bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy landscape picture of supercooled liquids: Application of a generalized random energy model
Authors: Sasai Masaki
Published: May 2003

The thermodynamic and kinetic anomalies of supercooled liquids are analyzed from the perspective of energy landscapes. A mean-field model, a generalized random energy model of liquids, is developed which exhibits a dynamical transition of the onset of slow dynamics at T0, alteration of the nature of motion from saddle-to-saddle to minimum-to-minimum motion at Tc, and an ideal glass transition at Tk. If the energy spectrum of the configurations has a low energy tail, the model also allows a thermodynamic liquid–liquid transition at Tl. The liquid–liquid transition of the model is correlated to the kinetic fragile–strong transition accompanied by the anomalous slowing down of motion. Fragility of the system is classified in terms of features of the energy landscape such as ruggedness of the potential energy surface, size of the cooperative motion invoked in transition from one configuration to another, and energy needed to deform the local structure in the cooperative motion. A simple relation is found between diffusion constant, D and the saddle index of the potential energy surface, f as D∝fa, where a depends on the size of the cooperative motion.
Complexes of polyelectrolytes and oppositely charged ionic surfactants
Authors: von Ferber C. , Löwen H.
Published: May 2003

Complex formation between a single polyelectrolyte chain and ionic surfactant molecules is studied by computer simulation of a “primitive” electrolyte model with explicit charges. The surfactant head carries a charge opposite to that of the polyelectrolyte. The neutral flexible tail is modeled by tethered hard spheres. A molecular bottle-brush architecture of the resulting polyelectrolytesurfactant-complex is observed. The end-to-end distance of the polyelectrolyte is found to behave in a nonmonotonic fashion for increasing Coulomb coupling: it first gets stretched and then the stretching is reduced by self-assembling of surfactant molecules along the polyelectrolyte. The end-to-end distance of the polyelectrolyte in the complex is more pronounced for long surfactant tails. Upon addition of salt to the complex, ionic surfactant molecules condensed onto the polyelectrolyte are replaced by salt microions which leads to a weakening of the complex and to reduced end-to-end distance.
Homeotropic-planar anchoring transition induced by trans-cis isomerization in ultrathin polyimide Langmuir–Blodgett films
Authors: Zakharov A. V. , Iwamoto Mitsumasa
Published: May 2003

The influence of the charge separation during the trans-cis conformational change between the surface azobenzene 6Az5PVA monolayer on polyimide Langmuir–Blodgett film on the surface charge density is investigated, using the Maxwell displacement current technique. It is theoretically shown, in the framework of the molecular model, which takes into account interactions between the surface polarization (in the quadrupole approximation) and surface electric field, that the experimentally observed changes of the surface charge density in ∼3×10−4 C/m2, caused by the charge separation in ∼2 pC, taking place during the conformational change, may lead to changing of the surface alignment of liquid crystalline molecules, such as 4-n-pentyl-4′-cyanobiphenyl (5CB), having contact with that solid substrate.
Molecular orientation of CN adsorbed on Pd(110)
Authors: Bondino F. , Vesselli E. , Baraldi A. , Comelli G. , Verdini A. , Cossaro A. , Floreano L. , Morgante A.
Published: May 2003

The bonding geometry of the C–N molecule in the saturated c(2×2) layer on the Pd(110) surface has been determined by combining polarization-dependent near edge x-ray absorption fine structure and full-solid-angle x-ray photoelectron diffraction (PED). The N K-edge spectra display a strong dependence on the polar and azimuthal orientation of the light polarization with respect to the sample surface. A strong forward scattering peak along the [001] direction is present in the full-solid-angle photoelectron diffraction data of the C1s core level. Both the position of the C1s PED forward scattering peak and the angular dependence of the N K-shell absorption spectra provide direct evidence that the CN molecules is oriented with the molecular axis along the [001] surface direction, at variance with earlier conclusions based on angle-resolved valence level photoemission data. The forward scattering peak in the C1s PED data further indicates that the N atoms lie above the C atoms, with the C–N molecular axis tilted by 25°±4° with respect to the surface plane. The close analogy of this geometry with the results of previous structure determinations of CN adsorbed on Ni and Rh (110) surfaces is discussed.
Nuclear magnetic resonance implementation of the Deutsch–Jozsa algorithm using different initial states
Authors: Ermakov Vladimir L. , Fung B. M.
Published: May 2003

The Deutsch–Jozsa algorithm distinguishes constant functions from balanced functions with a single evaluation. In the first part of the work, we present simulations of the nuclear magnetic resonance application of the Deutsch–Jozsa algorithm to a 3-spin system for all possible balanced functions. Three different kinds of initial states are considered: a thermal state, a pseudopure state, and a pair (difference) of pseudopure states. Then, simulations of several balanced functions and the two constant functions of a 5-spin system are described. Finally, corresponding experimental spectra obtained by using a 16-frequency pulse to create an input equivalent to either a constant function or a balanced function are presented, and the results are compared with those obtained from computer simulations.
Melting of 55-atom Morse clusters
Authors: Shah Pooja , Roy Sharani , Chakravarty Charusita
Published: May 2003

Canonical ensemble Monte Carlo simulations of 55-atom Morse clusters are used to study the effect of the range of the pair interaction on the cluster melting transition. Several different structural indicators are employed to monitor the solid–liquid transition and to locate the melting and freezing temperatures. The behavior of Landau free energy curves in the solid–liquid phase coexistence regime is correlated with the distribution of inherent minima sampled by the system. The melting transition temperatures, the width of the phase coexistence regime, and the internal energy change on melting are shown to increase with decreasing range of the pair interaction, which parallels the behavior seen in bulk Morse systems. Unlike in the case of bulk melting, cluster melting falls into three distinct categories based on the range of the pair interaction: (i) a rigidity transition in long-range systems with a low density of metastable states, (ii) the cluster analogue of bulk melting where the system transits from the basin of an ordered global minima into a set of metastable, amorphous packing minima, and (iii) transition from a set of defected solid-like minima into a set of amorphous packing minima.
Quantifying multiple-body interaction terms in H-bonded HCN chains with many-body perturbation/coupled-cluster theories
Authors: Rivelino Roberto , Chaudhuri Puspitapallab , Canuto Sylvio
Published: May 2003

Many-body perturbation/coupled-cluster calculations have been carried out to investigate the multiple-body energy terms and their contribution to the interaction energy of linear (HCN)N chains. All minimum energy geometries of the clusters (N=2–7) are obtained at the second-order many-body perturbation (MP2) levels of theory. Electron correlation and cooperative effects in the C–H⋯N hydrogen bonds are also quantitatively characterized during the aggregation process. It is found that the two- and three-body terms account for nearly all of the total interaction energy, but all high-body terms increase with the size of the cluster. Detailed numerical values are given for all the many-body contributions of the (HCN)N chains. Electron correlation effects are found to be important for the two- and three-body terms but have decreased importance for the higher-body terms. Cooperative effects are also investigated for the binding energy and dipole moment. The dipole moments of the HCN oligomers are larger than the sum of the individual monomers with differences ranging between 12% (N=2) and 28% (N=7). The limiting values for the binding energy and dipole moment of (HCN)N, per monomer, corresponding to very large N values, are estimated to be 22.9 kJ/mol and 3.87 D, per monomer, respectively. These results correspond to cooperative contributions of 5.8 kJ/mol to the energy, and 1.0 D to the dipole moment.
Equation of state and intermolecular interactions in fluid hydrogen from Brillouin scattering at high pressures and temperatures
Authors: Matsuishi Kiyoto , Gregoryanz Eugene , Mao Ho-kwang , Hemley Russell J.
Published: May 2003

Brillouin scattering spectra of fluid hydrogen were measured at high pressures (1 to 13 GPa) and temperatures (293 to 526 K). From these sound velocity data together with previously reported volume and ultrasonic velocity data at low pressures and temperatures, we determined a Benedict-type P-V-T equation of state valid for fluid hydrogen up to the maximum pressures and temperatures of this study with an average deviation of 1.0% from the new and previously published experimental data. Using the equation of state, the pressure and temperature dependences of thermodynamic properties were calculated. We examined three types of intermolecular potentials for fluid hydrogen, and found that the Hemley–Silvera–Goldman potential gives superior fits to the experimentally derived equation of state over a wide temperature range above 6 GPa. Discrepancies found in the high temperature range at low pressures provide additional constraints on determination of the intermolecular potential.
Integral equation theories for monodisperse and polydisperse sticky hard sphere chain fluid: Thermodynamic and structural properties in the polymer Percus–Yevick and ideal chain approximations
Authors: Wu Ning , Feng S. S. , Chiew Y. C.
Published: May 2003

The thermodynamic and structural properties of a freely jointed homonuclear sticky hard sphere chain fluid are studied using one-component and multi-component multi-density Ornstein–Zernike integral equation theories. In this formalism, a polydisperse chain fluid is modeled as a one-component system of associating sticky hard spheres with finite association strength, while a monodisperse system is modeled as an equal molar m-component mixture of associating sticky hard spheres with infinite association strength in the complete association limit. General analytical solutions to both models are obtained within the polymer Percus–Yevick and ideal chain approximations. Explicit analytical expressions for the contact values of correlation functions are obtained. The coordination number around a sticky hard sphere is calculated and its relationship with the contact value of the correlation function is discussed. Both intermolecular and intramolecular correlation functions beyond the hard core region are calculated numerically. Radial distribution functions of monodisperse dimer and tetramer are compared with those of polydisperse chains (with mean chain lengths of 2 and 4), and it is found that significant discrepancy exists at low density. This disparity, however, diminishes as chain density increases. The Helmholtz energy and pressure of monodisperse homonuclear chains are obtained via the energy route. The critical temperature, critical density, and phase coexistence of the fluid are also obtained.
Connectedness percolation in athermal mixtures of flexible and rigid macromolecules: Analytic theory
Authors: Wang Xiaoling , Chatterjee Avik P.
Published: May 2003

A semianalytic theory is developed for calculating percolation thresholds for rod-like nanoparticles dispersed in a flexible polymeric matrix. Methods of macromolecular integral equation theory are combined with the connectedness Ornstein–Zernike equation and an explicitly two-component model in which both the molecules constituting the matrix as well as the filler species are accounted for. The effects on the percolation threshold of explicitly including the matrix species are examined and compared with predictions based on an analogous approach which restricts attention to the rod–rod second virial coefficient. Explicit inclusion of the polymeric matrix does not alter the qualitative dependence of the percolation threshold on rod aspect ratio. However, accounting for the matrix leads to a quantitative reduction of the critical volume fraction by a factor independent of the rod length. Although the present work focuses on the athermal situation (excluded volume interactions alone), the methodology developed in this account can be readily extended to model matrix-filler specific interactions as well.
Peculiarities of time dependence of the current–current correlation function
Authors: Lokotosh T. V. , Malomuzh N. P. , Shakun K. S.
Published: May 2003

The similarity and difference in the behavior of the current–current correlation function (CCCF) and the velocity correlation function of a molecule are discussed in detail. It is shown that the oscillations and long-time decay of the transversal and longitudinal components of CCCF are explained naturally within the Lagrange theory of thermal hydrodynamic fluctuations.
Nonpolar solvation dynamics in supercritical fluids
Authors: Egorov S. A.
Published: May 2003

A mode-coupling treatment of nonpolar solvation dynamics in supercritical fluids is presented. Both neat fluids and dilute attractive supercritical solutions are considered. The equilibrium solvation time correlation function for the solute fluctuating transition frequency is obtained from the mode-coupling theory method and from molecular dynamics simulations. Theory is shown to be in good agreement with simulation for all solvent thermodynamic conditions studied. The microscopic origins of the density dependence of the time correlation function are discussed.
Casimir force between colloidal particles immersed in a critical polymer blend
Authors: Ridouane H. , Hachem E.-K. , Benhamou M.
Published: May 2003

We consider here a low-density assembly of spherical colloids immersed in a mixture of two incompatible polymers A and B. We assume that, near the consolute point Tc of the host mixture, colloids adsorb preferentially A polymer. The preferential adsorption has as a consequence that particles aggregate in the nonpreferred B phase. We aim at the computation of the induced force F(r), responsible for this aggregation, as a function of the interparticle distance r. To achieve this, use is made of a field-theoretical approach based on ψ4 theory, where the field ψ is simply the composition fluctuation (order parameter). Combining this approach with the standard cumulants method, we first demonstrate that the effective pair potential is proportional to the two-point correlation function of the host mixture. Second, very close to the critical point, we find that the effective force is universal and decays with interparticle distance r>d0 according to: F(r)/kBTc=−(64π2/27)Nd02/r3, where N is the common polymerization degree of polymers and d0 is the particle diameter. Incidentally, this force is similar to the van der Waals one between two parallel plates.
High-resolution electronic spectroscopy of a nonlinear carbon chain radical C6H4+
Authors: Araki Mitsunori , Linnartz Harold , Cias Pawel , Denisov Alexey , Fulara Jan , Batalov Anton , Shnitko Ivan , Maier John P.
Published: May 2003

A high-resolution gas-phase spectrum of a molecular absorption band around 604 nm is assigned as due to an electronic transition of a nonlinear C6H4+ planar species starting from its A″2 electronic ground state. The spectrum is observed in direct absorption by cavity ringdown spectroscopy through a supersonic planar discharge through a mixture of acetylene in helium. The spectrum has a clear rotational and K-type structure. This allows an accurate determination of the B and C rotational constants and an estimate for the A rotational constant in ground and electronically excited states. The resolved spectrum of the fully deuterated species C6D4+ has been obtained as well. The results are compared both to the outcome of ab initio geometry optimizations and low-resolution absorption spectra in 6 K neon matrices obtained after mass-selective deposition.
Mössbauer acquisition system for Rayleigh scattering experiments
Authors: Kluger A. , Enescu S. E. , Bibicu I. , Ciortea C. , Enulescu A.
Published: May 2003

A data acquisition system is reported with a number of improvements over similar systems currently used in Rayleigh scattering of Mössbauer radiation (RSMR) experiments. It is based on a data acquisition board including a Mössbauer function generator with adjustable frequency reference signal delivery, an internal single channel analyzer, and an internal 32 kB random access memory for data storage. The system performances were tested in RSMR measurements on pyrolytic graphite C (002) single crystal by using an iron enriched 57Fe (30 at. %) in rhodium matrix absorber. We want to demonstrate that the reported data acquisition system is suitable for the experimental separation of the elastic and inelastic components of the scattered radiation. The system can be used also in the ordinary Mössbauer measurements as a compact and rapid data acquisition system. In this case it presents the advantage of including also the function generator.
Ion beam charging of silicon nanoparticles in helium background gas: Design of the ion beam aerosol charger
Authors: Seto Takafumi , Orii Takaaki , Hirasawa Makoto , Aya Nobuhiro , Shimura Hirofumi
Published: May 2003

An ion beam aerosol charger that ionizes aerosol nanoparticles of less than 10 nm diameter using an ion beam was designed for use in the electrostatic manipulation of gas-suspended nanoparticles. Pulsed laser ablation of a solid target in a high purity helium gas under pressure of 2–10 Torr (266–1330 Pa) was employed to fabricate nanometer-sized silicon particles. The ion beam, which was generated by cold cathode Penning ionization of He atoms, was accelerated with an energy of 0–5 keV, penetrated a skimmer located within the differential pumping system, and then entered the aerosol ionization chamber. The silicon nanoparticles were both positively and negatively charged by the direct impact of the ion beam or the secondary electrons generated from the surrounding He gas. The change in the concentration of ions and charged aerosols was measured by ion probes. It was found that the concentration of charged particles was drastically increased to 2–50 times that at baseline.
Improvement to a bench top instrument for measuring spectral emittance at high temperatures
Authors: Bonzani Peter J. , Florczak Elizabeth H. , Scire James J. , Markham James R.
Published: May 2003

Advanced ceramic materials are widely being developed and studied for application as thermal barrier coatings in the next generation of gas turbine engines. Knowledge of the spectral radiative properties at high temperatures is important so as to ensure the desired effect as a thermal barrier and for accurate radiation thermometry measurements. A bench top instrument previously introduced in this journal has been utilized to determine the high temperature spectral emittance of these materials from measurements of hemispherical-directional reflection and hemispherical-directional transmission in the infrared range of 500–12 500 wave numbers (20–0.8 μm). However, a temperature limitation of the instrument’s flat, near-blackbody source of infrared radiance has been shown to result in spectral dependent measurement error that is unacceptable when the sample of interest is a few hundred degrees or more higher than the source. This article describes an improved flat near-blackbody source that allows operation to higher temperatures. Benefits to the desired measurement of high-temperature spectral radiative properties of ceramic thermal barrier coatings are also presented.
Measurement of acetylene in breath by ultraviolet absorption spectroscopy: Potential for noninvasive cardiac output monitoring
Authors: Baum Marc M. , Kumar Sasi , Lappas Anastasios M. , Wagner Peter D.
Published: May 2003

A new, miniaturized, noninvasive instrument for rapid acetylene analysis in breath gas is described. Acetylene is a blood-soluble gas and for many years its uptake rate during rebreathing and/or nonrebreathing tests has been used to calculate the volume of lung tissue as well as the flow rate of blood through the lungs. The instrument relies on dispersive UV absorption spectroscopy as its measurement principle and is employed in an extractive (side-stream) configuration. The analyzer afforded fast (276±43 ms, 0%–90%, at 2 L min−1 flow rates), interference-free detection of acetylene, with signal-to-noise ratios in excess of 50. Comparison tests with a mass spectrometer using calibration gas samples gave an excellent correlation {[C2H2]MS=0.999. [C2H2]UV, R2=1.000}, which validated the linearity and accuracy of the UV system. A similar level of correlation between these devices also was observed during human subject C2H2 uptake tests, with both instruments sampling a common extracted gas stream {[C2H2]UV=0.940. [C2H2]MS, R2=0.998}. These results indicate that a miniature, low-cost, rugged, ultraviolet spectrometer system measuring acetylene holds promise for human breath analysis in a clinical setting.
Compact atomic vapor cells fabricated by laser-induced heating of hollow-core glass fibers
Authors: Knappe S. , Velichansky V. , Robinson H. G. , Kitching J. , Hollberg L.
Published: May 2003

A method for fabricating atomic vapor cells with physical dimensions of order 1 mm3 or below is described. Cells with integrated lenses are made from hollow-core glass fiber, and fused shut at either end using highly localized heating from a CO2 laser beam. Such cells, subsequently loaded with alkali atoms and a buffer gas, could form the basis for future generations of compact frequency references or magnetometers.
Bulk metallic glass gasket for high pressure, in situ x-ray diffraction
Authors: He Duanwei , Zhao Yusheng , Sheng T. D. , Schwarz R. B. , Qian J. , Lokshin K. A. , Bobev S. , Daemen L. L. , Mao H. K. , Hu J. Z. , Shu J. , Xu J.
Published: May 2003

Amorphous metallic alloys lack long-range atomic order and consequently exhibit excellent homogeneity, no microstructure discontinuities, and no sharp x-ray diffraction peaks. Moreover they have higher tensile fracture strength and hardness than those of traditional crystalline metals. These excellent physical properties make bulk metallic glasses good candidates for high pressure gaskets for in situ x-ray/neutron diffraction experiments. We tested the Pd40Ni40P20 amorphous alloy as a gasket material in three experiments. The behavior of the Pd40Ni40P20 amorphous alloy under a hydrostatic/nonhydrostatic pressure of over 100 GPa was investigated by in situ synchrotron x-ray diffraction. The pressure gradient of the amorphous metallic gasket in the diamond anvil cell was measured on the ruby fluorescence scale during compression and decompression. The results show that bulk metallic glasses are good high-pressure gasket materials for in situ x-ray diffraction experiments.
Bifurcation in kinetic equation for interacting Fermi systems
Authors: Morawetz Klaus
Published: May 2003

The recently derived nonlocal quantum kinetic equation for dense interacting Fermi systems combines time derivatives with finite time stepping known from the logistic mapping. This continuous delay differential equation is a consequence of the microscopic delay time representing the dynamics of the deterministic chaotic system. The responsible delay time is explicitly calculated and discussed for short-range correlations. As a novel feature oscillations in the time evolution of the distribution function itself appear and bifurcations up to chaotic behavior occur. The temperature and density conditions are presented where such oscillations and bifurcations arise indicating an onset of phase transition.
Food chain chaos due to transcritical point
Authors: Deng Bo , Hines Gwendolen
Published: May 2003

Chaotic dynamics of a classical prey-predator-superpredator ecological model are considered. Although much is known about the behavior of the model numerically, very few results have been proven analytically. A new analytical result is obtained. It is demonstrated that there exists a subset on which a singular Poincaré map generated by the model is conjugate to the shift map on two symbols. The existence of such a Poincaré map is due to two conditions: the assumption that each species has its own time scale ranging from fast for the prey to slow for the superpredator, and the existence of transcritical points, leading to the classical mathematical phenomenon of Pontryagin’s delay of loss of stability. This chaos generating mechanism is new, neither suspected in abstract form nor recognized in numerical experiments in the literature.
Spatial resonator solitons
Authors: Taranenko V. B. , Slekys G. , Weiss C. O.
Published: May 2003

Spatial solitons can exist in various kinds of nonlinear optical resonators with and without amplification. In the past years different types of these localized structures such as vortices, bright, dark solitons, and phase solitons have been experimentally shown to exist. Many links appear to exist to fields different from optics, such as fluids, phase transitions, or particle physics. These spatial resonator solitons are bistable and due to their mobility suggest schemes of information processing not possible with the fixed bistable elements forming the basic ingredient of traditional electronic processing. The recent demonstration of existence and manipulation of spatial solitons in semiconductor microresonators represents a step in the direction of such optical parallel processing applications. We review some proof of principle soliton experiments on slow systems, and describe in more detail the experiments on semiconductor resonator solitons which are aimed at applications.
Discrete nonlinear dynamics of weakly coupled Bose–Einstein condensates
Authors: Smerzi A. , Trombettoni A.
Published: May 2003

The dynamics of a Bose–Einstein condensate trapped in a periodic potential is governed by a discrete nonlinear equation. The interplay/competition between discreteness (introduced by the lattice) and nonlinearity (due to the interatomic interaction) manifests itself on nontrivial dynamical regimes which disappear in the continuum (translationally invariant) limit, and have been recently observed experimentally. We review some recent efforts on this highly interdisciplinary field, with the goal of stimulating interexchanges among the communities of condensed matter, quantum optics, and nonlinear physics.
Single-component light-emitting electrochemical cell with improved stability
Authors: Edman L. , Pauchard M. , Liu B. , Bazan G. , Moses D. , Heeger A. J.
Published: May 2003

We report a single-component polymeric light-emitting electrochemical cell with poly[9,9′-bis[6″-(N,N,N-trimethylammonium)hexyl]fluorene-alt-co-phenylene]bromide (PFN+Br−) as the active material. Indium tin oxide/PFN+Br−/aluminum sandwich structures demonstrate a low and thickness-independent turn-on voltage (2.9 V) for blue light emission. Thermophysical characterization shows that PFN+Br− is in a metastable amorphous phase after spin casting, but that crystallization takes place at elevated temperatures. With this information at hand, we allowed devices to turn-on via ionic redistribution (and the formation of a p–i–n junction) in the amorphous phase, and then stabilized this desired configuration through crystallization. We find significantly improved lifetimes and relatively fast turn-on times for these single-component devices operating at room temperature.
Mode analysis in He+-implanted lithium fluoride planar waveguides
Authors: Mussi V. , Somma F. , Moretti P. , Mugnier J. , Jacquier B. , Montereali R. M. , Nichelatti E.
Published: May 2003

The depth refractive index profiles of broadband visible-emitting planar waveguides produced in LiF crystals with 1.5- and 2-MeV He+ ions at different doses have been derived from mode analysis. They show that there are two competitive mechanisms responsible for positive and negative modifications of the refractive index in the irradiated volume associated with different processes of energy deposition of the incident ions, so as to induce a complex coloration profile along the penetration direction, which is strongly dependent on the irradiation dose.
Strain partition of Si/SiGe and SiO2/SiGe on compliant substrates
Authors: Yin H. , Hobart K. D. , Kub F. J. , Shieh S. R. , Duffy T. S. , Sturm J. C.
Published: May 2003

Strain partitioning of crystalline Si and amorphous SiO2 deposited on crystalline SiGe on a compliant viscous borophosphorosilicate (BPSG) glass has been observed. Pseudomorphic epitaxial Si was deposited on SiGe films, which were fabricated on BPSG by wafer bonding and the Smart-cut® process. The strains in SiGe and Si films were found to change identically during a high-temperature anneal which softened the BPSG film, indicating a coherent interface between SiGe and Si films and precluding slippage or the formation of misfit dislocations along the interface. The stress balance between the layers dictated the final state, which confirmed that BPSG was a perfectly compliant substrate and did not exert any force on the layers above it. Similar results were found for amorphous SiO2 deposited on SiGe on BPSG and then annealed. This shows that the viscous BPSG is an effective compliant substrate for the strain engineering of elastic films without the introduction of dislocations.
Wavelength tuning of surface plasmon resonance using dielectric layers on silver island films
Authors: Xu G. , Tazawa M. , Jin P. , Nakao S. , Yoshimura K.
Published: May 2003

A simple and effective method was demonstrated to tune surface plasmon resonance (SPR) wavelength of silver island films by introducing a dielectric medium to vary interisland dielectric constant. The medium, either overcoating or sandwiching the silver islands, can make a dramatic effect on the tunability. We had extended the SPR wavelength tunability of standard silver island film substrates from 432 to 482 nm to 506 to 1310 nm using two dielectric layering methods. A generalized Maxwell–Garnett theory was applied to interpret these results.
Morphology and electronic transport of polycrystalline pentacene thin-film transistors
Authors: Knipp D. , Street R. A. , Völkel A. R.
Published: May 2003

Temperature-dependent measurements of thin-film transistors were performed to gain insight in the electronic transport of polycrystalline pentacene. Devices were fabricated with plasma-enhanced chemical vapor deposited silicon nitride gate dielectrics. The influence of the dielectric roughness and the deposition temperature of the thermally evaporated pentacene films were studied. Although films on rougher gate dielectrics and films prepared at low deposition temperatures exhibit similar grain size, the electronic properties are different. Increasing the dielectric roughness reduces the free carrier mobility, while low substrate temperature leads to more and deeper hole traps.
Nanodomain engineering in RbTiOPO4 ferroelectric crystals
Authors: Rosenman G. , Urenski P. , Agronin A. , Arie A. , Rosenwaks Y.
Published: May 2003

A high voltage atomic force microscope has been applied for tailoring strip-like nanodomains in RbTiOPO4 ferroelectric crystal. Highly anisotropic nanodomain propagation has been observed owing to the difference in lattice constants along the principal axes of the RbTiOPO4 crystal. Studying the influence of the applied high voltage, and tip velocity on the domain strips has allowed us to fabricate fine nanodomain gratings, which is useful for backward-propagating quasi-phase-matched frequency conversion.
High electron mobility of epitaxial ZnO thin films on c-plane sapphire grown by multistep pulsed-laser deposition
Authors: Kaidashev E. M. , Lorenz M. , von Wenckstern H. , Rahm A. , Semmelhack H.-C. , Han K.-H. , Benndorf G. , Bundesmann C. , Hochmuth H. , Grundmann M.
Published: May 2003

A multistep pulsed-laser deposition (PLD) process is presented for epitaxial, nominally undoped ZnO thin films of total thickness of 1 to 2 μm on c-plane sapphire substrates. We obtain reproducibly high electron mobilities from 115 up to 155 cm2/V s at 300 K in a narrow carrier concentration range from 2 to 5×1016 cm−3. The key issue of the multistep PLD process is the insertion of 30-nm-thin ZnO relaxation layers deposited at reduced substrate temperature. The high-mobility samples show atomically flat surface structure with grain size of about 0.5–1 μm, whereas the surfaces of low-mobility films consist of clearly resolved hexagonally faceted columnar grains of only 200-nm size, as shown by atomic force microscopy. Structurally optimized PLD ZnO thin films show narrow high-resolution x-ray diffraction peak widths of the ZnO(0002) ω- and 2Θ-scans as low as 151 and 43 arcsec, respectively, and narrow photoluminescence linewidths of donor-bound excitons of 1.7 meV at 2 K.
Visible photoluminescence in amorphous SiOx thin films prepared by silicon evaporation under a molecular oxygen atmosphere
Authors: Molinari M. , Rinnert H. , Vergnat M.
Published: May 2003

A simple reactive evaporation method is proposed to prepare light-emitting amorphous SiOx thin films. By evaporating pure silicon in a controlled molecular oxygen atmosphere, it is possible to obtain a very large composition range. By changing the pressure in the preparation chamber, x can be varied from 0.7 to 1.85. The composition and the structure of the films were investigated using energy dispersive x-ray, infrared absorption and x-ray photoelectron spectroscopies. The samples contain amorphous silicon clusters dispersed inside an insulating silicon oxide matrix. The room-temperature photoluminescence properties were then measured. By conveniently choosing the oxygen pressure, the as-deposited films exhibit visible photoluminescence without any annealing post-treatments. The luminescence intensity initially increases with excess silicon concentration and then disappears for a too-high silicon excess. The above effect is interpreted in terms of confinement of the amorphous silicon clusters in the insulating matrix.
Tomography in the multiple scattering regime of the scanning transmission electron microscope
Authors: Levine Zachary H.
Published: May 2003

To date, nearly all tomography based on electron microscopy has been performed on samples 1 μm or less thick. It has also relied on Beer’s Law. In this work, tomographic reconstructions of simulated scans of a photonic band-gap crystal based on bright-field imaging with a scanning transmission electron microscope are made assuming (1) multiple scattering or (2) the standard Beer’s Law model. The results suggest that it should be possible to treat systems several times larger than those which appear in literature, albeit at a worse resolution. The multiple scattering theory leads to high-quality reconstructions. Beer’s Law does only a little worse despite being applied outside its range of validity.
Mixing characteristics of InGaAs metal–semiconductor–metal photodetectors with Schottky enhancement layers
Authors: Shen H. , Aliberti K. , Stann B. , Newman P. , Mehandru R. , Ren F.
Published: May 2003

We report on the optoelectronic (OE) mixing characteristics of a Schottky-enhanced InGaAs-based metal–semiconductor–metal photodetector (MSM–PD). The measured frequency bandwidth of such a mixer is less than that of a corresponding photodetector. The mixing efficiency depends on the light modulation, local oscillator, and mixed signal frequencies and decreases nonlinearly with decrease in optical power. This is not observed in GaAs-based and non-Schottky-enhanced InGaAs MSM–PDs. We present a circuit model of the OE mixer to explain the experimental results.
Hot-electron spectroscopy in parallel magnetic fields
Authors: Kast M. , Boxleitner W. , Pacher C. , Strasser G. , Gornik E.
Published: May 2003

Hot-electron spectroscopy in the presence of magnetic fields applied parallel to the current direction is studied. Inter-Landau-level transitions are observed due to scattering processes in the drift region of the hot-electron transistor. In high magnetic fields, the reduced phase space of elastic/inelastic scattering is directly observed as a decrease of the energetic widths of ballistic/phonon-replica peaks. This results in an increased resolution of the hot-electron spectroscopy to be well below ΔE=10 meV.
Spin-torque transistor
Authors: Bauer Gerrit E. W. , Brataas Arne , Tserkovnyak Yaroslav , van Wees Bart J.
Published: May 2003

A magnetoelectronic thin-film transistor is proposed that can display negative differential resistance and gain. The working principle is the modulation of the soure–drain current in a spin valve by the magnetization of a third electrode, which is rotated by the spin-torque created by a control spin valve. The device can operate at room temperature, but in order to be useful, ferromagnetic materials with polarizations close to unity are required.
Excited-state absorption in NdAl3(BO3)4 laser crystal
Authors: Brenier A. , Jaque D. , Garcia Solé J. , Luo Z. D.
Published: May 2003

We present an investigation in NdAl3(BO3)4 (NAB) crystal of the excited-state absorption (ESA) around the main laser lines (1060 and 1338 nm) by the so called excited-state excitation technique. The involved transitions are from the F3/24 level toward the G7/24+4G9/2+2K13/2 levels (1300–1400 nm range) or toward the G9/24+4G11/2+2D3/2+2K15/2 levels (1020–1100 nm range). We have performed the Judd–Ofelt analysis extended to anisotropic crystals in order to get the cross sections (cm2). In each case, the ESA peaks do not coincide with the laser emission ones, but a reduction of the effective laser emission cross section is observed at 1338 nm. Finally, the values obtained from the application of the Judd–Ofelt formalism have been used to estimate the influence of ESA in the pumping domain on the laser performance. It has been found that its contribution is not significant, indicating that NAB is an excellent candidate for efficient high-power microchip lasers emitting at 1060 and 1338 nm.
Failure modes of electrospun nanofibers
Authors: Zussman E. , Rittel D. , Yarin A. L.
Published: May 2003

Failure modes of electrospun polymer nanofibers are reported. The nanofibers have diameters in the range of 80–400 nm and lengths greater then several centimeters. The nanofibers fail by a multiple necking mechanism, sometimes followed by the development of a fibriliar structure. This phenomenon is attributed to a strong stretching of solidified nanofibers by the tapered accumulating wheel (electrostatic lens), if its rotation speed becomes too high. Necking has not been observed in the nanofibers collected on a grounded plate.
Spectral responsivity and quantum efficiency of n-ZnO/p-Si photodiode fully isolated by ion-beam treatment
Authors: Park C. H. , Jeong I. S. , Kim J. H. , Im Seongil
Published: May 2003

We report on the fabrication of a heterojunction photodiode for the visible range that consists of a transparent insulating ZnO overlayer and a transparent semiconducting n-ZnO layer on p-Si. For device isolation, we implanted Si+ ions into the n-ZnO layer. We have obtained a wide-range spectral responsivity curve for our isolated photodiodes, which showed a maximum quantum efficiency of 70% at 650 nm and a minimum of 10% at 420 nm. However, they exhibited an efficiency drop at 380 nm in the near-ultraviolet because the ZnO layers absorbed the photons of higher energy before they reached p-Si. The ion-beam-induced isolation considerably reduced dark leakage currents in our devices when the dose of Si ions was as high as 5×1015 cm−2.
Pentacene-based radio-frequency identification circuitry
Authors: Baude P. F. , Ender D. A. , Haase M. A. , Kelley T. W. , Muyres D. V. , Theiss S. D.
Published: May 2003

Pentacene-based thin-film integrated circuits patterned only with polymeric shadow masks and powered by near-field coupling at radio frequencies of 125 kHz and above 6 MHz have been demonstrated. Sufficient amplitude modulation of the rf field was obtained to externally detect a clock signal generated by the integrated circuit. The circuits operate without the use of a diode rectification stage. This demonstration provides the basis for more sophisticated low-cost rf transponder circuitry using organic semiconductors.
Sensitizing properties of amorphous Si clusters on the 1.54-μm luminescence of Er in Si-rich SiO2
Authors: Franzò G. , Boninelli S. , Pacifici D. , Priolo F. , Iacona F. , Bongiorno C.
Published: May 2003

In this letter, the role of amorphous Si clusters in the excitation of Er implanted in substoichiometric SiOx films will be elucidated. It will be shown that the temperature of the SiOx thermal process prior to Er implantation is crucial in determining the luminescence properties of the samples. In particular, the luminescence intensity at 1.54 μm is almost constant for SiOx samples not annealed or pre-annealed at temperatures lower than 800 °C, reaches the maximum at 800 °C, and decreases at higher temperatures. The structural properties of these samples have been studied by energy filtered transmission electron microscopy. It will be shown that for annealing temperatures lower than 1000 °C, only amorphous Si nanoclusters are present. We demonstrate that a large density of small amorphous Si clusters produces the best luminescence performance and enhances the fraction of optically active Er.
Energy level evolution at a silole/magnesium thin-film interface
Authors: Mäkinen A. J. , Uchida M. , Kafafi Z. H.
Published: May 2003

Photoemission spectroscopy of an interface formed through step-by-step deposition of Mg onto a film of a silole derivative, 2,5-bis[6′-(2′,2″-bipyridyl)]-1,1-dimethyl-3,4-diphenyl silacyclopentadiene (PyPySPyPy), reveals the formation of gap states arising from electron transfer from the metal to the organic. In addition, a 0.3-eV rigid shift of the molecular orbitals toward higher binding energy is observed, while the work function of the Mg-rich PyPySPyPy surface is reduced by 0.6 eV. The observed energy level evolution elucidates how the electronic structure of the Mg/PyPySPyPy interface depends on the chemical interaction between the metal and the organic. This is important for understanding and optimizing electron injection at the Mg/PyPySPyPy interface, which can be incorporated in electronic, electro-optic, and optoelectronic devices.
Effects of scaling the film thickness on the ferroelectric properties of SrBi2Ta2O9 ultra thin films
Authors: Celinska J. , Joshi V. , Narayan S. , McMillan L. , Paz de Araujo C.
Published: May 2003

We have investigated the effect of reducing the thickness of strontium bismuth tantalate film to as low as 25 nm on its ferroelectric characteristics. A degradation of ferroelectric properties such as significant reduction in remanent polarization is generally observed with reduction in film thickness, in particular below 100 nm. This has been overcome by using a modified deposition process sequence and a crystallization technique based completely on the rapid thermal annealing process. The resulting ultrathin films show good remanent polarization, low-voltage saturation, low leakage current, high breakdown strength, and good endurance. These films demonstrate the potential for scaling and are excellent candidates for several generations of ferroelectric random access memory applications.
Epitaxial (100) iridium on A-plane sapphire: A system for wafer-scale diamond heteroepitaxy
Authors: Dai Z. , Bednarski-Meinke C. , Loloee R. , Golding B.
Published: May 2003

Large-scale heteroepitaxial growth of diamond depends critically on the development of a suitable lattice-matched buffer layer and substrate system. Epitaxial (100) iridium films have been grown on terraced, vicinal a-plane (112̄0) α-Al2O3 (sapphire) by electron-beam evaporation. The epitaxial relationship, Ir(100)//Al2O3(112̄0) with Ir[011]//Al2O3[11̄00], was determined by x-ray diffraction and electron backscattering diffraction analysis. For a 300-nm thickness of Ir, a (200) rocking curve yielded a linewidth of 0.21°, and the film exhibited a macrostepped surface with low pinhole density. This Ir/sapphire system provides a basis for large-area growth of (100) heteroepitaxial diamond.
Orange and red upconversion laser pumped by an avalanche mechanism in Pr3+, Yb3+:BaY2F8
Authors: Osiac E. , Heumann E. , Huber G. , Kück S. , Sani E. , Toncelli A. , Tonelli M.
Published: May 2003

The letter reports on upconverted orange (607.5 nm, P03→3H6) and red (638.7 nm, P03→3F2) laser oscillation at room temperature observed in Pr3+, Yb3+:BaY2F8 under excitation at 822 or 841 nm at 300 K. The upconversion mechanism that populates the emitting level is an avalanche excitation mechanism. Output powers up to 55 mW and slope efficiencies up to 27% were demonstrated at 607.5 nm. At 638.7 nm, the maximum output power was 26 mW with a slope efficiency of about 13.5%.
A superconducting antenna-coupled hot-spot microbolometer
Authors: Luukanen A. , Pekola J. P.
Published: May 2003

We report the electrical properties of an antenna-coupled niobium vacuum-bridge bolometer, operated at a temperature of 4.2 K, in which the thermal isolation is maximized by the vacuum gap between the bridge and the underlying silicon substrate. The device is voltage-biased, which results in a formation of a normal state region in the middle of the bridge. The device shows a current responsivity of −1430 A/W and an amplifier limited electrical noise equivalent power of 1.4×10−14 W/Hz.
Polarization anisotropy of the photoluminescence of M-plane (In,Ga)N/GaN multiple quantum wells
Authors: Sun Yue Jun , Brandt Oliver , Ramsteiner Manfred , Grahn Holger T. , Ploog Klaus H.
Published: May 2003

We investigate the polarization anisotropy of the photoluminescence of an M-plane (11̄00) In0.1Ga0.9N/GaN multiple quantum well grown on γ-LiAlO2 (100) by molecular-beam epitaxy. In contrast to C-plane (0001) structures, a strong in-plane optical anisotropy with an energy-dependent polarization degree of up to 96% is observed for this M-plane sample. An apparent spectral shift of the emission with polarization angle is attributed to the impact of exciton localization on the polarization degree. The presence of localized states manifests itself further in the anomalous temperature dependence of the photoluminescence linewidth.
Ion-implanted In0.53Ga0.47As for ultrafast optoelectronic applications
Authors: Carmody C. , Tan H. H. , Jagadish C. , Gaarder A. , Marcinkevičius S.
Published: May 2003

Undoped In0.53Ga0.47As epilayers were implanted with 2-MeV Fe+ ions at doses of 1×1015 and 1×1016 cm−2 at room temperature and annealed at temperatures between 500 and 800 °C. Hall-effect measurements show that after annealing, layers with resistivities on the order of 105 Ω/square can be achieved. Carrier lifetimes as short as 300 fs are observed for samples annealed at 500 and 600 °C. For higher annealing temperatures, characteristic times of the optical response are on the order of a few picoseconds.
Observation of a scanning tunneling microscopy induced photocurrent during ballistic electron emission microscopy
Authors: Heller E. R. , Pelz J. P.
Published: May 2003

We report that a scanning tunneling microscope induced photocurrent (STM–PC) can occur during ballistic electron emission microscopy (BEEM) measurements on Schottky-barrier samples with typical efficiency of 10−4–10−6 and apparent BEEM threshold slightly above the substrate semiconductor band gap. This STM–PC resembles normal BEEM current, and hence, can interfere with BEEM measurements of structures with intrinsically low signal and/or intrinsic BEEM threshold voltage larger than the substrate band gap. We discuss a simple test for the existence of STM–PC during BEEM measurements.