bluuebunny/crossref_metadata_2025 huggingface dataset:
Proximity-Josephson effect (PJE) evidence for triplet pairing in UBe13 (invited)
Authors: Wolf E. L. , Han Siyuan , Khim Z. G. , Ng K.-W. , Millis A. J. , Smith J. L. , Fisk Z.
Published: July 2002

The proximity-Josephson effect (PJE) is a powerful general method of determining the symmetry of the pair wave function in exotic superconductors. The method is simple and relatively insensitive to the surface condition of the sample. A superconducting probe (S) of known pairing symmetry (typically Nb or Ta) is brought into contact with the sample (N). Observations and arguments based on the de Gennes boundary condition at the NS interface both indicate formation of a local, proximity-induced superconducting region of depth ξ in the sample (N) under the probe. The induced pairs have the same symmetry as those of S. The expected pair-phase dependence of the coupling energy between the pairs in N and S leads to a Josephson current Ic(T), which may be observed up to a junction critical temperature T* which is typically ∼0.8 of the Tc of S. When the measurement temperature falls below the bulk Tc of N (the exotic superconductor), a pair wave function of possibly different symmetry forms in the bulk of N and overlaps the induced pair wave function near the probe. Weak interactions between the induced and bulk pairs occur. In the case of UBe13 contacted with a Ta tip, the interaction weakly suppresses the induced pairs [which determine Ic(T)] leading to a reduction of the Josephson current at T<Tc. This observation of a negative S-wave proximity effect in superconducting UBe13, in good agreement with a Ginzburg–Landau analysis, is strong evidence for triplet pairing in this heavy fermion compound.
Slave boson large degeneracy expansion for the lattice Anderson model (invited)
Authors: Millis A. J. , Lavagna M. , Lee P. A.
Published: July 2002

The slave boson formalism will be reviewed, a comparison of Kondo spin compensation in the impurity and in the lattice will be given, results for the temperature- and frequency-dependent conductivity will be presented, the density-density correlation function will be discussed, and a calculation of the slave-boson mediated d-wave superconducting instability will be outlined. Throughout, we emphasize the differences between the lattice and one impurity Anderson models and the strengths and weaknesses of the slave boson method.
Neutron scattering studies of heavy fermion systems (invited) (abstract)
Authors: Kjems J. K.
Published: July 2002

We review our results of neutron scattering experiments on the heavy electron systems UPt3, U2Zn17, and URu2Si2. In the superconductor UPt3 we have established the existence of spin fluctuations on an energy scale of 0.5 meV and correlated in the same structure as the antiferromagnetic order in the Th- and Pd-doped systems. In the antiferromagnet U2Zn17 overdamped antiferromagnetically correlated excitations dominate the excitation spectrum above and below TN. However, in an applied field the resonances are induced in the transverse response. In the antiferromagnetic superconductor URu2Si2 the excitations in the ordered phases are propagating, longitudinal and similar to observations in singlet rare-earth ground-state systems. However, the ordered moment of 0.03μB is anomalously small and the transverse response is overdamped. We discuss a simple model of exchange coupled overdamped responses which gives a consistent description of the diffusive spin-fluctuations in several heavy electron systems.
Study of H
c enhancement in Co-modified γ-Fe2O3 films
Authors: Meng R. L. , Wang Y. Q. , Liu C. S. , Bensaoula A. , Chu C. W. , Hor P. H. , Ignatiev A.
Published: July 2002

The magnetic properties and depth profiles of Co-modified γ-Fe2O3 films have been studied. The Hc of these films varies between 0.3 and 2.5 kOe nonmonotonically with Co concentration and depends only slightly on temperature. The non-diffusion-like Co-rich layer that appears underneath the surface of the Fe-oxide films displaying an enhanced Hc has been positively demonstrated to be responsible for the Hc enhancement.
Angular dependence of hysteretic properties in a longitudinal particulate medium
Authors: Chang Ching-Ray , Fredkin D. R.
Published: July 2002

We calculate the variation of coercivity and squareness with magnetic field direction for a longitudinal particulate medium using a vectorial model including curling and interactions among the particles. Our results are in reasonably good agreement with recent experimental data on ISOMAX. In particular, we calculate a peak in the coercivity of the correct size at approximately 60° out of the plane of the medium. The peak shifts to smaller angle and its height decreases with increasing randomness of the particle orientations.
Magneto-optic Kerr effect hysteresis loop measurements on rf-sputtered iron oxide thin films
Authors: You Guang-Jian , Winters D. P. , Zhou Zeng-Jun , Mei Yu , Luo H. L.
Published: July 2002

Hysteresis curves of Fe3O4 and γ-Fe2O3 films were obtained using magnetio-optic Kerr effect measurements. The polar Kerr rotation angles of Fe3O4 and γ-Fe2O3 at 632.8 nm were determined to be 4.8 and 3.0 min, respectively.
Improvement of corrosion resistance of CoNi thin films by surface passivation
Authors: Wakai K.
Published: July 2002

This paper describes improvement of corrosion resistance of CoNi films by surface passivation. The CoNi films were obliquely evaporated on polyethylene terephthalate (PET) films, and passivated by a newly developed mild oxidation method. The passivated films were subjected to environmental exposure test at a relative humidity of 90% and a temperature of 60 °C. No changes of recording performance were observed even after a one-month exposure. The chemical structure of the passive layer formed on the CoNi films was studied by x-ray photoelectron spectroscopy and reflected electron diffraction. It was concluded that their strong corrosion resistance was attributed to the very thin, amorphous cobalt(III) oxyhydroxide formed on the surface, containing a small amount of Co2+ ions.
Magnetic properties and microstructures of Fe-Cr-Co-base cold-rolled magnets
Authors: Mukai T. , Furukawa T.
Published: July 2002

Sheet magnets of Fe-Cr-Co-base alloys can be inexpensively produced through a process consisting of spinodal-decomposition aging, intermediate cold rolling, and final aging. In the present study magnetic properties have been greatly improved by adding Si, Ti, and Cu to the base alloys. The addition of Si raises the coercive force by increasing the amount of paramagnetic (or weak ferromagnetic) Cr-rich matrix phase. The addition of Ti increases remanence and maximum energy product by suppressing the precipitation of nonmagnetic σ phase during the final aging. The addition of Cu leads to a slight increase in coercive force. The best magnetic properties obtained in this study are iHc=790 Oe, Br=10.6 kG, and (BH)max=4.5 MGOe with a Fe-33.3 wt. % Cr-11.9 wt. % Co-1.05 wt. % Si-0.22 wt. % Ti-2.07 wt. % Cu alloy.
Permanent magnet properties of sputter-deposited (FeCo)NdB films (abstract)
Authors: Sellmyer D. J. , Zhao Z. R. , Shan Z. S. , Zhao J. G.
Published: July 2002

Studies have been performed on sputtered thin films of Co-doped FeNdB alloys near the 14:2:1 composition. The films were rf sputter deposited onto mica substrates using a single bulk target of composition Fe71.5Co5Nd16.5B7. The thickness of the films ranged from 1 to 10 μm. Heat treatments were given to the samples at temperatures between 500 and 650 °C and in fields parallel to the films. The films deposited at 22 °C are amorphous with Tc =240 °C. After crystallization of the tetragonal 14:2:1 phase at 600 °C, Tc increased to 410 °C, and the room-temperature magnetization was σs ≂100 emu/g. Films annealed at 600 °C show a coercive force Hc >10 kOe and remanent induction Bs ≂10 kG. Films deposited at 622 °C and in the presence of an in-plane field of 1.3 kOe exhibit either in-plane or perpendicular anisotropy depending on sputtering parameters. The sputtering conditions affect the c-axis texturing of the films, as shown by x-ray diffraction. Correlations have been made between film-growth conditions, microstructure, and magnetic properties for these thin-film permanent magnets.
Si, SiO, Al, Pd interface effect on the magnetic behavior of quench-condensed Ni films
Authors: Moodera J. S. , Meservey R.
Published: July 2002

In studying the magnetic properties in quench-condensed Ni films by the depairing of a superconductor using a tunnel diode oscillator, we observed the following effects. SiO, Si, Al when condensed on ultrathin Ni films partially suppressed the magnetic moment in up to 1.5 atomic layers of Ni; Al showed the most effect, followed by Si and then SiO. Measurements were made with Pd films over Ni films and vice versa. Au or Cu over a Ni film affected the magnetic behavior of Ni very little. The present results are compared with spin-polarized tunneling and anomalous Hall effect results in Ni films.
Properties of amorphous FeZrBiSiB alloy on relaxation
Authors: Lu Q. , Jang E. Y. , Li J. E.
Published: July 2002

The relaxation phenomena of the amorphous FeZrBiSiB alloy have been investigated by DSC and electrical and magnetic measurements. It is found that there exist two different relaxation stages of the structural relaxation processes. The mechanism of forming these two relaxation stages is analyzed by the idea of short-range localized atomic arranging movement and medium or long-range cooperative atomic arranging movement. We consider that the effect of the annealing treatments on the Curie temperature of the specimens is caused by the additive effect of ferromagnetic and antiferromagnetic exchange interaction.
New results in the theory of wetting transitions (invited)
Authors: Kroll D. M.
Published: July 2002

The aim of this contribution is to draw attention to some recent developments in the theory of wetting transitions which may be of interest to the magnetism community. After presenting a qualitative discussion of wetting phenomena, the predictions of both the mean field and renormalization group (RG) theories of wetting with short range forces are reviewed. Recent Monte Carlo (MC) results are also described and possible causes of some of the discrepancies between the RG and MC results are discussed. Wetting phenomena in magnetic systems with a first-order bulk transition are considered and it is shown that metallic magnets and magnetic insulators (with short-range exchange) belong to different universality classes. Both the need for and the feasibility of experimental tests of the theory are emphasized.
Anomalous field dependence of the specifc heat in a CoO⋅Al2O3⋅SiO2 spin glass near T
f
Authors: Wallace W. D. , Hunter Gary W. , Wenger L. E.
Published: July 2002

Precise heat capacity measurements in magnetic fields to 2 T have been performed on a CoO⋅Al2O3⋅SiO2 (40–10–50 mol %) spin glass in the temperature range 2.5–10 K. Analysis of the magnetic field dependence shows that the magnetic specific heat Cm can be expressed as Cm/T=Cm(H=0)/T−bHp at a given temperature T. p(T) shows a broad minimum with values of p ranging from 2 at T≫Tf and T≪Tf to 0.9 as T approaches Tf(≊6 K), while b(T) shows a fairly sharp maximum also centered at Tf. This nonquadratic H behavior suggests that the free energy must contain a term similar to the singular term responsible for the nonlinear susceptibility and that this term also dominates the specific heat as T approaches Tf.
Magnetic response near the critical concentration for ferromagnetism: Linear and nonlinear susceptibility in concentrated spin glasses
Authors: Mazumdar P. , Bhagat S. M.
Published: July 2002

Low-field magnetization measurements are reported for a-Fe12Ni63G25 and a-Fe7Ni73G20. These are highly concentrated spin glasses since the critical Fe concentrations (xc) for onset of ferromagnetism are 12.4 and 7.7, respectively. Whereas the nonlinear susceptibility shows the expected rapid rise near Tg, it is remarkable that the close proximity to xc reveals itself via a similar sharp increase in the linear susceptibility. It turns out that all the data can be represented by a single empirical form: χ(t)=[χ(Tg)t−γ]/[Aχ(Tg)+t−γ].
Magnetism in the amorphous MnxB100−x system
Authors: Liao S. B. , Bhagat S. M. , Park M. J. , Manheimer M. A. , Moorjani K. , Satkiewicz F. G.
Published: July 2002

We report dc magnetization and electron-spin-resonance measurements on a-MnxB100−x thin films with 40≤x≤50. The nonmonotonic behavior of the magnetic parameters is used to propose a magnetic phase diagram in which a multicritical point appears at x between 48 and 49.
0.3-μm-diam bubble material of (BiSmLu)3(FeSc)5O12 grown from PbO-Bi2O3-V2O5 flux
Authors: Hosoe Yuzuru , Andoh Keikichi , Ikeda Tadashi , Suzuki Ryo
Published: July 2002

Garnet films of (BiSmLu)3(FeSc)5O12 supporting 0.3-μm-diam bubbles have been grown on Nd3Ga5O12 substrates by liquid-phase epitaxy using PbO-Bi2O3-V2O5 flux. The uniaxial anisotropy energy in the films can be increased by adding V2O5 to the PbO-Bi2O3 flux. The anisotropy energy of 0.3-μm-diam bubble material of (BiSmLu)3(FeSc)5O12 grown from PbO-Bi2O3-V2O5 flux was 2.9×105 erg/cm3. This value is greater than that of the 0.3-μm-diam bubble material grown from PbO-Bi2O3 flux by about 45%. The content of Bi in the film is increased by adding V2O5 to the PbO-Bi2O3 flux. The increase in the anisotropy energy is considered to be caused by this increase in Bi content.
Analysis and design of ion-implanted bubble memory devices
Authors: Wullert II J. R. , Kryder M. H.
Published: July 2002

4-μm period ion-implanted contiguous disk bubble memory circuits, designed and fabricated at AT&T Bell Laboratories, Murray Hill, NJ, have been investigated. Quasistatic testing has provided information about both the operational bias field ranges and the exact failure modes. A variety of major loop layouts were investigated and two turns found to severely limit bias field margins are discussed. The generation process, using a hairpin nucleator, was tested and several interesting failure modes were uncovered. Propagation on four different minor loop paths was observed and each was found to have characteristic failure modes. The transfer processes, both into and out of the minor loops, were investigated at higher frequencies to avoid local heating due to long transfer pulses at low frequencies. Again specific failure modes were identified. Overall bias margins for the chip were 9% at 50 Oe drive field and were limited by transfer-in.
Structure and crystal fields of PrBr3 and PrCl3: A neutron study
Authors: Schmid B. , Hälg B. , Furrer A. , Urland W. , Kremer R.
Published: July 2002

The crystal structures of PrX3 (X=Br, Cl) and particularly the detailed coordination of the halides X have been studied by neutron diffraction on polycrystalline samples in the temperature range between 4.2 and 293 K. Furthermore, the crystalline electric fields (CEF) in the two compounds have been investigated by inelastic neutron scattering experiments on single-crystal samples. The observed CEF transitions have been identified according to the transition matrix elements and the polarization factor in the neutron cross section, which allowed an unambiguous determination of the four CEF parameters for hexagonal symmetry. The energetic ordering of the CEF levels in PrBr3 and PrCl3 are considerably different which can be understood in terms of the different geometric coordination of the halides determined from the diffraction results.
Magnetism of R2Co14−xSixB systems (R=Y, Pr, and Nd)
Authors: Pedziwiatr A. T. , Wallace W. E.
Published: July 2002

The R2Co14−xSixB systems (R=Y, Pr, and Nd) have been synthesized for x ranging from 0.0 to 3.0 and found to have the tetragonal crystal structure for x≤2 in Pr- and Nd-based systems and for x≤1.6 in Y-based systems. Bulk magnetization measurements have been carried out in the temperature range 4.2–1100 K to determine the saturation magnetizations, anisotropy fields, Curie temperatures, TC, and spin-reorientation temperatures for different Si contents. A decrease of the TC and the saturation magnetization was observed with increasing Si content. The anisotropy field in Pr- and Nd-based systems was found to increase at 77 K and decrease at 295 K. The high-temperature spin reorientations for Nd- and Pr-based systems disappear for x≥1.3 and 1.0, respectively. The low-temperature spin reorientation observed in Nd2Co14B also vanishes for x>0.3. The observed features are discussed in terms of weakening the 3d sublattice magnetization and its anisotropy due to Si dilution.
Computer simulation of spin reorientations in polycrystalline materials—application to R2Fe14B (abstract)
Authors: Boltich E. B. , Pedziwiatr A. T. , Wallace W. E.
Published: July 2002

The easy direction of magnetization (DOM) is an extremely important property of a magnetic material, in regards to both permanent magnet and recording applications. In many magnetic materials, most notably Nd2Fe14B, the DOM is temperature dependent. When utilizing methods which permit the orientation of either a single crystal or pseudo-single crystal to be rigidly constrained (e.g., VSM and extraction), it is possible to determine the temperature dependence of the DOM directly. However, the determination of spin reorientation temperatures with powder samples is not always straightforward. In some cases, a peak is observed in the magnetization versus temperature curve, while in others either a drop or an increase is observed. Using a two-dimensional, two-crystallite grain as a model and assumed temperature dependencies of the anisotropy constants, K1 and K2, it is shown that these peaks and other features can be explained by polycrystalline particles (or, equivalently, imperfect alignment of the powder). It is further shown that spin reorientation temperatures are invariably characterized by the inflection points in the low-field magnetization versus temperature curve. Examples of such curves obtained from a Faraday balance for Nd2Fe12Si2B and Pr2Co14B are given.
Effect of spin-orbit interaction and exchange splitting on magneto-optic coefficient (abstract)
Authors: Misemer D.
Published: July 2002

Recent and impressive advancements in magneto-optical recording technology have not been matched by equal developments in understanding the critical properties of the materials involved. In particular, although spin-orbit interactions and exchange splitting are necessary to the existence of a magneto-optic Kerr effect, a quantitative understanding of the importance of the two interactions is lacking. Using interpolation schemes for representative electronic structures, I have calculated the off-diagonal optical conductivity for a variety of choices of spin-orbit interaction and exchange splitting. The effect of these changes on the magneto-optical coefficients will be discussed.
Additional considerations in the analysis of mixed conductivity in GaAs
Authors: Winter J. J. , Leupold H. A. , Ballato A. , Monahan T.
Published: July 2002

In an earlier study, Hall-effect and conductivity measurements made on semi-insulating GaAs were examined by a new approach to mixed conduction analysis. The analysis of 400-K measurements was based on the assumption of a fixed electron-to-hole mobility ratio. The effect of uncertainty in this ratio is examined in the present communication, and the nomographic presentation is simplified. The conductivity criterion for the onset of mixed conduction is revised and the quartic used earlier for comparative analysis is corrected.
Excimer laser-induced deposition of silicon nitride thin films
Authors: Jasinski J. M. , Meyerson B. S. , Nguyen T. N.
Published: July 2002

Silicon nitride films have been prepared by excimer laser photolysis of ammonia/silane or ammonia/disilane mixtures at temperatures in the range 225–625 °C in a hot-walled low-pressure reactor. The highest-quality films, deposited at 225 °C, have high breakdown-field strength, Ebd=8.8 Mv cm−1, low midgap interface-state-trap densities, Nit=1.7×1011 eV−1 cm−2, and a dielectric constant of ε=4.8.
Monte Carlo calculations on the influence of attachment on the thermalization of secondary electrons in an electron-beam-sustained discharge
Authors: Schaefer G. , Reinking G. F. , Schoenbach K. H.
Published: July 2002

Monte Carlo calculations have been performed on the relaxation of initial secondary electrons in electron-beam-sustained discharges at low values of the reduced electric field strength, E/N. In pure nitrogen, thermalizing electrons contribute to a secondary maximum of the distribution function in the energy range between 3.5 and 8 eV where the cross section for inelastic collisions in nitrogen has a minimum. This maximum is not found if the secondary electrons are produced at low energies. Admixtures of attachers with an attachment cross section in this energy range cause significant attachment of the initial secondary electrons. The calculations also demonstrate that even in molecular buffer gases, the inelastic cross sections of the attacher admixture have to be considered to gain correct distribution functions and attachment rates.
Faraday rotation in single-crystal ytterbium gallium garnet
Authors: Guillot M. , Le Gall H. , Ostorero J. , Artinian M. , Marchand A.
Published: July 2002

Faraday rotation (FR) measurements performed on single-crystal ytterbium gallium garnet (YbGG) at 0.6328- and 1.15-μm wavelengths are presented in a magnetic field up to 20 kOe applied along the three main crystallographic directions and in the 6–300 K temperature range. At 0.6328 μm, the FR is proportional to the magnetic field and a strong anisotropy of the Verdet constant (V) is evidenced below 50 K. The FR in the infrared does not present a linear field dependence but V is isotropic. Accurate magnetic susceptibility measurements are reported on the same samples in identical H-T conditions. The temperature dependence of the Faraday rotation susceptibility differs strongly from that of the magnetic susceptibility. The results are briefly analyzed in terms of electric dipole transitions.
Magnetic and transport properties of ion-beam-mixed amorphous Fe-Zr alloys (abstract)
Authors: Rao K. V. , Karpe N. , Chen D.-X. , Goldfarb R. , Bo/ttiger J. , Pampus K. , Torp B.
Published: July 2002

Ion-beam mixing has become a new and powerful technique to amorphize alloys systems in an extended concentration range while at the same time providing much more homogeneous films. In this paper we will present magnetic, thermal, and glavanomagnetic property studies on binary Fe-Zr amorphized alloys produced by irradiating multilayers of evaporated Fe-Zr crystalline films with Kr, Xe, and/or Ar ions at 500 keV with doses of 2×1016 ions/cm2. The final compositions of the amorphized films, containing 10–27 at. % Zr, were determined from Rutherford backscattering measurements. Further characterization of these x-ray amorphous films have been carried out using TEM and Mössbauer techniques. Comparison with melt-spun amorphous alloys reveals that the frequently quoted model for amorphization in ion-irradiation experiments of fast quenching spikes is questionable. From low-field ac-susceptibility data we obtain the magnetic phase diagram which is then compared with that obtained for melt-spun alloys. All the ion-beam-mixed alloys are found to be ‘‘ferromagnetic’’ below room temperature which is then followed by a ‘‘spin-glass-like’’ behavior below TC. It thus appears that the line of ‘‘spin-glass transitions’’ extends to a much wider concentration range than known before. Electrical and Hall resistivity data along with their temperature dependencies will also be discussed in relevance to the loss of long-range order in these systems at lower temperatures.
Mediation of surface recombination in a II-VI powder by palladium microislands
Authors: Sahyun M. R. V.
Published: July 2002

The recombination mechanisms in a Zn(Cd)S:Ag phosphor powder have been probed by luminescence and flash-photolysis time-resolved dielectric loss techniques. The influence of Pd-microislands chemically deposited thereon, alone, and in conjunction with recombination mediators phenylhydrazine and phenylacetic acid (in xylene solution) on the recombination pathways was studied. The Pd deposit affects recombination by increasing the fraction of the particle volume dominated by the surface processes, by providing a pathway for photoelectrons to reach the (negative) surface to participate in surface recombination, and by providing recombination centers per se. The implications of these results for heterogeneous photocatalysis are discussed.
Initial susceptibility of a textured fine particle system
Authors: Ayoub N. Y. , Laham N. , Popplewell J. , Chantrell R. W.
Published: July 2002

The initial susceptibility of a ferrofluid containing Fe3O4 particles with a lognormal distribution of volume fraction, median diameter Dvm=72 Å, and σ=0.4 has been measured in the temperature range 80–300 K. The measurements were taken after the sample had been cooled from the liquid to the solid state in different magnetic fields (0–5000 Oe). The effect of these fields was to introduce a ‘‘texture’’ in the solid state. The initial susceptibility of the textured system was found to reach a maximum at a characteristic temperature. The value depends on the freezing field and is lower the larger the freezing field. This behavior, associated with the degree of texture, is more noticeable in samples containing a large variation in particle size, σ=0.4.
Surface alloying of silicon by laser aluminothermy
Authors: Ursu I. , Crăciun V. , Alexandrescu Rodica , Mihăilescu I. N. , Morjan I. , Popa Al , Popescu M.
Published: July 2002

A new method is proposed for getting highly adherent Mo films on silicon wafers based upon laser-induced aluminum reduction of metallic oxides.
Linewidths for resonant ring fluxon oscillators coupled to a thermal bath
Authors: Marchesoni Fabio
Published: July 2002

Previous determinations of the linewidth for radiation emission from a resonant long Josephson-junction transmission line are revised. It is shown that the effects of thermal noise on fluxon oscillations are overestimated when an independent soliton model for fluxon states obeying periodic boundary conditions is adopted. An alternative determination of the line broadening in resonant ring fluxon oscillators is proposed according to McLaughlin and Scott perturbation theory [Phys. Rev. A 18, 1652 (1978)]. The role of non-Markovian statistics of the thermal bath coupled to the fluxon oscillator in modeling stochastically perturbed transmission lines is also investigated. The properties of resonant ring fluxon oscillators are accurately determined in view of new applications to microelectronics.
Operation of a small high-pressure laser using 13CO2
Authors: Fox Jay , Ahl Jeffrey L.
Published: July 2002

The operating characteristics of a tunable, high-pressure laser operating with 13CO2 and 12CO2 are described. The laser was of a size comparable to those in operation with easily transportable rangefinders and lidars. It was operated at 2.4 atm and measurements were made of the spectral output, as well as the peak power and pulse duration.
Range and shape factors, damage, regrowth, and redistribution for Ag implants in (100) and (111) Si
Authors: Wilson R. G. , Jamba D. M. , Sadana D. K. , Hopkins C. G.
Published: July 2002

The nature of regrowth of implantation-damaged (100) and (111) Si was investigated by measuring the depth distribution of implanted Ag atoms following annealing at 550 °C for fluences of 1×1012 to 1×1015 cm−2. Cross-section transmission electron microscope measurements were made for a few conditions to compare damage depth distributions. Other factors studied were anneal time, Si growth technique, Ag atom densities, and the transition region between amorphous and crystalline Si. Ranges and profile shape factors are reported for 150, 300, 450, and 600 keV Ag implants into Si.
Microstructure of hot-pressed and die-upset magnequench magnets (abstract)
Authors: Mishra Raja K.
Published: July 2002

Hot pressing is a convenient method for preparing fully dense Nd-Fe-B magnets from the melt-spun ribbons. Die-upsetting the hot-pressed material produces an aligned high-energy product magnet.1 Transmission electron microscopy was used to study the microstructures of both the hot-pressed and the die-upset magnets. For a starting composition of Nd14Fe81B5, it is found that the magnetic Nd2Fe14B phase comprises over 95% of the material. In the hot-pressed magnet, most of the Nd2Fe14B grains are nearly spherical and their distribution nearly isotropic, the average grain size around 100 nm. In contrast, the die-upset magnets consist of flat parallel grains with their c axes parallel to the stress axis. In the case of hot-pressed materials, a thin intergranular layer of an amorphous Nd-rich phase (like the one found in the melt-spun alloys)2 is seen. In the die-upset material, the flat surfaces between adjacent grains are free of any such intergranular phase. In both these magnets, 100–200 nm size noncrystalline particles with Nd/Fe over nine are found, their number and amount being an order of magnitude higher in the die-upset magnet. Also found are a crystalline phase of approximate composition Nd7Fe3 (boron content unknown) and an fcc crystal structure with lattice parameter 0.56 nm at the grain junctions. No Nd1+εFe4B4 phase is ever found in any of these samples. Lorentz electron microscopy indicates that the second and third phases act as pinning sites for the magnetic domain walls in these materials.
Effect of alloying elements on the double-transition behavior of a Gd-rich spin-glass system
Authors: Al-Sharif A. , O’Shea M. J.
Published: July 2002

We report the effects of alloying both magnetic and nonmagnetic elements on a double-transition system. The system studied is Gd72–xTxGa18B10, where T=Al, Fe, Co, Mo, Pd, Th for 0≤x≤24. Fe incorporates strong ferromagnetic exchange and leads to a crossover to ferromagnetic behavior with a rapid increase in the ordering temperature. Co produces a crossover to ferromagnetic behavior, but in this case the ordering temperature decreases with increasing x. Mo, up to 24 at.%, has only a small effect on the double-transition behavior as seen in the ac susceptibility. The other elements all induce paramagnetic to spin-glass transition behavior and the reasons for this are discussed. We also show that while some of the samples with larger x are partially crystalline, no transitions associated with these crystalline precipitates are present in ac susceptibility.
Separation of crystal-field levels and phonons in Pr dideuteride using polarized neutrons
Authors: Arons R. R. , Cable J. W. , Nicklow R. M.
Published: July 2002

Polarized neutrons with polarization analysis are used for the first time successfully for distinguishing crystal-electric-field (CEF) excitations from phonons by investigating both the spin-flip and non-spin-flip cross sections. From this, it is shown that the 20 meV peak in Pr dideuteride, observed previously with unpolarized neutrons, arises from CEF excitations. Since this energy is nearly half the value of the CEF level at 41 meV known before, the 20 meV peak is composed of two contributions. At low temperatures it only arises from transitions from the ground state into the 20 meV level. At room temperature, on the other hand, the 20 meV level is thermally populated, so that transitions from the 20 meV into the 41 meV level are also obtained. This leads to the unexpected increase of the intensity of the 20 meV peak at increasing temperatures observed previously. The present result gives a strong contribution to the knowledge of the CEF parameters of the Pr3+ ions in PrD2.
Angular distribution of x-ray radiation from optically thick z-pinch plasmas
Authors: Stormberg H.-P. , Murayama S. , Watanabe Y.
Published: July 2002

A z-pinch plasma is an x-ray radiation source of small size concerning the z-direction radiation. However, the plasma is optically thick with respect to the resonance lines, which contain a large fraction of the total radiation. The influence of the opacity on efficiency and spatial radiation distribution has been examined. A computer simulation solving the radiation transport equation demonstrates that the efficiency of the x-ray output decreases due to absorption, but only slightly because photon trapping is mostly followed by reemission. Using this result another computer code could determine the following features concerning the angular radiation distribution: (1) The average r-direction intensity is larger than the z-direction intensity. (2) The ratio of z-direction intensity to r-direction intensity varies from shot to shot. (3) The standard deviation of z-direction intensity is larger than that of the r-direction intensity. Several plasma focus experiments were carried out, the results of which provide good qualitative proof of the above predictions.
Rapid laser-induced growth of nitride and oxide layers at a beryllium/liquid interface
Authors: Dijkkamp D. , Wu X. D. , Chan Siu-Wai , Venkatesan T.
Published: July 2002

Excimer laser irradiation was used to induce rapid formation of nitride and oxide layers on beryllium samples immersed in liquid nitrogen and water, respectively. The elemental composition of the irradiated surfaces was determined by means of Rutherford backscattering spectrometry. Compound formation of Be3N2 and BeO was confirmed by x-ray diffraction. The results show that extensive reaction occurred only if the laser energy was sufficient to melt the beryllium surface. The amount of incorporated nitrogen or oxygen atoms was initially proportional to the laser energy density and to the number of laser shots. Saturation occurred when a near stoichiometric layer of Be3N2 or BeO was formed at the surface. The rate of compound formation was extremely high, on the order of 10–100 nm per shot.
Heteroepitaxial growth of SiC polytypes
Authors: Yoshida S. , Sakuma E. , Okumura H. , Misawa S. , Endo K.
Published: July 2002

Heteroepitaxial growth of SiC polytypes, 3C- and 6H-SiC, has been studied by chemical vapor deposition. Raman spectra were used to identify the polytypes. 3C-SiC and 6H-SiC were grown on 6H-SiC at low (1330–1500 °C) and high temperatures (1700–1800 °C), respectively. On the other hand, on 3C-SiC, only 3C-SiC was grown at all the temperatures. 3C-SiC epilayers grown at high temperatures have smooth surfaces and good electrical properties compared with those grown at low temperatures.
Laser action from s
y
n-(methyl,chloro) bimane
Authors: Pavlopoulos Theodore G. , McBee Christopher J. , Boyer Joseph H. , Politzer I. R. , Lau Chun M.
Published: July 2002

Laser action under flashlamp excitation of syn-(methyl,chloro) bimane, dissolved in trifluoroethanol, was observed at 516 nm. This new dye lases about 60% as efficiently as coumarin 30. The heavy atom effect, as related to the laser action properties of syn-(methyl,chloro) bimane, is discussed. The concentration dependence on the laser output of the new laser dye was studied. The spectral location of the fluorescence maximum as a function of the syn-(methyl,chloro) bimane concentration was measured. The effect of solvent mixture ratio on the lasing wavelength of syn-(methyl,chloro) bimane was studied. Different options available for further improving the laser-action properties of syn-bimanes are presented.
Quasiclassical kinetic equation for charge-carrier transport in a semiconductor
Authors: Schenter Gregory K. , Liboff Richard L.
Published: July 2002

Starting with the Uehling–Uhlenbeck quasiclassical generalized Boltzmann equation, a kinetic equation is derived for the distribution function f(ε,t) for charge carriers of energy ε and effective mass m in a semiconductor in the presence of an electric field E. Charge-carrier scattering with optical and acoustic phonons through strain and polar interactions are taken into account. Introducing a Legendre-polynomial expansion of the distribution function and assuming spherical constant energy surfaces, the following equation emerges in the limit of large charge carrier-to-phonon energy: (∂f0/∂t)+(eE/3)  ((2ε/m))1/2 ((∂/∂ε) +(1/ε))(f1(ε,0)e−t/τ−T̂eE ((2ε/m))1/2 (∂/∂ε)  f0)=(P−aQf0) (∂f0/∂ε) +(F−aGf0) (∂2f0/∂ε2)+Cf0 (1−af0). Collision integrals P,Q,F,G, and C, as well as the collision frequency τ, are evaluated explicitly. The quantum parameter a is 1 in the degenerate domain and 0 in the classical domain. The first two Legendre components of f(ε,t) are written f0 and f1, respectively, and T̂ is a time-dependent operator. Working in steady state and passing to the classical limit it is found that acoustic-strain interactions dominate over all others. Leading terms in this expansion give a new quasiclassical equation for the distribution of charge carriers of a semiconductor in an electric field. Further reducing this equation in the limits of equipartion and mu/p≪1, where p is carrier momentum and u is acoustic phonon velocity, gives a generalized Druyvesteyn equation which incorporates exclusion effects.
Injection-locked flashlamp-pumped dye lasers of very narrow linewidth in the 570–720 nm range
Authors: Boquillon J. P. , Ouazzany Y. , Chaux R.
Published: July 2002

Tunable and very narrow bandwidth flashlamp-pumped dye lasers are presented, in which spectral narrowing is achieved by injection locking of the pulsed lasers to the radiation of tunable single-mode cw dye lasers. We describe the electronic feedback stabilization of the amplifying ring cavity allowing a complete injection. Peak powers up to 10 kW at a bandwidth of 6 MHz were obtained over a 200-nm tuning range with three different dyes between 572 and 720 nm. The repetition rate is 10 Hz, limited by the dye circulating pumps. The emphasis of this work relates to the two following points: efficient injection locking over a broad frequency range, and special electronic design for accurate synchronization of several amplifying lasers. An example of application for high-resolution coherent anti-Stokes Raman spectroscopy is given.
Raman scattering of hydrogen- and deuterium-implanted cadmium fluoride
Authors: Stutzmann M. , Tatarkiewicz J.
Published: July 2002

The effects of proton and deuteron implantation on the Raman spectra of CdF2 crystals have been investigated. It is found that Raman scattering can provide a quantitative measure for the structural damage caused by the implantation procedure. These results also elucidate the intrinsic or extrinsic origin of Raman peaks observed in semiconducting CdF2.
Selective area deposition of silicon-nitride and silicon-oxide by laser chemical vapor deposition and fabrication of microlenses
Authors: Sugimura Atsuhiko , Fukuda Yasushi , Hanabusa Mitsugu
Published: July 2002

Silicon-nitride and silicon-oxide films were deposited by laser chemical vapor deposition (CVD) with high area selectivity. Deposition was induced by thermal reactions of source gases at laser-heated substrate surface. Area selectivity for the dielectrics varied with the composition of source gases. Using CO2 lasers, the size for nitrides deposited on quartz substrates from SiH4/NH3 mixtures was much smaller than beam sizes, and could be made as small as 15 μm; it was reduced to a few micrometers with an argon-ion laser, where the substrate was silicon. The observed thickness profile was explained by a combination of a predicted surface temperature distribution and an observed temperature dependence of deposition rates. Similar results with high area selectivity were obtained for silicon-oxide films using SiH4/N2O mixtures. However, the thickness profile of oxides was completely different for SiH4/O2 mixtures. Silicon-nitride films could be used as microlenses with the shortest focal length being 0.6 mm. The thickness profile was modified from an as-grown bell shape to a more spherical form by wet etching; this was made possible because etch rates were not uniform in the deposits. Concave lenses can be fabricated by evaporation of quartz substrates by the CO2 laser. Laser CVD thus proved to be a useful new technique for the fabrication of microlenses.
Transient photocurrent response in polycrystalline silicon thin films
Authors: Pandya R. , Khan B. A.
Published: July 2002

Photocurrent transients have been measured in hydrogenated and unhydrogenated (as-deposited) polycrystalline silicon thin-film transistors as a function of gate voltage. For both types of samples, the transients demonstrate dispersive transport and a gate voltage independent shape over a large range of gate voltages. The multiple trapping model for trap controlled transport has been used to develop a schematic model for the gap states. According to this model, the major effect of hydrogenation is the removal of shallow trapping states and it is also accompanied by a small change in dangling bond spin density.
Index guided single stripe lasers fabricated by selective area growth in a metalorganic chemical vapor deposition system
Authors: Yang J. J. , Ou S. S. , Jansen M. , Wilcox J. , Sergant M.
Published: July 2002

Index guided single stripe lasers have been fabricated by using a one-step selective area growth technique in the metalorganic chemical vapor deposition system. By pyrolytically depositing SiO or SiO2 layers on GaAs substrate, and lithographically defining the stripes, single stripe heterostructure lasers can be achieved on the uncovered substrate while polycrystalline films are observed beyond the stripe regions. The device operated with a single spatial mode for up to more than three times the threshold current.
An explanation of optically induced excess conductivity in compensated a-Si:H films
Authors: Chen Yang-Fang , Huang Ying-Sheng
Published: July 2002

In order to explore the creation process of optically induced excess conductivity in compensated a-Si:H films, we investigated the effect of monochromatic light exposure with different photon energies: 2.54, 1.96, 1.17, and 0.95 eV. The experimental results show that the threshold energy is below 0.95 eV. We suggest that the most likely explanation is the introduction of localized states originating from boron-phosphorus complexes.
Al-related recombination center in polycrystalline Si
Authors: Rodot M. , Bourée J. E. , Mesli A. , Revel G. , Kishore R. , Pizzini S.
Published: July 2002

Aluminum-related traps in polycrystalline silicon are investigated by deep-level transient spectroscopy and laser-beam-induced current measurements. One of these traps is found to be responsible for electron recombination.
Effective removal of oxygen from Si layer on buried oxide by implantation of hydrogen
Authors: Mizuno B. , Kubota M. , Nomura N. , Iwasaki H.
Published: July 2002

Effects of implanted hydrogen on removal of oxygen from a Si top layer on buried oxide by the post-implantation annealing were studied. The Si top layer and the buried oxide layer were analyzed by secondary ion mass spectroscopy (SIMS) and cross-sectional transmission electron microscopy (X-TEM). With implanted hydrogen, oxygen concentration in the Si top layer could be reduced below the SIMS detection limit by annealing at relatively lower temperature 1150 °C for 2 h in an ambient of N2. It is verified by X-TEM that the Si top layer is precipitate-free. An amount of hydrogen comparable to the amount of oxygen contained in the Si top layer is needed to remove the oxygen completely. This effective removal of oxygen is attributed to the suppression of oxygen precipitation and the enhanced dissolution of oxide precipitates by hydrogen.
Photoluminescence characteristics of selectively grown GaAs and AlGaAs/GaAs quantum wells
Authors: Lau Kei May , Jones Stephen H. , Hsu Jung-Kuei , Bertolet Daniel C.
Published: July 2002

GaAs and AlGaAs/GaAs multiple quantum wells (MQW) were selectively deposited on GaAs substrates patterned with native oxide, and photoluminescence (PL) characteristics of both the single crystal grown in open windows and the polycrystalline material deposited on the oxide masks were studied. Well-resolved distinct quantum-well (QW) transition peaks indicate no degradation of the epitaxial material quality in the small single-crystal areas. The PL of polycrystalline GaAs is very weak and the peak is centered around the near-band-edge transition energy of GaAs. Polycrystalline MQW structures exhibit much stronger PL signals, and the peak position shifts corresponding to the widths of the QWs grown. These results suggest that the quantum size effect is preserved in the polycrystalline material.
Density of kinks on a dislocation segment in thermodynamic equilibrium and the interaction between solitons
Authors: Pawel/ek A.
Published: July 2002

The paper deals with a modification of the classical expression derived by John P. Hirth and J. Lothe [Theory of Dislocations (McGraw-Hill, New York, 1972)] for the density of kinks on a dislocation segment in thermodynamic equilibrium imposed by external stresses. The dislocation kink–kink interaction is discussed in terms of soliton-antisoliton interaction, the analytical results obtained by J. Rubinstein [J. Math. Phys. 11, 258 (1970)] and the ones numerically obtained by M. Peyrard and David K. Campbell [Physica 9D, 33 (1983)] being applied for that purpose.
Reduced density channels in air produced by a double pulsed electron beam
Authors: Bieniosek F. M.
Published: July 2002

The radial profile of a reduced density channel in air produced by a double pulsed electron beam has been measured by use of a simple laser deflection technique, sensitive to density changes of 1016 cm−3 in air. Measurements indicate a pressure dependence in channel depth and in the relationship between beam and channel profiles. Measured channel and shock wave behaviors agree with predictions of a one-dimensional hydrodynamics code. Channel decay rates were negligible for times t<1 ms.
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u electrical conductivity and amorphous-crystalline transition in vacuum-deposited amorphous thin films of a Se50Te50 alloy
Authors: Damodara Das V. , Jansi Lakshmi P.
Published: July 2002

I n situ electrical conductivity measurements have been made on vacuum-deposited amorphous thin films of various thicknesses of a Se50Te50 alloy in the temperature range 300–430 K. From the electrical conductivity, x-ray studies, and electron diffraction studies it is found that the as-grown films are amorphous and undergo an irreversible amorphous-crystalline transition on heating in situ. The amorphous-crystalline transition takes place in the temperature range 320–360 K for the different films. However, no systematic variation of the transition temperature with the thickness of the films is observed. All the films except the thinnest ones have a sharp transition temperature. X-ray and electron diffraction analyses show that the Se50Te50 films above 360 K are polycrystalline. Above 360 K the electrical conductivity of the polycrystalline Se50Te50 films varies as an exponential function of reciprocal temperature.
Electrostatic solution to a specialized wire-routing problem
Authors: Hechtman Charles D. , Levine Zachary H.
Published: July 2002

Potential theory and graph theory are used to create a specialized automatic router. Members of one set of points are completely connected to members of another set of points by nonintersecting curves all contained in the plane. Choices are offered for the linking paths from local information. The problem domain may be the plane or a bounded subset of the plane containing excluded areas
High-efficiency InGaAsP/InP flat-surface buried heterostructure distributed feedback lasers at 1.55 μm
Authors: Wakao K. , Kihara K. , Kotaki Y. , Kusunoki T. , Sudo H. , Isozumi S. , Yamakoshi S. , Ishikawa H. , Imai H.
Published: July 2002

A new buried heterostructure has been developed. High-efficiency (29%), high-power (37-mW) operation has been achieved with InGaAsP/InP distributed feedback lasers emitting at 1.55 μm by using the novel buried heterostructure.