bluuebunny/crossref_metadata_2025 huggingface dataset:
Raman determination of structures of long-period SiC polytypes
Authors: Nakashima S. , Kisoda K. , Gauthier J.-P.
Published: July 2002

Raman spectroscopy has been applied to identification of longer-period SiC polytypes. The stacking structures of 51R and 132R polytypes have been examined, the result of which is consistent with electron- and x-ray-diffraction analyses. The possibility is discussed for Raman determination of the period and stacking structure of longer period polytypes. It is demonstrated that Raman scattering is useful for the determination of the structure of SiC polytypes.
Non-mass-separated ion shower doping of polycrystalline silicon
Authors: Mishima Yasuyoshi , Takei Michiko
Published: July 2002

Practical polycrystalline silicon thin-film transistors need a low-temperature doping technique. Ion shower doping with a main ion source of P2Hx (x=1,2,...) was studied. This technique implants a molecule in the polycrystalline silicon surface with a low acceleration voltage. A critical impurity density from polycrystalline phase to amorphous phase for phosphorus in polycrystalline silicon of 2.0×1020 ions/cm3was found. Sheet resistance with ion shower doping was lower than with conventional ion implantation at low temperature. This is a result of an increase in sheet carriers, because the low-temperature recovering of defects is done by molecular implantation and hydrogen atoms compensate defects. Implanted polycrystalline Si with a Hall mobility of 5 cm2/V s was obtained.
Solid-state ultraviolet tunable laser: A Ce3+ doped LiYF4 crystal
Authors: Okada F. , Togawa S. , Ohta K. , Koda S.
Published: July 2002

A large gain and a wide tunability have been achieved over the Ce3+ (5d-4f) transition in a LiYF4 crystal. A gain coefficient in excess of 180 cm−1 and a superradiant beam of 2.5 mrad divergence are observed at the laser transition, 325.2 nm, when the crystal is optically excited either at 193 or at 248 nm. Gain measurements indicate that the laser is tunable over a wavelength range of more than 10 nm.
Modeling the behavior of photogenerated charge in semi-insulating GaAs
Authors: Hurd C. M. , McKinnon W. R.
Published: July 2002

The transient response of photogenerated carriers in semi-insulating (SI) GaAs is expected to be influenced by the inevitable deep traps in the material. To investigate this effect, and its dependence on the trap-compensation scheme, we have simulated the dynamical behavior of carriers in a planar structure consisting of Schottky electrodes applied directly to SI-GaAs that is either doped (with Cr) or undoped (with EL2 compensation). We show by a two-dimensional, finite-difference calculation how the deep traps lead to photoinduced space charge at the electrodes. This space charge screens the bias field and modifies the transient response of the carriers, but the details vary with the type of trap compensation used in the SI-GaAs. Although we consider for illustration the simplest possible planar structure, our results relate directly to a class of metal-semiconductor-metal photodetectors that is potentially important in integrated optoelectronics.
Dyadic Green’s functions and dipole radiations in layered chiral media
Authors: Ren Wei
Published: July 2002

Dyadic Green’s functions in the unbounded chiral medium are expanded by the vector wave functions in unbounded chiral media for Cartesian, cylindrical, and spherical coordinate systems. These expressions are useful to treat the radiation and scattering in planarly, cylindrically, and spherically layered media. Instead of the eigenfunction expansions of the dyadic Green’s functions, the dyadic Green’s functions in isotropic media are used, remarkably simplifying the derivation of dyadic Green’s functions in chiral media. As the first illustrative application, Sommerfeld integral representations of the dyadic Green’s functions and dipole radiations in a planarly layered chiral medium are presented via a novel derivation. As the second application example, by the method of images the closed expression of dyadic Green’s functions are obtained for an isotropic chiral half-space bounded by a perfectly conducting plane. The established asymptotic and numerical methods for Sommerfeld integrals in isotropic media are therefore applicable to the corresponding problems in multilayer chiral media.
Extended bond graph reticulation of magnetostrictive continua
Authors: Lee Fu-Shin , Moon Tess J. , Masada Glenn Y.
Published: July 2002

The extended bond graph (EBG) method is used to model the distributed coupled magnetoelastic effects of general magnetostrictive continua. The mechanical and magnetic fields are described in terms of defined displacement and momentum states, and Galerkin’s discretization technique is applied to reticulate the dynamics of the fields into power flows which are defined as the inner products of extended efforts and flows. The power-based EBG descriptions are consistently used to represent the discretized inertia, compliance, reluctance, coupled fields, and external sources of the magnetostrictive continua. The power bonds associated with the multienergetic fields are directed separately to the magnetic and mechanical energetic domains to enforce energy conservation laws. Details of the development of the general formulation for the model are provided. The EBG network model provides a unified way to analyze the coupling effects and dynamics of complex systems using general magnetostrictive continua.
A resistive superconducting quantum interference device with two quantization loops
Authors: Krivoy G. S. , Koch H.
Published: July 2002

A simplified theoretical analysis and experimental investigations of a partially resistive superconducting quantum interference device with two quantization loops have been performed. The advantage of this device is an extremely large output signal. It is shown that the output signal oscillates with a period determined by the nonstationary Josephson relation. This device was experimentally compared to the dc resistive superconducting quantum interference device used as a test structure.
Growth and characterization of Al1−yInyAs/Ga1−xInxAs strained multiple quantum wells
Authors: Ruiz A. , Mestres N. , Calleja J. M. , Wagner J. , Briones F.
Published: July 2002

Highly strained Al1−yInyAs/Ga1−xInxAs multiple quantum wells have been grown by atomic layer molecular beam epitaxy on [001]-GaAs substrates. Raman scattering and x-ray diffraction techniques have been used to determine layer composition and strain for a wide range of In concentration (0≤x≤0.44). When a thick buffer layer of AlInAs is used, commensurate growth of the quantum wells takes place if the In content of the barriers equals that of the buffer layer. Then the strain is only accumulated in the wells. The GaInAs wells can be either under biaxial tension or compression depending on the relative In content in wells and barriers.
Magnetization reversal mechanism of the chain of two oblate ellipsoids
Authors: Han Dehua , Yang Zheng
Published: July 2002

A model of magnetization reversal for the chain of two oblate ellipsoids is proposed. The magnetization loops, the angular dependencies of coercivity Hc and the critical field H0 were calculated with the considerations of the uniaxial magnetocrystalline anisotropy, the shape anisotropy, as well as the interaction anisotropy of the ellipsoids. The results show that for small anisotropic factor ω(=2K1/M2s), the magnetization reversal of the chain is inclinable to the fanning process, while for the large one, the reversal to parallel rotation process. When the crystalline anisotropy of the ellipsoids was considered, the coercivity of the chain of two oblate ellipsoids was larger than that of Jacobs and Bean’s chain of two spheres by a factor of (1+6ω/π) for fanning process and of (1+2ω/π) for parallel rotation process. When ω equals 0 and the ellipsoids become spheres, the results of the model become those of Jacobs and Bean’s model of chain of two spheres. The results show also that the effect of the crystalline anisotropy on the magnetization reversal of the chain is larger than that of interaction anisotropy. This model could be used to explain the magnetization reversal mechanism of the oriented Ba-ferrite particulate media.
Donor complex formation due to a high-dose Ge implant into Si
Authors: Gupta Ashawant , Rahman M. Mahmudur , Qiao Jianmin , Yang Cary Y. , Im Seongil , Cheung Nathan W. , Yu Paul K. L.
Published: July 2002

To investigate boron deactivation and/or donor complex formation due to a high-dose Ge and C implantation and the subsequent solid phase epitaxy, SiGe and SiGeC layers were fabricated and characterized. Cross-sectional transmission electron microscopy indicated that the SiGe layer with a peak Ge concentration of 5 at. % was strained; whereas, for higher concentrations, stacking faults were observed from the surface to the projected range of the Ge as a result of strain relaxation. Photoluminescence (PL) results were found to be consistent with dopant deactivation due to Ge implantation and the subsequent solid phase epitaxial growth of the amorphous layer. Furthermore, for unstrained SiGe layers (Ge peak concentration ≥7 at. %), the PL results support our previously proposed donor complex formation. These findings were confirmed by spreading resistance profiling. A model for donor complex formation is proposed.
Angular and energy distributions of surface produced H− and D− ions in a barium surface conversion source
Authors: Heeren R. M. A. , de Graaf M. J. , Ćirić D. , Hopman H. J. , Kleyn A. W.
Published: July 2002

The production of negative hydrogen and deuterium ions is studied in the foundation for fundamenteel Onderzoek der Materie surface conversion experiment. In this experiment a Barium surface is used to convert positive ions into negative ions. We have developed a detector able to analyze the characteristics of the surface produced negative ion beam. Measurements with this detector show that in barium surface conversion sources negative ions can be formed by recoiling and direct reflection of positive ions from the barium surface. The broad angular distribution of the surface produced negative ions is determined to extend over 16°.
Model of the frost deformation in thermoplastic-photoconductor films
Authors: Carreño F. , Bernabeu E.
Published: July 2002

The dynamics of thermoplastic-photoconductor films is reviewed. A theory of thermoplastic film deformation is presented for a three-layer structure in air with modified boundary conditions. The amplitude of the deformation A versus the spatial frequency k is of bandpass type (A-k curve). The influence of the thickness of the layers and the heating and electric parameters on the A-k curve are analyzed. The predictions of the model are compared to others previously reported and with experimental data. The validity and limitations of the model are also discussed.
Line shapes of field-dependent nonresonant microwave and rf absorption in high-T
c superconductors
Authors: Srinivasu V. V. , Thomas Boben , Hegde M. S. , Bhat S. V.
Published: July 2002

The field-dependent nonresonant absorption at microwave (9.1 GHz) and radio (19.5 MHz) frequencies has been studied in the superconducting state of YBa2Cu3O7−x pellets and epitaxially grown c-axis oriented thin films using conventional continuous-wave electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectrometers. The line shapes of the signals from the thin-film samples are observed to depend sensitively on the operating frequency; at 19.5 MHz derivative looking signals saturating at low magnetic fields (∼10 Oe) are obtained while at 9.1 GHz, signals saturate only at fields of the order of a kOe. Two different possible origins of the losses, namely, diffraction reduction of junction currents in the weak links and the viscous motion of the fluxons are considered and compared. We find that the observed frequency dependence of the line shape can be explained only following the latter model.
A modification of the three-point method of measuring contact resistivities of metal-superconductor interfaces
Authors: Hsi Chi-Shiung , Haertling Gene H. , Skaar Eric C. , Wang Feiling
Published: July 2002

Axisymmetric three-point measurement of the contact resistance between a metal electrode and a superconductor substrate shows significant variation as a function of the placement of the voltage measuring probe on the metal electrode. This study explored this variation by the use of an analytical model simulating the voltage variation in the metal electrode. The model used a simplified scheme of mapping the electrode-superconductor interface to an equivalent layer with the same resistivity as the metal electrode. The voltage in the electrode was obtained by solving Laplace’s equation. Using a numerical approximation process, three simplified equations for calculating the contact resistivities from the voltage measured from the three-point method were developed. The contact resistivities calculated from the modified equations and those measured from the lap-joint method were compared in order to show the validity of the modified equations. The radii of the electrode and current leads, and the ratio of the voltage measured at the top edge of the electrode to the voltage measured at the current lead determine the selection of the modified equations.
Mass spectrometric study of the reaction of photo-oxidized GaAs with Ga
Authors: Sasaki Masahiro , Yoshida Seikoh
Published: July 2002

The Ga-induced reaction of photo-oxidized GaAs, which is used as a mask material for the in situ selective-area growth of GaAs, has been studied by mass spectrometry. An anomalous behavior of photo-oxidized GaAs was observed by measuring the temperature-programmed desorption after Ga predeposition and the desorption response to pulsed Ga injection onto it. Deposited Ga, less than 3 monolayers, did not directly deoxidize the photo-oxidized GaAs into a volatile product, but, on the contrary, stabilized it. This anomalous behavior was not observed for dark-oxidized GaAs. It is considered that Ga-induced stabilization of the oxide makes the photo-oxidized GaAs more effective as a mask for selective-area growth.
Hole kinetics in metal-oxide-semiconductor oxides investigated by a hot-carrier degradation experiment
Authors: Brox M. , Weber W.
Published: July 2002

In this work fast-changing bias conditions in the nanosecond regime are applied to n-channel metal-oxide-semiconductor field effect transistors. Short bunches of holes are injected into the silicon dioxide (SiO2) and subjected to different field conditions which influence the final trapping. It is shown that by this experiment the kinetics of hole movement in the oxide can be studied. The model of polaron formation originating from work on high-energy irradiation is essentially confirmed. Evidence for a prepolaron formation phase is found, however, with a smaller scattering length for which we propose the different hole formation process in this experiment to be responsible. On this basis the interface trap formation by injected holes is investigated. It is found that not the number of trapped holes but the one of injected holes is decisive for interface trap formation.
Analysis of the scanning electron microscope mirror image based on the dielectric surface microstructure
Authors: Asokan T. , Sudarshan T. S.
Published: July 2002

This paper addresses hitherto unexplained phenomena associated with the electrostatic mirror technique, such as (i) the influence of the surface microstructural parameters of a polycrystalline dielectric (e.g., alumina) on mirror images, and (ii) the distortion of mirror images. The formation of a mirror image on an as-machined alumina surface was found to be nearly impossible, but on a polished specimen, possessing low surface damages, mirror images were easily formed. A smooth and low-damage surface seems to be a prerequisite for the formation of a mirror image. The size of mirror images, observed at different locations on a polished alumina surface, was found to vary significantly, indicating that an inhomogeneous surface charging occurs in polycrystalline dielectrics. It was shown that the variation in the grain and grain boundary volumes constituting the charged region is responsible for the variation in the size of the mirror image. The distortion of the mirror images was studied using single crystal quartz specimens. The asymmetry of the equipotential boundary—caused by (i) the tilt of the crystal axis (θ≠0°) with respect to the probing electron beam, or by (ii) the asymmetrical electron interaction volume, i.e., deviation from the standard pear shape—was demonstrated to be responsible for the distortion of the mirror images.
Charge collection and thermalization in a composite calorimetric and ionization x-ray detector
Authors: Stahle C. K. , Wouters J. , Kelley R. L. , Moseley S. H. , Szymkowiak A. E.
Published: July 2002

A combination calorimetric and ionization x-ray detector has been made by attaching a silicon p-i-n diode to a monolithic silicon microcalorimeter. We were able to measure a charge signal in the absence of applied bias on the diode at a temperature as low as 0.1 K, demonstrating that the junction potential is sufficient to drift the ionized charges to the contacts. A fraction of the electron-hole pairs created became trapped, as was manifested by excess broadening in the measured thermal signal. The fraction of charge trapped was determined from the variation of the thermal signal magnitude with reverse bias. The ability to collect charge without applying a bias is an encouraging result in the development of high resolution combination thermal and ionization detectors. At higher biases high resolution is precluded, but the enhancement of the thermal signal due to the work done on the ionized charges can lead to a low detection threshold. With an applied bias of −25 V, we achieved a detection threshold of 8 eV, based upon energy scaling of the 1σ value of the baseline noise distribution.
Harmonic synchronization in resistively coupled Josephson junctions
Authors: Blackburn James A. , Gro/nbech-Jensen Niels , Smith H. J. T.
Published: July 2002

The oscillations of two resistively coupled Josephson junctions biased only by a single dc current source are shown to lock harmonically in a 1:2 mode over a significant range of bias current, even when the junctions are identical. The dependence of this locking on both junction and coupling parameters is examined, and it is found that, for this particular two-junction configuration, 1:1 locking can never occur, and also that a minimum coupling coefficient is needed to support harmonic locking. Some issues related to subharmonic locking are also discussed.
Mapping of the structural perfection of vapor grown α-HgI2 crystals by means of γ-ray rocking curves
Authors: Rossberg A. , Piechotka M. , Magerl A. , Kaldis E.
Published: July 2002

Mapping of perfection of as-grown mercuric iodide crystals has been performed in order to assess the distribution of structural defects produced during growth and cooling. Nearly perfect areas have been found between the {001} crystal facets with the full width at half maximum values of the rocking curves approaching the resolution limit of the γ-ray spectrometer (±0.015 deg arc). On the other hand, deterioration of the structure in regions close to the crystal bottom as well as bending of the crystal lattice have been revealed. Possible reasons for these defects are discussed.
The effect of ultraviolet radiation on a ZnS:Tb thin film electroluminescent device
Authors: Kong W. , Solanki R.
Published: July 2002

The effect of UV laser radiation on the emission of a ZnS:Tb thin film electroluminescent (EL) device has been investigated. It was found that the EL emission can be enhanced near threshold and attenuated at higher voltages by irradiating the device with UV radiation from an argon ion laser. It is shown that these effects are related to the photogenerated carriers that alter transport and build up of charge and the electric field. Both the charge and the field have been determined in real time to examine the enhancement and attenuation of the EL emission.
Radiation effects in high-temperature thermal diffusion measurements using the laser-flash method
Authors: Srinivasan N. S. , Xiao X. G. , Seetharaman S.
Published: July 2002

A theoretical analysis has been made to account for radiation effects in thermal diffusivity measurements at high temperatures. The analysis considers the laser-flash method based on the three-layer technique for melts. The gray-body approximation is assumed to be valid for the liquid sample which is sandwiched between two metal layers. The analysis considers radiation from the upper and lower metallic plates to the surroundings and the radiative flux due to multiple reflections between the two plates. Finite pulse time effects and the absorption of radiation in the liquid sample are also considered. The model equations have been solved numerically using a finite difference scheme. Calculations have been made for a typical liquid sample representing an oxide melt in a platinum cell assembly in the temperature interval 1273–1673 K. The effects of parameters such as sample thickness, thermal diffusivity, effective absorptivity, etc. on the temperature transient of the back surface of the lower platinum layer have been investigated. The results indicate that the radiation flux at the top surface is relatively very high initially (time≪1 s). It shows a rapid decrease with respect to time and attains a small but finite value. The radiation flux from the bottom surface increases rapidly and approaches this finite value as expected. A comparison of the maximum temperature increase of the back surface of the lower platinum layer, with and without radiation correction at 1673 K, shows a typical difference of about 8%, which is quite significant. Calculations also show that liquid samples with effective absorption coefficients in the range zero to 100 m−1 can be considered to be completely transparent to radiation.
Formation of Cu-rich particles on the surface of YBa2Cu3O7−x thin film grown by in situ off-axis sputtering
Authors: Han Zhenghe , Selinder T. I. , Helmersson U.
Published: July 2002

Experiments on the formation of Cu-rich particles on the surface of high quality YBa2Cu3O7−x thin films have been carried out systematically. The films on (001) LaAlO3 were grown using in situ off-axis sputtering. The particle formation observed in our experiment can be described using a classical thin film nucleation and growth model based on the concept of capture zones. In the temperature range from 670 to 750 °C, the nuclei density saturates at the early stage of deposition, and the formation of the Cu-rich particle belongs to the case of initial complete condensation. The saturation nuclei density of the particles N decreases as the temperature increases. It has been also found that N is deposition rate dependent and substrate dependent. Based on the experiments, the activation energy for surface diffusion of the Cu atoms that form the particles is estimated to be 1.5 eV in this temperature range.
Plasma chemistry at long mean-free-paths
Authors: Harvey R. E. P. , Hitchon W. N. G. , Parker G. J.
Published: July 2002

A long mean-free-path (lmfp) model of transport of neutral particles has been developed and applied to the chemistry of a low neutral-pressure (≲2 mTorr) plasma etching system. In cylindrical geometry, using coordinates (r,z) while ignoring angle φ, a transition matrix is set up for an arbitrary mfp that indicates the fraction of the particles originating in the cell at (r′,z′) that experience their next collision in the cell at (r,z). This matrix can be iterated, allowing for chemical reactions, to obtain the steady state density of the neutral species. It can also provide angular distributions of neutrals; at present, their energy distribution is not kept track of, although it will be in the future. The method has been applied to an electron cyclotron resonance plasma in CF4. Using the measured electron energy distribution, the breakdown of CF4 into the species responsible for etching is calculated. Densities of CF4, CF3, CF2, and F are presented for a wide range of conditions.
Effect of substrate misorientation on x-ray rocking curves from InGaAs relaxed epitaxial layers
Authors: Maigné P. , Baribeau J. -M. , Coulas D. , Desruisseaux C.
Published: July 2002

The effect of substrate misorientation and epitaxial tilt on asymmetrical {hkl} reflections is discussed and a general procedure for characterizing the unit cell geometry of epitaxial layers is proposed. The absolute positions of {hkl} diffraction lines, and hence the line splittings, are derived as a function of the substrate misorientation, epitaxial layer tilt, and azimuthal angle. The procedure is applied to a 3-μm-thick In0.15Ga0.85As layer grown on a misoriented (100) GaAs substrate by recording (400) and {511} reflections as a function of the azimuthal angle. The analysis reveals the presence of residual strain in the epilayer and suggests that relaxation includes a triclinic distortion of the epitaxial film where the [100] direction of the epilayer is not parallel to the [100] direction of the substrate.
Main characteristics of a Brayton refrigeration cycle of paramagnetic salt
Authors: Chen Lixuan , Yan Zijun
Published: July 2002

The characteristics of a magnetic Brayton refrigeration cycle are investigated on the basis of the general equation of state of a simple paramagnetic salt. The refrigeration heat and the coefficient of performance of the magnetic Brayton refrigeration cycle are derived, and the effect of regeneration on the performance is discussed. It is expounded that the magnetic Brayton refrigeration cycle possesses both advantages of the magnetic Ericsson and the magnetic Carnot refrigeration cycles.
Carrier recombination in indium-doped HgCdTe(211)B epitaxial layers grown by molecular beam epitaxy
Authors: Wijewarnasuriya P. S. , Lange M. D. , Sivananthan S. , Faurie J. P.
Published: July 2002

We report the recombination mechanisms of minority carrier lifetime in indium-doped layers of (211)B Hg1−xCdxTe(x ≊ 23.0% ± 2.0%)n-type grown by molecular beam epitaxy. Measured lifetimes were explained by an Auger limited band-to-band recombination process in this material, even in the extrinsic temperature region. Frequently, in some of the layers, a combination of the band-to-band recombination mechanisms together with recombination at the Shockley–Read single level 33 to 45 meV below the conduction band was necessary to explain the measured data. Results indicate that these defects have acceptorlike characteristics and their origin is related to Hg vacancies.
Ion implantation into (x11)A-oriented InP and GaAs (x≤4)
Authors: Rao Mulpuri V. , Dietrich Harry B. , Klein P. B. , Fathimulla Ayub , Simons David S. , Chi Peter H.
Published: July 2002

Si, Ge, and Be implantations were performed into (x11)A-oriented semi-insulating InP and GaAs substrates for x≤4. For comparison some of the implantations were also performed into (110)- and (100)-oriented substrates. For 200 keV/5×1013 cm−2 Si and 200 keV/3×1013 cm−2 Ge implants after 850 °C/7 s annealing, the InP is always n type with similar sheet resistance independent of the substrate orientation. No in-diffusion of Si or Ge was observed after annealing for any substrate orientation. Similar behavior was observed for Si implants in GaAs and for Si/B co-implants in both InP and GaAs. Photoluminescence measurements were performed on the Si- and Si/B-implanted InP and GaAs. For 30 keV/1.5×1014 cm−2 Be implants in both InP and GaAs, the in-diffusion of Be in (311)A-oriented substrates is less compared to the (100) material.
Electronic and shallow donor impurity states in GaAs-Ga1−xAlxAs quantum-well wires: Effects of dielectric mismatch
Authors: Deng Zhen-Yan , Lai Ting-Rong , Guo Jing-Kun , Gu Shi-Wei
Published: July 2002

The effects of image potential due to dielectric mismatch on electronic and shallow donor impurity states in quasi-one-dimensional GaAs-Ga1−xAlxAs quantum-well wires with rectangular cross section for both finite barrier and infinitely high barrier are investigated. The results have shown that, when the image potential is included, the variations in electronic energy level and impurity binding energy are considerable, especially when the cross-section dimensions of the quantum wire become small. The results also showed that the effects of the impurity ion image potential on impurity binding energy are much larger than those of electron image potential.
The effect of Au impurities at the interfaces on the magnetoresistance of MBE-grown Co/Cu multilayers
Authors: Wellock K. P. , Hickey B. J. , Greig D. , Walker M. J. , Xu J. , Wiser N.
Published: July 2002

We have grown Co/Cu multilayers by MBE using a shuttering arrangement wherein half of the sample receives an amount of Au impurities at each interface. Under these controlled conditions, the differences in measurements between each half is attributed only to the effect of the impurities. The samples were characterized by x-ray diffraction and RHEED. We have found that small fractions of a monolayer of Au deposited at the Co/Cu interface significantly decreased the GMR. These results are discussed in the light of current theories on the role of bulk and interface scattering.
Giant magnetoresistance in Ag1−xNix−yFey heterogeneous alloy films
Authors: Watson M. L. , Lewis V. G. , O’Grady K.
Published: July 2002

We have investigated the effects of phase segregation and compositional variation on the giant magnetoresistance (GMR) observed in heterogeneous AgNiFe alloy films. The films were sputtered from a mosaic Ag/NiFe/Fe target onto glass substrates at the system ambient temperature. They had a thickness of 200–300 nm, and were rapidly thermally annealed (RTA) under vacuum in order to promote phase segregation. By altering the amount of Fe in the target mosaic, the Ni:Fe ratio was systematically varied from 80:20 to 34:66 atomic percent. The Ag concentration for all films was fixed at 78±5 atomic percent. The GMR was maximized using a RTA temperature of 650 °C. Annealing at higher temperatures decreased the saturation field of the GMR, but also lowered its size. Changing the film composition had little effect on the saturation field of the GMR, but for both as-deposited and optimally annealed samples the magnetoresistance was found to decrease as the Ni concentration decreased.
Dependence of the magnetic properties Gd2−xCexCuO4, 0≤x≤0.15, on their particle size
Authors: Mahía J. , Vázquez-Vázquez C. , Mira J. , López-Quintela M. A. , Rivas J. , Jones T. E. , Oseroff S. B.
Published: July 2002

Gd2−xCexCuO4, 0≤x≤0.15, have been synthesized by the solid state reaction, the sol-gel technique and the water-in-oil microemulsion, in order to vary the particle size. The samples have been characterized by x-ray diffraction, photon correlation spectroscopy and transmission electron microscopy. Magnetization and ac susceptibility measurements were performed between 4 and 300 K. The extrapolated linear part of the inverse magnetization shifts to lower temperatures as the particle size decreases. The internal field associated to the WF of the Cu moments diminishes with the particle diameter. Differences between the zero-field-cooling and the field-cooling magnetization curves were observed for T<TN. These differences depend on the particle size.
Structural and magnetoresistance studies in granular (Ni81Fe19,Ni80Co20)/Ag synthesized from annealed multilayers
Authors: Bian X. , Altounian Z. , Stöm-Olsen J. O. , Zaluska A. , Huai Y. , Cochrane R. W.
Published: July 2002

The structural and magnetotransport properties have been studied in (Ni81Fe19,Ni80Co20)/Ag granular alloy films synthesized by the annealing of sputtered multilayers containing ultrathin magnetic layers. The magnetic concentration, particle size, and morphology of the precipitates can be controlled by adjusting the magnetic layer thickness during the deposition process. Magnetoresistance as large as 30% was found at 4.2 K with a rather small saturation field (<2 kOe), leading to relatively high field sensitivity. Magnetoresistance and saturation field in these alloy films essentially depend on the magnetic precipitate size, concentration, and annealing temperature. The temperature dependence of magnetization and magnetoresistance was also studied, and the correlations among the microstructure, magnetotransport, and magnetic properties are discussed.
Schottky barrier height dependence on the compensation doping in the interfacial Si layer of Al/Si/n:GaAs Schottky diodes
Authors: Miller T. J. , Nathan M. I.
Published: July 2002

Al/Si/n:GaAs Schottky diode structures have been grown by molecular-beam epitaxy utilizing thin (100 Å) Si interfacial layers. These Si layers are unintentionally very heavily n-type doped with As from the system or from the substrate. This n-type doping is intentionally compensated with p-type (Al) doping during the growth of the Si layer in an attempt to modulate the Schottky barrier height. The resultant barrier height, as determined by I-V and C-V measurements, increases with increased acceptor doping in the Si (from 0.34 eV for no Al doping to a maximum of 1.07 eV) as per Poisson’s equation.
Surface potential determination in metal-oxide-semiconductor capacitors
Authors: Moragues J. M. , Ciantar E. , Jérisian R. , Sagnes B. , Oualid J.
Published: July 2002

Different methods using the relationship between surface potential ΨS and gate bias VG in metal-oxide-semiconductor (MOS) capacitors have been compared. These methods can be applied even if the doping profile is very abrupt and the interface state density very high. The shifts of midgap, flatband, and threshold voltages, observed after Fowler–Nordheim electron injection, and deduced from the various ΨS(VG) relationships obtained by these different methods, are in good agreement. These shifts give the number of effective oxide trapped charges (Nox) per unit area and acceptor-like and donor-like interface states (NSSA and NSSD) which are created during the electron injection. We reveal that the number of positive charges created in the gate oxide, unlike the number of generated interface states, strongly depends on the position of the post-metallization annealing step in the process. After relaxation of the stressed MOS capacitors, most of the generated positive charges can be attributed, in the MOS capacitors studied, to hydrogen-related species. It seems that the interface states are essentially created by the recombination of holes generated by electron impact.
Characterization of the Si/SiGe heterojunction diode grown by ultrahigh vacuum chemical vapor deposition
Authors: Jung T. G. , Chang C. Y. , Liu C. S. , Chang T. C. , Lin H. C. , Tsai W. C. , Huang G. W. , Chen L. P.
Published: July 2002

The unipolar Si/SiGe heterojunction diode grown by ultrahigh vacuum chemical vapor deposition at 550 °C is demonstrated. The dark current density measured at 77 K is (2.5±0.1)×10−7 A/cm2 for the barrier height of 176±8 meV, at a reverse bias of 1 V. The barrier heights are measured from the activation analysis of the saturation current and compared to the theoretical values. The barrier height decreases as the thickness of the SiGe strained layer exceeds the critical thickness.
Calorimetric analysis of thin-film reactions: Experiments and modeling in the nickel/silicon system
Authors: Knauth P. , Charaï A. , Bergman C. , Gas P.
Published: July 2002

Thin-film reactions between nickel and silicon are investigated by differential scanning calorimetry and transmission electron microscopy on evaporated bilayers with different compositions and thicknesses. The thermograms are interpreted by a computer modeling, based on diffusion-controlled growth. Experiments and simulation reveal the simultaneous formation of crystalline Ni2Si and of an amorphous phase of composition probably near NiSi. The derived kinetic data confirm literature values from isothermal experiments.
Nonlinear optical properties of proton-exchanged waveguides in z-cut LiTaO3
Authors: Åhlfeldt Henrik
Published: July 2002

Reflection second-harmonic generation from the polished waveguide end face is used to investigate the second-order nonlinear optical properties of as-exchanged and annealed proton-exchanged waveguides in z-cut LiTaO3. It is found that proton exchange results in a strongly reduced nonlinearity which, however, can be restored by thermal annealing. Selective etching is used as a method to further investigate the structural changes following proton exchange and annealing. A correlation is found between the etching properties and the nonlinear optical properties. The results are discussed and related to the hydrogen concentration profile using a linear diffusion model for the anneal process.
Brillouin scattering study of the pseudosurface acoustic mode on the (110) face of cubic crystals having elastic anisotropy ratio above unity
Authors: Aleksandrov V. V. , Gladkevitch A. , Mozhaev V. G. , Giovannini L. , Nizzoli F.
Published: July 2002

We report the experimental observation of a pseudosurface mode in (110)-cut cubic crystals having the anisotropy ratio η=2C44/(C11−C12)≳1, where C11, C12, and C44 are elastic constants. The measurements have been performed with Brillouin light-scattering spectroscopy for GaAs, InSb, Ge, and InAs crystals. Results are shown for GaAs and InSb. An additional Brillouin satellite has been observed in the bulk velocity range for general propagation directions on the (110) plane; this peak is attributed to the presence of the pseudosurface mode. For all the crystals investigated, we have found that the pseudosurface mode exists for propagation directions within the range θ=±55°, where θ is the azimuthal angle measured from the [001] crystal axis. The results of calculations of the light-scattering cross section and of the propagation velocity of the pseudosurface mode are in a good agreement with the measurements.
Materials and processing aspects of CoCrTa/Cr longitudinal recording media. II. Microstructure
Authors: Shen Y. , Wong B. Y. , Laughlin D. E.
Published: July 2002

In the CoCrTa/Cr system, it has been postulated that segregation of nonmagnetic constituents to grain boundaries is responsible for the low noise and high coercivity. However, direct experimental evidence is still lacking. In this investigation, we have carried out microstructural studies using transmission electron microscopy (TEM) and atomic resolution transmission electron microscopy (ARTEM) of CoCrTa/Cr films produced under varying processing conditions. We found that the stacking fault density and the degree of crystalline perfection between the faults is most important in increasing the coercivity and improving signal-noise properties as indicated by ΔM measurement. High substrate temperatures and high Cr and Ta concentrations promote the occurrence of the stacking faults in the films. In conjunction with ARTEM results, we propose that these faults provide possible sites for elemental segregation which is partially responsible for reducing the magnetic coupling among the unfaulted hcp regions in the CoCrTa films. We also provide microstructural evidence supporting the picture that the high-frequency mechanical texture lines break the intergranular coupling normal to the texture lines resulting in circumferential anisotropy. Grains are crystallographically correlated to form clusters between the texture lines but such correlation is broken up by the texture lines. This gives rise to an effective shape-induced anisotropy. We believe that the cluster size plays a more important role than does the grain size in determining the magnetic properties of CoCrTa/Cr media.
Control of Terfenol-D under load
Authors: Jenner A. G. , Greenough R. D. , Allwood D. , Wilkinson A. J.
Published: July 2002

A vibration control case study is described which demonstrates the application of magnetostrictive (Terfenol-D) actuators. The magnetomechanical properties of the material suggests that when incorporated in devices for applications a nonlinear response will result. This case study compares the performance of two kinds of control strategy (both discrete), a conventional proportional and integral (PI) algorithm and a variable structure algorithm (DVSC) in both servo and cancellation/regulation roles. Both strategies were implemented on an INMOS transputer based microcontroller with a sampling period of 300 μs. The results presented show that the control behavior of the DVSC strategy offers significant advantages over the PI strategy when controlling actuators with nonlinear characteristics, i.e., the rejection of a 5 Hz disturbance with a gain of −36 dB compared to a gain of −15 dB when using the PI strategy.
Magnetization, Young’s moduli, and magnetostriction of rare-earth–iron eutectic alloys with R=Tb0.6Dy0.4
Authors: Clark A. E. , Wun-Fogle M. , Teter J. P. , Restorff J. B. , Cheng S. F.
Published: July 2002

Rare-earth–iron alloys, R0.9Fe0.1, R0.72Fe0.28, and R0.42Fe0.58 (R=Tb0.6Dy0.4), containing the R/RFe2 eutectic composition were prepared by Bridgman and free-standing zone-melting techniques. Magnetization measurements were made in fields up to 800 kA/m between 55 and 300 K. A huge increase in magnetization below 210 K occurs as the R component becomes ordered. At low applied magnetic fields there is clear identification of both the ferromagnetic ordering temperature TC and the Néel spiral ordering temperature TN of R. (For Tb0.6Dy0.4, TC=165 K, TN=210 K.) Magnetization and magnetostriction measurements reveal very large magnetocrystalline anisotropies for both the R and the RFe2 components. Unexpectedly, at 77 K, were the rare-earth component of the eutectic system is ordered and the magnetostriction is large (λhγ≳0.6%), the magnetostriction is largest in the samples containing the largest amount of the RFe2 phase. Young’s modulus measurements reveal the reduction in the stiffness with the addition of the softer rare earth to the stiff RFe2 compound.
Surface barriers and two-dimensional-collective pinning in single crystal Nd1.85Ce0.15CuO4−δ superconductors
Authors: Zuo F. , Khizroev S. , Jiang Xiuguang , Peng J. L. , Greene R. L.
Published: July 2002

We report detailed magnetization studies on a single crystal Nd1.85Ce0.15CuO4−δ superconductor in the magnetic field parallel to the c-axis direction. Two characteristic peaks are observed in the magnetization data, corresponding to surface barriers and two-dimensional (2-D) collective pinnings. The critical currents corresponding to the maximum and minimum widths in the hysteresis loops increases with decreasing temperature exponentially. We propose that the fishtail magnetization in this compound is due to the presence of a surface barrier and the pinning of collective 2-D vortices. The initial peak in magnetization is due to the presence of Bean–Livingston surface barriers and the larger peak in M at higher H corresponds to 2-D pinning.
A three-material passive dI/dt limiter
Authors: Young S. J. , Dawson F. P. , Konrad A.
Published: July 2002

This article introduces and examines a composite magnetic device (called a dI/dt limiter) which functions as a bilevel inductor. For dc currents below a designed threshold level, the inductance and resistance of the device is quite low. However, the inductance of the device increases dramatically for all currents greater than the threshold level. In this article a set of performance equations are derived which describe the inductance of the dI/dt limiter as a function of current. The data obtained from these performance equations are compared to the results of a set of finite element simulations.
Investigation of the magnetic structures in giant magnetoresistive multilayer films by electron microscopy
Authors: Heyderman L. J. , Chapman J. N. , Parkin S. S. P.
Published: July 2002

The magnetic structures which occur in (Co/Ni81Fe19/Co)/Cu multilayer films showing giant magnetoresistance have been investigated using electron microscopy. Rather similar fine domains, with sub-μm dimensions, were found in films comprising 14 and 6 magnetic layers. Whilst the observed structure depended greatly on the magnetic history of the sample, a combination of differential phase contrast imaging and low angle diffraction allowed an estimate to be made of the extent to which neighboring magnetic layers were aligned antiparallel to each other. For both samples typically two layers were found to have parallel alignment leading to the possibility that departures from the expected antiferromagnetic behavior are more prevalent at the surfaces rather than in the bulk of the multilayer.
Magnetic properties of FeSi-SiO2 granular films
Authors: Jiang Z. S. , Ge X. , Ji J. T. , Sang H. , Guo G. , Du Y. W. , Zhang S. Y.
Published: July 2002

The ferromagnetic resonance (FMR) spectra and coercivities of FeSi-SiO2 granular films have been measured over a wide range of FeSi volume fractions (fv). The films were prepared using the ion-beam sputtering technique and transmission electron microscopy showed that the FeSi alloy granules are embedded in a matrix of SiO2. An enhanced coercivity (Hc), as high as 329 Oe at room temperature, is observed. For some samples, there are several resonance peaks in the FMR spectra, which include one major peak and several minor peaks. The major and minor peaks correspond to the usual uniform mode and spin-wave respectively. In our experiments, the field separations between the major and the minor peaks show a complex fashion. Our results are discussed in comparison with some theoretical models.
Mesoscopic model for the primary response of magnetic materials (invited)
Authors: Chamberlin R. V.
Published: July 2002

A model for the relaxation of thermal fluctuations is applied to the dynamical response of magnetic materials. Systems investigated include paramagnets, spin glasses, and ferromagnets. The key feature which distinguishes the model is that it describes the behavior of localized normal modes (e.g., magnons), not barrier hopping or domain-wall motion. Mathematical approximations to the model reproduce several previously used empirical formulas, such as the stretched exponential, power-law, and logarithmic time dependences, but the unapproximated model gives generally better agreement with observed response. Data of sufficient quality and range allow quantitative confirmation of all assumptions of the model. The model provides a common physical basis for observed magnetic after-effects, the magnitude and distribution of Landau–Lifshitz damping parameters, and 1/f noise.
Study on the effect of the previous hydrogenation of the nitride formation of a Sm2Fe17(4 at. % Nb) alloy
Authors: Kwon H. W. , Harris I. R.
Published: July 2002

In order to find an effective means of production of the interstitial Sm2Fe17Nx-type nitride, an alloy modification by the addition of small amount of alloying element (4 at.% Nb) and a hydrogenation treatment prior to the nitriding process have been employed. The effect of previous hydrogenation on the nitride formation of the Sm2Fe17(4 at. % Nb) alloy has been investigated systematically by means of thermopiezic analysis, thermomagnetic analysis, and vibrating sample magnetometer. It has been found that the previous hydrogen treatment facilitates significantly the formation of the nitride, and this may be due to the clean surface and the finer size of the particles caused by the hydrogen decrepitation. It has also been found that the combination of the alloy modification with the addition of Nb and the previous hydrogen treatment can be utilized effectively for the production of a Sm2Fe17Nx-type nitride.
Energy band structures of Si-SixGe1−x superlattices
Authors: Cole J. Vernon , Lee Hong H.
Published: July 2002

Energy band structures are presented for three different types of Si-SixGe1−x superlattices using an approach more rigorous than the envelope function approach and including spin-orbit and strain effects. The directness of the energy bands has been found to depend exclusively on the superlattice period. The energy extrema of the valence and conduction bands depend primarily on the thickness of the well material. The valence-band energy maxima vary much more with layer thickness than the conduction-band minima. The maximum attainable band gaps correspond approximately to the band gap of the germanium-containing material.