bluuebunny/crossref_metadata_2025 huggingface dataset:
Bifurcations in biparametric quadratic potentials
Authors: Lanchares V. , Elipe A.
Published: July 2002

Numerous dynamical systems are represented by quadratic Hamiltonians with the phase space on the 𝒮 2 sphere. For a class of these Hamiltonians depending on two parameters, we analyze the occurrence of bifurcations and we obtain the bifurcation lines in the parameter plane. As the parameters evolve, the appearance–disappearance of homoclinic orbits in the phase portrait is governed by three types of bifurcations, the pitchfork, the teardrop and the oyster bifurcations. We find that the teardrop bifurcation is associated with a non-elementary fixed point whose Poincaré index is zero.
A unifying definition of synchronization for dynamical systems
Authors: Brown Reggie , Kocarev Ljupčo
Published: July 2002

We propose a unifying definition for synchronization between stationary finite dimensional deterministic dynamical systems. By example, we show that the synchronization phenomena discussed in the dynamical systems literature fits within the framework of this definition, and discuss problems with previous definitions of synchronization. We conclude with a discussion of possible extensions of the definition to infinite dimensional systems described by partial differential equations and/or systems where noise is present.
Evaluation of diffusion length and surface-recombination velocity from a planar-collector-geometry electron-beam-induced current scan
Authors: Kuiken H. K. , van Opdorp C.
Published: July 2002

For performing electron-beam-induced current (EBIC) measurements on sufficiently large samples, the use of a ‘‘planar-collector geometry’’ (i.e., with the collector covering part of the irradiated surface itself) is very attractive. However, the pertinent theoretical EBIC curves for finite surface-recombination velocities s have so far been lacking. This paper presents the complete theoretical expressions for arbitrary values of s and diffusion length L. Simple asymptotic solutions are given for point- and finite-size generation sources. Easy methods are developed to facilitate the application of these solutions in the practical evaluation of L and s from experimental EBIC curves. These methods are applied to experimental data available through the literature.
Plasma etching in a multipolar discharge
Authors: Wicker T. E. , Mantei T. D.
Published: July 2002

Etching of silicon and SiO2 has been investigated in a dc plasma discharge confined by a multipolar surface magnetic field layer. The reactive plasma is produced by primary ionizing electrons drawn from heated tungsten filaments and confined by permanent magnets. Electrical probe measurements show that a uniform high-density plasma (1010–1011 cm−3) is sustained in SF6-O2 at very low pressure (0.2–2.0×10−3 Torr). Substrates are biased independently of plasma production by a low-frequency alternating voltage (0–400 V) applied to the substrate through a blocking capacitor. Anisotropic profiles are etched into Si in SF6-20% O2 with etch rates in excess of 1 μm/min at 2×10−3 Torr. The etch rate increases with increasing primary electron current (up to 3 A) and energy (up to 60 eV), gas pressure (up to 2.0×10−3 Torr), substrate bias voltage, and the addition of up to 20% O2. For higher ionizing electron energies (>60 eV) and higher gas pressure (>2.0×10−3 Torr), etching is partially blocked by residue formation. The etch anisotropy depends mainly on substrate bias, increasing for higher values of bias voltage. The Si:SiO2 etch selectivity is typically 10–20, becoming large with decreasing substrate bias and plasma ion density.
Angular dispersion of ‘‘backward’’ Raman scattering: Weakly absorbing cubic materials (Si)
Authors: Anastassakis Evangelos , Raptis Yannis S.
Published: July 2002

We have shown that the angular distribution of Raman scattering power from the surface of diamond-type opaque materials can be adequately described by use of classical optics. It turns out that within the commonly-used nearly backward scattering geometries there are significant variations of the scattered power due to purely geometrical factors. Only crystals with small extinction coefficients are considered. Families of curves for the scattered power are derived in terms of the angles of incidence and detection and of the index of refraction for three of the most widely-used crystal orientations. The analysis reveals the optimum scattering configuration for a given geometrical situation and provides a quantitative measure for the deviation from the selection rules when a ‘‘backward’’ geometry for forbidden scattering is less than exact. The importance of incidence and/or detection at the Brewster angle is examined. The experimental data obtained in Si are consistent with the theoretical predictions. The applicability of these results to other situations is discussed.
UFe4P12 and CeFe4P12: Nonmetallic isotypes of superconducting LaFe4P12
Authors: Meisner G. P. , Torikachvili M. S. , Yang K. N. , Maple M. B. , Guertin R. P.
Published: July 2002

The new compound UFe4P12, which was found to be isostructural to superconducting LaFe4P12 and have a lattice constant of 7.7729 Å, is a semiconductor and shows ferromagnetic order below 3.15 K. CeFe4P12 is also a semiconductor, and its magnetic susceptibility is unusually small in comparison to LaFe4P12. The semiconducting behaviors of both UFe4P12 and CeFe4P12 seem anomalous and may arise from strong f-electron hybridization.
Upper critical fields of superconducting Nb3Ge films
Authors: Suzuki Mitsumasa , Anayama Takeshi , Kido Giyuu , Nakagawa Yasuaki
Published: July 2002

The upper critical field Hc2 (4.2 K) of superconducting Nb3Ge films prepared by sputtering and chemical vapor deposition (CVD) has been measured in a pulsed field. The Hc2 of these films is generally related to their superconducting critical temperature Tc. Sputtered films exhibit a linear increase of Hc2 from 25.4 to 33.3 T for a Tc range 18.6–21.3 K. Although the data of CVD-prepared films are scattered due to nonuniformity in the films, a similar dependence of Hc2 on Tc has been found.
Antiferromagnetism and metal-semiconductor transition in iron sulfides FeSx, 1≤x<1.25
Authors: Sakkopoulos S.
Published: July 2002

An explanation of the semiconductor-to-metal transition in iron sulfides FeSx1≤x<1.25 at the β transformation temperature Tβ is given, based on the splitting of a half-filled impurity band by the antiparallel arrangement of the magnetic moments on the iron atoms on successive cation layers in these compounds. This impurity band originates from the energy levels associated with dislocations and lattice defects, mainly Fe vacancies. For TTβ, the antiparallel arrangement of the atomic magnetic moments ceases to exist and the impurity band as a whole bridges completely the energy gap between the valence and conduction bands, giving metallic properties to the sulfides.
Rate of heat conduction from a heated sphere to a matrix containing passive spheres of a different conductivity
Authors: Chang Eric , Acrivos Andreas
Published: July 2002

Using a multipole expansion scheme, we calculate the rate of heat conduction Q from a heated sphere with constant surface temperature to a matrix of conductivity k, containing a dilute dispersion of equal-sized passive spheres of conductivity αk, and whose temperature far away from the heated sphere vanishes. Values are presented for Q for various choices of α and λ, the ratio of the radius of a passive sphere to that of the heated sphere, and asymptotic expressions are derived for the cases λ≪1 and λ≫1, respectively. When the passive spheres are very small compared to the heated sphere, the composite can be viewed as an effective continuum on the length scale of the latter with an effective thermal conductivity relative to the matrix given by Maxwell’s expression, k*=1+3βc, where β=(α−1)/(α+2) and c is the inclusion volume fraction assumed to be small. We find, however, that this effective continuum approach can still be applied with a surprising degree of accuracy over the whole range of α even when λ is as large as O(10), provided that the effective thermal conductivity is allowed to vary with r, the distance from the center of the heated sphere, according to the expression k*≡1+3βρ(r), where ρ(r) denotes the probability that a point in the composite lies within a passive sphere. It is shown, furthermore, that this effective continuum approach becomes exact to O(α−1) for all λ.
A novel perturbation approach to dielectric measurements
Authors: Deri R. J.
Published: July 2002

A new cavity perturbation method for measuring dielectric properties is demonstrated. Transmission line theory is used to analyze a typical cavity perturbation experiment and show that waveguide impedances can be measured by standard resonator techniques. Cavity perturbation measurements of the impedance of a dielectric post provide a useful method for determining dielectric properties, particularly when the dielectric constant and/or conductivity is large. The transmission line analysis is used to evaluate the ‘‘quasistatic’’ field approximation commonly used in cavity perturbation theory. Application to experimental measurements on Si:As near the metal-insulator transition is also discussed.
Acoustic properties of proton-exchanged LiNbO3 studied using the acoustic microscopy V(z) technique
Authors: Burnett P. J. , Briggs G. A. D. , Al-Shukri S. M. , Duffy J. F. , De La Rue R. M.
Published: July 2002

We report measurements of proton-exchanged LiNbO3 using acoustic microscopy in the V(z) mode, together with optical waveguide mode observations. In the present case, samples were prepared using dilute benzoic acid containing a small mole percent of lithium benzoate. Substantial changes in surface acoustic wave (SAW) propagation velocity due to proton exchange have been observed on all three major-axis crystal cuts, with both increase and decrease in velocity occurring, depending on propagation direction. Changes in attenuation are also observed. Using the V(z) technique with a line-focus cylindrical lens has enabled complete velocity surfaces for proton-exchanged lithium niobate to be obtained with reasonable precision, based on simplified isotropic calculations of acoustic propagation in layered media and the assumption that the proton-exchange region is uniform with a depth obtainable from optical waveguide mode calculations. It is concluded that the V(z) acoustic microscopy technique can provide a powerful tool in the study of the SAW properties of proton-exchanged LiNbO3.
Hydrogenated amorphous silicon films deposited in a helium atmosphere
Authors: Chu T. L. , Chu Shirley S. , Ang S. T. , Duong A. , Han Y. X. , Liu Y. H.
Published: July 2002

Hydrogenated amorphous silicon (a-Si:H) films have been deposited on Corning 7059 glass and other substrates by the thermal decomposition of disilane in a helium flow. The deposition rate of a-Si:H films in a He atmosphere has been found to be significantly higher than that deposited in a hydrogen atmosphere under the same conditions. The a-Si:H films deposited in a He atmosphere showed improved structural properties as compared with those deposited in a hydrogen atmosphere. The properties of a-Si:H films deposited in a helium atmosphere such as density, photoconductivity, minority-carrier diffusion length, gap-state density, etc., have been determined. These films appear to have better electronic properties than the chemical-vapor-deposited a-Si:H films heretofore reported.
Correlation between high-frequency Rayleigh wave attenuation and dc magnetoresistance in nickel thin films
Authors: Wiegert R. F. , Levy M.
Published: July 2002

We present experimental data showing a correlation between the magnetic field dependence of the attenuation of 601.4-MHz Rayleigh-mode surface acoustic wave propagating through evaporated thin films of Ni and the dc magnetoresistance of these films. This correlation provides (1) a method for characterizing the magnetoelastic coupling between the Rayleigh waves and the films’ magnetic moment and (2) insight into the magnetic domain structure and anisotropy dispersion of these films which typically have uniaxial magnetic anisotropy. Upon application of relatively modest dc magnetic fields (<80 Oe) in the film plane both the variation in surface wave attenuation (70 dB/cm) and magnetoresistance (≂1%) can be quite large.
Magnetic and dielectric properties of the spinel ferrite system Ni0.65Zn0.35Fe2−xMnxO4
Authors: Dionne Gerald F. , West Russell G.
Published: July 2002

The recent development of a high-magnetization nickel–zinc ferrite with stress-insensitive square hysteresis loop achieved through substitution of Mn3+ ions has prompted a study of the family Fe3+0.65Zn2+0.35 [Ni2+0.65Fe3+1.35−xMn3+x]O4. The magnetic and dielectric properties of compositions with x ranging from 0 to 0.4 were measured to determine the effects of the manganese substitutions over this concentration range. As anticipated, the saturation magnetizations decreased gradually with increasing x because of reduced magnetic moments in the B sublattice. Of greater importance, however, was the observation that maximum hysteresis loop squareness and minimum stress sensitivity occurred with x∼0.2. A single-ion magnetostriction model is used to interpret this result. Since the electrical resistivity remained above 106 Ω cm and the dielectric loss tangent stayed below 10−3 for the entire series, Fe2+ ion formation is probably negligible.
Magnetocrystalline anisotropy in Nd-Fe-B magnet
Authors: Otani Yoshichika , Miyajima Hideki , Chikazumi Sōshin
Published: July 2002

A torque magnetometer used in a 100-kOe superconducting magnet was designed to measure magnetic anisotropy constants for hard magnetic materials with high magnetocrystalline anisotropy. This magnetometer consists of a pulley system and a motor driven shaft, on which strain gauges are pasted to detect the torque exerted on the sample. Using this torque magnetometer, the magnetic torque curves in the (110) and (100) planes for a Nd2Fe14B single crystal sphere were measured in magnetic fields up to 100 kOe and over the temperature range from 4.2 to 300 K. The temperature and field dependencies of the anisotropy constants K1, K2, and K3 in tetragonal symmetry were obtained. The apparent anisotropy constants strongly depend on temperatures as well as magnetic fields. The intensity of magnetic field is insufficient to rotate the internal magnetization to the field direction. The demagnetization curve in the second quadrant for Nd15Fe77B8 permanent magnet showed stepwise decrease. An attempt to interpret this behavior in terms of the instability of the magnetization direction estimated from the observed anisotropy energy was unsuccessful.
Superconductivity and magnetism in transition-element-substituted YBa2Cu3O7 compounds
Authors: Xiao Gang , Streitz F. H. , Gavrin A. , Cieplak M. Z. , Chien C. L. , Bakhshai A.
Published: July 2002

Superconducting properties of YBa2Cu3O7 have been investigated by a systematic substitution of 3d transition elements for 10% of the Cu ions. Early transition elements Ti, V, and Cr affect the superconducting temperature of YBa2Cu3O7 only slightly. Local magnetic moment formation is observed in Mn, Fe, Co, and Ni substituted compounds. Tc strongly correlates with the size of the paramagnetic moments, possibly due to scattering from the magnetic sites. Zn displays a phenomenal ability to suppress Tc because of the elimination of the 3d holes. The Zn compositional dependence of Tc indicates that the superconductivity completely disappears at 13–14 at. % of Zn. It is suggested that Zn preferentially substitutes the Cu(2) sites.
Absorption and electroabsorption spectra of an In1−xGaxP1−yAsy/InP double heterostructure
Authors: Satzke K. , Weiser G. , Höger R. , Thulke W.
Published: July 2002

Electroabsorption spectra of an InGaAsP/InP double heterostructure are compared with absorption and luminescence spectra. The alloy tuned to emission at 1.33 μm at room temperature shows a surprisingly narrow spectrum at the fundamental gap with many Franz–Keldysh oscillations. The analysis of the electroabsorption data yields the energy gap, its dependence on temperature, and the spin-orbit splitting. Line shape analysis provides information on lifetime broadening, on internal fields, and space charges, and reveals the presence of excitonic effects. Although discrete exciton levels were not observed, an exciton binding energy of 2.3 meV is obtained from the continuum states which is consistent with a reduced effective mass of 0.03m0. While absorption and electroabsorption data yield the same value of the energy gap, emission of light at low temperature occurs at significantly lower energies pointing to the presence of tail states below the gap.
Possibility of a soliton description of acoustic emission during plastic deformation of crystals
Authors: Pawel/ek A.
Published: July 2002

Two basic sources of acoustic emission (AE) during plastic deformation of pure crystals are discussed. One is related to nonstationary dislocation motion (the bremsstrahlung type of acoustic radiation), and the other to dislocation annihilation processes (the main component of the transition type of acoustic radiation). The possible soliton description of the bremsstrahlung acoustic radiation by oscillating dislocation kink and by a bound kink-antikink pair (dislocation breather) is considered on the basis of Eshelby’s theory [Proc. Roy. Soc. London A 266, 222 (1962)]. The dislocation annihilation component of the transition acoustic emission is considered only in relation to the Frank–Read source operation. A soliton model for this type of acoustic radiation is proposed and the simple quantum-mechanical hypothesis is advanced for the purpose. Both soliton descriptions are discussed on the basis of available experimental data on the AE intensity behavior during tensile deformation of crystals.
A closer look at the effect of lens aberrations and object size on the intensity distribution and resolution in electron optics
Authors: Rempfer Gertrude F. , Mauck Michael S.
Published: July 2002

A geometrical optics approach is used to calculate the intensity distribution in the image of a small object centered on the axis. The calculations take into account the size of the object as well as the spherical and chromatic aberrations of the lens. The intensity distribution curves, calculated as a function of depth in the image, reveal the existence of a compact high intensity image peak in the caustic region between the paraxial image plane and the plane of least confusion. The intensity distribution curves show that the geometrical resolution is better in the plane with the high intensity peak than in the plane of least confusion. As the object radius approaches zero the plane in which the high intensity peaks occurs moves toward the paraxial plane, and the geometrical resolution approaches zero. For an object of finite brightness the intensity in the image peak also approaches zero. A geometrical error rg is introduced, which depends on the size of the smallest object providing the required intensity or current in the image peak. The geometrical error and the diffraction error are combined quadratically to obtain a resultant error. An adaptation of the geometrical approach, combined with wave optics, is explored in the case of a point source. Discussions of the intensity-distribution approach as it affects the resolution calculations in the transmission electron microscope and the emission electron microscope are included. In the case of a probe-type instrument a perhaps unexpected finding is that a larger source size along with a smaller angular aperture is preferable in some cases to a smaller source size and larger angular aperture.
Particle size dependence of the magnetic properties of ultrafine granular films
Authors: Liou S. H. , Chien C. L.
Published: July 2002

Magnetic granular solids consist of ultrafine metal granules of nanometer sizes embedded in an insulating medium. The magnetic properties are dictated by the microstructure such as particle size, metal volume fraction, which are process controlled. We report the results of a series of granular Fe60(SiO2)40 films in which the particle size has been systematically varied. The magnetic coercivity, ranging from 500 to 2200 Oe, increases with particle size. The ferromagnetic-superparamagnetic transition had been studied by SQUID magnetometry and Mössbauer spectroscopy. The value of the magnetic anisotropy energy is found to be much larger than that due to magnetocrystalline anisotropy.
Optical dielectric functions for amorphous Al2O3 and γ-Al2O3
Authors: Chu Y. T. , Bates J. B. , White C. W. , Farlow G. C.
Published: July 2002

Using the classical oscillator model, the optical dielectric functions for amorphous alumina (a-Al2O3) and gamma alumina (γ-Al2O3) thin films prepared by ion implantation and subsequent annealing of sapphire (α-Al2O3) substrates were determined for the first time from analysis of infrared reflection spectra. Two transverse optical modes at 422 and 721 cm−1 were obtained for the a-Al2O3 film while four modes at 357, 536, 744, and 807 cm−1 were identified for the γ-Al2O3 film. Also, the problems involving the analysis of modes with large damping are discussed.
Effects of a depth-dependent specimen potential on x-ray photoelectron spectroscopic data
Authors: Lau W. M.
Published: July 2002

Effects of a depth-dependent specimen potential on x-ray photoelectron spectroscopic data were analyzed using both numerical simulation and experimental spectral data. The analysis shows that when the potential gradient near the specimen surface is larger than 0.1 V/nm, it will cause significant broadening of the photoelectron spectra. As the sampling depth is decreased by increasing the polar angle of analysis, the broadening effect is minimized together with a shift of each spectral peak because the contribution of photoelectrons emitted from a large depth is discriminated. However, the shifting of the peak maximum is much smaller than the actual overall potential drop. Quantitative measurements of the actual potential gradient using x-ray photoelectron spectroscopy are possible but require a spectral deconvolution procedure, a spectrometer with good energy resolution, and a relatively simple sample structure.
Electrical and spin resonance characteristics of low-temperature plasma-enhanced chemical-vapor-deposited SiO2
Authors: Devine R. A. B.
Published: July 2002

Electrical and electron-spin-resonance measurements have been carried out on plasma-enhanced chemical-vapor-deposited SiO2 obtained using an N2O:SiH4 flow-rate ratio of 40 and a temperature of 300 °C. As-deposited films contain 2×1016 oxygen vacancy centers per cm3 while none were detectable in films annealed at 950 °C in Ar. 60Co γ radiation-induced defect creation is enhanced (>80 times for a dose of 20 Mrad) in as-deposited films with respect to thermal SiO2 consistent with the deposited film being in a state of densification (∼10%) with respect to undensified, fused silica. This result is in agreement with the results of density, refractive index, and infrared spectroscopy measurement. Annealed films, having a density close to thermal SiO2, are found to be very radiation sensitive in terms of positive fixed oxide charge creation but the relevant defects are not associated with paramagnetic centers. The origin of the enhanced radiation sensitivity in annealed samples may be related to the presence of incorporated nitrogen or excess silicon.
Effect of crystal alignment on the remanence of sintered NdFeB magnets
Authors: Kawai T. , Ma B. M. , Sankar S. G. , Wallace W. E.
Published: July 2002

Nd15.4Fe77.8B6.8 magnets of various degrees of crystal alignment have been prepared by the conventional powder metallurgy technique. The alignment of these magnets have been determined by x-ray diffraction and fitting the standard deviation of a Gaussian distribution for the relative intensity versus the angle between the normals of (hkl) and the tetragonal c axis. The standard deviation is a good indicator for crystal alignment. An aligning field of 8 kOe is found to be essential to obtain a well-aligned NdFeB magnet. The remanence of sintered magnets is directly affected by the crystal alignment. Furthermore, the effect of crystal alignment on the remanence follows the theoretical prediction of the Stoner–Wohlfarth model. Below the spin reorientation temperature, the effect of crystal alignment on the shape of hysteresis loop becomes more significant. The remanences extrapolated from first and second quadrant of the hysteresis loops have been found to be consistent with the prediction of Stoner–Wohlfarth model.
Thermal relaxation over a barrier in single domain ferromagnetic particles
Authors: Klik I. , Gunther L.
Published: July 2002

We present a summary of our general results on the theory of magnetization switching via thermal decay (the classical case) in a small, single domain ferromagnetic (superparamagnetic) particle. Our results allow us to calculate the prefactor of the thermal decay rate and apply them to realistic models, viz., to systems of cubic symmetry (both the Fe and Ni type) and to uniaxial systems with tetragonal, triclinic, and hexagonal symmetry in the basis plane. In each case an external magnetic field parallel to an easy axis can be present. We compare our results with the strictly axially symmetric model often quoted in the literature. This model is singular in that it lacks a saddle point, i.e., it is qualitatively different from any realistic system, which always exhibits a saddle. The singular model results in a temperature-dependent prefactor in the entire range of dissipation while any regular model leads to a temperature-independent prefactor for not too low dissipation.
Effect of Mn concentration on the cathodo- and photoluminescence of ZnS:Mn
Authors: Bhise Milind D. , Katiyar Monica , Kitai Adrian H.
Published: July 2002

A novel method of calibrated doping of Mn in ZnS thin films has been used to study room-temperature cathodo- and photoluminescence characteristics of ZnS:Mn films for a Mn concentration range of 0.07–26.4 wt. %. It was observed that the luminescent intensity increases with Mn concentration up to ∼2 wt. %, beyond which intensity decreases. Emission spectra revealed a lower energy peak in addition to the 580-nm yellow peak for higher dopant concentration. The occurrence of this red peak and quenching of yellow emission is probably at approximately the same activator concentration (∼2 wt. %). We attribute these to the phenomenon of energy transfer to energy sinks via unexcited Mn.
Effective thermal conductivity of binary dispersed composites over wide ranges of volume fraction, temperature, and pressure
Authors: Håkansson Björn , Ross Russell G.
Published: July 2002

The effective thermal conductivity of binary dispersed composites prepared from mixed and compacted powders of AgCl and low-density polyethylene was measured over the entire range of volume fraction at temperatures in the range 100–330 K together with pressures up to 1.75 GPa. Measurements were made using the transient hot-wire method. The ratio of the thermal conductivities of AgCl and LDPE was an adjustable parameter in the range 2–8 at the temperatures and pressures employed. The rigorous effective medium approximation (EMA) provided a good description for most of our results although some limits to its applicability were also indicated. An empirical theory due to Nielsen provided a significantly less successful description. Suggestions are made for an improved theoretical approach going beyond the limits of the EMA.
High-frequency permeability of laminated and unlaminated, narrow, thin-film magnetic stripes (invited)
Authors: Webb Bucknell C. , Re Mark E. , Jahnes Christopher V. , Russak Michael A.
Published: July 2002

The permeability of the magnetic material in a thin-film magnetic head is an important, but hard to characterize, parameter since the magnetic permeability depends on the head domain structure, the drive frequency, and the shape and size of the head. We have measured the high-frequency permeability from 1 MHz to 300 MHz, hysteresis loops, and domain structure of unlaminated and multilayer magnetic thin-films as a function of stripe width for arrays of long narrow stripes. Monolithic permalloy films and permalloy films laminated with SiO2 have been photolithographically patterned and ion-milled to create 3 to 1000 μm wide rectangles, 1 cm long, with the hard axis oriented along the long axis of the rectangles. The high-frequency permeability of each array of a given width is measured by the signal detected by a nonresonant butterfly-coil pickup loop when the film is driven by a uniform radio-frequency magnetic field generated by a strip-line waveguide. The changes in domain pattern as the film structure and stripe width are varied are observed with a Kerr-effect imaging microscope. In unlaminated films, which exhibit standard closure domains, a reduction in high-frequency permeability is observed in agreement with simple models when the closure domains become a significant fraction of the film area. In laminated films with thick magnetic layers, the transition from the laminated domain state to closure domains as the stripe width is decreased occurs where expected from straightforward energy arguments. However, for magnetic layers less than 1 μm thick, where a transition from the easy-axis laminated domain state to a uniform hard-axis state is expected as the stripe width is reduced, the films first change from the easy-axis state to a complicated, low-Kerr-contrast domain pattern before switching to the hard-axis state at much larger widths than predicted. While the laminated state and hard-axis permeabilities are frequency independent, the permeability of the intermediate state rolls off beginning at between 10 and 100 MHz. For still thinner magnetic layers (250 Å), the multilayer retains the high-permeability easy-axis laminated domain state to the narrowest width measured, 3 μm.
Evidence for improvement of critical current by Ag in YBaCuO-Ag thick films
Authors: Dwir B. , Kellett B. , Miéville L. , Pavuna D.
Published: July 2002

The evidence is reported for enhancement of critical current density Jc in YBa2Cu3O7−δ thick films with the addition of Ag, which is correlated with improvements in structural properties. An improvement of 50% in Jc (up to ∼500 A/cm2 at T=4.2 K) was obtained in films made from YBCO+60wt % Ag powder, fabricated by the spin-on technique on (100) SrTiO3, which is correlated with improvements in structure. The resulting films are 10 μm thick, uniform, partially textured, and show good adherence. The critical temperature Tc is improved by the addition of Ag, and a reduction in the density of microcracks and in the amount of secondary phases in the sintered films was observed. Normal-state resistivity is reduced by almost three orders of magnitude, making these films potentially useful for electronic applications in interconnects and novel hybrid circuits.
Superconducting YBa2Cu3O7 thin films on MgO by KrF laser ablation: Optimization of deposition parameters
Authors: Sakeek H. F. , Higgins M. , Graham W. G. , Morrow T. , Turner R. J. , Walmsley D. G.
Published: July 2002

The optimization of interrelated deposition parameters during deposition of in situ YBa2Cu3O7 thin films on MgO 〈001〉 substrates by KrF laser ablation was systematically studied in a single experimental chamber. The optimum condition was found to be a substrate temperature of 720 °C and a target-substrate distance of 5 cm in an oxygen partial pressure of 100 mTorr. These conditions produced films with Tc = 87 K. The presence of YO in the plasma plume was found to be important in producing good quality films. The films were characterized by resistance-temperature measurements, energy dispersive x-ray analyses, scanning electron microscopy, and x-ray-diffraction measurements, and the physical reasons underlying film quality degradation at parameter values away from optimal are discussed.
An inverse-scattering model for an all-optical logic gate
Authors: Tamil Lakshman S. , Jordan Arthur K.
Published: July 2002

Electromagnetic inverse scattering theory is used to model the ON and OFF states of an all-optical logic gate. The scattering data are two phase-conjugate reflection coefficients that were obtained by pole reflection.
Comparison of defects produced by 14-MeV neutrons and 1-MeV electrons in n-type silicon
Authors: Chaudhari Pratima , Bhoraskar S. V. , Padgavkar Swarupa , Bhoraskar V. N.
Published: July 2002

Defects produced in lightly doped crystalline silicon by 1-MeV electrons and 14-MeV neutrons are studied. Deep level transient spectroscopy (DLTS) and Hall voltage measurements have been used for investigating the energy depth, nature, and density of radiation-induced defects. The extent of damage caused by 14-MeV neutrons is found to be comparatively high as inferred from the continuous distribution of gap states in the DLTS measurement. Identical defects were observed in both cases where the A-center (Ec−0.17 eV), E-center (Ec−0.39 eV), and divacancy (Ec−0.23 eV) were prominent. An additional defect level (Ec−0.86 eV) was observed from DLTS for neutron-irradiated samples.
Discharge impedance of an ultraviolet preionized XeCl laser
Authors: Leo M. , Leo R. A. , Nassisi V. , Marsigliante L. , Pecoraro A.
Published: July 2002

We present the experimental results and the theoretical analysis of the discharge impedance and the output performance of an UV preionized XeCl laser. During the breakdown the discharge impedance is time dependent and its value changes as the preionizator changes position. By fitting the experimental results to the results obtained by the equation of the discharge electrical circuit, it is possible to get exactly the electric element values which simulates the discharge impedance. These results are very important to design driving circuit devices which must have an output impedance very close to the laser discharge impedances in order to improve the impedance matching. Papers, which report laser behavior analysis, have utilized laser systems having a fixed preionizator position. In this work, we have found that the laser characteristics, in particular the laser discharge impedance and the output energy, changes as the preionization position changes.
Tl-Ba-Ca-Cu-O superconducting thin films with postdeposition processing using Tl-containing thin films as Tl source
Authors: Naziripour A. , Dong C. , Drexler J. W. , Swartzlander A. B. , Nelson A. J. , Hermann A. M.
Published: July 2002

We describe a new method of processing Tl-Ba-Ca-Cu-O (TBCCO) superconducting thin films. In this method, two identical elemental multilayer films containing Tl layers were prepared using an electron-beam deposition technique. The thin-film samples were then placed in face-to-face contact in a quartz crucible and heat treated at 740 °C for 10 min in flowing air. The x-ray microanalysis of the bottom sample indicates promising results for obtaining the desired chemical composition. Random characterization from different sections of the sample showed that the microanalysis values had less scatter than those for samples prepared using the usual bulk postdeposition method. The average chemical composition of the 13 points obtained from the random section is Tl1.8Ba1.8Ca1.9Cu2.0Ox. However, oxygen analysis showed that the concentration of oxygen is low and poorly distributed, presumeably attributable to the low oxygen flow. This method has several advantages over the conventional Tl-O vapor processing using pure metallic thallium, thallium oxide or bulk TBCCO. These advantages include: (a) increase in uniformity of thallium deposition, (b) safer processing as a result of a smaller release of thallium, and (c) reduction of processing cost.
Local density of states in the vicinity of a Kondo hole
Authors: Sollie R. , Schlottmann P.
Published: July 2002

The substitution of magnetic ions by nonmagnetic impurities in a Kondo lattice gradually destroys the coherence of the heavy fermion groundstate. These nonmagnetic impurities are frequently referred to as Kondo holes. We consider a simple cubic Anderson lattice without orbital degeneracy and study the effects of the scattering off the Kondo hole in the local density of f states in the neighborhood of the nonmagnetic impurity. The correlations within the f band are introduced via a self-energy, evaluated to second order perturbation in U. We use the 1/d expansion method of Schweitzer and Czycholl to leading order (d=∞) in which the k integrations are properly carried out, but the k dependence of the self-energy is neglected. For a Kondo insulator we find a δ-function-like boundstate in the gap. The spectral weight of the boundstate decreases rapidly with increasing distance from the impurity. In the metallic case we obtain a resonance of finite width in the pseudogap of the lattice, which again is localized in the neighborhood of the Kondo hole. These states only appear in the coherent phase and disappear in the continuum at higher temperatures.
Nanolithography on III-V semiconductor surfaces using a scanning tunneling microscope operating in air
Authors: Dagata J. A. , Tseng W. , Bennett J. , Schneir J. , Harary H. H.
Published: July 2002

Nanometer-scale pattern generation on III-V semiconductor substrates using a scanning tunneling microscope (STM) operating in air is demonstrated. The sample substrates, consisting of arsenic-capped, epitaxial layers of n-doped GaAs, AlxGa1−xAs and InyGa1−yAs were prepared by molecular beam epitaxy and characterized by time-of-flight secondary-ion mass spectrometry and x-ray photoelectron spectroscopy. The direct patterning of features of width ≤50 nm on GaAs and In0.2Ga0.8As surfaces is shown to be the result of the formation of a strongly bonded surface oxide induced under high electric field conditions existing between the scan tip and the substrate. The significance of STM pattern generation of nanometer-scale oxide masks for use in the fabrication of low-dimensional heterostructures is discussed.
Fluorescence bands of Nd3+ sites in LiNbO3:Nd,Mg laser system
Authors: Tocho J. O. , Sanz Garcia J. A. , Jaque F. , Solé J. Garcia
Published: July 2002

This paper presents a systematic investigation on the fluorescence (emission and excitation) spectra for the different Nd3+ sites which appear in the LiNbO3:Nd,Mg laser crystal. The study includes the spectral region associated to the 4F3/2 → 4I11/2 and 4F3/2 →4I9/2 radiative transitions. Three sites, denoted as Nd-1, Nd-2 (which also appear in the crystal without Mg2+), and Nd-Mg, have been optically characterized and their corresponding energy levels reported. This information should be taken into account when making a laser with this material.
Measurement of lattice strain in Au–Ni multilayers and correlation with biaxial modulus effects
Authors: Jankowski Alan F.
Published: July 2002

Measurement of lattice strain within each atomic plane of sputter-deposited, gold–nickel multilayer films is accomplished using x-ray diffraction and high resolution electron microscopy. Experimental determination of strain along the composition modulation direction [1 −1 1] from x-ray diffraction scans fit to dynamical theory compare well with values measured from high-resolution electron micrographs and selected-area-diffraction patterns. The measured strain in-plane (2 2 0) and along the composition modulation (1 −1 1) reveal the gold layers to be in compression and the nickel layers in tension. The experimental strain values are used within the framework of the ‘‘coherency strain model’’ to predict an enhancement of the biaxial elastic modulus Y(111), which is in good agreement with the original experimental measurements on thermal-evaporated films.
Microstructural dependence of magnetic properties of Pt/Co multilayer thin films
Authors: Li Z. G. , Carcia P. F.
Published: July 2002

The magnetic properties of thin film Pt/Co multilayers with perpendicular magnetic anisotropy depend on their preparation. Vapor-deposited and Xe-sputtered multilayers have the largest anisotropy energy and coercivities, attractive for magneto-optical recording media. Films sputtered with a smaller mass gas (Ar) have less attractive magnetic properties. In this paper it is shown by high resolution electron microscopy that microstructural differences, related to the energetics of the deposition process, caused the differences in magnetic properties. Films prepared by Ar-sputtering experienced energetic bombardment by reflected Ar neutrals and consequently had smooth, continuous Co and Pt layers, but only modest (111) fcc texture. Vapor-deposited and Xe-sputtered films, which experienced much less energetic bombardment, had superior (111) texture and sharp column boundaries, although Co–Pt layer interfaces were rougher. It was concluded that the superior (111) fcc texture was responsible for a large magnetic anisotropy energy. And both the larger anisotropy energy and the sharper column boundaries contributed to large coercivities.
A modified theory for electrostatic probe measurements of particle mass flows in dense gas-solid suspensions
Authors: Zhu C. , Soo S. L.
Published: July 2002

Measurements of mass flows of a dense gas-solid suspension have led to a modification of the electrostatic probe theory. Previous ball probe theory based on dilute gas-solid suspensions has been extended to account for the effects of multiple scattering and sliding when applied to a dense gas-solid suspension. The validation of the theory was shown by the experimental results.
The effects of the electric field associated with a laser-induced pulsed discharge on the ablation-generated plumes of YBa2Cu3O7−X
Authors: Fried Daniel , Kushida Toshimoto , Reck Gene P. , Rothe Erhard W.
Published: July 2002

The effects of a pulsed discharge on the luminous plume generated during the excimer laser ablation of YBa2Cu3O7−X are investigated in an oxygen environment. A high-voltage capacitor discharge circuit is used to generate a pulsed discharge. The pulsed discharge is initiated by the laser-induced plume. The electric fields are applied along the trajectory of the plume. The time evolution of the discharge current exhibits a distinct dependence on the polarity and magnitude of the electric field and the oxygen background pressure. When an electric field is applied parallel to the plume trajectory two successive plumes may be observed. The first plume, directly induced by the impact of the ablation pulse upon the target, emits bright light, but is electrically neutral. The second plume (reentrant plume), accompanied by a discharge current (charged plume) is observed a few to 100 μs after the first electrically neutral plume. When the parallel field contains a large radial component, i.e., a perpendicular component to the plume trajectory, the charge neutrality of the first plume is lost and only a single charged plume is observed. When the direction of E is reversed (antiparallel field), only a single charged plume is observed directly induced by the laser ablation. The peak current that accompanies the charged plume exceeds 10 A. The time lag of the charged plumes and the minimum voltage required for the discharge are studied as a function of the ambient oxygen pressure. Time-resolved spectra of the plumes are investigated by using a gated intensified diode-array spectrometer. Two-dimensional images of the evolving plume are taken every 100 ns, using a gated, intensified charge-coupled-device camera. A simple model for the observed plume phenomena is proposed.
Theoretical study of subband transitions in strain-induced quantum well wires
Authors: Tan I-Hsing , He Ming Yuan , Yi Jong Chang , Hu Evelyn , Dagli Nadir , Evans Anthony
Published: July 2002

We have modeled the lateral quantum confinement in a GaAs quantum well due to partial strain release on the side walls of an InGaAs stressor located on the top of the well. We used the finite element method to solve both the continuum elasticity equation and the Luttinger four-band Hamiltonian with strain. This model was used to systematically study the wire width dependence of lateral band edge modulation, subband splitting, and relative transition strength in the strain-induced quantum well wire structures.
Electrical characteristics and hydrogen concentration of chemical vapor deposited silicon dioxide films: Effect of water treatment
Authors: Li S. C. , Murarka S. P.
Published: July 2002

The effect of exposing chemical vapor deposited silicon dioxide directly to water has been investigated. Unlike the effect of the water-related traps in thermally grown silicon dioxide, the capacitance-voltage (C-V) shift due to diffused-in water molecules is directly observed without using the method of avalanche injection. The resonate nuclear reaction technique with 15N ion beam has been used to measure the hydrogen concentration of water-boiled, as-deposited, and rapid thermal-annealed silicon dioxide films. These depth profiles show that the hydrogen-containing species, that are most likely water molecules, diffuse in and out and redistribute in the as-deposited and rapid thermal-annealed films. These hydrogen depth profiles also indicate that the amount of diffused-in water molecules in the oxide is limited by the solubility of the water in the oxide. The solubility of water in the oxide annealed at high temperatures is found to be significantly lower than that in the as-deposited oxide. It is found that diffused-in water molecules, in order to satisfy the water solubility of the oxide, play a compensating role in controlling the oxide charges. Water molecules would continue to diffuse in, and interact with oxide charges and produce charges with reverse polarity that compensate the existing oxide charges until water solubility is satisfied.
Control of thermocapillary convection in a liquid bridge by vibration
Authors: Anilkumar A. V. , Grugel R. N. , Shen X. F. , Lee C. P. , Wang T. G.
Published: July 2002

The streaming induced in a short vertical liquid column (L/R≤1, L: length, R: radius) by the vibration of one of the supporting end walls has been utilized in this novel study. Vibration essentially drives a surface flow in the zone away from the vibrating wall, with the return flow in the bulk towards the wall. Preliminary measurements of the surface streaming velocity show that it increases with the frequency and amplitude of vibration and the zone length, and decreases with the viscosity of the zone liquid. This controlled surface streaming has been employed to balance an opposing, steady thermocapillary flow in a model half-zone of silicone oil. In addition to the evidence gathered through flow visualization, temperature measurements in the zone reveal that the radial temperature gradients set up by the thermocapillary flow are weakened/offset by this balancing.
Heavy doping effects in the diffusion of group IV and V impurities in silicon
Authors: Larsen A. Nylandsted , Larsen K. Kyllesbech , Andersen P. E. , Svensson B. G.
Published: July 2002

Studies of the diffusion of Ge, Sn, As, and Sb in Si at high donor concentrations provided by phosphorous doping have been performed. It is found that for donor concentrations, CD below ∼2×1020 cm−3, the diffusivity depends linearly on CD; for doping concentrations above ∼2×1020 cm−3, however, the diffusivity increases dramatically with increasing donor concentrations. This behavior has been successfully modeled within the vacancy–percolation model, and it is concluded that collective phenomena play a significant role at high donor concentrations.