bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a negative hydrogen ion source for tandem proton accelerator using transformer couled plasma sources
Authors: Hong I. S. , Hwang Y. S. , Cho Y. S.
Published: July 2002

A negative hydrogen ion source based on the transformer coupled plasma (TCP) source has been developed for 1.75 MeV tandem proton accelerator to detect underground explosives and mines. The TCP-based ion source has been designed and constructed for H− beam currents of 10 mA at the extraction voltage of 30 kV. High-density hydrogen plasmas of 1012 cm−3 are generated by 13.56 MHz radio frequency (rf) power with the threshold power of 1 kW. Negative hydrogen beam currents of up to 0.7 mA at the extraction voltage of 30 kV are extracted with the rf power of 1.5 kW. Extracted beam currents follow the magnitudes of plasma densities which can be adjusted by changing rf power and neutral gas pressure. The e/H− ratio of down to 70 has been achieved with a simple magnetic filter.
Effect of plasma electrode position on the beam intensity of heavy ions from a RIKEN 18 GHz electron cyclotron resonance ion source
Authors: Higurashi Y. , Nakagawa T. , Kidera M. , Aihara T. , Kase M. , Yano Y.
Published: July 2002

To investigate the effect of the plasma electrode position on the beam intensity, we measured the beam intensity of Ar ions, with various charge states as a function of the electrode position. In this experiment, we observed that the beam intensity of highly charged Ar ions is strongly dependent on the electrode position and that there is the suitable position to maximize the beam intensity. The optimum position varies with the charge state of ions. The beam intensity of 1.3 mA for Ar8+ was obtained at the optimum plasma electrode position.
Production of low energy, high intensity metal ion beams by means of a laser ion source
Authors: Gammino S. , Torrisi L. , Andò L. , Ciavola G. , Celona L. , Láska L. , Krasa J. , Pfeifer M. , Rohlena K. , Woryna E. , Wolowski J. , Parys P. , Shirkov G. D.
Published: July 2002

The ECLISSE (ECR coupled to Laser Ion Source for charge State Enhancement) project started in 1999 with the aim to obtain an intense beam of highly charged ions (pulsed mode) by means of the coupling between a laser ion source (LIS) and an electron cyclotron resonance (ECR) ion source. The major points to be investigated appeared to be the coupling efficiency between the ion beam produced by the LIS and the ECR plasma, as well as the possibility to enhance the available charge state by an ECRIS with respect to the standard methods which are used to produce ion beams from solid samples (e.g., evaporation, sputtering). The calculations have confirmed that this concept may be effective, provided that the ion energy from the LIS is lower than a few hundred eV. The main features of the calculations will be shown, along with the results obtained in the off-line test facility at laser power densities below 1011 W/cm2.
Flexible electrochromic reflectance device based on tungsten oxide for infrared emissivity control
Authors: Bessière A. , Marcel C. , Morcrette M. , Tarascon J-M. , Lucas V. , Viana B. , Baffier N.
Published: July 2002

Instead of the usual sputtered anhydrous tungsten oxide thin films, a powder of monohydrated tungsten oxide (WO3.H2O) was used for the making of an electrochromic infrared emissivity modulator. The WO3.H2O powder was embedded in a porous plastic matrix before being laminated with other appropriate layers of the battery-like device, leading then to a complete flexible emissivity modulator. The widely open structure of the hydrated tungsten oxide makes lithium intercalation easier, which is particularly suitable for the realization of plasticized devices. Compared to a classical battery assembly, a porous plastic graphite layer laminated with a conductive grid was sandwiched between the WO3.H2O and the electrolyte layers. Such an original device allowed both a perfect uniformity in current collection and a sufficient porosity for the liquid electrolyte displacement. The complete device demonstrated a satisfying electrochemical behavior under 1 mV/s potential sweeps, allowing the insertion of a large amount of lithium ions into the WO3.H2O structure. Hemispherical reflectance measurements were carried out both over the VIS/NIR (0.4–2.5 μm) and the mid-infrared (2.5–25 μm) spectral ranges. Reflectance over the 2.5–25 μm spectral range was found to switch from 2% to 32% upon intercalation of 0.65 Li per tungsten. This value is comparable to previous literature results obtained for rigid devices.
Equivalent-time sampling force microscopy using pulse position modulation method
Authors: Said R. A.
Published: July 2002

This paper presents a homodyne pulse-sampling electrostatic force microscopy technique using a pulse position modulation method for the noncontact measurement of internal voltage waveforms in integrated circuits. The measurement system operates by monitoring the mechanical deflection of a micromachined probe as it responds to electric forces induced by the circuit voltage waveform. Although the mechanical response of typical probes used in such systems is limited to few kHz, measurement of high frequency repetitive waveforms is enabled by applying a high speed sampling pulse signal to the probe with the pulse position modulated at a rate below the probe mechanical resonance. This results in down conversion of the circuit induced electric force harmonics to within the probe mechanical response, thus allowing the measurement of high frequency signals. The proposed technique is modeled using Fourier analysis of the measurement system response, and is demonstrated by the measurement of a 0.8 Mbit/s digital pattern on a CMOS test pad. The performance of the measurement system is analyzed based on obtained measurements and simulated system response. An analysis of the method capabilities shows a measurement sensitivity of 13 mVrms/√Hz.
Connecting a sapphire window to a high pressure flange
Authors: Baroni P. , Pépy G.
Published: July 2002

In pressure cells, optical windows are usually fastened to clamping disks by a metallic cover and screws. We show that it is possible instead to glue the window on the disk through a polymer composite made of a polyimide foil between melted fluorinated coatings.
Permanent magnet PIG ion sources and injectors used in RFQ accelerators
Authors: Jinxiang Yu , Chia-erh Chen , Xiaotang Ren , Zhizhong Song , Zhongyi Wang , Zhengfang Zhang , Weijiang Zhao
Published: July 2002

Two kinds of PIG ion sources with permanent magnets and the injector used for radio frequency quadrupole (RFQ) are described here. The O+ and O− ion beams of 1–2 mA can be extracted from both sources and the ion ratio of both O− and O+ ions is 70%–80%. The beam lines of the injector were calculated with the program LEADS. The injector is used in our 300 kV and 1 MV integral split ring RFQ successively, and the beam transmission of the injector system is about 70%–80%. The O+ and O− ion beams were accelerated singly or simultaneously. Several hundred μA of O+ and O− ion beams after the both RFQs were measured, and the total current of O+ and O− ion beams simultaneously accelerated is much larger than that of O+ or O− ion beam accelerated singly.
Effect of argon additive in negative hydrogen ion sources
Authors: Bacal M. , Nishiura M. , Sasao M. , Hamabe M. , Wada M. , Yamaoka H.
Published: July 2002

Using the photodetachment technique we investigated the hydrogen negative ion density in the extraction region of a magnetically filtered multicusp ion source when argon is added to hydrogen. We found that the negative-ion density goes up at most by a factor of 1.5 when argon is added to low base hydrogen pressure (0.05 or 0.1 Pa), but goes down when argon is added to higher initial hydrogen pressure (0.5 or 1 Pa). Adding argon did not enhance the Werner and Lyman bands in the vacuum ultraviolet, which indicates that argon addition does not increase the production rate of vibrationally excited H2 molecules. The increase of the negative-ion density by adding argon into a low-pressure hydrogen discharge is probably due to the increase of the low-energy electron density.
Permanent magnet plasma lens
Authors: Goncharov A. , Gorshkov V. , Gubarev S. , Dobrovolsky A. , Protsenko I. , Brown I.
Published: July 2002

We have designed and fabricated, for the first time, a simple, compact, and low-cost electrostatic plasma lens based on the use of permanent magnets rather than an electrically driven solenoid to establish the magnetic field. Characteristics of the focused ion beam passed through the lens have been measured. Some of the beam characteristics depend strongly on the applied magnetic field strength and the precise form of the external potential distribution applied along the lens electrodes. The experimental results obtained at the Institute of Physics (Kiev) and at the Lawrence Berkeley National Laboratory (Berkeley) show that this plasma optical device can be used beneficially for focusing and manipulating moderate energy, large area, heavy metal ion beams.
Measurement of the beam emittance of the Frankfurt proton source
Authors: Hollinger R. , Volk K. , Klein H.
Published: July 2002

For the International Fusion Materials Irradiation Facility project (IFMIF) the Institut für Angewandte Physik at the University of Frankfurt is concerned with developing a high current proton/deuteron ion source. The 1999 “Frankfurt 200 mA Proton Source” is a volume type belonging to the high-efficient ion-sources family. This type of ion source has proven its capability to produce high-current ion beams of a single mass-to-charge ratio at very low-beam emittances. The arc discharge ion source delivers a 200 mA full beam (93% protons) at 55 keV with very high-beam intensities (outlet aperture 8 mm diam). Thus, the beam requirements for the IFMIF project are fulfilled. After having done the basic plasma investigation with a 127° cylinder spectrometer, the quality of the ion beam was a point of interest. Therefore, the beam emittance was measured with a conventional slit-grid measurement device. The goal was to measure the beam emittance at high-beam currents. The article will give a detailed description of the measurement of a 56 mA beam at 26 keV with 85% protons. Theoretical considerations of the emittance value, given by ion temperature and aberrations of the extraction system, allows an estimation of the emittance of a 170 mA at 55 keV proton beam. In a second step, an estimation of a postaccelerated 140 mA at 100 keV deuteron beam was completed.
Developing high brightness beams for heavy ion driven inertial fusion
Authors: Kwan J. W. , Anders A. , Bieniosek F. M. , Chacon-Golcher E. , Henestroza E. , Leung K. N. , Ahle L. A. , Grote D. P. , Molvik A. W.
Published: July 2002

Heavy ion fusion (HIF) drivers require large currents and bright beams. In this article we review the two different approaches for building HIF injectors and the corresponding ion source requirements. The traditional approach uses large aperture, low current density ion sources, resulting in a very large injector system. A more recent approach merges high current density mini-beamlets into a large current beam and significantly reduces the injector size. Experiments are being prepared to demonstrate this approach.
Topography of an electron cyclotron resonance plasma in the vacuum-ultraviolet spectral range
Authors: Grübling P. , Hollandt J. , Ulm G.
Published: July 2002

The plasma topography of the vacuum-ultraviolet (VUV) radiation source ELISA (electron cyclotron resonance light source assembly) was investigated. ELISA is operated at a VUV spectrometer which allows two-dimensional images of the axially observable plasma shape to be taken with a spatial resolution of 150 μm in the spectral range from 40 to 400 nm. The VUV radiance profile of the electron cyclotron resonance plasma was investigated for different working conditions of the source, with the source operated with nitrogen and krypton. Under specific operating conditions, the observed plasma radiance profile shows a structure similar to calculations performed by the group of Andrä. It was shown for the first time that the plasma topography can be interpreted by an electron density distribution as simulated there for a monomode electron cyclotron resonance ion source.
Comparative study of time-resolved K-shell spectra from aluminum plasmas generated by ultrashort laser pulses at 395 and 790 nm
Authors: Andiel U. , Eidmann K. , Witte K. , Uschmann I. , Förster E.
Published: July 2002

A comparative study of temporally and spectrally resolved K-shell emission from aluminum targets heated with 150 fs Ti:sapphire laser pulses at 790 and 395 nm is presented at an intensity of 5×1017 W/cm2. Whereas at 395 nm spectrally broad intense plasma lines and a weak Kα line with durations (full width at half maximum) of 1–2 ps are observed, the spectrum at 790 nm shows weak narrow plasma lines and an intense Kα line with durations of 3–5 ps.
Development of a low-energy oxygen 14 ion beam (abstract)
Authors: Burke J. T. , Wutte D. , Vetter P. , Freedman S. J. , Fujikawa B. K. , Lyneis C.
Published: July 2002

At the 88 Inch Cyclotron at the Lawrence Berkeley National Laboratory (LBNL) we have developed an intense (3×107 pps), low-energy O14 ion beam for precision tests of the standard model. The 70 s half-life of O14 requires on-line production of the isotope. O14 is produced in the form of C1412O in a high-temperature carbon aerogel target using a 20 MeV He3 beam from the LBNL 88 Inch Cyclotron via the reaction C12(3He,n)14O. In order to minimize the background radiation for the experiments, the O14 atoms must be separated from the other radioactive isotopes produced in the carbon target. For this purpose, we have developed an experimental setup including the target, transfer line, the electron cyclotron resonance ion source IRIS, and a low-energy ion beam transport line. The major components of the setup are described. The release and transport efficiency for the CO molecules from the target through the transfer line was measured for various target temperatures. The on-line and off-line ion source efficiencies for radioactive and stable oxygen beams are presented.
Status of ion source development for the KSTAR neutral beam system (abstract)
Authors: Oh B. H. , Seo C. S. , Chang D. H.
Published: July 2002

A high-current, high-energy, and long-pulse positive ion source for the KSTAR neutral beam system is being developed on the basis of proven technology. The original prototype ion source was the TFTR developed by LBNL, but the accelerator slit grid brazed with shaped molybdenum tubes was a barrier for success of the copied work. In order to cover the technical and economical problems caused by the molybdenum tubes, a new OFH copper grid with circular apertures has been designed and manufactured. Cooling circuits aligned along every line of the aperture arrays are made with the help of gun drills. The test and the first experimental results of the upgraded ion source, such as high-voltage characteristics, cooling characteristics, discharge characteristics, and first beam extraction characteristics are described.
Irradiation facility for boron neutron capture therapy application based on a rf-driven D–T neutron source and a new beam shaping assembly (abstract)
Authors: Cerullo N. , Esposito J. , Leung K. N.
Published: July 2002

Selecting the best neutron source for boron neutron capture therapy (BNCT) requires optimizing neutron beam parameters. This involves solving many complex problems. Safety issues related to the use of nuclear reactor in hospital environments, as well as lower costs have led to interest in the development of accelerator-driven neutron sources. The BNCT research programs at the Nuclear Departments of Pisa and Genova Universities (DIMNP and DITEC) focus on studies of new concepts for accelerator-based DT neutron sources. Simple and compact accelerator designs using relatively low deuteron beam energy, ∼100 keV, have been developed which, in turn, can generate high neutron yields. New studies have been started for optimization of moderator materials for the 14.1 MeV DT neutrons. Our aim is to obtain an epithermal neutron beam for therapeutic application at the exit end, with minimal beam intensity losses, the specific goal is to achieve an epithermal neutron flux of at least of 1×109 n/cm2 s at the beam port, with low gamma and fast neutron dose contamination. According to the most recent neutron BNCT beam parameters some moderating and spectrum shifter materials and geometrical configurations have thus far been tested, and neutron and gamma beam data at beam port have been computed. A possible beam shaping assembly model has been designed. This research demonstrates that a DT neutron source could be successfully implemented for BNCT application, with performance surpassing the minimum requirements stated above, using DT neutron sources with yields in the range 1013–1014 n/s. The latest Monte Carlo simulation results of an accelerator based facility which relies on a rf-driven DT fusion neutron generator will be presented.
Quantum dynamics of the D2+OH reaction
Authors: Zhang Dong H. , Yang Minghui , Lee Soo-Y.
Published: July 2002

This paper presents fully converged integral cross sections for the D2(j1=0,2,4)+OH(j2=0,2,4)→HOD+D reaction on the YZCL2 potential energy surface. It is found that the influence of reagent rotation excitation on reactivity is relatively mild compared with that of the D2 vibration excitation, but is fairly important to the thermal rate constant at low temperature. In general, the OH rotation excitation tends to hinder the reaction, and the D2 rotation excitation tends to enhance the reactivity. The simultaneous reagent rotation has some correlated effect, with the influence of the D2 rotation excitation considerably dependent on the OH rotation excitation. It is also found that the reaction is strongly dependent on j12 (the coupled angular momentum between j1 and j2), K0 (the projection of the reagent rotation on the body fixed axis), and the parity of the system, in particular for either the OH or D2 rotationally excited initial states, but this dependence becomes relatively weaker as the collision energy increases. Excellent agreement achieved between theory and experiment on the thermal rate coefficients for temperatures up to 400 K clearly shows that the YZCL2 potential energy surface is capable of producing “quantitatively” accurate results for the title reaction.
Transport coefficients at metastable densities from models of generalized hydrodynamics
Authors: Srivastava Sudha , Das Shankar P.
Published: July 2002

The fully wave vector dependent extended mode coupling model is studied with the inclusion of an additional slow variable of the defect density for the amorphous system. We use the extremely slow relaxation of the density correlation function observed in the light scattering experiments on colloids to estimate the input parameters for the model. We demonstrate here that even in the case of colloids, the mode coupling model with an ergodicity restoring mechanism is applicable. We compute the enhancement in the long time transport coefficients which in the present case are finite unlike the simple version of the model.
Co/Pd multilayer media with Pd inorganic granular seed layer for perpendicular recording
Authors: Matsunuma S. , Yano A. , Fujita E. , Onuma T. , Takayama T. , Ota N.
Published: July 2002

We have investigated the Co/Pd multilayer media with a Pd–SiN granular seed layer as perpendicular recording media. The Pd–SiN granular seed layer and the Co(0.2 nm)/Pd(0.8 nm) multilayer were formed by dc and rf sputtering at room temperature on a FeTaC soft magnetic underlayer. The Pd–SiN granular seed layer of 3 nm was very effective to get good magnetic properties with coercivity of 3.9 kOe, a nucleation field of −2.1 kOe, and a M–H slope parameter 4π(dM/dH)H=Hc of 1.4. In addition, it was found that growth of multilayer grains is sensitive to surface conditions of the soft magnetic underlayer. The average column diameter of 13.7 nm with a dispersion of 21.7% was evaluated from the plan-view transmission electron microscope image of well-separated Co/Pd columns with a boundary, which was grown on the Pd–SiN seed layer and the soft magnetic underlayer with Ar plasma etching. Atomic force microscope measurements showed that mean roughness (Ra) of the FeTaC surface decreased from 0.46 to 0.39 nm by the plasma etching. This surface treatment on the soft magnetic underlayer gave better signal to noise ratio by 1.6 dB in playback performance by using of a spin stand with a merged-type ring writer and giant magnetoresistance reader.
Temperature dependence of anisotropy in exchange biased Fe/KCoF3 system
Authors: Malkinski L. , Cramer N. , Hutchison A. , Camley R. , Celinski Z. , Skrzypek D.
Published: July 2002

We used molecular beam epitaxy to deposit a novel ferro-/antiferromagnet (Fe/KCoF3) system on gallium terminated GaAs (100) substrates. We varied the thicknesses of single crystal Fe (001) layers from 1.05 to 3 nm. The antiferromagnetic fluoride, with a thickness of 30 nm, was deposited either in a single-crystal or a polycrystalline form, depending on the deposition conditions. KCoF3 is an antiferromagnet with a Néel temperature of 114 K. Its cubic structure almost perfectly matches the Fe film structure. The growth was monitored by reflection high energy electro diffraction. The magnetic properties of the system were studied using ferromagnetic resonance. Uniaxial and unidirectional anisotropy fields, due to exchange bias, were measured at low temperatures in the field-cooled samples and were smaller than 45 and 72 Oe, respectively. Both anisotropy fields, unidirectional and uniaxial, decreased with increasing thickness of the Fe film or with increases in temperature. The temperature dependence of the fourfold anisotropy was studied for the samples with different thicknesses of Fe films and different crystalline states of the fluoride layer. Room temperature values of the fourfold anisotropy also increased with increasing thickness of the Fe layer and were in a fairly good agreement with previously reported values for single crystal Fe films. Also, the temperature characteristics of the fourfold anisotropy for the structures with single crystal fluoride seemed to reproduce low-temperature literature data for Fe (001) films. In contrast, the structures with polycrystalline KCoF3 demonstrated a significant enhancement of the fourfold anisotropy at low temperatures. For the thinnest sample (tFe=1.05 nm) the low temperature anisotropy is more than tripled compared to room temperature values. It is believed that the surface effects can be responsible for this enhancement.
Mn diffusion in the plasma oxidized AlOx insulation layer in the magnetic tunnel junctions
Authors: Lee J. H. , Yoon C. S. , Kim C. K. , Yuh J. H. , Kim Y. W.
Published: July 2002

The extent of Mn diffusion to the plasma-oxidized AlOx tunnel barrier in the magnetic tunnel junctions is explored using Rutherford backscattering spectroscopy (RBS) and Auger electron spectroscopy (AES). A thin film stack consisting of Ta/AlOx/CoFe/IrMn/NiFe/Ta is deposited with the AlOx layer treated under different plasma oxidation durations. When the film stack is annealed at 300 °C, RBS and AES analysis showed that the Mn diffusion to the AlOx layer progressively increased as the tunnel barrier layer is overoxidized. The Mn diffusion appears to be enhanced and controlled by the presence of the oxygen near the tunnel barrier due to the relatively high oxygen affinity of Mn. This observation implicates that the oxidation condition of the tunnel barrier not only determines the as-deposited state of the junction, but also has a large bearing on the thermal stability of the exchange-biased tunnel junctions.
Lattice effects and phase competition in charge ordered manganites
Authors: Rivadulla F. , Hueso L. E. , Miguéns D. R. , Sande P. , Fondado A. , Rivas J. , López-Quintela M. A. , Ramos C. A.
Published: July 2002

A complete characterization of the magnetotransport and magnetoelastic properties of two classical examples of half doped manganites, Nd0.5Sr0.5MnO3 (NSMO) and La0.5Ca0.5MnO3 (LCMO), was carried out by electrical resistivity, magnetoresistance, thermoelectric power, electron spin resonance (ESR), and thermal expansion measurements. We have identified a mixed paramagnetic (charge localized) plus ferromagnetic (FM) (conductive) state between the low temperature antiferromagnetic (AF) and high temperature paramagnetic (itinerant) phases, which in the case of LCMO exists over a temperature range of about 100 K. The magnetic field completely separates the FM and AF phases, suppressing the intermediate paramagnetic-localized phase. This mixed state is only observed in a narrow temperature interval for NSMO, and shows how the relative strength of the competing phases can be tuned by the lattice distortion. We also observed a large gap at the charge ordering temperature in the activation energy of the resistivity, which is almost independent of the sample. ESR results will be presented to show that this technique could be a very useful tool with which to investigate the multiphase microscopic state characteristic of manganites.
Magneto-optical properties of scandium-substituted ytterbium iron garnet single crystals
Authors: Ostoréro Jean , Guillot Maurice
Published: July 2002

This article deals with the investigation of temperature and magnetic field dependencies of the Faraday rotation (Fr) in the scandium-substituted ytterbium iron garnet Yb3Fe5−xScxO12 (x=0.5) (YbIG: Sc) single crystals regarding the contributions from magnetic sublattices. Fr was measured at 1152 nm wavelength in the 6 K–TNéel temperature range under a magnetic field up to 20 kOe applied parallel to the three principal crystallographic directions. When T<20 K, a strong anisotropy (larger than 30%) of Frspont is observed with [111] corresponding to the “easy” axis, [100] the “hard” and [110] to intermediate ones, respectively. It is worth noting that contrary to other ferrimagnetic garnets, χF is positive for [111]. A strong χF anisotropy is found below 20 K. Even if, because of the Sc substitution, the magnetic compensation point has disappeared, a magneto-optical compensation point is still observed as in pure YbIG. Through the analysis of rare earth contribution to Fr, the first-order electric dipole transition coefficient of the Yb3+ ion is strongly temperature dependent as observed also in pure YbIG.
Effect of seed layers in improving the crystallographic texture of CoCrPt perpendicular recording media
Authors: Roy Anup G. , Laughlin David E.
Published: July 2002

In this work, we have systematically investigated the effect of Ti and Ta seed layers on the improvement of c-axis alignment of the CoCrPt film. We studied the film texture by x-ray diffraction and electron diffraction, and microstructure and morphology by high-resolution transmission electron microscopy. Both Ti and Ta improve the texture of CoCrPt perpendicular magnetic media depending on the seed layer thickness. The 5–10-nm thick seed layer shows the best c-axis alignment of CoCrPt films when the seed layer is amorphous. The c-axis alignment of magnetic layer deteriorates for random texture and mixed amorphous and crystalline microstructure of the seed layer. The texture of the magnetic layer improves for the film with about 40-nm-thick seed layer with the development of favorable texture in seed layer and with occasional epitaxial growth on seed layer.
The effect of the interlayer on the exchange bias in FeMn/Cu/Co system
Authors: Wang J. , Wang W. N. , Chen X. , Zhao H. W. , Zhao J. G. , Zhan W. Sh.
Published: July 2002

The effect of the Cu interlayer on the exchange bias in FeMn/Cu/Co trilayers has been investigated. It is found that a thin interlayer can lower the strength of the exchange coupling between antiferromagnetic and ferromagnetic layers. The temperature dependencies of the left and right coercivities show an entirely different behavior, and they are very similar, when the Cu is thin, to those of a FeMn/Co bilayer with a very thin antiferromagnetic layer. With increasing the thickness of the Cu interlayer, the bias field decreases in most cases, but at low temperature it still remains large even when the Cu thickness is as thick as 1.8 nm. When the temperature is lower than 150 K, the dependence of the exchange bias on the Cu interlayer thickness exhibits a fluctuation behavior. This behavior disappears gradually with increasing temperature.
Diameter dependence of the giant magnetoimpedance in hard-drawn CoFeSiB amorphous wires
Authors: Hu Jifan , Qin Hongwei , Zhang Fuzhong , Zheng R. K.
Published: July 2002

The as cast CoFeSiB amorphous wire with 135 μm was drawn out to wires with diameters of 84, 64, and 40 μm, respectively. The magnetoimpedance of the hard-drawn wires were investigated in comparison with the as cast one. For the hard-drawn wire of diameter 64 μm, the magnetoimpedance ratio ΔZ/Z0 can reach 269.9%. There is a transform of the domain structure from the inner core longitudinal to the circular in hard-drawn wires compared with the as cast one. The frequency dependence of the magnetoimpedance in longitudinal and transverse cases show that both circumferential and longitudinal axial anisotropies may depend on the radial distance from the axis of the wire.
A cluster model for the viscous flow of glass-forming liquids
Authors: Fan G. J. , Fecht H. J.
Published: July 2002

A model is developed to account for the viscous flow of glass-forming liquids. We consider that a supercooled glass-forming liquid is composed of a liquid phase and some solidlike clusters which have a higher activation energy for viscous flow than the liquid regions. This approach yields a fitting equation for viscosity with a simple form η=η0 exp(E/kBT)exp(ΦT/Tg), where E is the activation energy for viscous flow at low temperatures, and Φ represents the fragility of a glass-forming system. Our results suggest that kinetic viscous flow of glass-forming liquids is closely related to their thermodynamics.
Magnetoelastic properties of epitaxially grown Co35Pd65 alloy films on Cu/Si(001)
Authors: Jeong Jong-Ryul , Kim Jonggeol , Kim Sang-Koog , Lee Jeong-Won , Shin Sung-Chul
Published: July 2002

Growth stress, magnetoelastic coupling, and growth structure of epitaxially grown Co35Pd65 alloy films on Cu/Si(001) are investigated in the monolayers regime via submonolayer sensitivity stress/magnetoelastic coupling measurements system and scanning tunneling microscopy (STM). In situ stress and STM study revealed that the formation of three-dimensional (3D) islands is a dominating stress relaxation mechanism in Co35Pd65 alloy films. The magnetoelastic coupling of Co35Pd65 alloy films, determined from the curvatures of a substrate, was found to be sensitively dependent on the alloy thickness in the thickness range of 2–10 ML: it is increased from 0.72×107 to 3.31×107 J/m3 with increasing Co35Pd65 layer thickness.
Magnetoelastic effects of iron-group ions in exchange fields
Authors: Dionne Gerald F.
Published: July 2002

Magnetoelastic properties of magnetic oxides can be enhanced by select 3dn transition ions. Spin–orbit coupling can survive in a cubic crystal field where a ground-state orbital triplet degeneracy is split by an axial deformation of the ligands. If the distortion stabilizes a singlet by a Jahn-Teller effect, there is reduced orbital angular momentum, and magnetoelastic effects are less significant; if the doublet is stabilized by a distortion of opposite sign the spin–orbit effect dominates, and the result is a strongly magnetoelastic ion. An analytical solution for the threshold of ligand distortion reversal confirms: (i) that the doublet cannot be stabilized without an exchange field, and (ii) that the smallest allowable ratio of spin-orbit coupling constant to the spontaneous distortion splitting is 2/3, which is reached only in the limit of an infinite exchange field.
Inhomogeneous broadening of single photon transitions in molecular magnets
Authors: Parks Beth , Loomis Joseph , Rumberger Evan , Yang En-Che , Hendrickson David N. , Christou George
Published: July 2002

Single photon transitions in molecular magnets provide valuable probes of the widths of energy levels. We use time-domain terahertz spectroscopy to measure the width of the transition from the ground state to the first excited state in Mn12 acetate in zero applied field. The width of this transition, approximately 5.5 GHz full width at half maximum, is too large to be caused by local magnetic fields. Experiments by Mukhin et al. rule out homogeneous broadening as the source of the linewidth [Phys. Rev. B 63, 214411 (2001)]. The linewidth can be explained if the anisotropy constant in the spin Hamiltonian is not uniform due to crystal defects such as dislocations. Since similar linewidths are observed in several other materials, we conclude that whatever disorder causes this broadening is not limited to Mn12 acetate.
The role of the exchange coupling and applied field strength in the magneto-optical effects of magnetic insulators
Authors: Yang Jie Hui , Zhang Fang , Xu You , Guillot Maurice
Published: July 2002

A theoretical investigation on the role of some microscopic parameters in the Faraday rotation (Fr) in paramagnetic and ferrimagnetic insulators is presented. Fr scales linearly with the exchange interaction and applied magnetic field H in a wide range. However, the Fr magnitude approaches saturation and then decreases as the exchange interaction continues to increase. The distinction between the spontaneous Fr and H-induced Fr is explained. The interesting difference between the dependency of Fr in 3d metals on the spin-orbit (SO) coupling strength and the similar dependency in rare earth (RE) compounds is studied. It is related to the relatively weak crystal field and exchange interaction and the relatively strong SO coupling in the RE compounds compared with the 3d metals.
Interface characterization and thermal stability of Co/Al–O/CoFe spin-dependent tunnel junctions
Authors: Lin Minn-Tsong , Ho C. H. , Yao Y. D. , Huang R. T. , Liao C. C. , Chen F. R. , Kai J. J.
Published: July 2002

A detailed study of the interface properties as well as the thermal stability has been done for the Co/Al–O/CoFe/NiFe magnetic tunnel junction, by using high resolution transmission electron microscopy equipped with energy dispersive x-ray spectrum. The Al behaves more stable against thermal annealing compared with the Fe, Co, Ni, and O elements. The reduction of the tunnel magnetoresistance ratio for the low annealing temperature (200 °C) may be caused by the spin flip scattering at oxide ion, rather than by the change in magnetic properties. The annealing at higher temperatures (300 °C and 400 °C) results in a strong interdiffusion, and in turn the disappearance of the magnetoresistance due to the shortcut of the junction.
CoB/Pd multilayers with indium tin oxide seedlayer on NiFe underlayer for perpendicular magnetic recording
Authors: Peng Wenbin , Zhu Wenzhong , Victora R. H. , Judy Jack H.
Published: July 2002

CoB/Pd multilayers have been fabricated on ultrathin (2 nm) indium tin oxide seed layers with NiFe soft underlayer for perpendicular magnetic recording. In situ heating to 230 °C was applied to increase the mobility of the boron atoms so that they can presumably migrate to the grain boundaries to promote grain segregation and inhibit grain growth. It gave a coercivity of 5 kOe and a D50 about 330 kfci for differentiated output signals. Magnetic force microscopy analysis shows that the magnetic domain size has been decreased due to the addition of B in Co layer, which may lead to better recording performances. An areal density of 11 Gb/in2 was achieved at a bit-error-rate of 10−6. As the recording was limited by the wide track width of the head, high flying height, and noisy soft underlayer, it is expected that the media has the potential of more than 30 Gb/in2 in areal density.
Undulation instabilities in laterally structured magnetic multilayers
Authors: Eimüller T. , Scholz M. , Guttmann P. , Köhler M. , Bayreuther G. , Schmahl G. , Fischer P. , Schütz G.
Published: July 2002

Undulation instabilities of magnetic domains have been observed in nanostructured strips of a ferromagnetic Fe/Gd multilayer. The novel technique of magnetic transmission x-ray microscopy, which is based on the x-ray magnetic circular dichroism, was used for imaging. Below a critical magnetic field, sinus-like modulations of the magnetic domains could be observed. At a higher rate of field induced strain rectangular patterns occur. They seem to be characteristic for the reduced lateral width of the magnetic system and are in contrast to chevron patterns observed in extended systems. The domain morphologies found in different magnetic fields H, and in nanowires of various widths Lz, have been summarized in a H–Lz “phase” diagram. An analogy with theoretical predictions for extended systems could be found.
Solvation of a solvophobic sphere
Authors: Henderson J. R.
Published: July 2002

I consider the solvation of a hard sphere, or cavity, when the solute is bigger than the solvent molecules. I point out that scaled particle theory (SPT) is not obviously suited to this regime and thus consider the consequences of re-optimizing SPT to be accurate in the large length scale regime. The significance to hard-sphere colloidal systems is found to be minor but, in contrast, is of qualitative importance to understanding the solvation of large solvophobic solutes by Argon-like liquids at low pressure, where drying phenomena occur. The relevance to hydrophobicity in water is also discussed.
Diffusion into a nanoparticle with first-order surface reaction confined within a sphere
Authors: Chen Shing Bor , Tsao Heng-Kwong
Published: July 2002

The exact series solution for the reaction rate of a spherical sink confined within a sphere is presented from reaction- to diffusion-limited condition based on the bispherical coordinate method. The reaction rate varies with the particle location and the size ratio of particle to enveloping sphere. The maximum and minimum rates take place when the particle and the confining sphere are at contact and concentric, respectively. A thin-gap analysis is employed to derive the rate expression analytically for a near contact case. While the reaction rate at near contact diverges logarithmically for a purely diffusion-limited condition, it remains finite for a fast surface reaction with finite rate constant. The average reaction rate is then calculated based on a prescribed particle distribution function. It is found that for a uniform distribution, the mean rate is at most 50% higher than that for the concentric case. Other than the hard-body interaction, additional attractive and repulsive interactions will enhance and reduce the mean rate, respectively.
Band gap changes of GaN shocked to 13 GPa
Authors: McCluskey M. D. , Gupta Y. M. , Van de Walle C. G. , Bour D. P. , Kneissl M. , Johnson N. M.
Published: July 2002

The band gap of GaN under uniaxial-strain compression was determined using time-resolved optical transmission measurements in shock-wave experiments. Shock waves were generated by impacting the GaN samples with c-cut sapphire impactors mounted on projectiles fired by a gas gun. Impact velocities were varied to provide longitudinal stresses ranging from 4.5 to 13 GPa. An abrupt increase of the band gap is observed upon shock-wave compression, followed by a slower increase. By measuring the absorption threshold before and during shock compression of the GaN layer, the band-gap shift for a particular longitudinal stress was obtained. A linear fit to the data yields a band-gap shift of 0.02 eV/GPa. Comparison with ab initio calculations show that this slope lies between the calculated bounds for isotropic and uniaxial compression. Potential reasons for the differences are indicated.
Field dependent anisotropic magnetoresistance measurements on CoFe/IrMn bilayers
Authors: Brown Heather L. , Dan Dahlberg E. , Kief Mark , Hou Chunhong
Published: July 2002

The exchange anisotropy field, along with the qualitative distribution of the local pinning field at the ferromagnetic/antiferromagnetic interface, has been studied in polycrystalline CoFe/IrMn bilayers. The exchange anisotropy was studied using both the anisotropic magnetoresistance (AMR) technique and hysteresis loop measurements. The AMR technique determines a larger value for the exchange anisotropy than the hysteresis loop technique. It is observed that Hea extracted via the AMR technique for the majority of samples shows a quantifiable dependence on the applied measurement field, even at fields much less than the exchange bias measured by hysteresis loop. It is believed that a reversible measurement of the soft dispersive moments takes place at these low fields, and that the field dependence is indicative of a distribution of the local magnetization direction.
Dust electro-acoustic and Coulomb modes in dense dusty plasmas
Authors: Verheest Frank , Shukla Padma K.
Published: July 2002

A careful derivation is given of the dispersion properties of dust electro-acoustic and Coulomb modes, existing in dusty plasmas with charge fluctuations and high dust densities. It is shown that both concepts refer to the same wave phenomenon and only differ by mathematical emphasis and physical interpretation. Because the main mechanism to sustain the waves is the response of the Coulomb shielding inside the Debye cloud, the name dust-Coulomb modes is more illustrative, even though the restoring force can be described as an equivalent electric pressure.
Balistic magnetoresistance in nanocontacts electrochemically grown between macro- and microscopic ferromagnetic electrodes
Authors: Garcı́a N. , Qiang G. G. , Saveliev I. G.
Published: July 2002

Our results prove the local origin of magnetoresistance in electrochemically deposited Ni nanocontacts. Experiments have been done using a complex setup for both in situ growth and ballistic magnetoresistance (BMR) measurements. Nanocontacts have been grown between two macroscopic Ni wires. In situ experiments with variation of the nanocontact diameter from 3 to 20 nm have been done using the same pair of wires. BMR values from 0.5% to 100% have been observed but no correlation of BMR value with the sample resistance, i.e., with the nanocontact cross section, has been found. These results show that the BMR in the nanometric size contact is determined by local geometrical and magnetic structures near the nanocontact rather than by the contact cross section itself. The hypothesis of existence of the intrinsic nonmagnetic dead layer in the ferromagnetic nanocontact is proposed to account for the BMR properties of the nanometric size contacts. Additionally, we report a BMR value of 200% in a Ni nanocontact (5 nm diameter) electrochemically grown between two nonmagnetic macroscopic gold wires. An external magnetic field has been used during the electrochemical deposition to fix the easy magnetic axis of the deposited Ni layer.
Neoclassical poloidal plasma rotation in an ion cyclotron heated tokamak revisited
Authors: Liu Caigen , Weyssow Boris
Published: July 2002

An equation for the neoclassical poloidal plasma rotation in tokamaks, which applies to ion cyclotron resonant heating (ICRH), has been obtained in an earlier work [Phys. Plasmas 8, 4390 (2001)]. The present work is devoted to a detailed study of the properties of an additional contribution arising from the non-Maxwellian part of the ion distribution. In a first approach, the effect of a temperature anisotropy is modeled by the use of a bi-Maxwellian equilibrium distribution function. In a second approach, the effect of the high energy ion tail is analyzed using the solution of a Fokker–Planck equation valid when ICRH fundamental heating is used. In both cases, a poloidal rotation speed larger than the poloidal ion sonic speed is expected at levels of ICRH power commonly encountered in tokamak experiments.
Deep levels and trapping mechanisms in chemical vapor deposited diamond
Authors: Bruzzi Mara , Menichelli David , Sciortino Silvio , Lombardi Luano
Published: July 2002

Detector-grade undoped chemical vapor deposited (CVD) diamond samples have been studied with thermally stimulated currents (TSC) and photoinduced current transient spectroscopy (PICTS) analyses in the temperature range 300–650 K. Two previously unknown defects have been identified, characterized by activation energies E1=1.14 eV and E2=1.23 eV, cross sections of about σ≈10−13 cm2 and concentrations of Nt≈1016 cm−3. They have been clearly observed by PICTS and isolated in TSC measurements by use of a fractional annealing cycle in the temperature range 300–400 K. Due to their trap parameters, in particular the high cross section, the levels corresponding to E1 and E2 are characterized by capture times of the order of 10–100 ps. A dominant TSC peak observed at ≈500 K has been also investigated and has been resolved into four components with activation energies of the order of 1 eV and cross sections in the range 10−19–10−17 cm2. Three of these levels exhibit a fast capture rate (0.1–10 ns) in spite of their small cross sections, due to their high concentration in the investigated sample. Correlating our results with room temperature charge collection studies, we propose that the observed traps with their fast capture rates can be effective in limiting the carrier lifetimes and, consequently, the charge collection efficiency of CVD diamond particle detectors
Inelastic electron tunneling spectroscopy: Capabilities and limitations in metal–oxide–semiconductor devices
Authors: Salace G. , Petit C. , Vuillaume D.
Published: July 2002

We report on inelastic electron tunneling spectroscopy of a tunneling metal–oxide–semiconductor (MOS) device over an extended energy range compared to previous results. We have clearly observed the vibrations of the hydrogen-passivated (111)Si Pb center in this extended energy range. The assignment of this mode has been confirmed by a comparison with infrared experiments. Capabilities and limitations of the technique to detect and observe molecular vibrations in tunneling MOS devices are discussed.
Laser-induced fluorescence of the CHXCFO (X=F,Cl) radicals
Authors: Inomata Satoshi , Yamaguchi Makoto , Washida Nobuaki
Published: July 2002

Laser-induced fluorescence spectra of the B̃←X̃ transition for three new halogen substituted vinoxy radicals were observed in the 306–333 nm region. The spectra of the trans- and cis-CHFCFO radicals were observed in the reactions of CHFCHF and CHFCF2 with atomic oxygen, and the spectrum of the cis-CHClCFO radical was observed in the reactions of CHClCHF and CHClCF2 with atomic oxygen. From an analysis of the laser-induced single vibronic level fluorescence, some of the vibrational frequencies could be determined for the ground electronic states (X̃); these frequencies are listed in Tables III and V. Some of the vibrational frequencies for the excited state (B̃) were also determined. These vibrational assignments are supported by ab initio calculations. The experimental results show that the electronic B̃←X̃ transition energy is increased by halogen atoms, especially by fluorine atoms at either the 1- or 2-positions. The C–C–O skeleton and the spectroscopic characteristics of trans-, cis-CHFCFO, and cis-CHClCFO are close to those of CH2CFO. It is suggested that the C–C–O skeleton of the vinoxy-type radicals is influenced more by the substitution of a halogen atom at the 1-position than at the 2-position.
Electrostatic ion-cyclotron waves driven by parallel velocity shear
Authors: Merlino R. L.
Published: July 2002

Using a fluid treatment, it is shown that electrostatic waves with angular frequencies ∼ωci (ion cyclotron frequency) propagating at large angles to the ambient magnetic field can be excited in a magnetized plasma by perpendicular shear in the magnetic field aligned plasma flow. The role of density gradients in determining the stability of shear-driven electrostatic ion-cyclotron (EIC) modes is also considered. These shear-driven modes may provide an explanation for observations of high frequency waves in the ionosphere.