bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of liquid pool temperature on the critical impact Weber number for splashing
Authors: Manzello Samuel L. , Yang Jiann C.
Published: December 2002

An experimental study is presented to determine the influence of liquid pool temperature on splashing behavior. Water droplets with initial diameter of 3.1 mm±0.1 mm impacted a water pool 40 mm in depth. The impaction process was recorded using a high-speed digital camera at 1000 frames/s. The impinging droplet was fixed at room temperature and the liquid surface was heated using a hotplate. To determine the critical Weber number for splashing, the impact velocity was varied. The critical impact Weber number for splashing was found to be dependent on liquid pool temperature, decreasing with an increase in liquid temperature.
Quantum reactive scattering in three dimensions using adiabatically adjusting principal axis hyperspherical coordinates: Periodic distributed approximating functional method for surface functions
Authors: Zhang Keming , Parker Gregory A. , Kouri Donald J. , Hoffman David K. , Iyengar Srinivasan S.
Published: December 2002

Periodic distributed approximating functionals are proposed and used to obtain a coordinate representation for the adiabatically adjusting principal axis hyperspherical coordinate kinetic energy operator. The approach is tested and accurate results for adiabatic surface functions for the reaction F+H2→HF+H are calculated and compared to those of some existing methods.
Photonic crystal enhanced narrow-band infrared emitters
Authors: Pralle M. U. , Moelders N. , McNeal M. P. , Puscasu I. , Greenwald A. C. , Daly J. T. , Johnson E. A. , George T. , Choi D. S. , El-Kady I. , Biswas R.
Published: December 2002

We have experimentally and theoretically developed a unique thermally stimulated midinfrared source that emits radiation within a narrow range of wavelengths (δλ/λ⩽0.2). The emission wavelengths are defined by the periodicity of a metal coated silicon–air photonic crystal etched into the emitter surface. The lattice of the holes in the metal mediate the coupling of light into discrete surface plasmon states. This yields surfaces with spectrally nonuniform infrared reflection properties where over much of the IR 90+% of photons are reflected yet, in a narrow spectral region, 90% absorption is observed. Transfer matrix calculations simulate well the position and strength of the absorption features. This technology will afford tunable infrared emitters with high power in a narrow spectral band that are critical for sensing, spectroscopy, and thermophotovoltaic applications.
Air bubble entrapment under an impacting droplet
Authors: Mehdi-Nejad V. , Mostaghimi J. , Chandra S.
Published: December 2002

We simulated impact of water, n-heptane, and molten nickel droplets on a solid surface. A numerical code was developed to model the motion of both the liquid in the droplet and the surrounding air. The model used a volume-of-fluid method to track the droplet surface and assumed that only one flow field governed the motion of all the fluids present. Predicted droplet shapes during impact agreed well with photographs. When a droplet approached another surface, air in the gap between them was forced out. Increased air pressure below a droplet created a depression in its surface in which air was trapped. The magnitude of pressure rise could be predicted using a simple analysis of fluid between two solid planes moving closer together. The air bubble formed at the solid–liquid interface remained attached to the solid surface in a water droplet. In an n-heptane droplet the bubble moved away from the surface and broke into two or three smaller bubbles before escaping through the droplet surface. This difference in behavior was attributed to the contact angle of water being much larger than that of n-heptane.
Relationship between hydriding and Nd magnetic moment in Nd2Fe14B
Authors: Chaboy J. , Piquer C. , Plugaru N. , Artigas M. , Maruyama H. , Kawamura N. , Suzuki M.
Published: December 2002

We present an x-ray magnetic circular dichroism (XMCD) investigation performed at the Fe K edge in the intermetallic Nd2Fe14BHx and Y2Fe14BHx compounds with controlled hydrogen content. The present study clearly reveals that hydrogen exerts an appreciable influence on the electronic structure of the whole system, and in particular on the rare-earth sublattice. The combined study of both magnetization and XMCD indicates that the magnetic moments of Nd decrease upon hydrogen uptake.
Role of anomalous electron transport in a stationary plasma thruster simulation
Authors: Hagelaar G. J. M. , Bareilles J. , Garrigues L. , Boeuf J.-P.
Published: December 2002

Stationary plasma thrusters (SPTs) are advanced propulsion devices that use a gas discharge to ionize and accelerate the propellant. We present simulation results obtained with a two-dimensional hybrid model of an SPT discharge. The model characterizes the ill-understood anomalous electron transport in SPTs by empirical parameters, of which we demonstrate the influence on the simulation results. Although no optimal values for these parameters can clearly be identified, the model predicts many features of the SPT behavior and yields interesting insights in the SPT physics. Experimentally observed electric potential distributions can only be reproduced if the anomalous electron transport is assumed to be stronger outside than inside the SPT channel. The simulations reproduce experimentally measured oscillations at 10–20 kHz and predict additional oscillations at 100–200 kHz. We discuss the dynamics of these oscillations and their influence on the energy distribution of the ion beam leaving the thruster.
Dislocation effect on light emission efficiency in gallium nitride
Authors: Karpov Sergey Yu. , Makarov Yuri N.
Published: December 2002

We modify the model of nonradiative carrier recombination on threading dislocation cores [Z. Z. Bandić, P. M. Bridger, E. C. Piquette, and T. C. McGill, Solid-State Electron. 44, 221 (2000)] to estimate quantitatively the light emission efficiency in GaN as a function of the dislocation density and nonequilibrium carrier concentration. The model predictions are in good agreement with available data on the minority carrier diffusion length in GaN. The dislocation density must be reduced, at least, down to ∼107 cm−2 in order to provide a light emission efficiency close to unity. The n-type background doping is found to be favorable for the further efficiency improvement.
Ultrahigh-density, nonlithographic, sub-100 nm pattern transfer by ion implantation and selective chemical etching
Authors: Matsuura Naomi , Simpson Todd W. , Mitchell Ian V. , Mei Xiang-Yang , Morales Patrick , Ruda Harry E.
Published: December 2002

A self-assembled array of nanometer-sized holes in alumina has been adapted as a mask for conventional, broad-area, ion implantation. The mask pattern, made up of nanoholes arranged in a two-dimensional triangular array with a 100 nm period and a 55 nm diameter pore size, has been successfully transferred onto single crystal (100) SrTiO3 substrates using 200 and 500 keV energy Pt ion bombardments, at fluences sufficient to amorphize the exposed areas. The amorphized material was removed by selective chemical etching resulting in a periodic array of holes about 55 nm in diameter and 115 nm deep. This parallel, nonlithographic approach is adaptable to submicron depth, variable array geometry and scale, and to any material where a selective etch can be found for the irradiated volume.
Fine structure of the trion triplet state in a single self-assembled semiconductor quantum dot
Authors: Akimov I. A. , Hundt A. , Flissikowski T. , Henneberger F.
Published: December 2002

The emission from the charged biexciton is used to monitor the energy structure of the trion triplet state in a negatively charged CdSe/ZnSe quantum dot. The isotropic part of the electron–hole exchange interaction regroups the otherwise sixfold degenerated state in three Kramers doublets. The energy separation between the radiative pairs with total spin projection Fz=±3/2 and ±1/2 is 1.6 meV. The anisotropic part mixes states with ΔFz=±2 resulting in a partly linearly polarized transition dipole. Application of magnetic field lifts the degeneracy of the Kramers doublets. The g factors also manifest the anisotropic state mixing.
Analyses of Kolmogorov’s model of breakup and its application into Lagrangian computation of liquid sprays under air-blast atomization
Authors: Gorokhovski M. A. , Saveliev V. L.
Published: December 2002

This paper considers the breakup of liquid drops at the large Weber number within the framework of Kolmogorov’s scenario of breakup. The population balances equation for droplet radius distribution is written to be an invariant under the group of scaling transformations. It is shown that due to this symmetry, the long-time limit solution of this equation is a power function. When the standard deviation of droplet radius strongly increases and, consequently, the characteristic length scale disappears, the power asymptotic solution can be viewed as a further evolution of Kolmogorov’s log-normal distribution. This new universality appears to be consistent with the experimental observation of fractal properties of droplets produced by air-blast breakup. The scaling properties of Kolmogorov’s model at later times are also demonstrated in the case where the breakup frequency is a power function of instantaneous radius. The model completes the Liouville equation for distribution function of liquid particles in the phase space of droplet position, velocity, and radius. The numerical scheme is proposed for stochastic modeling of droplets production. Lagrangian simulation of the spray under air-blast atomization is performed using KIVA II code, which is a frequently used code for computation of turbulent flows with sprays. The qualitative agreement of simulation with measurements is demonstrated.
Experimental investigation of scalar-scalar-dissipation filtered joint density function and its transport equation
Authors: Rajagopalan Anand G. , Tong Chenning
Published: December 2002

The filtered joint density function (FJDF) of a conserved scalar and its dissipation rate and the FJDF transport equation are studied experimentally in the fully developed region of a turbulent jet with a jet Reynolds number Rej=UjDj/ν of 40 000. Filtered variables are obtained by a two-dimensional box filter having a size of 90 scalar dissipation scales, realized by using three discrete sensors aligned in the cross-stream direction and by invoking Taylor’s hypothesis. One-dimensional filters are also used to examine the effects of filter scales. The results show that for small and large subgrid-scale (SGS) scalar variance the FJDF and its dynamics have qualitatively different characteristics. The conditional mean FJDF for small SGS variance is generally unimodal and the dependence of the dissipation on the SGS scalar is moderate. The dissipation rate is diffused toward its conditional mean and its production rate is generally smaller than its destruction rate. These characteristics are similar to those of scalar-scalar-dissipation joint probability density functions in a fully developed turbulent flow. On the other hand, the conditional FJDF for large SGS variance is bimodal and the dissipation shows strong dependence on the SGS scalar. Diffusion of the dissipation toward values much larger than its conditional mean is observed. The production of the dissipation generally exceeds its destruction, indicating nonequilibrium scalar dissipation. These characteristics are found to be associated with diffusion-layer-like structure in the SGS scalar for large SGS variance. In addition to the SGS scalar variance, the time scale of the SGS scalar also affects the FJDF. A current assumed FJDF model is also examined. The results provide new fundamental understanding of the structure of the small-scale scalar, which is important for improving large eddy simulation of nonpremixed turbulent combustion as well as for studying local extinction and reignition phenomena.
Plasma etching of AlN/AlGaInN superlattices for device fabrication
Authors: Zhu K. , Kuryatkov V. , Borisov B. , Kipshidze G. , Nikishin S. A. , Temkin H. , Holtz M.
Published: December 2002

We report a study of plasma etching of GaN, AlN, and AlN/AlGaN superlattices for the processing of deep ultraviolet light emitting diodes. Etching was carried out using inductively coupled plasma of chlorine diluted with argon under reactive ion etching conditions. Using parameters selected for etch rate, anisotropy, and surface smoothness, we study etching of n- and p-type superlattices. The former etches at a rate of 250 nm/min, which is intermediate to that of AlN and GaN, while the latter exhibits a slower etch rate of 60 nm/min. Based on these studies, we prepare low-leakage p–n junctions and mesa light emitting diodes with peak emission at 280 nm.
Vacancy trapping and annealing in noble-metal films grown at low temperature
Authors: Botez C. E. , Li K. , Lu E. D. , Elliott W. C. , Miceli P. F. , Conrad E. H. , Stephens P. W.
Published: December 2002

We have used synchrotron x-ray diffraction to study the homoepitaxial growth on Cu(001), Ag(001), and Ag(111), at temperatures between 300 and 65 K. The growth on all of these surfaces exhibits a consistent trend towards a large compressive strain that is attributed to the incorporation of vacancies into the growing film below 160 K. In each case, the vacancy concentration is ∼2% at 110 K and we have measured the temperature dependence for incorporation on the (001) surfaces as well as the annealing behavior for Cu(001). These results, which suggest new kinetic mechanisms, have important implications for understanding epitaxial crystal growth.
On the application of nonextensive statistics to Lagrangian turbulence
Authors: Reynolds A. M.
Published: December 2002

A second-order Lagrangian stochastic model formulated in terms of the mean dissipation rate and satisfying the well-mixed condition for a Tsallis distribution of Lagrangian accelerations is shown to be incompatible with Kolmogorov’s similarity theory. This difficulty does not arise when, following the approach advocated by Beck [Phys. Rev. Lett. 87, 180601 (2001)], the Tsallis distribution is recovered from a Gaussian model through the employment of a distribution of dissipation rates. The effects caused by ignoring fluctuations in dissipation along trajectories are evaluated in numerical simulations in which Lagrangian accelerations and dissipation histories evolve jointly as a Markovian process.
Distribution of correlation radii in disordered ferroelectrics
Authors: Glinchuk M. D. , Eliseev E. A. , Stephanovich V. A. , Jastrabik L.
Published: December 2002

The calculation of the correlation radius distribution function is performed for the cases of undamped and overdamped soft mode dispertion laws. Taking into account the correlation radius dependence on the random field and this field distribution function, we carried out the calculation of the correlation radius distribution function dependence on temperature, damping coefficient and random field distribution function parameters. It was shown that in paraelectric phase (T>Td, Td is the Burns temperature) the most probable value of the correlation radius is equal to its maximal value, independently of the degree of system disorder, while at the dipole glass state it is close to the minimal value, with a broad “tail” of the distribution function in the region of larger radii.
Spacer-dependent transport and magnetic properties of digital ferromagnetic heterostructures
Authors: Kreutz T. C. , Zanelatto G. , Gwinn E. G. , Gossard A. C.
Published: December 2002

We examine the relationship between the transport and magnetic properties of digital ferromagnetic heterostructure superlattices in which 0.5 monolayer MnAs planes alternate with undoped GaAs spacer layers. The data show that as the thickness t of the GaAs spacers increases, charge transport and the Curie temperature both approach their independent-layer limits at comparable values of t. An increase in the per-layer conductivity with decreasing t accompanies a rise in TC. This behavior is consistent with an enhancement of interlayer ferromagnetic interactions by charge coupling across the spacers.
Modulation of the peak effect in melt-processed (Sm1−xEux)Ba2Cu3O7−δ superconductors with compositional fluctuation
Authors: Hu A. , Zhou H. , Sakai N. , Murakami M.
Published: December 2002

The peak effect in melt-processed (Sm1−xEux)Ba2Cu3O7−δ crystals was modified with varying initial Sm/Eu ratios and was investigated up to 9 T down to 4.2 K. The experiment unveiled a linearly-temperature-dependent magnetization peak Bp(T). The fitting yielded a slightly lower critical temperature than bulk transition temperature Tc at null field. The scaling analysis of normalized pinning force versus reduced field B/Birr, where Birr is the irreversible field, showed a low peak at 0.37 in (Sm0.75Eu0.25)Ba2Cu3O7−δ and at 0.5 in (Sm0.25Eu0.75)Ba2Cu3O7−δ. The presence of regular compositional modulation is evident in both cases with transmission electron microscopy, and fluctuation diminishes in the latter composition. The modulation of flux pinning was thus attributed to the controlled compositional fluctuation.
Depth profiling of Si nanocrystals in Si-implanted SiO2 films by spectroscopic ellipsometry
Authors: Chen T. P. , Liu Y. , Tse M. S. , Ho P. F. , Dong Gui , Fung S.
Published: December 2002

In this letter, we report an approach to depth profiling of Si nanocrystals embedded in SiO2 film based on spectroscopic ellipsometry. The SiO2 film is divided into many sublayers with equal thickness, and each sublayer is characterized by its nanocrystal concentration. In the spectral fittings, the effective dielectric function of each sublayer is obtained from an effective medium approximation by using the dielectric function of Si nanocrystal that is calculated with either the bond contraction or the phenomenological models for the band gap expansion of nanocrystals. The fittings yield the nanocrystal depth profiles and the nanocrystal sizes as well. The depth profiles from the two models are similar, and they are in good agreement with secondary ion mass spectroscopy analysis.
Electrical properties of sol-gel-derived Pb(Zr0.52Ti0.48)O3 thin films on a PbTiO3-coated stainless steel substrate
Authors: Cheng Jin-Rong , Zhu Wenyi , Li Nan , Cross L. Eric
Published: December 2002

Lead zirconate titanate (PZT) thin films were deposited on stainless steel (SS) substrates by a sol-gel spin-on technique, and crystallized by a low-temperature annealing process. A lead titanate thin coating was deposited between the PZT film and SS substrate in order to decrease the annealing temperature. X-ray diffraction revealed that amorphous PZT thin layers crystallized into a perovskite phase on annealed at 550 °C for 0.5 h. No second phase formation, due to chemical reactions with the substrate, was observed. For films with a thickness of 1.68 μm, the dielectric constant, tan δ, remnant polarization and coercive field were determined to be 280, 0.07, 35 μC/cm2, and 99 kV/cm, respectively. The transverse piezoelectric constant d31 was measured using a wafer flexural technique.
Sound propagation in a porous medium filled with superfluid helium
Authors: Kekutiya Sh. E. , Chkhaidze N. D.
Published: December 2002

A theory of the propagation of acoustic waves in a porous medium filled with superfluid helium is developed. The elastic coefficients in the system of equations are expressed in terms of physically measurable quantities. The equations obtained describe all volume modes which propagate in a porous medium saturated with superfluid helium. The propagation velocities of longitudinal and transverse waves are calculated in the limit of high and low oscillation frequencies of the thermodynamic quantities.
Key role of intramolecular Jahn–Teller vibrations and multivalley nature of the band spectrum in the mechanism of superconductivity in doped C60 fullerites
Authors: Loktev V. M. , Pashitskiı̆ É. A. , Shekhter R. , Jonson M.
Published: December 2002

The possible mechanisms of superconductivity and of the increase in the critical temperature Tc of the phase transition into the superconducting state in doped cubic and hexagonal C60 fullerine crystals are analyzed. It is shown that the intramolecular Jahn–Teller vibrations (which are due to the high symmetry of C60 molecules and fullerene crystals and arise as a result of a change in the charge state of fullerene in an electron-phonon interaction), the degeneracy (multivalley nature) of the structure of narrow bands with a high density of states, and multiparticle Coulomb correlations such as local field effects (which increase the coupling constant in Cooper pariing of current carriers) all play a key role in the mechanism of superconductivity in this molecular metal.
Magnetic polarons in Y–Ba–Cu–O chains
Authors: Eremenko V. V. , Lukashev D. V. , Ponomarchuk B. L.
Published: December 2002

Mössbauer spectroscopy is used to study electron self-localization in the superconducting cuprate paramagnetic compound Y–Ba–Cu–O. It is shown that the electrons in chains with self-localization form a phase with local magnetic ordering and relaxation time greater than 10−7 s. Analysis of the magnitude of the accompanying charge redistribution suggests that when an electron undergoes self-localization a pair of exchange-coupled electrons localized predominantly on the oxygen is formed. Such a quasiparticle, consisting of a pair of antiferromagnetically oriented atomic moments and a pair of self-localized electrons, possesses integral spin and can form a Bose condensate.
Guided vortex motion in faceted niobium films
Authors: Soroka A. K. , Huth M.
Published: December 2002

Guided vortex motion has been observed in niobium films on a faceted Al2O3 substrate. The even and odd components of the longitudinal and transverse magnetoresistances of the samples are measured for various orientations of the transport current relative to the facetting direction. The even and odd components of the magnetoresistance are separated according to a change in the sign of the magnetic field.
Magnetic properties of a LaMn0.46Co0.54O3 single crystal
Authors: Barilo S. N. , Gatal’skaya V. I. , Shiryaev S. V. , Kurochkin L. A. , Shimchak R. , Baran M.
Published: December 2002

The magnetic properties of a LaMn0.46Co0.54O3 single crystal, grown by electrochemical deposition, are studied in a wide range of fields and temperatures. The two-phase magnetic state model of the crystal is used to analyze the results.
Giant resistance switching effect in nano-scale twinned La0.65Ca0.35MnO3 film
Authors: Prokhorov V. G. , Kaminsky G. G. , Komashko V. A. , Lee Y. P. , Tovstolytkin A. I. , Pogorily A. N.
Published: December 2002

The magnetic and transport properties of a 20 nm-scale twinned La0.65Ca0.35MnO3 film are investigated in a temperature range of 77–300 K. The coexistence of ferromagnetic metallic and charge-ordered insulating phases is suggested by analyzing the temperature and current dependences of the resistance at low temperatures. It is shown that thermocycling leads to the formation of a nonequilibrium state in the ensemble of charge-ordered domains and to the appearance of a giant switching in resistance of up to 100%. The experimental results are discussed on the basis of phase separation.
Magnetotransport in a quasi-one-dimensional electron system on superfluid helium
Authors: Nikolaenko B. A. , Kovdrya Yu. Z. , Gladchenko S. P.
Published: December 2002

Magnetotransport in a nondegenerate quasi-one-dimensional electron system on superfluid helium is investigated experimentally. The measurements are performed in perpendicular magnetic fields B⩽2.6 T in the temperature range 0.48–2.05 K with 100–400 nm wide conducting channels. In the region where the carriers are scattered by the helium atoms in the vapor (T>0.9 K) and in the region where the electrons are scattered by ripplons (T<0.9 K) the longitudinal component ρxx of the magnetoresistance of the conducting channels predominantly increases with B. The experimental data in the region of carrier scattering by helium atoms in the vapor agree with the classical Drude law, and in the quantum transport regime with ωcτ>1 (ωc is the cyclotron frequency and τ is the relaxation time of the electron system) the self-consistent Born approximation for a 2D electron system above helium gives a qualitative explanation of the data. It is conjectured that the quantitative differences between the experimental data and the theoretical calculations are due to the difference of the specific features between the experimentally studied and theoretically analyzed systems. The experimental values of the electron mobilities at low temperatures and in weak magnetic fields agree with theoretical calculations for a quasi-one-dimensional system. Weak carrier localization in the experimental electron system explains the negative magnetoresistance of the conducting channels, which was observed in the gas and ripplon carrier scattering regions.
Magnetoelastic waves in multisublattice systems
Authors: Kyzyrgulov I. R. , Kharrasov M. Kh.
Published: December 2002

Coupled magnetoelastic waves in antiferromagnetic crystals with a 2n sublattice magnetic subsystem (n=0, 1, 2,…) are studied. An explicit relation is found between the interaction parameters of the subsystems and the phenomenological constants. A dispersion equation for the characteristic frequencies of the coupled magnetoelastic waves is obtained.
Laser processing effect on magnetic properties of amorphous wires
Authors: Grigorenko A. N. , Panina L. V. , Sandacci S. I. , Makhnovskiy D. P. , Mapps D. J. , Khrushchev I. Y. , Dubov M. V. , Larin V. , Torkunov A.
Published: December 2002

Controllable, spatially selective treatment of glass-covered amorphous magnetic wires by laser irradiation is demonstrated. Local annealing by an argon laser has resulted in the formation of weakly interacting heterogeneous structures with different magnetic properties. Two large and stable Barkhausen jumps were detected in the magnetization reversal of high and positive magnetostriction wires with treated portions of 200 μm and 0.5 cm. The local annealing of negative magnetostrictive wires has modified wire magnetoimpedance: the maximum of the impedance plot flattens and the working field interval increases. These favorable changes are due to the creation of local stresses and structure interfaces.
Polycrystalline silicon thin-film transistor with self-aligned SiGe raised source/drain
Authors: Peng Du Zen , Chang Ting-Chang , Shih Po-Sheng , Zan Hsiao-Wen , Huang Tiao-Yuan , Chang Chun-Yen , Liu Po-Tsun
Published: December 2002

We have fabricated a polycrystalline silicon thin-film transistor with self-aligned SiGe raised source/drain (SiGe-RSD TFT). The SiGe-RSD regions were grown selectively by ultrahigh vacuum chemical vapor deposition at 550 °C. It was observed that, with SiH4 and GeH4 gas flow rates of 5 and 2 sccm, respectively, the poly-SiGe could be selectively grown up to 100 nm for source/drain regions. The resultant transistor structure features an ultrathin active channel region (20 nm) and a self-aligned thick source/drain region (120 nm), which is ideally suited for optimum performance. The significant improvements in electrical characteristics, such as higher turn-on current, lower leakage current, and higher drain breakdown voltage have been observed in the SiGe-RSD TFT, compared to the conventional TFT counterpart. These results indicate that TFTs with SiGe raised source/drain structure would be highly promising for ultrathin TFTs applications.
Electroluminescence from strain-compensated Si0.2Ge0.8/Si quantum-cascade structures based on a bound-to-continuum transition
Authors: Diehl L. , Menteşe S. , Müller E. , Grützmacher D. , Sigg H. , Gennser U. , Sagnes I. , Campidelli Y. , Kermarrec O. , Bensahel D. , Faist J.
Published: December 2002

Intersubband electroluminescence from strain-compensated Si/Si0.2Ge0.8 quantum cascade (QC) structures, consisting of up to 30 periods grown by molecular beam epitaxy on Si0.5Ge0.5 pseudosubstrates is reported. The design of the active region is based on a so-called “bound-to-continuum transition.” The intersubband radiation is emitted at a wavelength of 7 μm and is polarized, as expected for intersubband transitions between heavy hole states. A good agreement with photocurrent measurements is also found.
Enhanced absorption and quantum efficiency in locally modified single-crystal Si
Authors: Kuznicki Z. T.
Published: December 2002

The experimental collection efficiency of a nanoscale Si-layered system formed around a buried amorphization is investigated. A self-consistent calculation that takes into account the number of photons removed in the front deactivated zone and those transmitted to deeper layers leads to the result that more than one electron per absorbed short-wavelength photon is collected in the active zone lying below a carrier collection limit. This result suggests that it could be possible to make an efficient third generation Si solar cell based on such a design on the condition that photocarriers generated in the surface zone be collected.
Electrical and physical characteristics of PrTixOy for metal-oxide-semiconductor gate dielectric applications
Authors: Jeon Sanghun , Hwang Hyunsang
Published: December 2002

The electrical and physical characteristics of PrTixOy, for use in metal-oxide-semiconductor gate dielectric applications were investigated. An amorphous layer of PrTixOy with an equivalent oxide thickness of 1 nm and a dielectric constant of 23 was formed by means of e-beam evaporation. Compared to Pr2O3, PrTixOy was found to exhibit excellent characteristics such as a high accumulation capacitance, a low leakage current density, a thin interfacial layer, and a lower reactivity to water. The superiority of PrTixOy can be attributed to the addition of TiO2 to the praseodymium oxide matrix.
Spin-memory loss at 4.2 K in sputtered Pd and Pt and at Pd/Cu and Pt/Cu interfaces
Authors: Kurt H. , Loloee R. , Eid K. , Pratt W. P. , Bass J.
Published: December 2002

We derive spin-diffusion lengths at 4.2 K in sputtered Pd and Pt of lsfPd=25−5+10 nm and lsfPt=14±6 nm, interface specific resistances of sputtered Pd/Cu and Pt/Cu of 2ARPd/Cu=0.9±0.1 fΩ m2 and 2ARPt/Cu=1.5±0.1 fΩ m2, and the amount of spin-memory loss at the Pd/Cu and Pt/Cu interfaces as δPd/Cu=0.24−0.03+0.06 and δPt/Cu=0.9±0.1. We compare our values with those from metals in similar rows of the Periodic Table, Nb for Pt and W for Pd.
Rigid bubble pit formation and huge signal enhancement in super-resolution near-field structure disk with platinum-oxide layer
Authors: Kikukawa T. , Nakano T. , Shima T. , Tominaga J.
Published: December 2002

Huge signal enhancement was observed by a super-resolution near-field structure disk with a platinum-oxide layer. The carrier-to-noise ratio of 200-nm-mark trains reached 46.1 dB, and 42.3 dB was obtained even at 150-nm-mark trains. The sizes of the marks were one-fifth to one-seventh of the laser spot diameter of the readout system. The cross section of the mark trains was also observed by transmission electron microscopy. It was confirmed that 200-nm-size bubble pits were rigidly formed in good separation and ∼20-nm-platinum particles precipitated inside the bubble. The computer-simulation based on the model supported the huge signal enhancement.
Optically driven diffusion and mechanical softening in azobenzene polymer layers
Authors: Mechau N. , Neher D. , Börger V. , Menzel H. , Urayama K.
Published: December 2002

A study of the thermally induced and photoinduced changes in the mechanical properties of thin azobenzene polymer layers utilizing electromechanical spectroscopy is presented. Upon illumination at room temperature, weak photoinduced plasticization is observed. This is well below the degree of softening induced by heating the layer above the glass transition temperature. At the same time, the polymer layer roughens, indicating light-induced diffusion of the macromolecules over micrometer distances. We propose an active photoinduced diffusion mechanism, in which free volume generated during the photoisomerization of one chromophore is reoccupied in the course of the photoinduced isomerization of an adjacent azobenzene molecule.
Light-induced backward scattering in LiNbO3:Fe,Zn
Authors: Wu Qiang , Xu Jingjun , Sun Qian , Zhang Xinzheng , Qiao Haijun , Tang Baiquan , Zhang Guangyin , Gu Min
Published: December 2002

We investigated the light-induced backward scattering in doubly doped lithium niobate crystals and observed an intensity threshold effect. It will be shown that scattering microregions are locally recorded in the sample by holographic interaction due to the existence of the threshold effect. Experimental results of multilayer recording point out that this property could be used for high-density multilayer-like bit data optical storage while keeping high signal-to-noise ratio.
Dielectric behavior of three-phase percolative Ni–BaTiO3/polyvinylidene fluoride composites
Authors: Dang Z.-M. , Shen Y. , Nan C.-W.
Published: December 2002

A three-phase percolative composite with a ferroelectric phase (BaTiO3) and metallic inclusions (Ni) embedded into polyvinylidene fluoride matrix was prepared by using a simple blending and hot-molding technique. Effective medium approximations and percolation theory were employed in order to design and describe the dielectric behavior of such three-phase composites. Our experimental results showed that the static dielectric constant of such a three-phase composite can reach above 800 when the Ni concentration is close to its percolation threshold. Such composites have a potential to become capacitors and can be easily fabricated into various shapes due to its flexibility.
Leakage mechanism of (Ba0.7Sr0.3)TiO3 thin films in the low-temperature range
Authors: Yang Hao , Tao Kun , Chen Bin , Qiu Xianggang , Xu Bo , Zhao Bairu
Published: December 2002

Pt /( Ba 0.7 Sr 0.3 ) TiO 3 ( BST )/ YBa 2 Cu 3 O 7−x ( YBCO ) capacitors on SrTiO3 substrates were fabricated, and the temperature dependence of their current–voltage characteristics was studied in the temperature range from 100 to 300 K. It was found that the leakage current strongly depends on the voltage polarity and temperature. In the case of a Pt electrode negatively biased at a high electric field (>400 kV/cm), the Pt/BST interface acts as a Schottky barrier with the barrier height of 0.47 eV in the temperature range from 200 to 300 K. When the YBCO electrode was biased negatively and the electrical field was maintained higher than 64 kV/cm, the leakage mechanism shows space-charge-limited-current behavior.
Relaxor behavior of PbxBi4Ti3+xO12+3x (x=2,3) Aurivillius ceramics
Authors: Fernández J. F. , Caballero A. C. , Villegas M. , de Frutos J. , Lascano L.
Published: December 2002

The relaxor response of the PbxBi4Ti3+xO12+3x (x=2,3) Aurivillius ceramics is reported. The relaxor behavior appears with an increase of the symmetry in the ab plane of the structure and a decrease of the transition temperature. By the application of a bias field on nonpoled samples, it is possible to induce the piezoelectric response. The piezoelectric coefficient in the planar mode of −72 pC/N was measured at 210 °C for Pb2Bi4Ti5O18 ceramic disks. These results represent a step in the search of high-temperature piezoelectric ceramics.
Regularization modeling for large-eddy simulation
Authors: Geurts Bernard J. , Holm Darryl D.
Published: December 2002

A new modeling approach for large-eddy simulation (LES) is obtained by combining a “regularization principle” with an explicit filter and its inversion. This regularization approach allows a systematic derivation of the implied subgrid model, which resolves the closure problem. The central role of the filter in LES is fully restored, i.e., both the interpretation of LES predictions in terms of direct simulation results as well as the corresponding subgrid closure are specified by the filter. The regularization approach is illustrated with “Leray-smoothing” of the nonlinear convective terms. In turbulent mixing the new, implied subgrid model performs favorably compared to the dynamic eddy-viscosity procedure. The model is robust at arbitrarily high Reynolds numbers and correctly predicts self-similar turbulent flow development.
Investigation of trap-assisted tunneling current in InAs/(GaIn)Sb superlattice long-wavelength photodiodes
Authors: Yang Q. K. , Fuchs F. , Schmitz J. , Pletschen W.
Published: December 2002

Trap centers with an energy level positioned 1/3 of the band gap below the effective conduction band edge are observed in the electroluminescence spectra of InAs/(GaIn)Sb superlattice photodiodes with a cutoff wavelength of 11 μm. The trap centers are recognized by simulating the low-temperature current–voltage characteristics of the diodes. Excellent quantitative agreement on both, the I–V characteristic and the differential resistance between the experimental data and the theoretical prediction is achieved. The quantitative simulation of the I–V characteristics shows, that the 77 K performance of InAs/(GaIn)Sb photodiodes is dominated by generation-recombination processes even at long wavelengths. Above 50 K, tunneling currents are not of importance.
Low-temperature synthesis of large-scale single-crystal molybdenum trioxide (MoO3) nanobelts
Authors: Li Xiao-Lin , Liu Jun-Feng , Li Ya-Dong
Published: December 2002

Bulk quantities of single-crystal MoO3 nanobelts were synthesized by a low-temperature, simple solution method without using any templates or catalysts. X-ray powder diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction, and energy-dispersive x-ray analysis indicated that as-synthesized nanobelts were pure orthorhombic structured MoO3 grown along [001], with the lengths up to more than 10 μm, width ranging between 50 and 400 nm, and width-to-thickness ratios of about 5 to 20. The possible growth mechanism and the influence factors were reported.
Dislocation annihilation by silicon delta-doping in GaN epitaxy on Si
Authors: Contreras O. , Ponce F. A. , Christen J. , Dadgar A. , Krost A.
Published: December 2002

The addition of bursts of silicon has been observed to correlate with the reduction of threading screw dislocations during epitaxial growth of GaN on silicon by metalorganic chemical vapor deposition. The reduction is associated with bending of screw dislocations and “pairing” with equivalent neighboring dislocations with opposite Burgers vectors. This results in the formation of square dislocation loops. When the right type of dislocation is not available, the dislocation continues propagating in the original direction, leaving behind a kink at the silicon-rich position. These observations apply only to dislocations with a screw component. Edge dislocations are not affected by silicon delta-doping. A mechanism for the termination of threading screw dislocation is proposed, which involves pinning by the silicon impurities of the surface lattice steps associated with screw dislocations.
Electronic band structure of ferroelectric SrBi2Ta2O9
Authors: Zhang J. , Yin Z. , Zhang M. S.
Published: December 2002

The electronic band structures of both the ferroelectric and paraelectric phases of SrBi2Ta2O9 (SBT) were calculated, by first-principle methods. We find that the band gap in the ferroelectric phase increases by 0.7 eV, compared with the paraelectric phase. The edges of the valence band and the conduction band are mainly derived, respectively, from Bi 6s and O 2p states, and from Ta 5d and Bi 6p states. The partial Bi–O covalency indirectly strengthens the Ta–O hybridization, favoring stabilization of the ferroelectric phase. We attribute the SBT fatigue-free property to weak pinning of its domains by the trapped centers formed by both Bi+3 at the top of the valence band and Ta+5 at the bottom of the conduction band, and the high nonlinear refractive index in SBT to a large contribution from Ta 5d states.
Anomalous charge-transfer behavior in the scattering of hyperthermal Br+(3P2) on Pt(111)
Authors: Maazouz M. , Maazouz P. L. , Jacobs D. C.
Published: December 2002

In contrast to conventional charge-transfer theory, the scattering of state-selected Br+(3P2) on Pt(111) shows a dramatic enhancement in the yield of Br−(1S0) at an impact energy of 26 eV. Coincident with this resonance, the Br−(1S0) product scatters with additional translational energy. The observed scattering behavior is consistent with a collision-induced deformation of the lattice that evolves in phase with the departing projectile. The experimental data demonstrate the strong coupling between the motion of the platinum lattice and the surface electronic states responsible for charge transfer.
Optical switching of Mg-rich Mg–Ni alloy thin films
Authors: Yoshimura K. , Yamada Y. , Okada M.
Published: December 2002

Mg–Ni alloy thin films were prepared by dc magnetron sputtering using Mg and Ni targets, and their optical switching property for hydrogen exposure has been investigated. Pd-capped MgNix (0.1<x<0.3) films show a good switchable mirror property. Optical transmittance of these Mg-rich Mg–Ni thin films in the hydride state is much improved compared with that of Mg2Ni thin film. We speculate that the variation of the ratio of Mg2NiH4 to MgH2 formed in the hydride state may cause this difference. Such a wide modulation range of optical switching is important for the application of this material to energy efficient smart windows.
Change in photoluminescence from Er-doped TiO2 thin films induced by optically assisted reduction
Authors: Komuro Shuji , Katsumata Tooru , Kokai Hideki , Morikawa Takitaro , Zhao Xinwei
Published: December 2002

Erbium-doped TiO2 (TiO2:Er) thin films with the anatase structure have been prepared on Si substrate by laser ablation. Sharp and intense Er-related emission in the visible region as well as in the IR region has been observed under over-band-gap excitation. The broad photoluminescence (PL) peaking at about 530 nm newly appears at low temperature. It has been understood that the broad PL is induced by an optically assisted reduction effect that is caused by both the H2O adsorption and the reduction process of TiO2 to Ti2O3 by UV illumination. In the IR region, Er-related emission consisted of one main peak located at 1.534 μm and many subpeaks located at around 1.54 μm can be observed even at room temperature. The drastic thermal quenching of the Er-related 1.54 μm emission is also considered due to the optically assisted reduction effect.
Perovskite oxide tricolor superlattices with artificially broken inversion symmetry by interface effects
Authors: Yamada Hiroyuki , Kawasaki M. , Ogawa Y. , Tokura Y.
Published: December 2002

We have designed and fabricated spin superlattices composed of three kinds of perovskite oxides: ferromagnetic La0.6Sr0.4MnO3 (LSMO) sandwiched by two nonmagnetic insulators, SrTiO3 (STO), and LaAlO3 (LAO). Conventional superlattices, structured as alternating stack of two components, preserve centrosymmetry. By stacking three compounds repeatedly in an asymmetric sequence such as (LAO/LSMO/STO)n, one can break the inversion symmetry. Magnetic and transport properties of the superlattices clearly indicate that the STO and LAO layers modulate the ferromagnetic spin order in LSMO layers adjacent to the interfaces in a different manner, giving rise to broken inversion symmetry of magnetic structure in the (LAO/LSMO/STO)n superlattices.
Quantum tunneling of vortices in MgB2 superconductor
Authors: Zhang Y. Z. , Deltour R. , Wen H. H. , Jin C. Q. , Ni Y. M. , Jia S. L , Che G. C. , Zhao Z. X.
Published: December 2002

Magnetic relaxation in a MgB2 superconductor was measured. The temperature dependence of the normalized relaxation rate was determined for three different magnetic fields. By extrapolating these rates to T=0 K, we find that these extrapolations do not approach zero, indicating quantum tunneling of vortices in the superconductor. A quantum correction of the relaxation rate, followed by the correction of the magnetic moment, is proposed. Using the quantum correction, we find that U0 increases with decreasing temperature and approaches a maximum at T=0.
Spin-dependent properties of a two-dimensional electron gas with ferromagnetic gates
Authors: Ciuti C. , McGuire J. P. , Sham L. J.
Published: December 2002

A theoretical prediction of the spin-dependent electron self-energy and in-plane transport of a two-dimensional electron gas in proximity with a ferromagnetic gate is presented. The application of the predicted spin-dependent properties is illustrated by the proposal of a device configuration with two neighboring ferromagnetic gates which produces a magnetoresistance effect on the channel current generated by nonmagnetic source and drain contacts. Specific results are shown for a silicon inversion layer with iron gates. The gate leakage current is found to be beneficial to the spin effects.
Magnetic properties of (Pr0.17Co0.83)69C31 nanocomposite films prepared by pulsed filtered vacuum arc deposition
Authors: Chen P. , Wong S. P. , Chiah M. F. , Wang H. , Cheung W. Y. , Ke N. , Xiao Z. S.
Published: December 2002

Nanocomposite (Pr0.17Co0.83)69C31 thin films were prepared by pulsed filtered vacuum arc deposition. Rapid thermal annealing was performed at various temperatures in argon. The variations of the structure and magnetic properties of these films with various annealing temperatures were studied systematically. The sample annealed at 700 °C for 1 min shows a large coercivity of 5.2 kOe and a small grain size of 7.8 nm. The overall small negative ΔM of this film indicates that virtually all the Pr0.17Co0.83 grains are isolated single domain particles with only weak dipolar interactions among them. These results indicate that (Pr0.17Co0.83)69C31 nanocomposite thin films would be a promising candidate for high-density magnetic recording medium applications.
Highly effective metal vapor absorbents based on carbon nanotubes
Authors: Liu Zongwen , Gao Yihua , Bando Yoshio
Published: December 2002

It was shown that, when filled with gallium, carbon nanotubes can absorb copper vapor with extraordinarily high efficiency. The copper vapor generated from the supporting copper grid upon heating to 800 °C in an electron microscope under a pressure of 1.0×10−5 Pa quickly deposited into the carbon nanotubes and formed an alloy with gallium where the vapor pressure is up to 500 times higher (5×10−3 Pa). These filled carbon nanotubes may be used as highly sensitive toxic or radioactive metal vapor absorbents since gallium also tends to form alloys with metals like mercury and uranium.
Thermally induced decomposition of single-wall carbon nanotubes adsorbed on H/Si(111)
Authors: Hunt Michael R. C. , Montalti Massimo , Chao Yimin , Krishnamurthy Satheesh , Dhanak Vinod R. , Šiller Lidija
Published: December 2002

The thermally driven reaction of carbon nanotubes with a silicon substrate is studied by photoemission spectroscopy and atomic force microscopy. Carbon nanotubes with a relatively high defect density are observed to decompose under reaction with silicon to form silicon carbide at temperatures (650±10 °C) substantially lower than the analogous reaction for adsorbed C60. The morphology of the resultant silicon carbide islands appears to reflect the morphology of the original nanotubes, suggesting a means by which SiC nanostrutures may be produced.
Polymer scaffolding model for holographic polymer-dispersed liquid crystals
Authors: Vardanyan K. K. , Qi J. , Eakin J. N. , De Sarkar M. , Crawford G. P.
Published: December 2002

A polymer scaffolding model is proposed to describe the electro-optic performance parameters of holographic polymer-dispersed liquid crystals (H-PDLC). Using a simple phenomenological approach to model the interaction between the liquid crystal and polymer scaffolding, the observed increase in critical field and reduced dynamic response times are well described, and the molecular interaction energy is deduced to be ∼10−4 J/m2.