bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical properties of C60 nanocrystals embedded in a SiO matrix
Authors: Ohno T. , Matsuishi K. , Onari S.
Published: July 2002

Photoluminescence spectra of (C60)n nanocrystals (1000<n<10 000) in a SiO matrix have been investigated in order to study electronic and vibronic states of mesoscopic phase of C60 crystals. We have found that both vibronic bands, which are derived from the gerade- and ungerade-parity vibrational modes, obviously appear in the spectrum of the C60 nanocrystals at 80 K. Results indicate that Herzberg–Teller transitions become strong with a decrease in the size of the crystal. It has been also found that Herzberg–Teller vibronic bands become relatively dominant with an increase in the temperature compared to Jahn–Teller vibronic bands. We analyzed the data by the temperature dependence of quantum efficiency, and found that the thermal activation energy for nonradiative relaxation can be classified into two groups; 190 and 90 meV for the Herzberg– and Jahn–Teller vibronic bands, respectively. This indicates that two kinds of electronic origins coexist in the C60 nanocrystals at a temperature above 80 K.
Metastable size distributions of molecular clusters in supersaturated vapors
Authors: Bauer S. H. , Zhang Yi-Xue , Wilcox C. F.
Published: July 2002

The shapes of size distributions of molecular clusters in highly supersaturated vapors, assuming they remain unrelaxed, i.e., in “constrained equilibrium,” were derived for three representative systems. The required thermochemical parameters were estimated via the kinetic molecular model that accurately reproduced the measured condensation fluxes over a wide range of temperatures and supersaturation levels. The computed size distributions are neither log–normal nor follow an exponential-type decline with increasing cluster size.
Alkoxy sol-gel derived Y3−xAl5O12:Tbx thin films as efficient cathodoluminescent phosphors
Authors: Choe Jae Young , Ravichandran D. , Blomquist S. M. , Morton D. C. , Kirchner K. W. , Ervin M. H. , Lee Unchul
Published: July 2002

Thin-film Y3−xAl5O12:Tbx3+ (YAG:Tb) phosphor derived from a sol-gel chemistry is analyzed by x-ray diffraction, scanning electron microscopy, photoluminescence (PL) and cathodoluminescence (CL). The metal alkoxides organic precursors were chosen as the starting materials to form the sol-gel. This liquid sol-gel was spin coated on sapphire and silicon substrates to form the uniform thin films, then crystallized by annealing. The PL intensity of the crystallized film at 545 nm green emission was 15 times higher than that of the as-coated noncrystalline film. CL measurements show that luminance and efficiency are comparable to the films deposited by other techniques.
Sliding and decohesion of Σ3〈111〉 grain boundary in tungsten: Monte Carlo simulations with many-body ab initio potentials
Authors: Dorfman Simon , Mundim Kleber C. , Liubich Vlad , Fuks David
Published: July 2002

We perform atomistic simulations of the properties of the Σ3〈111〉 grain boundary (GB) in W and demonstrate the influence of many-body interactions on the resistance of the grain boundary with respect to sliding and decohesion shifts. The distribution of the elastic field in the vicinity of the GB is considered. The interatomic potentials used in these simulations are obtained from ab initio total energy calculations using a recursion procedure to extract interatomic potentials.
Impact ionization rates of semiconductors in an electric field: The effect of collisional broadening
Authors: Madureira Justino R. , Semkat Dirk , Bonitz Michael , Redmer Ronald
Published: July 2002

A gauge invariant quantum kinetic equation which includes impact ionization, intracollisional field effect, and collisional broadening is derived in the frame of nonequilibrium Green’s functions. We obtain analytical expressions for the impact ionization rate. For the wide band gap material ZnS, a substantial increase of the rate due to collisional broadening is obtained for moderate field strengths E⩽500 kV/cm.
Deep levels and their impact on generation current in Sn-doped InGaAsN
Authors: Kaplar R. J. , Arehart A. R. , Ringel S. A. , Allerman A. A. , Sieg R. M. , Kurtz Steven R.
Published: July 2002

We have investigated deep levels in 1.05 eV, Sn-doped, n-type In0.075Ga0.925As0.975N0.025 lattice-matched to GaAs. The samples were grown by metal–organic chemical vapor deposition. Capacitance–voltage measurements were used to determine the electron concentration in both as-grown and postgrowth annealed samples, and a decrease in net electron concentration of about 1.5×1017 cm−3 was observed following annealing. Deep level transient spectroscopy measurements are consistent with the presence of four majority-carrier electron traps, E1 (a broad distribution extending from the conduction band edge to approximately EC−0.2 eV), E2(0.36 eV), E3(0.34 eV), and E4(0.82 eV), as well as one minority-carrier hole trap, H1(0.71 eV), in our material. It is shown that E2 and H1, both of which are present in the annealed material only, are likely the same defect observed under conditions of electron and hole emission, respectively. Current–voltage-temperature measurements indicate a thermal activation energy of 0.35 eV for reverse bias current transport, which is in close agreement with the activation energy of E2. It is thus demonstrated that the E2/H1 defect is a recombination–generation center which contributes to current transport in our InGaAsN-based test diode.
Superalgebras for the Penning trap
Authors: Russell Neil
Published: July 2002

The Hamiltonian describing a single fermion in a Penning trap is shown to be supersymmetric in certain cases. The supersymmetries of interest occur when the ratio of the cyclotron frequency to the axial frequency is 32 and the particle has anomalous magnetic moment 43 or 23. At these supersymmetric points, the spectrum shows uniformly spaced crossed levels. The associated superalgebras are su(2|1) and su(1|1). The phase space for this problem has an osp(2|6) structure and contains all the degeneracy superalgebras.
Transformation formulas for double hypergeometric series related to 9-j coefficients and their basic analogs
Authors: Lievens S. , Jeugt J. Van der
Published: July 2002

In a recent paper, Ališauskas deduced different triple sum expressions for the 9-j coefficient of su(2) and suq(2). For a singly stretched 9-j coefficient, these reduce to different double sum series. Using these distinct series, we deduce a set of new transformation formulas for double hypergeometric series of Kampé de Fériet type and their basic analogs. These transformation formulas are valid for rather general parameters of the series, although a common feature is that all the series appearing here are terminating. It is also shown that the transformation formulas deduced here generate a group of transformation formulas, thus yielding an invariance group or symmetry group of particular double series.
An approach for simulating the transport of spherical particles in a rarefied gas flow via the direct simulation Monte Carlo method
Authors: Gallis M. A. , Torczynski J. R. , Rader D. J.
Published: July 2002

An approach is presented for computing the force on and heat transfer to a spherical particle from a rarefied flow of a monatomic gas that is computed using the direct simulation Monte Carlo (DSMC) method. The particle concentration is taken to be dilute, and the gas flow around the particle (but not necessarily throughout the flow domain) is taken to be free-molecular. Green’s functions for the force and heat transfer are determined analytically, are verified by demonstrating that they yield certain well-known results, and are implemented numerically within a DSMC code. Simulations are performed for the case of gas confined between two parallel plates at different temperatures for broad ranges of pressures and particle velocities. The simulation results agree closely with analytical results, where applicable. A simple approximate expression relating the thermophoretic force to the gas-phase heat flux is developed, and the drag and thermophoretic forces are found to be almost decoupled for a wide range of particle velocities.
Temperature dependence for the photovoltaic device parameters of polymer-fullerene solar cells under operating conditions
Authors: Katz E. A. , Faiman D. , Tuladhar S. M. , Kroon J. M. , Wienk M. M. , Fromherz T. , Padinger F. , Brabec C. J. , Sariciftci N. S.
Published: July 2002

We report on the temperature dependence of various photovoltaic device parameters of solar cells, fabricated from interpenetrating networks of conjugated polymers with fullerenes, in the wide temperature range of their possible operating conditions (25–60 °C). The open-circuit voltage was found to decrease linearly with increasing temperature. For the short-circuit current, we observed a monotonic increase with increasing temperature, followed by a saturation region. The rate of this increase (coupled to a corresponding increase for the fill factor) was found to overtake the corresponding rate of decrease in voltage, resulting in an overall increase of the energy conversion efficiency. The efficiency was observed to reach a maximum value in the approximate range 47–60 °C. The results are discussed with respect to possible mechanisms for photovoltage generation and charge carrier transport in the conjugated polymer-fullerene composite, and in particular, thermally activated charge carrier mobility.
Photovoltaic response and dielectric properties of epitaxial anatase-TiO2 films grown on conductive La0.5Sr0.5CoO3 electrodes
Authors: Park B. H. , Li L. S. , Gibbons B. J. , Huang J. Y. , Jia Q. X.
Published: July 2002

We have grown epitaxial anatase-TiO2 (001) films on La0.5Sr0.5CoO3 (001) bottom electrodes using pulsed-laser deposition. The small lattice mismatch (0.5%) between the anatase-TiO2 and the La0.5Sr0.5CoO3 makes it possible to grow anatase-TiO2 films with excellent crystallinity on conductive metal oxides. The photovoltaic properties of the epitaxial anatase-TiO2 on the La0.5Sr0.5CoO3 were characterized using a Kelvin probe. The optical band-gap energy was found to be 3.05 eV. The dielectric properties of the epitaxial anatase-TiO2 films were characterized using a capacitor structure of Au/anatase-TiO2/La0.5Sr0.5CoO3 on a LaAlO3 substrate. The dielectric dispersion exhibited a power-law dependence, and the dielectric constant measured at room temperature and 1 MHz was 38.
A practical method for the use of curvilinear coordinates in calculations of normal-mode-projected displacements and Duschinsky rotation matrices for large molecules
Authors: Reimers Jeffrey R.
Published: July 2002

While use of curvilinear coordinates such as bond lengths and bond angles is common in accurate spectroscopic and/or scattering calculations for triatomic and other small molecules, their use for large molecules is uncommon and restricted. For large molecules, normal-mode analysis is feasible but gives sensible results only if the dynamical or spectroscopic process being considered involves changes in angular coordinates, including ring deformations, which are so small that the motion can be approximated by its tangential component. We describe an approximate method by which curvilinear normal-mode-projected displacements and hence Franck–Condon factors, reorganization energies, and vibronic coupling constants, as well as Duschinsky (Dushinsky, Duschinskii) rotation matrices, can be evaluated for large systems. Three illustrative examples are provided: (i) to understand the nature of the first excited state of water, illustrating properties of large-amplitude bending motions; (ii) to understand the nature of the “boat” relaxation of the first excited state of pyridine, illustrating properties of large-amplitude torsional motions; and (iii) to understand the coupling of vibrational modes to the oxidation of bacteriochlorophyll-a, a paradigm with many applications to both chemical and biological electron transfer, illustrating properties of macrocyclic deformations. The method is interfaced to a wide variety of computational chemistry computer programs.
Material and electrical characterization of carbon-doped Ta2O5 films for embedded dynamic random access memory applications
Authors: Chu K. , Chang J. P. , Steigerwald M. L. , Fleming R. M. , Opila R. L. , Lang D. V. , Van Dover R. B. , Jones C. D. W.
Published: July 2002

This work is a systematic study of carbon incorporation in Ta2O5 and its effect on the material and electrical properties of Ta2O5, a promising replacement for silicon oxide in embedded dynamic random access memory applications. Using pulsed-dc reactive and rf-magnetron sputtering of Ta2O5 performed in an argon/oxygen/carbon-dioxide plasma, we have methodically doped the Ta2O5 films with carbon. In thick (70 nm) Ta2O5 films, an optimal amount (0.8–1.4 at. %) of carbon doping reduced the leakage current to 10−8 A/cm2 at +3 MV/cm, a four orders of magnitude reduction compared to a leakage current of 10−4 A/cm2 in an undoped Ta2O5 film grown in similar conditions without CO2 in the plasma. This finding suggests that carbon doping can further improve the dielectric leakage property at an optimal concentration. X-ray Photoemission Spectroscopy analysis showed the presence of carbonate (carbon bonded to three oxygen) in these electrically improved carbon-doped films. Analysis by high-resolution transmission electron microscopy and Nomarsky microscopy exhibited no morphological or structural changes in these carbon-doped thin films. Moreover, carbon doping showed no improvement in the leakage current in thin (10 nm) Ta2O5 films. This phenomenon is explained by a defect compensation mechanism in which the carbon-related defects remove carriers at low concentrations but form a hopping conduction path at high concentrations.
Energy-level alignment at the tris-(8-hydroxyquinolate)-aluminum/Gd interface and Gd-electron-injection layer for organic electroluminescent device
Authors: Kim Shin Cheul , Kwon Soon Nam , Choi Myung-Woon , Whang Chung Nam , Jeong Kwangho , Lee Sam Hyeon , Lee Jae-Gyoung , Kim Sunwook
Published: July 2002

The energy-level alignment for the tris-(8-hydroxyquinolate)-aluminum (Alq3)/Gd interface is determined by ultraviolet photoemission spectroscopy. The energy difference between the Fermi level in Gd and the low-energy edge of the highest occupied molecular orbital in Alq3 is 2.63 eV, and the vacuum level in the Alq3 layer is moved upward to 0.35 eV with respect to its intrinsic level. Gd/Al, Al:Li (0.1%), and Al were employed as a cathode for the organic electroluminescent device. Among these devices, the device with the Gd-electron-injection layer has operated at the lowest voltage.
He+Ni
4
elastic scattering near the Coulomb barrier and optical model parameters
Authors: Nurmela A. , Pusa P. , Rauhala E. , Räisänen J.
Published: July 2002

Cross sections for the elastic scattering system of He+Ni4 have been investigated. Natural nickel was bombarded by He4 ions in the laboratory energy range of 3.0–14.3 MeV and the intensity of helium backscattering through laboratory angles of 96°, 117°, and 137° was observed. From measured yield data, the cross sections were extracted for the direct Ni(4He,4He)Ni scattering process as well as for the inverse recoil scattering process He4(58Ni,4He)58Ni by calculating the kinematical reversal of the reaction. The experimental helium scattering angles convert to helium recoil angles of 20°, 30°, and 40°, and the incident helium ion energies to 43.5–207 MeV for incident Ni58 ions in the reversed reaction. Optical model parameters for helium elastic scattering were determined by using a measured scattering angular distribution at helium ion energy of 14.0 MeV and the energy distributions. These parameters were then used to calculate the elastic scattering of the He+Ni4 system for both the direct and reversed processes over the entire energy-angle plane within the energy ranges studied. Threshold energies for the He+Ni4 system above which the nuclear effects render the Rutherford cross sections invalid have been determined for the angles measured. The optical model was then again used to predict the thresholds for all scattering and recoil angles.
Cerium oxide nanoparticles: Size-selective formation and structure analysis
Authors: Zhang Feng , Chan Siu-Wai , Spanier Jonathan E. , Apak Ebru , Jin Qiang , Robinson Richard D. , Herman Irving P.
Published: July 2002

Nanoparticles of cerium oxide with a narrow size distribution (±15%) are prepared by mixing cerium nitrate solution with an ammonium reagent. High-resolution transmission electron microscopy (TEM) indicates that over 99% of the synthesized particles are single crystals. TEM and photon absorption are used to monitor particle size. The lattice parameter increases up to 0.45% as the particle size decreases to 6 nm, as observed with x-ray diffraction. Raman spectra also suggest the particle-size effect and concomitant lattice expansion. The lattice expansion can be explained by increased concentrations of point defects with decreasing particle size.
Two-dimensional quantum mechanical modeling of nanotransistors
Authors: Svizhenko A. , Anantram M. P. , Govindan T. R. , Biegel B. , Venugopal R.
Published: July 2002

Quantization in the inversion layer and phase coherent transport are anticipated to have significant impact on device performance in “ballistic” nanoscale transistors. While the role of some quantum effects have been analyzed qualitatively using simple one-dimensional ballistic models, two-dimensional (2D) quantum mechanical simulation is important for quantitative results. In this paper, we present a framework for 2D quantum mechanical simulation of a nanotransistor/metal oxide field effect transistor. This framework consists of the nonequilibrium Green’s function equations solved self-consistently with Poisson’s equation. Solution of this set of equations is computationally intensive. An efficient algorithm to calculate the quantum mechanical 2D electron density has been developed. The method presented is comprehensive in that treatment includes the three open boundary conditions, where the narrow channel region opens into physically broad source, drain and gate regions. Results are presented for (i) drain current vs drain and gate voltages, (ii) comparison to results from Medici, and (iii) gate tunneling current, using 2D potential profiles. Methods to reduce the gate leakage current are also discussed based on simulation results.
Drag force in the open-loop control of the cylinder wake in the laminar regime
Authors: Protas B. , Wesfreid J. E.
Published: July 2002

In this paper we are interested in identifying the physical mechanisms that accompany mean drag modifications in the cylinder wake flow subject to rotary control. We consider simple control laws where the obstacle rotates harmonically with frequencies varying from half to more than five natural frequencies. In our investigation we analyze the results of the numerical simulations at Re=150. All the simulations were performed using the vortex method, which in the paper is outlined and benchmarked. We confirm the earlier findings concerning mean drag reduction at higher forcing frequencies and show that for the considered values of Re this control technique is energetically inefficient. The main result is that changes of the mean drag are achieved by modifying the Reynolds stresses and the related mean flow correction. The controlled flows are carefully characterized in terms of these fields. Drag reduction is related to elongation of the recirculation bubble. It is argued that mean drag reduction is associated with control driving the mean flow toward the unstable symmetric state (the basic flow).
Generation of multimacroion domains in polyelectrolyte solutions by change of ionic strength or pH (macroion charge)
Authors: Sedlák Marián
Published: July 2002

Multimacroion domains in polyelectrolyte solutions were generated by decrease of ionic strength (sodium poly(styrenesulfonate) solutions) or by pH-induced increase of macroion charge (solutions of poly(acrylic acid)). Generation of domains was investigated by static and dynamic light scattering experiments in which scattering contributions from individual polyions (fast mode) and domains (slow mode) were separated such that amplitudes of both modes were expressed in absolute units. Both generation of domains in a fully homogeneous solutions (without domains) and growth of smaller domains already existing in solution were observed. An interesting feature of obtained results is that formation of domains was neither immediate nor gradual in many cases.
Magnetostriction of ternary Fe–Ga–X alloys (X=Ni,Mo,Sn,Al)
Authors: Restorff J. B. , Wun-Fogle M. , Clark A. E. , Lograsso T. A. , Ross A. R. , Schlagel D. L.
Published: July 2002

Investigations were made into the effect of small additions of Ni, Mo, Sn, as well as larger additions of Al on the magnetostriction of single crystal Fe100−xGax alloys (x≅13). The Fe–Ga and Fe–Al systems are seemingly unique among the Fe-based alloys in having very large magnetostrictions in spite of Ga and Al being nonmagnetic. In this paper, we show how additions of Ni, Mo, Sn, and Al affect λ100 and λ111 of the binary Fe–Ga alloys. We substituted small amounts of Ni into a binary Fe–Ga alloy in an attempt to reduce the magnitude of the negative λ111, as Ni does in Fe, in order to improve the magnetostriction of polycrystals. The measured λ111’s were reduced to a very small value, ∼3 ppm, but λ100 fell dramatically to +67 ppm for Fe86Ga11Ni3. Mo was substituted for Ga to determine the effect of a partially filled 4d shell on the magnetostriction. Here |λ111| is affected the most, increasing to a value greater than all known α-Fe-based alloys (λ111=−22 ppm for Fe85Ga10.2Mo4.8). We find that the addition of Sn, with its very large atomic radius, makes only small changes in both λ100 and λ111. For Fe86.1Ga12.4Sn1.5 at room temperature, λ100=+161 ppm and for Fe86.7Ga12.0Sn1.3, λ111=−15 ppm. The decrease of λ100 in Fe87(GayAl1−y)13 was approximately linear, going from 67 ppm at y=0 to 154 ppm at y=1.
Quantitative analysis of transition curvature by magnetic force microscopy
Authors: Liu Feng , Li Shaoping , Liu Yan , Gray George , Schultz Allan
Published: July 2002

A technique, based on magnetic force microscopy (MFM), has been developed to quantify the curvature of recording written transitions. By evaluating the phase deviation and coherence of MFM imaged recording tracks, the on-track transition curvature can be precisely measured to nanometer level or less while minimizing relevant imaging noise associated with MFM tips or recording media. The magnetization curvature properties are characterized quantitatively using the proposed technique at different recording conditions.
Structure of macrodomain walls in polytwinned magnets
Authors: Belashchenko K. D. , Antropov V. P.
Published: July 2002

We propose a microscopic approach to the studies of magnetic configurations in hard magnets which may be conveniently used for nanoscale systems; the microstructure of the magnet is easily and naturally included in the calculations. This approach is applied to find the structure of macrodomain walls in polytwinned magnets of the CoPt family. Magnetostatic fields are small compared to the anisotropy field in these magnets; direct simulation shows that in this case the macrodomain wall is not continuous, but rather comprised of segments held together by relatively small magnetostatic forces. This segmentation is expected to have a strong effect on magnetization processes.
Magnetic grain size reduction by using oxygen exposure process onto very thin islandlike WCr seedlayer in longitudinal recording media
Authors: Yoshimura S. , Djayaprawira D. D. , Takahashi M. , Mikami M. , Komiyama K. , Horii A. , Ohno A. , Katayama S.
Published: July 2002

To reduce the grain size and the media noise in CoCrPtB/CrMo longitudinal media, a sputtering process which includes the exposure of oxygen onto the surface of a very thin (0.5 nm) WCr50 seedlayer has been developed. The purpose of oxygen exposure onto the seedlayer surface is to enhance the nucleation sites of the seedlayer. It is found that (a) the exposure of 25 and 100 L (1 L corresponds to the adsorption of one layer of the oxygen atom when the sample is exposed to oxygen atmosphere) of oxygen onto the seedlayer reduces the mean grain diameter of the magnetic film from 8.3 to 7.5 and to 7.0 nm, respectively, (b) the exposure of 25 and 100 L of oxygen onto the seedlayer decreases the media noise by 15% and 45% and improves the media signal to noise ratio by 1.5 and 5 dB, respectively.
Formation process of nanocrystalline materials from x-ray diffraction profile analysis: Application to platinum catalysts
Authors: Ascarelli P. , Contini V. , Giorgi R.
Published: July 2002

It’s well known that x-ray line profile analysis is a powerful and convenient method to probe the microstructural characteristics of nanocrystalline samples. In the literature well-documented techniques are normally used to obtain crystalline size distributions from x-ray line-broadening analysis. However, it is less considered that the shape of such size distributions may be a means to determine by which mechanism the particles have grown. A simple method is presented here to distinguish between two different growth mechanisms: the coalescence and Ostwald ripening process. An application of the method to platinum nanoparticle electrocatalysts with different size distributions, dispersed on high-surface-area carbon blacks, is discussed.
A design of a two-phase permanent magnet vibration motor used for mobile phones
Authors: Chung Shi-Uk , Hwang Sang-Moon , Kim Tae-Jong , Hwang Gun-Yong , Kang Beom-Soo
Published: July 2002

With the advent of the telecommunications era, a mobile phone becomes a necessary communication device in modern society. However, a paging signal by a sound transducer often acts as an unpleasant noise, thus necessitating a paging signal by a vibration motor. The conventional flat type vibration motor uses three-phase windings with three phase coils. In this article, a new design of a vibration motor using a V connection with two phase coils is presented, increasing mass productivity. For electromagnetic field analysis, due to the motor symmetry, two-dimensional modeling can be implemented for fast computation, and performance is predicted by the finite element method. The winding distribution angle turns out to be the most important design parameter for the elimination of dead points, and a new coil configuration is suggested which has no adverse effect on motor size and weight. Experimental tests of vibration confirm the validity of the proposed design.
Study of interface structure of α-Fe/Nd2Fe14B nanocomposite magnets
Authors: Zhang X. Y. , Guan Y. , Zhang J. W.
Published: July 2002

In this study, the interface structure of α-Fe/Nd2Fe14B nanocomposite magnets has been investigated by employing both the positron lifetime spectroscopy and the two-detector Doppler broadening measurements of the positron–electron annihilation γ quanta. Positron lifetime studies show that there are two kinds of interface structures in the magnets. One characterized by a positron lifetime of 155 ps is determined to be the interfacial amorphous layer. The other has a slack atomic structure in which structural free volumes, which were detected to be predominantly surrounded by nonmagnetic atoms Nd and B by the Doppler broadening measurements, have a larger size than that of one to two lattice vacancies of Fe. This is believed to weaken the magnetic exchange coupling between α-Fe and Nd2Fe14B grains in the nanocomposites.
A novel technique to measure the Poisson’s ratio and submicron lateral dimensional changes of ultrathin polymeric films
Authors: Ma Tiejun , Bhushan Bharat , Murooka Hirofumi , Kobayashi Ieyasu , Osawa Toshifumi
Published: July 2002

A sensitive technique for measurement of lateral dimension of the ultrathin polymeric films is developed. By comparing width profiles at various loads, the lateral and longitudinal strains were obtained, and were used to get the Poisson’s ratio. Lateral dimensional changes at a very light load and a range of temperatures and relative humidities were used to measure coefficients of thermal and hygroscopic expansion. The Poisson’s ratio of standard polyethelene terephthalate (PET), tensilized PET, standard polyethelene terephthalate (PEN), tensilized PEN and supertensilized PEN were measured at 25 °C/15%RH, 25 °C/50%RH, 25 °C/80%RH, and 40 °C/50%RH. The data range from 0.29 to 0.47. It is found that tensilized films have a higher Poisson’s ratio than balanced films. The effects of temperature and humidity on the Poisson’s ratio are related to the materials’ molecular structure. An increase in temperature generally increases the Poisson’s ratio for the polymeric films. When relative humidity increases, the Poisson’s ratio of balanced films increases, while those of tensilized films remains constant or decreases slightly. The Poisson’s ratio is also affected by the stress magnitude that is used in the measurement; high stress usually results in a high Poisson’s ratio. By simultaneous loading and calibration, long term lateral dimensional deformation behavior of these films was studied. The results are consistent with the reported data measured by standard techniques.
Translational motion of a spherical bubble in an acoustic standing wave of high intensity
Authors: Doinikov Alexander A.
Published: July 2002

Using the Lagrangian formalism, coupled equations of radial and translational motions of a spherical gas bubble in an acoustic wave field are derived. The equation of radial motion is then modified, for the purpose of allowing for effects of liquid compressibility, using Keller–Miksis’ approach, and the equation of translation is added by the primary Bjerknes force and the viscous force in the form of the Levich drag. The resulting equations are solved numerically for the purpose of studying the translational motion of a bubble in a plane standing wave. It is shown that, if the acoustic pressure amplitude is high enough, a bubble driven below resonance, instead of moving to the pressure antinode as it does in a weak field, reciprocates about the pressure node plane. This result is of interest for an understanding of irregular bubble motions observed experimentally in strong acoustic fields.
A heterodyne refractometer for air index of refraction and air density measurements
Authors: Fang H. , Picard A. , Juncar P.
Published: July 2002

We briefly describe a heterodyne refractometer developed at the BIPM in collaboration with the BNM/INM conservatory. The heart of the refractometer, a double Fabry–Perot interferometer, is placed inside the balance case of a very sensitive 1 kg mass comparator, the FB2 balance. Comparisons between methods using refractometry and the NPL revised Edlén formulas, carried out for a period of nine months, yielded a difference in air index of refraction of 4×10−8 with a standard deviation of 1×10−8. The variation of air index of refraction was about 1.5×10−5 during the study. Precise determinations of the short-term and long-term stability of the Fabry–Perot cavity, made of Zerodur, were also achieved. For monitoring air density, results obtained with the refractometry method were compared with those deduced from two other methods: the CIPM formula for the density of moist air and the use of buoyancy artifacts. The response characteristics for the three determinations were comparable and the agreement among the air density determinations was within 1×10−5 kg m−3.
Obliquely propagating electron-acoustic solitary waves
Authors: Mamun A. A. , Shukla P. K. , Stenflo L.
Published: July 2002

A theoretical investigation is carried out for understanding the properties of obliquely propagating electron-acoustic solitary waves (EASWs) in a magnetized plasma whose constituents are a cold magnetized electron fluid, hot electrons obeying a vortex-like distribution, and stationary ions. It is found that the present plasma model supports EASWs having a positive potential, which corresponds to a dip (hump) in the cold (hot) electron number density. The effects of the external magnetic field and the obliqueness are found to significantly change the basic properties (viz. the amplitude and the width) of the EASWs. The present investigation can be of relevance to the electrostatic solitary structures observed in various space plasma environments (viz. the cusp of the terrestrial magnetosphere, the geomagnetic tail, the auroral regions, etc.).
Optical investigation of micrometer and nanometer-size individual GaN pillars fabricated by reactive ion etching
Authors: Demangeot F. , Gleize J. , Frandon J. , Renucci M. A. , Kuball M. , Peyrade D. , Manin-Ferlazzo L. , Chen Y. , Grandjean N.
Published: July 2002

We present an optical investigation of GaN pillars using both micro-Raman (μ-Raman) and microphotoluminescence (μ-PL) spectroscopy. GaN pillars of diameter ranging from 100 nm to 5 μm were fabricated by electron beam lithography and reactive ion etching (RIE) with SiCl4 plasma. Optical measurements of both μ-Raman and μ-PL on individual pillars show consistent variations in the properties of the fabricated GaN structures as a function of GaN pillar size. μ-PL mapping gives strong evidence for defect-induced donors and/or acceptors near the facets of the RIE etched pillars. RIE for the nanostructuration of GaN could be used in the future to allow spectroscopic studies of a few or single quantum objects such as GaN quantum dots.
Chemical bonding of nitrogen in low energy high flux implanted austenitic stainless steel
Authors: Riviere J. P. , Cahoreau M. , Meheust P.
Published: July 2002

AISI 304L austenitic stainless steel was implanted at 400 °C with 1.2 keV nitrogen ions using a high beam current density of 1 mA/cm2. The nitrogen depth profile, structure, and chemical composition in the modified surface layer were determined by nuclear reaction analysis (NRA) and x-ray diffraction (XRD). The chemical bonding of Fe, Cr atoms with nitrogen was investigated by x-ray photoelectron spectroscopy (XPS). For a treatment time of 1 h, the formation of a thick nitrided layer of about 3.5 μm with a high nitrogen content (∼20 at. %) is observed by NRA. The nitrogen depth profile is characterized by a nearly flat shape over a thickness of 2.5 μm followed by an abrupt decrease. XRD spectra show the formation in the nitrided layer of a phase usually called expanded austenite γN, which corresponds fairly well with a nitrogen solid solution of the fcc structure containing a high density of stacking faults. The XPS study of the Cr 2p3/2, Fe 2p3/2, and N 1s binding states indicate clearly the preferential bonding of chromium with nitrogen with a binding energy of about 1 eV. This value, which is lower than the expected one for chromium nitride CrN, would be characteristic of the binding energy of nitrogen with Cr in the γN expanded austenite phase. Moreover, it has been found that the atomic ratio N/Cr in the nitride layer deduced from both NRA and XPS is very close to 1. These experimental results support the specific role of chromium in the mechanisms of atomic transport of nitrogen over long distances at moderate temperature in austenitic stainless steels.
An extrapolation method for boundary conditions in lattice Boltzmann method
Authors: Guo Zhaoli , Zheng Chuguang , Shi Baochang
Published: July 2002

A boundary treatment for curved walls in lattice Boltzmann method is proposed. The distribution function at a wall node who has a link across the physical boundary is decomposed into its equilibrium and nonequilibrium parts. The equilibrium part is then approximated with a fictitious one where the boundary condition is enforced, and the nonequilibrium part is approximated using a first-order extrapolation based on the nonequilibrium part of the distribution on the neighboring fluid node. Numerical results show that the present treatment is of second-order accuracy, and has well-behaved stability characteristics.
Fluorine interaction with point defects, boron, and arsenic in ion-implanted Si
Authors: Mokhberi Ali , Kasnavi Reza , Griffin Peter B. , Plummer James D.
Published: July 2002

The role of fluorine in suppressing boron diffusion was investigated by utilizing a buried dopant marker to monitor the interaction of fluorine with interstitials. A boron spike with a peak concentration of 1.2×1018 cm−3 followed by 500 nm of undoped silicon was grown in a low pressure chemical vapor deposition furnace. The wafers were then preamorphized and implanted with either B, B and F, BF2, As, As and F, or F, respectively. Following the implants, the samples were rapid thermal annealed (RTA) at 1050 °C for very short times (spike). The use of preamorphization allows the chemical effect of fluorine to be analyzed independently of implant damage, and the buried layer functions as an indicator of point defect (in this case Si self-interstitial) perturbation. As expected, secondary ion mass spectroscopy shows that the presence of fluorine retards the diffusion of boron. In addition, the retained fluorine dose after the RTA is highest in the boron-implanted samples. In all samples the buried layer has diffused by the same amount, indicating that there is no change to the silicon self-interstitial population due to fluorine. These results suggest that fluorine has a chemical effect, and retards boron diffusion by mainly bonding with boron.
Ratio of deuterium to hydrogen termination on silicon surface in aqueous electrolyte solutions
Authors: Chikalova-Luzina Olga P. , Matsumoto Takahiro
Published: July 2002

The ratio of deuterium (D)- to hydrogen (H)-adatom concentrations on Si crystal surfaces in hydrogenated and deuterated electrolyte solutions was evaluated by the theory of the elementary act of proton transfer reactions. The result shows that the ratio is determined by the difference between configurational chemical potentials of the isotope reactants. In the temperature range of 273–373 K, the ratio is about 1 at steady-state conditions and somewhat lower at electrochemical equilibrium conditions, and decreases slowly as the temperature increases.
Characterizing strange nonchaotic attractors
Authors: Pikovsky Arkady S. , Feudel Ulrike
Published: July 2002

Strange nonchaotic attractors typically appear in quasiperiodically driven nonlinear systems. Two methods of their characterization are proposed. The first one is based on the bifurcation analysis of the systems, resulting from periodic approximations of the quasiperiodic forcing. Second, we propose to characterize their strangeness by calculating a phase sensitivity exponent, that measures the sensitivity with respect to changes of the phase of the external force. It is shown that phase sensitivity appears if there is a nonzero probability for positive local Lyapunov exponents to occur.
Determining the eigenvalues of a quaternion matrix with a band structure
Authors: Camarda H. S.
Published: July 2002

A Fortran program called QBAND has been developed which is capable of calculating the eigenvalues of relatively large quaternion matrices of dimension N≳10 000 with a band structure. For a quaternion band matrix with N=17 000 and bandwidth M=700, calculating eigenvalues with a general purpose program like the IMSL routine DEVLHF would require more than 2 Gbytes of random-access memory. QBAND, however, would need only 200 Mbytes of random-access memory. In addition, QBAND can be an order of magnitude faster than general purpose programs. Quaternion matrices are Hermitian but also have additional symmetries that were exploited to increase computational speed and to reduce computer memory requirements. QBAND reduces a band quaternion matrix of dimension N with M codiagonals to a Hermitian matrix with three codiagonals, and this three band matrix of dimension N forms the input to a routine called HBAND (previously discussed in this journal) which reduces a band Hermitian matrix to tridiagonal form. A standard routine can then be used to calculate the desired number of eigenvalues. Only the eigenvalues of the original matrix are calculated; eigenvectors are not determined. A simple application of QBAND, chosen to illustrate how a quaternion matrix arises and to demonstrate that QBAND calculates eigenvalues accurately, is presented by calculating the eigenvalues of a spin-1/2 particle confined to a circular two-dimensional box. Possible applications of QBAND to more complex problems are mentioned. © 1996 American Institute of Physics.
IMD—Software for modeling the optical properties of multilayer films
Authors: Windt David L.
Published: July 2002

A computer program called IMD is described. IMD is used for modeling the optical properties (reflectance, transmittance, electric-field intensities, etc.) of multilayer films, i.e., films consisting of any number of layers of any thickness. IMD includes a full graphical user interface and affords modeling with up to eight simultaneous independent variables, as well as parameter estimation (including confidence interval generation) using nonlinear, least-squares curve fitting to user-supplied experimental optical data. The computation methods and user interface are described, and numerous examples are presented that illustrate some of IMD’s unique modeling, fitting, and visualization capabilities. © 1998 American Institute of Physics.
Permeation characteristics of some iron and nickel based alloys
Authors: Mitchell Dean J. , Edge Ellen M.
Published: July 2002

The permeation characteristics of deuterium in several iron and nickel based alloys were measured by the gas phase breakthrough technique in the temperature range 100 to 500 °C with applied pressures ranging from 10 Pa to 100 kPa. The restriction of the gas flux imposed by surface oxides was modeled in order to evaluate the effects of surface oxide retardation of the gas flux on the effective values of the deuterium permeabilities and diffusivities in the alloys. The most permeable alloys were 430 and 431 stainless steels. The next most permeable alloy was Monel K-500, which exceeded the permeability of pure Ni by more than a factor of five at room temperature. The alloys with permeabilities less than pure Ni were, in order of decreasing permeability: the Inconels 625, 718, and 750, the Fe-Ni-Co glass-sealing alloys Kovar and Ceramvar, and the 300-series stainless steels. Deuterium trapping within the alloys appeared to influence the values of bulk diffusivities, which were not correlated with either the permeabilities or the chemical compositions of the alloys.
Effect of recombination on the open-circuit voltage of a silicon solar cell
Authors: von Roos Oldwig , Landsberg Peter T.
Published: July 2002

A theoretical study of the influence of band-band Auger, band-trap Auger, and the ordinary Shockley–Read–Hall mechanism for carrier recombination on the open-circuit voltage VOC of a solar cell is presented. Under reasonable assumptions for the magnitude of rate constants and realistic values for trap densities, surface recombination velocities and band-gap narrowing, we find the maximum VOC for typical back surface field solar cells to lie in the range between 0.61 and 0.72 V independent of base width.
Coagulation in processing of ceramic suspensions: Powder size distribution effects
Authors: Strauss M. , Ring T. , Bleier A. , Bowen H. K.
Published: July 2002

The origin of agglomerates in slips and slurries of ceramic particles due to particle size distribution effects is considered. Since agglomerates have been related to flaws in sintered ceramic bodies, the parameters which control coagulation of particles into agglomerates need to be defined. Computer calculations, based on Derjaguin, Landau, Verwey, and Overbeek theory, have been used to predict stability curves for particulate suspensions with log normal particle size distributions. Two regimes appear in the calculations: at width parameters (σz) corresponding to the inherent distribution of a powder the coagulation time decreases rapidly with increasing polydispersity; at larger σzs corresponding to mixing different sizes of powders to get very broad distributions the coagulation time decreases with increasing polydispersity. This change in behavior occurs at aproximately σz=1.0.
Electron-microscopic investigation of the morphology of a melt-crystallized polyaryletherketone
Authors: Lovinger Andrew J. , Davis D. D.
Published: July 2002

We have studied the structure and morphology of the useful high-temperature/high-strength polymer polyaryletherketone (PEEK) by transmission electron microscopy and three-dimensional electron diffraction after finding suitable solvents (α-chloronaphthalene and benzophenone) that allowed casting of the required ultrathin polymer films. When crystallized from the melt, PEEK grows in the form of spherulites consisting of narrow lamellae and having the b axis of the unit cell radial. Additionally, at high temperatures in these ultrathin films, the spherulites attain an extraordinary cylindrical symmetry as a result of growth of their lamellae on edge, with the c crystallographic direction parallel to the film plane and the a direction corresponding to the cylinder axis. Reasons for this mode of growth are attributed to the highly anisometric molecular cross section normal to the chain direction, which favors crystal nucleation on the substrate with the bc plane. At lower temperatures during crystallization from the melt, a more random lamellar disposition is seen in these thin-film spherulites, although lamellae on edge still predominate. Crystallization by heating from the quenched glassy phase yields random lamellar aggregates and small spherulites. The glassy phase in ultrathin PEEK shows no consistent morphological features down to a level of resolution of 1.0 nm. Scanning electron microscopic examination of the free surfaces of bulk samples crystallized under controlled conditions both from the melt and from the glass, show that our findings from ultrathin films (with the exception of the quasicylindrical spherulitic substructure) also apply to these thicker specimens.
Ternary Cd(Se,Te) alloy semiconductors: Synthesis, material characterization, and high-efficiency photoelectrochemical cells
Authors: Levy-Clement C. , Triboulet R. , Rioux J. , Etcheberry A. , Licht S. , Tenne R.
Published: July 2002

High-quality Cd(Se,Te) in two compositions were synthesized using the modified Bridgman technique. The Se-rich crystals had the hexagonal structure while the Te-rich phase consisted of crystals with cubic packing. Their quality could be gauged from the high-electron mobility and their low resistivity which suited the purpose of their synthesis, i.e., for high-efficiency photoelectrochemical cells. Photoelectrochemical etching was employed, which resulted in a heavily pitted surface with the density of the etch pits exceeding 109 cm−2. Quantum efficiency of the semiconductor/aqueous polysulfide interface increased considerably after photoetching. Solar to electrical conversion efficiencies in excess of 12% were obtained. Photoluminescence spectrum was measured for the two crystals prior to and after photoetching. The emission maximum is near the calculated band gap. The decline in the luminescence intensity, after photoetching, is attributed to the corrugation of the surface and the reduced density of the donor state near the semiconductor surface, which increases the thickness of the space-charge layer (dead layer model).