bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of dielectric constant of aqueous solutions
Authors: Suresh S. J. , Naik V. M.
Published: July 2002

We apply principles of statistical mechanics to derive simple expressions relating the hydrogen bond thermodynamic properties to the static dielectric constant of aqueous solutions. The approach followed by us was to develop an expression for the dipolar correlations between a centrally fixed molecule of a given type and its neighbors present in the surrounding shells, in terms of bonding probabilities, and combine the resulting expression with the Kirkwood–Frohlich equation. We considered only those neighboring molecules which are a part of the H-bonded cluster containing the central molecule. The bonding probabilities were evaluated by assuming a reaction equilibrium model, in which the formation of clusters between different association sites was represented by a series of chemical reactions. To demonstrate the utility of the theory, we provide comparison of the results for the temperature and composition variation of dielectric constant and H-bond stoichiometry of three model systems, methanol+water, ethanol+water, and acetone+water mixtures, against available experimental/simulation data.
A water-cooled compound refractive lens as a white beam collimator
Authors: Zhao J. Y. , Alp E. E. , Toellner T. S. , Sturhahn W. , Sinn H. , Shu D.
Published: July 2002

A white beam collimator has been built to increase the efficiency of a diamond high-heat-load premonochromator. The collimator is composed of a water-cooled beryllium compound refractive lens. We demonstrate a 30% increase in spectral flux of the diamond premonochromator (at 22.6 keV) by using the collimator.
Jitter-free subpicosecond streak cameras (invited)
Authors: Belzile C. , Kieffer J. C. , Cote C. Y. , Oksenhendler T. , Kaplan D.
Published: July 2002

We review here our recent work on a high dynamic range, subpicosecond x-ray streak camera. Our subpicosecond streak camera (PX1) has been coupled to a 10 Hz Ti: sapphire laser system and tested with 500 fs UV light pulses (266 nm) in jitter-free accumulation mode. A novel design for the photoconductive switches that are coupled to the camera’s deflection plates has been successfully used to eliminate the jitter induced by the laser intensity fluctuations and by the temporal shape of the laser beam. Results demonstrate that this detection system gives simultaneously a high dynamic range and a subpicosecond resolution at a repetition rate of 10 Hz.
Application of absorption and refraction matching techniques for diffraction enhanced imaging
Authors: Hasnah M. , Oltulu O. , Zhong Z. , Chapman D.
Published: July 2002

Diffraction enhanced x-ray imaging (DEI) has simultaneous contrast sources from absorption, x-ray refraction gradients, and scatter-rejection (extinction). The combination of these contrast mechanisms generally allows many more features in objects to be observed compared to conventional radiography. In some instances or in specially prepared systems it is possible to eliminate one of the contrast mechanisms so as to create features that arise from a single contrast mechanism. With the DEI technique it is most interesting to either eliminate the absorption contrast of an object or conversely eliminate the refraction gradient contrast. We have explored both extremes of this contrast scale in order to better understand the DEI contrast mechanisms and to exploit the absence of a contrast mechanism for technical purposes.
Ultrahigh vacuum instrument that combines variable-temperature scanning tunneling microscopy with Fourier transform infrared reflection-absorption spectroscopy for studies of chemical reactions at surfaces
Authors: Beck David , Batzill Matthias , Baur Christof , Kim Jooho , Koel Bruce E.
Published: July 2002

We describe the construction of an ultrahigh vacuum chamber that incorporates variable-temperature scanning tunneling microscopy (STM), Fourier transform infrared reflection-absorption spectroscopy (FT-IRAS), Auger electron spectroscopy, low-energy electron diffraction, and temperature programmed desorption, for studying structure and reactivity at surfaces. The chamber and manipulator design enables in situ sample preparation and analysis, and rapid access to several surface-analytical techniques by rotation only. This eliminates sample inconsistencies due to ex situ preparation or the necessity to run parallel experiments. Inclusion of FT-IRAS allows us to characterize surface species and identify adsorbates during studies using STM.
The characterization of a magnetron-sputter-type negative-ion source
Authors: Paik Nam-Woong , Kim Steven
Published: July 2002

Characteristics of an 8-in.-diam magnetron-sputter-type negative-ion source (MSNIS) were investigated. A negative sputtered ion beam is generated by a cesium-induced sputter type secondary negative-ion beam emission process. The plasma properties were obtained using a cylindrical Langmuir probe method. The measured electron temperature was approximately 2–5 eV, while the plasma density and plasma potential were of the order of 1011–1012 cm−3 and 5–20 V, respectively, depending on the pressure and power. A retarding field analyzer with four biasable grids measured the energy distributions of sputtered Mo− beams. The transparency of the analyzer was 22.4%. The negative-ion energy is defined by the potential of sputter cathode. The process pressure was found to have a negligible effect on ion-beam energy, but did affect the ion-beam energy spread. At low pressures (approximately 4×10−4 Torr), the energy spread was 2% of the beam energy, while an average energy spread of less than 5% of beam energy was measured at 10−3 Torr. The result shows that a well-defined negative metal ion beam can be effectively produced on a large scale.
Magnetoresistive properties of Pr0.65Ca0.21Sr0.14MnO3 ferromagnets: Evidence of phase separation
Authors: Hejtmánek J. , Jirák Z. , Maryško M. , Martin C. , Maignan A. , Tomioka Y.
Published: July 2002

Perovskite manganite Pr0.65Ca0.21Sr0.14MnO3 prepared as single crystal and ceramic specimens have been studied using magnetic, transport, and thermal measurements. All samples are identical metallic ferromagnets with TC=204 K, nonetheless, unusual thermal hysteresis of magnetic susceptibility, electrical resistivity, and thermoelectric power were observed for polycrystalline samples. In connection with the critical proximity of the Pr0.65Ca0.21Sr0.14MnO3 ferromagnet to an antiferromagnetic charge-ordered insulator suggests a link between the magnetic and transport behavior and phase instability and/or phase separation. We surmise more macroscopic phase separation in ceramics with the minor insulating phase associated with, or directly segregated in, the integrain regions whereas in a single crystal microscopic effects or dynamic phase fluctuations may occur.
Sputter growth and magnetic properties of exchange-biased La1/4Ca3/4MnO3–La2/3Sr1/3MnO3 epitaxial bilayers
Authors: Magnoux D. , Hrabovsky D. , Baules P. , Casanove M. J. , Snoeck E. , Fert A. R. , Bobo J. F.
Published: July 2002

We have grown La1/4Ca3/4MnO3–La2/3Sr1/3MnO3 (LCMO–LSMO) thin films by reactive facing target radio frequency sputtering on SrTiO3(001) substrates. After 1 bar oxygen annealing at 800 °C, the films have the desired oxygen stoichiometry and perovskite structure. Transport properties of single LCMO films reveal the charge order (CO) transition between 100 and 180 K depending on the LCMO layer thickness while LSMO films have a Curie temperature greater than 330 K. Kerr effect measurements show evidence of an increase of the LSMO coercive field HC from ∼50 Oe at room temperature up to 110 Oe at 40 K and a significant decrease in the squareness of the hysteresis loop. This effect is accompanied by a slight shift of the hysteresis loop HE due to exchange bias between the antiferromagnetic charge ordered LCMO layer and the LSMO ferromagnet which reaches 20 Oe at 40 K. Both the onset of HE and the drop in squareness are observed to be close to the charge order transition of a similar LCMO single layer and are assumed to be related to the CO transition.
Structure and pressure effect on the properties of La0.7Ca0.3−xSrxMnO3 manganites
Authors: Ulyanov A. N. , Maksimov I. S. , Nyeanchi E. B. , Medvedev Yu. V. , Yu S. C. , Starostyuk N. Yu. , Sundqvist B.
Published: July 2002

We report a study of the structure and pressure effects on magnetic and transport properties of a lanthanum manganite, La0.7Ca0.3−xSrxMnO3 (0⩽x⩽0.3, Δx=0.03). The pressure coefficient of the Curie temperature (Tc), dTc/dP, is shown to depend on x. The temperature Tc increases approximately linearly under applied pressure as dTc/dP≈14 K/GPa in the orthorhombic (Pbnm) phase and as dTc/dP≈7.5 K/GPa in the rhombohedral (R3̄c). The value of dTc/dP shows a minimum (≈3.5 K/GPa) and the temperature of the resistance maximum, Tp(x), shows a change of slope at x=0.15, corresponding to a concentration structural phase transition. Differences between the values of dTc/dP and the slopes of Tp vs x in Pbnm and R3̄c phases are explained by the different effect of external pressure on the Mn–O bond length and the Mn–O–Mn bond angle, and by the different internal pressure effect (depending on the value of x) in those phases, respectively.
Velocity distribution measurement and two-wire field effects for electric deflection of a neutral supersonic cluster beam
Authors: Tikhonov G. , Wong K. , Kasperovich V. , Kresin V. V.
Published: July 2002

The basic principle of deflection of a beam of polarizable particles by an inhomogeneous electric field is straightforward, but its application to realistic beams having spatial and velocity distributions of finite widths requires special care. We present a detailed treatment of these issues as developed for a measurement of electric polarizabilities of alkali clusters in a continuous supersonic beam. We begin by describing a general technique for extracting the beam velocity distribution from the time-of-flight profile generated by two separate 50–50 gating choppers. This method yields accurate model-free information directly from the experimental profile, without errors associated with detector delays, and with high signal throughput. We then use a simple but accurate approximation for the deflecting field variation over space, and derive analytical expressions for the deflection of beams of finite width and finite velocity spread. This allows us to evaluate the magnitude of a number of corrections to the ideal formula; the results are applicable to optimization of various electric and magnetic field deflection experiments. Finally, we demonstrate, both theoretically and experimentally, the phenomenon of local velocity variations across the beam profile which arise as a result of deflection.
Design of laminated antiferromagnetically coupled media for beyond 100 Gb/in2 areal density
Authors: Wang J. P. , Piramanayagam S. N. , Hee C. H. , Huang L. , Pang S. I. , Chow S. K. , Shi X. , Chong T. C.
Published: July 2002

In this report, we will present our experimental and micromagnetic simulation studies to show that laminated antiferromagnetically coupled media has potentials to push the areal density beyond 100 Gbit/in2. Exchange coupling constant as high as 0.32 erg/cm2 has been obtained for basic two layer configuration by inserting an ultrathin Co interface layer between CoCrPtB and Ru layers, which is 3–4 times higher than the reported values in literature. This technique improved the thermal stability factor by more than 40%. A type of sandwich three-layer configuration for the antiferromagnetic coupled media is proposed which may double the antiferromagnetic coupling effect for the recording CoCrPtB layer. It also can further reduce the Mrt value (less than 0.2 memu/cm2) while keeping high thermal stability that may be preferred for future application once extreme high sensitivity read head appears.
Optimization of EPU6 undulator at PLS
Authors: Kim D. E. , Park K. H. , Lee H. G. , Suh H. S. , Jung Y. G. , Lee T. Y. , Chung C. W.
Published: July 2002

Pohang Accelerator Laboratory (PAL) is developing an Elliptically Polarized Undulator (EPU) to produce polarized synchrotron radiation at Pohang Light Source (PLS). The EPU6 is an Apple-II type elliptical undulator, which changes the polarization of the field by translating the quadrant arrays. The PLS EPU6 features a period of 6 cm, a minimum gap of 19 mm, 25 full field periods, a maximum vertical flux density of 0.69 T, a maximum horizontal flux density of 0.46 T, and 1575 mm total magnetic structure length. The EPU6 is optimized for highly polarized synchrotron radiation from 117 to 1500 eV at 2.5 GeV electron energy. Using correction coils to compensate the orbit drift in the undulator increased the estimated photon flux by 15% compared to the case without the compensation.
Diffraction of ultrashort XFEL pulses by perfect crystals (abstract)
Authors: Shastri S. D. , Zambianchi P. , Mills D. M.
Published: July 2002

Planned fourth generation sources, i.e., XFELs, motivate the study of dynamical diffraction effects in the interesting regime where pulse durations (femtoseconds) become comparable to or shorter than extinction lengths (microns). The transient, time-dependent diffracted intensities arising from incident delta-function impulses are calculated for Bragg and Laue geometries, examining both reflected and transmitted beams. Furthermore, the alteration of an XFEL pulse’s spiky temporal structure as it passes through single- and double-crystal monochromators is discussed for both low- and high-order reflections.
Design of an undulator white beam profiler and test results on the Advanced Photon Source beamline (abstract)
Authors: Shu Deming , Ramanathan Mohan , Singh Om , Decker Glenn
Published: July 2002

At the Advanced Photon Source (APS), each insertion device (ID) beamline front end has two x-ray beam position monitors (XBPMs) to monitor the x-ray beam position for both the vertical and horizontal directions. The XBPMs measure photoelectrons generated by the chemical vapor deposited-diamond-based sensory blades and deduce the beam position by comparison of the relative signals from the blades [D. Shu, B. Rodricks, J. Barraza, T. Sanchez, and T. M. Kuzay, Nucl. Instrum. Methods. Phys. Res. A 319, 56 (1992)]. Performance challenges for an undulator XBPM during operation are contamination of the signal from the neighboring bending-magnet sources and the sensitivity of the XBPM to the ID gap variations. Problems are exacerbated because users change the ID gap during their operations, and hence the percentage level of the contamination in the front-end XBPM signals varies. The smart XBPM system partially solved these problems [D. Shu, H. Ding, J. Barraza, T. M. Kuzay, and M. Ramanathan, J. Synchrotron Radia. 5, 632 (1998)], but it is still very difficult to eliminate the contamination of the signal from the storage ring orbit-corrector magnets. A method was proposed by G. Decker and O. Singh [Phys. Rev. ST Accel. Beams 2, 112801 (1999)] that provides a solution to the long-standing problem of stray radiation-induced signals on photoemission-based XBPMs located on the ID beamline front end. The method involves the introduction of a chicane into the accelerator lattice that directs unwanted x rays away from the photosensitive XBPM blades. This technique has been implemented at the APS. In this paper, we present the design of an undulator white beam profiler that provides experimental confirmation of this technique.
Model of sagittally bent silicon crystals diffracting in the Laue mode: Effects of elastic anisotropy on the rocking-curve widths (abstract)
Authors: Zhong Z. , Siddons D. P. , Chapman D. , Kao C. C. , Zhong N. , Hastings J. B.
Published: July 2002

Sagittal focusing of synchrotron x rays with asymmetric Laue crystals has been proposed and demonstrated [Z. Zhong, C. C. Kao, D. P. Siddons, and J. B. Hastings, J. Appl. Crystallogr., Pts I&II (submitted)]. At high x-ray energies, sagittal focusing by a Laue crystal is preferred because of the small extent of the beam’s footprint on such a crystal, and the ability to use the inverse-Cauchois geometry in the meridional plane to improve energy resolution. Reflectivity curves of sagittally bent Laue crystals were measured at x rays energies from 15 to 70 keV. A model for the diffraction properties of sagittally bent Laue crystals, which takes into account the anisotropy in the elastic property of the crystals, was developed. Analytical formulas were derived for the rocking-curve width of such crystals, including both the contribution from the lattice angle change and the d-spacing change due to sagittal bending, across the thickness of the crystal. The contribution of the orientation-dependent elastic compliance S23 is as important as S13 in the specific case of sagittally bent Laue crystals. The widths of the rocking curves, calculated using the analytical model, were compared with measurements on crystals of two different orientations (111) and (100). Good agreements were found. An interesting sign reversal in the slope of the lattice angle versus depth curve between the (111)- and (100)-oriented crystals is predicted by the model, as a result of the highly anisotropic properties of silicon crystal. Results of depth-resolved rocking-curve measurements and high-resolution diffraction, designed to confirm these theoretical findings, are discussed.
Soft x-ray microscopy and extreme ultraviolet lithography: Imaging in the 20–50 nm regime (abstract) (invited)
Authors: Attwood David
Published: July 2002

Advances in short wavelength optics, covering the range from 1 to 14 nm, are providing new results and new opportunities. Zone plate lenses [E. Anderson et al., J. Vac. Sci. Techno. B 18, 2970 (2000)] for soft x-ray microscopy [G. Denbeaux, Rev. Sci. Instrum. (these proceedings); W. Chao, Proc. SPIE 4146, 171 (2000)] are now made to high accuracy with outer zone widths of 25 nm, and demonstrated resolution of 23 nm with proper illumination and stability. These permit important advances in the study of protein specific transport and structure in the life sciences [C. Larabell (private communication); W. Meyer-Ilse et al., J. Microsc. 201, 395 (2001)] and the study of magnetic materials [P. Fischer et al., J. Synchrotron. Radiat. 8, 325 (2001)] with elemental sensitivity at the resolution of individual domains. Major corporations (members of the EUV Limited Liability Company are Intel, Motorola, AMD, Micron, Infineon, and IBM) are now preparing the path for the fabrication of future computer chips, in the years 2007 and beyond, using multilayer coated reflective optics, which achieve reflectivities of 70% in the 11–14 nm region [T. Barbee et al., Appl. Opt. 24, 883 (1985); C. Montcalm et al., Proc. SPIE 3676, 710 (1999)]. These coated optics are to be incorporated in extreme ultraviolet (EUV) print cameras, known as “steppers.” Electronic patterns with features in the range of 50–70 nm have been printed. The first alpha tool stepper recently demonstrated all critical technologies [D. Tichenor et al., Proc. SPIE 4343, 19 (2001)] needed for EUV lithography. Preproduction beta tools are targeted for delivery by leading suppliers [ASML, the Netherlands, at the SPIE Microlithography Conference, Santa Clara, CA, March 2001] in 2004, with high volume production tools available in late 2006 for manufacturing in 2007. New results in these two areas will be discussed in the context of the synergy of science and technology.
Fixed-exit monochromator based on one rotation (abstract)
Authors: Caliebe W. A. , Lenhard A. , Siddons D. P.
Published: July 2002

A fixed-exit double crystal monochromator based on one rotation has been designed for an absorption spectroscopy beamline. The first crystal is mounted in the center of rotation, while the second crystal is translated by simple mechanical means. This change of the gap distance d keeps the beam offset constant. The second crystal is tuned by a simple digital feedback system, which allows us to control both θ and χ. The first crystal is mounted in the center of rotation to improve its cooling compared to the existing boomerang design, which only allows indirect cooling. In the present design, the cooling lines are fixed on the circle and are moved together with the crystal, so that no additional force acts on the crystal. The monochromator has been tested between 5 and 11 keV for the Si(111) reflection and between 6.5 and 8 keV for the Si(333) reflection. The beam motions were less than 300 μm with the mechanism not optimized. Measurements of the Cu K edge extended x-ray absorption fine structure in CuO gave the same result as from a conventional double crystal channel-cut crystal. See J. A. Golovchenko, R. A. Levesque, and P. L. Cowan, Rev. Sci. Instrum. 52, 509 (1981).
Theoretical analysis of an anisotropic metal–semiconductor–metal optoelectronic mixer
Authors: Shen H. , Aliberti K.
Published: July 2002

We present a detailed study of the optoelectronic mixing effect in metal–semiconductor–metal detectors. Both analytical and numerical results are presented and the anisotropic effect is included in the calculations. Under transient bias voltage, the device shows two transient current responses: a fast one related to the displacement current and a slow one related to removal of carriers from the device. The mixing efficiency of the device increases with an increase in applied ac voltage and decreases with an increase in ac frequency. For anisotropic devices, rectification current exists. This rectification current varies not only with the ac voltage and optical power, but also with the ac frequency. This variation in current results in a self-clutter signal being observed in the experiments.
Experimental procedure for crevice corrosion studies of Ni–Cr–Mo alloys in natural seawater
Authors: Martin F. J. , Lucas K. E. , Hogan E. A.
Published: July 2002

An experimental procedure intended for crevice corrosion studies on Ni–Cr–Mo alloys is demonstrated. In this procedure a potentiostatic control of crevice corrosion specimens is applied to an immersible crevice cell design that uses a fluoroelastomer gasket crevice former. The procedure is demonstrated for a crevice susceptibility study on Alloy 625 in elevated temperature natural seawater, where crevice corrosion initiation and propagation are shown to be influenced by the electrochemical potential. Potentiostatic current monitoring establishes the crevice initiation time and rate of propagation, while post-mortem inspections confirm the extent of crevice damage.
Measurement of local magnetic fields in photoelectron emission microscopy by restriction of the electron beams
Authors: Nepijko S. A. , Sedov N. N. , Ohldag H. , Kisker E.
Published: July 2002

The magnetic domain structure of a single crystal of Co (0001) and of polycrystalline AlNiCo was investigated in a photoelectron emission microscope making use of partial restriction of the electron beams. An external movable magnet was used for off-axis deflection of the electron trajectories in the microscope column such that parts of the trajectories are stopped by the apertures of the electron optical elements. As a result, the contrast caused by the stray fields of the magnetic domains is significantly enhanced. The distribution of the local magnetic fields at the surface is reconstructed from the image by means of a theory on the contrast mechanism.
Interlayer segregation of Cu atoms in Ta/NiFe/Cu/NiFe/FeMn/Ta spin-valve multilayers and its influence on magnetic properties
Authors: Yu G. H. , Li M. H. , Zhu F. W. , Li Q. K. , Zhang Y. , Chai C. L. , Jiang H. W. , Lai W. Y.
Published: July 2002

Experimental results show that the exchange coupling field (Hex) of NiFe/FeMn for Ta/NiFe/FeMn/Ta multilayers is higher than that for spin-valve multilayers Ta/NiFe/Cu/NiFe/FeMn/Ta. In order to find out the reason, the composition and chemical states at the surface of Ta(12 nm)/NiFe(7 nm), Ta(12 nm)/NiFe(7 nm)/Cu(4 nm), and Ta(12 nm)/NiFe(7 nm)/Cu(3 nm)/NiFe(5 nm) were studied using x-ray photoelectron spectroscopy. The results show that no elements from lower layers float out or segregate to the surface in the first and second samples. However, Cu atoms segregate to the surface of Ta(12 nm)/NiFe(7 nm)/Cu(3 nm)/NiFe(5 nm) multilayers, i.e., Cu atoms segregate to the NiFe/FeMn interface for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers. We believe that the presence of Cu atoms at the interface of NiFe/FeMn is one of the important factors which causes the exchange coupling field (Hex) of Ta/NiFe/Cu/NiFe/FeMn/Ta to be weaker than that of Ta/NiFe/FeMn/Ta.
Landau–Lifshitz magnetization dynamics and eddy currents in metallic thin films
Authors: Bertotti G. , Magni A. , Mayergoyz I. D. , Serpico C.
Published: July 2002

An analytical technique is presented to predict the magnetization dynamics in metallic thin films subjected to a dc magnetic field perpendicular to the film plane and a circularly polarized rf field in the film plane. By neglecting exchange effects, an approximate dynamic equation is derived in which the description of magnetization dynamics within the film is formally reduced to the study of an equivalent nonconducting uniformly magnetized system characterized by an effective damping constant also including the effect of eddy currents. Under this approximation, known results about uniform magnetization modes in nonconducting systems can be applied and analytical expressions are derived for the nonuniform magnetization in the film. The conditions yielding instabilities in the film response are discussed. The approximate analytical predictions are compared with the results of numerical simulations.
Temperature and ion irradiation dependence of magnetic domains and microstructure in Co/Pt multilayers
Authors: Kusinski G. J. , Thomas G. , Denbeaux G. , Krishnan K. M. , Terris B. D.
Published: July 2002

Microstructure and magnetic properties of Co/Pt multilayers with perpendicular anisotropy were studied as a function of growth temperature (TG) and ion irradiation. With increased TG, larger columnar grain size and an improved 〈111〉 texture were observed. Up to a critical temperature (Tcrit), a monotonic increase in coercivity (HC) with TG was measured, followed by a decrease in HC with further increase in TG. Magnetic domains of films grown below Tcrit were irregular, with their submicron size decreasing gradually with increasing TG. Films grown at 390 °C>Tcrit had fine domains on the sub-100 nm length scale. Both HC and domain size were reduced after the multilayers were exposed.
Effect of precursor on overcoat properties in ion beam carbon process
Authors: Pirzada Shahid , Liu Jia J. , Li Fred , Demczyk Brian , Spaulding Dave
Published: July 2002

Overcoat thickness is continuously being decreased to achieve higher areal density in magnetic media. The mechanical integrity of thin carbon films (∼30 Å) must be robust enough to act as an effective protection against wear and corrosion. Presently, technologies such as ion beam deposition and plasma-enhanced chemical vapor deposition are replacing sputtering to produce overcoats. Ion beam carbon (IBC) technology produces ultrathin durable and corrosion resistant overcoats. In the IBC process, a hydrocarbon (CxHy) gas is used as a precursor. In this article, we report the results of our work to study the effect of hydrocarbon precursors on the properties of the overcoat produced. Different precursors such as: ethane (C2H6), ethylene (C2H4), acetylene (C2H2), and a mixture of ethylene and acetylene were used for ion-beam carbon deposition. Hydrogen content in the carbon film varied depending upon the precursor used, which subsequently affected the overcoat hardness, resistivity, and lubricant–carbon interaction, which in turn influenced the head–media interaction.
Experimental study of the replenishment of ultrathin liquid perfluoropolyether films on carbon surfaces
Authors: Mayeed Mohammed Sajjad , Kato Takahisa
Published: July 2002

An experimental study is performed on the spreading and replenishment of ultrathin liquid films of perfluoropolyether Zdol on the same carbon coated disk. Carbon coated disks are partially dip coated, producing a spreading edge of the lubricant film, using Zdol with molecular weights of 2000 and 4000 g/mol. Away from the spreading edge of the film on the same carbon coated disk, the film is scratched by a semispherical slider. An ellipsometer is then used to measure the spreading and replenishment profiles consecutively with time. Diffusion coefficients are calculated from the spreading profiles and then used to simulate the replenishment profiles from the scratched profiles by solving the diffusion equation. The results are compared with the experimentally measured replenishment profiles with time from the same initially scratched profiles. The scratch depths are 1–3 nm for the sample with an initial film thickness of 5–7 nm. The comparison shows that the replenishment of ultrathin liquid films on solid surfaces can be calculated using the diffusion coefficients extracted from their spreading profiles at least for the scratch depth of more than 0.5 nm.
Structural, magnetic, and thermal stability of IrMn exchange biased layers
Authors: Lee Chan-Gyu , Jung Jung-Gyu , McMichael R. D. , Fry R. A. , Chen Andrew , Egelhoff W. F. , Gornakov V. S.
Published: July 2002

The magnetic domain structure, magnetic properties, and thermal stability of IrMn biased top spin valves containing Co and NiFe have been investigated. The magneto-optical indicator film pictures of Ni–Fe biased IrMn spin valve show the formation and motion of domain walls that separate large domains in the free film unlike the Co biased IrMn spin valve structure with many small microdomains. From the angular dependence of the ferromagnetic resonance linewidth (ΔH) and resonance field (Hres) it was found that the IrMn biased Co film is very different from the behavior of a NiO biased Permalloy film which exhibits two-magnon scattering. To investigate the thermal stability two kinds of magnetoresistance measurements at anneal temperature (TAnn) and room temperature (TRT) following anneals were accomplished.
Correlations between coercivity and exchange bias in epitaxial NiO–Co(110) bilayers
Authors: Dubourg S. , Bobo J. F. , Ousset J. C. , Warot B. , Snoeck E.
Published: July 2002

We have sputtered epitaxial NiO–Co samples on MgO (110) substrates. NiO epitaxially grows on the isostructural fcc MgO substrate but, due to surface energy minimization, its surface morphology is saw-tooth-like with terraces aligned along [001] direction and either (100) or (010) termination planes. The obtained nanostructures are 80–200 Å wide facets with micron-size length. Subsequently deposited Co layers adopt a fcc structure conformal with the NiO nanofacets. It consists thus in a set of connected nanostripes as evidenced by complementary structural characterizations. Shape anisotropy induces a strong easy axis along the stripe edges [001] and a hard axis along the [-110] MgO direction. Magnetization loops recorded along [001] have a total squareness. Thermal treatments were done in zero field for investigating the NiO/Co exchange thermal stability and activation. We observed thermally assisted exchange bias field (HE) variations on 1000 Oe field treated samples for various temperatures between 300 K and 400 K. Similar experiments were also performed on polycrystalline bilayers for comparison. For all samples (polycrystalline and epitaxial), thermal treatments induce a HE raise with a kinetics related to the anneal temperature. However, while the coercive field HC of epitaxial samples is significantly reduced, one of the polycrystalline samples remains constant. The ferromagnetic domain wall pinning at antiferromagnetic antiphase boundaries explains both results.
Effects of transition metal substitution on the glass-formation ability and magnetic properties of Fe62Co9.5Nd3Dy0.5B25 glassy alloy
Authors: Long Yi , Zhang Wei , Wang Xinmin , Inoue Akihisa
Published: July 2002

Fe–Co–Nd–Dy–B glassy alloys are a current type of ferromagnetic material. To increase their glass-forming ability against the growth of a crystallization phase, the effects of the addition of transition metals TM (TM=V, Nb, Ta, Cr, Mo, and W) on the glass-formation ability and magnetic properties of Fe62Co9.5Nd3Dy0.5B25 glassy alloy have been investigated. The substitution of 2 at. % elements TM (=Nb, Ta, Mo, and W) for Fe and Co increases crystallization temperature Tx and decreases the onset temperature of solidification Tm, leading to a significant increase in the thermal stability against crystallization for Fe60.3Co9.2TM2Nd3Dy0.5B25. The difference (ΔTx=Tx−Tg) between Tx and the glass transition temperature Tg increases from 55 K at 0 at. % TM to 87 K at 2 at. % TM. The bulk glassy alloy with a diameter up to 1.2 mm was produced by copper mold casting. Also no distinct changes in Tg, Tx and ΔTx are seen for the addition of Cr and V. The results can be explained by the difference of atomic size in the additional elements. The saturation magnetization decreases slightly by the addition of 2 at. % TM elements. The saturation magnetization and coercive force of glassy Fe60.3Co9.2TM2Nd3Dy0.5B25 alloys are 1.13 to 1.19 T and 3.85–4.98 A/m, respectively.
Comment on “On two-dimensional magnetohydrodynamic turbulence” [Phys. Plasmas 8, 3282 (2001)]
Authors: Verma Mahendra K. , Dar Gaurav , Eswaran V.
Published: July 2002

Biskamp and Schwarz [Phys. Plasmas 8, 3282 (2001)] have reported that the energy spectrum of two-dimensional magnetohydrodynamic turbulence is proportional to k−3/2, which is a prediction of Iroshnikov–Kraichnan phenomenology. In this Comment some earlier results are reported which conclusively show that for two-dimensional magnetohydrodynamic turbulence, Kolmogorov-like phenomenology (spectral index 5/3) is a better model than Iroshnikov–Kraichnan phenomenology; these results are based on energy flux analysis.
GaN tunnel junction as a current aperture in a blue surface-emitting light-emitting diode
Authors: Jeon Seong-Ran , Oh Chang Sok , Yang Jeon-Wook , Yang Gye Mo , Yoo Byueng-Su
Published: July 2002

We have demonstrated surface-emitting GaN-based diodes with a buried tunnel junction (TJ) current aperture. The current confinement aperture for lateral injection current was defined by mesa etch of a TJ structure and regrowth of current blocking layer surrounding the TJ mesa. Lateral electron current drives a tunnel contact junction providing hole injection into the active region. The very uniform light emission just through a buried TJ aperture represents that the buried TJ structure acts very effectively as a confinement aperture of lateral current injection, particularly in GaN-based vertical-cavity surface-emitting lasers.
Characterization of ferromagnetic perovskites for magnetically tunable microwave superconducting resonators
Authors: Wosik J. , Xie L.-M. , Strikovski M. , Przyslupski P. , Kamel M. , Srinivasu V. V. , Long S. A.
Published: July 2002

An investigation of electrical, magnetic, and microwave properties is presented for Nd1−xSrxMnO3−y (NSMO) thin films. The NSMO thin films were deposited on (100)-oriented LaAlO3 substrates using both high-pressure sputtering and laser-ablation methods. Several films with different doping concentration ranging from 0.17 to 0.33 were tested for microwave loss and their frequency dependence on the dc magnetic field. The films exhibited Curie temperatures ranging from 220 to 60 K, and saturation magnetization from 0.3 to 0.1 T. The feasibility of applications of magnetic perovskites for magnetic tuning of resonators is analyzed and discussed.
Formation of MnSb during the growth of MnSi layers in the presence of an Sb flux
Authors: Matsuda K. , Takano Y. , Kuwabara K. , Tatsuoka H. , Kuwabara H. , Suzuki Y. , Fukuda Y. , Hashimoto S. , Yan Y. , Pennycook S. J.
Published: July 2002

Structural and compositional analyses of a MnSi layer have been performed to elucidate the growth mechanism. The MnSi layer was grown by reactive deposition epitaxy in the presence of an Sb flux. The existence of Sb was found at the MnSi/Si interface and on the surface of MnSi layer by secondary ion mass spectrometry. In addition, x-ray photoelectron spectroscopy measurement shows that MnSb is formed on the surface of the grown MnSi layer. On the atomic scale, scanning transmission electron microscopy observations reveal the existence of an Sb–Mn–Sb structure at the interface between the MnSi layer and the Si substrate. The formation of the MnSb plays an important role for the improvement of crystalline quality of the silicide layer, acting both as a surfactant and as a compliant substrate for stress relief.
On reflection of ion acoustic waves
Authors: Raychaudhuri Santwana , Ichiki Ryuta , Kawai Yoshinobu
Published: July 2002

Reflection of ion acoustic waves from a bipolar potential structure was studied in a double plasma device. The existence of a reflected signal, even when no external bias was applied on the bipolar reflector, could be detected, although with much lower velocity than the incident wave. Application of proper bias on such a reflector resulted in an additional reflected image with greater velocity than the reflection obtained without bias. The experiment was also extended to study negative ion plasma waves.
New adjustment technique for time coincidence of femtosecond laser pulses using third harmonic generation in air and its application to holograph encoding system
Authors: Kawamura Ken-ichi , Ito Naoko , Sarukura Nobuhiko , Hirano Masahiro , Hosono Hideo
Published: July 2002

The third harmonic generation of light (266 nm) is enhanced, sensitively depending on the time delay between a pair of pulses split from a single 800 nm femtosecond laser pulse, when they are focused and collided in air. This finding offers a convenient and widely applicable technique to detect temporal and spatial overlapping of two femtosecond pulses. This technique has several advantages over the conventional sum frequency generation method using nonlinear optical crystals, since it obviates the need for expensive crystals, free from phase matching, and elimination of temporal walk off. By applying it to “a holographic encoding system using an interference femtosecond laser pulse,” a periodic fringe spacing is minimized to ∼430 nm by extending the colliding angle between two-pulse beams up to ∼160 °C.
Recombination dynamics for photogenerated carriers in germanium-doped ZnSe epilayers grown by molecular beam epitaxy
Authors: Wang S. Z. , Yoon S. F.
Published: July 2002

Germanium-doped ZnSe epilayers have been grown on (001)-oriented semi-insulating GaAs substrates by molecular beam epitaxy. The photoluminescence (PL) spectra exhibit strong near-band edge emission similar to those from undoped, chlorine-doped and gallium-doped samples, though some differences exist. The prominent PL peak at 2.795 eV (10 K) is attributed to the germanium-bound exciton recombination and is accompanied by free exciton (2.802 eV), Ia-type exciton (2.785 eV) and Iv-type exciton (2.775 eV) emission peaks. Following an increase in temperature, the intensity of all the IGe, Ia, and Iv emission peaks decreases gradually, indicating the presence of nonradiative recombination mechanisms with thermal activation energies of 40, 70, and 50 meV respectively. However, for the Iv peak, there is one additional nonradiative recombination mechanism in accordance with the thermally activated transfer of excitons from the Iv-type centers to Ia-type centers. This nonradiative recombination mechanism with activation energy of 9 meV is responsible for the decrease of the Iv peak intensity when the sample temperature is changed from 15 to 100 K. Following an increase in temperature, the Iv peak, Ia peak, and germanium-related peak disappear gradually and successively. Finally, the PL spectrum is dominated by free exciton emission at temperatures exceeding 210 K.
Effect of the buffer anisotropy on the rigidity of artificial antiferromagnetic hard magnetic layers in spin valve structures
Authors: Colis S. , Dinia A.
Published: July 2002

We report on the magnetic and transport properties of artificially antiferromagnetically coupled CoFe/Ir/CoFe sandwiches (AAF), grown by molecular beam epitaxy on MgO(001) substrates. The sandwiches are deposited on Fe/Co/Cu/Co buffer layers and their magnetic properties are found to be strongly influenced by the anisotropy of the Fe layer. The coercive field of the AAF is HC2=600 Oe for the samples with isotropic Fe. However, when the Fe layer is anisotropic, the coercive field of the AAF is HC2=600 Oe and 400 Oe, respectively along the hard bcc Fe[110] and the easy bcc Fe[100] axes. In addition, in this second case, the rigidity of the AAF is improved. This gives rise to a sharp reversal of the magnetization vectors of the AAF and to a flat magnetization and giant magnetoresistance plateau, which is very promising for spin electronic devices.
Deep levels in strongly Si-compensated GaAs and AlGaAs
Authors: Sato Tadashige , Ishiwatari Toshio
Published: July 2002

Five electron traps were detected successfully in heavily Si-doped GaAs and AlxGa1−xAs of low Al content with a Si concentration of above 1×1019 cm−3 using deep level transient spectroscopy. The junctions were grown by liquid phase epitaxy and were strongly compensated. The traps were investigated for functions of the Si concentration and the AlAs mole fraction. The traps are discussed in terms using their spectra and concentration as opposed to the previous results which used point defects in the GaAs and AlGaAs. The traps show distinctive features, which can be attributed to strongly Si-compensated crystals. Three traps among them were confirmed to be DX centers.
Experimental and theoretical study of line mixing in NH3 spectra. I. Scaling analysis of parallel bands perturbed by He
Authors: Hadded S. , Thibault F. , Flaud P.-M. , Aroui H. , Hartmann J.-M.
Published: July 2002

Line mixing effects have been studied in the ν2 and ν1 parallel bands of NH3 perturbed by He at room temperature. Experiments have been made with a Fourier transform spectrometer covering a wide range of total pressures up to about 400 atm. Analysis of the spectra demonstrates, for the first time, that the spectral shapes of entire ammonia bands can be significantly influenced by line mixing. A theoretical approach based on the energy corrected sudden approximation (ECS) is used to predict and analyze these effects. The model parameters include dynamical factors directly computed from an NH3–He potential energy surface and a scaling length which has been determined from a fit of line-broadening data. Comparisons with measurements show that the ECS model leads to surprisingly satisfactory predictions when considering the large spacing between rotational levels. The large effects of line mixing within the Q branches and in the far wing of the absorption bands are analyzed. It is shown that purely Lorentzian calculations can lead to underestimation of the Q branch peak by a factor of up to 4, whereas the overestimation of absorption in the band wing reaches one order of magnitude. On the contrary, the proposed ECS approach leads to much better results and accounts for most of the transfers of intensity among the various spectral components. It is used for the analysis of the shape of Q branches, P and R manifolds and line wings. Remaining discrepancies are discussed in terms of the model approximations and the improper dependence of the basis dynamical factors on quantum numbers induced by uncertainties on the potential energy surface used.
Relative sizes of atoms observed in electron momentum densities
Authors: Koga Toshikatsu
Published: July 2002

The radial electron momentum densities I(p) of atoms are known to reveal several local maxima and minima. For the 103 atoms from H to Lr in their ground states, we report that the reciprocal momenta 1/pmax and 1/pmin, where pmax and pmin are the locations of the maxima and minima in I(p), respectively, have good linear correlations with the relative sizes R of atoms, defined based on the spherically averaged densities ρ(r) in position space.
Interdiffusion-based optimal quantum-well profile shaping for unipolar quantum-fountain lasers
Authors: Tomić Stanko , Ikonić Zoran , Milanović Vitomir
Published: July 2002

A method is described for the design and realization of quantum-well (QW) structures optimized in respect to gain in optically pumped intersubband lasers. It relies on finding the optimal smooth potential (QW profile) by employing supersymmetric quantum mechanics, and then using the simulated annealing method to design a suitable QW structure with a small number of layers of different composition, such that it delivers the closest approximate to the optimal smooth profile after the interdiffusion process. This route towards achieving optimal QW profiles should be much easier to apply than a direct modulation of material composition at time of growing the structure.
Terahertz complex mobility of hot electrons in 3C– and 6H–SiC at high temperature
Authors: Bezerra E. F. , Caetano E. W. S. , Freire V. N. , Lemos V. , da Costa J. A. P. , da Silva E. F.
Published: July 2002

The complex mobility of hot electrons in 3C– and 6H–SiC at 300, 673, and 1073 K is calculated through the numerical solution of balance transport equations within a nonparabolic band picture. The electric field, applied along the hexagonal c axis or [111] direction in the cubic material, is taken as the sum of a strong variable dc (200–800 kV/cm) and a weak (20  kV/cm) ac component whose frequency is varied in the 0.1–100 THz range. The real electron mobility presents a characteristic maximum peaking around 6–10 THz, while the imaginary electron mobility presents a characteristic maximum and minimum peaking around 20–40 THz and 2–5 THz, respectively. At the highest lattice temperature explored, the electron complex mobilities for both hexagonal and cubic SiC polytypes have nearly similar frequency dependent patterns.
Charge polarization effects and hole spectra characteristics in AlxGa1−xN/GaN superlattices
Authors: Assaoui Fatna , Pereyra Pedro
Published: July 2002

We study the effects of charge polarization on the extended physical properties of superlattices, such as transmission coefficients and valence band structure. We consider both linear and parabolic modulation of the band edge. Based on the theory of finite periodic systems, analytic expressions and high precision calculations of the relevant physical quantities for n-cell systems are obtained. Well-known features of these systems are identified. Besides the well-known energy band structure, we have also the field band structure, with interesting characteristics. Wider field gaps at stronger internal electric fields and higher density of field bands for larger layer widths are some of these characteristics. Well defined level density asymmetries identify the minibands induced by charge polarization or the so-called quantum confining Stark effect. We present the n-cell transmission amplitudes, transmission coefficients and miniband structures for different values of the relevant parameters.
Formation of Cu diffusion channels in Ta layer of a Cu/Ta/SiO2/Si structure
Authors: Li S. , Dong Z. L. , Latt K. Maung , Park H. S. , White T.
Published: July 2002

Three mechanisms for the formation of Cu diffusion channels in the Ta layer of a Cu/Ta/SiO2/Si structure are proposed. First, it is suggested that stacking faults formed during the recovery process induce localized regions of high internal energy in the Ta layer, from which Cu channels originate. Second, chemical reaction occurs at 800 °C and forms Ta4CuO11 across the Cu/Ta interface in Cu and Ta layers, which opens up channels for Cu diffusion. Third, triple junctions at the grain boundary of the Cu and Cu/Ta interface provide sites for the initiation of channel formation at 800 °C. At 950 °C, these channels in the diffusion barrier are absent, but Ta was oxidized into disordered Ta2O5 that may contain pathways for Cu diffusion.