime, and subsequently, the tunneling current across the potential barrier. The tunneling current is computed for a MOS structure with SiO2 and Si3N4 gate dielectrics. The computational results are compared with those obtained experimentally for similar structures, yielding an excellent agreement.
Raman scattering probe of anharmonic effects due to temperature and compositional disorder in GaNxAs1−x
Authors: Liu H. F. , Xiang N. , Tripathy S. , Chua S. J.
Published: June 2006

Using micro-Raman spectroscopy, we have investigated the vibrational properties of coherently strained GaNxAs1−x alloys grown on GaAs (001) substrates by molecular beam epitaxy. The effect of compositional disorder in GaNxAs1−x alloys has been studied by analyzing the broadening, asymmetry, and line shift of the first-order LO mode and nitrogen-induced localized vibration mode (NLVM). It is found that the line shape and peak shift of GaAs-like LO mode in GaNxAs1−x can be well described by the spatial correlation model. We have also analyzed Raman spectra of GaNxAs1−x alloys in the temperature range of 80–500K. The intensity of GaAs-like LO phonon and NLVM decreases with temperature and the linewidth of both these modes shows substantial broadening at higher temperature. The temperature dependence of phonon linewidth and peak frequency of LO modes are analyzed in terms of anharmonic damping effect induced by thermal and compositional disorders. We have observed that the anharmonicity in GaNxAs1−x is higher than that in GaAs, and increases with the N content in GaNxAs1−x alloys. In addition, both thermal and compositional disorder-induced anharmonicities lead to an appreciable change of the LO phonon lifetime. These results obtained from Raman investigations would lead to a better understanding of the anharmonic effects in dilute nitrides.
Acceleration of plasma flows in the closed magnetic fields: Simulation and analysis
Authors: Mahajan Swadesh M. , Shatashvili Nana L. , Mikeladze Solomon V. , Sigua Ketevan I.
Published: June 2006

Within the framework of a two-fluid description, possible pathways for the generation of fast flows (dynamical as well as steady) in the closed magnetic fields are established. It is shown that a primary plasma flow (locally sub-Alfvénic) is accelerated while interacting with ambient arcade-like closed field structures. The time scale for creating reasonably fast flows (≳100km∕s) is dictated by the initial ion skin depth, while the amplification of the flow depends on local plasma β. It is shown that distances over which the flows become “fast” are ∼0.01R0 from the interaction surface (R0 being a characteristic length of the system); later, the fast flow localizes (with dimensions ≲0.05R0) in the upper central region of the original arcade. For fixed initial temperature, the final speed (≳500km∕s) of the accelerated flow and the modification of the field structure are independent of the time duration (lifetime) of the initial flow. In the presence of dissipation, these flows are likely to play a fundamental role in the heating of the finely structured stellar atmospheres; their relevance to the solar wind is also obvious.
Modulational instability of dust acoustic waves in dusty plasmas: Modulation obliqueness, background ion nonthermality, and dust charging effects
Authors: El-Taibany W. F. , Kourakis I.
Published: June 2006

The oblique modulational instability of dust acoustic (DA) waves in an unmagnetized warm dusty plasma with nonthermal ions, taking into account dust grain charge variation (charging), is investigated. A nonlinear Schrödinger-type equation governing the slow modulation of the wave amplitude is derived. The effects of dust temperature, dust charge variation, ion deviation from Maxwellian equilibrium (nonthermality) and constituent species’ concentration on the modulational instability of DA waves are examined. It is found that these parameters modify significantly the oblique modulational instability domain in the k-θ plane. Explicit expressions for the instability rate and threshold have been obtained in terms of the dispersion laws of the system. The possibility and conditions for the existence of different types of localized excitations are also discussed. The findings of this investigation may be useful in understanding the stable electrostatic wave packet acceleration mechanisms close to the Moon, and also enhances our knowledge on the occurrence of instability associated to pickup ions around unmagnetized bodies, such as comets, Mars, and Venus.
High tolerance to total ionizing dose of Ω-shaped gate field-effect transistors
Authors: Gaillardin Marc , Paillet Philippe , Ferlet-Cavrois Véronique , Cristoloveanu Sorin , Faynot Olivier , Jahan Carine
Published: June 2006

Ionizing radiation effects are investigated in N-channel metal-oxide-semiconductor triple-gate field-effect transistors with Ω-shaped gate fin field-effect transistor (FinFET) architecture. The total dose response is shown to be dependent on device geometry. A wide FinFET structure behaves like a single-gate fully depleted silicon-on-insulator transistor, showing a noticeable degradation induced by ionizing radiation. By contrast, an optimized narrow FinFET shows a drastically reduced influence of ionizing radiation thanks to the efficient electrostatic control of the potential in the device provided by the Ω gate. A narrow FinFET is shown to be naturally tolerant to a significant total dose exposure.
“Sliding kinetics” of single-walled carbon nanotubes on self-assembled monolayer patterns: Beyond random adsorption
Authors: Im Jiwoon , Huang Ling , Kang Juwan , Lee Minbaek , Lee Dong Joon , Rao Saleem G. , Lee Nam-Kyung , Hong Seunghun
Published: June 2006

We present the experimental results and theoretical model describing new adsorption kinetics of single-walled carbon nanotubes (swCNTs) onto self-assembled monolayer (SAM) including their sliding motion. The adsorption behavior of swCNTs on large-size SAM patterns is similar to the Langmuir isotherm, while that on nanoscale patterns shows a significant deviation which can be explained by the sliding motion of adsorbed nanotubes. The “sliding chamber” experiment confirms that swCNTs can align along the SAM patterns by sliding motion right above the SAM surfaces. This result provides new scientific insights regarding the adsorption kinetics of one-dimensional nanostructures, and, from a practical point of view, it can be an important guideline to design SAM patterns to assemble carbon nanotubes and nanowires into desired device structures.
Magnetically insulated ion flow theory
Authors: Ottinger P. F. , Schumer J. W.
Published: June 2006

Initiation of an anode plasma and ion emission into a magnetically insulated transmission line can cause serious current losses unless the ions are magnetically insulated as well as the electrons. A model for magnetically insulated ion flow in a vacuum transmission line is developed. Particle-in-cell simulations are presented that show that this model accurately predicts properties of this flow. The model is applied to determine the current required to magnetically insulate ion flow for a given voltage and vacuum line impedance. Relevance of this work to system designs for Z-pinch-driven inertial confinement fusion is discussed.
Adiabatic approximations to internal rotation
Authors: Allen Wesley D. , Bodi Andras , Szalay Viktor , Császár Attila G.
Published: June 2006

A number of subtle and confusing issues are addressed concerning large amplitude motion (LAM) coordinates (χ) for internal molecular motions, using the methyl rotation in acetaldehyde (CH3CHO) as a model problem. If the LAM coordinate is chosen to be one of the H–C–C–O dihedral angles ρ1, ρ2, or ρ3, it lacks the required 2π∕3 periodicity, and its use is thus undesirable. An excellent local internal coordinate for this model problem is τ3=13(ρ1+ρ2+ρ3−2π). A similarly good but nonlocal coordinate for the adiabatic approximation of internal rotation is provided by the intrinsic reaction coordinate s. Comparison of the mass-independent V0(τ3) and the mass-dependent V0(s) internal rotation curves shows that the two are virtually identical for the parent isotopolog of acetaldehyde. A unified internal coordinate projection scheme for determining complementary vibrational frequencies and subsequently VZPVE(χ) along a path for LAM has been formulated, where VZPVE(χ) is the zero-point vibrational energy correction to the internal rotation curve. In addition to its simplicity, the projection scheme developed for a distinguished reaction path generated by constrained optimizations is appealing because the vibrational frequencies along the LAM path are invariant to chemically meaningful choices of the internal coordinates for the complementary modes.
Electronic structures of group-III–nitride nanorods studied by x-ray absorption, x-ray emission, and Raman spectroscopy
Authors: Pao C. W. , Babu P. D. , Tsai H. M. , Chiou J. W. , Ray S. C. , Yang S. C. , Chien F. Z. , Pong W. F. , Tsai M.-H. , Hsu C. W. , Chen L. C. , Chen C. C. , Chen K. H. , Lin H.-J. , Lee J. F. , Guo J. H.
Published: June 2006

Nitrogen (N) and metal (Al, Ga, and In) K-edge x-ray absorption near-edge structure (XANES), x-ray emission spectroscopy (XES), and Raman scattering measurements were performed to elucidate the electronic structures of group-III–nitride nanorods and thin films of AlN, GaN, and InN. XANES spectra show slight increase of the numbers of unoccupied N p states in GaN and AlN nanorods, which may be attributed to a slight increase of the degree of localization of conduction band states. The band gaps of AlN, GaN, and InN nanorods are determined by an overlay of XES and XANES spectra to be 6.2, 3.5, and 1.9eV, respectively, which are close to those of AlN and GaN bulk/films and InN polycrystals.
Polymer space-charge-limited transistor
Authors: Chao Yu-Chiang , Meng Hsin-Fei , Horng Sheng-Fu
Published: June 2006

A metal grid is sandwiched between poly(3-hexylthiophene) to form a solid-state version of vacuum tube triode, where the vertical space-charge-limited current is modulated by the grid potential. The Al grid contains random submicron openings formed by a nonlithographic method. The multilayer polymer structure is made by spin coating. The operating voltage of the polymer space-charge-limited transistor is 3V, and the current gain of 506 is obtained. The characteristics of the transistor can be tuned by the diameters and the density of the openings on the grid. Similar to the vacuum tube triode, the current follows a power law voltage dependence.
Stable dense plasma jets produced at laser power densities around 1014W∕cm2
Authors: Kasperczuk A. , Pisarczyk T. , Borodziuk S. , Ullschmied J. , Krousky E. , Masek K. , Rohlena K. , Skala J. , Hora H.
Published: June 2006

The results of investigations are presented that are connected with defocused laser beam–planar target interaction. Following the very large focus laser-plasma interaction experiments on the Nova [H. T. Powell, J. A. Caird, J. E. Murray, and C. E. Thompson, 1991 ICF Annual Report UCRL-LR-105820-91, p. 163 (1991)] and GEKKO-XII [C. Yamanaka, Y. Kato, Y. Izawa, K. Yoshida, T. Yamanaka, T. Sasaki, T. Nakatsuka, J. Kuroda, and S. Nakai, IEEE J. Quantum Electron. QE-17, 1639 (1981)] lasers, as well as on the National Ignition Facility (NIF) laser [W. J. Hogan, E. I. Moses, B. E. Warner, M. S. Sorem, and J. M. Soures, Nucl. Fusion 41, 567 (2001)] with generation of high Mach number jets, this paper is devoted to similar jet generation with very detailed measurements of density profiles by using high-power lasers at large focus conditions. The experiment was carried out with target materials of different mass densities (Al, Cu, Ag, Ta, and Pb) using the Prague Asterix Laser System (PALS) iodine laser [K. Jungwirth, A. Cejnarova, L. Juha, B. Kralikowa, J. Krasa, E. Krousky, P. Krupickova, L. Laska, K. Masek, A. Prag, O. Renner, K. Rohlena, B. Rus, J. Skala, P. Straka, and J. Ullschmied, Phys. Plasmas 8, 2495 (2001)]. The investigations were conducted for the laser radiation energy of 100J at two wavelengths of 1.315 and 0.438μm (the first and third harmonics of laser radiation), pulse duration of 0.4ns, and a focal spot radius of 300μm. Most of the experimental data were obtained by means of a three-frame laser interferometer and an x-ray streak camera; the crater parameters were obtained by using the crater replica technique. These investigations have shown that stable dense plasma jets can be produced in a simple configuration of laser beam–planar target interaction, provided that a proper target material is used.
Near-field optical micromanipulation with cavity enhanced evanescent waves
Authors: Reece Peter J. , Garcés-Chávez Veneranda , Dholakia Kishan
Published: June 2006

We show that the forces associated with near-field optical micromanipulation can be greatly increased through the use of cavity enhanced evanescent waves. This approach utilizes a resonant dielectric waveguide structure and a prism coupler to produce Fabry-Pérot-like cavity modes at a dielectric-fluid interface. Fabricated structures show a ten times enhancement in the optical interaction and optical force for micrometer-sized colloids. In addition, stable accumulation and ordering of large scale arrays of colloids are demonstrated using two counter-propagating cavity enhanced evanescent waves.
Plasma processes inside dispenser hollow cathodes
Authors: Mikellides Ioannis G. , Katz Ira , Goebel Dan M. , Polk James E. , Jameson Kristina K.
Published: June 2006

A two-dimensional fluid model of the plasma and neutral gas inside dispenser orificed hollow cathodes has been developed to quantify plasma processes that ultimately determine the life of the porous emitters inserted in these devices. The model self-consistently accounts for electron emission from the insert as well as for electron and ion flux losses from the plasma. Two cathodes, which are distinctively different in size and operating conditions, have been simulated numerically. It is found that the larger cathode, with outer tube diameter of 1.5cm and orifice diameter of 0.3cm, establishes an effective emission zone that spans approximately the full length of the emitter when operated at a discharge current of 25A and a flow rate of 5.5sccm. The net heating of the emitter is caused by ions that are produced by ionization of the neutral gas inside the tube and are then accelerated by the sheath along the emitter. The smaller cathode, with an outer diameter of 0.635cm and an orifice diameter of 0.1cm, does not exhibit the same operational characteristics. At a flow rate of 4.25sccm and discharge current of 12A, the smaller cathode requires 4.5 times the current density near the orifice and operates with more than 6 times the neutral particle density compared to the large cathode. As a result, the plasma particle density is almost one order of magnitude higher compared to the large cathode. The plasma density in this small cathode is high enough such that the Debye length is sufficiently small to allow “sheath funneling” into the pores of the emitter. By accessing areas deeper into the insert material, it is postulated that the overall emission of electrons is significantly enhanced. The maximum emission current density is found to be about 1A∕mm2 in the small cathode, which is about one order of magnitude higher than attained in the large cathode. The effective emission zone in the small cathode extends to about 15% of the emitter length only, and the power deposited at the emitter surface by returning electrons is found to be twice that deposited by ions. A previous study suggested that the computed particle flux and energy of ions to the emitter of the 1.5cm cathode were not high enough to change the barium evaporation rate compared to thermally induced evaporation. The same suggestion is made here for the 0.635cm cathode. The peak ion flux to the emitter is found to be 1.2A∕cm2 (7.6×1018∕scm2), and the corresponding peak sheath drop is 2.9V. Consequently, once the emitter operating temperature is known it is possible to determine directly the barium depletion-limited life of these cathodes using existing vacuum-cathode data.
Destabilization of magnetosonic-whistler waves by a relativistic runaway beam
Authors: Fülöp T. , Pokol G. , Helander P. , Lisak M.
Published: June 2006

Magnetosonic-whistler waves may be destabilized by runaway electrons both in fusion and astrophysical plasmas. A linear instability growth rate of these waves in the presence of a runaway avalanche is calculated both perturbatively and by numerical solution of the full dispersion equation. The local threshold of the instability depends on the fraction of runaways, the magnetic field, and the temperature of the background plasma. The quasilinear analysis shows that the main result of the instability is the scattering of the electrons in pitch-angle. It appears possible that this instability could explain why the number of runaway electrons generated in tokamak disruptions depends on the strength of the magnetic field.
Overannealing effects in GaInNAs(Sb) alloys and their importance to laser applications
Authors: Bank Seth R. , Yuen Homan B. , Bae Hopil , Wistey Mark A. , Harris James S.
Published: June 2006

The photoluminescence efficiency and linewidth are well-established metrics for characterizing potential laser active regions. We demonstrate the critical importance of a new parameter for predicting the performance of dilute-nitride lasers: the “optimal” postgrowth annealing temperature, defined as the annealing temperature giving the highest photoluminescence efficiency. We validate this assertion with two 1.55μm edge-emitting GaInNAsSb lasers containing active regions with different optimal annealing temperatures. Although both active regions showed comparable photoluminescence efficiency and linewidth under optimal annealing conditions, laser performance was significantly different. The room-temperature threshold current density for the active region with higher optimal annealing temperature was 630A∕cm2, compared with 2380A∕cm2 for the sample with lower optimal annealing temperature. We conclude that overannealing of the gain region during upper cladding growth is the responsible mechanism. The dependence of the optimal annealing temperature on composition and growth conditions is also discussed.
Gated lateral charge transport in self-assembled 1-pyrylphosphonic acid molecular multilayers
Authors: Dong J. , Yip H. L. , Ma H. , Jen A. K.-Y. , Parviz B. A.
Published: June 2006

We have synthesized a p-type organic semiconductor, 1-pyrylphosphonic acid, that can self-assemble onto silicon dioxide to form either a 0.9nm monolayer or a multilayer with well-defined 2.5nm step heights depending on the assembly conditions. We allowed polycrystalline multilayers to self-assemble between interdigitated gold electrodes on a SiO2∕Si substrate and measured the charge carrier transport as a function of applied voltages to the electrodes and the gate substrate, temperature, and electrode spacing. At room temperature for channel lengths larger than 400nm, the conduction was dominated by Poole-Frenkel emission at the metal/molecule interface. At low temperatures (∼240K) the space charge limited conduction dominated and an on-off ratio of 1000 was achieved.
Structural and electrical characterizations of the pulsed-laser-deposition-grown Sc2O3∕GaN heterostructure
Authors: Liu Chang , Chor Eng Fong , Tan Leng Seow , Dong Yufeng
Published: June 2006

Single-crystalline Sc2O3 was grown on GaN/sapphire template using pulsed laser deposition and the interface characteristics of the Sc2O3∕GaN heterostructure were investigated. An epitaxial relationship of [112]Sc2O3‖[213¯0]GaN and (222)Sc2O3‖(0002)GaN was revealed by x-ray diffraction and cross-sectional transmission electron microscopy. A valence band offset of 0.84eV was obtained by x-ray photoelectron spectroscopy, indicating a conduction band offset of 2.04eV across the Sc2O3∕GaN heterointerface. In addition, a low interface state density of 4×1011eV−1cm−2 was estimated from capacitance-voltage measurements. The epitaxial nature with good interface characteristics has rendered a substantially low leakage current of 1μA∕cm2 at a reverse gate bias of 30V in the Sc2O3∕GaN metal-oxide-semiconductor structures.
Polarizability of phthalocyanine based molecular systems: A first-principles electronic structure study
Authors: Ramprasad R. , Shi N.
Published: June 2006

A first-principles electronic structure study is performed to determine the optical and static polarizability tensors of various phthalocyanine (Pc) derived molecules, including H2Pc, CuPc, and MgPc. It is found that the dominant contribution to the polarizability is electronic in origin, and that the metal atoms only marginally enhance the polarizability. An analytical electrostatic model that relates the polarizability of an ellipsoid to its permittivity is then used to estimate the permittivity tensor of these molecular systems.
High performance organic light-emitting diodes fabricated via a vacuum-free lamination process
Authors: Liu Jie , Lewis Larry N. , Faircloth Tami J. , Duggal Anil R.
Published: June 2006

We demonstrate high performance organic light-emitting diodes (OLEDs) fabricated via a vacuum-free, direct lamination process. The OLEDs were made by laminating an anode component to a separately engineered cathode component using a roll laminator. We further present a solution-based chemical n-doping strategy to enable efficient electron injection from an inert cathode into polymeric organic semiconductors. The n-doping strategy is demonstrated by chemically reducing a conjugated light-emitting polymer with an alkali metal in an organic solvent. The metal reduced conjugated polymer, when employed as an electron injection layer, yields laminated OLEDs with efficiency comparable to conventionally fabricated devices utilizing a vacuum-deposited, reactive metal cathode. These designs and techniques should enable applications such as lighting where extremely low cost device fabrication is required.
Efficient blue organic light-emitting devices based on oligo(phenylenevinylene)
Authors: Zhang Yingfang , Cheng Gang , Chen Shufen , Li Yan , Zhao Yi , Liu Shiyong , He Feng , Tian Leilei , Ma Yuguang
Published: June 2006

Highly bright and efficient blue organic light-emitting devices based on two oligo(phenylenevinylene) derivatives, 1,4-di(4′-N,N-diphenylaminostyryl)benzene (DPA-DSB) and 2,5,2′,5′-tetrastyryl-biphenyl (TSB), are fabricated. Using poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) combined with 4,4′,4″-tri(N-carbazolyl) triphenylamine as the hole-transporting layer and DPA-DSB doped TSB as the blue emitter, a maximum luminous efficiency of 12.2 cd/A (corresponding to an external quantum efficiency of 6.2%) and a maximum power efficiency of 6.39lm∕W are obtained. The maximum brightness of 17350cd∕m2 is attained. These fairly high brightness and efficiencies are due to the efficient energy transfer from TSB to DPA-DSB and depression of concentration quenching by doping.
Bistable resistance state induced by Joule self-heating in manganites: A general phenomenon
Authors: Chen Y. F. , Ziese M. , Esquinazi P.
Published: June 2006

The magnetotransport properties of La0.7Sr0.3MnO3 films were investigated in the nonlinear regime of strong Joule self-heating. In this regime the resistance-current characteristics exhibit two sharp transitions between bistable resistance values. The critical currents corresponding to the transitions depend on base temperature, magnetic field, current sweep rate, film resistance, and thermal coupling to the surroundings. This phenomenon opens up the possibility for the development of a magnetoresistance sensor based on Joule self-heating tuned colossal magnetoresistance.
Preparation and thermoelectric properties of sintered iodine-containing clathrate compounds Ge38Sb8I8 and Sn38Sb8I8
Authors: Kishimoto Kengo , Arimura Shuntaro , Koyanagi Tsuyoshi
Published: June 2006

The iodine-containing cationic type-I clathrates Ge38Sb8I8 and Sn38Sb8I8 were prepared and their thermodynamic properties as well as their thermoelectric properties were investigated. Their atomic displacement parameters were as large as those of anionic clathrates such as Ba8Ga16Ge30 and Cs8Cd4Sn42. The room temperature thermal conductivities of Ge38Sb8I8 and Sn38Sb8I8 were 7 and 12mWcm−1K−1, respectively; these values were as low as that of the above anionic clathrates. Both cationic clathrates had negative Seebeck coefficients; the band gap energies of Ge38Sb8I8 and Sn38Sb8I8 were 1.16 and 0.80eV, respectively.
Multiphoton excitation of quantum dots by ultrashort and ultraintense laser pulses
Authors: Fu Y. , Han T.-T. , Luo Y. , Ågren H.
Published: June 2006

Multiphoton optical processes in semiconductor quantum dots (QDs) excited by ultrafast (femtosecond) and ultraintense (GW∕cm2) lasers are considered as the ultimate tags for cellular bioimaging. By solving the time-dependent Schrödinger equation unperturbatively, experimentally observed strong multiphoton excitation is reproduced when optical transitions among all confined states and a few hundred more extended states are taken into account. Model calculations indicate a significant excitation of a CdS QD of 3.7nm in radius by a 100fs laser pulse with a 10GW∕cm2 peak optical power. The excitation rate is almost constant between 1300 and 560nm, a useful region for bioimaging.