bluuebunny/crossref_metadata_2025 huggingface dataset:
Ionic polymer cluster energetics: Computational analysis of pendant chain stiffness and charge imbalance
Authors: Weiland Lisa Mauck , Leo Donald J.
Published: June 2005

In recent years there has been considerable study of the potential mechanisms underlying the electromechanical response of ionic-polymer-metal composites. The most recent models have been based on the response of the ion-containing clusters that are formed when the material is synthesized. Most of these efforts have employed assumptions of uniform ion distribution within spherical cluster shapes. This work investigates the impact of dispensing with these assumptions in order to better understand the parameters that impact cluster shape, size, and ion transport potential. A computational micromechanics model applying Monte Carlo methodology is employed to predict the equilibrium state of a single cluster of a solvated ionomeric polymer. For a constant solvated state, the model tracks the position of individual ions within a given cluster in response to ion-ion interaction, mechanical stiffness of the pendant chain, cluster surface energy, and external electric-field loading. Results suggest that cluster surface effects play a significant role in the equilibrium cluster state, including ion distribution; pendant chain stiffness also plays a role in ion distribution but to a lesser extent. Moreover, ion pairing is rarely complete even in cation-rich clusters; this in turn supports the supposition of the formation of anode and cathode boundary layers.
Effect of compressive strain relaxation in GaN blue light-emitting diodes with variation of n+-GaN thickness on its device performance
Authors: Kim Chi Sun , Kim Hyung Gu , Hong Chang-Hee , Cho Hyung Koun
Published: June 2005

The effects of compressive strain relaxation with increasing n-GaN thickness on device performances of GaN blue light-emitting diodes (LEDs) were investigated. It was found that the compressive strain relaxation in LEDs with thicker n-GaN occurred more considerably, following by the growth of active layer and p-GaN, and generated many stacking faults right beneath the InGaN active layer, which might be related to a decrease of the LED output power. On the contrary, the LED photoluminescence intensity increased surprisingly with n-GaN thickness. It was understood that the compressive strain relaxation enhanced localized states in InGaN wells.
Effect of cerium codoping in Er3+,Ce3+:NaLa(MoO4)2 crystals
Authors: Sani E. , Toncelli A. , Tonelli M. , Lis D. A. , Zharikov E. V. , Subbotin K. A. , Smirnov V. A.
Published: June 2005

The detailed polarized spectroscopic investigation of I11∕24 and I13∕24 states of Er3+ ions in Czochralski-grown NaLa(MoO4)2 single crystals doped with Er3+ and codoped with Ce3+ as a function of cerium concentration is presented. The main results of room-temperature lifetime investigation show that the I11∕24 lifetime reduces by about 50 times from the solely Er-doped sample to the crystal codoped with 50at.% of Ce, while in the same experimental conditions, the lifetime of the I13∕24 level reduces by less than two times in the most heavily Ce codoped sample. This result looks very promising from the point of view of obtaining low-threshold 1.5-μm laser oscillation.
Charge state effect on near-surface damage formation in swift heavy ion irradiated InP
Authors: Kamarou A. , Wendler E. , Wesch W.
Published: June 2005

Irradiation of single-crystalline InP with large fluences of swift heavy ions (SHI’s) causes formation of amorphous layers within the depth range of dominating electronic energy loss. However, unlike the bulk, a thin surface layer (tens of nanometers) remains almost undamaged. In the present paper this peculiarity is studied in more detail. One can make two plausible suppositions: (a) either the surface acts as an efficient sink for defects produced by SHI irradiation near the surface (i.e., they move towards the surface and annihilate there) or (b) SHI energy deposition within the thin surface layer is lower than that in the bulk. The latter effect takes place, for example, if the initial charge of the impinging ions is lower than the mean equilibrium one in the target bulk. Our results give an indication of a dominating influence of the SHI charge state. No noticeable influence of the surface as a sink for defects was observed.
Open-shell localized Hartree–Fock method based on the generalized adiabatic connection Kohn–Sham formalism for a self-consistent treatment of excited states
Authors: Vitale Vincenzo , Della Sala Fabio , Görling Andreas
Published: June 2005

An effective exact-exchange Kohn–Sham approach for the treatment of excited electronic states, the generalized adiabatic connection open-shell localized Hartree–Fock (GAC-OSLHF) method is presented. The GAC-OSLHF method is based on the generalized adiabatic connection Kohn–Sham formalism and therefore capable of treating excited electronic states, which are not the energetically lowest of their symmetry. The method is self-interaction free and allows for a fully self-consistent computation of excited valence as well as Rydberg states. Results for atoms and small- and medium-size molecules are presented and compared to restricted open-shell Hartree–Fock (ROHF) and time-dependent density-functional results as well as to experimental data. While GAC-OSLHF and ROHF results are quite close to each other, the GAC-OSLHF method shows a much better convergence behavior. Moreover, the GAC-OSLHF method as a Kohn–Sham method, in contrast to the ROHF approach, represents a framework which allows also for a treatment of correlation besides an exchange by appropriate functionals. In contrast to the common time-dependent density-functional methods, the GAC-OSLHF approach is capable of treating doubly or multiply excited states and can be easily applied to molecules with an open-shell ground state. On the nodal planes of the energetically highest occupied orbital, the local multiplicative GAC-OSLHF exchange potential asymptotically approaches a different, i.e., nonzero, value than in other regions, an asymptotic behavior which is known from exact Kohn–Sham exchange potentials of ground states of molecules.
Two-color resonantly enhanced multiphoton ionization and zero-kinetic-energy photoelectron spectroscopy of jet-cooled indan
Authors: He Yonggang , Kong Wei
Published: June 2005

We report studies of supersonically cooled indan using two-color resonantly enhanced multiphoton ionization and two-color zero-kinetic-energy photoelectron spectroscopy. With the aid of ab initio and density-functional calculations, vibrational modes of the first electronically excited state of the neutral species and those of the cation have been assigned, and the adiabatic ionization energy has been determined to be 68458±5cm−1. Similar to the ground state and the first electronically excited state of the neutral molecule, the ground state of the cation is also proven to be nonplanar, with an estimated barrier of 213cm−1 and a puckering angle of 15.0°. These conclusions will be discussed in comparison with a previous study of an indan derivative 1,3-benzodioxole.
Parametric instabilities in helicon-produced plasmas
Authors: Aliev Yu. M. , Krämer M.
Published: June 2005

Parametric instabilities arising in the pump field of a helicon wave are analyzed for typical parameters of helicon-produced plasmas. The pump wavenumber parallel to the magnetic field is assumed to be finite according to recent experimental findings obtained on a high-density helicon discharge. The parametric decay of the helicon pump wave into ion-sound and Trivelpiece–Gould waves is investigated. The approach takes into account that the damping rate of the Trivelpiece–Gould wave is generally much higher than the ion-sound frequency. The theoretical results are in agreement with the growth rates and thresholds of this instability, as well as the dispersion properties of the decay waves observed in helicon experiments. Estimates of the level of the decay parametric turbulence turn out to be sufficiently high to account for the strong absorption observed in helicon-produced plasmas.
Characterization of a picosecond laser generated 4.5keV TiK-alpha source for pulsed radiography
Authors: King J. A. , Akli K. , Snavely R. A. , Zhang B. , Key M. H. , Chen C. D. , Chen M. , Hatchett S. P. , Koch J. A. , MacKinnon A. J. , Patel P. K. , Phillips T. , Town R. P. J. , Freeman R. R. , Borghesi M. , Romagnani L. , Zepf M. , Cowan T. , Stephens R. , Lancaster K. L. , Murphy C. D. , Norreys P. , Stoeckl C.
Published: June 2005

K α radiation generated by interaction of an ultrashort (1ps) laser with thin (25μm) Ti foils at high intensity (2×1016W∕cm2) is analyzed using data from a spherical Bragg crystal imager and a single hit charge-coupled device spectrometer together with Monte Carlo simulations of Kα brightness. Laser to Kα and electron conversion efficiencies have been determined. We have also measured an effective crystal reflectivity of 3.75±2%. Comparison of imager data with data from the relatively broadband single hit spectrometer has revealed a reduction in crystal collection efficiency for high Kα yield. This is attributed to a shift in the K-shell spectrum due to Ti ionization.
Polarization-switching characteristics of flux-grown KTiOPO4 and RbTiOPO4 at room temperature
Authors: Canalias C. , Hirohashi J. , Pasiskevicius V. , Laurell F.
Published: June 2005

A study of polarization-switching characteristics under an applied electrical field at room temperature is presented for flux-grown KTiOPO4 and RbTiOPO4. By optimizing the experimental conditions, we determined the coercive field and the domain-switching time quantitatively by direct observation of the switching current. For both isomorphs, the inverse of the polarization-switching time, 1∕ts, follows an exponential dependence on the applied field E in low-field regime, and a linear dependence on E in the high-field regime. Domain morphology of KTiOPO4 based on selective etching reveals laminar structures elongated in the b crystallographic direction. An estimation of the domain-wall velocity shows that the domain speed in the polar direction is, at least, two orders of magnitude larger than in the a-b plane. The velocity along the b direction is ∼30 times larger than along the a axis.
Probe measurements of plasma potential nonuniformity due to edge asymmetry in large-area radio-frequency reactors: The telegraph effect
Authors: Howling A. A. , Derendinger L. , Sansonnens L. , Schmidt H. , Hollenstein Ch. , Sakanaka E. , Schmitt J. P. M.
Published: June 2005

In large-area radio-frequency (rf) capacitive reactors, the redistribution of rf current to maintain current continuity near asymmetric sidewalls causes a perturbation in rf plasma potential to propagate along the resistive plasma between capacitive sheaths. The damping length of the perturbation can be determined by a telegraph equation. Experiments are described using a surface array of unbiased electrostatic probes in the ground electrode to verify the theoretical model of the telegraph effect in Howling et al. [J. Appl. Phys. 96, 5429 (2004)]. The measured spatial dependence of the plasma potential rf amplitude and circulating nonambipolar current agree well with two-dimensional numerical solutions of the telegraph equation. The rf plasma potential can be made uniform by using symmetric reactor sidewalls.
Incoherent neutron-scattering determination of hydrogen content: Theory and modeling
Authors: Perego R. C. , Blaauw M.
Published: June 2005

Hydrogen concentrations of 0 up to 350mg∕kg in a titanium alloy have been determined at National Institute of Standards and Technology (NIST) with neutron incoherent scattering (NIS) and with cold neutron prompt gamma activation analysis. The latter is a well-established technique, while the former was demonstrated earlier at NIST by counting the neutrons scattered under 45° or 60° and establishing a linear relationship between hydrogen concentration and count rate. In this paper, it is shown that the NIS response is complicated by the dependence of the apparent hydrogen scattering cross section on the sample temperature and the hydrogen chemical binding. It is demonstrated that detection of scattered neutrons at two different angles as well as a more complex theoretical approach (i.e., including Monte Carlo modeling with the free-gas model) are required to correctly interpret NIS measurements. As a result, the process of matching standards and samples becomes less critical.
Asymmetry of lipid bilayers induced by monovalent salt: Atomistic molecular-dynamics study
Authors: Gurtovenko Andrey A.
Published: June 2005

Interactions between salt ions and lipid components of biological membranes are essential for the structure, stability, and functions of the membranes. The specific ionic composition of aqueous buffers inside and outside of the cell is known to differ considerably. To model such a situation we perform atomistic molecular-dynamics (MD) simulations of a single-component phosphatidylcholine lipid bilayer which separates two aqueous reservoirs with and without NaCl salt. To implement the difference in electrolyte composition near two membrane sides, a double bilayer setup (i.e., two bilayers in a simulation box) is employed. It turns out that monovalent salt, being in contact with one leaflet only, induces a pronounced asymmetry in the structural, electrostatic, and dynamical properties of bilayer leaflets after 50ns of MD simulations. Binding of sodium ions to the carbonyl region of the leaflet which is in contact with salt results in the formation of “Na-lipids” complexes and, correspondingly, reduces mobility of lipids of this leaflet. In turn, attractive interactions of chloride ions (mainly located in the aqueous phase close to the water-lipid interface) with choline lipid groups lead to a substantial (more vertical) reorientation of postphatidylcholine headgroups of the leaflet adjoined to salt. The difference in headgroup orientation on two sides of a bilayer, being coupled with salt-induced reorientation of water dipoles, leads to a notable asymmetry in the charge-density profiles and electrostatic potentials of bilayer constitutes of the two leaflets. Although the overall charge density of the bilayer is found to be almost insensitive to the presence of salt, a slight asymmetry in the charge distribution between the two bilayer leaflets results in a nonzero potential difference of about 85mV between the two water phases. Thus, a transmembrane potential of the order of the membrane potential in a cell can arise without ionic charge imbalance between two aqueous compartments.
An algorithm for extremely complicated interference pattern evaluation
Authors: Olejníček J. , Píchal J. , Blažek J. , Špatenka P.
Published: June 2005

A description of an easy algorithm for evaluation of interference patterns recording the light beam deflection in phase objects is presented in this paper. The method is suitable for digitizing and evaluating complicated interference patterns containing heavily distorted, double or closed interference fringes. The created algorithm and evaluation procedure result from the lines’ approximation and Delaunay triangulation. They were applied to a complex interference pattern taken in the pinch discharge burning in low-pressure deuterium. The results obtained were used for calculation of electron density values in the discharge channel. The influence of the phase shift deformation outside the region under study on the accuracy of results and on electron density estimation inside the shock wave of the pinch was also analyzed. The gathered data were verified with a calculation of the electron temperature in the discharge channel, which was performed providing kinetic and magnetic pressure equilibriums.
Partial trapping of secondary-electron emission in a Hall thruster plasma
Authors: Ahedo E. , Parra F. I.
Published: June 2005

Secondary-electron emission at the ceramic walls of a Hall thruster modifies the potential jump of the wall Debye sheaths and thus the electron energy losses to the wall. Because of the low plasma collisionality the two counterstreaming beams of secondary electrons are not expected to be totally trapped within the bulk of the discharge. In order to analyze the effects of partial trapping of secondary electrons on the presheath∕sheath radial structure, a macroscopic model is formulated. The plasma response depends on the secondary electron emission yield and the trapped fraction of secondary electrons. The sheath potential and wall energy losses are determined mainly by the net current of secondary electrons in the sheaths. For any practical value of the secondary emission yield, the zero-trapping solution is very similar to the zero secondary emission case. Space charge saturation of the sheaths is unattainable for weak trapping. In all cases, secondary electrons have a weak effect on the presheath solution and the ion flux recombined at the walls.
Ion thermal pressure effects on dust ion acoustic solitary waves in a dusty plasma obliquely propagating to an external magnetic field
Authors: Rim Choi Cheong , Ryu Chang-Mo , Lee Nam C. , Lee D.-Y. , Kim Yonggi
Published: June 2005

Effects of the isothermal ion pressure on the dust ion acoustic solitary waves (DIASWs) in a dusty plasma, which are obliquely propagating to an external magnetic field, are investigated based on the Sagdeev potential. It is found that as the ion temperature increases the speed of the DIASW increases. The increase is more effective for a higher value of the directional cosine lz. The small amplitude solutions of the Sagdeev potential Ψ(n) expanded up to δn3 and δn4, as was done in the previous study [Choi et al., Phys. Plasmas 12, 022304 (2005)], exhibit different behaviors with respect to the change in the ion temperature. The width and height of a double layer are found to decrease with the increase in the ion temperature for both the small and the large amplitude solutions.
Wave model for conservative bound systems
Authors: Popa Alexandru
Published: June 2005

In the hidden variable theory, Bohm proved a connection between the Schrödinger and Hamilton–Jacobi equations and showed the existence of classical paths, for which the generalized Bohr quantization condition is valid. In this paper we prove similar properties, starting from the equivalence between the Schrödinger and wave equations in the case of the conservative bound systems. Our approach is based on the equations and postulates of quantum mechanics without using any additional postulate. Like in the hidden variable theory, the above properties are proven without using the approximation of geometrical optics or the semiclassical approximation. Since the classical paths have only a mathematical significance in our analysis, our approach is consistent with the postulates of quantum mechanics.
Dynamics of propylene glycol and its oligomers confined to a single molecular layer
Authors: Swenson J. , Engberg D. , Howells W. S. , Seydel T. , Juranyi F.
Published: June 2005

The dynamics of propylene glycol (PG) and its oligomers 7-PG and poly-propylene glycol (PPG), with Mw=4000 (≈70 monomers), confined in a Na–vermiculite clay have been investigated by quasielastic neutron scattering. The liquids are confined to single molecular layers between clay platelets, giving a true two-dimensional liquid. Data from three different spectrometers of different resolutions were Fourier transformed to S(Q,t) and combined to give an extended dynamical time range of 0.3–2000 ps. An attempt was made to distinguish the diffusive motion from the methyl group rotation and a fast local motion of hydrogen in the polymer backbone. The results show that the average relaxation time ⟨τd⟩ of this diffusive process is, as expected, larger than the relaxation time ⟨τ⟩ averaged over all dynamical processes observed in the experimental time window. More interesting, it is evident that the severe confinement has a relatively small effect on ⟨τd⟩ at T=300K, this holds particularly for the longest oligomer, PPG. The most significant difference is that the chain-length dependence of ⟨τd⟩ is weaker for the confined liquids, although the slowing down in bulk PG due to the formation of a three-dimensional network of OH-bonded end groups reduces this difference. The estimated average relaxation time ⟨τ⟩ at Q=0.92Å−1 for all the observed processes is in excellent agreement with the previously reported dielectric α relaxation time in the studied temperature range of 260–380 K. The average relaxation time ⟨τ⟩ (as well as the dielectric α relaxation time) is also almost unaffected by the confinement to a single molecular layer, suggesting that the interaction with the clay surfaces is weak and that the reduced dimensionality has only a weak influence on the time scale of all the dynamical processes observed in this study.
Dependence on laser intensity and pulse duration in proton acceleration by irradiation of ultrashort laser pulses on a Cu foil target
Authors: Oishi Y. , Nayuki T. , Fujii T. , Takizawa Y. , Wang X. , Yamazaki T. , Nemoto K. , Kayoiji T. , Sekiya T. , Horioka K. , Okano Y. , Hironaka Y. , Nakamura K. G. , Kondo K. , Andreev A. A.
Published: June 2005

The dependence on laser intensity and pulse duration in energetic proton acceleration by irradiation of ultrashort laser pulses on a 5μm thick copper tape target was measured. The laser intensity was varied from 8.5×1017W∕cm2 to 1.1×1019W∕cm2, and the pulse duration from 55 fs to 400 fs. The maximum proton energy increased as the pulse duration was increased while the laser intensity was kept constant. The dependence of the maximum proton energy on laser intensity and pulse duration was in good agreement with an analytical plasma-expanding model.
Electron inertia contribution to soliton evolution in an inhomogeneous weakly relativistic two-fluid plasma
Authors: Singh Khushvant , Kumar Vinod , Malik Hitendra K.
Published: June 2005

The contribution of electron inertia to the evolution of solitons in weakly and strongly inhomogeneous plasmas having streaming ions and electrons with weak relativistic effect is studied on the basis of a relevant Korteweg–de Vries equation derived with the help of reductive perturbation technique. Three types of modes (fast, medium, and slow) are found to propagate in the plasma. In case of weak (strong) inhomogeneous plasma, only the fast (slow) mode corresponds to the soliton evolution. For the propagation of solitons in strongly inhomogeneous plasma, there is no restriction on the ion and electron velocities but in case of weak inhomogeneity the solitons are possible only for a particular range of velocity difference. This range shows the dependence on the temperature and mass ratios of the ions and electrons. In addition, it is realized that only the rarefactive solitons are possible in the present plasma model. The effect of electron inertia on the phase velocity, peak soliton amplitude, and soliton width is studied together with the effects of plasma density, ion temperature, and speeds (relativistic effects) of ions and electrons.
Measurements of laser-imprinting sensitivity to relative beam mistiming in planar plastic foils driven by multiple overlapping laser beams
Authors: Smalyuk V. A. , Goncharov V. N. , Boehly T. R. , Delettrez J. A. , Li D. Y. , Marozas J. A. , Maximov A. V. , Meyerhofer D. D. , Regan S. P. , Sangster T. C.
Published: June 2005

In a direct-drive, inertial confinement fusion implosion, a spherical target is irradiated by a large number of overlapped laser beams. Imprinting of laser modulations depends on the relative arrival time of laser beams and their angles of incidence. This dependence was measured in planar plastic targets using six overlapping beams on the OMEGA laser system [T. R. Boehly, D. L. Brown, R. S. Craxton, R. L. Keck, J. P. Knauer, J. H. Kelly, T. J. Kessler, S. A. Kumpan, S. J. Loucks, S. A. Letzring, F. J. Marshall, R. L. McCrory, S. F. B. Morse, W. Seka, J. M. Soures, and C. P. Verdon, Opt. Commun. 133, 495 (1997)]. One of the beams (the imprint beam) had a special phase plate that produced two-dimensional modulations on the target, easily distinguishable from the features imprinted by the other five drive beams. The timing of the imprint beam was varied with respect to the drive beams to study imprinting sensitivity to beam mistiming. Shifting the imprint beam to arrive before the other beams significantly increased the imprint efficiency. The results are in very good agreement with the model predictions.
Infrared spectra of water clusters in krypton and xenon matrices
Authors: Hirabayashi Shinichi , Yamada Koichi M. T.
Published: June 2005

The infrared absorption spectra of the water molecules and small water clusters, (H2O)n with n=2–6, trapped in solid argon, krypton, and xenon matrices have been investigated. The infrared bands of the water clusters with n=5 and 6 in krypton and n=3, 4, 5, and 6 in xenon matrices have been identified for the first time in the bonded OH stretching region. The frequency shifts in the bonded OH stretching band of the water dimer and trimer in xenon matrices show fairly large deviations to the red from the empirical correlation between the matrix shifts and the square root of the critical temperatures of the matrix material. The observed anomalous shifts suggest that the water dimer and trimer in solid xenon are trapped in multiple sites, and that the structures of the preferential trapping sites are different from those in argon and krypton matrices.
Nanometer scale marker for fluorescent microscopy
Authors: Hiraga Takashi , Iketaki Yoshinori , Watanabe Takeshi , Ohyi Hideyuki , Kobayashi Kazumasa , Yamamoto Noritaka , Mizokuro Toshiko , Fujii Masaaki
Published: June 2005

To establish a calibration method of optical performance in fluorescence microscopy, we fabricated a fluorescent nanometer-scale marker by combining a dry dye method for polymer film and fine lithography. The marker has a 50 nm line-and-space fluorescent pattern, finer than the optical diffraction limit. A spin-coated poly(methyl methacrylate) thin film on a silicon wafer was densely doped with Rhodamine 6G using a simple vacuum process, named the vapor-transportation method, and then the pattern was formed on the film using electron-beam lithography. The figure accuracy of the fabricated marker was calibrated by electron microscopes. Using this marker, one can quantitatively evaluate the optical properties; i.e., the contrast-transfer function, the point-spread function, magnification, and so on. To show practical use of the marker, we demonstrated the evaluation of a fluorescent microscope system.
A large distributed digital camera system for accelerator beam diagnostics
Authors: Catani L. , Cianchi A. , Di Pirro G. , Honkavaara K.
Published: June 2005

Optical diagnostics, providing images of accelerated particle beams using radiation emitted by particles impinging a radiator, typically a fluorescent screen, has been extensively used, especially on electron linacs, since the 1970's. Higher intensity beams available in the last decade allow extending the use of beam imaging techniques to perform precise measurements of important beam parameters such as emittance, energy, and energy spread using optical transition radiation (OTR). OTR-based diagnostics systems are extensively used on the superconducting TESLA Test Facility (TTF) linac driving the vacuum ultraviolet free electron laser (VUV-FEL) at the Deutsches Elektronen-Synchrotron facility. Up to 30 optical diagnostic stations have been installed at various positions along the 250-m-long linac, each equipped with a high-performance digital camera. This paper describes the new approach to the design of the hardware and software setups required by the complex topology of such a distributed camera system.
Nonlinear Zakharov–Kuznetsov equation for obliquely propagating two-dimensional ion-acoustic solitary waves in a relativistic, rotating magnetized electron-positron-ion plasma
Authors: Mushtaq A. , Shah H. A.
Published: June 2005

The purpose of this work is to investigate the linear and nonlinear properties of the ion-acoustic waves (IAW), propagating obliquely to an external magnetic field in a weakly relativistic, rotating, and magnetized electron-positron-ion plasma. The Zakharov–Kuznetsov equation is derived by employing the reductive perturbation technique for this wave in the nonlinear regime. This equation admits the solitary wave solution. The amplitude and width of this solitary wave have been discussed with the effects of obliqueness, relativity, ion temperature, positron concentration, magnetic field, and rotation of the plasma and it is observed that for IAW these parameters affect the propagation properties of solitary waves and these plasmas behave differently from the simple electron-ion plasmas. Likewise, the current density and electric field of these waves are investigated for their dependence on the above-mentioned parameters.
Piezoresistive microcantilevers for in situ stress measurements during thin film deposition
Authors: Seel Steven C. , Thompson Carl V.
Published: June 2005

Conventional thin film stress measurements detect the physical deflection of a cantilever substrate induced by the stress in a deposited film. We have developed an electrical technique for in situ stress measurement that detects the piezoresistive response of resistors fabricated within the surface of a 20-μm-thick Si microcantilever substrate. By using Si cantilevers fabricated from (110) wafers, boron-implanted resistors oriented along ⟨110⟩ in-plane directions, which have a large piezoresistive response, were used for sensing the biaxial stress in the substrate surface resulting from the stress that developed in a deposited film. Resistors oriented along ⟨001⟩ in-plane directions, which have the least sensitive piezoresistive response and a temperature-dependent resistivity, were used to monitor the substrate temperature during deposition. Intrinsic stresses related to the thin film formation process, excluding thermal stresses, were measured for Cu during deposition as a function of film thickness and as a function of time during interruptions of growth. The piezocantilever’s insensitivity to both mechanical vibration and substrate alignment, good signal-to-noise ratio, and the potential for stress measurement during chemical vapor deposition are improvements over conventional thin film stress measurement techniques.
Heuristic theory of nonlocally broken gyro-Bohm scaling
Authors: Waltz R. E. , Candy J.
Published: June 2005

Global gyrokinetic simulations of ion temperature gradient turbulent transport with piecewise-flat profiles are given to illustrate the breaking of gyro-Bohm scaling by a nonlocal mechanism. The nonlocal drainage of the turbulence from unstable regions spreading into stable (or less unstable) regions breaks the gyro-Bohm scaling toward Bohm in unstable regions and toward super-gyro-Bohm in stable (or less unstable) regions. A heuristic model for this nonlocal process is formulated in terms of a nonlocal growth rate resulting from a locally weighted radial average of the local linear ballooning mode growth rate. A nonlocality length L measured in ion gyroradii provides the exponential scale for the local weighting. The nonlocal growth rate can be incorporated into a local gyro-Bohm-scaled transport model in place of the local growth rate. The resulting nonlocal transport model will provide some transport in stable regions. A heuristic theory of this nonlocal transport mechanism based on the partial formation of global modes in toroidal geometry is detailed. The theory argues that the nonlocality length L increases with relative gyroradius and decreases with the linear growth rate.
Large-amplitude electrostatic solitary structures in dusty plasmas with vortexlike variable charge dust distribution
Authors: Tribeche Mouloud
Published: June 2005

A theoretical model is presented to show the existence, formation, and possible realization of large-amplitude solitary potentials in a charge varying dusty plasma with trapped dust particles. These nonlinear localized structures are self-consistent solutions of the Vlasov equation in which the dust response is non-Maxwellian due to the dust trapping in the large-amplitude plasma potentials. The soliton suffers the well-known anomalous damping, the importance of which is roughly proportional to the dust grain velocity. Our investigation may be taken as a prerequisite for the understanding of the electrostatic solitary waves that may occur in space dusty plasmas.
Noise suppression of a differential detector under high levels of illumination, relevant to terahertz electro-optic sampling
Authors: van der Valk N. C. J. , Schouten R. N. , Planken P. C. M.
Published: June 2005

In electro-optic detection of terahertz transients, the photodiodes of a differential detector are often illuminated with optical powers on the order of several milliwatts. We present measurements that show that the response of the photodiodes at these power levels is distorted, giving rise to frequency-dependent amplitude and phase changes in the electrical signal from these diodes. We find that these distortions significantly reduce the ability of the detector to suppress laser amplitude noise. Surprisingly, this occurs at power levels at which the dc output of each photodiode shows no sign of saturation. Based on our measurements, we provide experimenters with recommendations to improve the amplitude noise suppression of a differential detector under high levels of illumination.
Two-dimensional density and density fluctuation diagnostic for the edge plasma in fusion devices
Authors: Zoletnik S. , Petravich G. , Bencze A. , Berta M. , Fiedler S. , McCormick K. , Schweinzer J.
Published: June 2005

A technique is described for the two-dimensional measurement of electron density profile and fluctuations in edge regions of magnetically confined fusion plasmas. The method is based on existing lithium beam beam emission spectroscopy technique, two-dimensional resolution is achieved by electrostatically scanning the beam. If scanning is performed faster than the lifetime of the turbulent structures in the plasma, the diagnostic is capable of measuring the structure of electron density fluctuations as well. The beam strength of currently available beams makes the detection of single fluctuation events impossible, but the full two-dimensional spatial structure of correlations can still be determined. The article describes the technique and fast beam deflection tests up to 250kHz. The capabilities of such a diagnostic for fluctuation measurement are explored by simulating measurement signals. Measurement of both the two-dimensional density profile, fluctuation correlation function and poloidal flow velocity are demonstrated at the Wendelstein 7-AS stellarator. The shape of the density profile, the radial and poloidal correlation lengths and the flow velocity are in agreement with expectations and previous Langmuir probe measurement.
Scanning laser system to determine the corneal shape
Authors: Ascanio Gabriel , Caballero-Ruiz Alberto , Ruiz-Huerta Leopoldo , Gonzalez-Cardel Mario , Diaz-Uribe Rufino
Published: June 2005

The development and tests of a scanning system to be used to determine the corneal topography with the laser deflectometry method are presented. In this equipment, a He-Ne laser beam scans the cornea by describing a spiral trajectory generated by two components: radial and angular. The first component is produced by the displacement of a plane mirror moved by a linear pneumatic actuator. The second component is produced by passing the beam through a Dove prism which is rotating by means of a belt drive coupled to a high-speed electric motor. Tests were first performed by analyzing both components independently and then they were characterized by combining the two components. Results are discussed and compared to those of an earlier cited work.
In situ characterization of high-intensity laser beams on OMEGA
Authors: Forties R. A. , Marshall F. J.
Published: June 2005

This article details a means of inferring high-intensity laser beam shapes as applied to the 60-beam ultraviolet (UV) (351nm) OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Measurements of the shape, location, and relative fluence of beams on the OMEGA laser system are obtained from x-ray images of the emission from 4-mm-diam, Au-coated pointing targets irradiated by the focused beams. The images are digitally recorded with an array of up to eight pinhole cameras. The image of each beam is corrected for the effect of view angle and conversion efficiency from UV to x rays, and fit to an elliptical super-Gaussian. The best-fit values from multiple views are combined to obtain values of the beam’s shape, beam-to-beam relative peak fluence, beam position, and errors thereof. This method allows the beam-to-beam balance and beam pointing to be further improved, if so desired, by providing measurements of these quantities at the target.
Transit-time instability in Hall thrusters
Authors: Barral Serge , Makowski Karol , Peradzyński Zbigniew , Dudeck Michel
Published: June 2005

Longitudinal waves characterized by a phase velocity of the order of the velocity of ions have been recurrently observed in Hall thruster experiments and simulations. The origin of this so-called ion transit-time instability is investigated with a simple one-dimensional fluid model of a Hall thruster discharge in which cold ions are accelerated between two electrodes within a quasineutral plasma. A short-wave asymptotics applied to linearized equations shows that plasma perturbations in such a device consist of quasineutral ion acoustic waves superimposed on a background standing wave generated by discharge current oscillations. Under adequate circumstances and, in particular, at high ionization levels, acoustic waves are amplified as they propagate, inducing strong perturbation of the ion density and velocity. Responding to the subsequent perturbation of the column resistivity, the discharge current generates a standing wave, the reflection of which sustains the generation of acoustic waves at the inlet boundary. A calculation of the frequency and growth rate of this resonance mechanism for a supersonic ion flow is proposed, which illustrates the influence of the ionization degree on their onset and the approximate scaling of the frequency with the ion transit time. Consistent with experimental reports, the traveling wave can be observed on plasma density and velocity perturbations, while the plasma potential ostensibly oscillates in phase along the discharge.
Nondestructive evaluation of rice using two-dimensional imaging of photoluminescence
Authors: Katsumata T. , Suzuki T. , Aizawa H. , Matashige E. , Komuro S. , Morikawa T.
Published: June 2005

Evaluation technique of rice using photoluminescence (PL) imaging has been developed based on the visible light PL with broad peak at a wavelength of λ=462nm from starchy foods under illumination of ultraviolet (UV) light at λ=365nm. Peak intensity of PL varies with variety and source of the rice. Two-dimensional (2D) images of PL from rice reveal the uniformity of the rice product. Blended rice from different species can be detected using 2D PL image. Brightness over the 2D PL images of rice with a single breed from a single source distributes according to a Gaussian distribution curve. Deviation from a Gaussian distribution curve estimated as χ2 value and correlation coefficient increases in a rice specimen of various species of blended rice. Image processing of PL images from specimens reveals contamination and∕or mixing of other species or foreign objects. A 2D PL imaging technique is potentially useful for nondestructive and quick evaluation and quality control of the rice products.
Pulse micromagnet for practical high-field measurements
Authors: Ohmichi E. , Osada T.
Published: June 2005

We have developed a pulse micromagnet for versatile measurements in strong magnetic fields of up to 30T. Typical coil dimensions are 5.5mm in diameter and 6mm in length. The energy stored in the capacitor bank is 90J (2mF, 300V), three orders of magnitude smaller than conventional systems. One of the advantages of such a small magnet is low energy dissipation, allowing high-field experiments even in a He4 storage. Although the pulse duration is relatively short (∼600μs), we find that our micromagnet is useful for high-field experiments such as magnetoresistance measurement.
Hairiness measurement of textile yarns using crossed polarizers
Authors: Anand Arun , Chhaniwal Vani K. , Narayanamurthy C. S.
Published: June 2005

Some of the fibers making a textile yarn are not contained in the yarn body and these fibers represent the hairiness of the yarn surface. Hairiness measurement of textile yarns is very important from the point of view of the textile industry. It is necessary to have sensitive, accurate, and fast methods to measure hairiness. In this article, a method developed to measure hairiness of textile yarns is discussed. When a yarn is illuminated by a plane polarized light beam, a portion of the incident beam is scattered from the yarn body and the protruding fibers. The light beam after the yarn will contain polarized and depolarized components. An analyzer with its plane of polarization perpendicular to that of incident light will allow only the depolarized portion, which contains the information about the hairiness, to pass through. By calibrating the technique using textile yarns having known hairiness, the setup can be used to determine hairiness very accurately.
Study of low-temperature crystallization of amorphous Si films obtained using ferritin with Ni nanoparticles
Authors: Kirimura Hiroya , Uraoka Yukiharu , Fuyuki Takashi , Okuda Mitsuhiro , Yamashita Ichiro
Published: June 2005

A polycrystalline silicon thin film with a high crystallinity was obtained using ferritin with a Ni core (7nm), which enabled us to precisely control the density and position of the nucleus for crystal growth. The core density of ferritin adsorbed on the amorphous silicon surface was controlled in the range from 109cm−2to1011cm−2. Crystal growth was performed at 550°C in N2. Crystallinity or grain size strongly depended on Ni core density. Polycrystalline silicon film with the average grain size of 3μm and a high crystallinity was obtained at a low Ni atom density of 1012cm−2.
Electrochemical lithium doping of a pentacene molecule semiconductor
Authors: Fang Baizeng , Zhou Haoshen , Honma Itaru
Published: June 2005

Li-doped pentacene has been developed by using an electrochemical approach; that is, constant-potential electrolysis. Li-doped pentacene was characterized by Raman spectrometry and x-ray diffraction measurements. Lithium doping introduces a modification of the C–H vibrational modes located at the end of pentacene molecules. A low doping level has been observed for electrochemical synthesis of Li-doped pentacene, and lithium species are supposed to be intercalated between the two-dimensional pentacene layers. The lithium-doped pentacene exhibits a conductivity of ∼6×10−3Scm−1.
Chemical phase transitions of the HfO2∕SiON∕Si nanolaminate by high-temperature thermal treatments in NO and O2 ambient
Authors: Oh J. H. , Park Y. , An K.-S. , Kim Y. , Ahn J. R. , Baik J. Y. , Park C. Y.
Published: June 2005

Temperature-dependent chemical phase transitions of the HfO2∕SiON∕Si(100) nanolaminate in O2 and NO ambient have been investigated using high-resolution photoemission spectroscopy. Hf4f, Si2p, O1s, and N1s photoemission spectra were measured after annealing the nanolaminate at a temperature between 750 and 1150°C. These spectra show that the chemical phase transitions of the nanolaminate strongly dependend on the ambient gases. The nanolaminate in an O2 ambient is stable below 750°C but the HfO2 and SiON layers dissociate by producing Hf silicides above 950°C. In contrast, the nanolaminate in NO ambient does not transit into Hf silicides up to 1050°C. Interestingly, the HfO2 and SiON layers transforms into HfOxNy and SiNx layers, respectively, with a high thermal stability, where the HfOxNy layers are a high-k dielectric material and the SiNx layers work as a barrier against both Si and O diffusion
Identification of a determining parameter for resistive switching of TiO2 thin films
Authors: Rohde Christina , Choi Byung Joon , Jeong Doo Seok , Choi Seol , Zhao Jin-Shi , Hwang Cheol Seong
Published: June 2005

Electric-pulse-induced resistive switching of 43nm thick TiO2 thin films grown by metalorganic chemical vapor deposition was studied by current-voltage (I-V) and constant voltage-time measurements. The resistance ratio between the two stable states of the film constitutes approximately 1000. The allowed current level and voltage step width during the sweep mode I-V measurements influenced switching parameters, such as the switching voltage, time before switching, and resistance values. However, it was clearly observed that the power imparted to the film controlled mainly switching. The required power for successful switching was almost invariant irrespective of other measurement variables.
Strain dependence of lasing mechanisms in ZnO epilayers
Authors: Li H. D. , Yu S. F. , Abiyasa A. P. , Yuen Clement , Lau S. P. , Yang H. Y. , Leong Eunice S. P.
Published: June 2005

The lasing characteristics of highly disordered ZnO thin films deposited on SiO2∕Si substrates with and without a MgO buffer layer have been investigated. We observed that the emission spectra of the ZnO epilayers with and without a MgO buffer are associated with the radiative recombination of free-exciton (∼380nm) and electron-hole plasma (∼395nm), respectively. The difference in the lasing wavelength is due to the induced compressive (tensile) strain along the c axis of the ZnO epilayers as a result of the presence (absence) of the MgO buffer layer. It is demonstrated that the strain-induced variation of Mott density inside the ZnO epilayers is responsible for the observed lasing characteristics.
Reversible and irreversible trapping at room temperature in poly(thiophene) thin-film transistors
Authors: Salleo A. , Endicott F. , Street R. A.
Published: June 2005

We measured the bias stress characteristics of poly(thiophene) semicrystalline thin-film transistors (TFTs) as a function stress times, gate voltages, and duty cycles. At room temperature, the bias stress has two components: a fast reversible component and a slow long-lived component. We hypothesize that the irreversible component is due to charge trapping in the disordered areas of the semiconductor film. At low duty cycle (<2%), the fast bias stress component is reversed during the off-part of the cycle therefore the observed threshold voltage (VT) shift is only caused by long-lived trapping. Long-lived trapping follows power-law kinetics with a time exponent approximately equal to 0.37. We use these findings to estimate the lifetime of TFTs used as switches in display backplanes.
Potassium chloride nanowire formation inside a microchannel glass array
Authors: Zhang Daqing , Moore Sam , Wei Jiang , Alkhateeb Abdullah , Gangadean Dev , Mahmood Hasan , Lantrips Justin , Mcllroy David N. , LaLonde Aaron D. , Norton M. Grant , Young James S. , Wang Chongmin
Published: June 2005

The synthesis of KCl nanowires has been achieved by atomic layer deposition inside high aspect ratio channels of microchannel glass. The average diameter of the KCl nanowires is 250 nm, with a minimum observed diameter of 50 nm, and lengths up to 5μm. The Cl precursor was TaCl5, while the source of K was determined to be impurities in the microchannel glass substrate. The process for KC1 nanowire formation is a three-step chemical process that simultaneously etches K from the substrate concomitant with the formation of chlorine gas. It is postulated that the curvature of the channels may influence the diameters of the KCl nanowires.