bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability of interfacial oxide layers during silicon wafer bonding
Authors: Ahn K.-Y. , Stengl R. , Tan T. Y. , Gösele U. , Smith P.
Published: July 2002

The stability of thin interfacial oxide layers between bonded silicon wafers is investigated experimentally and theoretically. For usual bonding temperatures around 1100 °C and typical times of a few hours, the oxygen diffusivity is not high enough to allow the oxide layer dissolution. For aligned wafers of the same orientation, the oxide layer instead tends to disintegrate in order to minimize the SiO2/Si interface energy. It is possible to stabilize a uniform interfacial oxide layer by rotationally misorienting the two wafers by an angle θ exceeding a critical angle, θ crit, estimated to be between 1° and 5°.
Magnetic and magneto-optical properties of rare-earth transition-metal alloys containing Gd, Tb, Fe, Co
Authors: Hansen P. , Clausen C. , Much G. , Rosenkranz M. , Witter K.
Published: July 2002

Binary and ternary amorphous rare-earth transition-metal alloys of general composition RE1−x(Fe1−yCoy)x with RE=Gd, Tb and 0<x<1, 0≤y≤1 were prepared by evaporation. The saturation magnetization, uniaxial anisotropy, and Faraday rotation were investigated as a function of composition and temperature. Also, from the temperature-dependent measurements the compositional variation of the Curie temperature and the compensation temperature were determined. The experimental data have been analyzed in terms of the mean-field theory yielding spin values and effective exchange interaction energies. The compositional variation of the spin value was described by the environment model. The anisotropy data were fitted with a dipolar equation using the sublattice magnetizations inferred from the mean-field analysis. The magneto-optical effects are primarily caused by the transition metals. For the binaries GdFe and GdCo the compositional variation of the Kerr rotation typically peaks between 1000 and 1500 nm. The lowest magneto-optical effects for binary RE-Th alloys with respect to composition are reached at about x≊0.5 for T=4.2 K. The temperature dependence of the Faraday rotation can be well described in terms of the sublattice magnetizations.
Large displacement transducers based on electric field forced phase transitions in the tetragonal (Pb0.97La0.02) (Ti,Zr,Sn)O3 family of ceramics
Authors: Pan W. Y. , Dam C. Q. , Zhang Q. M. , Cross L. E.
Published: July 2002

Several properties associated with the field-induced phase change between the antiferroelectric and ferroelectric states in tetragonal (Pb0.97 La0.02 )(Sn,Ti,Zr)O3 antiferroelectric ceramic family were investigated for high-strain displacement transducer applications. The longitudinal field-induced strain accompanying the phase change is in the range of 0.2%–0.9%. The single-shot switching time between the two states is on the order of 1–2 μs. Under continuous ac field driving, the hysteretic heating effect introduces a temperature rise, changing the original room-temperature switching behavior. The ceramics degrade under ac field excitation, the average life cycles is in the range of 106 –107 cycles which can be greatly improved by carefully polishing the sample surfaces.
Magnetic fields generated by axially symmetric systems
Authors: Boridy Elie
Published: July 2002

A coherent and systematic multipole formulation of the magnetic field generated, both in the near and remote regions, by axially symmetric field and gradient systems is presented. These include an open spherical winding, an arbitrary number of coaxial coils, and a combination of coils and spherical or solenoidal windings. Optimum configurations for maximum uniformity of the field or field gradient are discussed and illustrated by numerical results. Legendre series resulting from the multipole expansion are analyzed at the system’s boundary where convergence is very slow, using a summation method particularly suitable for numerical computation.
Relationship between ThMn12 and Th2Ni17 structure types in the YFe11−xTix alloy series
Authors: Hu Bo-Ping , Li Hong-Shuo , Coey J. M. D.
Published: July 2002

A series of YFe11−xTix alloys with x=0.10, 0.25, 0.40, 0.50, 0.70, 1.00, 1.25, 1.50, and 2.00 have been investigated using x-ray diffraction, thermomagnetic analysis, the singular point detection technique, and 57Fe Mössbauer spectroscopy. A pure ThMn12 -type phase was observed when 0.7≤x≤1.25. It has Curie temperature of 524 K, anisotropy field of 2.3 T, and average iron magnetic moment of 1.47 μB at room temperature. The relationship between the CaCu5 and the Th2Ni17 or ThMn12 structure types is discussed in terms of substitution of transition-metal dumbbells on Ca sites, and a structural explanation is given for the directions of the iron anisotropy in the 2:17 and 1:12 compounds.
Magnetism of rare-earth disilicides
Authors: Labroo Sunil , Ali Naushad
Published: July 2002

Magnetic and electrical properties of polycrystalline RSi2 compounds, where R=La-Yb and Y, have been investigated at temperatures ranging from 1.8 K to room temperature using superconducting quantum-interference device (SQUID) magnetometry, ac susceptibility, resistivity, and magnetoresistance measurements. Our data indicate that while PrSi2, ErSi2, and TmSi2 order ferromagnetically at 11, 2.8, and below 1.8 K, respectively, other RSi2 compounds with R=Nd, Eu, Gd, Tb, Dy, and Ho order antiferromagnetically with TN≤39 K. All compounds show Curie–Weiss behavior in the paramagnetic region and the effective moments are found to be close to the free-ion values, gJ [J(J+1)]1/2. Another interesting feature is the observation of second transitions in the cases of Pr, Nd, Eu, Gd, Tb, and Dy compounds. SmSi2, CeSi2, and YbSi2 do not show any magnetic order down to 1.8 K. In the ordered state, all antiferromagnetic compounds have a T3 dependence of resistivity and show a positive magnetoresistance ranging from a few percent to a field of about 25% of the zero-field resistance, for GdSi2 at 4.2 K and a field of 5.5 T. The ferromagnetic compounds exhibit a T2 dependence of resistivity and a large negative magnetoresistance. These observations are found to be consistent with existing theories.
Reaction between Cu and PtSi with Cr, Ti, W, and C barrier layers
Authors: Chang Chin-An
Published: July 2002

The Cu/PtSi metallurgy is studied for reaction and thermal stability using several barrier layers, Cr, Ti, W, and amorphous C. Using preformed PtSi and Cr, Ti, and W barrier layers, Cu is found to react with PtSi around 350 °C. The results are compared with those using similar barriers for the Al/PtSi structure, where an improvement in thermal stability by 50–150 °C is observed. The low thermal stability of the Cu/PtSi structures is attributed to the high affinity of Cu to Si, with the Cu silicide formation starting around 200 °C for a Cu/Si structure. Using an amorphous carbon barrier for the Cu/PtSi structure, a small amount of Cu silicide is observed at 400 °C, but not at 600 °C. Migration of Cu into the structure, however, makes uncertain the effectiveness of the carbon barrier. The results are compared with those of Al/C/PtSi, Al/C/Pd/Si, and C/Cu/SiO2 to understand the mechanism involved.
An investigation of diamond film deposition in a premixed oxyacetylene flame
Authors: Cappelli M. A. , Paul P. H.
Published: July 2002

Diamond film has been deposited in a single-nozzle premixed oxyacetylene flame. Results of runs of varying duration suggest that diamond is deposited via the transport of hydrocarbon fragments produced at the secondary flame front. Planar laser-induced photodissociation fluorescence suggests that this region is rich in C2H species. Emission studies also suggest that the post-primary flame zone presents a source of C2 radicals that may account for the observed graphite and diamondlike carbon deposited on the substrate exposed to this region of the flame. The results on the premixed flame suggest that it would be possible and more convenient to attempt large area deposition using a multinozzle diffusion flame.
Determination of the effective conductivity of heterogeneous media by Brownian motion simulation
Authors: Kim In Chan , Torquato S.
Published: July 2002

A new Brownian motion simulation technique developed by Torquato and Kim [Appl. Phys. Lett. 55, 1847 (1989)] is applied and further developed to compute ‘‘exactly’’ the effective conductivity σe of n-phase heterogeneous media having phase conductivities σ1, σ2, ..., σn and volume fractions φ1, φ2, ..., φn. The appropriate first passage time equations are derived for the first time to treat d-dimensional media (d=1, 2, or 3) having arbitrary microgeometries. For purposes of illustration, the simulation procedure is employed to compute the transverse effective conductivity σe of a two-phase composite composed of a random distribution of infinitely long, oriented, hard cylinders of conductivity σ2 in a matrix of conductivity σ1 for virtually all volume fractions and for several values of the conductivity ratio α=σ2/σ1, including perfectly conducting cylinders (α=∞). The method is shown to yield σe accurately with a comparatively fast execution time.
Mechanical properties of a-C:H films prepared by plasma decomposition of C2H2
Authors: Jiang X. , Reichelt K. , Stritzker B.
Published: July 2002

Diamondlike a-C:H films have been deposited by decomposition of C2H2. By the combination of Brillouin scattering and the ultralow load indentation technique, the following mechanical properties of the films were studied: the microhardness H, the Young’s modulus E, the shear modulus μ, and the Poisson’s ratio ν. From the measured data of mass density, hydrogen concentration, and the ratio of sp3/sp2 bonds the filling factors of these films were calculated. The results show that the hardness, Young’s modulus, and shear modulus of these films depend strongly on the volume concentration of voids and are directly proportional to the filling factor.
Modeling of pulsed laser etching of high-T
c superconductors
Authors: Jette A. N. , Green W. J.
Published: July 2002

Modeling of pulsed laser ablation has been applied to investigate the etching of high-Tc superconducting films of YBa2Cu3O7−δ and Bi2Sr2CaCu2O8. Calculations based on solutions to the one-dimensional heat equation and using parameters characteristic of the experiments indicate that diffusion does not play a major role and the dominant process is an evaporation mechanism taking place at the surface. Hence the ablation is modeled by solving the dynamical equations for a very thin heated layer in local equilibrium with the ablated material. With reasonable assumptions for the heat of evaporation (sublimation) and the phase equilibrium curve, the etch depth per pulse can be determined along with a number of other parameters. The results are in accord with observation.
Quantitative measurement of the ablation rate of poly(methyl methacrylate) with 193-nm excimer laser radiation
Authors: van Saarloos P. P. , Constable I. J.
Published: July 2002

The ablation rate of poly(methyl methacrylate) (PMMA) from two different producers has been measured as a function of fluence, and the result compared with other published work. The two PMMA samples had distinctly different ablation rates. Differences between these two samples and the previously published work demonstrate the difficulties of obtaining quantitative ablation rate data. Possible sources of error in obtaining these data are discussed.
Rapid thermal annealing for 1-MeV arsenic-ion-implanted layers in silicon
Authors: Inada T. , Wakabayashi S. , Iwasaki H.
Published: July 2002

Rapid thermal annealing (RTA) has been carried out by using a graphite strip heater for Si substrates which are implanted with As+ ions at an incident energy of 1 MeV to a high dose of 1×1015/cm2. Annealing characteristics for As-implanted Si substrates have been investigated by Rutherford backscattering measurements and by transmission electron microscopic observations. The electrical properties for the buried n-type layer formed in the substrate during RTA have been examined by differential Hall measurements. A comparison between the annealing process of RTA and that of furnace annealing is made. The experimental results obtained from this work show clearly that the growth of secondary defects in high-energy As+-implanted layers in Si can be effectively suppressed by the use of RTA at 1050 °C, which is not the case for furnace annealing under conventional conditions, e.g., at 1000 °C for 60 min. It has been also shown that a high electrical activation of implanted As atoms is achieved by RTA at 1050 °C, resulting in the formation of a buried n-type layer with a maximum carrier concentration of around 1.5×1019/cm3. Some anomalous electrical properties have been measured in the samples treated by RTA.
Friction in collisions: Resolution of a paradox
Authors: Stronge W. J.
Published: July 2002

The coefficient of restitution e is usually defined as an empirically determined constant of proportionality that relates normal components of incident and rebound relative velocity for contact points CPi of colliding rigid bodies. Assuming that e represents inelastic behavior, this definition results in calculated kinetic energy increases during eccentric (noncollinear) collisions for some conditions of contact point slip. These paradoxical energy increases arise only in noncollinear collisions where slip at CPi is opposed by friction. In this case e must also depend on the slip process and friction, but then the ‘‘impact law’’ is valid for only a vanishingly small range of incident velocities. To resolve this paradox, we propose a new definition where e is independent of friction; thence e specifically represents internal dissipation by irreversible deformation processes. This definition clearly separates frictional and nonfrictional sources of energy dissipation. The two definitions are only equivalent in the case of nonfrictional or central (collinear) collisions.
Laser-beam deflection measurements and modeling of pulsed laser ablation rate and near-surface plume densities in vacuum
Authors: Ventzek Peter L. G. , Gilgenbach Ronald M. , Heffelfinger David M. , Sell Jeffrey A.
Published: July 2002

Quantitative measurements of ablated material from the surface of polyethyleneterephthalate (PET) by 248-nm excimer laser fluences up to 10 J/cm2 are performed by HeNe laser-beam deflection in vacuum and by photoacoustic depth profiling in air. HeNe laser-beam deflection measures the density of gas phase material present in the ablation plume. Photoacoustic depth profiling is a nonintrusive diagnostic that directly measures the etch depths from laser ablation. A hydrodynamic model consisting of a centered rarefaction wave that reflects off the PET surface is shown to describe the laser deflection signals. From these measurements an estimate of the initial temperature of the ablated species is found.
Temperature and thickness dependence of coercivity and magnetization of Co/Cu and Co/Si multilayers
Authors: Nafis S. , Woollam John A. , Shan Z. S. , Sellmyer D. J.
Published: July 2002

Co/Cu and Co/Si multilayers of total thickness ∼3000 Å were prepared by rf and dc magnetron sputtering. The nominal thicknesses of the individual layers were in the range of 4 to 100 Å. A large coercivity (Hc) at 10 K was observed for very thin layers of Co in Co/Cu samples, and it decreased with increase of the Co layer thickness. For very thin layers of Co in Co/Cu samples, the layer behaved superparamagnetically. Similar behavior was not to be observed in Co/Si samples. With increased substrate temperature (Ts) during deposition, Hc was also observed to increase (decrease) for Co/Cu (Co/Si) samples. Magnetization data were modeled to determine the diffusion layer thicknesses.
Magnetic order of Dy in DyBa2Cu3O7
Authors: Clinton T. W. , Lynn J. W. , Liu J. Z. , Jia Y. X. , Shelton R. N.
Published: July 2002

Neutron diffraction has been used to study the magnetic fluctuations and long range order of the Dy ions in single crystals of superconducting DyBa2Cu3O7. The temperature dependence of the rod of scattering, characteristic of 2D behavior, has been measured above and below the 3D Néel temperature (TN ≂ 0.9 K). This rod intensity is observed to increase as the temperature decreases until TN is reached, and then the intensity decreases rapidly below TN. The 2D magnetic correlation length, which is obtained from measurements of the width of the rod, grows continuously with decreasing temperature, then reaches a resolution-limited maximum at the Néel temperature when long range magnetic order sets in. At low T, two separate types of simple 3D antiferromagnetic structures are found, one characterized by a wave vector of (1/2 1/2 0), and the other by (1/2 1/2 1/2). We believe the two types of order occur because the (dipolar) energies for these two configurations are nearly identical. This behavior is analogous to the 2D and 3D magnetic order of Er observed in ErBa2Cu3O7.
Laser-target interactions during pulsed laser deposition of superconducting thin films
Authors: Bhattacharya Deepika , Singh R. K. , Holloway P. H.
Published: July 2002

The theoretical analysis of thermal effects induced by nanosecond laser irradiation on bulk YBa2Cu3O7 superconductor targets provides insight into the nature of the target’s ablation/evaporation characteristics during pulsed laser deposition of superconducting thin films. We have simulated the thermal history of YBa2Cu3O7 targets under intense nanosecond laser irradiation by numerically solving the one dimensional heat flow equation and taking into account the phase changes occurring at the near surface of the target. The numerical method is based on a higher-order finite difference scheme with a smaller truncation error and is not restricted by any stability criterion, thereby allowing faster convergence to the exact solution. Temperature-dependent optical and thermal properties of the irradiated material as well as the temporal variation in the laser intensity can be taken into account by this method. During planar surface evaporation of the target material, the subsurface temperatures were calculated to be higher than the surface temperatures as a result of combination of two unique effects. While the evaporating surface of the target is constantly being cooled due to the latent heat of vaporization, subsurface superheating occurs due to the finite absorption depth of the laser beam. The effects of various laser and target parameters, including pulse energy density, pulse duration, absorption coefficient, thermal conductivity, and latent heat on the transient thermal characteristics of the irradiated target, have been investigated in detail. Subsurface superheating was found to increase with decreasing absorption coefficient and thermal conductivity of the target, and with increasing energy density. The superheating may lead to subsurface nucleation and growth of the gaseous phase which expands rapidly leading to microexplosions and ‘‘volume expulsion’’ of material from the target.
Multi-ion-beam reactive sputter deposition of ferroelectric Pb(Zr,Ti)O3 thin films
Authors: Krupanidhi S. B. , Hu H. , Kumar V.
Published: July 2002

A multi-ion-beam reactive sputter (MIBERS) deposition technique was devised to grow ferroelectric lead zirconate titanate (PZT) thin films of different compositions (Zr/Ti ratios of 50/50 and 56/44) from individual metal targets of Pb, Zr, and Ti. This technique offers a highly controllable deposition process allowing excellent uniformity in composition and thickness over a large area (7.5 cm diameter) on a reproducible basis. The PZT films were deposited on a variety of unheated substrates and annealed by two different techniques, rapid thermal annealing and conventional furnace annealing. Both techniques induced a perovskite phase with good morphology. The effect of the excess Pb content was observed in terms of the crystallization and morphology. It was seen that the presence of excess Pb tends to enhance perovskite phase formation but degrades the morphology. The effect of the substrates was observed in terms of crystallization and orientation. A low-energy oxygen ion beam was employed to modify the film growth. Secondary-ion bombardment seems to be a promising approach to optimize the film quality as it showed a variety of effects such as enhancing crystallization, inducing preferred orientation, and improving the film morphology. The present MIBERS-grown PZT films showed fairly high dielectric constants, about 850 for PZT (50/50) and about 1150 for PZT (56/44), and low dielectric losses. Ferroelectricity of these films was established with the values of the remnant polarization and the coercive field for PZT (50/50) of 23 μC/cm2 and 80 kV/cm and for PZT (56/44) of 20 μC/cm2 and 60 kV/cm, respectively. The low-energy oxygen ion-beam bombardment during the growth of PZT (50/50) films caused an increase in the dielectric constant to about 1000, reduction in the dissipation factor to 0.02, increase in the remnant polarization to about 26 μC/cm2, and decrease in the coercive field to about 60 kV/cm. The C-V characteristics of PZT (50/50) films in a metal-ferroelectric-metal configuration also indicated a clear dielectric polarization hysteresis.
Molecular-beam epitaxial growth and characterization of silicon-doped AlGaAs and GaAs on (311)A GaAs substrates and their device applications
Authors: Li W. Q. , Bhattacharya P. K. , Kwok S. H. , Merlin R.
Published: July 2002

The possibility of reliable and reproducible p-type doping of (311)A GaAs by Si during molecular-beam epitaxial growth and the application of such doping in the realization of high-performance electronic devices have been investigated. It is seen that p-type doping upto a free hole concentration of 4×1019 cm−3 can be obtained under conditions of low As4 flux and high (≥660 °C) growth temperatures. n-type doping up to a level of 1×1019 cm−3 is obtained at low (≤500 °C) growth temperature and high As4 flux. The p-type doping is extremely reproducible and the incorporation of Si atoms into electrically active As sites is at least 95%. The doping behavior has been studied and confirmed by Raman spectroscopy. n-p-n heterojunction bipolar transistors grown by all Si doping exhibit excellent current voltage characteristics and a common emitter current gain β=240. Doped channel p-type heterojunction field-effect transistors have transconductance gm=25 mS/mm.
Experimental study of interaction of microwaves with a nonmagnetized pulsed-plasma column
Authors: Singh A. , Destler W. W. , Catravas P. , Rodgers J.
Published: July 2002

The time evolution of backscattered and sidescattered microwaves from a plane conductor covered by a pulsed-plasma column has been studied; transmitted signals along the axial and transverse directions of the column have also been studied. The incident microwaves are at a cw power level varying from a few milliwatts to a few watts. The cw nature of the signal makes it possible to observe the fine structure in the time evolution of the interactions. The plasma is generated by an array of plasma guns embedded in the conducting plate. The plasma density has a gradient in the axial direction and contains regions of subcritical and supercritical plasma density. Reductions in the backscattered radiation down to the lowest measurable levels with available equipment are observed for durations that are an order of magnitude longer than the duration of the current pulse that generated the plasma. Variations caused by changes in the charging potential on the plasma gun capacitor bank, the pressure of the background gas, and the frequency and power level of the incident microwaves are reported. The attenuation in the backscattered radiation decreases with increasing pressure, especially at lower charging potentials. There is a close correlation between the timing and location of sidescattered signals and the transition of the critical density layer across the axial position of the detectors for the scattered signal. The amplitude of the scattered signal was also measured. Estimates have been made for the percentage of incident power accounted for by scattering. Models are discussed for absorption of microwaves in the plasma.
The dominant diffusing species and initial phase formation in Al-Cu, Mg-Cu, and Mg-Ni systems
Authors: Hong Q. Z. , d’Heurle F. M.
Published: July 2002

The dominant diffusion species in the formation of Al2Cu, Mg2Cu, and Mg2Ni have been determined. These compounds, rich in the lower melting point elements, are the first phases formed in metal/metal binary reactions. It is quite surprising to find that in all three systems, the minority elements, i.e., Cu or Ni, are the dominant diffusing species. This is in marked difference with results obtained in many metal/metal and metal/Si systems, where the dominant diffusion species are usually the majority elements in the initially formed compounds.
Magnetic anisotropy of UCoGa
Authors: Nakotte H. , de Boer F. R. , Havela L. , Svoboda P. , Sechovský V. , Kergadallan Y. , Spirlet J. C. , Rebizant J.
Published: July 2002

Magnetization, ac and dc susceptibility of a UCoGa single crystal are presented. Magnetic ordering was detected below 47 K. The complicated magnetization behavior at low temperatures does not allow us to conclude unambiguously about the type of ground state. The observed strong uniaxial anisotropy is consistent with the behavior of other isostructural UTX compounds. The anisotropy field exceeds by far the highest field of 35 T applied in the experiments.
Relaxation phenomena after laser-induced photodetachment in electronegative rf discharges
Authors: Passchier J. D. P. , Goedheer W. J.
Published: July 2002

The response of a radio-frequency discharge in an electronegative gas to laser-induced photodetachment is considered. The discharge is described by a numerical fluid model, including the electron energy balance. The detachment event is simulated by transforming instantaneously all or part of the negative ions into electrons in the region of the discharge passed by the laser beam. In order to avoid severe restrictions on the computational time step, the evolution of the electron density and of the electric field is solved with a fully implicit numerical method. It turns out that the relaxation towards the periodic quasisteady state is mainly governed by a simultaneous increase of the production rate of negative ions and decrease of the ionization rate. The qualitative behavior of the calculated electron decay rate is in accordance with experimental observations.
Axial strain-induced microbending losses in double-coated optical fibers
Authors: Shiue Sham-Tsong
Published: July 2002

The microbending losses induced by axial strain in double-coated optical fibers have been analyzed. The microbending loss is dominated by the lateral pressure in the glass fiber, which is proportional to the axial strain and is affected by the material properties of primary coating and secondary coating and their thicknesses. To minimize the microbending losses induced by axial strain, it is found that if the lateral pressure is compressive, the thickness and Poisson’s ratio of primary coating should be increased; but the Young’s modulus of primary coating should be decreased. On the other hand, the thickness, Young’s modulus, and Poisson’s ratio of secondary coating should be decreased.
Noise-free parametric energy multiplication for frequency measurements of an anharmonic mono-ion oscillator
Authors: Yu N. , Dehmelt H. , Nagourney W.
Published: July 2002

We have used a mono-ion oscillator to demonstrate the usefulness of a spectroscopic technique for achieving high-resolution frequency measurements in the presence of anharmonicity. The technique uses a noise-free parametric process to amplify a weakly pre-excited oscillator that allows one to reduce anharmonic frequency shift and at the same time to detect the resonance signal with large amplitude. In our initial experiments using the parametric process, 100 times narrower spectral lines have been obtained. The technique is potentially useful in such high-precision experiments as the electron g-2 measurement and the ion mass spectroscopy in Penning traps. The possibility of using the parametric process to detect the n=0→n=1 transition of the cyclotron motion in geonium is also discussed.
Magnetic domain observation in amorphous wires
Authors: Reininger T. , Kronmüller H. , Gomez-Polo C. , Vazquez M.
Published: July 2002

The domain patterns of as-cast Fe-rich amorphous wires with 125 μm in diameter and a length of 10 cm have been observed by means of magneto-optical Kerr effect. Particular attention is paid to the observation of domains at the end and inside the wire after adequate polishing procedures. Four distinguishable regions within the wire namely, the shell, the core with diameter between 60 to 80 μm, and two different closure domain structures at the end of the wire depending on the two different remanent states, are observed. Investigating one end of the wire, we found conical-like domains with increasing diameter reaching at least several hundred μm into the wire in one remanent state, in the other remanent state we find a very small conical-like domain with decreasing diameter reaching only several ten μm into the wire. In addition, reversed domain patches inside the core up to a distance of about 3 cm from both ends can be observed. These results give a hint to enlighten the origin of the switching mechanism and its recently found alternating directional propagation.
Theory and experiments on flicker noise in In0.53Ga0.47As/AlAs/InAs resonant tunneling diodes
Authors: Ng Sze-Him , Surya Charles
Published: July 2002

We studied 1/fγ noise in strained-layer In0.53Ga0.47As/AlAs/InAs resonant tunneling diodes from 77 to 293 K and observed variations over temperature for both the noise magnitude and the spectral shape. Analyses of our data indicated a thermally activated noise process. Our measurement further showed that the current noise magnitude SI varied approximately as I2 at room temperature, but deviated significantly from an I2 dependence at low temperatures. Such observations are accounted for by a model based on the capture and emission of electrons by interface states through thermal activation. These traps cause fluctuations in the tunneling current by modulating the barrier potential and thus the transmission coefficient.
Determining elastic behavior of composites by the boundary element method
Authors: Eischen J. W. , Torquato S.
Published: July 2002

The boundary element method is applied to determine the effective elastic moduli of continuum models of composite materials. In this paper, we specialize to the idealized model of hexagonal arrays of infinitely long, aligned cylinders in a matrix (a model of a fiber-reinforced material) or a thin-plate composite consisting of hexagonal arrays of disks in a matrix. Thus, one need only consider two-dimensional elasticity, i.e., either plane-strain or plane-stress elasticity. This paper examines a variety of cases in which the inclusions are either stiffer or weaker than the matrix for a wide range of inclusion volume fractions φ2. Our comprehensive set of simulation data for the elastic moduli are tabulated. Using the boundary element method, a key microstructural parameter η2 that arises in rigorous three-point bounds on the effective shear modulus is also computed. Our numerical simulations of the elastic moduli for the hexagonal array are compared to rigorous two-point and three-point bounds on the respective effective properties. In the extreme instances of either superrigid particles or voids, we compare analytical relations for the elastic moduli near dilute and close packing limits to our simulation results.
Warm electron energy loss in GaInAs/AlInAs high electron mobility transistor structures
Authors: Arikan M. Ç. , Straw A. , Balkan N.
Published: July 2002

Electron energy loss rates via the emission of acoustic phonons in moderately degenerate GaInAs/AlInAs high electron mobility transistor structures are investigated at electron temperatures between Te=1.8 and 15 K. Two experimental techniques, Shubnikov–de Haas and mobility measurements were employed in the investigations. The results are compared with a model based on three-dimensional electron energy loss by piezoelectric and deformation potential scattering. It is shown that the enhanced loss rates at high electric fields as obtained using the former technique is the result of its failure at these fields. The agreement between the results of the mobility experiments and the theory is excellent over the temperature range of interest.
Angle-resolved time-of-flight studies on ground-state neutrals formed by near-threshold excimer laser ablation of copper
Authors: Kools J. C. S. , Dieleman J.
Published: July 2002

The angle-resolved velocity distributions of neutral copper atoms created by near-threshold ultraviolet excimer laser ablation of polycrystalline copper foils are measured as a function of the polar desorption angle and the laser fluence. The obtained time-of-flight spectra can be fitted by elliptical Maxwell–Boltzmann distributions on a stream velocity. Integration of the spectra allows one to determine the kinetic energy of these atoms. This kinetic energy is hyperthermal (1 eV).
Dielectric properties of polymer-liquid composite systems
Authors: Brosseau Christian
Published: July 2002

The dielectric properties of inhomogeneous media constituted by a glassy semicrystalline polymer (polypropylene) impregnated by an aromatic fluid (monodibenzyltoluene) are studied. The measured permittivity is compared to various forms of mixture equations. The closest agreement is obtained with the Lichteneker’s logarithmic mixing expression. The frequency dependence of ionic conductivity in these swollen materials has also been investigated at low electric fields. An attempt is made to interpret these measurements in terms of Niklasson’s [J. Appl. Phys. 62, R1 (1987)] fractal model taking into account the inner topology of the structure of the medium.
Three-dimensional reconstruction of magnetic vector fields using electron-holographic interferometry
Authors: Lai Guanming , Hirayama Tsukasa , Fukuhara Akira , Ishizuka Kazuo , Tanji Takayoshi , Tonomura Akira
Published: July 2002

A method of reconstructing three-dimensional magnetic fields using electron-holographic interferometry is described. First, measured two-dimensional phase distributions are shown to reveal the projected magnetic flux structure of a microscopic object. Second, an algorithm for reconstructing the magnetic flux density in three dimensions from the phase distributions at different viewing directions has been developed and tested. An application to a barium ferrite particle is presented.
Estimation of plasma absorption effects during pulsed laser ablation of high-critical-temperature superconductors
Authors: Singh Rajiv K. , Viatella John
Published: July 2002

During pulsed laser deposition of thin films, a significant amount of energy is coupled to the laser-generated plasma. The fraction of the energy absorbed in the plasma is a function of the incident laser wavelength, time-dependent plasma dimensions, and electron density. Due to time-varying parameters, a quantitative analysis of the plasma absorption is difficult. A method has been developed to estimate plasma absorption during deposition of thin films. In this model, the time-dependent plasma dimension is replaced by the time-dependent ablation depth, which can be easily determined. Using simulated absorption coefficient values, the ablation depth of the target as a function of energy density and laser wavelengths has been computed. These calculations have been compared with experimental results obtained from excimer laser deposition of high-Tc superconductors. Correlations between plasma absorption coefficient and incident laser photon energy have also been determined.
Characterization of the magnetic easy axis in pipeline steel using magnetic Barkhausen noise
Authors: Krause Thomas W. , Clapham L. , Atherton David L.
Published: July 2002

The angular dependence of magnetic Barkhausen noise (MBN) on eight surfaces through the thickness of a 2% Mn steel pipeline sample was investigated. The MBN signal was analyzed by integrating the square of the MBN voltage signal with respect to the time axis. The resulting value, referred to as the MBN energy signal, was modeled by considering the irreversible motion of 180° domain walls, under the influence of an oriented magnetic field. An expression for the angular dependence of the MBN energy signal was derived and was given by energy=α cos2 θ+β, where α and β are the fitting parameters and θ is the angle between the maximum MBN signal and the applied sweep field. The α parameter was associated with the irreversible motion of 180° walls that contributed to the net macroscopic easy axis near the surface of the sample, while the β parameter was associated with the isotropic background MBN signal. The energy equation could be used to fit the data for all sweep field amplitudes in which the MBN spectrum was observed. A dependence of the α and β parameters on the applied sweep field amplitude was observed.
Anisotropy and Faraday effect in Co spinel ferrite films
Authors: Zhang H. Y. , Gu B. X. , Zhai H. R. , Lu M. , Miao Y. Z. , Zhang S. Y. , Huang H. B.
Published: July 2002

Crystalline Co spinel ferrite films were prepared by rf sputtering on glass substrates without buffer layer and annealed at temperatures from 400 to 600 °C for 2 h in air. (100) texture was obtained in these films. The anisotropy constant, magnetic hysteresis loops, and magneto-optical Faraday spectra of the films were measured. The texture became poor when the films were annealed below 500 °C, but the perpendicular anisotropy constant Ku, squareness ratio R=(Mr/Ms)⊥/(Mr/Ms)∥ increased and showed peak values of 2.2×105 ergs/cm3 and 0.94, respectively, at an annealing temperature Ta=500 °C. For the film annealed at 600 °C (higher than the Curie temperature, 520 °C, of Co spinel ferrite), the texture recovered, but Ku and R dropped. The Faraday rotation spectra of Co spinel ferrite films showed a broad peak centered around 720 nm. The peak value increased monotonically with increasing annealing temperature. These results may be related to the Co ion-induced anisotropy and Co ion distribution in tetrahedral sites and octahedral sites.
Equation of motion of domain walls and equivalent circuits in soft ferromagnetic materials
Authors: Aguilar-Sahagun G. , Quintana P. , Amano E. , Irvine J. T. S. , Valenzuela R.
Published: July 2002

The equation of motion for ferromagnetic domain walls is compared with initial permeability measurements of Co-based soft ferromagnetic amorphous ribbons at frequencies in the range 100 Hz–13 MHz. The analysis of these results by complex permeability methods leads to an equivalent circuit formed by a parallel RL arrangement in series with a small resistance RW due to resistance of the measurement coil. This equivalent circuit, however, cannot model the irreversible magnetization behavior for fields higher than the pinning (or propagation) field. It is shown that the equation of motion is also consistent only with the reversible magnetization mechanism, if the displacement term, x, represents instead the bulging of the pinned wall. The correlations between the terms in the equation of motion and the elements of the equivalent circuit are established.
Transmission electron microscope study of the crystal structures and microstructures of ZrSi and HfSi in ultrahigh vacuum deposited metal thin films on (111)Si
Authors: Hseih W. Y. , Chen L. J.
Published: July 2002

Both conventional and high resolution transmission electron microscopy have been applied to study the crystal structures and microstructures of ZrSi and HfSi formed in the interfacial reactions of metal thin films on (111)Si. Both CrB and FeB type monosilicides were observed to form. The theoretically predicted and measured values of lattice parameters were found to be very close. A number of planar defects were detected to be present in ZrSi and HfSi. The textured growth of both monosilicides is explained in terms of preferential growth of these silicides along specific directions of silicon substrates which can be derived from the crystal structures and matching of atomic structures between silicides and silicon.
Models for ultrasonic characterization of environmental degradation of interfaces in adhesive joints
Authors: Lavrentyev A. I. , Rokhlin S. I.
Published: July 2002

In this paper we discuss two models of environmental degradation of adhesive joints developed from experimental observation of the joint failure mode. It is found that after severe degradation, failure is dominated by the interfacial mode, i.e., by failure at the interface between adhesive and adherend. The fraction of failure in the interfacial mode was found to be related to the joint strength and to be proportional to the frequency shift of a minimum in the spectrum of the reflected ultrasonic signal. One model considers an interface as an interphase in the form of a nonhomogeneous layer composed of two phases: ‘‘soft’’ which is viscoelastic (degraded part of the interphase) and ‘‘stiff’’ corresponding to the nondamaged interphase. Increase of the ‘‘soft’’ phase fraction corresponds to the process of degradation in the interphase. The second model describes degradation in a form of disbonds filled by absorbed water at the interface. The disbonded interface is modeled by transverse spring boundary conditions, with the complex spring stiffness representing the quality of the bond. The influence of different disbond growth scenarios is considered. Advantages and drawbacks of these models are discussed.
Self-consistent k⋅p band structure calculation for AlGaAs/InGaAs pseudomorphic high electron mobility transistors
Authors: Jogai B.
Published: July 2002

A self-consistent four-band k⋅p calculation for the band structure of AlGaAs/InGaAs pseudomorphic high electron mobility transistors (p-HEMTs) is presented. The eigenstates are described in a basis consisting of electron, heavy-hole, light-hole, and split-off bulk states. The k⋅p Hamiltonian derived in this basis includes strain-induced mixing between the conduction and light-hole and the conduction and split-off bands. It also includes additional splitting between the heavy- and light-hole bands, apart from that induced by the shear deformation potential, caused by strain-induced changes in the spin-orbit interaction. The Hartree potential is calculated from the Poisson equation and the exchange-correlation potential from density-functional theory within the local-density approximation. The model calculation accounts for deep level surface acceptor and donor states, both of which contribute to Fermi level pinning at the surface. Also included are acceptor interface states at the inverted GaAs/AlGaAs interface. The present calculation can be used as a characterization tool to analyze optical and Hall data from preprocessed p-HEMT material, since conduction-valence subband separations and mobile sheet charge densities are results of the calculation.
Investigation of barium titanate thin films on MgO substrates by second-harmonic generation
Authors: Bihari Bipin , Kumar Jayant , Stauf Gregory T. , Van Buskirk Peter C. , Hwang Cheol Seong
Published: July 2002

Barium titanate (BaTiO3) thin films grown by the metalorganic chemical vapor deposition (MOCVD) technique on MgO substrates have been investigated by second-harmonic generation at an incident wavelength of 1.064 μm. Transmission electron microscopy was used to show that substrate quality and pretreatment (annealing) has a strong influence on microstructure and optical properties of these films due to nucleation effects during MOCVD growth. Angular dependence of second-harmonic signal indicates both a- and c-textured growths in this film/substrate system. Stress-induced stabilization appears to determine the orientation of the microcrystallites in the films. Corona poling does not result in a preferred orientation of the film. Effective d coefficients as high as 2.13 pm/V have been obtained from as-grown films.
Investigation of nucleation and growth processes of diamond films by atomic force microscopy
Authors: George M. A. , Burger A. , Collins W. E. , Davidson J. L. , Barnes A. V. , Tolk N. H.
Published: July 2002

The nucleation and growth of plasma-enhanced chemical-vapor deposited polycrystalline diamond films were studied using atomic force microscopy (AFM). AFM images were obtained for (i) nucleated diamond films produced from depositions that were terminated during the initial stages of growth, (ii) the silicon substrate-diamond film interface side of diamond films (1–4 μm thick) removed from the original surface of the substrate, and (iii) the cross-sectional fracture surface of the film, including the Si/diamond interface. Pronounced tip effects were observed for early-stage diamond nucleation attributed to tip convolution in the AFM images. AFM images of the film’s cross section and interface, however, were not highly affected by tip convolution, and the images indicate that the surface of the silicon substrate is initially covered by a small grained polycrystalline-like film and the formation of this precursor film is followed by nucleation of the diamond film on top of this layer. X-ray photoelectron spectroscopy spectra indicate that some silicon carbide is present in the precursor layer.
Electrical and structural properties of Be- and Si-doped low-temperature-grown GaAs
Authors: Atique N. , Harmon E. S , Chang J. C. P. , Woodall J. M. , Melloch M. R. , Otsuka N.
Published: July 2002

Excess As is incorporated in GaAs grown at low substrate temperatures by molecular beam epitaxy. Excess As is distributed in the epilayer as defects and the material exhibits considerable strain. When annealed to moderate temperatures, the strain is seen to disappear and the excess As is now in the form of semimetallic clusters. It has been proposed that these As clusters form buried Schottky barriers with the GaAs matrix and are surrounded by spherical depletion regions. In this article, we examine the effects of doping on the material properties and compare our results to the buried Schottky barrier mode. Si-doped GaAs epilayers grown at 250 °C, with doping densities between 5×1017 and 5×1018 cm−3, were annealed to temperatures between 700 and 1000 °C for 30 s. Be-doped GaAs epilayers grown at 250 °C, with doping densities between 5×1017 and 5×1019 cm−3, were annealed to temperatures between 700 and 900 °C for 30 s. Using extensive Hall measurements and transmission electron microscopy, we observe that the As precipitates deplete the surrounding GaAs matrix.
Comment on ‘‘Analysis for determining thermal diffusivity from thermal pulse experiments’’
Authors: Josell D. , Warren J. , Cezairliyan A.
Published: July 2002

An error has been noted in the seminal work by Cape and Lehman [J. Appl. Phys. 34, 926 (1963)] for determining thermal diffusivity values from the results of pulse heating experiments. In the present communication, the correct formula has been determined and some estimates have been made of the errors resulting from application of the incorrect formulation.
Waveguide formation mechanism generated by double doping in ferroelectric crystals
Authors: Atuchin V. V. , Ziling C. C. , Savatinova I. , Armenise M. N. , Passaro V. M. N.
Published: July 2002

Physical mechanisms causing the refractive index increase Δn in uniaxial oxidized ferroelectric crystals subjected to double doping are discussed. The analysis shows that the index changes of the two different dopants, ΔnA and ΔnB, are additive only if the corresponding changes of the spontaneous polarization are small. Ti indiffusion and proton exchange (TIPE) waveguides in LiNbO3 are considered as an example of the case when this condition is not fulfilled. The hydrogen–lithium substitution in such waveguides leads to a strong reduction of the spontaneous polarization of the virgin crystals and the final index change Δn is not a sum of ΔnA and ΔnB. A physical model is developed to explain light waveguiding in double-doped ferroelectric structures. Experimental data obtained for TIPE waveguides confirm the model.