bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental studies of the laser-controlled collective ion accelerator
Authors: Destler W. W. , Rodgers J. , Segalov Z.
Published: July 2002

Detailed experimental studies of a collective acceleration experiment in which a time-sequenced laser-generated ionization channel is used to control the propagation of an intense relativistic electron beamfront are presented. Ions trapped in the potential well at the beamfront are accelerated as the velocity of the beamfront is increased in a manner controlled by the time-dependent axial extent of the ionization channel. Beamfront propagation data for two different accelerating gradients are presented, together with results of ion acceleration studies for both gradients.
Statistical time lags in low-pressure SF6 breakdown
Authors: Woolsey G. A. , Ogle D. B.
Published: July 2002

Statistical time lags have been measured in a discharge tube containing SF6 at a pressure of 1 Torr, with the aim of determining the source of the electrons which initiate breakdownY″Te,hf cx pressure SF6. Measurements with and without careful shielding of the discharge tube give similar values of mean statistical time lag showing that the initiating electrons are not produced by external radiation. Measurements, in which the time between the 500 successive breakdowns used for a single measurement of mean statistical time lag is increased over the range 1–103 s, provide values of mean statistical time lag which increase over the range 10−5–10−2s: This reveals that the breakdown process is controlled by the time since the discharge produced by a previous breakdown. Data from further such measurements, made for different applied tube voltages, are shown to fit well with the Fowler–Nordheim theory of field emission. The conclusion drawn is that the initiating electrons are produced at the cathode surface by field emission, and that the state of the surface at any time depends primarily on the intensity of the previous discharge and the length of time since it took place. During the time between successive breakdowns, a surface layer on the cathode surface is continually developing and reducing the rate of field emission from the cathode. Although the applied electric fields are well below that required for field emission, microscopic fields exist at protrusions and craters on the cathode surface which are high enough to provide field emission: This is supported by experiments on electron emission made with the discharge tube evacuated below 10−6 Torr.
Electron-beam-induced dislocations in GaAs and InP single crystals
Authors: Franzosi P. , Lazzarini L. , Salviati G. , Scaffardi M. , Fieschi R.
Published: July 2002

Dislocations have been induced in GaAs and InP single crystals by the electron beam exposure in a scanning electron microscope, with neither a mechanical bending nor a special pretreatment of the specimens. The generation and movement of the dislocations were not dependent upon the electron beam energy, crystal orientation, dopant nature, or doping level, but only on the electron beam current; a beam current of (1–2)×10−6 A was found to be the threshold for the dislocation release. By increasing the beam current up to 5×10−6 A, As or P losses from the specimen surface have been evidenced. In GaAs (001)-oriented crystals, the dislocations were found to be of pure edge type with the Burgers vector normal to the sample surface. A climb process, involving As or P vacancy migration, has been assumed to be the physical mechanism responsible for the dislocation origin.
Scanning electron acoustic microscopy observations of twins and grain boundaries in III-V materials
Authors: Dominguez-Adame F. , Piqueras J.
Published: July 2002

Polycrystalline GaP and InP have been observed by scanning electron acoustic microscopy. While grain boundaries show a weak contrast, twinned regions are clearly revealed. Results suggest that the contrast observed is related to signal generation by a piezoelectric-coupling mechanism.
Atomic populations of copper and gold in a room-temperature metal vapor laser
Authors: Anders A. K. , Tobin R. C.
Published: July 2002

Sputtering in the presence of a rapid flow of gas can project a column of metal vapor with a mean Cu i ground-state concentration along the optical axis of about 3×1014 cm−3. The effective gain length using a single cathode is limited to about 20 cm for both Cu i and Au i, due to the radial expansion of the metal vapor column. The laser has been studied for double pulsed operation during a single sputtering pulse. The ratio of the peak power for the second laser pulse to that of the first, ρ, increases with interpulse delay from zero at short delays to a constant value which is less than or equal to unity. The buildup of ρ occurs on a 700-μs time scale due to the residual ionization resulting from the first discharge pulse. The constant value decreases with increasing capacitor voltage for both the Cu i and Au i lines due to the radial flow of metal atoms from the optical cavity, which results from the transient heating of the metal vapor column.
Correlation between forward voltage at low current and catastrophic metal migration failure mechanisms in (AlGa)As laser diodes
Authors: Fritz William J.
Published: July 2002

Thirty-seven of 97 AlxGa1−xAs laser diodes from three tests conducted in vacuum (10−6 Torr) at a −20 °C heat sink temperature (Tj∼0 °C) failed catastrophically. Causes of failure varied from testing error to defects in the metallization. In all cases, p-side anomalies allowed indium solder (and probably gold in addition to indium in one case) to migrate into the GaAs bulk, causing the observed failures. The results of this research show that the integrity of the p-side metallization is crucial for reliable operation. Stringent controls have been implemented in the design and processing of the p-side metallization and catastrophic failures due to p-side anomalies have not been observed in subsequent life tests. A correlation was made between shifts in the forward voltage at 1 mA (Vf at 1 mA) and the specific failure mechanisms found in this research. In all cases Vf at 1 mA was found to decrease. The amount of decrease depended on the failure mechanism. A quantitative model is presented that explains the shift in Vf as a function of the type of defect in the active region.
Scatter emission in a ceramic dielectric thin-film electroluminescent device
Authors: Dalacu N. , Kitai A. H.
Published: July 2002

We show that a practical way to reduce capacitance in large-area ceramic dielectric thin-film electroluminescent devices is to utilize light that escapes under the edges of the electrodes. A striped electrode structure is demonstrated and shown to reduce capacitance without significant light loss. In addition, transparent electrodes are not needed. We suggest low-resistivity, low capacitance electrodes for large-area electroluminescent devices based on the edge emission technique.
Texture and textural evolution in explosively formed jets
Authors: Schiferl Sheila K.
Published: July 2002

The potential effects of crystallographic texture (preferred grain orientation) on the behavior of metallic shaped-charge jets are examined. There is some experimental evidence that strong initial liner textures can be beneficial to overall performance; in this paper we investigate the mode of action of such textures. A crystallographic-texture code was used to calculate the changes in preferred orientation, and the corresponding changes in yield anisotropies, for deformation paths typical of early jet formation. Simulations were performed for two different initial textures, and for two different regions in a hemispherical titanium liner. It was found that the initial texture and its corresponding pattern of anisotropy do not persist beyond the earliest stages of liner collapse; the state of the material in a well-formed solid jet reflects the most recent deformation, not the initial texture. Any initial texture effect on subsequent jet behavior would be exerted indirectly, e.g., through changes in flow patterns induced during the first few microseconds of deformation. During this time, the evolution of texture and the corresponding anisotropies were found to be significantly different, not only for different initial textures, but also for different regions of the liner. This is due to the variation in deformation paths, and, in our model for titanium, to differences in the relative importance of slip and twinning.
Growth of garnets for optical isolators by top-seeded solution growth method
Authors: Shiraishi Kazuo , Wang Yimin , Kawakami Shojiro
Published: July 2002

A method to grow garnets with high specific rotation for optical isolators is proposed. The method utilizes the top-seeded solution growth technique. Relatively large and homogeneous Gd3−xBixFe5O12 single crystals, which are nearly free from flux inclusions, have been grown from a high-temperature solution of Bi2O3. The crystal grown is found to have low transmission losses (0.018 dB for 45° Faraday rotation) with high extinction ratios (≥40 dB) at 1.3- and 1.5-μm wavelength regions. Some basic characteristics of the garnet are also given.
Origin and effects of carbon in low-pressure liquid encapsulated Czochralski GaAs
Authors: Duncan W. M. , Westphal G. H. , Purdes A. J.
Published: July 2002

We have investigated the origin and effects of carbon in semi-insulating GaAs grown by the low-pressure liquid encapsulated Czochralski (L-LEC) technique. The carbon concentration in the seed portion of boules grown from dry B2O3 was found to depend on the delay time between completion of melt compounding and solidification of the seed segment. This behavior for carbon with delay time after compounding demonstrates that the predominant source of carbon in L-LEC crystals is the initial charge material and not the puller ambient or graphitic parts. Effects of carbon on the transport properties of as-grown L-LEC are also observed and discussed. Comparisons are made between measured electrical properties and those calculated from carrier statistics and scattering theory. In addition, the effects of carbon on thermal stability and ion implantation behavior of this material is assessed.
Transport of ions at atmospheric pressure using an electrostatic surface wave
Authors: Stearns Richard G.
Published: July 2002

Ion motion is considered in a gas above a dielectric surface, upon which an electrostatic surface wave propagates. A field-independent mobility is assumed to adequately characterize the local ion motion in the field of the surface wave. For proper values of amplitude, wavelength, and phase velocity of the surface wave, stable transport of ions above the dielectric surface is found. Ion drift velocities of the order of 100 m/s or more may be obtained. The nature of the ion motion is discussed. Finally, an experiment is described which demonstrates the transport properties of the electrostatic surface wave. Excellent agreement is found between the experimental results and theoretical predictions.
Mössbauer study of hydrogenated amorphous germanium-tin thin-film alloys
Authors: Chambouleyron I. , Marques F. C. , Dionisio P. H. , Baumvol I. J. R. , Barrio R. A.
Published: July 2002

This work reports on the structure of defects around Sn atoms in amorphous germanium-tin alloys deposited by the rf sputtering of compound targets. The influence of atomic hydrogen on the structure of such defects is reported for the first time. The samples were analyzed by Rutherford backscattering spectrometry and conversion electron Mössbauer spectroscopy. The main conclusion of this research is that, besides the known substitutional position of Sn atoms in the a-Ge network, a new Sn bonding configuration appears, which may be at the origin of the degradation of the optoelectronic properties of the alloy found experimentally. This new configuration is an octahedrally coordinated Sn atom resulting from the trapping of Ge vacancies by Sn atoms, the energetically favored final site being the tin atom in the center of the Ge relaxed divacancy.
Electrical properties of B-ion-implanted Si layer preamorphized by Ge ions
Authors: Kuriyama K. , Aoki S. , Satoh M. , Kurebayashi M.
Published: July 2002

B+-implanted Si layers preamorphized with 100-keV Ge+ implantation have been evaluated using Rutherford backscattering spectrometry and the van der Pauw technique. We suggest that the lower structural recovery, 98% of Si occupies substitutional sites, arises from the difference in tetrahedral covalent radii among Si, Ge, and B atoms. Electrical properties of dual Ge+/B+-implanted layers are discussed by a two-carrier model consisting of both electron and hole. The conversion temperature from the p- to the n-type varies from ∼15 to ∼ 125 °C with increasing electrical activation of the boron acceptor. The activation saturates at annealing temperatures above 800 °C. This restriction is due to the presence of the level and/or the defect induced in the preamorphization process.
Growth of BaF2 and of BaF2/SrF2 layers on (001)-oriented GaAs
Authors: Clemens H. , Stromberger U. , Weilguni P. C. , Bauer G.
Published: July 2002

The epitaxial growth of BaF2 on (001)-oriented GaAs substrates as well as on thin intermediate (001)-oriented SrF2 buffers has been studied by in situ reflection high-energy electron diffraction. Despite the huge lattice mismatch of 9.7% between GaAs and BaF2, a perfect overgrowth, but in a three-dimensional manner, is observed at sufficiently high substrate temperatures (Ts=580 °C). With an intermediate SrF2 buffer of about 500 Å thickness the growth mode for BaF2 becomes quasi two dimensional. At room temperature, thermal misfit strains of about 5×10−3 are observed by x-ray diffractometry for both the SrF2 and BaF2 layers if their total thickness is lower then 1500 Å. For thicker BaF2 layers strain relief is observed.
Shielded-source, short-pulse microwave propagation experiments
Authors: Destler W. W. , Segalov Z. , Rodgers J.
Published: July 2002

The propagation of short-pulse, high-power microwaves through a neutral gas has been studied and breakdown limits determined in an experimental configuration in which the neutral gas test cell was carefully shielded from x-rays emanating from the high-power microwave tube. In this manner the possible x-ray generation of free electrons in the test cell was minimized. Results are compared with previous experiments in which the test cell was not shielded from the source.
Dependence of GaAs-AlxGa1−xAs heterostructures on Al composition for metal-semiconductor field-effect transistor operation
Authors: Hiruma Kenji , Mori Mitsuhiro , Kakibayashi Hiroji , Ihara Ayako , Takahashi Susumu , Yanokura Eiji
Published: July 2002

High-quality GaAs-AlxGa1−xAs heterostructures for metal-semiconductor field-effect transistor (MESFET) applications have been grown by metalorganic vapor-phase epitaxy. High electron Hall mobility of up to 4000 cm2/(V s) for a carrier concentration of 3.5×1017 cm−3 was obtained for Si-doped GaAs grown on AlxGa1−xAs. It was learned that the electron Hall mobility of GaAs is not dependent on the Al composition of the AlxGa1−xAs buffer layer for 0≤x≤0.8. Good drain current-voltage saturation characteristics were observed for GaAs MESFETs with a 0.3-μm gate length and AlxGa1−xAs buffer layers. At drain voltages below 3 V, the drain conductance was at its lowest for Al composition around x=0.6. However, an anomalous peak in the drain conductance was observed at drain voltages of 3–6 V and at Al compositions of x=0.6 and 0.8. Drain conductance also increased as x did for x≥0.45 when measured at a microwave frequency. These phenomena can be understood by considering electron injection into the buffer/substrate region from the GaAs channel. The amount of this injection coincided well with the reduction in the conduction-band energy barrier at the GaAs-AlxGa1−xAs heterointerface for x>0.45 for electron transport.
Phonon-assisted stimulated emission in strained-layer AlyGa1−yAs-GaAs-InxGa1−xAs quantum-well heterostructures
Authors: Nam D. W. , Holonyak N. , Hsieh K. C. , Gavrilovic P. , Meehan K. , Stutius W. , Williams J. E.
Published: July 2002

Data are presented demonstrating phonon-assisted laser operation (77 and 300 K) of photopumped strained-layer AlyGa1−yAs-GaAs-InxGa1−xAs (x∼0.15) quantum-well heterostructures (QWHs) grown using metalorganic chemical vapor deposition. When a cleaved rectangular sample (10–50 μm×100–500 μm) of the QWH, with GaAs substrate removed, is imbedded in In under a sapphire window (for 77-K data), and the In is folded upward along the cleaved edges to provide high edge reflection and high cavity Q, closely spaced end-to-end laser modes (9000 Å) occur along the sample at an energy one LO phonon below the lowest confined-particle transition (ΔE=ℏωLO≊36 meV), and widely spaced edge-to-edge laser modes occur across the sample on confined-particle transitions. For comparison, the experiment is repeated with rectangular QWH samples clamped on Au with a sapphire window, but with no metal folded onto the sample edges, thus insuring low reflectivity at the cleaved edges (low Q cavity). In the low Q resonator configuration, all of the high-energy modes (transitions on confined-particle states) disappear, and only the low-energy phonon-assisted laser modes are evident. This comparison (high Q versus low Q photoexcitation), as well as the abrupt turn-on of laser operation in a narrow spectral range one phonon (ΔE=ℏωLO≊36 meV) below the lowest confined-particle transitions, leads to unambiguous identification of phonon-assisted laser operation of a strained-layer AlyGa1−yAs-GaAs-InxGa1−xAs QWH. In addition, bandfilling is demonstrated through the entire well depth of an Lz≊125 Å InxGa1−xAs QW to well above 150 meV into the GaAs QW containing the strained layer.
NO dissociation on polycrystalline palladium studied with a Pd-metal-oxide-semiconductor structure
Authors: Dannetun Helen , Petersson Lars-Gunnar
Published: July 2002

The dissociation probability of NO when adsorbed on polycrystalline Pd as a function of temperature (323–523 K) has been studied with a Pd-metal-oxide-semiconductor (Pd-MOS) structure. For comparison the same experiments were also carried out with O2, which adsorbs dissociatively in the whole temperature region, and with CO, which adsorbs molecularly. It was found that the Pd-MOS structure can be used as a very sensitive sensor for NO dissociation and that dissociation of NO starts to be significant at temperatures around 400 K. The results are also compared with electron-energy-loss spectroscopy, ultraviolet photoemission spectroscopy, work-function, and desorption studies.
Resonance effects in Raman scattering in YBa2Cu3O7
Authors: Kirillov D. , Bozovic I. , Char K. , Kapitulnik A.
Published: July 2002

Raman spectra of YBa2 Cu3 O7 excited by different lines of Ar and Kr lasers have been studied. It was found that significant changes in relative intensity of phonon lines occurred in the spectra when the excitation frequency was shifted from the red into the blue region of the spectrum. The enhancement of high-frequency phonons, which involves stretching of CuO bonds, was attributed to resonance with an interband transition in YBa2 Cu3 O7 .
Photoelectric yield measurements of rare-earth trifluorides in the 30–250-eV photon energy range
Authors: Bartlett Roger J. , Wieliczka David M. , Olson Clifford G.
Published: July 2002

The total yield spectra of combinations of rare-earth trifluorides were measured in the 30–250-eV photon energy range to investigate their value as high-efficiency, customizeable photocathode materials. The yield spectra resemble the weighted sum of the absorption spectra of the constituent rare earths, but the amplitude of the yield spectra were compressed relative to the absorption coefficient data due to the large electron escape depths in these materials.
Metal/CaF2/Si heterostructures: Interface evolution and electronic properties
Authors: Vos M. , Xu F. , Weaver J. H.
Published: July 2002

Interface formation for Ti, Co, Pd, and Au overlayers grown on thin epitaxial CaF2 layers on Si(111) have been investigated with photoelectron spectroscopy and low-energy electron diffraction. In general, metal overlayer growth leads to rapid attenuation of emission from the substrate CaF2 core levels, but the low-energy electron diffraction (LEED) results demonstrate the persistence of surface order to high coverages, indicating the growth of small clusters followed by coalescence. The photoemission results showed that Au deposition produces sharp metal/insulator interfaces. In contrast, signs of disruption were found for Ti, Co, and Pd deposition. For Au and Pd, metal-induced energy shifts of ∼1 eV in the CaF2 core levels and valence bands were observed; Ti and Co deposition induced smaller shifts. This indicates that the Fermi level in the CaF2 layer depends on the electronegativity of the metal overlayer. Annealing at 200–300 °C produced dramatic changes in the overlayer morphology with reappearance of the photoemission signals of CaF2 and its LEED pattern as large metal clusters were formed and the CaF2 surface was exposed. The photoemission results also indicate that metal-induced reaction with Si occurs upon annealing.
Surface oxidation studies of rare earth–transition metal amorphous magnetic films
Authors: Shen D. F. , Yu X. Y. , Shan Z. S.
Published: July 2002

Gd-Tb-Fe amorphous films were prepared in an rf sputtering system. Torque measurements were performed systematically on samples which were as-deposited or annealed at 160 °C up to 98 h in air. The torque curves showed additional peaks near 0° and 180°, which increased in amplitude with annealing time. The origin of the anomalous torque curves was investigated with computer simulation, Auger analysis, Kerr rotation and magnetization measurements, and chemical etching. It is concluded that the additional peaks on the torque curve arise from the surface oxidation layer which can be characterized with parameters determined by the computer simulation.
Complex dynamics in domain wall motion
Authors: Bennett L. H. , Swartzendruber L. J. , Aviram I. , Satija I. I.
Published: July 2002

A simple model, exactly solvable except at two points, which simulates the dynamics of a single magnetic domain wall crossing a single impurity site in a ferromagnetic material, is solved numerically for some ranges of parameters. The dynamics are complex and very sensitively dependent on the physical parameters: the frequency and strength of the applied field, the strength of the pinning, the reversible permeability, the effective mass of the domain wall, the wall viscosity, and the amount of energy retained by the wall when it breaks free of the pinning site. An example of parameter choice that results in frequency quintupling is given. Phase space portraits, return maps, and total energy spectra are used to display the results.
New bonding pad process for thin-film heads using selective laser etching
Authors: Das Shyam C. , Khan Jamal
Published: July 2002

A new technique of exposing bonding pads of thin-film heads has been developed. This process is economically advantageous over the conventional thin-film head fabrication methods due to the reduction of (about (1)/(3) ) encapsulant alumina thickness and the elimination of process steps related to thick stud plating and mechanical lapping to expose it. Alumina over the bonding pads is removed by irradiating the wafer by a semifocused pulsed CO2-laser beam through a patterned copper mask while keeping the wafer covered with a thin layer of methylene chloride. The alumina etching continues until all alumina over the bonding pads is completely removed. Any further irradiation does not affect the wafer. This is explained in terms of selective absorption of CO2-laser radiation by alumina and almost complete reflection by mask and bonding pad metals.
Variable angle of incidence analysis of magneto-optic multilayers
Authors: McGahan William A. , Chen Liang-Yao , Woollam John A.
Published: July 2002

We have applied the technique of variable angle of incidence spectroscopic ellipsometry (VASE) to the analysis of multilayered magneto-optic structures. With this instrument we measure the complete pseudodielectric tensor (diagonal and off-diagonal elements) for the sample of interest at variable angles of incidence. We have also developed computer software to perform a best-fit analysis of the measured data, providing optical constants, Voigt parameters, and layer thicknesses for the individual layers in the sample. Additionally, given an estimate of the material parameters, this software will provide an estimate of the optimum spectral range and angles of incidence for accurate characterization of the sample. An example of the above is given for a series of thicknesses of Dy/Co compositionally modulated multilayers deposited on a thick silver layer and subsequently overcoated with a thick layer of SiO. Results confirm the predicted optimum range of accuracy for this material system and effectively delineate the useful spectral range of this technique.
Coercivity mechanism of sintered NdFeB magnets having high coercivities
Authors: Fukuno A. , Hirose K. , Yoneyama T.
Published: July 2002

The combination of some additions and substitutions to sintered Nd-Fe-B magnets was investigated in order to obtain high coercivity and good thermal stability. Some additions (Al,Ga,Nb,W) and a substitution (Dy for Nd) give Nd-Fe-B-based sintered magnets high coercivities without a large remanence loss. Small differences in the amount of additions (Nd,Dy)-Fe-(Al,Ga)-(Nb,W)-B for sintered magnets show no significant difference in magnetic hysteresis loops at room temperature. Those magnet alloys also have similar good thermal stability. Effects of additions in the high-coercivity materials are studied by measuring coercivities and anisotropy fields as a function of temperature. The small amount of additions (Nb,W) affects the large influence to the coercivity mechanism.
Crystal fields and exchange interactions in Yb2Fe17: A 174Yb Mössbauer study (abstract)
Authors: Czjzek G. , Bornemann H. J. , Kmiec R. , Buschow K. H. J.
Published: July 2002

Most rare-earth -(R) iron compounds R2Fe17 crystallize in the hexagonal Th2Ni17 structure with two inequivalent rare-earth sites in the unit cell. For Tm2Fe17 magnetic anisotropy of opposite character has been determined for the two Tm sites.1 Nevertheless, the axial anisotropy of one Tm site dominates at low temperatures and forces the magnetic moments to the direction parallel to the c axis below the spin-reorientation temperature TSR=74 K. Magnetization measurements on Yb2Fe17 gave no indication for a spin reorientation.2 In this compound, the Fe sublattice anisotropy seems to dominate at all temperatures, confining the moments to the plane perpendicular to the c axis. This has now been confirmed by 174Yb Mössbauer spectra of Yb2Fe17 in the temperature range 1.6–100 K. The different crystal fields acting on the Yb 4f shell at the two sites lead to a large difference in the static moments as revealed by the different hyperfine fields. From the temperature dependence of the magnetic and electric hyperfine interactions, values for the crystal-field parameters and exchange fields at both Yb sites have been derived. Structural disorder, probably due to random occupation of Yb sites by Fe2 dumbbells, leads to distributions of the crystal-field parameters and to considerable broadening of the Mössbauer spectra.
Flux-structure relaxation in a Bi2Sr2Ca1Cu2Ox monocrystal (abstract)
Authors: Puzniak R. , Rao K. V.
Published: July 2002

Recently, we have carried out extensive electronic and magnetic property studies on a rather good monocrystal of Bi2Sr2Ca1Cu2Ox in which we find transport critical currents of 105 A/cm2 along the a-b plane at 4.2 K and at fields as large as 3 T. These crystals, grown by the floating-zone technique by Balbashov (Moscow Power Institute), exhibit some unusual flux-flow, relaxation, and flux-melting properties. In our magnetic-relaxation measurements at any temperature, we go through the entire hysteretic cycle at least twice and stop at predetermined fields in both segments of the loop. A part of the typical relaxation data at 4.2 K in a field of 1 T is shown in the figure as a function of ln t. The data over 3 decades can be fitted with no measurable deviation to the form M(t)=A+Bln t. Both parameters A and B decrease, while the ratio B/A increases with increasing field, indicating that the flux structure becomes unstable at higher fields. At higher temperatures Jc (transport) decreases rather quickly (an order of magnitude less at 20 K than at 4.2 K) and the hysteretic loop collapses even at low fields (as low as 2 T at 20 K). Furthermore, the magnetization relaxes almost to a zero value at much shorter times (tens of seconds at 20 K, 1 T; see figure). Data on the effect of neutron-irradiation and flux-melting phenomena in these monocrystals will also be presented.
Deposition and patterning of Y-Ba-Cu-O superconducting thin films by sequential multilayer deposition
Authors: Case Francine C.
Published: July 2002

Y-Ba-Cu-O superconducting thin films on 100 and 110 SrTiO3 were deposited under identical conditions by annealing thick layers of sequentially e-beam evaporated Cu, Y, and BaF2. A comparison of these films is presented. Using a variation on the same technique, a 135-μm-wide superconducting strip was deposited on 100 SrTiO3 by patterning of the first layer (copper) in the multilayer stack. Resistance data for this sample are presented. Superconducting dipoles (50 ×850 μm) were also patterned on yttria-stabilized ZrO2 by this same technique.
The influence of the guiding magnetic field on the performance of a Smith–Purcell amplifier operating in the strong Compton regime
Authors: Schächter Levi
Published: July 2002

In a Smith–Purcell amplifier, the guiding magnetic field couples the TE and TM modes. However, for an incident TM wave it is shown that the scattered TM waves can be determined with the induced TE waves neglected, the latter being treated within a first-order approximation. The response function of the amplifier for the TM waves is derived, and the dependence of its poles on the intensity of the guiding magnetic field is investigated. It is found that there are five poles, two of them complex, irrespective of the guiding field intensity and related to the ‘‘pure’’ slow-wave-structure poles; two other poles may be complex only if the cyclotron frequency is below a ‘‘cutoff’’ (determined explicitly) and resemble ‘‘gyrotron’’ poles. The cutoff is shown to be proportional to the shift (due to collective effects) in the radiation wave vector. The first pair of poles emerges from the longitudinal electronic oscillation, while the second pair corresponds to the transverse oscillation. The real pole into which the gyrotronlike poles degenerate is precisely the third pole, which occurs in slow-wave structures under strong magnetic fields. By a suitable choice of the magnetic field a 10% increase is obtainable in the gain of the amplifier; this optimal field is determined and shown, within the relevant range of parameters, to be linear with the device length.
A convenient method for the analysis of the ionic thermocurrent data
Authors: Prakash Jai , Nishad A. K.
Published: July 2002

A convenient method is proposed for the analysis of the ionic thermocurrent data. Dielectric relaxation parameters in a number of cases have been evaluated following the suggested method of analysis. Evaluated parameters are found to be accurate. The correctness of the evaluated parameters has been checked through the retracing of the ionic thermocurrent spectrum.
Damage formed by electron cyclotron resonance plasma etching on a gallium arsenide surface
Authors: Hara Tohru , Hiyoshi Jun , Hamanaka Hiromi , Sasaki Masami , Kobayashi Fukuya , Ukai Katsumi , Okada Takashi
Published: July 2002

Radiation damage induced on a gallium arsenide surface by electron cyclotron resonance (ECR) plasma etching is studied. The number of displaced atoms (displaced atom density) formed by exposure to ECR plasma is determined quantitatively by Rutherford backscattering spectrometry aligned spectra. The density increases with increasing microwave power. The amount of increase of displaced atom density from the undamaged virgin surface ΔDda is 2.9×1015 and 4.4×1015 atoms/cm2 at microwave power of 500 W (ion current density, Ii: 0.80 mA/cm2) and 800 W (Ii: 2.00 mA/cm2), respectively. The reflection high-energy electron diffraction study shows that an amorphous layer is formed on the surface at 800 W (Ii: 2.00 mA/cm2). The effect of bias power and chamber pressure on the damage is also studied. The increase of damage (ΔDda: 3.2×1015 atom/cm2) from ECR plasma etching with an rf bias of 15 W is less by a factor of 2 than damage of reactive ion etching (ΔDda: 6.9×1015 atom/cm2) when compared at an ion current density of 1.17 mA/cm2. Low-damage anisotropic etching can be achieved by ECR plasma etching.
Respective mobilities of metal and silicon in disilicides: Bilayers of chromium with molybdenum or tungsten
Authors: Thomas O. , Finstad T. G. , d’Heurle F. M.
Published: July 2002

The behaviors of metallic bilayers, chromium-molybdenum and chromium-tungsten, on (100) silicon during isochronal annealing have been studied by Rutherford backscattering of 2.3-MeV 4He+ ions and x-ray diffraction. These experiments were conducted with the aim of obtaining information about the respective mobilities of silicon and metal atoms in the different silicides through a comparison of the temperatures at which the silicides form and those at which they mix (through metal-atom diffusion). The results confirm that the respective silicides form via silicon-atom motion and that the mobilities of the metal atoms are markedly smaller than that of the silicon atoms.
The method of coherent structures and metamagnetism
Authors: Dixon J. M. , Tuszynski J. A.
Published: July 2002

A number of metallic compounds such as FeRh, Mn3GaC, and FeCl2 exhibit the interesting property of metamagnetism, i.e., the presence of order–order magnetic-phase transitions. The microscopic Hamiltonian that is commonly used to describe this class of systems is of the Heisenberg type with competing exchange interactions between the nearest- and next-nearest neighbors. Starting from this quantum Hamiltonian, through several transformations, it is possible to obtain an effective Hamiltonian which has a two-body interaction term. A recent method of analyzing such Hamiltonians is then applied based on exact calculations for the corresponding nonlinear equation of motion. This is followed by quantization about the classical solutions. Stability conditions imposed on the classical solutions agree with earlier results. Their violation is interpreted in terms of modulational instability of the associated Landau–Ginzburg Hamiltonian.
Magnetostatic waves of anisotropic antiferromagnetic films
Authors: Zhang Huikang , Thibaudeau Claude , Caillé Alain
Published: July 2002

We study theoretically the magnetostatic waves of a thin antiferromagnetic film exhibiting uniaxial perpendicular anisotropy, in the presence of an in-plane static magnetic field. The film is deposited on a nonmagnetic substrate. The dispersion relations of the nonretarded waves are then obtained. We give the frequency domains of forward and backward volume waves and those of surface waves as a function of the direction of propagation. A computer routine allows us to numerically analyze the dispersion relations for physically attainable parameters of the magnetic medium. There are generally two frequency windows for the volume waves. One of them is almost insensitive to the applied field, and the other moves up in frequency with the applied field. The surface waves are found near this second frequency window. Our main result is that the surface waves are confined in a small angular domain of propagation. This domain is nearly parallel to the applied field when the latter is small and moves away as the strength of the field increases. A very strong field would be required to bring the domain perpendicular to the field. However, the angular domain is always of a few degrees at the most when realistic parameters are used in our model.
Wide-band linewidth measurements in yttrium iron garnet films
Authors: Chen H. , De Gasperis P. , Marcelli R. , Pardavi-Horvath M. , McMichael R. , Wigen P. E.
Published: July 2002

By exploiting a computerized technique based on an automatic network analyzer, the magnetic full linewidth ΔH0 has been measured in the frequency range 1–20 GHz on a series of yttrium iron garnet epilayers having thickness between 9 and 120 μm. A relevant result is that in the sample having the lowest damping, ΔH0 is almost frequency independent in the interval 2–9 GHz. The linewidth for all the three samples investigated exhibits a couple of peaks around 11.8 and 16.3 GHz, respectively. It is also shown that a moderate reducing heat treatment can decrease the linewidth up to 20%. By also utilizing the measurement of the linewidth versus the temperature, a numerical analysis of above results is attempted in terms of an intra-ionic slow relaxation model which leads to physically reasonable values for the involved parameters.
Superexchange interaction in dimeric Cs3Yb2Br9
Authors: Carlin Richard L. , Merabet K. E. , Shum D. P. , Darriet Jacques , Güdel Hans U.
Published: July 2002

The ac susceptibility of a polycrystalline sample of the dimeric rare-earth compound Cs3Yb2Br9 has been measured at 4He temperatures. The data display a broad maximum at about 2 K, and give direct evidence for an intradimeric magnetic interaction with 〈g〉=2.87(5) and a singlet-triplet separation of 2J/kB=−3.65(10) K. The superexchange path consists of the three bromide ions which bridge the metal ions.
Critical behavior in the reentrant phase of (P
dFe)Mn
Authors: Roshko R. M. , Ruan W. , Williams G.
Published: July 2002

The field and temperature dependence of the nonlinear magnetic response of a reentrant (PdFe)Mn alloy has been investigated within the reentrant phase with an ac SQUID susceptometer operating at 16 Hz. Comparison with numerical simulations based on a mean-field effective-field Ising model with a reentrant phase boundary indicates that the experimental susceptibility isotherms possess several features which may be critical in origin, and suggests a potentially valuable criterion for recognizing critically reentrant behavior.
Magnetic behavior of ferromagnets with random anisotropy
Authors: Tejada J. , Martinez B. , Labarta A. , Grössinger R. , Hernando A.
Published: July 2002

This article reports on a magnetometric study of the effects of diluted local random anisotropy in a ferromagnetic Fe80B20 amorphous matrix. In the low-temperature and low-field regime the samples, Fe74RE6B20 (RE=Nd, Ce), show a very rich behavior as a consequence of the competition between, and different dependence on T, of the correlation length associated with local random anisotropy and exchange interactions. In the high-field regime (Happlied≥1.5 kOe) we observe ferromagnetic behavior with the saturation magnetization varying with temperature according to Bloch’s law. The spin wave stiffness constant D could be determined and lies close to 100 meVÅ2.
A new self-aligned subtractive gate process for high-voltage and complementary polycrystalline silicon thin-film transistors
Authors: Wu I-Wei , Huang Tiao-Yuan , Lewis Alan G. , Chuang T. C. , Chiang Anne
Published: July 2002

A new self-aligned subtractive gate process is proposed by alternating several masking and polycrystalline silicon gate etching steps from a conventional process to build high-voltage (up to 100 V) and complementary thin-film transistors (TFT) on insulating substrates. The new process is compatible with conventional TFT mask sets and standard processing techniques. The advantage of using this new process is to eliminate the difficulty in stripping photoresist on insulating substrates after high-dose phosphorus implant and to improve the off-state breakdown voltage in high-voltage transistors. Complementary metal-oxide-semiconductor and high-voltage TFT devices were successfully fabricated by this new process.
Amplitude and phase measurement technique for photorefractive gratings
Authors: Montgomery R. M. , Lange M. R.
Published: July 2002

A new approach for signal processing and parameter measurement is reported. This new concept uses Bragg cells and photorefractive materials in a time-integrating structure to compute correlation values. It uses the same Bragg cell for both computing correlations and performing the final signal weighting and summation. The resulting structure not only provides a powerful signal processing method, it leads to a new measurement technique which is useful in measuring the characteristics of photorefractive materials. This latter application is the subject of this paper. Direct measurement of the photorefractive grating phase is demonstrated and the results are used to show the dependence of grating phase on intensity. Also a method for generating moving gratings electronically (without moving mirrors) is proposed and demonstrated. Amplitude and phase measurements are reported for the fringes produced by such an electronically generated moving grating.
An x-ray photoelectron spectroscopic study of chemical etching and chemo-mechanical polishing of HgCdTe
Authors: Chang W. H. , Lee T. , Lau W. M.
Published: July 2002

A study of chemical etching and chemo-mechanical polishing of Hg0.8Cd0.2Te (MCT) with bromine-methanol has been carried out. It was found that the etch rate could be controlled down to 0.1 nm/s when 0.001% of bromine-methanol was used. Surface analysis using x-ray photoelectron spectroscopy indicated that differential etching of the constituents and accumulation of elemental tellurium occurred even when only a few monolayers were etched from a stoichiometric MCT surface. The relative etch rates were determined to be Cd≫ Hg≳Te. Nevertheless, it was found that chemo-mechanical polishing could produce smooth surfaces with no significant accumulation of elemental tellurium. The production of such surfaces, however, required a balance of chemical etching and mechanical lapping. Furthermore, quick quenching of chemical etching was o required after chemo-mechanical polishing in order to prevent further surface degradation.
An all refractory NbN Josephson junction medium scale integrated circuit process
Authors: Kerber G. L. , Cooper J. E. , Fry H. W. , King G. R. , Morris R. S. , Spargo J. W. , Toth A. G.
Published: July 2002

The fabrication and electrical performance of an all refractory, eight mask step, NbN medium scale integrated circuit process are discussed. In situ rf sputter deposited trilayers of NbN/MgO/NbN are plasma etched to fabricate Josephson junctions. A novel low temperature, plasma enhanced chemical vapor deposited SiO2 film is used for wiring and resistor insulation. Sputter deposited molybdenum films are used for resistors. Tunnel junctions fabricated with this process have Vm=61 mV at jc=1100 A/cm2, and Vg = 5.1–5.2 mV at 4.2 K. Critical currents are uniform to within ±3% for 101 junction strings and are within ±25% over all die on 3 in. wafers. This process has been used to fabricate 8-bit single flux quantum counter circuits, squid magnetometer circuits, 870 junction strings, and arrays of 256 squids. Preliminary circuit testing indicates operation at temperatures within the range of small closed-cycle refrigerators.
A 1-V series-array Josephson voltage standard operated at 35 GHz
Authors: Müller F. , Köhler H.-J. , Weber P. , Blüthner K. , Meyer H.-G.
Published: July 2002

Josephson voltage standards utilize microwave-induced constant voltage steps in the dc characteristic of Josephson tunnel junctions. This paper describes the design and operation of array circuits with 108 and 2000 junctions connected in series. In contrast with similar realizations, simple Q-band equipment is used for the microwave supply. The microwave attenuation of 1000 junctions was about 1 dB. The version with 2000 junctions generated Josephson voltages up to 1.2 V when operated at 35 GHz. The stability times of the quantized levels were, under normal laboratory conditions (unshielded room), better than 10 min.
Ion-induced phase transformation in type 304 austenitic stainless steel by rare-gas ion irradiation
Authors: Sakamoto I. , Hayashi N. , Furubayashi B. , Tanoue H.
Published: July 2002

Foil specimens of austenitic stainless steel (type 304 stainless steel) were irradiated with 50– 400 keV Ar, Kr, and Xe ions in the fluence range of 1×1020–1×1021 ions/m2 at room temperature. It has been shown by glancing angle x-ray diffraction (GXRD) measurement that the amount of ion-induced phase transformation of γ →α′ in the foil specimens depends strongly on irradiation conditions such as ion species, energy, and fluence; the amount of the phase transformation at saturation increases linearly with increasing ion range. An ion-induced new peak was found in the GXRD pattern, which is shown to be due to solidification of implanted rare-gas atoms in the stainless steel. The solid phase inclusions of the rare-gas atoms have a close correlation with the phase transformation. It is shown that the phase transformation is induced by the formation of highly pressurized rare-gas inclusions, while the formation of the inclusions depends on a depth distribution of implanted rare-gas atoms.
Extended x-ray absorption fine structure study of bond lengths in epitaxially grown (Ga,In)(As,P) alloys from dilute limit to concentrated
Authors: Takeda Y. , Oyanagi H. , Sasaki A.
Published: July 2002

Extended x-ray absorption fine structure (EXAFS) measurement is the technique to measure nondestructively the nearest-neighbor distance, to the accuracy within 0.01 Å or better, coordination number, and atomic species. Especially, fluorescence-detected EXAFS is best suited to characterize the atomic scale microstructure of epitaxially grown thin layers on a thick substrate. We have investigated the microstructure for each atomic pair of Ga-P, Ga-As, and In-As in (Ga,In)(As,P) alloys lattice-matched with InP, over a wide range of composition from dilute limit, through quaternary, to ternary. Constant atomic distances over the wide range were revealed when the average lattice parameter was kept constant.
Negative charge emission due to excimer laser bombardment of sodium trisilicate glass
Authors: Langford S. C. , Jensen L. C. , Dickinson J. T. , Pederson L. R.
Published: July 2002

We describe measurements of negative charge emission accompanying irradiation of sodium trisilicate glass (Na2O⋅3SiO2) with 248-nm excimer laser light at fluences on the order of 2 J/cm2 per pulse, i.e., at the threshold for ablative etching of the glass surface. The negative charge emission consists of a very prompt photoelectron burst coincident with the laser pulse, followed by a much slower plume of electrons and negative ions traveling with a high density cloud of positive ions, previously identified as primarily Na+. Using combinations of E and B fields in conjunction with time-of-flight methods, the negative ions were successfully separated from the plume and tentatively identified as O−, Si−, NaO−, and perhaps NaSi−. These negative species are probably formed by gas phase collisions in the near-surface region which result in electron attachment.
Noise measurements in multiloop superconducting interferometers
Authors: Leoni R. , Schirripa Spagnolo G. , Carelli P. , Pullano M.
Published: July 2002

Noise measurements on multiloop dc SQUIDs, fabricated with Nb-NbOx-PbAuIn and Pb-alloy Josephson tunnel junctions and well coupled with the external world by an input coil, we performed in flux locked loop mode. To achieve this task, we built a reliable low-cost control electronics to detect the voltage output of the SQUID. The results show that for multiloop dc SQUIDs with single-junction critical currents larger than 20 μA and an inductive parameter βL less than 4.5, an intrinsic white-energy spectral density of about 100h can be obtained independently of the technology used to fabricate the junctions. Furthermore, the Nb-NbOx-PbAuIn dc SQUIDs have a lower 1/f  noise than the Pb-alloy ones.