bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal transport studies of 351-nm laser-produced plasmas using extreme ultraviolet spectroscopy
Authors: Moreno J. C. , Griem H. R. , Goldsmith S. , Krumbein A. , Epstein R. , Jaanimagi P. A. , Richardson M. C. , Yaakobi B.
Published: July 2002

Spectra from an extreme ultraviolet (XUV) grazing incidence spectrograph have been used in the study of thermal transport in laser plasmas. These measurements with XUV lines allowed a diagnosis of much lower temperatures in the heating front than had been previously measured. The OMEGA (24-beam, 351-nm) laser system at the University of Rochester was used to produce plasmas from glass microballoons coated with Al or Ti substrates and overcoated with a plastic ablator. Thermal transport was investigated by measuring the intensity of x-ray and XUV lines as a function of the thickness of the plastic overcoat. These measurements were then compared to the 1D hydrodynamic code lilac. Agreement between the hydrodynamic code and experiment could not be obtained with a reasonable value for the flux limiter ( f≤0.65). Consistent results were reached if nonuniform irradiation and flux inhibition is assumed. The measured burnthrough depths of around 9 μm are similar to previous measurements made with x-ray lines at fluxes below 1015 W/cm2. No evidence of preheat in the heat front was observed.
Remarks on channeling radiation
Authors: Schächter L.
Published: July 2002

For satisfactory determination of the radiation power emitted when an electron/positron beam interacts with the electrostatic lattice potential within a crystal film, the number of bound states and their population have to be known. A relative simple procedure to calculate these two, based on matrix method, is presented. Results are in full accordance with literature. While some physical insights are investigated, a full equivalence to the propagation of an electromagnetic wave in a dielectric slab is demonstrated.
Elastic interaction between a screw dislocation dipole and a surface crack
Authors: Lin K. M. , Hu C. T. , Lee Sanboh
Published: July 2002

Based on the result of Juang and Lee [J. Appl. Phys. 59, 3421 (1986)], we investigated the elastic interaction between a screw dislocation dipole and a surface crack. In addition to the image force, the image torque on the dipole is also significant. Under the action of an applied stress, the dipole is mechanically polarized with an orientation that depends on its location. The flipping energy of the dipole is also discussed. The mechanical equilibrium positions of the dipole are examined, and the regions containing these points can form a plastic zone by collecting other dipoles. The criterion of the stress intensity factor for generating dipoles is identified. In addition, a comparison between monopole and dipole interactions with a surface crack has been accomplished. Finally, this solution can be reduced to three special cases.
Evidence for correlations among the ordering processes responsible for the permeability disaccommodation in amorphous ferromagnets
Authors: Allia P. , Beatrice C. , Vinai F. , Mazzetti P.
Published: July 2002

The first experimental evidence is given for the presence of strong correlations among the ordering processes responsible for the aftereffect of the magnetic permeability in amorphous ferromagnetic alloys. An ad hoc experiment has been performed in order to verify if the current assumption of independent ordering processes having a large spectrum of activation energy is suitable in describing the kinetics of the permeability relaxation in these materials. The results are in striking contrast with such a simple assumption, indicating that more refined models have to be introduced in a realistic description of these processes.
Effects of rapid thermal processing on the formation of uniform tetragonal tungsten disilicide films on Si(100) substrates
Authors: Siegal Michael P. , Santiago Jorge J.
Published: July 2002

Thin films of tungsten silicide with resistivities of 30–35 μΩ cm have been formed by sputter depositing 710 Å of W metal onto (100)–oriented, 3–7 Ω cm, p-type silicon wafers. The samples were fast radiatively processed in a rapid thermal processing (RTP) system under high vacuum for time anneals ranging from 15–20 s at two temperatures (∼1100 and ∼1150 °C). The inevitable oxide barrier at the interface is shown to decrease with increasing RTP time and temperature, evidenced by both Auger electron spectroscopy and secondary ion mass spectrometry experiments. The high film stress produced by thermal considerations does not seem to effect the resulting resistivity and, furthermore, appears to relax at higher temperatures when the film surface becomes ‘‘buckled.’’
Two-wave mixing with time-modulated signal in Bi12SiO20 theory and application to homodyne wave-front detection
Authors: Hamel de Monchenault G. , Huignard JP.
Published: July 2002

We theoretically analyze a two-wave mixing interaction in photorefractive Bi12SiO20 crystals in which the amplitude of the signal beam is time modulated at high frequency. Calculations of the photoinduced space-charge field are derived for a sinusoidal modulation of the input signal. Due to the time-integrating properties of the nonlinear crystal, the transmitted signal exhibits a differential gain when the modulating frequency is much greater than the inverse of the material response time. Application to coherent homodyne detection of wave fronts carrying spatial and temporal information is also presented.
A photoacoustic measurement technique using acoustic phase perturbation
Authors: Stearns R. G.
Published: July 2002

A novel photoacoustic measurement technique is introduced, which is based on the phase perturbation of an external acoustic wave that propagates through a region of material irradiated by an optical beam. The mechanism of the perturbation is the local change in acoustic velocity due to heating of the irradiated sample. Because the acoustic phase perturbation may be calibrated directly, it is found that the absolute optical absorption coefficient of the irradiated sample may be determined using the technique. Both the experimental phase detection system and a theoretical analysis of the acoustic perturbation are discussed. Finally, an experiment is described in detail, where the measurement technique is used to determine the absolute optical absorption coefficient of a liquid.
Liquidus measurement of In-rich In-Sb solutions in the 300–525 °C range
Authors: DeWinter J. C. , Pollack M. A.
Published: July 2002

Measurements of liquidus composition versus temperature for In-rich In-Sb solutions in the range from 300 °C to the InSb melting point at 525 °C are reported. The data can be described approximately by a simple solution model using a linearly temperature-dependent interaction parameter.
Comment on ‘‘The absence of gap loss in erased-media noise floors’’ [J. Appl. Phys. 6
1, 4031 (1987)]
Authors: Cramer H. A. J. , Luitjens S. B. , de Bie R. W.
Published: July 2002

B. I. Finkelstein and E. L. Otter describe in their paper [J. Appl. Phys. 61, 4031, 1987] the apparent absence of gap loss in the noise spectra of erased media. They conclude that the expressions derived by both Mallinson and Thurlings are not valid in the case of random noise. Our measurements, however, show a clear gap loss in the noise spectra of dc and ac erased CrO2 tape.
Transport of thermodynamic information by self-interstitials between precipitates in silicon
Authors: Marioton B. P. R. , Gösele U.
Published: July 2002

Strain generated by the bulk precipitation of oxygen in silicon may be relieved by the emission of self-interstitials. The equations describing diffusion-controlled precipitation with a volume constraint relieved by the emission of self-interstitials are given and applied to two model systems which take into account the buildup of a self-interstitial supersaturation. In the first model system, it is shown that precipitates starting to grow within the same volume in which others have been growing for some time will finally shrink and disappear. The shrinkage is driven by the self-interstitial supersaturation. In the second model system the self-interstitials generated by growing precipitates in a given region are found to transport thermodynamic information on the precipitation in this region to adjacent volume regions, where they can influence nucleation and growth of precipitates. The correlation between oxygen fluctuations and precipitation fluctuations are discussed in terms of the effects occurring in the ideal model system. Finally, a similar approach is used to mathematically describe carbon and silicide bulk precipitation.
Neutron diffraction and magnetic investigations of Ga substituted MnAl permanent magnet materials
Authors: Moze O. , Pareti L. , Ermakov A. E.
Published: July 2002

The crystal and magnetic structure of Ga substituted MnAl alloys has been investigated by neutron diffraction. Gallium atoms are found to occupy both the (0,0,0) and ( (1)/(2) , (1)/(2) , (1)/(2) ) crystallographic sites [differently from Al which occupy ( (1)/(2) , (1)/(2) , (1)/(2) ) sites] and have a preference for the ( (1)/(2) , (1)/(2) , (1)/(2) ) site. The magnetic structure is tetragonal with antiferromagnetic coupling between the two sites and a Mn moment of approximately 1.90 μB. The magnetocrystalline anisotropy has been studied by the singular point detection method. Gallium substitution has been found to decrease the overall anisotropy. Similar investigations on MnAl and MnAlC alloys with Mn=68 wt. % have confirmed the crystal and magnetic structure and magnetic anisotropy of previous investigations of alloys with Mn>68 wt. %.
Resistivity of linear scratches in doped (100) n-type single-crystal silicon
Authors: Danyluk Steven , Lee Soo-Wohn , Ahn Ji-Hong , Kahn Arnold
Published: July 2002

Four-point probe measurements have been made on (100) n-type Czochralski silicon wafers of initial resistivities 0.016, 0.96, and 3.35 Ω cm. The probe tips straddled linear single scratches formed by a Vickers pyramid diamond. The diamond was dead-loaded with 0.25 N, and the scratches were made in a laboratory air environment with a relative humidity of 50%, as the silicon wafer was held at various elevated temperatures. The measurements show that the relative change in resistivity increases with temperature up to an optimum temperature, after which the resistivity decreases. The temperature at which the maximum occurs and at which the relative change in resistivity occurs depends on the initial resistivity of the wafers; the temperature at which the maximum change in relative resistivity occurs is 200 °C for the 0.016- and 0.96-Ω cm wafers and 250 °C for the 3.35-Ω cm wafer. The relative change between the undamaged wafer resistivity and the resistivity including the scratches for these same samples was 4%, 7%, and 9%. Scanning electron micrographs of the scratches showed that the scratch morphology also depended on the temperature; as the temperature is increased, the grooves become shallow and display evidence of ploughing. An analysis of the four-point probe geometry shows that the voltage in the four-point probe measurement depends on the size and the conductivity of the damage surrounding the scratches.
Analysis of plate and colony precipitates decorating stacking faults in a single-crystal silicon
Authors: Ryoo K. , Drosd R. , Wood W.
Published: July 2002

Oxidation of silicon wafers containing lattice damage at the surface normally results in the formation of extrinsic stacking faults. Optical microscope investigation following decorative etching shows that on certain specimens the faults have a straight line appearance while on others the ends of the defect are much enlarged giving a ‘‘dog-bone’’ shape. Analytical electron microscopy investigation confirmed that the dog-bone shaped faults were decorated with two types of precipitates near their edges, colonies and plate. Both resided on the (111) fault planes and extended over several thousand angstroms. Precipitate diffraction spots were not found due to the small volume fraction, but translational Moiré fringes were observed for certain matrix g vectors, thus aiding in the crystallographic analysis. Energy dispersive x-ray analysis revealed that colony precipitates were due to Ni and Cu contamination while plate precipitates were due to Ni. Crystal structures for both were determined to be NiSi2 type silicides.
Asymmetric hysteresis cycles as a probe of local fields in metallic spin glasses (abstract)
Authors: Lévy Laurent P. , Bouchiat Hélène
Published: July 2002

We have studied the magnetization in the spin-glass phase of AgMn under the repetitive application of a small (10 Oe≤h≤50 Oe) magnetic field [asymmetric hysteresis cycles (L. Néel, in Proceedings of the R. A. Welch Foundation Conference on Chemical Res. II, Atomic Structure, Houston, Texas, 1958)] after the sample has been cooled in a static field H (0≤H≤1.1 kOe). When H=0, the magnetization mn in the field off state (h=0) grows as the logarithm of the number of cycles (n), while the magnetization in the on state (h≠0) Mn decreases with cycle number. This weaker response reflects an increase of the stiffness of the spin system after each cycle. At low temperature mn grows linearly with temperature, reaches a maximum around T∼0.6 Tg and decreases as Tg is approached. The effects are larger when the system is prepared in a nonequilibrium state (rapid thermal quenching, or removal of the static field H). The irreversible growth of the magnetization mn scale linearly with Tg (i.e., exchange) for samples of 0.5 and 2.6 at. % Mn concentration. We find that mn grows as the value of H is increased, reaches a maximum around H∼Tg/15 and decreases slowly at higher fields. We suggest as a possible interpretation of this phenomenon, the existence of a cavity in the distribution of local fields acting on the low temperature excitations. Additional information on the role of anisotropic forces will also be presented.
Formation and thermal stability of amorphous Cu-Zr thin films deposited by coevaporation
Authors: Minemura T. , van den Broek J. J. , Daams J. L. C.
Published: July 2002

The formation and thermal stability of amorphous thin films have been characterized by comparing them with those of melt-spun ribbons. The various Cu1−xZrx thin films were deposited by coevaporation. The amorphous formation range and the crystallization behavior in the films were investigated with x-ray diffraction and differential scanning calorimetry. The amorphous thin films are formed in the composition range x=0.20–0.75, which is wider than that found for the melt-spun ribbons. The crystallization temperature and the activation energy for crystallization are lower than those of the melt-spun ribbons, although the composition dependencies show tendencies similar to those of the ribbons. These differences in thermal stability between amorphous films and ribbons might be due to a lower degree of the short-range ordering in the films.
Spin-glass behavior of cubic Tb0.3Y0.7Ag: A scaling of the thermoremanence
Authors: Said M. R. , Kouvel J. S. , Brun T. O.
Published: July 2002

Magnetization-versus-temperature (M-vs-T) measurements in a fixed field on cubic pseudobinary Tb0.3Y0.7Ag show that M for increasing and then decreasing T bifurcates at the antiferromagnetic Néel point (TN=36 K), where M is maximum. The resulting thermoremanence (MR), which decays very slowly with time, diminishes with increasing T and vanishes at TN. Thus, the long-range antiferromagnetism appears to coexist with spin-glass ordering. Measurements of MR with increasing T were also made for different cooling fields (Hc1) The changes of MR with Hcl and T are found to reduce to a universal relationship between the temperature-normalized quantities, m=MR/M0(T) and h=Hcl /H0(T). Setting both the initial slope of m vs h and the saturation m at high h equal to unity, we determine that M0(T)=M0(0) exp (−T/T0), with M0(0)=0.82μB/Tb atom and T0=4.3 K, and that H0(T) varies analogously, with H0(0)=225 kOe and the same T0. A similar temperature scaling of MR vs Hcl , with similar exponential forms for M0(T) and H0(T), has been deduced earlier for Ag-Mn and other canonical spin glasses.
Perturbations to the Stoner–Wohlfarth threshold in 2×20 μm M-R memory elements
Authors: Comstock C. S. , Yoo H. Y. , Pohm A. V.
Published: July 2002

Perturbations to the Stoner–Wohlfarth threshold in 2×20 μm M-R memory elements have been examined experimentally and analytically. For the small dimensioned elements studied the perturbations are large. The thresholds were reduced up to 50% for transverse elements and increased 10% or more for longitudinal elements.
Macroscopic quantum tunneling in single domain magnetic particles
Authors: DeFranzo A. , Klik I. , Gunther L. , Swanson A. G. , Brooks J. S.
Published: July 2002

Since the 1950’s there have been a number of experimental observations involving small single domain (SD) magnetic particles (≲200 Å diameter) which have been attributed to what we’d today call ‘‘macroscopic quantum tunneling’’ (MQT) of the magnetization in its switching from one easy axis direction to another. A comprehensive study of this phenomenon is not only of great interest for the sake of fundamental physics: It is of utmost practical importance in that MQT sets a limit on the lifetime of information storage on magnetic tapes and films. In this paper we present a brief summary of some of the latest results of our theoretical and experimental studies of this phenomenon.
Correlation between the superconducting properties and the oxygen stoichiometry in Y1Ba2Cu3Ox (abstract)
Authors: Marucco J. F. , Wang K. , Garoche P.
Published: July 2002

The phase diagram of the Y1Ba2Cu3Ox compound has been studied by thermogravimetric measurements. In order to reach the absolute value of the oxygen content, the starting oxides and carbonate were carefully weighted and reacted directly in the thermobalance. The temperature range for the respective formation of the Y1Ba2Cu3Ox and Y2BaCuO5 was determined; thus a single phase was obtained at high temperature. The phase diagram was constructed from the reacted material by a series of isothermal treatment under a precise partial pressure of oxygen. Step by step the oxygen partial pressure was reduced and both the kinetic of the reaction and the equilibrium value were monitored. For each step the oxygen partial pressure was cycled back and forward to insure a good equilibrium state. The change in the rate of evolution of the oxygen loss with temperature is possibly related to the orthorhombic to tetragonal structural transformation. The phases identified from the phase diagram where quenched and the correlation between the oxygen stoichiometry and superconducting properties established from the analysis of the low-temperature transport and calorimetric properties.
Properties of high T
c superconductors with modified compositions (abstract)
Authors: Jin S. , Sherwood R. C. , Tiefel T. H. , van Dover K. B. , Fastnacht R. A. , Yan M.
Published: July 2002

The recent discovery of high Tc superconductor materials such as Ba2YCu3O9−x stimulated worldwide interest in the subject. The interactions of the superconducting oxides with other oxides and metals are of considerable technical importance because of the need for (i) proper stabilizer for superconductor-normal metal composite wire, (ii) nonreactive crucible materials for crystal growth, and (iii) suitable substrate materials for thin-film/thick-film superconductor devices. In this paper, the effects of various metal and oxide additions (up to 10%–50% by weight) on superconducting transition properties have been investigated using magnetic susceptibility and resistivity measurement as a function of temperature. Fine particles of metals and oxides were intimately mixed with the Ba2YCu3O9−x powder, pressed into pellets, and then sintered at 900–1000 °C followed by slow cooling in oxygen atmosphere to achieve chemical homogeneity, desirable crystal structure and oxygen stoichiometry. Some of the oxides and metals were relatively benign and did not significantly affect the superconducting transition behavior, while others either caused less sharp transition (e.g., broad transition to below 77 K) or essentially eliminated the superconductivity. The experimental results and interpretations will be presented and their technical implications will be discussed.
Field ion microscopy of the high T
c superconductor Ba2YCu3O7−x (abstract)
Authors: Melmed A. J. , Shull R. D. , Chiang C. K. , Fowler H. A.
Published: July 2002

Field ion microscopy (FIM) observations (using either hydrogen or neon gas) were performed on both the high Tc superconducting oxide Ba2YCu3O7−x (0<x<0.5) and the related nonsuperconducting oxide Ba2YCu3O6. For the superconducting material, ac magnetic susceptibility measurements determined a transition temperature of 92 K. At 30 K strong preferential images of atomic or molecular layers were observed for Ba2YCu3O7−x perpendicular to the long c axis, but not for Ba2YCu3O6. The preferential field evaporation or field ionization responsible for the layered images (possessing a spacing of approximately 12 Å which is equivalent to the c-axis lattice parameter) in the superconducting oxide below its transition temperature is interpreted as possible evidence for the existence of relatively highly conducting atomic layers in the unit cell of this material at low temperatures. Computer simulations of FIM images expected under various assumptions of preferential imaging are most consistent with the layered images being due to the copper-oxygen end planes (those located between the planes of Ba atoms). FIM observations of Ba2YCu3O7−x performed above the superconducting transition temperature (at 100 K) showed primarily a highly intense disordered image similar to that obtained for the structurally related nonsuperconducting oxide Ba2YCu3O6 at low temperatures, and faintly discernible parallel rows of atoms. Both twins and grain boundaries in Ba2YCu3O7−x have been observed in the FIM at low temperatures; and no special images related to the superconducting state have been found to be associated with these structural features. To date, consistent observations have been performed on approximately 100 specimens, thereby assuring that the present observations are not artifacts, but representative of the bulk material. Similar FIM observations have also been obtained for the related high Tc superconductor Ba2YbCu3O7−x.
Electrical quality of low-temperature (Tdep=775 °C) epitaxial silicon: The effect of deposition rate
Authors: Burger W. R. , Reif R.
Published: July 2002

The results of an investigation of the effects of varying the deposition rate on the surface morphology and electrical characteristics of low-temperature (Tdep=775 °C) epitaxial silicon are presented. The data indicate that the electrical characteristics are a strong function of the growth rate, even more so than the deposition temperature. Varying the growth rate by a factor of 16 varies the minority-carrier lifetime and reverse-bias diode leakage current by five orders of magnitude, and has a strong impact on the surface morphology of the epitaxial layer. Deposition conditions will be reported that yielded a minority-carrier lifetime of 480 μs, which is the highest lifetime reported in low-temperature epitaxial silicon.
Refractive index of InGaAs/InAlAs multiquantum-well layers grown by molecular-beam epitaxy
Authors: Nojima S. , Asahi H.
Published: July 2002

Refractive indices of InGaAs/InAlAs multiquantum-well layers grown by molecular-beam epitaxy are determined by reflectance measurements as a function of photon energy and barrier width, i.e., average Al content. These results are well explained by the single-oscillator model; oscillator energy (E0) and dispersion energy (Ed) values vary linearly with average Al content. These values are, however, found to differ from the values obtained by the linear approximation of the parameters for binary alloys. Discussion of this discrepancy is also presented.
Enhancement of current peak-to-valley ratio in In0.52Al0.48As/In0.53Ga0.47As -based resonant tunneling diodes
Authors: Potter Robert C. , Lakhani Amir A. , Beyea Dana , Hier Harry
Published: July 2002

The electrical characteristics of In0.52Al0.48As/In0.53 Ga 0.47 As resonant tunneling diodes are reported. These devices exhibit current peak-to-valley ratios up to 6.7 at room temperature. Differences in the current-voltage characteristics for devices made from epilayers grown simultaneously on n+ and semi-insulating InP substrates demonstrate the importance of minimizing the parasitic series resistance. The enhanced peak-to-valley ratio has been attributed to thick In0.52Al0.48 As barriers (50 Å) and wide, undoped In0.53Ga0.47 As spacer-layers (400 Å).
Se passivation and regrowth of ZnSe(001) epilayers on GaAs(001)
Authors: Jonker B. T. , Krebs J. J. , Prinz G. A.
Published: July 2002

We report the use of a Se overlayer to passivate and protect the surface of ZnSe epilayers during prolonged exposure to atmosphere. The samples were grown by molecular-beam epitaxy (MBE) on GaAs (001) substrates and passivated by the deposition of a Se coating near room temperature before removal from the MBE system. The Se coating is readily desorbed in ultrahigh vacuum at substrate temperatures of 115–150 °C. The resultant single-crystal surfaces are clean, stoichiometric, and well ordered, as demonstrated by Auger electron spectroscopy and reflection high-energy electron diffraction. Regrowth of ZnSe on these surfaces yields epilayers which exhibit excellent crystalline order comparable to that of continuously grown reference samples, as shown by x-ray double-crystal rocking curves. This Se passivation technique offers a simple means of transferring such II-VI epilayers through atmosphere from the growth system to other facilities while preserving surface single-crystal order and cleanliness.
Amplified spontaneous emission and superradiant pulse from the flash-pumped atomic iodine system
Authors: Kim Gyu Ug , Lee Sang Soo , Hahn Jae Won
Published: July 2002

A superradiant and amplified spontaneous transition pulse is obtained from an iodine photodissociation laser amplifier which uses i-C3F7I as an active molecule and is pumped with a flashlamp (full width at half maximum=3 μs). We have observed a sharp leading pulse of superradiance whose rise time is less than 50 ns, and the amplified spontaneous emission follows the superradiance during the pumping flash. By measuring the population inversion density in the active medium of the amplifier, we have obtained the threshold condition for the superradiance to take place. Also, the buildup time and peak intensity of the pulse are measured as a function of the flashlamp input energy. By placing a reflecting mirror at a varying distance (from 173 to 673 cm) behind the amplifier, we have found a periodic intensity fluctuation in the superradiance; the period (Δt) depends linearly on the distance (d), i.e., Δt=2d/c, where c is the light velocity.
Anomalous electroabsorption in semi-insulating GaAs
Authors: Walpita L. M.
Published: July 2002

We discuss an optical modulation effect in semi-insulating gallium arsenide (GaAs) that can be used in electrically addressable optical memory. An enhanced absorption of photons below the band gap of GaAs is observed after an optical pulse tuned to the absorption edge of GaAs has been transmitted through a sample in the presence of an electric field. It is suggested that the effect is caused by the release of trapped carriers to the conduction band to reach thermal equilibrium with optical pulse generated conducting carriers and thereby causing further absorption of below band-gap photons. The magnitude of the effect is related to the optical pulse intensity, the strength of the applied voltage, and the traps in the sample.
Optical properties of polystyrene and benzoate ester of polystyrene thin layers
Authors: Hanna C. Y. Y. , Abass A. K.
Published: July 2002

The optical data of polystyrene and benzoate ester of polystyrene thin layers were investigated for evidence of indirect allowed transitions and assisting phonons. The optical data show the possibility of using polystyrene and benzoate ester of polystyrene as a cover in solar collectors and green houses.
(111) random and 〈110〉 channeled implantation profiles and range parameters in Hg1−xCdxTe
Authors: Wilson R. G.
Published: July 2002

We have measured, using secondary-ion mass spectrometry, the (111) random and 〈110〉 channeled profiles for about 45 ions implanted into Hg1−xCdxTe. Ion energies vary from 100 to 700 keV, and ion fluences from 1×1013 to 3×1015 cm−2. The specially preannealed device-quality Hg1−xCdxTe substrates were implanted at room temperature and not annealed after implantation. Ions implanted include 1H(C), 2H(C), He, Li(C), Be(C), B(C), C(C), N(C), O(C), F(C), Na(C), Mg(C), Al(C), Si(C), P(C), S(C), Cl(C), K(C), Ca(C), Ti(C), V, Cr(C), Mn(C), Fe(C), Co(C), Ni, Cu(C), Zn, Ga, Ge, As, Se, Br(C), Kr, Rb, Zr, Mo(C), Ag, In(C), Sn, Sb, Cs, and Ta, where (C) means that 〈110〉 channeled profiles were measured in addition to (111) random orientation profiles. Other ions were implanted but with poor profiling results. We report here implantation range data that include the peak depth Rm, the projected range Rp or first moment μ, the range straggle ΔRp or second moment σ, the third moment or skewness γ1, and the fourth moment or kurtosis β2, obtained from a Pearson IV fitting routine, and the maximum 〈110〉 channeling range. We show what densities and depths can be achieved using 〈110〉 channeled implantation in solid-state recrystallized Hg1−xCdxTe. Values of electronic stopping Se are calculated from the maximum 〈110〉channeling ranges and show the Z1-dependent nature of Se.
A thermostimulated creep study of blends of poly(vinyl chloride) and chlorinated polyethylene
Authors: del Val J. J. , Lacabanne C. , Hiltner A.
Published: July 2002

Thermally stimulated creep measurements have been carried out on polyvinylchloride and on blends of polyvinylchloride with chlorinated polyethylenes of various chlorine distributions. Global spectra show that the two polymers are immiscible. However, a fine structure study of the spectra shows that some degree of compatibility exists in samples blended with randomly and commercially chlorinated polyethylenes. The same analysis leads to the conclusion that the sample blended with blocky chlorinated polyethylene is segregated into incompatible chlorinated polyethylene and polyvinylchloride phases.
Implant-dose mapping using infrared transmission
Authors: Brierley Steven K. , Lehr Deborah S. , Grabinski Alek K.
Published: July 2002

Infrared transmission can be used for quantitative, nondestructive mapping of the dose distribution of Si+ implants into GaAs wafers prior to annealing. Calibration curves of absorption exponent (the product of the absorption coefficient and the layer thickness) as a function of total implant dose have been obtained for representative implant schedules. Wafer maps are presented which illustrate the results for both normal implants and severely channeled implants.
Observation of thermomagnetically written domains by Lorentz electron microscopy in Tb-Co and Tb-Fe-Co disks
Authors: Ichihara Katsutarou , Mizusawa Yumi , Yasuda Nobuaki , Suzuki Takao
Published: July 2002

For better understanding of the read/write properties of magneto-optical disks, thermomagnetically written domains were observed by Lorentz electron microscopy. The domains were written in the quadrilayered medium with 25-nm-thick Tb-Co film and in the trilayered medium with 50-nm-thick Tb-Fe-Co film, which were sputtered on pregrooved resinous substrates. Recording power and frequency were varied at intervals of 3.5 mm in a radial direction of the disk, and each recording position was observed individually. Qualitative understanding of the read/write properties, such as carrier-to-noise ratio (C/N) and jitter, were well achieved from Lorentz images of the domains. It is found that the C/N value of the Tb-Fe-Co film with a higher figure of merit (Rθk ) is lower than that of the Tb-Co film with a lower value of Rθk . The reason for this is believed to be due to a larger variation in domain shape in the Tb-Fe-Co film compared to the Tb-Co film. A careful observation based upon the image processing of domain bits reveals that the jitter is mainly caused by the irregularity of the domain shape near the edge in the Tb-Fe-Co film.
Electron conduction in GaAs atomic layer doped with Si
Authors: Makimoto Toshiki , Kobayashi Naoki , Horikoshi Yoshiji
Published: July 2002

This paper describes electronic transport characteristics of Si atomic-layer-doped GaAs grown by flowrate modulation epitaxy. This enables achievement of extremely heavy Si doping within one atomic layer without interupting growth. Electron concentrations are evaluated using Hall measurements and the phenomenon of electron concentration dependence on temperature and undoped GaAs layer thickness is explained by considering parallel conduction of electrons distributed in different levels with different mobilities.
On gain scaling of plasma recombination lasers
Authors: Khare Alika , Thareja R. K.
Published: July 2002

We propose the use of a simple electric network model to estimate electron temperature for Cd i and Cd ii by estimating the gain and population inversion for a recombination laser. The temperature estimated for a Cd ii laser is in agreement with that of an experimentally observed value.
Time-resolved investigations of laser-induced shock waves in water by use of polyvinylidenefluoride hydrophones
Authors: Schoeffmann H. , Schmidt-Kloiber H. , Reichel E.
Published: July 2002

Laser light from a Q-switched Nd:yttrium-aluminum-garnet laser (λ=1064 nm; pulse duration=20 ns; pulse energies up to 150 mJ) focused into water creates shock waves by rapidly expanding microplasmas. Using piezoelectric, thin-film polyvinylidenefluoride (PVDF) as a transducer, a broadband hydrophone (100-MHz bandwidth) was developed to investigate underwater shock waves. The electrical signal is analyzed with respect to reflections of the shock wave within the transducer and the input impedance of the measuring device. The shock waveform is determined, its peak pressure ranging to kbars (108 Pa), decreasing with r−1.12 and increases by the square root of the laser pulse energy. The time resolution of the hydrophone (4 ns) is sufficient to determine the plasma dimensions and the number of shock waves generated by a single laserpulse. Both vary statistically, primarily because of contaminations in the fluid. Because of the length of the region containing plasmas, different peak pressures are found in the direction of the laser beam and perpendicular to it.
Number of oxygen atoms in a thermal donor in silicon
Authors: Schroder D. K. , Chen C. S. , Kang J. S. , Song X. D.
Published: July 2002

The number of oxygen atoms in a thermal donor (TD) can be determined directly from the reduction of the concentration of interstitial oxygen in Czochralski (Cz) silicon after annealing at 450 °C for 75 h, when the effect of high-carbon concentration in Si crystals is considered. It is found that on the average a single TD cluster contains eight oxygen atoms. Some TD-inactive large oxygen clusters are produced if the annealing time is longer than the time for TDs to reach their maximum concentration or if the annealing temperature is higher than 475 °C. We also find that the smallest TD cluster contains five oxygen atoms and the largest TD cluster contains 13 oxygen atoms.
Theoretical study of irreversible jumps of 180° domain well separating infinitely long domains
Authors: Roman Andrzej
Published: July 2002

This paper presents an analysis of the static losses due to the irreversible Barkhausen jump of the 180° Bloch wall separating infinitely large domains. A relation between the area swept by the wall and the corresponding duration of the jumps is obtained both on the basis of considerations of the pressure acting on the wall and by direct calculation of the energy loss. A similar problem was considered by Allia and Vinai, who adopted a simplified assumption of the domain of an infinitely long cylindrical shape.
Isomer shift and magnetic properties of EuO under pressure
Authors: Taylor R. D. , Farrell J. N.
Published: July 2002

We have measured the Mössbauer effect of 151Eu in EuO at temperatures down to 4 K and pressures to 31 GPa. At ambient pressure EuO becomes ferromagnetic at TC=69 K; at 31 GPa, TC=105(2) K; and a maximum value of TC in the region 15–25 GPa is inferred. A Brillouin fit of the hyperfine-field-temperature data at 31 GPa gives a reduced magnetic moment compared to ambient although the magnitude of the saturation hyperfine field is not reduced. The isomer shift with pressure weakly supports the expectation of an intermediate-valence change with pressure above 14 GPa.
Instabilities of spin waves in parallel-pumped easy plane ferromagnets
Authors: Lim S. P. , Huber D. L.
Published: July 2002

By applying the S-theory formalism of Zakharov et al. to a microscopic hamiltonian with uniaxial easy plane anisotropy, we arrive at a set of equations for the system that describe the spin waves and their mutual interactions. The parameters in the theory are related to the various interaction constants of the microscopic hamiltonian. Numerical studies of this system of equations indicate that the stationary states are ones where all spin-wave pair correlation functions have the same phase. The phenomenon of phase locking is universal, independent of the mode of approach to equilibrium. It is found that there is no dependence on the number of modes (up to 100) for the above behavior. This, together with the form of the equations, indicates that a similar result should hold for a macroscopic number of modes. Results for the stationary magnon population are presented. In the phase-locked regime, the approach to a stationary state is governed by a pair of coupled first-order differential equations. Linearizing these equations about the stationary points, we find that the approach to equilibrium involves purely exponential decay just above threshold, and, at higher power levels, we have damped oscillatory decay.
Stabilization of the tetragonal phase of YBa2Cu3O7−δ through the addition of Fe impurities
Authors: Causa M. T. , Dutrús S. M. , Fainstein C. , Salva H. R. , Steren L. B. , Tovar M. , Zysler R.
Published: July 2002

We report normal and superconducting properties of Fe-doped YBa2Cu3O7−δ. Results from x-ray powder diffraction, electrical resistivity, magnetic susceptibility, and ESR measurements are presented. The structural effects of doping are described and their correlation with the change in superconducting properties is discussed. Similarities with the superconducting properties of oxygen deficient YBa2Cu3O7−δ are analyzed. The comparison of the average distance between impurities (or oxygen vacancies) with the coherence length of the material suggests the existence of a nonhomogeneous order parameter in the region of low concentration of defects.
Double-phase transition in Au82.5Fe17.5? (abstract)
Authors: Rakers L. D. , Beck Paul A.
Published: July 2002

The low steady field susceptibility measured as a function of increasing temperature in a field parallel to the plane of a thin (0.03-mm) disk of Au82.5Fe17.5 does not give any indication of magnetic ‘‘phase transitions’’ or for the presence of an intermediate long-range ferromagnetic phase. These findings are in accord with the earlier observation that the temperature of the hyperfine splitting in the 57Fe Mössbauer spectrum is distinctly lower than that of the ‘‘critical susceptibility peak’’; the latter clearly does not correspond to the onset of long-range ferromagnetism. If measured in a field of 9.6 Oe, the susceptibility has a well-defined maximum at ∼100 K, but in a field of 500 Oe the maximum shifts to ∼50 K. Showing isothermal remanence as well as magnetothermal history effects up to at least 130 K, the alloy is clearly spin-glass-like well above the temperature of the maximum. The magnetic viscosity increases gradually on cooling and ‘‘freezing’’ takes place in a temperature range extending over 100 K. The susceptibility maximum is a kinematic effect; it does not signify a phase transition. The crossover from the paramagnetic state into the spin-glass state is a very gradual one in Au82.5Fe17.5.
Study of field-driven wall-configuration conversions for laminated Permalloy in the easy-axis state
Authors: Herman D. A. , Argyle B. E. , Trouilloud P. L. , Petek B. , Romankiw L. T. , Andricacos P. C. , Krongelb S. , Rath D. L. , Canaperi D. F. , Komsa M. L.
Published: July 2002

Laminated Permalloy, with edge-curling walls replacing closure domains, has been proposed to increase permeability and reduce wall noise in recording. However, in structures meeting the criteria for Slonczewski’s ‘‘easy-axis’’ state, normal walls often coexist with edge-curling walls. We have used our laser magneto-optic microscope to study inductive-head-yoke shaped elements of two and four Permalloy layers separated by nonmagnetic, metallic spacers. In the four-magnetic-layer sample a state with a single wall, terminating at the edge-curling regions and lying along the easy-axis direction, is often observed on the top and bottom layers. Some elements may be driven into an easy-axis state with no observed domain walls. The two-magnetic-layer sample also exhibited simultaneous one-wall structures on the top and bottom layers. The other stable configuration was a no-wall state on the top layer and a two-wall (three-domain) state on the lower layer. These ‘‘coupled’’ states were exceptionally stable in both samples; fields on the order of 300 Oe were required to switch between configurations.
High-pressure study of the magnetic states of disordered Ni-Mn alloys
Authors: Aitken R. G. , Daneshvar K.
Published: July 2002

Low-field ac susceptibility measurements have been performed on disordered Ni1−x Mnx, where x=0.216, 0.225, and 0.265, under hydrostatic pressure up to 21 kbar. The measured susceptibility χm exhibits transitions from paramagnetic to quasiferromagnetic to spin-glass states on cooling. The pressure dependence indicates a decrease in the magnitude of χm and opposite shifts in the temperatures of the two transitions. The nature of the quasiferromagnetic state is discussed.
Prediction of magnetic phase diagrams of selected (RxR′1−x)2Fe14B systems
Authors: Boltich E. B. , Pourarian F. , Obermyer R. T. , Sankar S. G. , Wallace W. E.
Published: July 2002

Preliminary experiments on (TmxDy1−x)2Fe14B have suggested the presence of axial, conical and planar regions in the magnetic phase diagram. Here we report the magnetic phase diagram for this and other mixed rare-earth systems, as predicted by second-order crystal field theory. The specific systems considered were those containing (Er or Tm) and (Pr, Tb, or Dy). It is shown that in these systems, which contain two rare-earth ions of opposite second-order Stevens coefficients, the occurrence of all three regions can be accounted for by second-order crystal field theory. The shapes of the phase boundaries are discussed in terms of the stabilization energies of the various rare earth ions. In particular, it was found that the relatively strong temperature dependence of the stabilization energies of Pr and Tm is responsible for low-temperature contractions of the planar and axial phases, respectively. This temperature dependence is attributed to the weaker exchange interaction [(g−1)J<1] experienced by these ions.
Spin reorientation in (Y1−xSmx)2Fe14B
Authors: Lin Chin , Liu Zun-Xiao , Sun Yun-Xi , Lou Zheng-Hua , Bayinqilao
Published: July 2002

Magnetization measurements have been made on (Y1−xSmx)2 Fe14B compounds with x≤0.1 over the temperature range from 1.5 K to room temperature. The c axis is the easy magnetization direction for pure Y2Fe14B at all temperatures, reflecting the anisotropy of the Fe sublattice. X-ray diffraction analyses on aligned powders indicate that all samples studied have easy magnetization direction parallel to the c axis at room temperature. The addition of Sm results in a decrease of anisotropy at room temperature. At low temperatures it induces a spin reorientation in all systems studied. A transition to planar anisotropy is observed for x=0.08 and 0.1.
A magnetostrictive motor
Authors: Ida N. , Roemer L. E.
Published: July 2002

Magnetostriction can be used to effect a linear incremental motion device. Bidirectional incremental motion can be achieved in which the step size is set by the magnetostrictive coil’s current. Such a device possesses the variable step width, characteristic of analog devices (unlike salient pole stepper motors). Once the step size is selected by the coil’s current, the device behaves as a digital device with incrementally selected steps. Magnetostriction is a nonlinear function, dependent on the material. For the small incremental motion we examined, operation was essentially in the linear portion of the strain versus magnetic field strength curve.
Field enhancement in traveling wave tubes with tapered pole pieces
Authors: Clarke John P. , Leupold Herbert A.
Published: July 2002

In many millimeter and microwave devices, the heaviest component is the magnetic focusing structure. Therefore, a decrease in the bulk of this structure can produce a significant reduction in the mass of the entire device. In this paper, we propose a tapered pole piece designed to reduce bulk and/or enhance fields in periodic permanent-magnet focusing structures. To compare these structures with conventional designs, computer calculations have been performed by the finite-element method. The calculations show that the tapered pole piece can offer field enhancement or reduction of mass and bulk of the order of 50%. Finite-element analyses of heat conduction show a favorable comparison of the tapered pole piece with conventional structures in transporting heat away from the working space. The simplicity of form of the tapered pole-piece design, the considerable reduction of bulk it affords, and its adequate heat-handling capabilities make it a promising candidate for widespread traveling wave tube use.
SEM study of the effect of Zr additive on the microstructures of Sm(Co,Cu,Fe,Zr)7.64 magnets (abstract)
Authors: Lin Ying-Chun , Lin Jiang-Ching , Chiang Da-Pun , Fan Kang-Ming , Chang Wen Cheng
Published: July 2002

The effect of Zr on the magnetic properties of Sm(Co0.67−xCu0.05Fe0.28Zr6)7.64 permanent magnets has been examined by SEM to correlate their initial magnetization curves with microstructures. SEM shows clear network structures which are weaved by 1:5 phase along three directions and embedded in a 2:17 phase matrix. The precipitates cross each other at 120°. The structure is very likely the cellular structures observed by the transmission electron microscope (TEM). The size of network structures corresponds to cellular structures. The Zr controls the density of network structures and its formation of a Zr-rich phase. For Zr content around 1.0 wt. %, low density network structures are observed and low-density Zr-rich phases appear at grain boundaries, and the intrinsic coercivity is only about 800 Oe. For higher Zr content the network structures are more refined; also the density and size of the Zr-rich phase are increased. These may be the reasons why its intrinsic coercivity is exceeding 15 kOe.
Reentrant ferromagnetism in a two-dimensional Ising model with random nearest-neighbor interactions (abstract)
Authors: Benayad N. , Benyoussef A. , Boccara N.
Published: July 2002

Reentrant behavior seems to be characteristic of systems with competing interactions even when no spin-glass phase exists. Using various methods (finite cluster approximation,1 mean-field renormalization,2 finite cluster renormalization, etc.) we determined the phase diagram of a two-dimensional square Ising model with random nearest-neighbor interactions Jij distributed according to P(Jij)=(1−p)δ(Jij−J)+pδ (Jij−αJ), where J>0 and 0>α>−1. Such a model has been considered by Wolff and Zittartz.3 These authors discussed its qualitative features and argued that a reentrant behavior should be observed. Our calculations agree with this conjecture.