bluuebunny/crossref_metadata_2025 huggingface dataset:
A theoretical explanation for the red energy shift of a newly discovered, exclusively acceptor-associated emission in GaAs
Authors: Ohnishi Nobukazu , Makita Yunosuke , Mori Masahiko , Irie Katsuhiro , Takeuchi Yoshinori , Shigetomi Shigeru
Published: July 2002

Radiative mechanism of a newly discovered near-band-edge emission, [g-g], exclusively associated with acceptor impurities in GaAs, was theoretically discussed. Since the emission energy of [g-g] for the lowest acceptor concentration limit is nearly identical to that of the excited state of the acceptor impurities and it shows a noticeable shift towards lower-energy levels with increasing acceptor concentration, it was suggested that the energy of [g-g] corresponds to the 2pσ bond state of the acceptor-acceptor pair formed by the overlapping of the 2p excited state. The calculated energy of the 2pσ bond as a function of the distance between the acceptor-acceptor pair shows good agreement with the experimentally obtained value of [g-g] in Mg-doped GaAs grown by molecular-beam epitaxy (MBE). From a comparison of binding energies in the acceptor-doped GaAs samples prepared by ion implantation (Zn+ or Mg+) and by MBE, the activation ratio of the implanted atoms was estimated.
Measurement of dispersion in electrodeposited Cu2O
Authors: Rakhshani A. E.
Published: July 2002

By using an optical reflectance interferometry method the refractive index n of electrodeposited films of Cu2O was measured in the wavelength region of λ=0.466–1.2 μm. This measurement was an extension to the previously reported values. The result fits well to an empirical dispersion equation of the form n2=1+4.81λ2/(λ2−0.125), where λ is in μm. The dispersion values measured for electrodeposited films were found to be different from the reported values for other types of Cu2O.
Low-frequency noise in self-aligned bipolar transistors
Authors: Lu Pong-Fei
Published: July 2002

We report the first study of the low-frequency noise in self-aligned npn bipolar transistors, which use the polysilicon emitter. Some of these devices showed excess noise spectra different from the 1/f law generally observed in diffused junction transistors, and the spectral shape S( f ) was found to vary from sample to sample. For instance, we have observed two different characteristics, S( f )∼1/f and S( f )∼1/[1+( f/f0)2], in two adjacent transistors on the same chip. We attribute the latter to carrier trapping in the oxide barrier at the poly-/monosilicon boundary, whose inhomogeneity could explain the wide variation of the noise spectra.
High-resolution x-ray diffraction studies of InGaAs(P)/InP superlattices grown by gas-source molecular-beam epitaxy
Authors: Vandenberg J. M. , Hamm R. A. , Panish M. B. , Temkin H.
Published: July 2002

High-resolution x-ray diffraction studies have been carried out to determine the structural perfection and periodicity for a number of high-quality InGaAs/InP superlattices and one InGaAsP/InP superlattice grown by gas-source molecular-beam epitaxy. For comparison, high-resolution diffraction both with a three-crystal geometry and with a four-crystal monochromator was used along with conventional double-crystal x-ray diffractometry. The best resolution in the x-ray satellite patterns was obtained with the four-crystal monochromator, providing a resolution of one molecular layer in the periodicity of the superlattice. The presence of sharp satellite reflections in the x-ray diffraction profiles demonstrate smooth interfaces with well-defined modulated structures which could be derived from a kinematical diffraction step model. For some superlattices, excellent agreement between the step model and the measurements is obtained when the model assumes that each period consists only of the well and the barrier with ideally sharp interfaces. For other superlattices a thin strained layer had to be assumed on either one or both sides of each quantum well. The comparison of these structures demonstrates the extreme sensitivity of the high-resolution method in conjunction with the step model, to study very small modifications in superlattice periodicities.
Characteristics of molecular-beam epitaxially grown pair-groove-substrate GaAs/AlGaAs multiquantum-well lasers
Authors: Yuasa Tonao , Mannoh Masaya , Yamada Tomoyuki , Naritsuka Shigeya , Shinozaki Keisuke , Ishii Makoto
Published: July 2002

Growth and device characteristics of an index-guided GaAs/AlGaAs multiquantum-well (MQW) laser, called a pair-groove-substrate (PGS) MQW laser, are described in detail. The laser structure is fabricated by using single-step molecular-beam epitaxy on a (001) GaAs substrate with a pair of etched grooves along the 〈11̄0〉 direction. A mesa between a pair of grooves, where the lasing action occurs, becomes narrow during growth, and the narrow mesa offers lateral waveguiding that stabilizes a fundamental transverse mode. The superior crystalline quality of the mesa top, which is examined by a microprobe photoluminescence technique, serves to lower the lasing threshold currents. The lasers with mesa widths below 2 μm show stable transverse mode operation with a low threshold current of 20 mA, as well as a high external differential quantum efficiency of 68%. The low threshold and high characteristic temperature accomplish a high-temperature continuous-wave operation at 153 °C for the lasers mounted on silicon heat sinks.
Discharge properties of formed-ferrite plasma sources
Authors: Kashiwabara S. , Watanabe K. , Fujimoto R.
Published: July 2002

The discharge properties of a newly developed formed-ferrite plasma source intended for gas laser applications are described. The voltage-current characteristics of this new plasma source were measured as functions of the applied voltage ranging from 10 to 30 kV (corresponding to 100–900 J of input energy) for CF4 and Ar gases at atmospheric pressure and for N2 gas at pressures in the range of 1–760 Torr (133–1.01×105 Pa). The peak current through a plasma channel typically 7 cm in length reached 50 kA when the plasma source was driven by a 2-μF, 30-kV capacitor bank. The results obtained are of importance in order to understand the physical mechanism of the formed-ferrite plasma source.
Critical path length for the similarity of elastic multiple scattering processes
Authors: Liljequist D.
Published: July 2002

Multiple scattering processes characterized by or scaled to equal transport mean free path λtr are expected to give similar results (e.g., approximately equal particle distributions in space) at sufficiently large path lengths. By means of the Monte Carlo method, it is shown that the spatial and angular distributions generated by different elastic scattering processes with equal λtr clearly converge to similarity with increasing path length. The critical path length required for evident similarity is of order of magnitude such that the processes are at least plural. For scattering geometries where the effect of single large angle scattering is appreciable, the validity of this plural scattering condition may be restricted to suitably chosen scattering cross sections. Applications to electron penetration through matter are briefly discussed.
Magnetohydrodynamic liquid-metal flows and power losses in a rectangular channel with a moving conducting wall
Authors: Brown Samuel H. , Reilly Patrick J. , Sondergaard Neal A.
Published: July 2002

Fully developed, viscous liquid-metal flows and power losses in a rectangular channel in a uniform, external magnetic field were studied for moderate Hartmann numbers and different channel aspect ratios. The channel was assumed to have insulating side walls parallel to the field, a perfectly conducting moving top wall, and a stationary bottom wall perpendicular to the field. Exact series solutions and numerical calculations are presented for velocity profiles, induced magnetic field distributions, current densities, voltage profiles, and viscous and joulean power losses. The joulean and viscous dissipation are computed from squared quantities involving infinite series with double summations for finite M. The diverging series derived for the viscous power losses is made convergent by slightly modifying the velocity profile of the conducting fluid at the moving interface. The effect of the applied field is to produce an eddy current that accelerates the bulk fluid to velocities greater than those without the field, but because of the presence of the side walls, the velocities are less than in one-dimensional couette flow. Except at small aspect ratios and Hartmann number, almost the entire power loss resulted from the component of the induced current parallel to the applied field.
Defect identification in undoped and phosphorus-doped CuInS2 based on deviations from ideal chemical formula
Authors: Ueng H. Y. , Hwang H. L.
Published: July 2002

A theoretical model is proposed which is based on the electrical, photoluminescence, and stoichiometric analyses, and this model allows the calculation of the concentration of various defects in undoped and phosphorus-doped CuInS2 crystals grown by the traveling heater method. All the association and ionization reactions are described in terms of the law of mass action. The results indicate that it can be used to explain material compensation and phosphorus-doping effects in CuInS2.
Effective second-order elastic constants of a strained crystal using the finite strain elasticity theory
Authors: Rao R. Ramji , Padmaja A.
Published: July 2002

The finite strain elasticity theory of Murnaghan has been used to derive the expressions for the effective second-order elastic constants of tetragonal, trigonal, orthorhombic, monoclinic, and triclinic crystals in their strained state in terms of the second- and third-order elastic constants of the respective crystals in their natural state. These expressions are employed to obtain the pressure derivatives of the effective second-order elastic constants of some trigonal and tetragonal crystals for which experimental second- and third-order elastic constant data are available.
Reassessment of ionized impurity scattering and compensation in GaAs and InP including correlation scattering
Authors: Lancefield D. , Adams A. R. , Fisher M. A.
Published: July 2002

The pressure dependence of the electron Hall mobility has been measured in a wide variety of InP and GaAs samples. The results, analyzed by a number of techniques, indicate that, in general, very good agreement can be obtained between theory and experiment for pure material at temperatures where ionized impurity scattering is unimportant. When heavily doped samples of liquid-phase epitaxy (LPE) GaAs and vapor-phase epitaxy (VPE) InP were measured it was not possible to predict the experimental pressure dependence of the mobility using the Brooks–Herring theory of scattering from ionized impurities. The possibility of inaccuracies in analysis have been reduced by using an iterative solution of the Boltzmann equation, phase shift calculations, and also Moore’s analysis [Phys. Rev. 160, 618 (1967)] for dressing and multi-ion corrections. However, these proved to be inadequate and we obtain the best agreement with experiment using the theory of Yanchev et al. [J. Phys. C 12, L765 (1979)] for scattering from a correlated distribution of impurities. The important effects of impurity correlation have been substantiated by studying samples of GaAs grown by molecular-beam epitaxy (MBE) and bulk GaAs subjected to neutron transmutation doping. The inability of impurities to correlate in such material is demonstrated by the close agreement between Brooks–Herring theory and experiment for these samples. When correlation scattering is taken into account, it becomes possible to explain the observed mobilities in heavily doped materials without having to always postulate autocompensation, as has been done by other authors.
Luminescence and excitation energy transfer in monolayer assemblies incorporating organic dye molecules. I
Authors: Yonezawa Yoshiro , Möbius Dietmar , Kuhn Hans
Published: July 2002

Excitation energy transfer between organic dye molecules in monolayer assemblies is studied. Typical cyanine dyes: N, N′-dioctadecyl-oxacyanine perchlorate and N,N′-dioctadecyl-thiacyanine perchlorate are employed as a donor and acceptor, respectively. Inclusion of the acceptor into the monolayer composed of isolated donor and matrix molecules induces quenching of monomer fluorescence of the donor and consequent sensitization of acceptor fluorescence. Quenching of donor fluorescence by the acceptor obeys the Stern–Volmer relation with a weakly temperature-dependent Stern–Volmer constant. Lowering the temperature from T=293 to 77 K brings about the increase of both the Stern–Volmer constant and the intensity ratio of the sensitized fluorescence to the donor fluorescence. These observations indicate that the rate of thermal deactivation of the excited donor molecule is proportional to temperature in spite of temperature-insensitive energy-transfer rate. Energy transfer between donor and acceptor molecules occurs via a direct dipole-dipole mechanism.
Effect of carbon concentration on the electrical properties of liquid-encapsulated Czochralski semi-insulating GaAs
Authors: Chichibu Shigefusa , Matsumoto Satoru , Obokata Takeshi
Published: July 2002

Effects of carbon concentration on the electrical properties of liquid-encapsulated Czochralski semi-insulating GaAs crystals are investigated quantitatively for the first time by keeping other parameters such as melt stoichiometry, EL2 concentration, and dislocation density almost the same. Its dependence can be well explained by the mixed conduction model.
Coercivity after heat treatment of overquenched and optimally quenched Nd-Fe-B
Authors: Wecker J. , Schultz L.
Published: July 2002

Rapidly quenched Nd-Fe-B magnets show a pronounced composition dependence of the intrinsic coercivity HcI which increases with increasing Nd content to values of 23.5 kOe. The magnetic hardening is ascribed to a Nd-rich phase located at the phase boundaries of the Nd2Fe14B grains. Samples prepared by crystallization of amorphous ribbons have slightly lower coercivities but are less sensitive to prolonged heat treatment at higher temperatures. The microstructure obviously differs for the two types of material.
Noise measurements in thin-film interconnections: A nondestructive technique to characterize electromigration
Authors: Bagnoli P. E. , Diligenti A. , Neri B. , Ciucci S.
Published: July 2002

Electromigration in aluminum and aluminum-silicon (1%) resistors was detected by means of a new technique based on the particular features of an ultralow-noise amplifier, which made it possible to evaluate the stochastic resistance fluctuations associated with vacancy generation-recombination processes. The power spectra of these fluctuations display a 1/f γ behavior with 2≤γ≤2.6, in the frequency range 10 mHz–1 Hz, and the analysis of these spectra, recorded at various current densities and temperatures, led to an evaluation of the activation energies characteristic of the process. Scanning electron microscope observation of the damage induced by stressing the resistors at the same current density and temperature as the spectra measurement but for a longer time, showed that what was being observed was the electromigration phenomenon in its early stages.
Growth of GaAs on GaAs-coated Si by liquid-phase epitaxy
Authors: Sakai Shiro , Matyi R. J. , Shichijo H.
Published: July 2002

The liquid-phase-epitaxial growth of GaAs on partially masked GaAs-coated Si substrates prepared by molecular-beam epitaxy is described. Uniform layers were obtained in stripe windows narrower than 20 μm at an optimum growth temperatures of 800 °C. Smaller supercooling, however, resulted in smoother surface morphologies. The growth can be explained in terms of the mass transport of the growing species from bulk of the melt to the substrate surface and the subsequent incorporations into the solid. A marked difference between the growth on GaAs-coated Si and that on GaAs substrates was observed. The growth on GaAs substrates appears to be dominated by surface reaction while transport processes are the limiting factor on GaAs-coated Si. The migration length of the growing species was estimated to be very short on GaAs substrates and about 15 μm on GaAs-coated Si.
Platinum silicide contact to arsenic-doped polycrystalline silicon
Authors: Huang H.-C. W. , Cook R. , Campbell D. R. , Ronsheim P. , Rausch W. , Cunningham B.
Published: July 2002

PtSi contacts to As-doped polycrystalline silicon have been studied with respect to dopant redistribution, microstructure, and contact resistance. Arsenic was found to pileup at the PtSi-polysilicon interface upon silicide formation. Cross-sectional transmission-electron microscopy revealed columnar PtSi grains and a relatively flat interface between PtSi and polysilicon. These observations are similar to those reported for the case of PtSi formed on the single-crystal silicon. The specific contact resistance (ρc) has been investigated as a function of As concentration ranging from 8×1019 to 2×1021 cm−3 and of its dependence on substrate preclean procedures prior to Pt deposition. It was found that ρc decreases with increasing As concentration, as expected from theory. However, the contact resistance to As-doped polysilicon is about ten times higher than contacts to similarly doped single-crystal Si. The origin of this difference is attributed to the fact that not all of the implanted As was activated. Hall-voltage measurements showed that only about 10% of the implanted As was electrically active after an 880 °C, 20 min furnace annealing. Rapid-thermal annealing was then used to activate a higher fraction of the implanted As. Consequently, a much lower ρc was obtained: e.g., 7.5×10−8 Ω cm2 for samples annealed at 1050 °C for 30 s, in contrast to a value of 8.4×10−7 Ω cm2 for a furnace-annealed sample.
Spectroscopic properties of GdScAl garnet doped with Ti3+
Authors: Schepler K. L. , Kokta M.
Published: July 2002

Single crystals of GdScAl garnet were successfully doped with Ti3+ ions using a reducing atmosphere. Two broadband absorption peaks, typical of Ti3+ Jahn–Teller splitting, were observed at 520 and 620 nm. Fluorescence was observed in the 720–1050 nm region peaked at 840 nm. Fluorescence lifetime was 5.5 μs at 12–50 K but decreased rapidly at higher temperatures.
Magnetic susceptibility of sintered and powdered Y-Ba-Cu-O
Authors: Chen D.-X. , Goldfarb R. B. , Nogués J. , Rao K. V.
Published: July 2002

The real and imaginary parts of ac susceptibility of a sintered Y1Ba2Cu3O7−δ superconductor were measured before and after powdering. The temperature-dependent susceptibility may be separated into two contributions, one sensitive and the other relatively insensitive to the magnitude of the measuring field. The former is partially suppressed by coarsely crushing the sample. It is completely suppressed after finely powdering, whereupon the susceptibility curves become insensitive to the magnitude of the measuring field. Several models apparently consistent with the results are discussed.
Dopant effects on the superconductivity of YBa2Cu3O7 ceramics
Authors: Yan M. F. , Rhodes W. W. , Gallagher P. K.
Published: July 2002

We investigated the effects of SrTiO3 and 17 different oxide dopants, namely Ca, Sc, La, and Zr with possible substitution in the yttrium sites, K, Sr, and Pb in the barium sites, Li, Mg, Fe, Co, Ni, Zn, Al, Ti, Nb, and Si in the copper sites on the superconductivity of YBa2Cu3O7. These dopants can be classified into four categories depending on their solubilities and substitution in the different cation sublattices of YBa2Cu3O7 perovskite. Dopants in the first category dissolve and substitute in the copper sublattice and they can significantly reduce the transition temperature of the superconductivity of YBa2Cu3O7. For example, three dopants in this category, namely Zn, Mg, and Li, at 2 mole % dopant level, reduce the transition temperatures to 66, 65, and 82 K, respectively. The second category dopants substitute in the barium and yttrium sites, and these dopants, e.g., Sr at 2 mole % concentration, do not have any significant effect on the transition temperature of the superconductivity of YBa2Cu3O7. While dopants, e.g., AlO1.5 and SiO2, in the third category have a limited solubility in YBa2Cu3O7, they have a strong tendency to decompose the superconducting phase by leaching out some components of YBa2Cu3O7. The transition temperature of the undecomposed superconducting phase remains unaffected at ∼91 K even though the susceptibility signal is reduced substantially. Since the dopants in the fourth category have a limited solubility and very little reactivity with YBa2Cu3O7, they are present simply as an inert second phase among the superconducting matrix.
Magnetic properties and anisotropy of CoCr thin films for perpendicular recording
Authors: Khan Mahbub R. , Lee Jae I. , Seagle D. J. , Fernelius N. C.
Published: July 2002

CoCr thin films, 50 Å to 1 μm thick, have been rf sputtered onto a number of different substrates. These films have been studied for their nucleation, microstructure, magnetic properties, and anisotropy. It has been observed that at lower thicknesses, the grains are extremely small (200 Å at 0.1 μm) but cover the entire substrate surface quite uniformly. Below the thickness of 100 Å, the coercivity Hc approaches zero very rapidly and the film approaches superparamagnetic state. As the film thickness is increased, the grains get larger (800 Å at 1 μm) and the coercivity of the film increases. The Δθ50 value for the (0002) x-ray peak reached 2°. The grain size clearly dominates the coercivity of these films. The effective anisotropy constants increased from 1.31 to 3.16×105 ergs/cm3 for the above thickness range. Estimates of the magnetocrystalline anisotropy field are determined from a uniform thin-film model and a model that accounts for the columnar grains. When the circular magnetic columns are in contact, the shape anisotropy field is 5% lower than the uniform thin-film approximation. When the magnetic radius is 80% of the grain radius, then the shape anisotropy field is 34% lower.
Evaluation of crystalline quality of zirconium dioxide films on silicon by means of ion-beam channeling
Authors: Osaka Yukio , Imura Takeshi , Nishibayashi Yoshiki , Nishiyama Fumitaka
Published: July 2002

Zirconium dioxide (ZrO2) films have been grown on Si(100) and Si(111) substrates at 800 °C by vacuum evaporation. A channeling spectrum of the Rutherford backscattering on the ZrO2 films shows that ZrO2 films [tetragonal (200)] are epitaxially grown on Si(100) substrate at 800 °C, which is consistent with x-ray diffraction and reflection high-energy electron diffraction observations. The spread of crystallite orientation in the epitaxial film is estimated to be 0.32°, by analyzing the angular dependence of the total backscattering yield.
Low-threshold interrupted-growth step-index separate-confinement heterostructure GaAs/(Al,Ga)As lasers grown by molecular-beam epitaxy
Authors: Pion Martin , Specht Alisa , Appelman Howard , Ebersohl Richard , Begley David , Waters Robert , Guido Thomas , Stazak Susan
Published: July 2002

We report preliminary results on the low-threshold operation of interrupted-growth GaAs/(Al,Ga)As step-index separate-confinement heterostructure lasers grown on misoriented substrates by molecular-beam epitaxy. Growth was performed simultaneously on (100) substrates misoriented 1° and 6°, respectively, towards the nearest (111)A face. The 6° orientation exhibited the better morphology and lowest threshold current density (260 A cm−2 for a cavity length of 607 μm). The 1° orientation yielded the higher slope efficiency (0.43 W/A for a single facet). The growth was twice interrupted for 3 min each time for Al effusion cell temperature adjustment between the growth of the inner and outer cladding layers.
Shallow p+ layer in In0.53Ga0.47As using P/Be and As/Be co-implant
Authors: Wang Kou-Wei , Long Judith , Mitcham Deborah
Published: July 2002

Be is implanted into an n-InGaAs epitaxial layer. Both electrical and atomic profiles indicate that Be in-diffusion occurs during annealing, resulting in a p layer thicker than that desired. A co-implant of P or As with Be significantly reduces this Be in-diffusion resulting in shallow (2000 Å) p+-n junctions with 4×1018 cm−3 surface hole concentration and 70% electrical efficiency.
Enhanced spin-density waves in Co-Cr superlattices
Authors: Ge Shihui , Stearns M. B.
Published: July 2002

The electrical resistivity of a series of Co-Cr multilayered thin films (MLS) of equal layer thickness of ∼30–30 Å made at various substate temperatures and deposition rates of 0.5 and 2 Å/s was measured over the temperature range of 4.2–350 K. The most striking feature seen in several of these MLS was that the bump near the Néel temperature TN of the spin-density wave (SDW) of Cr was 2–4 times greater than that seen in CrCo alloys. The bump in the MLS is also much sharper than that of the alloys. The resistivity bump and an increase in TN in the alloys has been attributed to an enhancement of the SDW due to the exchange interaction between the Co moments and the SDW. It is proposed that the even larger enhancement of the SDW in the MLS is due to the superlattice structure of the MLS. This changes the Cr Fermi surface by introducing new Brillouin zones and thus increases the nesting which gives rise to the SDW. The variation of the TN values of the MLS varies systematically with the substrate temperature. Other similarities and differences between the MLS and the alloys resistivity behavior are discussed.
Magnetic properties of ion-beam sputter-deposited Fe-Ni-B-Si films
Authors: Ryu J. , Huang Y. , Vittoria C.
Published: July 2002

We have produced Fex-Ni80−x -B15-Si5 (x=20, 40, and 75) and permalloy thin films on a silicon substrate using ion-beam sputtering technique. Four-point probe measurement indicated that quarternary films had 3–4 times higher resistivity than permalloy films, and this ratio was not changed after thermal annealing. The values of saturation magnetization were determined to be 5–13 kG depending on Fe concentration. The anisotropy fields of these films were in the ranges of 2–15 Oe after deposition, however, these values were reduced by more than 50% after annealing with field. The lowest value of the anisotropy field was 1.3 Oe for the permalloy film after thermal annealing without field.
Comparative x-ray spectroscopy of various-Z elements with wavelength calibration
Authors: Lampart W. , Weber R. , Balmer J. E.
Published: July 2002

X-ray spectra in the 5–15 Å spectral region are presented for various elements with atomic numbers between 9 and 82. Plasma was produced by irradiating plane targets with 1-J, 800-ps frequency-doubled Nd:glass laser pulses at λ=527 nm. The characteristics of the spectra can be varied from pronounced K- and L-shell line emitters (F to As) to nearly continuous x radiators such as W or Au.
Single crystals of Al-Mn superlattice grown by molecular-beam epitaxy
Authors: Nishihata Yasuo , Nakayama Masaaki , Sano Naokatsu , Terauchi Hikaru
Published: July 2002

Single crystals of an Al-Mn superlattice have been grown by molecular-beam epitaxy. For thicknesses less than the critical thickness dc ≂30 Å, Mn atoms form the fcc lattice in the [111] direction of an Al surface grown on sapphire-C substrate. The modulated structure of the Mn surface has been observed in situ by reflection high-energy electron diffraction. On the other hand, for thicknesses more than dc, Mn grows in the [110] direction of the bcc lattice (α phase). After annealing a compression of the lattice has been observed by x-ray diffraction. The annealing has produced well-oriented alloys with fairly large domain sizes.
Thermal diffusivity of superconducting YBa2Cu3O7−x
Authors: Gomes L. , Vieira M. M. F. , Baldochi S. L. , Lima N. B. , Novak M. A. , Vieira N. D. , Morato S. P. , Braga A. J. P. , Cesar C. L. , Penna A. F. S. , Filho J. Mendes
Published: July 2002

Thermal diffusivity results for superconducting YBa2Cu3O7−x systems are reported. Two laser excitation techniques were used: photoacoustic phase-lag and the flash method. We observed an anomalous jump in the thermal diffusivity at the critical temperature and related it to the electronic specific heat anomaly. This correlation yielded a characteristic phonon frequency of 320 cm−1 in the range of an active Raman mode already observed in a single crystal of the same compound. This result reinforces the current electron-phonon coupling mechanism as responsible for superconductivity.
Variable angle spectroscopic ellipsometry: Application to GaAs-AlGaAs multilayer homogeneity characterization
Authors: Alterovitz Samuel A. , Snyder Paul G. , Merkel Kenneth G. , Woollam John A. , Radulescu David C. , Eastman Lester F.
Published: July 2002

Variable angle spectroscopic ellipsometry has been applied to a GaAs-AlGaAs multilayer structure to obtain a three-dimensional characterization using repetitive measurements at several spots on the same sample. The reproducibility of the layer thickness measurements is of order 10 Å, while the lateral dimension is limited by beam diameter, presently of order 1 mm. Thus, the three-dimensional result mainly gives the sample homogeneity. In the present case we used three spots to scan the homogeneity over 1 in. of a wafer, which had molecular-beam epitaxially grown layers. The thickness of the AlGaAs, GaAs, and oxide layers and the Al concentration x varied by 1% or less from edge to edge. This result was confirmed by two methods of data analysis. No evidence of an interfacial layer was observed on top of the AlGaAs.
Formation of PtSi in the presence of W and Al
Authors: Chang Chin-An
Published: July 2002

The formation of PtSi is studied in the presence of W and Al using the Al/W/Pt/Si structure, with 1000-Å W acting as the barrier layer. The PtSi layer formed stays intact at 400 °C, starts to react with Al around 450 °C, and is completely converted to PtAl2 at 500 °C, with the released Si migrating to the surface. In contrast, using the W/Pt/Si structure without an Al layer, the PtSi formed remains little changed up to about 600 °C. The W-Pt interface of the binary W/Pt structure shows no interaction up to at least 600 °C. The results are compared with those using the Al/Pt/Si structure, and their relation to contact metallurgies is discussed.
Superconductivity and spin-glass ordering in RBa2 (Cu1−xFex)3Oz: R=Y,Gd; 0≤x≤0.12
Authors: Moorjani K. , Bohandy J. , Kim B. F. , Adrian F. J. , Du Y. W. , Tang H. , Qiu Z. Q. , Walker J. C.
Published: July 2002

Samples of oxygen deficient perovskites, YBa2 (Cu1−x Fex )3Oz and GdBa2 (Cu1−x Fex )3 Oz (z≂7) were prepared with up to 12% Fe substituting for Cu. A novel variation of the microwave absorption technique was employed to establish the superconducting transition in these samples and to show that the reduction in the transition temperature with increasing Fe concentration is faster in the Gd samples than in the Y ones. In both series of samples, the room-temperature Mössbauer spectra reveal two distinct Fe sites corresponding to two local oxygen coordinations, and more significantly the spectra at 4.2 K for specimens with x≥0.03 show that the Fe moments are magnetically ordered, leading to the coexistence of superconductivity and magnetism.
Magnetic properties of Y-Ba-Cu-O superconductors
Authors: McGuire T. R. , Holtzberg F. , Kaiser D. L. , Shaw T. M. , Shinde S.
Published: July 2002

We report on the superconducting magnetic properties of two polycrystalline YBa2Cu3Ox samples which have high densities and show current densities of 7×104 A/cm2. In addition, two single crystals are studied, one of which can support a current density of 3×106 A/cm2. The diamagnetic shielding in these samples in fields of 14 Oe is almost 100%, but the Meissner effect in applied fields above 1000 Oe is less than 1%.
Flux creep in high T
c superconductors
Authors: Giovannella C. , Rouault P. , Campbell I. A. , Collin G.
Published: July 2002

We have performed torque experiments on ceramic samples of the new superconducting perovskites and we studied the flux creep properties of both LaSrCuO and YBaCuO. In addition to its higher Tc, the latter shows stronger flux pinning. Nevertheless, flux pinning in both samples well below Tc is so weak as to be very detrimental to possible high-current applications. Some consequences of our observations on the superconducting ‘‘glassy’’ state are pointed out.
Spin-wave FMR in annealed NiFe/FeMn thin films
Authors: Layadi A. , Lee J.-W. , Artman J. O.
Published: July 2002

Ferromagnetic resonance (FMR) investigations have been made at 33 GHz on as-deposited and on annealed bilayer NiFe/FeMn thin films. Supplemental investigations were made at 9 GHz. Following a 350 °C anneal, for 1 h or longer in duration, the NiFe FMR spectrum was found to be characterized by a sequence of spin-wave resonance (SWR) modes. The behavior of the SWR modes is in accord with the presence of a thin ferromagnetic layer at the NiFe/FeMn interface with magnetization different from the bulk. Transmission electron microscopy (TEM) examinations indicate that annealing promotes formation of an interdiffused layer at the NiFe/FeMn interface and favors NiFe grain growth. Magnetic field limitations precluded FMR at 0° (perpendicular) field orientation. At various field orientations below the critical angle, the resonant fields, Hn, were found to vary with mode number n as n2. Also, for n>1, the FMR-SWR linewidth ΔHn has a component varying as n2. From the 33-GHz 16° orientation data, the exchange constant A is computed to be (1.03±0.15)×10−6 erg/cm. The application of an in-plane magnetic field during anneal produces a reduction of the SWR mode intensities and a broadening of the principal peak. A perpendicular magnetic field had little effect.
Magnetization reversal dynamics in magneto-optic media (invited)
Authors: Mansuripur M. , McDaniel T. W.
Published: July 2002

Dynamics of magnetization reversal in thin films of amorphous rare earth-transition metal alloys are investigated. Using computer simulations for a two-dimensional square lattice of dipoles with nearest-neighbor exchange interaction and random axis anisotropy, the Landau–Lifshitz–Gilbert equation is numerically integrated to yield the static wall structure and its motion under an applied field. The simulated results show excellent agreement with theory in the special cases where analytic solutions exist.
Improvement of the C/N ratio and corrosivity of TbFeCo amorphous films by controlling their microstructure
Authors: Naoe M. , Kitamura N. , Ito H.
Published: July 2002

The dependence of structural and magneto-optical (MO) properties of TbFeCo films on Ar pressure, deposition rate, and magnetic field have been investigated by using the facing-target sputtering (FTS) system. The films prepared at high deposition rate and/or with the plasma-free substrate did not have any appreciable columnar structure. The Kerr rotation angle of the films was as high as 0.37°. No significant change in the magneto-optical properties of the films was observed after exposing them to air for 250 days. MO disks fabricated by the FTS system had a high C/N ratio of 57 dB at a bit length of 5 μm.
Elevated temperature study of Nd-Fe-B–based magnets with cobalt and dysprosium additions
Authors: Gauder D. R. , Froning M. H. , White R. J. , Ray A. E.
Published: July 2002

This paper discusses the elevated temperature performance of Nd-Fe-B magnets containing 0–15 wt. % cobalt substitutions for iron and 0–10 wt. % dysprosium substitutions for neodymium. Test samples were prepared using conventional powder metallurgy techniques. Elevated temperature hysteresis loop and open-circuit measurements were performed on the samples to investigate irreversible losses and long term aging losses at 150 °C. Magnets with high amounts of both cobalt and dysprosium exhibited lower losses of coercivity and magnetization. Dysprosium had more influence on the elevated temperature performance of the material than did cobalt.
Mn magnetism and magnetic structures in RMn2
Authors: Ballou R. , Deportes J. , Lemaire R. , Ouladdiaf B.
Published: July 2002

Because of the tetrahedral arrangement of the Mn atoms in the Laves phases, the magnetic structures of the RMn2 are frustrated. To reduce this frustration, very unusual magnetic structures are stabilized with large crystallographic distortion.
Overwrite modulation in Ba-ferrite particulate media
Authors: Speliotis D. E.
Published: July 2002

Overwrite modulation (OWM) represents one of the more difficult problems in utilizing Ba-ferrite particulate media for high density recording applications. Any thick particulate medium of high coercivity with preferred perpendicular anisotropy is subject to OWM problems, but Ba-ferrite is even more susceptible in that some of the fundamental properties that contribute to its outstanding recording performance exacerbate its OWM behavior. These properties include a large angular dependence of the remanence coercivity of oriented media, which is reflected in a small transverse field demagnetization and derives from the high uniaxial anisotropy field and the high morphological perfection of the Ba-ferrite platelets. Several possible solutions to the OWM problem are discussed: use separate wide-gap erase heads, wider write gaps, metal-in-gap or other high flux density heads; lower the coercivity; lower the thickness of the media; and longitudinal instead of perpendicular orientation. In addition to these, two other novel solutions are presented: one involves the use of higher than optimum write currents; the other involves the use of thin-film and MR heads (a rather surprising result).
Static and dynamic magnetic properties of Fe-Cr-layered structures with antiferromagnetic interlayer exchange
Authors: Saurenbach F. , Walz U. , Hinchey L. , Grünberg P. , Zinn W.
Published: July 2002

Thin films of Fe when separated by approximately 8 Å of Cr couple antiferromagnetically. Evidence for this comes from spin-wave-mode spectra as measured by means of light scattering and hysteresis curves, here obtained by means of the magneto-optic Kerr effect. Based on new and more-detailed data we would like to discuss the behavior of a particular spin-wave mode due to the spin canting induced by the antiferromagnetic coupling. It is related to a Goldstone mode. The experiments also show that antiferromagnetic coupling occurs not only for films grown along [100] but also for films grown along [110]. We discuss the implications of this observation.
Photothermal characterization of inhomogeneous ferromagnetic resonance absorption in ferrites
Authors: Geisau O. V. , Netzelmann U. , Pelzl J.
Published: July 2002

The depth and lateral dependence of ferromagnetic resonance (FMR) microwave absorption of a plate of sintered Ni ferrite has been studied at 9.35 GHz using photoacoustic detection and the photothermal laser-beam deflection technique. The photoacoustic response of the sample has been measured with a microwave input of 200 mW at modulation frequencies from 10 Hz to 5 kHz, corresponding to thermal depths of 200 to 9 μm. A significant depth dependence of the absorbed microwave power density contributing to a conventionally recorded FMR spectrum has been found. Lateral resolved resonance spectra from the same ferrite have been obtained by using the photothermal laser-beam deflection technique with a power input up to 7 W. Spatial dependences of standing-wave body-resonance modes as well as local variations of the demagnetization field inside the sample were observed. The lateral resolution achieved was about 200 μm.
Micro/magnetic structural development in Co-Ni-Cr and Co-Ni-Cr/Cr films for longitudinal recording media
Authors: Lee J.-W. , Mountfield K. R. , Laughlin D. E.
Published: July 2002

A series of Co-Ni-Cr and Co-Ni-Cr/Cr films have been examined using transmission electron microscopy in conventional bright/dark-field imaging, selected-area diffraction, convergent beam electron diffraction, as well as in Lorentz electron microscopy imaging mode. The crystallographic orientation and magnetic domain structure have been characterized as a function of film thickness. The results indicate that amorphous Co-Ni-Cr films form prior to the formation of small randomly oriented equiaxed grains during deposition on amorphous substrates. As the film thickness increases, some of the small grains grow preferentially with their c axis parallel to film plane, but others with their c axis at an angle of 62° from the film plane. Longitudinal domain structures of the films were found to consist of Néel walls associated with cross-tie walls and Bloch lines. Each domain contains a large amount of the magnetic ripple-type structure.
Evidence for domain wall pinning by a magnetic grain-boundary phase in sintered Nd-Fe-B based permanent magnets
Authors: Strnat K. J. , Mildrum H. F. , Tokunaga M. , Harada H.
Published: July 2002

Low-field thermomagnetic analysis of sintered Nd(Dy)-Fe(Co)-B magnets provides new evidence that the high coercivity near room temperature is due to the pinning of residual domain walls in a ferromagnetic grain-boundary phase. The temperature where MHc drops to near zero appears to be the Curie point of that phase. It is 50–80 °C below the Tc of the 2-14-1 matrix.
Modeling of magnetization characteristics and faster magnetodynamic field computation (invited)
Authors: Saito Y. , Kishino Y. , Fukushima K. , Hayano S. , Tsuya N.
Published: July 2002

A Chua-type magnetization model is derived by means of a Fourier series while the magnetic flux density is sinusoidally varying with time. It is shown that this Chua-type model is well suited for practical computations of magnetodynamic field. A geometrical duality between the Delaunay triangles and associated Voronoi polygons is utilized to implement a dual energy finite element approach. As an example, the magnetodynamic fields in a toroidal reactor including the effects of transients, eddy currents, and hysteresis are computed.
Harmonic signal generation from metallic glasses
Authors: Hasegawa Ryusuke
Published: July 2002

When an exciting field of a given frequency is applied to glassy alloys with perminvarlike properties, odd and even harmonics of that frequency are generated with similar amplitudes. The perminvar characteristics required can be approximated, for low fields, by B=μ1H+μ2H2+μ3H3, where μ’s are constant. The quantity μ3 introduces an additional nonlinearity to the conventional B-H behavior, which in turn results in even harmonic terms in B.
Determination of the bilinear product Preisach function
Authors: Kádár György , Della Torre Edward
Published: July 2002

The implications of assuming bilinearity in the product model Preisach function are that only two single variable functions have to be determined experimentally: one that is magnetization dependent and one that is field dependent. In a discussion of noncongruency, a method was described to obtain the magnetization dependent function from a set of minor hysteresis loops. This paper discusses a practical algorithm to obtain the remaining bilinear Preisach function.
Variation in the effective Richardson constant of a metal-silicon contact due to metal-film thickness
Authors: Tōyama Naotake
Published: July 2002

Metal-Si Schottky contacts have been made by using various metals in order to investigate the dependence of typical diode parameters, such as the barrier height and the effective Richardson constant, on a film thickness of the metal electrode. In any contact with a metal-electrode film below 400 Å thickness, the Schottky barrier height evidently varies with the film thickness. The effective Richardson constant obtained by a photoelectrical measurement shows different values, depending upon the choice of metal, and also shows a metal thickness dependence, contrary to the generally accepted theory for metal-semiconductor contacts. In particular, the effective Richardson constant in a sample made by rf sputtering shows a much larger film thickness dependence than that in a sample by vacuum evaporation.
Laser-induced thermal strains in isotropic media: Polycrystalline Si
Authors: Liarokapis E. , Anastassakis E.
Published: July 2002

Analytic solutions for the spatial distribution of elastic deformations, strains, and stresses induced on the surface and interior of an isotropic semi-infinite material by an arbitrary temperature distribution are applied to an isotropic medium which is exposed to an intense cw laser beam. We demonstrate results of such calculations in the case of polycrystalline silicon. The method can be applied to any polycrystalline material, or even moderately anisotropic cubic crystals. The calculations show the presence of considerable amounts of thermal strains or stresses for laser power densities below melting.
Field-effect transistor using a solid electrolyte as a new oxygen sensor
Authors: Miyahara Yuji , Tsukada Keiji , Miyagi Hiroyuki
Published: July 2002

A field-effect transistor (FET) using a solid electrolyte is proposed in the present study as a new oxygen sensor. The sensor is fabricated by depositing a thin layer of yttria-stabilized zirconia (YSZ) on a gate insulator of an insulated gate field-effect transistor (IGFET). As an IGFET has an ability to transform impedance, the potential change produced at the interface between the YSZ layer and a platinum gate electrode can be detected stably, even if the impedance of the YSZ is very high. The response of the fabricated sensor showed good reproducibility at 20 °C. A linear relationship between output voltage and logarithmic partial pressure of oxygen was obtained in the range from 0.01 to 1 atm. Sensitivity of the sensor was found to depend on the thickness of the Pt-gate electrode and sputtering conditions of the YSZ layer. Although selectivity to hydrogen and carbon monoxide was not good at room temperature, it could be improved by increasing the operating temperature to 100 °C. The developed sensor has several advantages including small size, low output impedance, and solid-state construction. It is potentially applicable to medical uses, process control, and automobiles.
The cutoff wavelength and minority-carrier lifetime in implanted n+-on-bulk p Hg1−xCdxTe photodiodes
Authors: Nemirovsky Y. , Rosenfeld D.
Published: July 2002

The cutoff wavelength λco at 77 K of implanted n+-on-bulk p-type Hg1−xCdxTe photodiodes is calculated with the minority-carrier lifetime of the bulk material as a parameter: 1.24/λco=[T+81.9/3.267×104(1+x)] {18.88−53.61x− 1/2  ln [(kT/q) μnτn]} −0.3424+1.838x+0.148x4 (eV). The composition x is obtained from the zero-intercept transmission spectra measured at 300 K. The minority-carrier lifetime τn of the photodiodes and its temperature dependence have been obtained from the photodiode dynamic resistance at zero-bias voltage versus reciprocal temperature 1/T data. The temperature dependence of the minority-carrier mobility μn is also taken into account. The results indicate that the lifetime in the bulk p-type material is determined by Shockley–Read generation-recombination centers. For undoped, p-type substrates obtained from Cominco Inc., the trap energy is approximately 45 meV. Gold-doped crystals grown by the method of solid-state recrystallization exhibit a trap energy of the order of 30–35 meV.
States of copper during diffusion in semi-insulating GaAs
Authors: Tin C. C. , Teh C. K. , Weichman F. L.
Published: July 2002

Photoinduced transient spectroscopy (PITS) and photoluminescence spectroscopy measurements were carried out on samples of liquid-encapsulated Czochralski-grown semi-insulating GaAs which have been diffused with copper at 550 °C. The PITS curves, taken at different depths from the surface, confirm that the copper-related acceptor level at 0.51 eV is due to a complex, which we assign to CuGaVAs. The PITS results show that an acceptor level at 0.51 eV in GaAs, previously assigned to iron impurity, can also be caused by copper. Photoluminescence studies show that the emission peak at 1.36 eV, commonly attributed to CuGa, also varies with depth. This variation is explained by the predominance of copper in the form Cu+i near the copper-covered surface. We have shown, from both PITS and photoluminesence results, the significance of the capping effect of a copper film during annealing, and this effect must be taken into account in the analysis of copper diffusion data in GaAs.