bluuebunny/crossref_metadata_2025 huggingface dataset:
Domain size and spin waves in a reentrant spin glass
Authors: Erwin R. W.
Published: July 2002

Neutron depolarization measurements on the amorphous alloys, (FexNi1−x )75P16B6Al3, above the multicritical concentration x>0.15, indicate that low-field domain sizes are in the range of 2–4 μm. This is approximately two orders of magnitude larger than the length scales observed with magnetic small-angle neutron-scattering techniques. The depolarization shows evidence of domain size changes and/or canting as the reentrant-spin-glass state is entered, in agreement with the small-angle scattering results. Sufficiently near to the multicritical concentration the results cannot be interpreted solely in terms of a canting transition, because the change in depolarization is too great. In the samples where anomalous low-temperature spin waves have been observed, the depolarization behaves as in a conventional ferromagnet, indicating that the reentrant-spin-glass spin-wave behavior is related to a canting transition. The spin-wave spectrum calculated for a model canting system reasonably explains the observed spin-wave measurements.
Anomalous ultrasonic attenuation by the spin-density wave in a dilute Cr(V) alloy
Authors: de Camargo P. C. , Fawcett E. , Perz J. M.
Published: July 2002

A single crystal of Cr+0.5 at. % V was field cooled through its Néel temperature TN≂ 260 K, with a field B=12 T, along a cube axis to produce a single-Q state. The attenuation α was measured for 10-MHz longitudinal ultrasound propagating parallel and perpendicular to Q, and also in the non-field-cooled poly-Q state. The resultant anisotropy in the change in α at the spin-flip temperature TSF≂40 K, shows the sample to be largely single-Q, but its nature suggests that the change of the magnetic structure at the low-temperature phase transition may differ from that in pure Cr.
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1Eu Mössbauer study of the high-T
c superconductor Bi2Ca0.5Eu0.5Sr2Cu2Ox (abstract)
Authors: Oliver F. W. , May L. , Violet C. E.
Published: July 2002

Isomer shift measurements show the Eu to be trivalent and nonmagnetic with no apparent anomaly between measurements made above and below the transition temperature (Tc=87 K). The value of the isomer shift at room temperature (0.69±0.02 mm/s) falls within the values observed by previous researchers on other types of Eu-based high-Tc superconductors. A discussion on the isomer shift and f factor as a function of temperature will be reported and compared with previous results found in Eu-based high-Tc superconductors.1–3
Preparation of high-T
c oxide superconductors at low substrate temperature by facing-targets sputtering
Authors: Hirata T. , Naoe M.
Published: July 2002

Y-Ba-Cu-O thin films were prepared at low substrate temperature (Ts≤500 °C) by a facing-targets-sputtering (FTS) system. MgO〈100〉 and SrTiO3〈110〉 substrates were used in this study. According to the x-ray-diffraction patterns, as-deposited Y-Ba-Cu-O thin films prepared by the FTS system crystallized in the tetragonal phase. The composition of the Y-Ba-Cu-O thin films was almost the same as that of the targets. In the FTS system the growing film on the substrate would not be bombarded by high-energy particles such as γ electrons and negative ions since the substrate is set in a plasma-free position. Consequently, the difference between the film composition and that of the target does not occur due to resputtering. Finally, at a Ts of about 410 °C, high-Tc oxide superconductors of Y-Ba-Cu-O thin films were obtained by the FTS system. The film surfaces were very smooth. There was no difference between the film composition and that of the target. Tc was about 85 K.
Specific-heat investigation of magnetic ordering in La2−xSrxCuO4
Authors: Aldrovandi S. , Borsa F. , Lascialfari A. , Tognetti V.
Published: July 2002

Measurements of the specific heat in the temperature range 2–300 K are presented for La2−xSrxCuO4 at selected values of doping: x=0.01, 0.025, 0.05, 0.1, and 0.2. Peaks are found in correspondence to the onset of long-range magnetic order, in good agreement with nuclear-quadrupole-resonance and muon-spin-resonance results. A contribution due to the excitation spectrum of the holes introduced by Sr substitution is observed for x=0.025 and 0.05. These results are compared with the predictions of a simple model.
Superconductivity of Nb/Cr multilayers
Authors: Cheng Y. , Stearns M. B.
Published: July 2002

Multilayers of Nb/Cr have been fabricated by a UHV e-beam evaporation system with the nominal Cr layer thickness of 30 Å and the Nb layers varying from 30 to 1000 Å. The structural properties have been studied by computer modeling of the measured large angle x-ray spectra. It was found that the Nb/Cr films have symmetric interfaces. The resistivity temperature variation was measured using the dc four-probe method. For ML with bilayer thickness, Λ less than 250 Å, it varied inversely as Λ−1 indicating that the resistivity is dominated by electron scattering from the interfaces at low temperature. The Tc of Nb/Cr films varies from 9.1 K for dNb=1000 Å to below 4.2 K for dNb=26 Å. This can be explained by the de Gennes–Werthamer theory with corrections for the interface thicknesses. It was also found that the resistivity drop occurs in two steps for samples with dNb<1000 Å. The areas under the second steps increased almost linearly with the number of the interfaces. The parallel critical fields were measured for several of the multilayers.
Thickness and aspect-ratio dependence of the magnetoresistance effect in NiCo alloy films
Authors: Kim H. S. , Hur C. S. , Im J. B. , Han J. B.
Published: July 2002

Films of thickness 350, 500, and 1100 Å rf-magnetron-sputtered onto Corning 7059 glass at a substrate temperature of 250 °C were patterned into aspect ratios of from 10 to 100 with a fixed width of 10 μm by the photolithographic procedure. Gold pads were formed for electrical contacts. Magnetoresistance ratio, saturation field, and in-plane coercivity were measured. The domain patterns were studied by the Bitter method. Results show that the magnetoresistance ratio increases as film thickness increases. In a 500-Å-thick film, the coercivity decreases from 14 to 9.8 Oe with increasing aspect ratio due to closure domain effects.
Large magnetoresistance anisotropy in a new class of amorphous ferromagnets: U100−x−ySbxMny
Authors: Freitas P. P. , Plaskett T. S.
Published: July 2002

U100−x−ySbxMny amorphous ferromagnets were prepared that have an anisotropic magnetoresistance (AMR) as high as 9.3% at 15 K and a 2-T field. This is a striking result, since the AMR of typical amorphous ferromagnets does not exceed 1%. These materials are random anisotropy ferromagnets, with large coercive fields (Hc =1.2 T, 15 K) following a thermally activated regime at low temperature. The Curie temperatures range from 95 to 112 K. Resistivity values vary from 200 to 400 μΩ cm and the Hall angle can reach 20° at 15 K. For T>TC, the resistivity follows a field-independent ln T behavior with dρ/dT showing a sharp anomaly at TC. Below TC, both these quantities are strongly anisotropic, depending on the angle between the magnetization and the current. Magnetization reversal process are inferred from the magnetoresistance hysteresis cycles—both coherent rotation and 180° domain-wall motion occur.
Development of a 48-turn thin-film head
Authors: Tamura K. , Nagao E. , Ohdoi Y.
Published: July 2002

A conventional 30-turn thin-film head does not yield sufficient output when applied to a small-size rigid disk drive, especially 3.5 in. or less. A head of higher output voltage with more turns is required to obtain larger signal-to-noise ratio. A 48-turn thin-film head with two-layered spiral coil has been successfully developed, and 1.6 times the output voltage and larger signal-to-noise ratio by about 3 dB compared with the conventional 30-turn head were obtained. The head has a 0.55-μm gap length, 17-μm track width, and 4-μm-thick Permalloy films on the 3370-type slider. Yoke length was designed to be the same as that of the 30-turn head to prevent the reduction of the head efficiency. To minimize the increase of the coil resistance due to increasing the coil turns, the copper coil was fabricated with a high-aspect-ratio process using oxygen-ion milling of photoresist. Coil width was 3 μm; coil pitch was 4.5 μm, and coil thickness was 4 μm. These heads were evaluated using a 3.5-in. sputtered disk and showed good electromagnetic performance.
Low-frequency (<10 kHz) surface magnetic energy losses measured with polarized secondary electrons (abstract)
Authors: Woods J. , O’Handley R. C.
Published: July 2002

The polarization of low-energy secondary electrons emitted from iron- and cobalt-based amorphous melt-spun ribbons is measured as a function of the applied in-plane magnetic field yielding surface hysteresis loops. The polarization is measured in real time up to a frequency of 10 kHz and hysteresis loops are displayed on an oscilloscope. The bulk losses are measured on the same samples in the same configuration with a secondary winding. The area of the loop (energy loss/cycle) is measured as a function of applied magnetic field switching rate for both the surface polarization and bulk magnetization measurements. The surface loss per cycle increases linearly with the switching rate and the bulk loss per cycle increases much more slowly with switching rate. This is the first discrimination of bulk and surface losses we are aware of.
Neutron-diffraction and Mössbauer-effect studies of Pr2(Fe1−xMnx)14B
Authors: Pringle O. A. , Fu Jie , Long Gary J. , James W. J. , Xie D. , Yelon W. B. , Grandjean F.
Published: July 2002

A neutron-diffraction investigation of a series of Pr2(Fe1−xMnx)14B samples, with x values of 0.00, 0.11, 0.22, 0.30, and 0.35, reveals a preference for the manganese to occupy the 8j2 transition-metal site,the transition-metal site with the largest Wigner–Seitz cell volume. Similar site occupancies have been reported previously for Er2(Fe1−xMnx)14B and Y2(Fe1−xMnx)14B. An analysis of the 295-K Mössbauer spectrum of Pr2(Fe0.89Mn0.11)14B indicates that the internal hyperfine fields on the six iron sites are more substantially reduced from those found in Pr2Fe14B than would be expected from a simple magnetic dilution with manganese. The extent of the field reduction for a specific site increases with the number of manganese near neighbors for the site. Fits of the Mössbauer spectra of Pr2(Fe0.78Mn0.22)14B, Pr2(Fe0.70Mn0.30)14B, and Pr2(Fe0.65Mn0.35)14B, which are paramagnetic at room temperature, give quadrupole splittings consistent with the quadrupole interactions in Pr2Fe14B.
Intrinsic magnetic hardness of R2(Fe1−xMnx)14B
Authors: Yang Ying-chang , Zhang Xiao-dong
Published: July 2002

The crystallographic structure and magnetic behavior of R2(Fe1−xMnx)14B have been studied, where R represents Nd, Pr, and Y. A large coercive force of up to 20 kOe has been observed at 1.5 K in as-cast bulk samples of the pseudoternary compounds. The coercivity does not depend on treatment such as milling, sintering, and annealing. It is intrinsic. The intrinsic coercive iHc shows a composition dependence. The form of the virgin magnetization curves is characterized by a propagation field Hp, indicating that the coercive force is created by domain wall pinning. Based on the magnetic measurements, the domain wall thickness of these compounds was calculated. The magnetic behavior of R2(Fe1−xMnx)14B can be understood in terms of narrow domain walls.
Reflectivity in PbFe12O19 from 1 to 30 eV
Authors: Krishnan R. , Kolobanov V. N. , Mikhailin V. V. , Orekhanov P. A. , Široký P. , Šrámek J. , Višňovský Š.
Published: July 2002

The optical reflectivity at 300 K in magnetoplumbite PbFe12O19 was measured at photon energies up to 30 eV using synchrotron radiation spectroscopy. The sample surface was a natural face perpendicular to the crystalline c axis. The crystal was prepared by the flux evaporation technique. By means of the Kramers–Kronig analysis and with the aid of the previous reflectivity and ellipsometry results, the spectra of the complex permittivity ε, the optical constants n and k, the absorption coefficient, and −Im ε−1 were obtained in the spectral range from 2 to 29 eV. At the photon energies below 10 eV the reflectivity spectrum of PbFe12O19 shows a strong analogy with that of lithium ferrite Li0.5Fe2.5O4. This may be due to the fact that the magnetoplumbite unit cell contains the spinel blocks. At photon energies above 10 eV the amplitudes of maxima of the two compounds differ significantly: the peak centered near 18.5 eV observed in the magnetoplumbite reflectivity spectrum is much stronger than the corresponding structure in lithium ferrite. This is consistent with the higher refractive index in magnetoplumbite at the low-energy end of the spectrum.
Theoretical calculations of electronic states in magnetic alloys of II-VI compounds with manganese (abstract)
Authors: Ali Dahr A.-I. , Lee P. M.
Published: July 2002

The problem of the electrical and magnetic properties of manganese-doped II-VI semiconductors requires a detailed understanding of the electronic states and excited states of these materials.1 Information about such states has been obtained by using the LMTO method to calculate electronic energy bands and densities of states for various alloys of manganese with cadmium telluride, zinc telluride, and cadmium selenide as well as for manganese telluride and managese sellenide. These are based on ordered structures for 25%, 50%, and 75% concentration of manganese. Structures for paramagnetic, ferromagnetic, and antiferromagnetic ordering have been studied and information obtained concerning the p-d hybridization and spin-orbit interaction effects on states at the top of the valence band. Comparisons with ground-state properties and binding energies are presented along with those for excited states, optical data, and x-ray absorption. In addition comparisons with other theoretical work2 are made.
Topological duality in three-dimensional eddy-current problems and its role in computer-aided problem formulation
Authors: Kotiuga P. R.
Published: July 2002

When a region containing a three-dimensional magnetoquasistatic field is broken up into a nonconducting region R and a conducting region Rc, which share a common boundary ∂R, the Alexander duality theorem expresses a topological duality which induces a lumped parameter duality: The ‘‘electromotive forces’’ in Rc are related, via Faraday’s law, to the time rate of change of magnetic fluxes in R just as the magnetomotive forces in R are related, via Ampere’s law, to the conduction currents in Rc. From this vantage, cuts in R are surfaces used to calculate magnetic flux linkage while, in the zero-frequency limit, cuts in Rc are surfaces used to calculate conduction currents. This paper shows how the formal description of the boundaries of the cuts and the topological interrelationship between R and Rc yield insight into the generation of cuts in R which are related to a given set of currents or closed loop voltages in Rc. We show how a computational treatment of lumped parameter aspects is possible.
Arrays of fluxoids in the high-TC superconductors and their putative phase transitions (invited)
Authors: Gammel P. L.
Published: July 2002

The static and dynamic properties of the magnetic vortices which penetrate films and crystals of the high-TC superconductors in fields above Hc1 have been examined in a variety of experiments. Direct visualization at low fields has been augmented with frequency dependent ac susceptibility, penetration depth, magnetization relaxation (using high-Q mechanical oscillators), and resistance measurements at high fields in an effort to obtain a complete understanding of the vortex dynamics. The various models for the vortex phase diagram, including isolated and collective vortex pinning, vortex lattice melting, and thermodynamic glass transitions are compared to the data. The bulk of the data presently available are consistent with strong pinning of independent vortices. Deviations from this model suggest where more complicated dynamics may become important.
Novel magnet structures for free-electron lasers
Authors: Leupold H. A. , Potenziani II E. , Abele Manlio G.
Published: July 2002

The high-energy rare-earth permanent magnets afford iron-free wiggler and twister field sources with greater field strengths in less massive structures than are possible when iron pole pieces and flux conductors are employed. However, the iron-free configurations have been notoriously difficult to adjust, as operational efficiency is very sensitive to the influence of small defects incurred in magnet manufacture and assembly. A general method for the compensation for such defects with small strategically placed magnetic dipoles is discussed and applied to structures of square, triangular, and circular cross section. The various configurations are compared with respect to design and convenience of defect compensation. The compensation of permanent magnet structures with mechanically variable field strength is also described together with a procedure for reversibly changing the function of such structures from wiggler to twister.
Magnetic dynamics of La2CuO4 studied by Mössbauer spectroscopy
Authors: Tang H. , Xiao Gang , Singh Avinash , Tes̆anović Zlatko , Chien C. L. , Walker J. C.
Published: July 2002

By doping a very small amount of 57Fe into La2CuO4, Mössbauer spectroscopy has been applied to study the magnetic property of the parent compound. From the measurement of the magnetic hyperfine field at the Fe nuclei for various temperatures between 4.2 K and TN, the temperature dependence of the sublattice magnetization for La2CuO4 has been discussed. A theoretical calculation shows that, with temperature increasing a 3D-2D dimensional crossover occurs in the magnetic dynamics of an anisotropic antiferromagnetic, which is indeed confirmed by the data. The best fit to the data using this theory yields J=1600 K and r=0.011.
A first principles calculation of anisotropic Cu NMR Knight shift satellites caused by 3d impurities
Authors: Drittler B. , Ebert H. , Zeller R. , Dederichs P. H.
Published: July 2002

The anisotropic hyperfine interaction of Cu atoms caused by nearby 3d-impurity atoms has been extensively studied some years ago by the Slichter group performing NMR measurements on single crystals. A first principles description of these interesting and challenging experiments is given in terms of self-consistent calculations of the electronic structure of the corresponding 3d-impurity systems. Our theoretical approach is based on the Korringa-Kohn-Rostoker-Green’s function method of band structure calculations and takes perturbations of Cu-host atoms up to the fourth neighboring shell around the impurity into account. In addition to our former work [B. Drittler et al., Phys. Rev. B 39, 6334 (1989)] dealing only with the dominating isotropic Fermi contact interaction, we also treat the dipolar spin part of the hyperfine interaction, which we assume to be the most important source of the anisotropic Knight shift deduced from single-crystal measurements.
Theory of the junction capacitance of an abrupt diode
Authors: Van Mieghem P. , Mertens R. P. , Van Overstraeten R. J.
Published: July 2002

A new theory for the junction capacitance of mathematically abrupt diodes is presented. In contrast with previous theories, Fermi–Dirac statistics are applied, and instead of using a parabolic density of states, a more appropriate function can be taken into account as this is required for heavily doped material. The main approximation is that of constant quasi-Fermi levels. Besides the study of symmetrical junctions, the behavior of asymmetrical abrupt junctions is both analyzed and explained. Anomalies resulting from the calculations are shown to be due to the mathematical discontinuity.
Heat conduction from a heated particle placed in a two-phase medium with a dispersed phase size comparable to the particle size
Authors: Sangani A. S.
Published: July 2002

The steady rate of heat conduction Q from a heated sphere maintained at a constant temperature different from that of a surrounding two-phase medium, which consists of an array of spherical particles of thermal conductivity αk and a matrix of conductivity k, is determined by a method of multipole expansion to O(φ4), where φ is the volume fraction of the particles in the array, and by a lubrication analysis for highly conducting and closely packed arrays. The results of the two analyses are combined to obtain estimates of Q that are expected to be accurate over the complete range of α and φ. These results are compared with the predictions of an effective-medium theory, and it is shown that the predictions of this theory are quite accurate over a rather wide range of α, 0<α<103, for the case of a simple cubic array, even at its maximum allowable volume fraction, but differ by as much as 60% for the case of a face-centered cubic array.
Characterization of the ZnSe heteroepilayer on a GaAs/Si substrate
Authors: Lee M. K. , Yeh M. Y. , Chang J. H. , Yu K. Y. , Lin Y. F.
Published: July 2002

ZnSe is a semiconductor with a direct band gap of 2.68 eV at room temperature, which makes it one of the most important materials for blue electroluminescent devices and short wavelength laser diodes. In this communication, heteroepitaxial growth of ZnSe on a GaAs/Si substrate by low-pressure organometallic chemical vapor deposition is reported. The ZnSe/GaAs/Si epilayer exhibits a uniform surface morphology. Strong photoluminescence near-band-edge emission was observed. The thickness of the GaAs buffer layer seems to be an important factor in the energy shift of the photoluminescence peak.
A two-layer model to explain the thickness dependence of conductivity and thermoelectric power of semiconductor thin films and application of the model to PbTe thin films
Authors: Das V. Damodara , Bhat K. Seetharama
Published: July 2002

A two-layer model to explain the thickness dependence of conductivity and thermoelectric power of semiconducting thin films has been developed assuming that the film is a parallel combination of resistances of the three layers: The first is the interior ‘‘grain-boundary’’ layer, and the other two, outer layers on opposite sides, whose conductivities are altered by the band bending (and is also affected by surface-gas interactions). The equations obtained in this model lead to an inverse thickness dependence of both the conductivity and thermoelectric power of thin films. The model is applied to analyze the conductivity and thermoelectric variation with thickness of PbTe thin films and the parameters Ug, the energy dependence of the ‘‘grain-boundary’’ mean free path lg, and σg the surface conductivity, have been evaluated.
A study of the annealing of heavily arsenic-doped silicon using x-ray photoelectron spectroscopy
Authors: Lau W. M. , Feng Xinghong , Kumar S. N.
Published: July 2002

The effects of incoherent light rapid thermal annealing and furnace annealing of arsenic-implanted silicon (6×1015/cm2 of arsenic at 70 keV) have been studied by x-ray photoelectron spectroscopy (XPS) and secondary-ion mass spectrometry (SIMS). The XPS analysis revealed two chemical states of arsenic with a 0.9-eV chemical shift of the 3d core level, which coexisted in both the as-implanted and annealed samples. The arsenic with a higher binding energy is interpreted as substitutional arsenic, whereas the other arsenic component is assigned as either interstitial or clustered arsenic. SIMS and XPS results also indicate that surface segregation and clustering of the implanted arsenic during annealing are enhanced by the presence of implantation-induced structural defects.
Magnetization reversal in cobalt-aluminum fine-particle ferromagnets: Microstructure and coercivity
Authors: Zeltser A. M. , Soffa W. A.
Published: July 2002

The magnetic age hardening produced by decomposition of a β-CoAl(B2) alloy has been studied by correlating the microstructure with the changes in magnetic properties during aging. A model based on coherent rotation has been developed to describe quantitatively the intrinsic coercivity of these fine-particle ferromagnets as well as the temperature dependence of the coercivity over the temperature range from 77 to 757 K. The model incorporates both magnetocrystalline anisotropy constants K1 and K2 in addition to the shape anisotropy of the elongated single-domain particles of metastable HCP cobalt which precipitate from solid solution during heat treatment. The magnetic properties of the particles are shown to depend critically on the crystallography of the solid-state transformation and particle morphology which were determined by transmission electron microscopy and diffraction.
Particular behavior of the initial susceptibility in weakly stressed polycrystalline soft magnetic materials
Authors: Le Floc’h M.
Published: July 2002

The effect of perpendicular compression on initial susceptibility of polycrystalline soft magnetic materials is investigated. In particular, it is shown that susceptibility magnitude does not decrease immediately with the stress applied. Consequently, a threshold is pointed out below which the domain-wall susceptibility keeps constant and equal to the initial value. Investigations of this threshold, between room temperature and the Curie temperature (550 K), has allowed a tight connection with intrinsic parameters of the spontaneous domain-wall arrangement to be established. In order to demonstrate this result, two types of materials have been prepared: perfect materials with domain-wall configuration approaching ideal orientation and defective materials with randomly dispersed domain-wall arrangement.
Methods of calculating the Barkas-effect correction to Bethe–Bloch stopping power
Authors: Porter L. E. , Lin Hong
Published: July 2002

The low-velocity Barkas-effect correction term for the Bethe–Bloch stopping-power formula has been calculated with each of the three extant formalisms for targets with atomic numbers from 1 to 18 and for projectile velocities from 0.025c to 0.3c. Comparison of each with measurements on aluminum revealed which formalism provided the best fit over three different projectile velocity intervals. The method yielding the generally superior agreement was used to calculate the stopping power of each element (except Li, F, Na, Mg, P, and Cl) for protons and alpha particles with energies between 0.5 and 5.0 MeV. Results corresponded very closely to those of an existing fit to most known experimental data.
Electromagnetic radiation from doubly rotated piezoelectric crystal plates vibrating at thickness frequencies
Authors: Lee P. C. Y. , Kim Y-G. , Prevost J. H.
Published: July 2002

Exact solution of the three-dimensional linear equations of piezoelectromagnetism is obtained for doubly rotated piezoelectric crystal plates surrounded by vacuum and excited by face traction. A generalized Poynting’s theorem is derived for general media in which electromagnetic and mechanical fields interact with each other. For linear piezoelectric crystals it is shown that the generalized theorem may still be interpreted as an energy theorem, and hence densities of energy stored in the electric, magnetic, and elastic strain fields can be identified. Radiated power, per unit surface area and averaged over the period, and induced strain and electric fields in the middle plane of the plate are calculated for doubly rotated quartz plates whose cut orientations follow the upper and lower loci of zeros of the first-order temperature coefficient of frequency of the x1 -thickness-shear mode. Quality factors and partition of stored energies are also examined.
Intensity dependent photorefractive properties of BaTiO3
Authors: Temple Doyle A. , Hathcock R. Scott , Warde Cardinal
Published: July 2002

We have used the light-induced grating erasure technique to measure the photorefractive properties of pure and iron doped BaTiO3. Our experiments were performed using an anisotropic configuration which forbids beam coupling and self-diffraction between the writing beams, resulting in plane parallel intensity fringes that do not change with time. This allowed direct measurement of the charge transport processes without any feedback on the grating due to wave-mixing processes. The results from these experiments show that the photorefractive parameters known as the trap density Npr and the mobility-recombination time product μτr, vary with intensity and are not material constants.
Copper emissions from pulsed discharges in CF4/O2 and Ar
Authors: Nieman George C. , Colson Steven D. , Hansen S. G. , Luckman G.
Published: July 2002

Emission from atomic copper and CuF is characterized in a pulsed dc discharge in CF4/O2/Ar with a copper electrode. Similar emission is seen from neat Ar discharges, provided that a F- (or H2O-) containing plasma has been operated first. Near the electrode surface emissions from CuF and lower-energy states of Cu are observed. In the bulk of the plasma, additional emission is seen from more energetic states of Cu at the end of the pulse. Lifetime and energy considerations suggest that much of the Cu emission seen in Ar plasmas may arise from collisions between argon metastables and some molecular species, such as CuF.
A laser-driven electron injector for laser acceleration experiments
Authors: Ebrahim Nizar A. , Martin F.
Published: July 2002

We report a novel technique for producing a source of high-energy (0.1–1.0 MeV) electrons for studies of laser acceleration concepts. We have designed, built, and implemented a laser-driven electron injector that is simple and compact and can be optically synchronized with a short-pulse laser beam.
Optical dispersion relations for AlSb from E=0 to 6.0 eV
Authors: Adachi Sadao
Published: July 2002

A complete set of the model dielectric functions, ε(ω), for calculation of the optical dispersion relations of semiconductors are presented. The model is based on the Kramers–Kronig transformation and includes the E0, E0+Δ0, E1, E1+Δ1, E′0 (E0+Δ′0), E2, E1, and Eidg (indirect-band-gap) transitions as the main dispersion mechanisms. Detailed analyses are presented for AlSb, and results are in satisfactory agreement with the experimental data over the entire range of photon energies (0–6.0 eV). Dielectric-related optical data of AlSb, such as the refractive index, the extinction coefficient, and the absorption coefficient, are also presented as an example of the ability of our model.
Growth and properties of thin GaAs epitaxial layers on Al2O3
Authors: Kuech T. F. , Segmüller A. , Kuan T. S. , Goorsky M. S.
Published: July 2002

The metalorganic vapor-phase epitaxy of GaAs on Al2O3 substrates was carried out over a growth temperature range of 600–800 °C. Several physical characterization techniques were used to obtain information on the initial stages of epitaxial growth and its influence on the physical properties of the epitaxial layer. The initial GaAs growth proceeds by island formation and coalescence, and the initial density of GaAs islands is a strong determinant of the epitaxial layer crystalline quality. An incommensurate growth model is presented to explain the dependence of the film properties on the growth parameters. The presence of defects in even very thick layers limits the applicability of these materials in device structures.
Solid phase reaction of molybdenum-nickel alloy thin films with silicon
Authors: Rastogi R. S. , Vankar V. D. , Chopra K. L.
Published: July 2002

Solid phase reaction behavior of polycrystalline and amorphous alloys of MoNix (x=12, 20, and 88) with silicon in the temperature range 500–700 °C has been studied by glancing angle x-ray diffraction and Auger electron spectroscopy techniques. Two types of reaction mechanisms are observed in these alloy/silicon reactions and both are controlled by the composition of the refractory metal component. In molybdenum-rich polycrystalline alloy (Mo88Ni12) the reaction at 500 °C occurs due to out-diffusion of nickel from the alloy, while at 550 °C the reaction between the alloy and silicon mainly occurs due to in-diffusion of silicon. On the other hand, in nickel-rich alloy (Mo12Ni88), the reaction at 500 °C is dominated by nickel out-diffusion. The amorphous alloy (Mo80Ni20) was found to be stable on silicon up to 500 °C and a reaction at 550 °C occurs due to crystallization followed by out-diffusion of nickel and large amounts of silicon in-diffusion. In all these alloy/silicon reactions, a macroscopic phase separation between MoSi2 and NiSi or NiSi2 is observed and results in a two-layer structure consisting of [MoSi2+NiSi(or NiSi2)]/NiSi (or NiSi2)/Si(100).
Characterization of hydrogenated amorphous boron films prepared by electron cyclotron resonance plasma chemical vapor deposition method
Authors: Shirai Koun , Gonda Shun-ichi
Published: July 2002

This paper presents characterization of amorphous boron (a-B) films prepared by the electron cyclotron resonance plasma chemical vapor deposition method using diborane (B2H6) and hydrogen mixtures. Compositional analyses show that hydrogen is the only impurity which influences film properties appreciably. The infrared absorption study shows that the hydrogen is incorporated into the film in the terminal bonding form. The hydrogen concentration has been estimated using the semiempirical equation given by Blum, Feldman, and Satkiewicz [Phys. Status Solidi A 41, 481 (1977)], which can be verified by the more fundamental principle. The infrared absorption study also shows that the amorphous films possess some short-range order related with the icosahedral structure. These observations allow us to consider that this film belongs to one of alloyed materials and is true hydrogenated a-B. In order to study the contributions of hydrogen to the film properties, variations of the color and the electrical resistivity of the film have been examined with changing the substrate temperature and the B2H6 concentration in source gases. These variations can be described with consistency in terms of the optical absorption edge. The films are a-B:H at substrate temperatures below 350 °C. The hydrogen incorporation results in increase in the resistivity and increase in the optical transparency. At substrate temperatures above 350 °C, the hydrogen is evolved from the film regardless of the B2H6 concentration, and intrinsic a-B films are obtained.
Interaction between a sheet source and a moving compressible plasma
Authors: Nakagawa Kimio
Published: July 2002

The problem of radiation from a sheet current source in a moving compressible plasma is treated. In order to know the interaction between the sheet source and the moving plasma, first the sign of the radial component of the propagation constant is determined accurately on the basis of the radiation condition. Then the radiation power is investigated numerically for various sets of the direction of the source and that of the moving plasma. In particular, it is found that the source is given an energy by the surrounding plasma medium under certain conditions.
Thermally induced optical bistability and self-oscillation in a nonlinear etalon filled with optical adhesive
Authors: Kong Hong Jin , Hwang Wol Yon
Published: July 2002

We report the optical bistability and the self-oscillation of a nonlinear Fabry–Perot etalon filled with Norland optical adhesive 81. A normal and an inverted bistable loop were observed for a short (80msec) and a long (1.2sec) input optical pulse duration, respectively. The self-oscillation properties depended sensitively on the substrate and the spacer thicknesses. The measured self-oscillation period became longer with an increase of the spacer thickness and was in the range o 0.2 to 3 seconds. The inversion of the bistable loop, and the self-oscillation in this experiment can be explained by the competition between the fast thermal refractive index change and the slow linear thermal expansion of the etalon.
Observation of the donor-bound light-hole free exciton in AlGaAs-GaAs quantum wells
Authors: Reynolds D. C. , Merkel K. G. , Stutz C. E. , Evans K. R. , Yu P. W.
Published: July 2002

The neutral donor-bound light-hole free exciton has been observed in AlxGa1−xAs-GaAs multi-quantum wells (MQWs). The transition was observed using selective excitation photoluminescence spectroscopy on two nominally 350-Å-wide AlxGa1−xAs-GaAs MQW structures in the energy region between the light-hole and heavy-hole free-exciton transitions, where no other intrinsic transitions exist. The neutral donor-bound heavy-hole free-exciton transition was also observed in both MQW structures. A third 150-Å-wide MQW structure which showed no evidence of a donor-bound heavy-hole free exciton also showed no evidence of a donor-bound light-hole free exciton.
Anisotropy in transport critical current density of a Bi-Sr-Ca-Cu-oxide single crystal
Authors: Nomura S. , Yamada Y. , Yamashita T. , Yoshino H.
Published: July 2002

Critical current densities and upper critical fields were measured for a single crystal of the high Tc oxide superconductor, Bi2Sr2CaCu2O8+d, by transport within the ab basal plane and along the c axis. The anisotropy in critical current densities was observed to be Jc⊥/Jc∥=10, in agreement with the anisotropy in resistivity for the normal state. The scaling of the critical current density with the magnetic field was found. The critical current density scaled to zero at fields Bc2 in the ab plane and along the c axis which were in good agreement with the upper critical fields measured by transport.
Transmission of an electrostatic potential through an arbitrary stack of dielectric plates: Theoretical and experimental study
Authors: Tremblay Gerard , Meyrueix Paul , Peuzin Jean Claude
Published: July 2002

We consider in this paper an arbitrary stack of dielectric plates with given voltage distributions at both lower and upper free surfaces of the stack. We address the problem of finding the potential distribution at any interface within the stack. This problem is of fundamental importance regarding a recently proposed electro-optical technique for testing printed-circuit boards. We have developed a simple and powerful matrix formalism relying on Fourier transformations of voltage distributions. The theory is verified against a particular kind of stack that is of practical importance in the already mentioned application. This stack is composed of three successive layers: an isotropic dielectric, a one-dimensional elastomeric conductor, and an electro-optic crystal (Bi4Ge3O12). The last surface of the stack is grounded using a conductive (and transparent) electrode, whereas a given potential distribution is applied to the first surface. The potential distribution on the ungrounded face of the electro-optic plate (that side in contact with the elastomer) is measured using an optical reflective polarimetric technique. Our results demonstrate good agreement between theory and experiment.
The statistical orientation of uniaxial single-domain magnetic particles
Authors: Perlov C. M.
Published: July 2002

The collective orientation of uniaxial magnetic particles in a Newtonian fluid is reviewed. The quartic term in the equation for the anisotropy torque leads to different conclusions when considering the alignment of a collection of particles than when considering a single particle. Both two- and three-dimensional initial distributions of orientations suggest that larger fields orient the particle assembly more rapidly than the ‘‘optimum’’ field for a single particle.
Development of an Airy stress function of general applicability in one, two, or three dimensions
Authors: Bradley Fred E.
Published: July 2002

The utilization of Airy stress functions, and various modifications thereto, to the solution of two dimensional, or three dimensional with one axis of symmetry, stress-strain problems in elasticity is well known. A generalization of the Airy methodology to solutions of linear isotropic or anisotropic problems in one, two, or three dimensions is presented.
Fourth-order elastic constants of nonideal hcp crystal Mg and Er
Authors: Ramji Rao R. , Padmaja A.
Published: July 2002

The expressions for the 19 fourth-order elastic constants of an hcp crystal with nonideal axial ratio have been derived with interactions extending up to second neighbors and using sublattice displacements to the second degree in strains. These formulas have been used to evaluate the fourth-order elastic constants of magnesium and erbium. The results reveal higher-order elastic anisotropy in erbium. The second pressure derivatives of the effective second-order elastic constants of magnesium and erbium have been obtained using their fourth-order elastic constants and are positive. The magnitudes of the second pressure derivatives of C112, C133, and C111 in magnesium and that of C112 in erbium are extremely large, lending support to the phase changes that occur in these metals when subjected to hydrostatic pressure.
The use of high-order TM0m0 modes of a resonant cavity for magnetized plasma density measurements
Authors: Paris P. J. , Sawley M. L. , Tran M. Q. , Voser K.
Published: July 2002

A study of the application of high-order TM0m0 modes of a cylindrical cavity to the measurement of the density of a magnetized plasma column is presented. It is shown theoretically that judiciously chosen high-order modes have the potential advantages of both a wide operational range of densities, and a wide range for which a simple perturbation theory is valid. Furthermore, an experiment is described which shows that the TM060 mode can be excited with a sufficiently high Q value to allow accurate determination of the resonant frequencies, and hence plasma density. Favorable comparison between densities in the range 1010–1012 cm−3 measured by means of the resonant cavity technique and microwave interferometry is presented.
An experimental investigation of refraction-induced distortions in harmonic-light images of laser-produced plasmas
Authors: Darrow C. , Montgomery D. S. , Estabrook K. , Drake R. P. , Busch G. E. , Gabl E. F.
Published: July 2002

In this paper the results of a simple experiment designed to study refraction-induced distortion of images of narrow-band-light-emitting regions in a laser-produced plasma are described. Source regions were formed by relaying the image of a backlit pinhole array into the plasma (25 μm-diam. pinhole; 30-ps, 0.25-μm backlighter beam). Images of these source regions were recorded on film and compared with and without plasma present. Refraction effects, evidenced by translation of the apparent pinhole locations and blurring of the pinhole spots, are compared for different plasma sizes and for different delays of the backlighter pulse with respect to the plasma-production laser pulse. These results were then compared with expectations based on numerical raytraces through a plasma-density profile derived from a hydrodynamic simulation of our exploding-foil plasma. The significance of these results in the imaging of harmonic and half-harmonic light as a plasma-density diagnostic is discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.
On 1/f noise in nonlinear physical systems described by infinite dimensional integrable equations
Authors: Dragoman M.
Published: July 2002

The nonlinear physical systems which are described by infinite dimensional integrable equations have two types of solutions: solitons which can be viewed as nonlinear localized ‘‘normal modes’’ and radiation solution which can be viewed as linear modes (termed as phonons, photons, spin waves, etc., in condensed matter physical systems). These linear modes are modulationally unstable to nonlinear normal modes and this instability is expressed by a time domain decay of their amplitude as t−1/2, which corresponds to 1/f spectrum. This mechanism is explored for three types of nonlinear equations and an analogy with 1/f noise generated as a result of low-frequency bremsstrahlung is revealed.
Fully ion-implanted p-n junctions in InP
Authors: Häussler W. , Römer D.
Published: July 2002

The electrical characteristics of p+-n junctions in undoped InP fabricated by using a deep Si implant and a shallow Be implant are reported. It proved advantageous to anneal the two implants separately. The influence of annealing, implantation temperature, and Si dose on leakage current is studied systematically. It is found that prolonged anneals and elevated temperatures reduce leakage currents and that raising the implantation dose increases junction leakage considerably. It is shown that junction behavior can be modeled by assuming a trap-assisted tunneling mechanism. In this model the magnitude of the electric field at the junction is the most decisive parameter. For a 15-min-long anneal at 850 °C leakage current densities <10−7 A/cm2 are obtained for an electric field of 40 V/μm at the junction.
Electron multiplication in the glow-discharge cathode fall
Authors: Paulick Thomas C.
Published: July 2002

A one-dimensional model is formulated for electron multiplication in the cathode fall of a glow discharge. The associated Boltzmann equation in z and v is converted to an integrodifferential equation in new variables that can be solved numerically using standard methods for ordinary differential equations in a single variable. The resulting distribution function in the (z,v) phase space is also the energy distribution of electron flux, which is used to find the current multiplication factor and the energy transport per unit electron current. Even in low-voltage discharges with large current multiplication, the nonionizing collisions play a small role in determining the electron-energy distribution and swarm behavior. Comparison with highly complex simulation, and with experiment, is very favorable.
Interaction of overlayers of Al and Rb with single-crystalline surfaces of Bi2Sr2CaCu2O8
Authors: Lindberg P. A. P. , Wells B. O. , Shen Z.-X. , Dessau D. S. , Lindau I. , Spicer W. E. , Mitzi D. B. , Kapitulnik A.
Published: July 2002

Photoemission results from Al and Rb interfaces with single crystals of Bi2Sr2CaCu2O8 high-temperature superconductors are reported. The Al and Rb adsorbates are found to react quite differently with the Bi2Sr2CaCu2O8 substrate. While adatoms of Rb significantly affect only the Bi and O atoms in the top atomic layer, the Al adsorbate profoundly disrupts the bonding character of the whole Bi2Sr2CaCu2O8 material. For Al, the Bi and Cu states are strongly reduced, and the Sr and O states show evidence of oxidized components. In addition, Al causes a strong out-diffusion of oxygen from the bulk. The differences in the reactivity of Al and Rb are discussed in terms of the different mobility of the two atoms.
Range profiles of Xe+ and Xe2+ of energy 50 to 400 keV in quartz crystal
Authors: Wang Ke-Ming , Shi Bo-Rong , Guo Hai-Yan , Liu Ji-Tian , Liu Xiang-Dong , Chen Lu
Published: July 2002

The Rutherford backscattering technique has been used to determine the depth profile of Xe+ and Xe2+ implanted into amorphized quartz crystal at energies from 50 to 400 keV. Based on Biersack’s angular diffusion model, an efficient method has been developed for comparison with experimental data. The results show that the measured mean projected range is in quite good agreement with calculated value for first-order treatment. A marked improvement in range straggling is obtained after considering the second order energy loss. Also the results are compared to transport of ions in matter prediction.
Traps in molecular-beam epitaxial In0.53(GaxAl1−x)0.47As/InP
Authors: Biswas Dipankar , Chin Albert , Pamulapati Jagadeesh , Bhattacharya Pallab
Published: July 2002

Deep-level transient spectroscopy measurements have been made on molecular-beam epitaxial In0.53(GaxAl1−x)0.47As lattice matched to InP. Several electron and hole traps, with activation energies ranging from 0.14 to 0.79 eV, have been identified and characterized. In particular, systems of electron traps (0.30≤ΔET≤0.79 eV) and hole traps (0.14≤ΔET≤0.31 eV) with monotonically changing activation energies have been identified in these alloys. We believe these traps are dominant in this alloy system.