bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical absorption of the intersubband transitions in GaAs/Al0.4Ga0.6As multiple quantum wells with superlattice barriers
Authors: Manasreh M. O. , Jogai B. , Stutz C. E. , Reynolds D. C.
Published: July 2002

The optical absorption of intersubband transitions in n-type GaAs/Al0.4Ga0.6As multiple quantum wells with superlattice barriers is studied as a function of temperature. The room-temperature spectrum shows a strong intersubband transition at 118.64 meV (10.45 μm) and a shoulder at 137.00 meV (9.05 μm). A broad transition is also observed at 204.6 meV (6.06 μm). The 118.64 meV intersubband transition exhibits a blue shift (∼5.33 meV) as the temperature is decreased from 295 to 4.2 K. The intensity of this transition is increased dramatically while the intensity of the shoulder observed at 137.00 meV is reduced as the temperature is decreased. Theoretical calculations based on a self-consistent k⋅p model which include many-body effects of Hartree, exchange-correlation, depolarization, and vertex effects indicate that the 118.64 meV intersubband absorption is due to the electronic transition between the ground and excited states in the well. On the other hand, the shoulder seems to correspond to a transition between the ground state and the miniband formed in the superlattice barrier.
Departures from the law of approach to the principal anhysteretic in a ferromagnet
Authors: Maylin M. G. , Squire P. T.
Published: July 2002

Recent attempts to describe the magnetic induction changes induced by tensile or compressive loads in a variety of carbon steels have centered on the empirical law proposed by Jiles and Atherton. Their model gives good predictions of such changes for points on the initial induction curve and from major loop points. Results in this work show that departures from the law are widespread for less simple magnetic histories for 3% nickel steel and iron specimens. This suggests that increased complexity will be required in future modeling work. A mechanism is proposed that explains these departures in terms of a distribution of domain wall pinning site energies.
Laser-beam pulse shaping using spectral beam deflection
Authors: Skupsky S. , Kessler T. J. , Letzring S. A. , Chuang Y.-H.
Published: July 2002

Laser-beam temporal pulse shaping is examined using a technique based on beam deflection. The deflection is induced by encoding the beam with phase-modulated bandwidth and passing the beam through a diffraction grating. Pulse-shaping examples are modeled numerically to determine the resolution of this technique. Other applications using this method of spectral beam deflection are discussed.
Spectral interference effects in the light emission from Fabry–Perot cavities
Authors: Lei C. , Huang Z. , Deppe D. G. , Pinzone C. J. , Dupuis R. D.
Published: July 2002

It has recently been demonstrated that somewhat anomalous spectral characteristics are achieved in the emission from localized dipoles contained in Fabry–Perot cavities. More extensive data are presented demonstrating the spectral characteristics of emission from 5-μm-long AlGaAs Fabry–Perot cavities containing spatially localized dipoles. The dipole localization is achieved by using a GaAs quantum well, and the quantum well is placed a quarter emission wavelength away from one of the cavity reflectors. The spectral characteristics are derived analytically using a model that accounts for interference between two simultaneously emitted coherent spontaneous wave packets which travel in opposite directions upon emission.
Electro-optical waveguide microscopy
Authors: Aust Emil F. , Knoll Wolfgang
Published: July 2002

Optical waveguide microscopy is used to image lateral heterogeneities of the electro-optic (EO) response of poled polymer waveguide structures. The sensitivity of the technique is demonstrated for a poly(methylmethacrylate) thin film doped with Disperse Red 1 between gold electrodes in a modified Kretschmann configuration. Even after aging of the poled polymer for one week, heterogeneities due to the anisotropy of the refractive index tensor can be distinguished from those owing to fluctuations of the EO coefficients.
Energy distributions of argon neutrals at the rf-powered electrode of a parallel-plate reactor
Authors: Janes Joachim , Börnig Karla
Published: July 2002

In a parallel-plate 13.56 MHz rf reactor energetic argon neutrals are created by charge-exchange collisions in the sheath adjacent to the powered electrode. Energetic argon neutrals are detected by sampling neutrals through a 100 μm orifice in the cathode. Downstream the orifice neutrals are analyzed parallel to the cathode normal with a quadrupole mass spectrometer equipped with an energy filter having an angular acceptance of about 2.5°. The pressure range considered was between 5 and 50 mTorr with dc bias potentials between −100 and −400 V. The measured neutral energy distributions for low pressures and low dc bias potentials have a maximum intensity at low energies slowly decreasing toward higher energies. For higher pressures and higher dc bias potentials the energy distributions have minimal intensities at low energies, exhibit a maximum at roughly 40 eV, subsequently decreasing toward higher energies. This behavior is explained as being caused by multiple scattering of energetic neutrals in the sheath. Experimental neutral energy distributions are compared with Monte Carlo simulations. In the calculations charge exchange collisions, elastic scattering, and multiple collisions are taken into account. Experimental and theoretical neutral energy distributions are in fairly good agreement clearly indicating that multiple scattering of neutrals in the sheath is an important mechanism determining their energy distributions.
Annealing in a mercury bath of In+ and B+ implanted Cd0.23Hg0.77Te studied by resonant Raman scattering and Hall effect measurements
Authors: Wagner J. , Koidl P. , Bachem K. H. , Uzan-Saguy C. , Kalish R. , Bruder M.
Published: July 2002

Resonant Raman scattering by longitudinal optical phonons has been used to study the effect of annealing in a hot Hg bath on 113In+ and 11B+ implanted Cd0.23Hg0.77Te. Up to the highest doses of 1×1013 cm−2 for In and 1×1014 cm−2 for B, respectively, Raman spectroscopy indicates a full recovery of the crystalline perfection for annealing temperatures around 320 °C and annealing times ≥10 min. This recovery is accompanied by an electrical activation of the implants. Control experiments have been carried out to prove that the electrical activity is not due to residual lattice damage and that the immersion in the Hg bath by itself has no effect on the Raman spectrum.
A deep-level transient spectroscopy variation for the determination of displacement threshold energies in GaAs
Authors: Lehmann B. , Bräunig D.
Published: July 2002

The deep-level transient spectroscopy (DLTS) method is optimized for the observation of radiation damage in semiconductors. A new isothermal variation of the technique is applied to the study of displacement defects in GaAs in order to determine threshold energies and displacement cross sections. A pronounced anisotropy is found for the threshold energy. A linearly increasing displacement probability function is shown to properly model the displacement cross section in <100≳ direction, as compared with the <111≳ direction which requires only a simple step function. Anisotropy leads to a tailing off in the displacement cross section at energies below an ‘‘effective’’ threshold of about 15.5 eV in the <100≳ direction, indicating that the <111≳ direction is more sensitive to displacement damage than the <100≳ direction. Differences in the damage between these two directions are as large as a factor of 2.
The role of hydrogen in excimer-laser-induced damage of fused silica
Authors: Levy D. H. , Gleason K. K. , Rothschild M. , Sedlacek J. H. C.
Published: July 2002

Hydrogen nuclear magnetic resonance (NMR) was used to probe defect reactions in fused silica during 193 nm ultraviolet irradiation and thermal treatment. Hydrogen concentration and Carr–Purcell measurements indicate that the majority of hydrogen atoms are isolated and do not segregate or evolve from the fused silica during annealing or irradiation. Previously, NMR spin-lattice relaxation measurements have revealed that a small fraction of hydrogen in fused silica exists as centers that undergo molecular motion and are consumed during annealing. Here, a detailed analysis of the NMR spin-lattice relaxation behavior is used to support the identification of this center as a pair of adjacent silanol groups. These silanol pairs react during annealing to form a strained bond, thus increasing the susceptibility of fused silica to E′ formation. Excimer laser irradiation, like thermal treatment, is shown to directly reduce the number of relaxation centers in the material. The measured dependence of spin-lattice relaxation as a function of irradiation for identically prepared samples is consistent with silanol pair center consumption by a two-photon process.
Fabrication of an organic superlattice film by molecular beam deposition
Authors: Nonaka T. , Mori Y. , Nagai N. , Matsunobe T. , Nakagawa Y. , Saeda M. , Takahagi T. , Ishitani A.
Published: July 2002

A superlattice film of 5, 10, 15, 20 tetraphenylporphyrin (H2TPP; C44H30N4) and 5, 10, 15, 20 tetraphenylporphyrinato zinc (ZnTPP; C44H28N4Zn) was grown on a hydrogen terminated surface of Si (100) wafer which was kept at −25 °C. The organic molecular beam deposition technique was used for the fabrication under ultrahigh vacuum between 3×10−9 and 3×10−10 Torr. The small angle x-ray diffraction study has revealed that the period of the superlattice was 4.4 nm, which was also confirmed by the oscillation of the same period observed in a secondary ion mass spectrometry depth profile of Zn. The Fourier-transform infrared spectroscopy measurement indicated that the quasi-planar molecules of H2TPP and ZnTPP were inclined at an angle of 70° with respect to the substrate surface. The film surface was very flat and any roughness could not be detected by field emission secondary electron microscope observation. An atomic force microscope (AFM) therefore was used to investigate the surface. The root mean square roughness calculated from the AFM image was 0.37 nm.
Analysis of magnetic response in thin-film heads by simulation
Authors: Shiiki Kazuo , Yuitoo Isamu , Sasaki Shinobu
Published: July 2002

Quasi-three-dimensional magnetic recording simulation using the finite-element method was compared with experimental results obtained by electron-beam tomography and scanning Kerr microscopy. Using this simulation, magnetic response in the pole of the thin-film heads was studied. It is shown that the leakage flux is one of the most important factors in designing the pole thickness.
Microstructural changes in confined submicrometer aluminum films
Authors: Chou M. L. , Rishton S. A. , Tu K. N. , Chen Haydn
Published: July 2002

The stress effect on microstructure evolution in submicrometer Al dots in confinement has been studied by transmission electron microscopy. Direct observation of grain growth and void formation in the dots, unconfined as well as confined by sputtered quartz, was investigated. In the as-deposited state, most of the grains were larger than the film thickness of 300 Å, indicating that the grains have grown during the Al deposition and/or the quartz deposition. Voids were only found in the confined samples. Grain growth was retarded in the confined samples upon a stepwise annealing from room temperature to 400 °C, yet secondary grain growth occurred at temperatures above 500 °C. For the unconfined samples, abnormal grain growth occurred at 200 °C. The retardation of grain growth in the confined sample was attributed to the lack of stress gradient and vacancy sources and the hinderance of dislocation motion. The mechanism of secondary grain growth in the confined samples was observed to be the coalesence of adjacent grains.
Effect of electron launcher structures on AlAs/GaAs double barrier resonant tunneling diodes
Authors: Yang L. , Mars D. E. , Tan M. R. T.
Published: July 2002

We have studied experimentally the effect of several electron launcher structures on AlAs/GaAs double barrier resonant diodes (RTDs). The experimental results show that a linearly graded AlGaAs launcher structure improves the tunneling current by presumably removing the hump in the conduction band caused by the space charges near the n-i junction in the spacer layer. Peak current densities as high as 170 kA/cm2 with a peak-to-valley current ratio of 3.2 were obtained from these graded launcher RTDs. Compared with the conventional RTD, the graded launcher gives a 50% improvement in the peak current density while reducing the peak-current voltage by 40% and maintaining a similar peak-to-valley current ratio.
Electrical characterization of low-pressure chemical-vapor-deposited silicon dioxide metal-oxide-silicon structures
Authors: Ang S. S. , Shi Y. J. , Brown W. D.
Published: July 2002

The electrical characteristics of as-deposited and oxygen-annealed low-pressure chemical-vapor-deposited (LPCVD) silicon dioxide (SiO2) metal-oxide-silicon (MOS) structures were investigated. As-deposited LPCVD SiO2 MOS structures exhibit a high oxide fixed charge density in the mid-1011 cm−2 and an interface state density in the low-1011 cm−2 eV−1 due to the large number of oxygen and silicon dangling bonds. A low electron barrier height in these structures (1.2 eV) is presumed to be due to lowering of the barrier by excess silicon microclusters. Oxygen-annealed LPCVD SiO2 MOS structures exhibit oxide fixed charge and interface state densities in the mid-1010 cm−2 and mid-1010 cm−2 eV−1, respectively. Both the as-deposited and annealed devices exhibit turnaround in flatband voltage shift with avalanche electron injection. However, the direction of shift is opposite for the two devices with the annealed device being very similar to that of thermally grown SiO2 MOS structures. Apparently, oxygen annealing restructures and oxidizes the partial SiOx in the as-deposited LPCVD oxide into stochiometric SiO2. However, the residual nonstochiometric SiO2 microclusters in the bulk result in an electron barrier height of only 2.3 eV.
Energy levels of charged particles confined in a multiply connected structure in a magnetic field
Authors: Ishibashi A. , Ravenhall D. G. , Schult R. L. , Wyld H. W.
Published: July 2002

We have calculated the wave functions and energy levels of a two-dimensional mesoscopic electron system having four-fold symmetry and multiply connected topology, in both zero and finite magnetic fields (B fields). The electron distribution can be controlled in the multiply connected structure by changing the peripheral channel thickness. The energy levels oscillate as a function of the B field, with pronounced gaps, and the electronic states are classified into four kinds of eigenstates under the 90° rotation operation. The three-dimensional wave functions of cylindrical and helical structures having this cross section are constructed.
Radiation detection from phase-locked serial dc SQUID arrays
Authors: Kaplunenko V. K. , Mygind J. , Pedersen N. F. , Ustinov A. V.
Published: July 2002

We report on synchronous operation of series arrays of inductively coupled superconducting quantum interference devices (SQUIDs). Each array consisted of N=3 or 11 dc SQUIDs with common inductances providing a strong interaction between neighboring cells. Externally shunted (βc≊1) trilayer Nb—AlOx—Nb Josephson junctions were used. Coherent radiation was detected in the frequency range f=67–73 GHz while the array voltage was VN=NfΦ0 (Φ0=2.07×10−15 V s). The stability of the coherent state was influenced by the external dc magnetic field. The linewidth depended on the external loading. For small loading it was N times smaller than expected for a single cell. The influence of the inductive coupling mechanism on the operation of discrete Josephson junction circuits and the similarity to the coupling in layered structures of long Josephson junctions is discussed.
Evanescent channels in calculation of phonon-assisted tunneling spectrum of a semiconductor tunneling structure
Authors: Fu Y. , Willander M.
Published: July 2002

The one-dimensional electron resonant tunneling spectrum is calculated for a GaAs/AlGaAs double barrier resonant tunneling structure in the presence of electron-optical-phonon scattering using a model similar to the independent-boson model. The calculation scheme developed by Cai et al. [Phys. Rev. Lett. 63, 418 (1989)] is examined in the situation when the electronic evanescent state is involved. Via the electron-phonon interaction, the coupling between an unbounded electronic state and an evanescent state is studied and found to be weakened. The calculated tunneling spectrum shows the one-phonon emission sideband as indicated in the experimental data [V. J. Goldman, D. C. Tsui, and J. E. Cunningham, Phys. Rev. B 36, 7635 (1987)] and in another theoretical calculation [N. S. Wingreen, K. W. Jacobsen, and J. W. Wilkins, Phys. Rev. Lett. 61, 1396 (1988)].
ac low-frequency magnetic measurement of the proximity effect between fine filaments of superconducting NbTi wires
Authors: Fabbricatore P. , Gemme G. , Menicatti A. , Musenich R. , Parodi R. , Zhang B. , Bottino C.
Published: July 2002

The magnetic weak coupling between superconducting fine filaments of multifilamentary NbTi wires for high-energy-physics applications (dipole magnets for large hadron collider at CERN) is studied through ac magnetic measurements down to very low frequencies (0.5 Hz). The shielded and trapped magnetic fluxes are measured versus the temperature at fixed ac field superimposed on a constant dc field. The measured curves look like measurements on high-Tc superconductors with the characteristic two maximum values of the trapped magnetic flux. One of these two peaks can be related to the superconducting transition of NbTi filaments, the other one to the weak coupling between the filaments. The measurements of the field and the temperature dependence of the latter peak allow the critical current of the weak coupling versus the field to be calculated giving interesting information about the proximity effect in the superconducting-normal-superconducting array.
Dependence of luminescence decays from GaAs/electrolyte contacts on excitation power and applied bias: Examination of the modified dead layer model
Authors: Kauffman J. F. , Richmond G. L.
Published: July 2002

Photoluminescence decays from n-GaAs/Na2S contacts following picosecond pulse excitation are presented. Decays measured at several different potentials from depletion to accumulation regimes all exhibit a strong dependence on excitation power when the photon flux is greater than 1010 photons/cm2/pulse. Using a flux of 4×1012 photons/cm2 we model the potential dependence of the decays by adjusting only the value of the surface minority trapping velocity. These results are used to evaluate the applicability of the modified dead layer model in the analysis of photoluminescence intensity versus potential measurements as a means of measuring surface minority trapping velocities in photoelectrochemical cells.
Transient current interruption mechanism in a magnetically delayed vacuum switch
Authors: Morris Gibson , Dougal Roger A.
Published: July 2002

The capacity of a magnetically delayed vacuum switch to conduct current depends on the density of plasma injected into the switch. Exceeding the current capacity results in the switch entering a lossy mode of operation characterized by a transient interruption of the main current (opening behavior) and a rapid increase of voltage across the vacuum gap. Streak and framing photographs of the discharge indicate that a decrease of luminosity near the middle of the gap precedes the transition to the opening phase. The zone of low luminosity propagates toward the cathode. This evidence suggests that the mechanism causing the opening phase is erosion of the background plasma in a manner similar to that in a plasma-opening switch. The resulting ion depletion forces a space-charge-limited conduction mode. The switch inductance maintains a high discharge current even during the space-charge-limited conduction phase, thus producing high internal fields. The high accelerating voltage, in turn, produces electron and ion beams that heat the electrode surfaces. As a result of the heating, jets of electrode vapor issue from the electrodes, either cathode or anode, depending on the selection of electrode materials.
The linear and nonlinear optical properties of the organic nonlinear material 4-nitro-4′-methylbenzylidene aniline
Authors: Bailey R. T. , Bourhill G. , Cruickshank F. R. , Pugh D. , Sherwood J. N. , Simpson G. S.
Published: July 2002

The organic crystal 4-nitro-4′-methylbenzylidene aniline (NMBA) was identified as a promising nonlinear material by the powder technique. The material gave a second harmonic intensity 16 times that of urea. Large single crystals of dimensions 5×3×1 cm3 were grown by the temperature lowering of a seeded supersaturated ethyl acetate solution. The principal dielectric axes were defined by orthoscopic examination. The dispersions of the refractive indices were determined to an accuracy of ±0.0015 using the minimum deviation technique and Maker fringe spacings. These dispersion curves were fitted to a Sellmeier equation which allowed the indices to be determined to ±0.0006. The nonlinear d coefficients d11, d33, d31, and d13 were evaluated at 1000, 1064, and 1300 nm using the Maker fringe technique. The coefficient d11 was over 200 times larger than potassium dihydrogen phosphate (KDP) d36. In addition, the nondiagonal coefficient d31 was similar to the phase-matching coefficient in the organic material 3-acetamido-4-dimethylamino-nitrobenzene (DAN). Critically phase-matched second harmonic signals were observed at all fundamental wavelengths. There was excellent agreement between the experimentally determined and theoretical phase-matched incidence angles. Noncritical phase-matched conditions have been calculated and are reported. Both angle and wavelength noncritical phase matching is possible with this crystal.
Monolithic integration of glass waveguides with semiconductor lasers
Authors: Wu MingCho , Chen Yung Jui , Fitz John
Published: July 2002

Glass waveguides, in a geometry of air–SiO2–Au, were monolithically integrated with graded-index separate confinement heterostructure single quantum well AlGaAs/GaAs lasers. A ridged glass waveguide was fabricated and single mode operation was observed from the output of the glass waveguide. Efficient optical coupling of more than 50% between the glass waveguide and the semiconductor laser was achieved with very low propagation loss in the waveguide. A propagation loss as low as 0.44 cm−1 was predicted theoretically. The waveguide process, which has the potential to achieve wafer scale integration of optoelectronic devices, is a simple extension of the conventional optoelectronic device processes and can be readily incorporated in the photonic integrated circuit processes.
An amorphous silicon alloy stable under solar illumination
Authors: Lin G. H. , He M. Z. , Bockris J. O’M.
Published: July 2002

Hydrogenated amorphous silicon selenium alloy was prepared by plasma enhanced chemical vapor deposition with hydrogen dilution. The alloy films exhibited a low hydrogen content and a dense amorphous network. Light induced photoconductivity degradation and light induced variation of dangling bond density of the alloy films were investigated under 1 sun white light and an intense light illumination. The results show that the amorphous silicon selenium alloy is a stable photovoltaic material.
On the origin of ferromagnetism in Mn-Al multilayered films
Authors: Hirayama Y. , Takeuchi T. , Futamoto M.
Published: July 2002

Microstructure and magnetic properties of Mn-Al multilayered films are studied by high-resolution transmission electron microscopy (TEM), x-ray diffraction, and vibrating sample magnetometry to investigate the origin of ferromagnetism. High-resolution TEM images show that the Mn-Al interface is sharp and that the crystal lattice is continuous across the interface. The possibility of ferromagnetic alloy formation is ruled out for explaining the origin of ferromagnetism. The magnetic measurements are made on films with various layer thicknesses and numbers of layers. The saturation magnetization increased as the number of interfaces increased. Magnetic anisotropy differs between films with odd and even numbers of layers. These results suggest that the ferromagnetic regions are located around the Mn-Al interfaces, where large strain and/or stress exists.
X-ray double-crystal analysis of misorientation and strain in GaAs/Si and related heterostructures
Authors: Fatemi M. , Chaudhuri J. , Mittereder J. , Christou A.
Published: July 2002

A detailed x-ray double-crystal-diffractometry investigation of GaAs on Si tilted towards [110] direction has been carried out to understand the structure, misorientation, and residual stress present in this system. The structure of the GaAs epilayer is approximately triclinic, with the in-plane lattice parameters a and b being in most cases slightly larger than, and that along the growth direction c less than, the bulk GaAs. For vicinal angles between 0° and 5°, a tilt angle of up to 0.12° between GaAs and Si lattice is observed, inclined mostly in the same direction as the vicinal angle, but also having a small component in a perpendicular direction. A residual tensile stress of the order of 109 dyn/cm2 exists in the epilayer, which can be accounted for by the difference in the thermal expansion coefficients of GaAs and Si. The strain due to the lattice parameter mismatch between the two materials is found to be negligibly small.
Study of the compositional control of the antimonide alloys InGaSb and GaAsSb grown by metalorganic molecular beam epitaxy
Authors: Itani Y. , Asahi H. , Kaneko T. , Okuno Y. , Gonda S.
Published: July 2002

MOMBE (metalorganic molecular beam epitaxy) growth characteristics of Sb containing ternary alloys, InGaSb, and GaAsSb are investigated. In the growth of InGaSb using TEGa (triethylgallium), TMIn (trimethylindium), and Sb4 (elemental antimony), the enhanced desorption of methyl-In molecules at a substrate temperature Tsub of around 500 °C as well as the enhanced desorption of ethyl-Ga molecules at around 515 °C are observed. They are due to the weak bond strength of antimonide compounds. Furthermore, the decrease of Ga solid composition with increasing Sb4 flux and the increase of GaSb partial growth rate with TMIn flow rate are also observed at as high as 500 °C. This is caused by the fact that the site blocking effect of excess Sb atoms exists up to higher Tsub. In the growth of GaAsSb using TEGa, TEAs (triethylarsine), and TESb (triethylstibine), the Sb composition versus TESb/(TEAs+TESb) curve exhibits a bowing characteristic, which is similar to that in the MOVPE (metalorganic vapor phase epitaxy) growth and is different from that in the MBE (molecular beam epitaxy) growth. Mass transport properties of Sb molecules in the MOMBE are considered to be similar to that in the MOVPE. It is found that the Tsub dependence of Sb composition is much weaker than that in the MBE, which is a superior point of MOMBE in the growth of antimonide alloys.
Optical properties of the dominant Nd center in GaP
Authors: Taniguchi Moriyuki , Takahei Kenichiro
Published: July 2002

The optical properties of the Nd centers in Nd-doped GaP samples grown by metalorganic chemical vapor deposition have been studied. By using resonant photons to excite the Nd ions directly, we found that the energy separations between the spin-orbit-splitting levels are smaller for Nd in GaP when compared with the corresponding energy separations of Nd in ionic crystals. The crystal field-induced splittings of the dominant Nd center are also found to be smaller compared with the splittings of the other Nd centers in the GaP host. The luminescence lifetime value as a function of sample temperature was also studied. It was found that the luminescence lifetime value of the dominant Nd center remains at a constant 25 μs up to 150 K and becomes smaller as the sample temperature is further increased.
Mechanical properties of Al and Al alloys and their relationship to interconnection reliability
Authors: Ozawa Kiyoshi
Published: July 2002

Pure Al, Al-3 wt %Si, and Al-15 at. % C films are characterized macroscopically in terms of yield stress and hardness and microscopically in terms of a grain structure to investigate the effects of Si and carbon additives to modify mechanical properties of the Al matrix. A theory is presented to estimate the yield stress of metal films. The experimental method is based on laser interferometer measurements of the varied substrate curvature involved with thermal treatment of a film–substrate composite. It is shown that carbon addition increases yield stress and hardness of Al, whereas Si addition decreases these properties. Carbon addition suppresses grain growth by 450 °C annealing as small as about 0.04 μm. Reliability tests on Al and Al-alloy interconnects revealed that increased yield stress improves resistance against failures due to the stress at high temperatures and high current densities, but degrades resistance against cycled thermal shock. The double layered Al–C/Al structure was highly resistant against both thermal and current stress.
Atomic structure and defects in decagonal quasicrystals of Al62Cu20Co15Si3
Authors: Zhang Z. , Li N. C. , Williams D. B.
Published: July 2002

The nature of the atomic structure and the characteristics of both line and planar defects in decagonal quasicrystals of as-cast Al62Cu20Co15Si3 were studied by means of conventional diffraction contrast and high-resolution electron microscopy. Two types of dislocations were observed. The magnitude and direction of the Burgers’ vector of type A dislocations and the Burgers’ vector direction of type B dislocations were determined. The direction of the displacement vector of the planar faults was defined.
Desorption spectra of laser ablation of Tl-Ca-Ba-Cu-O superconductors
Authors: Chen C. H. , Phillips R. C. , McCann M. P.
Published: July 2002

Quantitative measurements of desorbed ions and neutral molecules by a quadruple mass spectrometer from laser ablation of Tl-Ca-Ba-Cu-O were obtained. The results indicate that more neutral atoms and molecules desorbed than the corresponding ions. More elementary ions desorbed than the corresponding oxide compounds.
Thermodynamic limits on multigap photovoltaic cells: Design mismatch for a varying meteorological environment
Authors: Spirkl W. , Sizmann R.
Published: July 2002

The actual performance of series-connected photovoltaic multigap cells may substantially deviate from the design point performance. The influence of variations in cell temperature, solar irradiance, and its spectral distribution on thermodynamically ideal cells with one to five gaps is assessed. It is found that multigap cells behave equally sensitive to average meteorological conditions as one-gap cells. When exposed to direct radiation only, the performance of multigap cells can decrease strongly for extreme conditions; however, generally these conditions give such small output that they do not significantly decrease the energy yield.
Current-voltage curves for a spatially periodic Ge diode
Authors: Abraham-Shrauner Barbara , Weeks William , Zitter Robert N.
Published: July 2002

The current-voltage curves for a germanium diode at 4.2 K are calculated by two methods and the calculations compared with experimental data. The diode is modeled by a one-dimensional, semiclassical semiconductor. The nonlinear transport differential equations are solved by numerical integration and by evaluating parametric equations for the voltage and current.
Characterization of SiC whiskers through infrared-absorption spectroscopy
Authors: DiGregorio J. F. , Furtak T. E.
Published: July 2002

The infrared-absorption spectra of commercially available SiC whiskers were measured. The spectra were dominated by the small particle resonances associated with finite ionic crystals. Analysis of these resonances allowed characterization of both morphological and electronic properties of the whiskers. The data were analyzed using Rayleigh and Mie theories as well as an effective medium model based on the Maxwell–Garnett approximation. It was possible to determine whisker radius and identify whiskers with a high free-carrier density and a core-shell structure. The effects of decreasing aspect ratio were also studied. The results showed that infrared-absorption spectroscopy provides an effective and relatively simple means to characterize SiC whiskers.
Self-defocusing in GaP induced by band-gap resonant nonlinear refraction
Authors: Ji W. , Tang S. H. , Kukaswadia A. K.
Published: July 2002

We report the observation of self-defocusing in GaP with nanosecond, 532-nm laser pulses. An electronic refractive nonlinearity (−1×10−21 cm3) has been obtained. We also present a band-filling theory for the band-gap resonant nonlinear refraction in indirect–band-gap semiconductors. A comparison shows that the theory is in good agreement with the experimental result.
Magnetic behavior and morphology of evaporated Fe/Mo multilayered thin films (abstract)
Authors: Anderson E. C. , Stearns M. B.
Published: July 2002

Fe/Mo multilayered thin films were grown on oxidized Si substrates by UHV e-beam evaporation. Both magnetic and structural results obtained from SQUID magnetometry, magnetoresistance (MR), small-angle x-ray scattering, large-angle x-ray scattering, and cross-sectional high-resolution electron microscopy are reported. Fe (30 Å)/Mo films with Mo thickness ranging from 7 to 25 Å display oscillatory interlayer magnetic coupling. The maximum low-temperature negative MR is 2% for 11 Å Mo layer thickness, while the minimum MR is 0.1% for 16 Å Mo layer thickness. A series of Fe (30 Å)/Mo (11 Å) films were grown at substrate temperatures (Ts) ranging from 150 to 475 K. Films grown at low Ts exhibit decreased coherence length and increased layer roughness, but only moderately reduced saturation field (Hs) and MR. Films grown at high Ts exhibit increased coherence length, increased interface thickness, and greatly reduced Hs and MR. Structural models for these films will be presented and correlated with magnetization and MR results.
Domain-wall dynamics in thick Permalloy films
Authors: Yuan Samuel W. , Bertram H. Neal
Published: July 2002

Micromagnetic numerical simulations are extended to study domain-wall structures and dynamics in micron-thick Permalloy films with an in-plane anisotropy easy axis. The equilibrium domain-wall structure is a flux-closure vortex elongated along the film thickness direction for films thicker than 2 μm. The dynamics of such a vortex wall under an easy-axis field is studied to yield velocity dependence and wall mass. The effect of eddy current damping is simplified by including a larger damping constant in addition to the intrinsic spin damping. With large damping, the steady-state wall structure is more stabilized under applied fields. Under a hard-axis field, wall structure transitions take place for small damping and low-frequency fields; for large damping and higher-frequency fields, these transformations are more suppressed, and the flux conduction is dominated by magnetization rotations instead of wall motions.
Preparation and Mössbauer study of Gd2Fe17Cx (x≤2) with higher carbon concentration by melt quenching
Authors: Li Fashen , Sun Jijun , Xue Desheng , Zhang Xiaozhou , Ge Shihui , Zhang Yide , Mao Mingxi , Shen Baogen , Kong Linshu , Cao Lei
Published: July 2002

Carbides Gd2Fe17Cx with composition up to x=2 were successfully prepared. The single phase Gd2Fe17Cx (x=1.5, 2.0) carbides with higher carbon concentration were first obtained by the melt quenching technique. 57Fe Mössbauer spectra of all compounds were measured and the results show that the average hyperfine field and isomer shift increase with increasing carbon concentration in the studied composition range. The effects of the interstitial carbon atoms on the hyperfine parameters are discussed. According to the result of the quadrupole splitting, the easy magnetization direction at room temperature for all carbides was determined.
Magnetic property of GdCo4B in high field
Authors: Ito T. , Ogata H. , Ido H. , Kido G.
Published: July 2002

Temperature dependence of saturation magnetization and magnetization process of a field oriented sample in a pulsed field up to 13T at several temperatures are measured for GdCo4B. The following main conclusions have been obtained: (1) the Curie temperature and the compensation point are 517 K and 421 K, respectively, (2) the averaged Co-moment is 1.04 μB, suggesting the 6i-Co has about a half of that of the 2c-site Co, (3) the exchange parameter between Gd and Co spins, JGd-Co/k, is estimated to be 8.5 K from the temperature dependence of Gd-sublattice magnetization, (4) Gd-sublattice anisotropy constants have been estimated as follows; 5.8×106 erg/c.c. at T=78 K, 3.9×106 erg/c.c. at T=147 K and 2.9×106 erg/c.c. at T=225 K, which are well explained by Gd–Gd and Gd–Co dipole–dipole interactions, and (5) the anisotropic saturation moment has been observed and can be attributed to anisotropic Co moment.
Different types of anisotropy in amorphous SmCo films
Authors: Chen K. , Hegde H. , Jen S. U. , Cadieu F. J.
Published: July 2002

Amorphous SmCo films were sputter synthesized at room temperature in the presence of strong in-plane magnetic fields. Both in-the-film-plane and perpendicular anisotropy could be formed in the films depending upon the film preparation conditions. Post deposition annealing in the presence of in-plane magnetic fields directed perpendicular to the original field direction were performed to distinguish the behaviors of the various types of anisotropies. The physical origin of in-the-film-plane anisotropy can be explained as directional pair ordering. Perpendicular anisotropy was only formed in films synthesized through thermalized sputtering and was caused by growth induced structure. If formed, the microcrystallites also have large contributions to the anisotropy with their easy axes in the film plane, but without any preferred direction in the film plane. Both the formation of growth induced structure, which caused the perpendicular anisotropy, and the formation of microcrystallites, prevented the formation of the pair ordering, which decreased the in-the-film-plane anisotropy.
Effects of Pd predeposition layer on magnetic properties in compositionally modulated Co/Pd multilayers
Authors: You Chun-Yeol , Hur Jeen , Shin Sung-Chul
Published: July 2002

We have investigated the effects of Pd predeposition layer on magnetic properties in compositionally modulated Co/Pd multilayers. The samples were prepared at the Ar sputtering pressure of 10 mTorr by dc magnetron sputtering. The thickness of the Pd predeposition layer was varied from 0 to 1000 Å with a 100 Å interval. It was observed that the magnetic properties of the saturation magnetization, the perpendicular anisotropy energy, and the coercivity remained relatively constant until the thickness of the predeposition layer was up to 600 Å. However, those were rapidly increased with the predeposition-layer thickness when the thickness was thicker than 600 Å. The results were caused by a change in the microstructure of the multilayers deposited on different predeposition-layer thicknesses.
Rotational vortex-flux properties of Ba0.575K0.425BiO3
Authors: Goeckner H. P. , Kouvel J. S.
Published: July 2002

Measurements of the magnetization vector M of a polycrystalline (Ba,K)BiO3 sample turned in a fixed field H at 4.2 K show that the rotational behavior of MP, the penetrating vortex-flux component of M, depends sensitively on the magnetic state of the sample before rotation. For the field-cooled state at 240 Oe, the vortex lines represented by MP are seen to bifurcate into two groups, one of which rotates rigidly with the sample while the other is held by H and turns frictionally relative to the sample. This behavior, seen earlier in polycrystalline YBa2Cu3O7, is directly ascribable to a distribution in the strength of the vortex pinning forces. For the hysteretic state in which H is raised from a large negative value to +240 Oe, a vortex-flux bifurcation is again observed but with an important difference. The strongly pinned vortices (rotating rigidly) reflect the original negative polarity of H, whereas the weakly pinned vortices (turning frictionally) are those produced by the positive H. Hence, in this hysteretic state before rotation, there is a coexistence of vortices of opposing polarity.
Applications of ultrasensitive magnetic measurement technologies (invited) (abstract)
Authors: Hirschkoff Eugene C.
Published: July 2002

The development of reliable, easy-to-use magnetic measurement systems with significantly enhanced levels of sensitivity has opened up a number of broad new areas of application for magnetic sensing. Magnetometers based on optical pumping offer sensitivities at the picotesla level, while those that utilize superconducting quantum interference devices can operate at the femtotesla level. These systems are finding applications in areas as diverse as geophysical exploration, communications, and medical diagnostics. This review briefly surveys the capabilities and application areas for a number of magnetic sensing technologies. The emphasis then focuses on the application of the most sensitive of these to the field of medical diagnostics and functional imaging. Protocols for specific applications to noninvasive presurgical planning and to the noninvasive assay of cortical dysfunction in diseases ranging from epilepsy to migraine and schizophrenia will be described in detail. Data will be presented reporting independent validation of these techniques in ten patients who subsequently underwent surgery. Routine and reliable utilization of this ultrasensitive magnetic sensing technology in the clinic is now feasible and practical.
Emerging instrumentation, measurements, and standards for magnetics (invited) (abstract)
Authors: Fickett F. R.
Published: July 2002

Magnetics is second only to semiconductor technology in its importance to electronic and electrical products. The affected markets include magnetic materials, electronic components, magnetic information storage equipment, and electrical equipment. Our measurement capability strongly determines the ease with which commercial goals can be achieved. The existence of internationally recognized standards of measurement and standard reference materials assists in ensuring product compatibility. Magnetic measurement technology has made significant strides in the last few years. Usually this was driven by the demands of ever-increasing storage densities in magnetic recording, although superconductivity and high frequency electronics contributed as well. In this presentation, I will discuss an array of new instruments and measurement techniques with emphasis on the small scale measurement of magnetic parameters. In addition, I will present results of a recent NIST assessment of the present status and future development of measurements and standards in the field of magnetics.
Magnetic coupling of Fe/Mo/Fe and Co/Cu/Co sandwiches across wedged spacer layers (invited)
Authors: Qiu Z. Q. , Pearson J. , Bader S. D.
Published: July 2002

Fe/Mo/Fe and Co/Cu/Co sandwiches were grown by molecular beam epitaxy onto Mo(100) and Cu(100) single crystals, respectively, and characterized by high- and low-energy electron diffraction and in situ surface magneto-optic Kerr-effect measurements. The spacer layer in both case was fabricated to have a wedged shape in order to create a continuous change of the spacer-layer thickness. Oscillatory behavior between ferromagnetic and antiferromagnetic coupling was found; and is shown to originate at the interface between the magnetic layer and the spacer layer. For Fe/Mo/Fe, short-period oscillations are observed with a periodicity of ∼3 ML of Mo. Hysteresis loops for antiferromagnetically coupled cases are calculated from a simple model, and the results reproduce the general characteristics observed experimentally.
Quantum well states and magnetic coupling between noble metals and ferromagnets (invited)
Authors: Ortega J. E. , Himpsel F. J. , Mankey G. J. , Willis R. F.
Published: July 2002

We have searched for the electronic states that mediate oscillatory magnetic coupling in superlattices, and have found strong evidence that these are quantum well states, which are created by quantizing the momentum of s,p-band states perpendicular to the interfaces. In noble metal layers on ferromagnets we find such states at the Fermi level, where they are able to influence magnetic coupling and transport. They exhibit several traits connecting them with oscillatory magnetic coupling, such as periodicity and spin polarization.
A model of write noise in magneto-optical media
Authors: Madison M. R.
Published: July 2002

Analytic models for calculating the contribution to noise power from the writing of periodic patterns of marks in magneto-optical recording are presented. The write noise power distributions are calculated assuming three different models of stochastic variation of the mark edge placement. The standard deviations of the edge placements are estimated from experimental power spectrum.
High density near-field optical recording (invited) (abstract)
Authors: Betzig R. E. , Trautman J. K. , Wolfe R. , Gyorgy E. M. , Finn P. L. , Kryder M. H. , Chang C-H.
Published: July 2002

Near-field scanning optical microscopy (NSOM) has been used to image and record domains in thin-film magneto-optic (MO) materials (e.g., a Co/Pt multilayer). In this technique, a subwavelength-sized source or detector of visible light is placed in close proximity to a sample and raster scanned to read or write data on a scale inaccessible to traditional lens based systems. The technique, therefore, represents a hybridization of conventional magnetic and MO storage technologies. In the imaging mode, resolution of 30–50 nm has been consistently obtained, whereas in the recording mode, domains down to −60 nm have been written reproducibly. Data densities of −45 Gbits/in.2 have been achieved, well in excess of current magnetic and MO methods. A brief analysis of speed and other issues indicates that the technique may represent a viable alternative to these and other methods for anticipated high density data storage needs.