bluuebunny/crossref_metadata_2025 huggingface dataset:
Towards controlled production of specific carbon nanostructures— a theoretical study on structural transformations of graphitic and diamond particles
Authors: Hermann Helmut , Fugaciu Florin , Seifert Gotthard
Published: July 2002

Structural transformations of carbon nanoparticles are studied by means of molecular dynamics using a density-functional-based tight-binding method. The starting particles consist of 64 to 275 atoms arranged on a graphitic or diamond lattice. At elevated temperatures (1400 to 2800 K), the particles transform into spherical or elongated closed cages, concentric shell fullerenes, carbon nanotips, and spiraloidal and irregularly shaped clusters. The type of the final cluster depends essentially on the size and the atomic order of the starting particles, and on the temperature applied. The results show a way to proceed towards controlled preparation of specific carbon nanostructures.
Binary symmetry constraints of N-wave interaction equations in 1+1 and 2+1 dimensions
Authors: Ma Wen-Xiu , Zhou Zixiang
Published: July 2002

Binary symmetry constraints of the 𝒩-wave interaction equations in 1+1 and 2+1 dimensions are proposed to reduce the 𝒩-wave interaction equations into finite-dimensional Liouville integrable systems. A new involutive and functionally independent system of polynomial functions is generated from an arbitrary order square matrix Lax operator and used to show the Liouville integrability of the constrained flows of the 𝒩-wave interaction equations. The constraints on the potentials resulting from the symmetry constraints give rise to involutive solutions to the 𝒩-wave interaction equations, and thus the integrability by quadratures are shown for the 𝒩-wave interaction equations by the constrained flows.
Bend loss in surface plasmon polariton band-gap structures
Authors: Bozhevolnyi Sergey I. , Volkov Valentyn S. , Leosson Kristjan , Boltasseva Alexandra
Published: July 2002

Using near-field optical microscopy, we investigate propagation of surface plasmon polaritons (SPPs) excited in the wavelength range of 720–830 nm at a corrugated gold-film surface with areas of 200-nm-wide and 45-nm-high scatterers arranged in a 410-nm-period triangular lattice containing line defects with double bends. We find that, for ∼2-μm-wide line defects and the wavelength of ∼740 nm, the double bend losses for bend angles of 15° and 30° are below 2 and 10 dB, respectively. Our data indicate that the bend loss increases approximately quadratically with the bend angle. We also demonstrate splitting and combining of two SPP line-defect modes in a 20-μm-long Y junction.
Unbiased density functional solutions of freezing in binary mixtures of hard or soft spheres
Authors: Valera M. , Bielby R. F. , Pinski F. J. , Johnson D. D.
Published: July 2002

We investigated the freezing of equi-concentration binary hard or soft sphere mixtures for various size ratios, σ2/σ1, using density functional theory. The Grand Potential is minimized using an unbiased, discrete, real-space mesh that does not constrain the shape of the density, and, in many cases, leads to solutions qualitatively different from those using Gaussians and plane-waves. Besides the usual face-centered-cubic solid-solution phase for σ2/σ1≈1.0, we find a sublattice-melt phase for σ2/σ1=0.85–0.5 (where the small-sphere density is nonlocalized and multi-peaked) and the NaCl phase for σ2/σ1=0.45–0.35 (when the small-sphere density again sharpens). For a range of size ratios of soft sphere mixtures, we could not find stable nonuniform solutions. Preliminary calculations within a Modified-Weighted Density-Approximation suggest that such multiple-peaked solutions are not unique to a particular density functional theory.
Aluminum–barium interfaces on some processable poly(p-phenylene vinylene) polymers studied by photoelectron spectroscopy
Authors: Crispin A. , Jonsson A. , Fahlman M. , Salaneck W. R.
Published: July 2002

Control of the deposition of metals on the surfaces of conjugated polymers determines the electronic properties of the electrical contacts. The detrimental effects arising from the physical vapor deposition of metal atoms on conjugated polymer surfaces can be controlled by using a carefully chosen intermediate ultrathin layer of a “protection material.” In particular, the influence of an intermediate layer of barium atoms on the chemical effects that occur when aluminum atoms are deposited on the surfaces on substituted poly(p-phenylenevinylene)s has been studied using x-ray and ultraviolet photoelectron spectroscopy. In order to render the results somewhat more general, a series of substituted poly(p-phenylenevinylene)s was used, each with bulky side groups containing at least one oxygen atom, and the results presented are generalized beyond one particular substituted polymer system.
On the spectral shape of low-frequency excess scattering in Raman spectra of glasses
Authors: Novikov V. N. , Surovtsev N. V. , Kojima S.
Published: July 2002

The low-frequency Raman spectra of silica and lithium borate glasses in the frequency range 50–3000 GHz are analyzed. It is shown that the high frequency wing of the quasielastic excess scattering susceptibility has a significantly steeper slope than it is expected from any superposition of the Debye relaxations with different relaxation times. This rules out the possibility that the quasielastic Raman line arises due to the direct light scattering by relaxation centers. The predictions of the phonon-mediated quasielastic light scattering model are considered.
Simultaneously enhanced thermoelectric power and reduced resistivity of NaxCo2O4 by controlling Na nonstoichiometry
Authors: Motohashi T. , Naujalis E. , Ueda R. , Isawa K. , Karppinen M. , Yamauchi H.
Published: July 2002

Electrical resistivity (ρ) and thermoelectric power (S) were measured for NaxCo2O4 samples with various Na contents (x). A highly precise control of Na nonstoichiometry was facilitated by optimizing the synthesis procedure. With increasing x, the absolute value of ρ monotonically decreased, while the value of S increased. For the x=1.5 sample, S reached a value as high as ∼120 μV/K (at 300 K).
Ab initio molecular dynamics simulation of the Ag(111)-water interface
Authors: Izvekov Sergei , Voth Gregory A.
Published: July 2002

The results of a first-principles study of the structure of the Ag(111)–water interface are presented. The calculations were carried out using an ab initio Car–Parrinello molecular dynamics simulation within a pseudopotential formalism and the generalized gradient approximation to the exchange-correlation potential. Periodic five layer slabs covered with 48 water molecules were employed to simulate the structure of the interface. An analysis of the structural properties of the interface shows that the preferable places of residence of H2O molecules in the contact overlayer are the metal top sites. The electronic structure of the interface has also been explored. It was found that there is a strong coupling of the water overlayer with the metal crystal electronic states. However, the surface-state charge density is only slightly disturbed by the presence of water. The empty surface states are seen to not be quenched by the presence of water, which is in qualitative agreement with existing experiments. The electrons donated to the metal by the water fill the metal crystal electronic states, which is responsible for the dominant coupling of the metal with the water system.
Liquid-to-crystal nucleation: Automated lag-time apparatus to study supercooled liquids
Authors: Heneghan A. F. , Wilson P. W. , Wang Genmiao , Haymet A. D. J.
Published: July 2002

The statistics of liquid-to-crystal nucleation are studied using an automated lag-time apparatus. A single 500 μL sample of distilled water is repeatedly supercooled to a fixed temperature below its equilibrium freezing temperature, held until freezing occurred, and then thawed. Our raw data is then a set of approximately 300 lag-times for each of three set supercooling temperatures. In each case, a small insoluble AgI crystal was added to ensure heterogeneous nucleation and average nucleation temperatures around ΔT=8 K. The distribution of lag-times is analyzed, and shown to be well approximated by a single exponential decay, with average lag-times in the range of 1000–3000 seconds. This average lag-time decreases markedly at deeper levels of supercooling, and for the present data, this decrease is fit equally well by exponential, power law decay, and classical nucleation functional forms.
Polariton and free-exciton-like photoluminescence in ZnO
Authors: Reynolds D. C. , Look D. C. , Jogai B. , Collins T. C.
Published: July 2002

An unusual photoluminescence line X has been observed in ZnO at an energy between that of the common donor-bound excitons (DBEs) and the free excitons (FEs). In the presence of a high carrier concentration, induced by a second below-band gap laser, the DBEs decrease in intensity, due to screening, and both the FEs and X increase. Thus, X has free-exciton, rather than bound-exciton, character. However, its electric-field vector lies in the plane perpendicular to the c axis, as is also found for the DBEs. The appearance of X is discussed in terms of the polariton picture.
Electrical characterization of transparent p–i–n heterojunction diodes
Authors: Hoffman R. L. , Wager J. F. , Jayaraj M. K. , Tate J.
Published: July 2002

Transparent p–i–n heterojunction diodes are fabricated using heavily doped, p-type CuYO2 and semi-insulating i-ZnO thin films deposited onto a glass substrate coated with n-type indium tin oxide. Rectification is observed, with a ratio of forward-to-reverse current as high as 60 in the range −4–4 V. The forward-bias current–voltage characteristics are dominated by the flow of space-charge-limited current, which is ascribed to single-carrier injection into the i-ZnO layer. Capacitance measurements show strong frequency dispersion, which is attributed to i-ZnO traps. The diode structure has a total thickness of 0.75 μm and an optical transmission of ∼35%–65% in the visible region.
Indium-surfactant-assisted growth of high-mobility AlN/GaN multilayer structures by metalorganic chemical vapor deposition
Authors: Keller S. , Heikman S. , Ben-Yaacov I. , Shen L. , DenBaars S. P. , Mishra U. K.
Published: July 2002

AlN/GaN single and multilayer structures with various AlN and GaN layer thicknesses were grown by metalorganic chemical vapor deposition. Step flow growth of AlN was achieved using trimethylindium as a surfactant. Defect formation in the AlN layer could be largely prevented for AlN layers thinner than 2.9 nm. In the multiquantum-well samples, which consisted of five (AlN/GaN) periods, a two-dimensional electron gas (2DEG) was formed at the interface between the GaN base layer and the first AlN barrier layer. When the thickness of the AlN barrier layer in the multiquantum well was increased from 0.9 to 2.6 nm at a constant GaN well thickness of 5 nm, the sheet carrier density of the 2 DEG increased from 5×1012 to 2.1×1013 cm−2 and the electron mobility measured at 77 K decreased from 11780 to 3140 cm2/V s. The effect of the GaN well thickness was also investigated.
Mosaicity reduction during growth of heteroepitaxial diamond films on iridium buffer layers: Experimental results and numerical simulations
Authors: Schreck M. , Schury A. , Hörmann F. , Roll H. , Stritzker B.
Published: July 2002

Heteroepitaxial diamond films can be grown by bias enhanced nucleation on iridium buffer layers followed by an appropriate textured-growth step. Unlike epitaxial diamond films on silicon, the mosaicity reduction during textured growth includes tilt as well as twist. We conclude that different mechanisms causing the grain coarsening are working in the two cases. It is shown that the principle of evolutionary selection can be excluded as a decisive mechanism in the present films. Merging of neighboring grains by disclination formation yields an alternative explanation, that can convincingly substantiate the differences between the textured growth on iridium and silicon. From a Monte–Carlo type simulation describing the texture evolution due to merging of grains, a simple functional correlation between grain coarsening and mosaicity reduction is deduced. Comparison between simulation and experiment allows one to estimate the contributions of different processes. Finally, the general significance of the present findings for other materials is discussed.
Miniature Nernstian oxygen sensor for deposition and growth environments
Authors: van Setten E. , Gür T. M. , Blank D. H. A. , Bravman J. C. , Beasley M. R.
Published: July 2002

A miniature Nernstian-type oxygen sensor employing an ionically conducting stabilized zirconia solid electrolyte and an embedded internal reference electrode is developed and is tested in the temperature range 275–425 °C. It is intended for in situ monitoring of oxygen content in deposition and growth environments. Advantages of this sensor are in situ generation of the Ni/NiO two phase internal reference thin film electrode using a solid-state oxygen Coulometric titration technique, its small size (5 mm×10 mm), flat geometry (<1 mm thick), relatively low operating temperature, and the fact that the entire sensor can be immersed in the gaseous environment with the unknown oxygen content. The latter feature is distinctly different from commercially available Nernstian oxygen sensors, which employ two-compartment geometries. Depending upon temperature, the time constants for the sensor response to changes in oxygen pressure ranged from seconds to minutes, which is exceptionally fast for these moderately low temperatures. The small thermal mass and size of this single-compartment electrochemical sensor make it suitable for in situ and noninvasive real time monitoring of oxygen content during thin-film deposition or bulk growth of complex oxides.
Production of multiply charged fullerene and carbon cluster beams by a 14.5 GHz ECR ion source
Authors: Biri S. , Valek A. , Kenéz L. , Jánossy A. , Kitagawa A.
Published: July 2002

We report our first results on the study of normal and endohedral fullerene plasmas and beams produced by a 14.5 GHz electron cyclotron resonance (ECR) ion source (ECRIS). A mixed plasma of mainly N, N2, C, C2, and C60 was produced in the plasma chamber. Formation of caged nitrogens in the fullerene balls requires a careful, unusual tuning of the 14.5 GHz ECRIS. We deposited macroscopic quantities of the solid solution of N@C60 in C60 within the ECRIS. The N@C60/C60 ratio measured off-line using electron-spin-resonance spectroscopy may exceed typical values using conventional, non-ECR techniques. High intensities of C60Q+ ions (Q=1–5) were recorded in the extracted beam spectra. The highest measured C60+ beam current was 410 nA at 700 V extraction voltage. The method may be applied to produce carbon cluster beams from fullerenes, as well. We produced CnQ+ ions (n=2–15, Q=1,2) with intensities of 10–100 nA.
Remarkable lattice recovery and low sheet resistance of phosphorus-implanted 4H–SiC (112̄0)
Authors: Negoro Y. , Miyamoto N. , Kimoto T. , Matsunami H.
Published: July 2002

High-dose ion implantation of phosphorus into 4H–SiC has been investigated. Phosphorus ion implantation with a 1×1016 cm−2 dose at 800 °C into 4H–SiC (0001) has resulted in a sheet resistance of 80 Ω/□ after annealing at 1700 °C. A similar sheet resistance of 110 Ω/□ was achieved even by room-temperature implantation when 4H–SiC (112̄0) was employed, owing to excellent recrystallization of this face revealed by Rutherford backscattering channeling spectroscopy. The sheet resistance could be further reduced down to 27 Ω/□ by 800 °C implantation into 4H–SiC (112̄0) followed by annealing at 1700 °C. 4H–SiC (112̄0) showed a very flat surface after annealing.
The effect of reactor geometry on frontal polymerization spin modes
Authors: Pojman John A. , Masere Jonathan , Petretto Enrico , Rustici Mauro , Huh Do-Sung , Kim Min Suk , Volpert Vladimir
Published: July 2002

Using reactors of different sizes and geometries the dynamics of the frontal polymerization of 1,6-hexanediol diacrylate (HDDA) and pentaerythritol tetraacrylate (PETAC), with ammonium persulfate as the initiator were studied. For this system, the frontal polymerization exhibits complex behavior that depends on the ratio of the monomers. For a particular range of monomers concentration, the polymerization front becomes nonplanar, and spin modes appear. By varying the reactor diameter, we experimentally confirmed the expected shift of the system to a greater number of “hot spots” for larger diameters. For square test tubes a “zig–zag” mode was observed for the first time in frontal polymerization. We confirmed the viscosity-dependence of the spin mode instabilities. We also observed novel modes in cylinder-inside-cylinder reactors. Lastly, using a conical reactor with a continuously varying diameter, we observed what may be evidence for bistability depending on the direction of propagation. We discuss these finding in terms of the standard linear stability analysis for propagating fronts.
Magnetostriction and angular dependence of ferromagnetic resonance linewidth in Tb-doped Ni0.8Fe0.2 thin films
Authors: Russek Stephen E. , Kabos Pavel , McMichael R. D. , Lee C. G. , Bailey William E. , Ewasko Ricky , Sanders Steven C.
Published: July 2002

We present the dependence of the magnetostriction in Ni0.8Fe0.2 films on Tb and Gd doping concentration and compare with the measured doping dependence of the high-frequency damping. While the magnetostriction and the high-frequency damping are correlated, the dependence is complicated. In particular, the high-frequency damping parameter α increases rapidly (α=0.008–0.84) with a modest increase in the magnetostriction (λs=−0.6×10−6 to 5.7×10−6) for Tb doping concentrations up to 10%. For Gd doping, the high-frequency damping changes slowly (α=0.008–0.02) as the doping concentration is increased to 10%, whereas the increase in magnetostriction is similar to that observed in the Tb-doped films. Further, it is possible to achieve low magnetostriction (λs=2×10−6) near the region of critical damping. Measurements of the angular dependence of the ferromagnetic resonance linewidth in Tb-doped Ni0.8Fe0.2 films show little change similar to the behavior observed in undoped Ni0.8Fe0.2 films, although the linewidths are considerably larger. This is in contrast to systems such as Ni0.8Fe0.2 on NiO, which have a large angular dependence indicating that the relaxation process proceeds through the generation of spin waves. The enhanced damping in the Tb-doped films appears, therefore, to be mediated through direct phonon generation.
Magnetism and electronic structure in ZnFe2O4 and MnFe2O4
Authors: Singh D. J. , Gupta M. , Gupta R.
Published: July 2002

Density functional calculations are used to study magnetic and electronic properties of the spinel ferrites, ZnFe2O4 and MnFe2O4. Correct magnetic orderings are obtained. ZnFe2O4 is predicted to be a small gap insulator in agreement with experiment. MnFe2O4 is found to be a low carrier density half metal in the fully ordered state. However, strong effects on the electronic structure are found upon partial interchange of Fe and Mn atoms. This indicates that the insulating character may be due to Anderson localization associated with the intersite Mn–Fe disorder.
Self-sustained Maser oscillations of a large magnetization driven by a radiation damping-based electronic feedback
Authors: Abergel Daniel , Louis-Joseph Alain , Lallemand Jean-Yves
Published: July 2002

In this paper, the dynamics of a magnetization undergoing a radiation-damping based feedback radio-frequency field is investigated both theoretically and experimentally. It is shown that due to the presence of T1 relaxation the evolution equations predict the existence of self-sustained maser pulses. This phenomenon is a consequence of the competition between two different processes, namely, T1 relaxation and a precession about a magnetization-dependent radio-frequency field. Experiments show the existence of periodic revivals of the free induction decay over unusually long periods of time, on the order of tens of seconds.
Structural sensing using fluorescence nanotomography
Authors: Rolinski Olaf J. , Birch David J. S.
Published: July 2002

Fluorescence nanotomography is a newly developed experimental technique enabling determination of the molecular distributions with ångstrom resolution in complex structures such as soft solids, porous materials, and biomacromolecules. In this approach to structural sensing, Förster resonance energy transfer is used as the mechanism of detection of molecular separations, and fluorescence decay measurements with nanosecond resolution are used for determination of the molecular distribution function. Unlike the traditional Förster-type approach, wherein a model fluorescence decay function is derived for an assumed donor–acceptor distribution and then fitted to the experimental decay, returning the values of the parameters of assumed distribution, fluorescence nanotomography makes no a priori assumptions regarding the distribution function. In this paper we present the theoretical background of the method and demonstrate its applicability to various molecular systems by testing the method on artificial fluorescence decay data, generated for specific molecular structures.
Stabilizing unstable steady states using extended time-delay autosynchronization
Authors: Chang Austin , Bienfang Joshua C. , Hall G. Martin , Gardner Jeff R. , Gauthier Daniel J.
Published: July 2002

We describe a method for stabilizing unstable steady states in nonlinear dynamical systems using a form of extended time-delay autosynchronization. Specifically, stabilization is achieved by applying a feedback signal generated by high-pass-filtering in real time the dynamical state of the system to an accessible system parameter or variables. Our technique is easy to implement, does not require knowledge of the unstable steady state coordinates in phase space, automatically tracks changes in the system parameters, and is more robust to broadband noise than previous schemes. We demonstrate the controller’s efficacy by stabilizing unstable steady states in an electronic circuit exhibiting low-dimensional temporal chaos. The simplicity and robustness of the scheme suggests that it is ideally suited for stabilizing unstable steady states in ultra-high-speed systems.
Resonant modes in Nb baselayer interferometers with two Josephson junctions
Authors: Paternò G. , Cucolo A. M. , Modestino G.
Published: July 2002

Resonances in the current-voltage characteristics of interferometers with two Nb-NbOx-Pb window junctions have been experimentally investigated. The data are compared with the theoretical curves computed both for the voltage and for the magnetic field dependence of the resonance amplitudes. Very good agreement is found in all the range of values of the damping parameter Γ=I0 R/Vr, where Vr is the resonant voltage and I0 and R are the maximum Josephson current and the parallel resistance of each junction. New features that cannot be explained in terms of the existing theory have been observed in devices with larger values of the parameter β=2πLI0/Φ0, where L is the loop inductance, and Φ0 is the flux quantum.
Temperature considerations in the study of surfaces using a four-ball wear apparatus
Authors: Munro R. G.
Published: July 2002

The evolution and distribution of temperature have been studied theoretically for an idealized model of a four-ball wear-test apparatus which can be used to study macroscopic effects of surfaces interacting under frictional conditions. The finite-difference method was used to solve the coupled equations of heat generation, conduction, and cooling. Parameters were chosen to represent two types of material, a typical steel with relatively good thermal conductivity, and a ceramic with relatively poor thermal conductivity. Two values for the coefficients of friction were used to simulate dry and lubricated surfaces. A significant dependence on thermal conductivity was found.
Electron heating studies in silicon dioxide: Low fields and thick films
Authors: DiMaria D. J. , Fischetti M. V. , Arienzo M. , Tierney E.
Published: July 2002

Novel metal-oxide-semiconductor structures with very large areas have been used together with the vacuum emission and carrier separation techniques to study electron heating down to low fields (≊1 MV/cm) and out to large oxide thicknesses (5200 Å). At electric field magnitudes between 1.5 and 2.0 MV/cm, the threshold field for the onset of electron heating in silicon dioxide is observed. This onset is independent of oxide thickness and composition. Its value is consistent with all of the current theoretical calculations. At fields near threshold, a minimum average electronic energy of ≊1.0 eV is shown to be necessary to observe emission of the electrons into vacuum. Although the general trends in most of the data are approximately independent of oxide thickness out to 5200 Å, certain thick oxide samples with higher water content and lower physical density do show deviations from stabilization at higher fields, particularly in the vacuum emission experiments. Also, the data tend to appear ‘‘noiser’’ as the oxides become thicker. These apparently hotter electronic distributions are discussed in relationship to the proposed formation of microscopic channels in the oxide bulk.
Quantum confinement effects of semiconducting microcrystallites in glass
Authors: Borrelli N. F. , Hall D. W. , Holland H. J. , Smith D. W.
Published: July 2002

The optical properties of glasses containing a small amount of thermally developed CdSexS1−x microcrystalline phase are studied with emphasis on quantum confinement effects exhibited at small crystallite size. Optical absorption, photoluminescence, x-ray diffraction, and transmission electron microscopy are used to examine microcrystallites as a function of composition and development. Results are presented for a series of commercially available CorningR filter glasses with a selenium mole fraction in the range 0.28≤x≤0.74, as well as for several experimental glasses in which the average microcrystallite diameters range from 30 to 80 Å. Optical effects observed in the experimental glasses that are due to electron and hole confinement are not present in the filter glasses considered; variations in optical properties of the filters are due to changes in stoichiometry of the CdSexS1−x mixed anion system. A brief discussion of other microcrystalline phases in glass is also presented. These microcrystallites show room-temperature optical absorption structure analogous to bulk crystal excitons; the temperature dependence of this structure is contrasted with that resulting from quantum confinement in CdSexS1−x glasses.
A chromogenic limulus test for detection of microbes that decreases the laser damage threshold of potassium dihydrogen phosphate crystals
Authors: Yokotani A. , Nishida Y. , Fujioka K. , Sasaki T. , Yamanaka T. , Yamanaka C.
Published: July 2002

The chromogenic limulus test has been applied for the first time to detect an organic impurity contained in potassium dihydrogen phosphate (KDP) crystals. Impurities arise from microbes present during crystal growth, and are responsible for a reduced laser damage threshold. A sensitivity of 10 pg/g KDP (10−5 ppm) was achieved, provided that the KDP solution was neutralized to ∼pH 7. Endotoxin content in the prismatic region of KDP crystals grown in a microbe-rich solution was approximately 100 pg/g KDP. The presence of an organic material in seemingly perfect KDP crystals could be experimentally confirmed.
Refinements in the method of moments for analysis of multiexponential capacitance transients in deep-level transient spectroscopy
Authors: Ikossi-Anastasiou K. , Roenker K. P.
Published: July 2002

The analysis of multiexponential capacitance transients that arise in deep-level transient spectroscopy has been examined. The method of moments, a technique that provides a reliable method for resolution of a multiexponential capacitance transient into its exponential components, has been adapted and enhanced by incorporating an initial fast Fourier transform to extract the base-line offset, and a refinement in the cutoff correction to the moments integrals which improves convergence and accuracy. In addition, the mean displaced ratio smoothing algorithm has been incorporated and shown to improve the method’s accuracy in the presence of noise. For the case where the response is not significantly convoluted with the excitation, a simplified form of the method of moments technique provides a simple and more direct determination of the exponential components. Examples of results for simulated data are provided illustrating application of the analysis. The limitations of the technique in determining the number of exponential components, their amplitudes and emission rates, and the applicability of the smoothing algorithm are discussed.
A mechanism of deformation and recrystallization texture changes in grain-oriented silicon steel sheets
Authors: Li Zhen-Chuan , Lü Qi-Chun , He Zhong-Zhi
Published: July 2002

Deformation and recrystallization textures as well as orientation dependence of lattice strain energy in two kinds of the grain-oriented silicon steel sheets with MnS and MnS+AlN precipitates as inhibitors have been investigated by means of x-ray diffraction techniques. Orientation relations corresponding to the textural changes that occurred during primary recrystallization have also been calculated. According to a model of the textural changes concurrently controlled by the stored energy differences and the orientation differences, the textural changes and mathematical relations have been deduced. A qualitative coincidence between the theoretical analysis and experimental results indicated that the mechanism of deformation and recrystallization texture changes in the grain-oriented steel sheets is mainly a preferred growth process controlled in common by the stored energy difference and the orientation difference.
Oxygen precipitation and bulk microdefects induced by the pre- and postepitaxial annealing in N/N+(100) silicon wafers
Authors: Wijaranakula W. , Matlock J. H. , Mollenkopf H.
Published: July 2002

Substrate wafers used for fabrication of epitaxial silicon wafers heavily doped with antimony at the concentration of 1020 atoms/cm3 were preannealed at a temperature between 500 and 900 °C prior to epitaxial deposition. Device fabrication thermal simulation was performed by heat treating the preannealed epitaxial wafers at 1050 °C in dry oxygen ambient for 16 h. Postepitaxial nucleation heat treatment at 750 °C for 4 h prior to the 1050 °C heat treament cycle was also applied on some epitaxial wafers for the purpose of enhancing the oxygen precipitation in silicon. It was observed that morphology and density of the bulk defects induced by the thermal treatment are affected by the preannealing temperature. The results also indicate that nucleation and growth kinetics of oxygen precipitates in preannealed n+ degenerate silicon substrate is strongly governed by oxygen and point defect diffusion.
Comparison of minority-carrier diffusion length measurements in silicon by the photoconductive decay and surface photovoltage methods
Authors: Saritas Müzeyyen , McKell Harry D.
Published: July 2002

Diffusion lengths of minority carriers in the range 50–1200 μm were measured in n- and p-type silicon single crystals with a wide range of resistivities by the surface photovoltage (SPV) and photoconductive decay (PCD) methods. Previously published values for the optical absorption coefficient of Si differed sufficiently to result in a substantial uncertainty in the minority-carrier diffusion length determined by the SPV method. In order to minimize the uncertainty in diffusion length values obtained by the SPV method, the optical absorption coefficient of Si was measured in the wavelength interval 0.8≤λ≤1.16 μm [M. Saritas and H. D. McKell, J. Appl. Phys. 61, 4923 (1987)]. When our absorption coefficient data were used, the diffusion lengths measured by the SPV and PCD methods were found to be in agreement.
Optical remote sensing system for hydrocarbon gases using infrared fibers
Authors: Saito M. , Takizawa M. , Ikegawa K. , Takami H.
Published: July 2002

An infrared optical fiber made of As2S3 glass has been applied for remote sensing of hydrocarbon gases. The fiber has enabled a transmission of the radiation at 3.39-μm wavelength, where hydrocarbon molecules have strong absorption bands. Using a 3.39-μm He-Ne laser as a light source, an effective remote sensing system has been established. A detection limit of the gas concentration is ∼300 ppm for CH4 gas, which is ∼0.6% of the lower explosion limit. The system is also expected as a pressure monitor since it is highly sensitive to the gas pressure.
On the effective conductivity of polycrystals and a three-dimensional phase-interchange inequality
Authors: Avellaneda M. , Cherkaev A. V. , Lurie K. A. , Milton G. W.
Published: July 2002

We derive optimal bounds on the effective conductivity tensor of polycrystalline aggregates by introducing an appropriate null-Lagrangian that is rotationally invariant. For isotropic aggregates of uniaxial crystals an outstanding conjecture of Schulgasser is proven, namely that the lowest possible effective conductivity of isotropic aggregates of uniaxial crystals is attained by a composite sphere assemblage, in which the crystal axis is directed radially outwards in each sphere. By laminating this sphere assemblage with the original crystal we obtain anisotropic composites that are extremal, i.e., attaining our bounds. These, together with other results established here, give a partial characterization of the set of all possible effective tensors of polycrystalline aggregates. The same general method is used to prove a conjectured phase interchange inequality for isotropic composites of two isotropic phases. This inequality correlates the effective conductivity of the composite with the effective tensor when the phases are interchanged. It leads to optimal bounds on the effective conductivity when another effective constant, such as the effective diffusion coefficient, has been measured, or when one has information about ζ1 which is a parameter characteristic of the microgeometry, or when one knows the material is symmetric, i.e., invariant under phase interchange like a three-dimensional checkerboard.
Entropy optimization in quantitative texture analysis
Authors: Schaeben H.
Published: July 2002

The mathematical model of entropy optimization is introduced into texture goniometry to provide a solution of the problem of quantitative texture analysis, i.e., of reproducing an orientation distribution function from its corresponding experimental pole distribution function data.
Helicity modulus behavior of a frustrated X
Y model
Authors: Granato Enzo , Kosterlitz J. M.
Published: July 2002

A frustrated XY model on a square lattice with unequal ferromagnetic and antiferromagnetic bonds is considered. This model can be related, via a Landau–Ginzburg expansion and renormalization-group arguments, to a coupled XY-Ising model. We use this relation to show that, at the Ising transition, the helicity modulus has a logarithmic singularity and its temperature derivative diverge logarithmically. Preliminary results of Monte Carlo simulations in the original model are consistent with this.
Impact of copper contamination on the quality of silicon oxides
Authors: Wendt H. , Cerva H. , Lehmann V. , Pamler W.
Published: July 2002

To study the impact of metal contamination on the quality of gate oxides, (100) silicon wafers were intentionally contaminated with copper from the backside. The in-diffusion of copper and/or oxidation were performed in a rapid thermal annealing system. Gate oxide areas with low breakdown fields of about 2–3 MV/cm were located in a pinhole detector and correlate very well with the contaminated areas revealed by Secco defect etching. Using various analytical tools the failure mechanism was found to be related to the formation of Cu-rich precipitates at the SiO2/Si interface. Depending on the in-diffusion temperature (and hence on the supersaturation of Cu in Si), two different mechanisms were observed: At high supersaturation (1200 °C/30 s) Cu-rich silicide particles can bend, crack, and finally penetrate the oxide layer. At lower in-diffusion temperatures (900 °C/60 s) lens-shaped Cu silicides form at the SiO2/Si interface and reduce the oxide thickness.
Titanium dioxide dielectric films formed by rapid thermal oxidation
Authors: Burns G. P.
Published: July 2002

High dielectric constant titanium dioxide thin films have been formed on silicon substrates by the rapid thermal oxidation of evaporated titanium. Oxidation of titanium at temperatures between 450 and 800 °C for periods of 1–60 s has been studied. Rutile polycrystalline layers of 800–2000 Å thickness were formed. Dielectric constants were in the range of 58–77 for titanium dioxide on silicon. High oxidization temperatures gave leakage currents of 10−7 A at 0.3 MV cm−1 for a 1500-Å-thick layer, and potential is seen for improved results with thinner layers.
Effect of oxidation-induced stacking faults on dielectric breakdown characteristics of thermal silicon dioxide
Authors: Shirai Hideki , Kanaya Kotaro , Yamaguchi Akira , Shimura Fumio
Published: July 2002

The dielectric breakdown characteristics of thermal silicon dioxide has been qualitatively and quantitatively correlated with grown-in and thermally induced defects in Czochralski silicon wafers. It is shown that grown-in latent stacking faults and SiO2 precipitates have little effect on oxide integrity, but stacking faults without any involvement of metallic impurities greatly degrade oxide integrity. Although more stacking faults can result in poorer oxide integrity, the correlation between oxide breakdown degradation and stacking fault density is not straightforward.
Submicron nickel-oxide-gold tunnel diode detectors for rectennas
Authors: Hoofring A. B. , Kapoor V. J. , Krawczonek W.
Published: July 2002

Integrated circuit technology has been successfully applied to the design and fabrication of submicron metal-oxide-metal (MOM) tunneling diodes for application in far infrared (FIR) rectennas. The MOM diode and a stripline antenna to enhance collection of FIR radiation were integrated on a silicon substrate using state of the art microelectronic technology and were produced simultaneously. A nickel-oxide-gold MOM tunnel diode was made up of a 0.8-μm-wide nickel layer with approximately 22 Å of a nickel-oxide tunnel barrier layer on top crossed by a 0.8-μm-wide gold layer resulting in a junction area of 0.64 μm2 . The antenna consisted of two 0.8-μm-wide and 6.6-μm-long parallel metal conductors, one nickel and the other gold, separated by a gap of 0.8 μm. The dc current-voltage characteristics of the MOM diode showed that the current dependence on voltage was linear about zero bias up to a bias of about 70 mV. Beyond 70 mV, the characteristics were very nonlinear. The average breakdown field was determined to be 6.6×106 V/cm for nickel-oxide film thicknesses ranging from 15 to 39 Å. The current stressing of the MOM diode produced charge trapping within the nickel-oxide layer. The maximum detection of a low level signal (10-mV ac) was determined to be at a dc voltage of 70 mV across the MOM diode using rectifier current sensitivity measurements. The rectified output signal due to a chopped 10.6-μm CO2 laser incident upon the rectenna device was found to increase with dc bias with a maximum value of 1000 nV for a junction bias of 100 mV at room temperature.
Reactions of atomic nitrogen and trimethyl aluminum downstream from a nitrogen microwave plasma
Authors: Meikle Scott , Nomura Hideaki , Nakanishi Yoichiro , Hatanaka Yoshinori
Published: July 2002

The feasibility of aluminum nitride thin-film deposition from chemical reactions of trimethyl aluminum (TMA) with active nitrogen downstream from a N2 microwave plasma has been investigated. Chemiluminescence spectra of the downstream reaction showed the presence of CN and Al and the luminescence has been proposed to result from reactions between atomic nitrogen and methyl groups of the TMA. From nitrous oxide titration measurements of the atomic nitrogen concentration, the reaction rate constant has been estimated to be k=3×10−12 cm3  s−1. Auger and infrared absorption spectroscopy measurements of a typical film indicated that AlN with carbon contamination in the form of CN had formed.
A broken-bond model for grain boundaries in face-centered cubic metals
Authors: Wolf D.
Published: July 2002

The interrelation between the number of nearest-neighbor atomic bonds broken upon formation of a grain boundary in an fcc metal and the related zero-temperature boundary energy is investigated by atomistic simulation. Using both a Lennard–Jones and an embedded-atom-method potential, the structures and energies of symmetrical and asymmetrical tilt and twist boundaries are determined. As in free surfaces, a practically linear relationship between the nearest-neighbor miscoordination per unit area of the grain boundary and the related interface energy is obtained. The so-called random-boundary model, in which the interactions across the interface are assumed to be entirely randomized, is shown to provide a basis for understanding the role of broken bonds in both high-angle grain boundaries and free surfaces, thus naturally permitting the analysis of ideal cleavage-fracture energies. A detailed study of low-angle boundaries shows that only the dislocation cores—but not their strain fields—give rise to broken bonds. The complementarity between the dislocation model of Read and Shockley for low-angle boundaries and a broken-bond model for high-angle boundaries is thus elucidated.
High reverse voltage amorphous silicon p-i-n diodes
Authors: Pochet T. , Dubeau J. , Equer B. , Karar A. , Hamel L. A.
Published: July 2002

New types of a-Si:H p-i-n diodes, capable of sustaining high reverse electric fields up to 6×105 V/cm with very low leakage currents, have been designed specifically for charged particle detection. Because of the low hole mobility and lifetime in this type of material, very high applied fields are required to collect a large fraction of the charge carriers generated by an ionizing particle. Since the leakage current is shown to be essentially due to electron tunneling through the p-doped layer, the new design includes a thicker p layer (300 nm) at the expense of an increased surface leakage current. An appropriate etching of the top doped layer around the electrode is then required to eliminate such currents. A model, taking into account the doped layer conductivities, is presented to roughly compare the reverse current-voltage characteristics of the samples before and after etching.
Magnetoresistance origin for nonresonant microwave absorption in antiferromagnetically coupled epitaxial Fe/Cr/Fe(001) sandwiches
Authors: Krebs J. J. , Lubitz P. , Chaiken A. , Prinz G. A.
Published: July 2002

Nonresonant microwave-absorption signals have been observed in a series of molecular-beam-epitaxy-grown Fe/Cr/Fe (001) sandwiches which were previously shown to exhibit an antiferromagnetic coupling of the two Fe layers. Using field-modulation detection, one observes signals which display an unusual magnetic-field dependence containing sharp features in the range 0–2 kOe. The magnetic-field locations of these features are independent of the microwave frequency, but their intensity depends strongly on the field-modulation amplitude. The features also have a strong in-plane angular dependence. Comparison with earlier magnetization and magnetoresistance data on the same samples shows that a sharp feature occurs when the magnetization orientations in the Fe films change abruptly, and that one can explain the microwave-absorption signals in terms of magnetoresistance effects in the sandwich. Thus, microwave absorption provides a contactless way to investigate the magnetoresistance in such samples.
Electrically neutral nitrogen dangling-bond defects in amorphous hydrogenated silicon nitride thin films
Authors: Warren W. L. , Lenahan P. M. , Kanicki J.
Published: July 2002

We have investigated the effects of different post-deposition temperature anneals and N-H concentrations, on the generation of ultraviolet (UV)-induced two-coordinated nitrogen dangling bonds in plasma-enhanced chemical vapor deposited (PECVD) silicon nitride films using electron spin resonance (ESR). It is shown that the nitrogen dangling bond is activated by post-deposition anneals with temperatures as low as 500 °C in N-rich PECVD nitride films followed by subsequent UV broadband illumination. It also appears that there is a possible correlation between the initial N-H concentration in the films and the concentration of generated nitrogen dangling bonds following the anneal/UV sequence. We also report the charge state associated with the nitrogen dangling bond using a combination of ESR and capacitance versus voltage measurements; these measurements suggest that this two-coordinated defect is electrically neutral when paramagnetic.
Wet oxidation of GeSi at 700 °C
Authors: Liu W. S. , Lee E. W. , Nicolet M-A. , Arbet-Engels V. , Wang K. L. , Abuhadba N. M. , Aita C. R.
Published: July 2002

About 500-nm-thick films of Ge0.36Si0.64 and Ge0.28Si0.72 grown epitaxially on (100)Si have been oxidized at 700 °C in wet ambient. A uniform GexSi1−xO2 oxide layer forms with a smooth interface between it and the unoxidized GexSi1−x layer below. The composition and structure of that layer remains unchanged as monitored by backscattering spectrometry or cross-sectional transmission electronic microscopy. The oxide of both samples grows as square root of oxidation duration. The parabolic rate constant increases with the Ge content and is larger than that for wet oxidation of pure Si at the same temperature. The absence of a regime of linear growth at this relatively low temperature indicates a much enhanced linear rate constant.
The electro-optic coefficients of GaAs: Measurements at 1.32 and 1.52 μm and study of their dispersion between 0.9 and 10 μm
Authors: Berseth C.-A. , Wuethrich C. , Reinhart F. K.
Published: July 2002

The linear (r41) and quadratic (R11 and R12) electro-optic coefficients of GaAs have been measured at the wavelengths 1.32 and 1.52 μm using single-mode AlGaAs/GaAs strip-loaded waveguides. The results are r41=−(1.54±0.08)×10−10 cm/V, R11=−(9.3±2.8)×10−17 cm2/V2 and R12=−(5.1±l.9)×10−17 cm2/V2 at 1.32 μm and r41=−(1.50±0.08)×10−10 cm/V, R11=−(3.2±2.3)×10−17 cm2/V2 and R12=−(5.1±2.6)×10−17 cm2/V2 at 1.52 μm. These results, together with those previously measured at different wavelengths, are compared with published theoretical models. The linear electro-optic coefficient r41 is slightly dispersive near the band gap and roughly constant for longer wavelengths, in good agreement with the models. The quadratic electro-optic coefficients drop rapidly with increasing wavelength, in good agreement with a model based on electroabsorption.
Temperature dependence of coercivity in MnBi
Authors: Guo X. , Chen X. , Altounian Z. , Ström-Olsen J. O.
Published: July 2002

In contrast to most ferromagnetic materials, the low-temperature phase of MnBi exhibits an increased coercivity, Hc, with temperature. μ0Hc has a value of 0.2 T at room temperature, and rises dramatically to a maximum value of 1.9 T at 550 K. In the temperature region near its maximum value, Hc is much larger than that of Nd-Fe-B and has a very-low-temperature coefficient. For this reason, MnBi has a great potential as a permanent magnet material at high temperatures. To describe the temperature dependence of Hc, we develop a hybrid domain-wall pinning model which combines Hilzinger and Kronmüller’s scaling theory for an anisotropic domain wall with Gaunt’s theory of thermal activation. The hybrid model gives an excellent fit to the temperature dependence of Hc and provides good estimates for the domain-wall energy and thickness over the temperature range studied.