bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic quadrupolar excitation in PrO2
Authors: Kern S. , Trouw F. , Loong C.-K. , Lander G. H.
Published: July 2002

A 5.4-meV excitation has been measured in PrO2 using inelastic neutron scattering. The excitation is identified as the energy splitting of the Γ8 ground state, corresponding to the dynamic Jahn–Teller process responsible for producing a reduced magnetic moment below the 14-K Néel point. Its magnitude and temperature dependence are in keeping with the predictions of Allen and of Sasaki and Obata for UO2, as scaled to PrO2. We had previously invoked this mechanism to explain the broadening of the 130-meV Γ8-to-Γ7 transition. Implications of these results for the magnetic response of PrO2, and other f-electron systems will be discussed.
Field of thin-film head of finite dimensions
Authors: Minuhin V. B.
Published: July 2002

A rigorous solution is presented for the fields of two-dimensional capacitor with finite dimensions of plates or for a symmetrical two-dimensional thin-film magnetic head of finite size. The solution has been obtained by a succession of conformal mapping in conjunction with an iterative computer procedure for the determination of constants in the Schwarz–Christoffel transformation. The advantage of the presented model is in its conceptual simplicity. The field distribution of the model is calculated by a straightforward method: by the fine integration in a complex plane. It does not require iterative solutions of systems of nonlinear and transcendental equations with associated problems of convergence. The finite size of the model facilitates easy calculation of wavelength responses of magnetic heads. The practical procedure is described for the calculation of the external field and wavelength response of the model. The results of calculations illustrate serious problems in practical magnetic heads arising from a limited pole size in conjunction with sharp pole corners.
The strength of the R-T exchange coupling in R2Fe14B compounds; an approach based on high-field magnetization measurements
Authors: Verhoef R. , Quang P. H. , Franse J. J. M. , Radwański R. J.
Published: July 2002

By performing high-field magnetization measurements on Gd2Fe14−xMnxB and Tb2Fe14−xMnxB powdered samples that are oriented in the sample holder by the applied field it is possible to improve the accuracy of earlier reported values for the R-T exchange-coupling constant of these R2Fe14B compounds. In addition, the two-sublattice model that has been applied previously has been extended to a three-sublattice model with two magnetic rare-earth sublattices for the Er and Tm compounds in an attempt to describe the experimentally observed low-field susceptibility. It turns out however, that mainly the iron-manganese sublattice is responsible for this susceptibility.
Influence of a large amount of Co substitution on the magnetic properties of NdFeCoGaB magnets (abstract)
Authors: Tsutai A. , Sakai I. , Sahashi M. , Inomata K.
Published: July 2002

We have found that a NdFeCoGaB sintered magnet containing 30 at. % Co still shows high coercive force in spite of such a large amount of Co substitution. The Curie temperature of the magnet is higher than that of the ternary NdFeB magnet by 280 °C. As a result, the following magnetic properties have been attained for Nd14.5Fe46Co30Ga1B8.5: Tc=590 °C, Br =11.7 kG, Hci =14.3 kOe, and (BH)max=32 MG Oe. Furthermore, in this magnet there exists an additional phase, Nd1(FeCoGa)4B1 with Ce1Co4B1 structure, which, as far as authors know, has not been reported to exist in the NdFeB-based magnets. In this study we investigated the magnetic properties and microstructure of Nd14.5Fe76−xCoxGa1B8.5 (x=16–50) sintered magnets. The high coercive force can be obtained in the Co-content region from 16 to 30 at. %. In particular, the magnet with 30 at. % Co shows coercive force as high as 14.3 kOe. However, further substitution of Co drastically deteriorates the magnetic properties. The coercive force of the magnet with 50 at. % Co is less than 1 kOe. From the metallographical point of view, the above-mentioned Nd1(FeCoGa)4B1 phase is not observed in the magnets containing less than 30 at. % Co. This phase abruptly appears in the magnet with 30 at. % Co and its amount increases with increasing Co content. The strongest x-ray-diffraction peak observed in the magnet with 50 at. % Co comes from the Nd1(FeCoGa)4B1 phase. The demagnetization-curve measurements suggest that reverse magnetic domains are nucleated in the Nd1(FeCoGa)4B1 phase at a low reverse magnetic field. It is noteworthy that the magnet with 30 at. % Co maintains the high coercive force in spite of the existence of such a soft magnetic phase. Details will be discussed in the coming session.
Effect of nitrogen upon enhancement of the magnetic Kerr rotation in ZnS(O,N)/TbFeCo bilayer films
Authors: Kudo T. , Johbetto H. , Ichiji K.
Published: July 2002

In ZnS(O)/TbFeCo bilayer films, a large Kerr rotation angle of θK =−12° has been detected at a short wavelength of 363 nm. The peak wavelength of the enhanced Kerr rotation is situated between the high transmittance region and the fundamental absorption region in the optical transmission spectrum of the ZnS(O) layer. The increase of the N2 flow rates in a mixture of sputtering Ar+N2 gases moves the threshold of the fundamental absorption in the ZnS(O,N) layer towards the shorter wavelengths. Under a constant thickness of the ZnS(O,N) layer, the peak position of the enhanced Kerr rotation for the ZnS(O,N)/TbFeCo bilayer films moves in the same way, too. The degree of Kerr rotation enhancement becomes maximum for the N2 flow rate of 0.3 cm3/min in the wavelength range 360–400 nm and the most enhanced Kerr rotation reaches θK =−17.5° at λ=373.5 nm. The strong enhancement of θK is induced by a singular phenomenon in the optical-constant spectra of the ZnS(O,N) layer on the TbFeCo layer.
Evidence for acoustic-wave coupling in the magnetostatic-wave–optical interaction
Authors: Bilaniuk Nykolai , Stancil Daniel D.
Published: July 2002

We have observed the collinear interaction between optical guided modes and magnetostatic forward-volume waves in a film of yttrium iron garnet (YIG) with microwave frequencies between 500 MHz and 12 GHz. The interaction occurred in one of two 5.3-μm films of YIG on either side of a 470-μm substrate of gadolinium gallium garnet (GGG). The intensity of the diffracted optical beam was measured as the microwave frequency was swept about the center frequency, with magnetic bias field held constant. We refer to this measurement as the interaction passband. Below 1 GHz, we observed absorption notches in the interaction passband with a regular period of 3.7 MHz. These are interpreted as evidence of coupling to transverse acoustic resonances through the sample thickness. This spacing agrees with a simple calculation based on transverse acoustic velocities in YIG of 3843 m/s and GGG of 3568 m/s.
The Faraday effect in magnetic semiconductors (abstract)
Authors: Liu Gong-qiang , Huang Yan-ping , Le Zhi-qiang
Published: July 2002

In n-type ferromagnetic semiconductors, both bound electrons and free carriers make contributions to the Faraday effect. The spin-orbital interaction of bound electrons, and the spin-spin exchange interaction between bound electrons and between bound electrons and free electrons exist. Thus, the Faraday rotation θ has been deduced as follows: θ=(eμ0/mc)∑∞l=1blλ2lL (He+ν′M)+(eμ0/mc) ∑∞n=1(an/λ2n) L[He+(ν+ν′)M] =θS+θF, where L is the thickness, He the external field, M the magnetization, ν′M the effective field related to the exchange interaction between bound electrons and free electrons, νM the effective field related to the spin-orbital interaction of bound electrons and so on, an and bl the constants related to the concentration N1 of free electrons and the concentration N2 of bound electrons, respectively. While λ>λ0, the wavelength at θ=0, or N1>N0∼1022/m3, θS>θF. Conversely, θS<θF. When θS≪θF, θ∼(a1/λ2+a2/λ4+...). The temperature behavior of θ mainly depends on that of M. θ tends to saturation with M. When θS≫θF, θ∼(b1λ2+b2λ4+⋅⋅⋅). θ is directly proportional to approximately He. The calculations are confirmed by the experimental results in CdCr2S4, etc.
Eddy-current analysis of isolated permanent-magnet drives using two- and three-dimensional finite-element methods (abstract)
Authors: Ferreira C. A.
Published: July 2002

Present drive systems which rely on mechanical devices for torque transmission have some negative features: the driven component cannot be isolated from the drive motor, rotating seals have inherent leakage and friction problems, and mechanical failures often occur due to torque overloads. Magnetic couplings are especially well suited for use in isolated-drive systems. This is often the case in military and aerospace applications where pumps and compressors are vital parts of the thermal and fuel operating systems. The application of permanent-magnet couplings in isolated drives requires accurate calculation of the eddy-current losses induced on the hermetic vessel. This is because the losses along with the required output torque dictate the size and efficiency of the permanent-magnet coupling. The vessel isolates the drive member from the driven member of the turbocompressor. The paper will show the formulation of the computational method based on the Poynting-vector theorem and the concept of motional electric field intensity. The eddy-current losses are calculated using two- and three-dimensional magnetostatic finite-element (FE) analysis. A comparison of the results obtained by two- and three-dimensional FE analysis is made. The results of the analysis will be compared to test data for verification. The test-facility setup and procedure will also be described. This state-of-the-art technique for computation of eddy-current losses has several advantages over conventional analysis methods: the nonlinearities of the magnetic circuit are taken into account, magnetic field fringing and end-leakage effects are not neglected, and the method does not rely on the use of empirical factors. The significant benefits of this approach are that trial-and-error experimental design approaches are eliminated and test data provide validation of analytical results.
Physical factors affecting the corrosion resistance of CoCr thin-film media
Authors: Merchant K. , Smallen M. , Fisher R. , Smith S.
Published: July 2002

Various factors such as film porosity, stress, type of underlayer, and the presence of an overcoat were found to affect the corrosion resistance of CoCr and CoCrTa thin-film magnetic disks exposed to high-humidity, corrosive environments. It was found that corrosion products form preferentially along the polishing and texture lines of the NiP substrate. Relieving internal stresses in the disk layers using a low-temperature annealing process improved the corrosion resistance of these Co alloy films. Additionally, eliminating the carbon overcoat allowed the formation of an oxide layer which was more protective in chlorine-containing environments.
H-formulation boundary-element method analysis for skin and proximity effect eddy-current problems
Authors: Ahmed M. Taher
Published: July 2002

This paper presents a new formulation for skin and proximity effect eddy-current problems. The formulation is given in terms of a system of second kind Fredholm direct boundary integral equations (BIE). The main advantage of the present formulation is that its highest singularity is a weak singularity and it is more accurate than previous formulations, especially for bodies with sharp corners. To achieve the proposed formulation, the first-order effect of the impressed current is presented as an average component of the tangential magnetic field intensity Ht over each conductor periphery. The value of Hav is not known until the final solution is obtained. Ampere’s law is applied over each conductor boundary to force the total current in this conductor to the desired value. Results are obtained for two test problems. The first is of two circular cylinders carrying opposite currents, and the second is for one rectangular conducting cylinder to examine the effect of the sharp corners on the solution accuracy.
Design and optimization of short-period wigglers for free-electron lasers
Authors: Radack D. J. , Mayergoyz I. D.
Published: July 2002

In this paper, simple expressions for optimized dimensions of the electromagnet wiggler are derived and experimentally verified.
Track edge fluctuations
Authors: Muller M. W. , Indeck R. S. , Murdock E. S. , Ornes R.
Published: July 2002

Track edge fluctuations on recording media affect signal-to-noise ratio and servo control, and can provide clues to the medium’s magnetic microstructure. We write track edges on longitudinal thin-film magnetic recording media by dc erasing the medium and writing a saturated dc track of opposite magnetization direction on the erased band. We then ‘‘read’’ the position fluctuations of the x-component reversal of one edge of the written track by centering a head on that edge, and by stepping the head across the edge. Since a straight track edge would not produce any flux change in the read head coil, the voltage output of the head arises from flux changes due to track edge fluctuations. The spectrum of the fluctuations can be deduced by decorrelating the read head sensitivity function from the voltage spectrum. We have used this procedure with several low- and high-noise thin-film media and we find in each case a k−b spectrum (k=wave number) with b near 1. We propose a model which interprets the fluctuations as a superposition of uncorrelated protuberances from a nominal straight edge, and we deduce the size distribution of the protuberances which will generate the observed fluctuation spectrum. Simulated reconstruction of the track edge resulting from a weighted superposition of the protuberances permits semiquantitative inferences to be drawn from the model about the medium microstructure.
NMR study of the low temperature spin canting in Nd2(CoFe)14B with low Fe content
Authors: Jȩdryka E. , Wójcik M. , Panissod P. , Buschow K. H. J.
Published: July 2002

5 9Co NMR was studied in a series of Nd2(Co1−xFex)14B compounds with x=0.001, 0.01, 0.02, 0.05, 0.10 between 4.2 and 77 K. A fast increase of the canting angle between the magnetization and c axis upon Fe substitution has been found. Nonregular local environment effects in the form of rapidly developing satellite structure with significant intensity have been observed and tentatively attributed to the Fe influence on the crystal field experienced by the Nd sublattice.
Frequency dependence of the magnetic irreversibility line in high-temperature superconductors
Authors: Flippen R. B. , Askew T. R.
Published: July 2002

The magnetic irreversibility line (IL) has been measured as a function of magnetic field and frequency using an ac inductance technique in single crystals of YBaCuO and BiSrCaCuO and in consolidated YBaCuO fibers. The IL is defined as the temperature of the peak in X″ as a function of magnetic field. Above the IL magnetic flux is mobile in the superconductor and the critical current Jc is zero; below the IL flux is pinned and a Jc can exist. Very small (<1 K) shifts in the temperature of the peak in X″ in YBaCuO crystals are seen in fields up to 400 Oe, and for frequencies up to 20 kHz. In contrast, crystals of BiSrCaCuO show shifts downward of the X″ peak temperature of more than 40 K at 100 Hz, and in fields of 400 Oe. Intermediate behavior is seen for YBaCuO fibers. These data and particularly the frequency dependence of the IL are discussed in terms of flux creep/flux flow in these materials.
Crystal-field excitations and superconductivity in Nd1+xBa2−xCu3O7
Authors: Loong C.-K. , Goodman G. L. , Soderholm L. , Dabrowski B. , Hinks D. G.
Published: July 2002

The f-electron excitation spectra of Nd ions in superconducting NdBa2Cu3O7 and semiconducting Nd1.5Ba1.5Cu3O7 have been determined by inelastic neutron scattering. Transitions within the paramagnetic ground-state multiplet due to crystal-field splittings have been observed up to about 120 meV in these materials. The temperature dependence of the width of the low-lying transition at ∼21 meV shows significant differences in the superconducting and normal states. Adopting the CF level assignments for HoBa2Cu3O7, we rescaled the CF parameters to account for the larger radial wave functions of Nd3+ ions and obtained a level scheme for the Nd using the lowest 100 states of the f3 configuration. The calculated level structures for REBa2Cu3O7 (RE=Nd, Pr, Ho) are in good agreement with neutron and susceptibility measurements. Influence of superconducting ordering on crystal-field transitions in the Nd1+xBa2−xCu3O7 system is also discussed.
Third harmonics in the minor loop of a sintered Y-Ba-Cu-O superconducting disk and its dc-field dependence
Authors: Okamoto K. , Makino Y. , Watanabe N. , Rao K. V.
Published: July 2002

We have investigated the low-field M-H minor loop of a sintered YBa2Cu3O7−δ disk (Tc=87 K at R=0) at liquid nitrogen temperatures both in the zero-field and field-cooled states. It is found that the M-H minor loop is of the Rayleigh type with only odd harmonics of the Fourier series as is well known in ferromagnetic materials. The third harmonic component shows a dc-bias field dependence with symmetric and asymmetric hysteresis in the respective zero-field and low field-cooled states. These results are qualitatively explained in terms of the vortex dynamics and the associated losses in an external bias field.
The mathematical modeling of the acquisition of gyroremanent magnetization in a single domain particle
Authors: Dean B. , Chantrell R. W. , Hart A. , Parker D. A. , Stephenson A.
Published: July 2002

The origins of gyroremanent magnetization (GRM) in single domain particles are studied using a dynamic model based on the Landau–Lifschitz equation. The results show an asymmetry in the motion of the magnetic moment of a particle with three unequal axes of anisotropy. This asymmetry is interpreted in terms of an effective bias field which gives a good qualitative explanation of the origins of GRM.
Repetition of negative differential resistance in vertically integrated double-barrier resonant tunneling structures
Authors: Wu J. S. , Lee C. P. , Chang C. Y , Chang K. H. , Liu D. G. , Liou D. C.
Published: July 2002

We propose and demonstrate a novel operation in the vertical integration of double-barrier resonant tunneling structures (DBRTS’s) in which the negative differential resistance (NDR) region can be repeated. When two DBRTS’s are combined in series, one of which has a higher peak current, a lower valley current, and a larger operation range of voltage in the NDR region than those of the other, the current-voltage (I-V) characteristic shows three current peaks instead of the conventional two. This phenomenon is based on the fundamental requirement of current continuity in serially combined devices. This operation provides a method to obtain a large number of current peaks by using less DBRTS’s.
Mixed magnetization states for field modulation writing of MO media
Authors: Madison M. R. , McDaniel T. W.
Published: July 2002

Direct overwrite of thermomagnetically written domains in rare-earth transition-metal thin films using magnetic field modulation has previously been reported. The written magnetization during the low field portion of the field modulation is unsaturated. A new technique for directly measuring the amount of mixed magnetization produced during continuous power laser writing was developed. The field dependence of both the measured amount of mixed magnetization and the measured integrated noise demonstrates a continuously varying mixture of microdomains, plus it yields a direct measure of the saturation field. A comparison to theory using a thermomagnetic write and read simulation was performed. Patterns corresponding to those written experimentally (long, continuous strips) were modeled and characterized. Measures of the mixed states were extracted from the simulation results as a function of applied bias field. From the simulations we computed the average signal, as well as an estimate of the integrated noise power spectrum. These simulation measures of mixed magnetization and its associated noise as sensed in magneto-optic readout have been found to closely match experimental results.
Superconducting YBa2Cu3O7−δ thin films with three different orientations
Authors: Wang X. K. , Li D. X. , Li D. Q. , Lu Y. P. , Song S. N. , Shen Y. H. , Zheng J. Q. , Chang R. P. H. , Ketterson J. B. , Chabala J. M. , Hansley D. , Levi-Setti R.
Published: July 2002

Epitaxial thin films of YBaCuO have been prepared with (1) the a axis perpendicular to (100) SrTiO3 ; (2) the c axis perpendicular to (100) SrTiO3 ; and (3) the [110] axis perpendicular to (110) SrTiO3. Films were fabricated using a multilayer deposition technique involving three electron guns containing Y, BaF2, and Cu under a pressure of 5×10−5 Torr of O2. As deposited films, which contained polycrystalline and amorphous regions, were later annealed in a furnace under a flowing O2-H2 O atmosphere. X-ray diffraction patterns as well as scanning electron microscopy and high-resolution electron microscopy images confirm that the films are highly oriented, essentially epitaxial. The a-axis oriented film exhibits zero resistance at 90 K and a critical current density of 2.9×106 A/cm2 at 4.2 K while the c-axis oriented film exhibits a Tc of 88 K and a Jc of 0.9×107 A/cm2 at 4.2K; the Jc values were determined magnetically. The [110]-orientation film shows the sharpest transition with a transition width of 1 K and zero resistance at 85 K.
Photoluminescence studies of bound excitons in copper-doped GaAs
Authors: Villemaire A. , Charbonneau S. , Steiner T. , Thewalt M. L. W.
Published: July 2002

The photoluminescence (pl) of copper-related bound excitons (BE’s) in GaAs is investigated by means of resonantly excited and time-resolved photoluminescence, as well as photoluminescence-excitation (ple) spectroscopy. Observation of the 2s and 3s two-hole transitions leads to a precise value of 193 meV for the hole binding energy of the acceptor associated with the F complex. No evidence for such two-hole transitions was ever detected for the C complex. The lifetimes of the C0 and the F0 BE’s are reported in addition to that of a line found at 1501.5 meV. C0 BE exhibit an excited state 3.7 meV above the ground state, while no excited states were detected for F0.
Performance characteristics of In0.53Ga0.47As/In0.52Al0.48As modulation-doped field-effect transistors realized by two-step epitaxy: Effects of molecular-beam epitaxial regrowth
Authors: Lai R. , Bhattacharya P. K.
Published: July 2002

Epitaxial regrowth is emerging as an important step in the processing and realization of optoelectronic integrated circuits. We have studied the dc and microwave characteristics of regrown In0.53Ga0.47As/In0.52Al0.48As modulation-doped field effect transistors on InP substrates and have compared these with the characteristics of normally grown devices. The low-field transport properties of the heterostructures are degraded due to the increased interface roughness caused by processing and regrowth. The dc and microwave characteristics in terms of gm (399 mS/mm), fT (20 GHz), and fmax (35 GHz) are slightly degraded in the regrown devices compared to the normally grown ones. The density of states at the active heterointerface is not appreciably increased compared to normally grown devices. The low-frequency 1/f noise level is higher in the saturation regime in the regrown devices. Our results indicate that there may be increased density of trapping centers in the regrown In0.52Al0.48As buffer layer below the active channel.
Conformationally incommensurate form of poly(vinylidene fluoride) induced by electric field
Authors: Takahashi Yasuhiro
Published: July 2002

Poly(vinylidene fluoride) form II is transformed to polar II under a high electric field. Servet and Rault [J. Phys. (Paris) 40, 1145 (1979)] found few weak so-called superlattice spots on the fiber diagram of polar II. In the present study these spots are clarified to arise from a new form, which is considered to be the intermediate structure between polar II (TGTḠ)n and form I (T)n, a conformationally incommensurate structure.
Effect of dopants on the conductivity of electrodeposited CdTe
Authors: von Windheim Jesko , Renaud Ian , Cocivera Michael
Published: July 2002

Thin-film polycrystalline CdTe was electrodeposited as described previously onto indium-tin-oxide coated glass under argon and then stored either under argon or air before and after the annealing step. Dopants were incorporated into films by several methods. Indium, Cadmium, and silver were introduced into the films either by codeposition or by electromigration techniques as described previously for copper, and the doping process was followed by heat treatment. Tellurium was introduced into two films by heating the samples in a tellurium atmosphere, and the effect of oxygen on the CdTe was investigated by a high-temperature heat treatment in air. The effect of these doping procedures on the conductivity was investigated at various temperatures. For this purpose, a system was built to measure extremely high resistances (>1012) over a large and well-controlled temperature range. Because of the polycrystalline nature of the films, the results are discussed in terms of a model in which the conducitivity is affected by the density of grain boundary states.
Acoustic material signature from frequency analysis
Authors: Nagy Peter B. , Adler Laszlo
Published: July 2002

An alternative approach to obtain the acoustic material signature in scanning acoustic microscopy as the periodicity of the output voltage in the frequency domain V( f ) is suggested. Certain advantages of this technique over the conventional V(z) approach are demonstrated through experimental results.
Incoherent resonant tunneling without reflection in asymmetric double-barrier structures
Authors: Kan S. C. , Yariv A.
Published: July 2002

The scattering processes inside the quantum well, which destroy the coherency of the wave function of the electron in a double-barrier resonant tunneling structure, are modeled by an imaginary scattering potential. The reflection coefficient, which is nonzero for an asymmetric structure without the imaginary potential, becomes zero at the resonance energy of the structure having an imaginary potential of a particular magnitude. The dependence of this particular magnitude of the imaginary potential on the ratio of the thicknesses of the two barriers is examined. For a structure in which one of the barriers is infinitely wide, this particular magnitude of the imaginary potential is equal to the width of the resonance of the structure without the imaginary potential.
Theoretical evaluation of a short-pulse electron-beam-excited XeF(B→X) laser using a low-pressure, room-temperature Ar/Xe/F2 gas mixture
Authors: Nishida Naoto , Takashima Toshiaki , Tittel Frank K. , Kannari Fumihiko , Obara Minoru
Published: July 2002

A simulation code for an electron-beam-excited XeF(B→X) laser using Ar/Xe/F2 gas mixtures is described. The validity of the code was checked by comparing the computed results to those obtained in a previously reported experiment with a 65-ns, 1.14-MW/cm3 excitation pulse. Good agreement is demonstrated for sidelight fluorescence, laser waveforms, output power, and energy. Furthermore, the simulation code analysis suggests that the XeF laser can be operated effectively with low-pressure (<1 atm) Ar/Xe/F2 mixtures at room temperature. A maximum intrinsic efficiency of ∼3% is obtained at a total pressure of 0.5 atm. Such a low-pressure Ar/Xe/F2 laser gas mixture would permit operation of a scaled-up XeF laser system since the intrinsic efficiency is as high as that with conventional high-pressure (∼3 atm) Ne/Xe/NF3 mixtures.
Very-high-frequency–ultrahigh-frequency shape demagnetizing effects
Authors: Ratliff S. T.
Published: July 2002

Previous studies by various researchers show the influence of material shape ofn apparent permeability at zero frequency and predict that this will still be valid at higher frequencies. In this paper we demonstrate the influence of shape demagnetizing effects for the attenuation of transverse electromagnetic waves in a stripline transmission line at frequencies where the material thickness is small compared to the free-space wavelength in the frequency range 100–600 MHz.
Infrared stimulated photoconductivity overshoot in a-Si:H
Authors: Han Daxing , Wu Lei
Published: July 2002

At low temperatures, a subband-gap-light-excited photoconductivity overshoot Δσ was observed following a millisecond pulse of visible-light excitation in hydrogenated amorphous silicon. The relative change Δσ/σ was attributed to an increase in the optical absorption, Δα/α, due to deeply trapped carriers. Both the spectral distribution of Δα/α and its relaxation in the annealed state A are different from those in the light-soaked state B. Silicon dangling bonds generated by the Staebler–Wronski effect having different configuration than the thermally generated bonds are suggested as the explanation for the different behavior.
Pinning of a fluxon chain in a long Josephson junction with a lattice of inhomogeneities: Theory and experiment
Authors: Malomed Boris A. , Ustinov Alexey V.
Published: July 2002

A pinning force acting upon a periodic fluxon chain in a long Josephson junction with a commensurable periodic lattice of local inhomogeneities is calculated by means of a perturbation theory. The pinning force for a single fluxon is also calculated. Dynamics of a chain and of a single fluxon are also studied. The experimental part of the paper reports results of measurements of a critical bias current Ic versus external magnetic field H. The measurements have been performed for long overlap Nb-NbOx-Pb junctions Ic(H) curve were observed at multiple values of H. Agreement between the theory and experiment for different spatial periods of the fluxon chain is satisfactory.
A criterion for the suppression of plastic deformation in laser-assisted chemical vapor deposition of GaAs
Authors: Hussien S. A. , Fahmy A. A. , El-Masry N. A. , Bedair S. M.
Published: July 2002

Laser-induced chemical vapor deposition (LCVD) of GaAs allows deposited film to trace the path of the laser beam, thus making it attractive for several applications. However the localized thermal expansion resulting from the laser-induced temperature rise has to be elastically accomodated in order to prevent lattice defects in the LCVD film. We report on the growth conditions that can be allowed without the occurrence of plastic deformation in the epitaxial films. A model is presented to explain the thermal expansion induced distortion during the deposition process and is compared with experimental results.
Study of the ionized cluster beam technique using energy-analyzed gold depositions
Authors: Urban Frank K.
Published: July 2002

The ionized cluster beam technique (ICB) is under development as a thin-film deposition method. The key difference between ICB and other techniques is that the material to be deposited is said to arrive at the substrate in the form of ionized, accelerated atom clusters, previously reported to average 1000 atoms in size. A number of advantages have been attributed to ICB depositions including low-temperature epitaxy, epitaxy for materials with a relatively large lattice mismatch, low surface damage, and near bulk density. However, for the majority of depositions reported, the beam cluster state was not measured directly but inferred from theory. Consequently, little is known about the conditions required for significant cluster formation and how clusters influence film properties. The purpose of this study was to investigate the cluster state of a gold beam in a Kyoto University ICB deposition instrument. Electrostatic deflection experiments showed no significant cluster formation over the full operating range of the instrument.
Mechanical properties of a-Si:H films studied by Brillouin scattering and nanoindenter
Authors: Jiang X. , Goranchev B. , Schmidt K. , Grünberg P. , Reichelt K.
Published: July 2002

A series of a-Si:H films has been prepared by rf sputtering in a H2-Ar gas mixture. To obtain films with different hydrogen content the hydrogen portion of the gas mixture was changed from 0% to 20%. The shear modulus μ was then measured by the frequency of the surface phonon (Rayleigh wave). The stiffness S and the ultramicrohardness H were measured by using a nanoindenter. From the shear modulus μ and the stiffness S, the Young’s modulus E and Poisson’s ratio ν were calculated. The intrinsic mechanical stress was measured by the bending-beam method. With increasing hydrogen content of the films, the decrease of Young’s modulus, microhardness, and internal stress are observed.
Diffraction of obliquely incident P waves by two parallel and coplanar Griffith cracks
Authors: Verma S. K. , Jain D. L.
Published: July 2002

The solution of the problem of diffraction of obliquely incident longitudinal waves by two equal, parallel, and coplanar Griffith cracks embedded in an infinite, isotropic, and homogeneous elastic medium is solved by a simple integral equation technique. Approximate expressions for the stress intensity factors, far-field amplitudes, and scattering cross section are obtained when the wavelengths are large compared to the distance between the outer edges of the two cracks. By taking appropriate limits in these expressions, we derive some interesting and new results. The values of stress intensity factors and the scattering cross section are computed and various graphs of these physical quantities of interest are plotted.
Transport properties of liquid-phase epitaxial Hg1−xCdxTe n/p structures
Authors: Koppel P. , Owens K.
Published: July 2002

We report Hall-effect results of controlled Hg-diffused n regions on as-grown, p-type liquid-phase epitaxial Hg0.8Cd0.2Te, for varying diffusion times. The Hall-effect results of Hg diffusion through CdTe passivation layers of varying thickness for fixed time on as-grown p-type Hg0.8Cd0.2Te are also reported. From additional measurements of the electrical properties for the n- and p-type cases, the Hall data are analyzed in terms of the two-layer model [R. L. Petritz, Phys. Rev. 110, 1254 (1958)]. From this analysis, junction depth is estimated for a variety of experimental diffusion conditions using a fitting procedure in conjuction with a theoretical transport model. The fitting procedure results are verified by differential Hall measurements and also compared to diffusion theory [R. B. Allen, H. Bernstein, and A. D. Kurtz, J. Appl. Phys. 31, 334 (1960)]. The sensitivity of determining junction depth to errors in estimates of the donor and acceptor concentration, and mobility within each layer, are discussed.
Evolution of point to extended defects in low-temperature implanted Hg0.76Cd0.24Te
Authors: Richter V. , Kalish R.
Published: July 2002

The transition from point defects, frozen-in at low-temperature ion implanted Hg1−xCdxTe (x=0.24), to extended defects has been monitored through ion channeling experiments in the temperature range 100–360 K. It is found that the transition exhibits time and temperature dependencies characteristic for diffusion processes with exceptionally low parameters. The extended defects formed by the agglomeration of frozen-in point defects are found to roughly correspond in depth to the implant range, in contrast to defects directly created by room-temperature implantation which extend much deeper into the crystal.
Novel types of surface acoustic wave microreflectors: Performance analysis and simulations
Authors: Golan G. , Griffel G. , Seidman A. , Croitoru N.
Published: July 2002

Surface acoustic waves for micrograting reflectors have been characterized. Based on the perturbation theory, eight different types of structures on an acoustic waveguide were analyzed. Results of simulations of all eight types of corrugation structures were evaluated in order to find the least leaky waveguide, the most efficient reflector (with minimum necessary perturbations), and the optimal mode shape for improved performances. General design curves are presented in order to illustrate the behavior of the incident and reflected waves under a variety of structural conditions. Analytic expressions for the calculations of the mode amplitude and mode shape, and for general acoustic corrugations are derived and then the simulations results are presented.
Some properties of the circular waveguide with azimuthally magnetized ferrite
Authors: Ivanov Kamen P. , Georgiev Georgi N.
Published: July 2002

A comprehensive analysis of normal rotationally symmetric TE modes in a circular waveguide, filled with ferrite, magnetized azimuthally to remanence by a coaxial switching conductor of finite radius, is presented. The characteristic equation of the structure, derived in terms of Kummer and Tricomi confluent hypergeometric functions of complex parameter and variable, is solved numerically, using specially compiled tables of wave functions. Families of theoretically calculated nonreciprocal phase characteristics of the gyrotropic waveguide are shown in normalized form for the two latched states of remanent magnetization, a variety of ferrite parameters, and different values of switching conductor to waveguide radius ratio. The influence of structure geometry and parameters of anisotropic ferrite on normalized differential phase shift and cutoff frequency spectrum of the TE01 mode is discussed.
Separation of optical thin-film and substrate absorption by means of photothermal surface deformation technique
Authors: Welsch Eberhard , Walther Heinz-Guenter , Friedrich Kerstin , Eckardt Peter
Published: July 2002

The photothermal surface deformation (PTD) technique is shown to be feasible to separate absorption losses of single-layer film and substrate absorption from each other by a completely contactless detection of the thermoelastic sample response only appropriately varying the focus radius of the heating beam. This offers a method for a depth-resolved distinction of absorptive regions within a layered structure by the help of lateral resolved PTD absorption measurements. Additionally, both the sensitivity and feasibility of the apparatus is demonstrated by selected results at 10.6 μm.
Hydrogen incorporation scheme in hydrogenated amorphous silicon/silicon carbon multilayers
Authors: Yoshimoto Masahiro , Matsunami Hiroyuki
Published: July 2002

Using infrared absorption spectroscopy, we investigated the scheme of hydrogen incorporation into the well layer (a-Si:H) of a-Si:H/a-Si1−xCx :H (x=0.2, 0.5, and 0.8) multilayers fabricated by a glow discharge method. Hydrogen atoms are incorporated into the well layer in the form of the 2090-cm−1 mode, i.e., SiH monohydride bonds on internal microvoid surfaces or SiH2 dihydride bonds up to a well-layer thickness of 40 Å, and then SiH monohydride bonds of the 2000-cm−1 mode are formed. Even up to 100 Å, hydrogen atoms of the 2090-cm−1 mode are dominant rather than SiH monohydride bonds of the 2000-cm−1 mode. The optical energy gap of the multilayer is also discussed in connection with the scheme of hydrogen incorporation.
Role of recoil implanted oxygen in determining boron diffusion in silicon
Authors: Fan D. , Jaccodine R. J.
Published: July 2002

Annealing of silicon implanted with boron through a surface oxide results in an enhanced diffusion of boron. This enhanced diffusion is suppressed during an initial incubation period. An activation energy of 2 eV is associated with the enhanced diffusion, indicating excess silicon interstitials may be involved. On the other hand, the process leading to the onset of enhanced diffusion possesses an apparent activation energy of 3.7 eV. Two-step annealing reduces the latter value to 2.6 eV, the activation energy for interstitial oxygen diffusion. The different activation energies evaluated for the saturation process will be discussed. Transmission electron microscopy shows that the coalescence of dislocations, as well as the growth of faulted loops, proceeds rapidly after the incubation period for enhance diffusion. Precipitates along small dislocation loops are also observed after the incubation period. It is proposed that oxygen precipitation, with emission of silicon interstitials, predominates for annealing beyond the incubation period and is therefore responsible for the enhanced diffusion of boron. The enhanced diffusion sequence is initially incubated by trapping oxygen at dislocations. The real onset of the enhanced diffusion occurs when the dislocations are saturated and the oxide precipitation at the dislocations commences.
Frequencies of confined longitudinal-optical phonon modes in GaAs/GaP short-period strained-layer superlattices
Authors: Kim K. W. , Stroscio M. A. , Hall J. C.
Published: July 2002

The linear-chain approximation is used to calculate the spectrum of confined longitudinal-optical (LO) phonon frequencies in short-period strained-layer superlattices. The frequencies for confined LO-phonon modes are reported explicitly for the case of GaAs/GaP short-period strained-layer superlattices grown in the 〈001〉 direction. These results are compared with the few existing experimental measurements for such superlattices.
Pulsed laser treatment of Fe2O3 film on Al2O3
Authors: Bhagwat Sunita
Published: July 2002

Fe2O3 film (∼110 Å) on crystalline Al2O3 substrate is treated by ruby laser pulses at different energy densities up to a maximum of ∼7.5 J/cm2, and the transformations are examined by conversion electron Mössbauer spectroscopy and small-angle x-ray diffraction measurements. It is observed that transformations begin to appear in the sample at an energy density of ∼3.0 J/cm2 although significant modifications are observed only at energy densities higher than about 7.0 J/cm2. The values of hyperfine interaction parameters reveal that the laser treated samples contain FeAlO3 and FeAl2O4 phases, along with the residual α-Fe2O3 phase. The laser-mixed state undergoes structural modifications upon thermal annealing, leading to formation of the Fe3O4 phase and complete disappearance of the FeAlO3 phase.
Simple analytic potentials for linear ion traps
Authors: Janik G. R. , Prestage J. D. , Maleki L.
Published: July 2002

We have developed a simple analytical model for the electric and ponderomotive (trapping) potentials in linear ion traps. We have used this model to calculate the required voltage drive to our mercury trap, and the result compares well with our experiments. The model gives a detailed picture of the geometric shape of the trapping potential and allows an accurate calculation of the well depth. The simplicity of the model allowed us to investigate related, more exotic trap designs which may have advantages in light-collection efficiency.
Eddy-current inspection of cracks in a multilayer conductor
Authors: Burke S. K.
Published: July 2002

A theoretical model is presented to describe the time-harmonic induction of eddy currents in a layered conductor containing a crack. The layered system consists of two parallel conducting plates separated by an insulating gap and it is assumed that the thickness tS of the plate containing the (through-the-thickness) crack is small compared with the electromagnetic skin depth δS. Explicit expressions for the magnetic vector potential in the absence of the crack are derived for the particular case of induction by a circular air-cored coil, and these results are used to calculate the change in coil impedance ΔZU due to the induced currents in the uncracked system. The effect of a through-the-thickness crack is represented by an equivalent distribution of current sources along the line of the crack. The form of these generalized current vortex sources is examined and explicit expressions are presented for the current density and vector potential due to a single vortex. The vortex density, and hence the induced current distribution, are obtained by solving a one-dimensional singular integral equation. This formalism is used to calculate the change in coil impedance ΔZC due to a first- or second-layer crack. Experimental measurements of ΔZ were carried out for several model systems and the theoretical calculations were found to agree with experiment to within 10% or better for tS/δS up to 0.4. The implications for the detectability of cracks using eddy-current nondestructive inspection is discussed.
Thermodynamic calculations of the graphitization of carbon blacks
Authors: Speck J. S.
Published: July 2002

A thermodynamic model is presented to account for the nongraphitizing behavior of small (<200 Å) carbon black particles. Only pure carbon is considered, hence no compositional effects are included in these calculations. The ungraphitized carbon black particle is modeled as concentric turbostratic spheres of graphene layers. The partially graphitized particle is modeled to consist of a graphitic dodecahedral shell and a spherical turbostratic core. Free-energy differences are calculated between a fully turbostratic particle and a partially graphitized particle. The temperature dependence of the free-energy difference has not been included in these calculations. It is found that the effective activation barrier to graphitization increases with decreasing particle size. The concepts developed in this model are extended to explain the nongraphitizing behavior of all hard carbons.
Linear motion sensor using the Doppler effect with magnetostatic waves
Authors: Koros Nina L. , Bilaniuk Nykolai , Stancil Daniel D.
Published: July 2002

Observation of the Doppler shift of magnetostatic waves and a new linear velocity and position sensor based on this effect are reported. The sensor consists of a magnetostatic surface-wave delay line in which one transducer is allowed to move along the direction of propagation. Position and velocity are indicated by the phase and Doppler shift of the transmitted signal, respectively. These effects are much larger than would be observed with ordinary electromagnetic waves at the same frequency owing to the shorter wavelengths of magnetostatic waves.
Improved uniformity of PtSi Schottky barrier diodes formed using an ion mixing scheme
Authors: Hewett C. A. , Fernandes M. G. , Lau S. S.
Published: July 2002

Low dose ion implantation through the Pt/Si silicon interface prior to annealing has been shown to yield a more planar PtSi/Si interface after annealing. The electrical characteristics of these ion mixed diodes have also been shown to be more uniform from device to device as well as more nearly approaching theoretical performance than conventionally prepared diodes.
Defect states in carbon and oxygen implanted p-type silicon
Authors: Awadelkarim O. O. , Suliman S. A. , Monemar B. , Lindström J. L. , Zhang Y. , Corbett J. W.
Published: July 2002

The presence of electrically active defects in C+ and CO+ implanted boron-doped silicon has been monitored using deep level transient spectroscopy and resistivity measurements. Activation energies of trapped carriers, implanted ion dependencies, and annealing behavior of these defects have been determined. The introduction of defects by annealing has been observed. A total of ten hole and electron traps are reported. Among these traps, a dominant hole trap 0.65 eV above the valence band, and an electron trap 0.53 eV below the conduction band, are tentatively ascribed to the silicon di-interstitial and the carbon-oxygen pair, respectively. Other traps detected in the samples have been correlated with multi-oxygen- and carbon-related complexes. Annealing at temperatures up to 400 °C gives rise to similar deep level transient spectroscopy spectra comprising the same traps in both C+ and CO+ implanted material. However , annealing at temperatures >500 °C produces defect states that are dependent on the implanted ion species.