bluuebunny/crossref_metadata_2025 huggingface dataset:
Parametric fluorescence in periodically poled silica fibers
Authors: Bonfrate G. , Pruneri V. , Kazansky P. G. , Tapster P. , Rarity J. G.
Published: July 2002

We report the observation of quasiphase matched parametric fluorescence from a periodically poled silica fiber. A pair-photon production rate of more than 100 MHz around 1532 nm was achieved in second-order nonlinear gratings for 300 mW of pump power at 766 nm. These results are very promising for the realization of reliable all-fiber single-photon sources for quantum cryptography systems and metrology applications.
Free-space electro-optic detection of continuous-wave terahertz radiation
Authors: Nahata Ajay , Yardley James T. , Heinz Tony F.
Published: July 2002

We present a scheme for the coherent detection of freely propagating continuous-wave terahertz radiation using electro-optic detection. The terahertz radiation is generated by photomixing two single-mode laser diodes in an antenna fabricated on low-temperature-grown GaAs. This radiation is detected using the electro-optic effect in 〈110〉 ZnTe. In contrast to typical terahertz detection techniques, this is a frequency-domain measurement that relies on coherent up-conversion of the terahertz field combined with optical homodyning to suppress background noise.
Self-ordered pore structure of anodized aluminum on silicon and pattern transfer
Authors: Crouse D. , Lo Yu-Hwa , Miller A. E. , Crouse M.
Published: July 2002

A practical approach of transferring a hexagonal array of nanosized pores produced in porous alumina into silicon and other substrates is discussed. The alumina pores have dimensions of 25–250 nm pore diameters and 50–300 nm pore spacings depending on the anodization conditions used. The characteristics of the alumina pores and the alumina–silicon interface are studied for different substrate materials and anodizing conditions. The unique structure of the barrier layer allows for the alumina to be directly used as an etch mask for pattern transfer into the silicon substrate.
Refined model for spectroscopic ellipsometry analysis of SixGe1−x/Si strained heterostructures
Authors: Ferrieu F.
Published: July 2002

A simple model based on the optical stress birefringence induced by the lattice mismatch in the epitaxy of a SixGa1−x layer on Si is discussed. With this model, spectroscopic ellipsometry provides not only layer thickness and alloy composition, but also control of the coherently strained-to-unstrained material ratio.
Epitaxial growth and magnetic properties of single-crystal Co2MnGe Heusler alloy films on GaAs (001)
Authors: Ambrose T. , Krebs J. J. , Prinz G. A.
Published: July 2002

Single-crystal Co2MnGe Heusler alloy films were epitaxially grown on GaAs (001) substrates by molecular beam epitaxy. In situ reflection high-energy electron diffraction patterns and Auger spectroscopy confirmed the high-quality growth and stoichiometry. At 5 K, a saturation magnetization of 1000 emu/cm3 was measured. In-plane ferromagnetic resonance shows narrow linewidths and four-fold plus uniaxial anisotropy. A room-temperature resistivity of 115 μΩ cm has also been determined. The temperature dependence of the resistivity shows metallic behavior down to low temperatures.
Current-voltage curves of gold quantum point contacts revisited
Authors: Hansen K. , Nielsen S. K. , Brandbyge M. , Lægsgaard E. , Stensgaard I. , Besenbacher F.
Published: July 2002

We present measurements of current–voltage (I–V) curves on gold quantum point contacts (QPCs) with a conductance up to 4 G0 (G0=2e2/h is the conductance quantum) and voltages up to 2 V. The QPCs are formed between the gold tip of a scanning tunneling microscope and a Au(110) surface under clean ultra-high-vacuum conditions at room temperature. The I–V curves are found to be almost linear in contrast to previous reports. Tight-binding calculations of I–V curves for one- and two-atom contacts are in excellent agreement with our measurements. On the other hand, clearly nonlinear I–V curves are only observed when the sample has been cleaned in air.
Symmetry analysis and exact solutions of the 2+1 dimensional sine-Gordon system
Authors: Lou Sen-yue
Published: July 2002

According to the space variable exchange symmetry, we change the 2+1 dimensional sine-Gordon system obtained by Konopelchenko and Rogers (KR) to a variant form. Some types of similarity reductions are obtained by using some Lie symmetry analysis. From these similarity reductions, we find that the soliton structure of the system possesses quite a rich structure. The line solitons parallel to the lines x+y=0 and x−y=0 may have an arbitrary shape. In addition to the well-known dromion solution, which is constructed by two line solitons, one may find many other kinds of soliton solutions localized in all directions. For instance, some kinds of ring type (basin-like, plateau-like and bowl-like) and instanton type soliton solutions, can be found directly by selecting the arbitrary functions included in the “single” soliton solution. The dromion solutions may also be constructed by straight line and curved line solitons.
Modeling and experimental studies of wave evolution on free falling viscous films
Authors: Nguyen Luan T. , Balakotaiah Vemuri
Published: July 2002

A new simplified model is developed for describing the characteristics of free falling wavy liquid films. The model consists of a set of three partial differential equations (in x and t) for the local film thickness, volumetric flow rate, and wall shear stress. It is shown that the new model is a substantial improvement over all existing simplified models of wavy films such as the long wave equation, the Nakaya model (extended third-order long wave equation), the Shkadov model, and the Kapitza boundary layer model. These prior models predict nonphysical negative wall shear stress when the wave amplitude is large and cannot explain the experimentally observed relationship between the maximum wave amplitude and the Reynolds (Re) and Kapitza (Ka) or Weber (We) numbers. In contrast, the present model yields physically meaningful results and quantitative predictions of large amplitude waves. Local bifurcation analysis of the model for small Re gives the following analytical relations for the velocity (Ce) and maximum amplitude of the solitary waves: hmax−1=0.132 Re5/3 Ka−1=16(3−Ce)=1.925 We−1. Experimental studies of free falling viscous films were conducted using water–glycerin solutions for Reynolds numbers in the range of 2–20 and Kapitza numbers in the range of 6–22. Comparison of the experimental data on wave amplitudes with analytical correlations shows excellent agreement. Numerical simulations of the wave profiles generated from the simplified model also match closely with the experimentally observed wave profiles.
Low-temperature resistivity minimum in ceramic manganites
Authors: Rozenberg E. , Auslender M. , Felner I. , Gorodetsky G.
Published: July 2002

Measurements of magnetoresistance and magnetization were carried out on ceramic samples of La0.5Pb0.5MnO3 and La0.5Pb0.5MnO3, containing 10 at. % Ag in a dispersed form. The results obtained for the resistivity at zero applied magnetic field exhibit a shallow minimum at the temperature T∼25–30 K which shifts towards lower temperatures upon applying a magnetic field and disappears at a certain field Hcr. Also the resistivity at helium temperature decreases upon applying magnetic fields. It is shown that the model of charge carriers tunneling between antiferromagnetically coupled grains may account for the results observed.
Feedback stabilization of nonaxisymmetric resistive wall modes in tokamaks. II. Control analysis
Authors: Fransson C. M. , Lennartson B. , Breitholtz C. , Bondeson A. , Liu Y. Q.
Published: July 2002

Active feedback of nonaxisymmetric resistive wall modes in tokamaks is investigated using control theory. Control systems are designed to stabilize the resistive wall mode of toroidal mode number n=1 and meet certain performance specifications for a set of test equilibria. The response of the plasma and resistive wall is described by low order rational functions from an electromagnetic model [Y. Q. Liu et al., Phys. Plasmas 7, 3681 (2000)]. Simple coil arrangements are assumed, both for the sensor and feedback coil arrays, and the sensors detect the perturbed poloidal field. The active coils are modeled both as broad strips and as thin wires, and several different controllers: P (proportional), PD (proportional plus derivative) and H∞ are investigated. An important parameter is the ratio, τ, of control system response time to the resistive wall time, and the analysis shows the restrictions on this ratio for acceptable performance. For an equilibrium that exceeds the no-wall beta limit by 63%, good control with broad strips and a PD controller is possible for τ≲5.4, while thin-wire coils require τ≲2.1. H∞ controllers give some improvement for thin wires and about a factor of 2 increase in τ for broad strips. The upper limit in τ decreases with increasing pressure. A control system designed to stabilize a certain pressure generally works well at lower pressures.
Precision microwave dielectric and magnetic susceptibility measurements of correlated electronic materials using superconducting cavities
Authors: Zhai Z. , Kusko C. , Hakim N. , Sridhar S. , Revcolevschi A. , Vietkine A.
Published: July 2002

We analyze microwave cavity perturbation methods, and show that the technique is an excellent, precision method to study the dynamic magnetic and dielectric response in the GHz frequency range. Using superconducting cavities, we obtain exceptionally high precision and sensitivity for measurements of relative changes. A dynamic electromagnetic susceptibility ζ̃(T)=ζ′+iζ″ is introduced, which is obtained from the measured parameters: the shift of cavity resonant frequency δf and quality factor Q. We focus on the case of a spherical sample placed at the center of a cylindrical cavity resonant in the TE011 mode. Depending on the sample characteristics, the magnetic permeability μ̃, the dielectric permittivity ε̃=ε′+iε″, and the complex conductivity σ̃=σ′+iσ″ can be extracted from ζ̃H. A full spherical wave analysis of the cavity perturbation indicates that: (i) In highly insulating samples with dielectric constant ε′∼1, the measured ζ̃H∼χ̃M, enabling direct measurement of the magnetic susceptibility. The sensitivity of the method equals or surpasses that of dc superconducting quantum interference device measurements for the relative changes in magnetic susceptibility. (ii) For moderate ε̃ and conductivity σ̃, ζ̃H∝ε̃+iωσ̃/ε0−1, thus enabling direct measurement of the sample dielectric constant ε̃, even though the sample is placed in a microwave magnetic field. (iii) For large σ we recover the surface impedance limit. (iv) Expressions are provided for the general case of a lossy dielectric represented by ε̃+iωσ̃/ε0. We show that an inversion procedure can be used to obtain ε̃+iωσ̃/ε0 in a wide range of parameter values. This analysis has led to the observation of new phenomena in novel low-dimensional materials. We discuss results on magneto dynamics of the three-dimensional (3D) antiferromagnetic state of the spin chain compound Sr2CuO3. In dielectric susceptibility measurements in Sr14Cu24O41, we directly observe a dielectric loss peak. Dimensional resonances in the paraelectric material SrTiO3 are shown to occur due to the rapid increase of dielectric constant with decreasing temperature. The cavity perturbation methods are thus an extremely sensitive probe of charge and spin dynamics in electronic materials.
A theory for the deliquescence of small particles
Authors: Mirabel Philippe , Reiss Howard , Bowles Richard K.
Published: July 2002

A theory is developed for the deliquescence of small particles that incorporates the effect of surface phenomena on the deliquescence process. The theory is based on rudimentary surface thermodynamics since we are primarily interested in the orders of magnitude of the various effects. Applying the theory to a generic crystal with properties similar to NaCl, in water vapor, we find that the surface tension has a significant effect for crystals with a radius smaller than 10−5 cm. We suggest an experiment for the determination of the surface tension of soluble crystals that utilizes the deliquescence of these small particles. Serendipitously, such an experiment has just been performed by another group of authors. The qualitative analysis of this experiment should eventually be accompanied by a further development of the rigorous thermodynamic theory of solid surfaces.
Hydration shell structure of the OH−(H2O)n=1–15 clusters from a model potential energy function
Authors: Vegiri Alice , Shevkunov Sergei V.
Published: July 2002

The structural properties of the hydrated hydroxide ion are studied in terms of a many-body potential energy function that has been parameterized according to the experimentally determined [Arshadi et al., J. Phys. Chem. 74, 1475, 1483 (1970)] enthalpy and entropy changes for the first five association reactions of the ion with H2O. Clusters in the n=1–15 size range are examined through a canonical Monte Carlo simulation at T=297 K. The resultant structures, irrespective of the cluster size, are predominantly linear of the dendrite type, with the first shell consisting of two water molecules. Minimum energy structures at T=0 K for n=2 and 3 compare well with ab initio conformations.
Growth of stress-released GaAs on GaAs/Si structure by metalorganic chemical vapor deposition
Authors: Soga T. , Jimbo T. , Arokiaraj J. , Umeno M.
Published: July 2002

A stress-released GaAs layer was grown on GaAs bonded to Si substrate with the combination of epitaxial lift-off technique and regrowth by metalorganic chemical vapor deposition. The GaAs thin film was bonded to Si substrate using SeS2 and another GaAs layer was regrown. The photoluminescence peak wavelength and the slope of the time resolved photoluminescence decay of GaAs/Si are almost the same as those of GaAs grown on GaAs substrate.
AlN films on GaN: Sources of error in the photoemission measurement of electron affinity
Authors: Bermudez V. M. , Wu C.-I. , Kahn A.
Published: July 2002

This communication corrects an error in the value previously reported by one of the authors for the electron affinity (EA) of AlN. A brief discussion is given of the potential errors in photoemission measurements of EA which affect this and other studies. Finally, a recommendation is given for 1.9 eV as the “true” EA of wurtzite AlN.
Evolution of deep centers in GaN grown by hydride vapor phase epitaxy
Authors: Fang Z.-Q. , Look D. C. , Jasinski J. , Benamara M. , Liliental-Weber Z. , Molnar R. J.
Published: July 2002

Deep centers and dislocation densities in undoped n GaN, grown by hydride vapor phase epitaxy (HVPE), were characterized as a function of the layer thickness by deep level transient spectroscopy and transmission electron microscopy, respectively. As the layer thickness decreases, the variety and concentration of deep centers increase, in conjunction with the increase of dislocation density. Based on comparison with electron-irradiation induced centers, some dominant centers in HVPE GaN are identified as possible point defects.
A diamond gasket for the laser-heated diamond anvil cell
Authors: Zou Guangtian , Ma Yanzhang , Mao Ho-kwang , Hemley Russell J. , Gramsch Stephen A.
Published: July 2002

Advances in laser heating techniques with diamond anvil cells have enabled direct investigations of materials under extreme pressure-temperature conditions. The success of uniform heating to the maximum temperatures at megabar pressures relies critically on maximizing the gasket thickness which in turn depends upon the shear strength of the gasket. We have used diamond powder, the strongest possible material, to formulate a gasket for in situ x-ray diffraction with double-sided laser heating. The increase in gasket thickness allows increases in sample and insulator thickness, thereby improving the quality and pressure-temperature range of the measurement. We did not observe any pressure difference within 40 μm of the center of the sample chamber and the temperature distribution across the sample itself is within ±47 K. These improvements as well as the fact that the diamond gasket can allow the sample to remain in good condition after high P–T processing make it an extremely useful technique in diamond cell laser-heating experiments. As an example of the technique, we present in situ x-ray diffraction results for FeO to above 86 GPa and 3500 K.
Parallel atomic force microscopy with optical interferometric detection
Authors: Sulchek T. , Grow R. J. , Yaralioglu G. G. , Minne S. C. , Quate C. F. , Manalis S. R. , Kiraz A. , Aydine A. , Atalar A.
Published: July 2002

We have developed an atomic force microscope that uses interferometry for parallel readout of a cantilever array. Each cantilever contains a phase sensitive diffraction grating consisting of a reference and movable set of interdigitated fingers. As a force is applied to the tip, the movable set is displaced and the intensity of the diffracted orders is altered. The order intensity from each cantilever is measured with a custom array of silicon photodiodes with integrated complementary metal–oxide–semiconductor amplifiers. We present images from five cantilevers acquired in the constant height mode that reveal surface features 2 nm in height. The interdigital method for cantilever array readout is scalable, provides angstrom resolution, and is potentially simpler to implement than other methods.
Study of dielectric relaxation modes in poly(ε-caprolactone): Molecular weight, water sorption, and merging effects
Authors: Grimau M. , Laredo E. , Pérez Y. M. C. , Bello A.
Published: July 2002

The behavior of the various relaxation modes in poly(ε-caprolactone) (PCL), is studied by Broad Band Dielectric Spectroscopy in the frequency range from 3×10−3 to 1.8×109 Hz and from 133 to 313 K. The experimental trace of the dielectric loss as a function of the angular frequency, ε″(ω), is analyzed by best fitting a sum of Cole–Cole distributions corresponding to the γ and β local modes and to the α relaxation which is the dielectric manifestation of the dynamic glass transition. The kinetic parameters of the three predominant relaxations are determined and relaxation plots describing the temperature dependencies of the relaxation times are given as a function of 1/T. These relaxation plots are insensitive within experimental errors, either to the molecular weight or to the water concentration. The hydration level (<1%) only affects the intensities of the local processes and no plasticization effect is observed. At temperatures higher than those recorded for the α mode a fourth intense process, α′ is observed as a shoulder in the conductivity rise. The position of this peak is the only one that changes with the molecular weight but not as much as it should if it were only caused by a normal mode. As the temperature increases the local β relaxation and the cooperative α mode merge into an αβ mode. The traces can be fitted below the merging temperature with three Cole–Cole distributions which after 219 K reduce to 2, the αβ and γ modes. This decomposition is confirmed by extracting the relaxation time distribution with the Simulated Annealing Direct Signal Analysis. In PCL, there is no necessity of invoking the existence of a change in the relaxation mechanism, a simple superposition of the α and β modes is adequate. This α–β crossover affects the intensity and shape of the distant γ relaxation. At still higher temperatures this αβ mode merges with the more localized γ mode, thus evidencing a new crossover and the persistence of the γ mode in the whole temperature range. The activation energy of the γ process changes after the crossover temperature, together with the α Cole–Cole shape parameter and its dielectric strength.
Conditions for optimum giant magnetoresistance in granular metals
Authors: Kechrakos D. , Trohidou K. N.
Published: July 2002

The dependence of the giant magnetoresistance (GMR) of a metallic granular system on the concentration of magnetic particles is studied numerically. The effect of particle coalescence and dipolar interactions between the particles on the value of optimum GMR and the shape of the concentration dependence curve are discussed. The micromagnetic configuration of the system is obtained by a Monte Carlo algorithm that involves short-range effective exchange couplings and long range dipolar interactions. The conductivity is obtained using Kubo’s formula for a tight binding Hamiltonian. A comparison of our results to experiments on metallic granular films is made.
Pulsed liquid microjet for microsurgery
Authors: Fletcher D. A. , Palanker D. V.
Published: July 2002

The precision of soft tissue dissection with pulsed lasers in liquid media is typically limited by collateral damage from vapor bubbles created during energy deposition. We present an alternative technique for creating incisions using a pulsed liquid microjet driven by an electric discharge-induced vapor bubble generated inside a micronozzle. We use this technique to create a pulsed jet 30 μm in diameter with a peak velocity of 90 m/s and total ejected volume on the order of 100 pl. Incision tests on a polyacrylamide gel simulating soft tissue show that the width of the cut is comparable to the diameter of the micronozzle and that collateral damage is significantly less than that produced by a vapor bubble not confined by the nozzle.
Wetting reaction versus solid state aging of eutectic SnPb on Cu
Authors: Tu K. N. , Lee T. Y. , Jang J. W. , Li L. , Frear D. R. , Zeng K. , Kivilahti J. K.
Published: July 2002

The reaction kinetics of eutectic SnPb solder on Cu were studied and compared in the liquid state at 200 to 240 °C and in the solid state aged at 125–170 °C. The ternary phase diagrams of SnPbCu, the morphology of intermetallic compound (IMC), and the kinetics of growth of the intermetallics were used in the comparison. The temperature difference between these two reactions is only 30 °C, but the kinetics of reaction, as well as the morphology of IMC formation, are very different. The kinetics in the wetting reaction is four orders of magnitude faster than that in solid state aging. The Cu6Sn5 intermetallic morphology in solid state aging is a layer type, but it has a scallop-type morphology in the wetting reaction. The morphology strongly affects the kinetics. While the kinetic difference can be attributed to the difference in atomic diffusivity between the liquid state and the solid state, it is the morphology that determines the kinetic path in these reactions. We conclude that a fast rate of reaction, which leads to a high rate of Gibbs free energy change, controls the reaction, not the Gibbs free energy change itself.
Monte Carlo simulation of double-gate silicon-on-insulator inversion layers: The role of volume inversion
Authors: Gamiz F. , Fischetti M. V.
Published: July 2002

The electron mobility in a double-gate silicon-on-insulator (DGSOI) device is studied as a function of the transverse effective field and silicon layer thickness. The contributions of the main scattering mechanisms (phonon scattering, surface roughness scattering due to both Si–SiO2 interfaces, and Coulomb interaction with the interface traps of both interfaces) are taken into account and carefully analyzed. We demonstrate that the contribution of surface scattering mechanisms is by no means negligible; on the contrary, it plays a very important role which must be taken into account when calculating the mobility in these structures. The electron mobility in DGSOI devices as Tw decreases is compared with the mobility in single-gate silicon-on-insulator structures (i) when only phonon scattering is considered, (ii) when the effect of surface-roughness scattering is taken into account, and (iii) when the contribution of Coulomb interaction with charges trapped at both interfaces is taken into consideration (in addition to phonon and surface roughness scattering). From this comparison we determined (in the three cases above) the existence of the following three regions: (i) A first region for thick silicon layers (Tw>20–30 nm), where mobility for both structures tends to coincide, approaching the bulk value. (ii) As Tw decreases we show that volume inversion modifies the electron transport properties by reducing the effect of all scattering mechanisms. Accordingly, the electron mobility in DGSOI inversion layers increases by an important factor which depends on the silicon thickness and the transverse effective field. (iii) Finally, for very small thicknesses, the limitations to electron transport are due to geometrical effects, and therefore the two mobility curves, which again coincide, fall abruptly. We show the existence of a range of thicknesses of a silicon layer (between 5 and 20 nm in which electron mobility is improved by 25% or more.
Low-loss polymeric optical waveguides using electron-beam direct writing
Authors: Wong W. H. , Zhou J. , Pun E. Y. B.
Published: July 2002

Low-loss optical waveguides based on a negative tone epoxy Novolak resin polymer have been fabricated using electron-beam direct writing. This polymer has a high refractive index, high sensitivity, large hardness, and Tg>200 °C. For single-mode channel waveguides with upper claddings, the propagation losses measured were 0.22 and 0.48 dB/cm at 1330 and 1550 nm, respectively. For waveguides without upper claddings, the losses were 0.5 dB/cm at both wavelengths. The stability of these waveguides was also investigated, and no significant change was observed after 200 h at 90 °C and 95% relative humidity.
Composite magnetostrictive materials for advanced automotive magnetomechanical sensors
Authors: McCallum R. W. , Dennis K. W. , Jiles D. C. , Snyder J. E. , Chen Y. H.
Published: July 2002

In this paper we present the development of a composite magnetostrictive material for automotive applications. The material is based on cobalt ferrite, CoO⋅Fe2O3, and contains a small fraction of metallic matrix phase that serves both as a liquid-phase sintering aid during processing and enhances the mechanical properties over those of a simple sintered ferrite ceramic. In addition the metal matrix makes it possible to braze the material, making the assembly of a sensor relatively simple. The material exhibits good sensitivity and should have high corrosion resistance, while at the same time it is low in cost.
Advanced ac loss measurement methods for high-temperature superconducting tapes
Authors: Rabbers J. J. , ten Haken B. , ten Kate H. H. J.
Published: July 2002

Advanced ac loss measurement methods for superconducting tapes are described in detail and demonstrated on BSCCO/Ag (Bi2Sr2Ca2Cu3Ox with a Ag matrix) tapes in liquid nitrogen at 77 K. The aim of the measurements is to simulate the situation of a tape conductor in an electric power application like a transformer coil or a power cable. In this class of devices the conductor is fed with an alternating transport current and simultaneously exposed to an alternating magnetic field. In many devices the magnetic field vector points in a single direction but in some devices such as three-phase power cables and motors the magnetic field rotates around the conductor. In all cases described above an electromagnetic approach with pick-up coils and voltage taps is used to measure the ac loss. This method enables a separate study of magnetization loss and transport current loss when both the magnetic field and transport current are present simultaneously. The magnetization loss measurement setup for unidirectional and rotating magnetic field is described. The transport current loss measurement setup is described, focusing on the suppression of cross effects of ac transport current and ac magnetic field that disturb accurate measurements. Finally several relevant examples of the results obtained are shown.
Study of the electron field emission and microstructure correlation in nanocrystalline carbon thin films
Authors: Gupta S. , Weiss B. L. , Weiner B. R. , Morell G.
Published: July 2002

Nanocrystalline carbon thin films were deposited by hot-filament chemical vapor deposition using a 2% concentration of methane in hydrogen. The films were deposited on molybdenum substrates under various substrate biasing conditions. A positive bias produced a continuous flow of electrons from the filament onto the substrate, while a negative bias caused the substrate to be bombarded with positive ions. Films were also grown under no bias, for comparison. Differences in the electron field emission properties (turn-on fields and emitted currents) of these films were characterized. Correspondingly, microstructural differences were also studied, as characterized with atomic force microscopy and Raman spectroscopy. Films grown under electron bombardment showed lower turn-on fields, smoother surfaces, and smaller grains than those grown under ion bombardment or no bias. A correlation between the enhanced emission properties and the nanocrystalline carbon material produced by the low-energy particle bombardment was found through the parameters obtained using spectroscopic ellipsometry modeling. The results confirm the significant role of defects on the electron field emission mechanism.
Positioning of nanometer-sized particles on flat surfaces by direct deposition from the gas phase
Authors: Krinke Thomas J. , Fissan Heinz , Deppert Knut , Magnusson Martin H. , Samuelson Lars
Published: July 2002

Arrangements of nanometer-sized particles were obtained on plane oxidized silicon substrates by direct deposition from the gas phase. The particles were attracted onto charge patterns created by contact charging. Monodisperse, singly charged indium aerosol particles with a diameter of 30 nm were used as a test case to illustrate this process. Due to the surface treatment, the deposition is highly selective. We were able to create lines of particles with widths as narrow as 100 nm and several millimeters in length. The resolution of the pattern depends mainly on the surface treatment and the tool geometry. Our approach opens the possibility of creating patterns composed of nanometer-sized particles on a flat substrate surface by the simple transfer of charge patterns, without a lithographical process.
“On”/“off” fluorescence intermittency of single semiconductor quantum dots
Authors: Kuno M. , Fromm D. P. , Hamann H. F. , Gallagher A. , Nesbitt D. J.
Published: July 2002

Single molecule confocal microscopy is used to investigate the detailed kinetics of fluorescence intermittency in colloidal II–VI (CdSe) semiconductor quantum dots. Two distinct modes of behavior are observed corresponding to (i) sustained “on” episodes (τon) of rapid laser absorption/fluorescence cycling, followed by (ii) sustained “off” episodes (τoff) where essentially no light is emitted despite continuous laser excitation. Both on-time and off-time probability densities follow an inverse power law, P(τon/off)∝1/τon/offm, over more than seven decades in probability density and five decades in time. Such inverse power law behavior is an unambiguous signature of highly distributed kinetics with rates varying over 105-fold, in contrast with models for switching between “on” and “off” configurations of the system via single rate constant processes. The unprecedented dynamic range of the current data permits several kinetic models of fluorescence intermittency to be evaluated at the single molecule level and indicate the importance of fluctuations in the quantum dot environment.
Models for Marangoni drying
Authors: Matar O. K. , Craster R. V.
Published: July 2002

Marangoni drying is a new ultra-clean drying process, which relies on surface-tension gradient forces, so-called Marangoni stresses. This method is of particular use in the semiconductor industry wherein obtaining ultra-clean surfaces is of paramount importance. The present work provides a mathematical description of this novel process involving four coupled partial differential equations, derived in the thin-layer approximation, for the film thickness, the concentration of chemicals in the air, at the air–liquid interface and in the bulk of the liquid film. Numerical solution of these equations yields prediction of typical profiles that accompany the spreading and drying processes. Particular attention is aimed at the prediction of the minimum film thickness as a function of system parameters with a view to optimizing the drying process.
Structure of the exact wave function. II. Iterative configuration interaction method
Authors: Nakatsuji Hiroshi , Davidson Ernest R.
Published: July 2002

This is the second progress report on the study of the structure of the exact wave function. First, Theorem II of Paper I (H. Nakatsuji, J. Chem. Phys. 113, 2949 (2000)) is generalized: when we divide the Hamiltonian of our system into ND (number of division) parts, we correspondingly have a set of ND equations that is equivalent to the Schrödinger equation in the necessary and sufficient sense. Based on this theorem, the iterative configuration interaction (ICI) method is generalized so that it gives the exact wave function with the ND number of variables in each iteration step. We call this the ICIND method. The ICIGSD (general singles and doubles) method is an important special case in which the GSD number of variables is involved. The ICI methods involving only one variable [ICION(one) or S(simplest)ICI] and only general singles (GS) number of variables (ICIGS) are also interesting. ICIGS may be related to the basis of the density functional theory. The convergence rate of the ICI calculations would be faster when ND is larger and when the quality of the initial guess function is better. We then study the structure of the ICI method by expanding its variable space. We also consider how to calculate the excited state by the ICIGSD method. One method is an ICI method aiming at only one exact excited state. The other is to use the higher solutions of the ICIGSD eigenvalues and vectors to compute approximate excited states. The latter method can be improved by extending the variable space outside of GSD. The underlying concept is similar to that of the symmetry-adapted-cluster configuration-interaction (SAC-CI) theory. A similar method of calculating the excited state is also described based on the ICIND method.
The true nature of space-charge-limited currents in electron vacuum diodes: A Lagrangian revision with corrections
Authors: Akimov P. V. , Schamel H. , Kolinsky H. , Ender A. Ya. , Kuznetsov V. I.
Published: July 2002

The physics of space-charge-limited current (JSCL) in diodes with finite electron injection velocities v0 is investigated within the Lagrangian flow description. The space-charge-limited (SCL) current is shown to be given by JSCL=(X+1+X2)3JCL, where JCL∼U3/2/L2 is the familiar Child–Langmuir current, X=(mv02/2eU)1/2, 𝒰 and L are the diode voltage and length, respectively. It results from an intrinsic property of the diode rather than from electron reflexion, the current picture of SCL accepted since Langmuir’s days. For field emitted electrons, on the other hand, JCL is proved to be universally valid, because in this case v0=0 holds. A number of further diode properties are derived analytically and presented numerically.
The reactions CHnD4−n+OH→P and CH4+OD→CH3+HOD as a test of current direct dynamics multicoefficient methods to determine variational transition state rate constants. II
Authors: Masgrau Laura , González-Lafont Àngels , Lluch José M.
Published: July 2002

In this paper we have carried out a test of current multilevel electronic structure methods to give accurate rate constants for the reactions CHnD4−n+OH→P and for the reaction of methane with OD. These multilevel methods are single-point energy techniques designed as general parametrizations for extrapolation to the full configuration interaction limit and, in some cases, to attain also the infinite basis set limit. By means of variational transition state theory including multidimensional tunneling corrections, the rate constants for these reactions, over a wide range of temperatures, have been computed using two recently developed multicoefficient schemes for extrapolating correlated electronic structure calculations: multicoefficient scaling all correlation (MCSAC) and multicoefficient correlation methods (MCCM). For comparison purposes, we have also evaluated the same rate constants using two other multilevel extrapolation techniques, namely, the multicoefficient quadratic configuration interaction (MC-QCISD) method and the complete basis set extrapolation model for free radicals (CBS-RAD). Two dual-level direct dynamics techniques have been employed within the scheme of variational transition state theory: the interpolated single-point energy corrections (ISPE) and the interpolated optimized corrections (IOC), with the purpose to analyze the importance of correcting a low level potential energy surface with the optimizations of the stationary points carried out at the highest computational level affordable. We have shown that the so-called MCCM-CCSD(T)-1sc multilevel scheme provides the best results for the set of reactions studied. A slight difference from the experimental rate constants still persists, specially at the lowest temperatures, although we think that the best theoretical rate constants of the present paper are accurate enough for most of the practical applications. However, the kinetic isotope effects (KIEs) are not so well reproduced because the deviations of the individual theoretical rate constants from the experimental ones, although being very small, do not go in the same direction and these errors are reinforced when the corresponding KIE is calculated.
Nonlinear development of weak beam–plasma instability
Authors: Ziebell L. F. , Gaelzer R. , Yoon Peter H.
Published: July 2002

Nonlinear interactions of tenuous electron beam, background, unmagnetized plasma, and self-consistently generated Langmuir and ion-sound waves are analyzed in the framework of plasma weak turbulence kinetic theory. Full numerical solutions of the complete weak turbulence equations are obtained for the first time, which show the familiar plateau formation in the electron beam distribution and concomitant quasi-saturation of primary Langmuir waves, followed by fully nonlinear processes which include three-wave decay and induced-scattering processes. A detailed analysis reveals that the scattering off ions is an important nonlinear process which leads to prominent backscattered and long-wavelength Langmuir wave components. However, it is found that the decay process is also important, and that the nonlinear development of weak Langmuir turbulence critically depends on the initial conditions. Special attention is paid to the electron-to-ion temperature ratio, Te/Ti, and the initial perturbation level. It is found that higher values of Te/Ti promote the generation of backscattered Langmuir wave component, and that a higher initial wave intensity suppresses the backscattered component while significantly enhancing the long-wavelength Langmuir wave component.
Cohomology of the infinite-order jet space and the inverse problem
Authors: Giachetta G. , Mangiarotti L. , Sardanashvily G.
Published: July 2002

Cohomology of the bicomplex of exterior forms on the infinite-order jet space of a smooth fiber bundle of a field model is computed. This provides a solution of the global inverse problem of the calculus of variations in Lagrangian field theory and time-dependent mechanics. In the case of an affine fiber bundle, the outcomes to BRST theory are discussed. We show that there is no topological obstruction to constructing global descent equations in the even field sector of BRST theory.
Role of terminal OH groups on the electrical and hydrophilic properties of hydro-oxygenated amorphous TiOx:OH thin films
Authors: Nakamura Masatoshi , Kato Shinichi , Aoki Toru , Sirghi Lucel , Hatanaka Yoshinori
Published: July 2002

Electrical and hydrophilic properties of TiOx films obtained by plasma enhanced chemical vapor deposition (PECVD) were investigated in connection with OH group content of the films. A microcrystalline TiOx film prepared by rf magnetron sputtering deposition (RFMSD) was used as a reference sample in this study. Compared to the RFMSD film, the PECVD TiOx films had good hydrophilicity after ultraviolet (UV) light irradiation, low dark, and high photoexcited currents in a vacuum and high sensitivity of their dark and photoexcited currents to surface adsorbates. Low dark and high photoexcited currents measured in vacuum for the PECVD TiOx films were explained by the effect of inactivation of the defect states such as dangling bonds by the termination of OH group. Due to this effect, the PECVD TiOx films are referred to as hydro-oxygenated TiOx:OH films in this article. The sensitivity of the photoexcited currents to surface adsorbates noticed for the TiOx:OH films suggests that the surface potential is modified in response to electron affinity of the surface adsorbates during UV light irradiation. This effect contributes to generation of oxidants due to interaction between photoexcited carriers and surface adsorbates and, hence, improves the hydrophilicity of the TiOx:OH films. These results suggest that both the hydrophilicity and electrical properties of the TiOx:OH films are strongly related to the film OH groups.
Pulsed liquid-injection metalorganic chemical vapor deposition of (La0.7Sr0.3MnO3/SrTiO3)15 superlattices
Authors: Dubourdieu C. , Rosina M. , Roussel H. , Weiss F. , Sénateur J. P. , Hodeau J. L.
Published: July 2002

( La 0.7 Sr 0.3 MnO 3 / SrTiO 3 ) 15 superlattices have been grown by pulsed liquid-injection metalorganic chemical vapor deposition on monocrystalline substrates such as LaAlO3, SrTiO3, and MgO. The pulsed-injection technique allows one to control precisely the amount of precursors delivered to the deposition chamber and thus the thickness of each individual layer. The period of the superlattices depends indeed linearly on the number of injected droplets. In our deposition conditions, the average growth rates are ∼0.130 nm/injection for La0.7Sr0.3MnO3 and 0.042 nm/injection for SrTiO3, with no significant difference as regard to the substrate used. The strain’s state of the superlattices depends on the relative thicknesses of the La0.7Sr0.3MnO3 and SrTiO3 layers and also on the substrate used. Finally, the deposition of superlattices with ultrathin interlayers of few unit cells has been demonstrated.
Monte Carlo simulation of polymer brushes in narrow pores
Authors: Viduna David , Limpouchová Zuzana , Procházka Karel
Published: July 2002

We present the model of a cylindrical pore with chains tethered by one end to its inner surface. The conformational and “quasistatic” (under low and medium shear rates) hydrodynamic properties of the system are studied. Since it was shown by other researchers that the density profile of the polymer layer is only slightly affected by flow in the region of low and medium shear rates, we do not take flow into account when calculating chain conformations. The conformational properties of the concave layer are very similar to those of the flat one. They are characterized by the layer thickness h. The hydrodynamic properties are characterized by the hydrodynamic thickness Lh. We show that Lh depends strongly on the chain surface density σ under conditions of the “mushroom” regime in contrast to h. Finally, we predict that the net permeability of the cylinder could decrease with the increasing temperature. It enables us, principally, to control the pore permeability with temperature.
Measurement of bipolar moments for photofragment angular correlations in ion imaging experiments
Authors: Nestorov Vilen K. , Hinchliffe Robert D. , Uberna Radoslaw , Cline Joseph I. , Lorenz K. Thomas , Chandler David W.
Published: July 2002

A general numerical method is given to extract angular correlations from photodissociation experiments with ion imaging detection. The angular correlations among the transition dipole moment of the parent molecule, μ, the photoproduct recoil velocity, v, and its angular momentum, j, are parametrized analytically using the semiclassical bipolar moment scheme due to Dixon. The method is a forward-convolution scheme which allows quantitative extraction of all measurable bipolar moments and can be applied in experiments with both linearly and circularly polarized probe light. It avoids the cylindrical symmetry limitations of the inverse Abel transform method, traditionally used for extracting photoproduct recoil anisotropy and speed distribution from imaging data. The method presented here also takes into account the possibility of multiple photodissociation channels. The features of the method are illustrated in a two-color 1+1′ REMPI-ion imaging study of the NO photoproduct trajectories resulting from the 650 nm photodissociation of 2-chloro-2-nitrosopropane (CNP). A comparison between experimental and synthetic images is presented for selected experimental geometries. The experimental images for CNP and the results from their fit confirm earlier TOF studies showing that the recoil speed distribution is bimodal with the low and high speed components having average values of approximately 500 and 910 m/s. These components have been previously assigned to dissociation from the S0 and T1 electronic states of the parent molecule, respectively. The experimental results from the current study also confirm that for the high-speed component the product NO velocity vector, v, is preferentially perpendicular to its angular momentum, j [β00(22)=−0.21], and that there is no significant correlation between v and the transition dipole moment μ of the CNP molecule [β02(20)=−0.02].
On the nature of bursting in transport and turbulence in drift wave–zonal flow systems
Authors: Malkov M. A. , Diamond P. H. , Rosenbluth M. N.
Published: July 2002

The predictions of the extended predator–prey model of the coupled spectral dynamics of drift wave–zonal flow turbulence are presented. The model exhibits three possible types of time-dependent solutions, depending on system parameters, which are: (1) quasiperiodic bursting of the transport and turbulence intensity levels; (2) oscillatory relaxation to a stationary state, and in the collisionless limit; (3) an intensity pulse followed by saturation of zonal flow. These solutions are consistent with the time dependent behavior recently observed in the global gyrokinetic simulations.
Creep behavior and elastic properties of annealed cold-drawn poly(ethylene terephthalate): The role of the smectic structure as a precursor of crystallization
Authors: Flores A. , Baltá Calleja F. J. , Asano T.
Published: July 2002

The creep behavior and elastic properties of cold-drawn poly(ethylene terephthalate) (PET) films, annealed in the range 60–240 °C have been investigated by means of microindentation testing. Two indentation methods have been used. The imaging method has been employed to examine the viscoplastic properties of the polymer materials while the depth-sensing method was used for the determination of Young’s modulus values. The creep behavior (plastic flow) of cold-drawn PET is shown to be intimately correlated to the nanostructural changes occurring upon annealing. The observed decrease in the rate of creep, when the glassy material is annealed at 60 °C, has been associated with the emerging smectic structure, which confers to the material a higher mechanical performance. The elastic properties of the smectic phase are found to be comparable to those of the glassy state. Young’s modulus E values of the semicrystalline samples are discussed in light of the parallel model of crystalline and amorphous layers. E values are shown to depend on the crystalline lamellar thickness and the degree of crystallinity. Results suggest that Young’s modulus values of the amorphous constrained regions within the crystals are higher than the E value of the fully amorphous material.