bluuebunny/crossref_metadata_2025 huggingface dataset:
pVT
–Second Virial Coefficients B(T ), Viscosity η(T ), and Self-Diffusion ρD(T) of the Gases: BF3, CF4, SiF4, CCl4, SiCl4, SF6, MoF6, WF6, UF6, C(CH3)4, and Si(CH3)4 Determined by Means of an Isotropic Temperature-Dependent Potential
Authors: Zarkova L. , Hohm U.
Published: July 2002

We present results on self-consistent calculations of second pVT–virial coefficients B(T), viscosity data η(T), and diffusion coefficients ρD(T) for eleven heavy globular gases: boron trifluoride (BF3), carbon tetrafluoride (CF4), silicon tetrafluoride (SiF4), carbon tetrachloride (CCl4), silicon tetrachloride (SiCl4), sulfur hexafluoride (SF6), molybdenum hexafluoride (MoF6), tungsten hexafluoride (WF6), uranium hexafluoride (UF6), tetramethyl methane (C(CH3)4, TMM), and tetramethyl silane (Si(CH3)4, TMS). The calculations are performed mainly in the temperature range between 200 and 900 K by means of isotropic n−6 potentials with temperature-dependent separation rm(T) and potential well depth ε(T). The potential parameters at T=0 K (ε, rm, n) and the enlargement of the first level radii δ are obtained solving an ill-posed problem of minimizing the squared deviations between experimental and calculated values normalized to their relative experimental error. The temperature dependence of the potential is obtained as a result of the influence of vibrational excitation on binary interactions. This concept of the isotropic temperature-dependent potential (ITDP) is presented in detail where gaseous SF6 will serve as an example. The ITDP is subsequently applied to all other gases. This approach and the main part of the results presented here have already been published during 1996–2000. However, in some cases the data are upgraded due to the recently improved software (CF4, SF6) and newly found experimental data (CF4, SiF4, CCl4, SF6).
Spectroscopic investigation of an expanding surface wave produced plasma
Authors: Berndt J. , Douai D. , Winter J.
Published: July 2002

In this paper a spectroscopic investigation of an expanding surface wave produced plasma is presented. The electron temperature is evaluated by means of emission spectroscopy. The results show a strong and sharp increase of the electron temperature toward the end of the discharge, where the plasma is expanding into a region with lowered gas pressure.
Microstructure and magnetization reversal in nanocomposite SmCo5/Sm2Co17 magnets
Authors: Yan A. , Bollero A. , Gutfleisch O. , Müller K.-H.
Published: July 2002

A comparative investigation has been made of the microstructure and magnetization reversal behavior of nanocomposite SmCo5/Sm2Co17 powders prepared by intensive milling and subsequent annealing. It was found that the saturation magnetization increases monotonically with the increase of the volume fraction of Sm2Co17 at the expense of the coercivity. However, the remanence and the energy product first increase and then decrease with further increase of the fraction of Sm2Co17. The highest remanence of 0.72 T and energy product of 78 kJ/m3 are obtained in the powders with 80% and 60% Sm2Co17, respectively. All the hysteresis loops exhibit a magnetically single-phase behavior. X-ray diffraction results reveal that the coexistence of two phases is found in the mixture of SmCo5/Sm2Co17 powders. The demagnetization processes of the SmCo5/Sm2Co17 powders are similar to those of nanocomposites consisting of hard and soft phases, in which the exchange-spring magnet behavior was observed. Positive as well as negative deviations in Wohlfarth’s remanence analysis (δM-plot) have been observed, indicating complex magnetic interactions in these materials.
Ultrahigh vacuum preparation and characterization of TiO2/CdTe interfaces: Electrical properties and implications for solar cells
Authors: Tiefenbacher S. , Pettenkofer C. , Jaegermann W.
Published: July 2002

The semiconductor cadmium telluride (CdTe) has been grown in ultrahigh vacuum by standard molecular beam epitaxy on thin films of anatase titanium dioxide (TiO2) to investigate the interface properties of solid state injection type solar cells. These interfaces were studied by photoelectron spectroscopy and the band alignment was determined. The interface is characterized by a valence band offset ΔEV of 2.6 eV, a conduction band offset ΔEC of 0.7 eV, and a strong dipole δ of about 0.9 eV in contradiction to the electron affinity rule (Anderson model). Therefore this system is not very favorable for solar power generation.
Targeting mass-selected cluster ions for the deposition of advanced carbonaceous materials using an inductively coupled plasma
Authors: Zeze D. A. , Silva S. R. P. , Brown N. M. D. , Joyce A. M. , Anderson C. A.
Published: July 2002

Study has been initiated of the deposition of thin films using cluster ions in differing abundances generated in a pulsed inductively coupled plasma. A pulse unit controlling the “on” and “off” timing ratio of a 13.56 MHz rf power supply is used to alter systematically the composition of the contents of the plasma. Adamantane (C10H16) vapor, in argon or nitrogen, was selected as precursor for the deposition of CxHy or CxNyHz thin films using this pulsed source. The effect of varying the relative abundances of the cluster ions present in the resultant plasmas on the films produced, by changing driving power on/off ratio, is investigated. The mass-energy diagnostic data recorded under 50/150 and 150/50 μs on/off pulse sequences showed that fragmentation of C10H16 is a function of the switching ratio selected, i.e., clusters of different sizes and abundances are thus produced. Langmuir probe data also suggest that the electrical characteristics of the plasma generated under these regimes can be monitored. Postdeposition x-ray photoelectron spectroscopy (XPS) analysis of specimen films deposited under the same on/off regimes, within a 200 μs cycle, indicate clear differences are present in these films in terms of the atomic concentration, the C 1s envelope bandwidths, and profiles. Contact angle measurements and optical data performed were found to reflect the variations in the differently deposited films already indicated in the XPS data. For example, specimens deposited under a 50/150 on/off ratio show a high contact angle (low surface energy) and lower refractive index, whereas those deposited under a 150/50 ratio exhibit a low contact angle (high surface energy). Films prepared using the same precursor streams but with the further on/off ratios, 20/180, 100/100, and 20/180 μs, were also considered. Postdeposition analyses confirmed the same tends in the fragmentation behavior of C10H16. Finally, the significance of such a cluster ions selection technique is discussed.
Strong critical adsorption at the liquid-vapor surface of a nonpolar mixture
Authors: Cho J.-H. J. , Law B. M. , Gray K.
Published: July 2002

For a critical binary liquid mixture where the surface tension difference between the two components is very large, the component with the lowest surface tension completely saturates the liquid-vapor surface. The variation in the local volume fraction v(z), with depth z into the liquid mixture, is described by a universal surface scaling function P±≡P±(z/ξ±), which takes differing forms in the one- (+) and two-phase (−) regions, where ξ represents the bulk correlation length. Carpenter et al. [Phys. Rev. E 59, 5655 (1999); 61, 532 (2000)] determined P± using the ellipsometric critical adsorption data of four different critical binary liquid mixtures. A deficiency of this prior study was that each of the liquid mixtures possessed at least one polar component, which could have generated distortions in the function P±(z/ξ±). In this publication, we demonstrate that P±, determined in the previous study, provides an excellent description of the nonpolar critical binary liquid mixture 1,1,2,2-tetrabromoethane+n-dodecane.
Ab initio adiabatic and diabatic energies and dipole moments of the KH molecule
Authors: Khelifi Neji , Oujia Brahim , Gadea Florent Xavier
Published: July 2002

An ab initio adiabatic and diabatic study of the KH molecule is performed for all states below the ionic limit [i.e., K (4s, 4p, 5s, 3d, 5p, 4d, 6s, and 4f)+H(1s)] in 1Σ+ and 3Σ+ symmetries. Adiabatic results are also reported for 1Π, 3Π, 1Δ, and 3Δ symmetries. The ab initio calculations rely on pseudopotential, operatorial core valence correlation, and full valence CI approaches, combined to an efficient diabatization procedure. For the low-lying states, our vibrational level spacings and spectroscopic constants are in very good agreement with the available experimental data. Diabatic potentials and dipoles moments are analyzed, revealing the strong imprint of the ionic state in the 1Σ+ adiabatic states while improving the results. The undulations of the diabatic curves and of the triplet–singlet diabatic energy difference which we found positive, as in Hund’s rule, are related to the Rydberg functions. As for LiH, the vibrational spacing of the A state is bracketed by our results with and without the improvement taking into account the diabatic representation. Experimental suggestions are also given.
Scaling theory for the free-energy barrier to homogeneous nucleation of a noncritical phase near a critical point
Authors: Sear Richard P.
Published: July 2002

Homogeneous nucleation of a new phase near an Ising-type critical point of another phase transition is studied. A scaling analysis shows that the free energy barrier to nucleation contains a singular term with the same scaling as the order parameter associated with the critical point. The total magnetization of the nucleus scales as the response function and so it diverges. Vapor–liquid critical points are in the Ising universality class and so our results imply that near such a critical point the number of molecules in a nucleus of another phase, such as a crystalline phase, diverges as the isothermal compressibility. The case where symmetry prevents coupling between the nucleus and the order parameter is also considered.
Liquid-like ordered colloidal suspensions of lipid A: The influence of lipid A particle concentration
Authors: Thies M. , Quitschau P. , Zimmermann K. , Rusch V. , Faunce C. A. , Paradies H. H.
Published: July 2002

Electrostatically stabilized aqueous dispersions of nm-sized free lipid A particles at low volume fractions (1.0×10−4⩽∅⩽3.5×10−4) in the presence of 1.0–10.0 mM NaCl (25 °C) have been characterized by static and quasielastic light scattering (QELS) techniques, electron microscopy (SEM and TEM), conductivity measurements, and acid–base titrations. QELS and electron microscopy (ρ̄TEM=8.0±0.6%) yield similar values for the particle size and particle size distribution (ρ̄QELS=10.9±0.75 %), whereas conductivity and acid–base titrations estimate surface chemical parameters (dissociation constant, ionizable sites, and Stern capacitance). Effective particle charges were determined by fits of the integral equation calculations of the polydisperse static structure factor, S̄(Q), to the light scattering data. Using the particle properties as determined from these experiments, the polydisperse structure factor, S̄(Q), was calculated as a function of volume fraction, ∅, which was found to be consistent with a S̄(Q) dependence on the number particle density. It can be concluded that, at low volume fractions and low ionic strength, the light scattering data are well represented by a Poisson–Boltzmann model (PBC) of fluid-like ordering of free lipid A in aqueous solution. We find that the light scattering data of this dispersion are best described by a model where only a small fraction of the ionizable phosphate groups is dissociated at neutral pH. Finally, light scattering studies of lipid A dispersions of volume fractions of 3.9×10−4⩽∅⩽4.9×10−4 indicate the presence of long-range order, resulting in distinct peaks which can be assigned either to a face-centered cubic (fcc) lattice (a=51.7 nm) or a body-centered cubic (bcc) lattice (a=41.5 nm), respectively.
Enhanced low-field magnetoresistance in La2/3Ca1/3MnO3/Pr2/3Ca1/3MnO3 superlattices
Authors: Li H. , Sun J. R. , Wong H. K.
Published: July 2002

We report on the observation of enhanced low-field magnetoresistance in La2/3Ca1/3MnO3/Pr2/3Ca1/3MnO3 (LCMO/PCMO) superlattices with ultrathin PCMO layers. In particular, [LCMO(100 Å)/PCMO(10 Å)]17 superlattice exhibits magnetoresistance MR=Δρ/ρ0=−55% in a magnetic field of 500 Oe and at temperature 219 K. The enhancement is associated with the ultrasharp metal–insulator transition.
Improving SiO2/SiGe interface of SiGe p-metal–oxide–silicon field-effect transistors using water vapor annealing
Authors: Ngai T. , Chen X. , Chen J. , Banerjee S. K.
Published: July 2002

SiGe p-metal–oxide–silicon field-effect transistors (p-MOSFETs) were fabricated with ultrathin thin (∼20 Å) remote plasma chemical vapor deposition gate oxides deposited directly on SiGe. A low temperature water vapor annealing was used to improve the SiO2/SiGe interface and performance of SiGe p-MOSFETs. After the wet annealing, dangling Si and Ge bonds at the interface are passivated by atomic hydrogen, the threshold voltage of SiGe p-MOSFETs decreases from −0.39 to −0.20 V, the subthreshold slope from 117 to 87 mV/dec, and more than 20% output current enhancement is observed in these SiGe p-MOSFETs compared with Si control devices.
Epitaxial growth and characterization of CuInSe2 crystallographic polytypes
Authors: Stanbery B. J. , Kincal S. , Kim S. , Chang C. H. , Ahrenkiel S. P. , Lippold G. , Neumann H. , Anderson T. J. , Crisalle O. D.
Published: July 2002

Migration-enhanced epitaxy (MEE) has been successfully employed to grow epitaxial films of the ternary compound CuInSe2 on (001) GaAs that exhibit distinct coexisting domains of both a nonequilibrium crystallographic structure characterized by CuAu (CA) cation ordering, and the compound’s equilibrium chalcopyrite structure. X-ray diffraction, transmission electron diffraction, and Raman scattering data provide evidence for this structural polytype. Distinctive signatures of the CA polytype are found in the data from each of these methods, and their analyses are consistent with assignment of this crystallographic structure to the P4̄m2 space group. This structure is found to preferentially segregate into domains that constitute a distinct metastable phase, which may be stabilized by surface kinetic effects favored by the MEE growth process.
Two-color quantum-well infrared photodetector with voltage tunable peaks
Authors: Majumdar Amlan , Choi K. K. , Reno J. L. , Rokhinson L. P. , Tsui D. C.
Published: July 2002

A two-color quantum-well infrared photodetector with voltage tunable detection peaks is demonstrated. It is based on electron transfer between two asymmetric coupled quantum wells under an applied bias. At 10 K, the peak detection wavelength is 7.5 μm for positive bias when the electrons reside in one of the wells, and switches to 8.8 μm at a large negative bias when the electrons are transferred to the other well. The electron activation behavior of dark current in this detector depends on both temperature and bias. We observed two distinctive activation energies under negative bias for two different temperature regimes and only one under positive bias. The voltage tunability of the detector and the activation energy are well explained by the calculated energy levels and oscillator strengths of intersubband transitions in the structure.
Growth characteristics of Al oxide formed by ozone in magnetic tunnel junctions
Authors: Park B. G. , Bae J. Y. , Lee T. D.
Published: July 2002

Magnetic tunnel junctions with Al2O3 barrier layer oxidized by ozone and oxygen mixture gas (ozone atmosphere) were fabricated and Al oxidation characteristics were investigated. The tunneling magnetoresonance ratio and junction resistance of ozone oxidized junctions were 33% and several kΩ μm2. In this study, oxidation kinetics and its chemistry were investigated using transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). To study the growth characteristics of Al oxide in ozone atmosphere, the Al layers were oxidized under zero, positive, and negative bias conditions. The results of cross sectional TEM showed that the oxide thickness exposed to the ozone gas for 70 min is 3.2, 3.75, and 3.47 nm at 0, +100, and −100 V bias conditions, respectively. Both positive and negative bias accelerated aluminum oxidation. This result indicates that both electron tunneling and ion migration are rate controlling steps in this oxidation process. From the results of the angle resolved XPS, the O/Al ratio was not uniform through the oxide layer grown under positive bias condition. The oxygen content at the top side of the AlOx barrier was richer than other positions.
Development of structural, magnetic, and transport properties in NiFe/Co-based top spin valve: Studies by sequential addition of constituent layers
Authors: Leung C. W. , Blamire M. G.
Published: July 2002

We have studied the structural variations in top spin valve (SV) structure Si(100)/SiOx/Nb(5 nm)/Ni80Fe20(4 nm)/Cu(3 nm)/Co (5 nm)/Fe50Mn50(10 nm)/Nb(5 nm) with respect to the number of layers sequentially deposited onto the substrate. Built-up samples (samples with different numbers of constituent layers in the SV structure described above) were deposited by dc magnetron sputtering. Specular x-ray reflectivity (XRR) was used to study the thickness and roughness of these samples. Simulation of XRR scans has been done, starting with samples consisting of fewer layers. Results obtained from these simulations were kept constant and utilized for the simulations of later samples. Such a strategy successfully yielded self-consistent results along the line of samples. M(H) measurements and four-point probe resistance measurements were also performed to probe the magnetic and transport properties of the samples. These results provided information for a simple analysis of the coupling between NiFe and Co layers across the Cu spacer, which is manifested as a loss of double coercivity in our pseudo- SV (Nb/NiFe/Cu/Co) sample.
Alfvén wave tomography for cold magnetohydrodynamic plasmas
Authors: Dodin I. Y. , Fisch N. J.
Published: July 2002

Alfvén wave propagation in slightly nonuniform cold plasmas is studied by means of ideal magnetohydrodynamics (MHD) nonlinear equations. The evolution of the MHD spectrum is shown to be governed by a matrix linear differential equation with constant coefficients determined by the spectrum of quasistatic plasma density perturbations. The Alfvén waves are shown not to affect the plasma density inhomogeneities, as they scatter off of them. The application of the MHD spectrum evolution equation to the inverse scattering problem allows tomographic measurements of the plasma density profile by scanning the plasma volume with Alfvén radiation.
Photoluminescence dependence on heterointerface for metalorganic chemical vapor deposition grown GaInNAs/GaAs quantum wells
Authors: Kawaguchi M. , Miyamoto T. , Gouardes E. , Kondo T. , Koyama F. , Iga K.
Published: July 2002

We investigate the effect of the sequence of gas flows at heterointerfaces on optical quality of GaInNAs/GaAs quantum wells grown by metalorganic chemical vapor deposition (MOCVD). We point out that the degradation mechanism of photoluminescence of GaInNAs grown by MOCVD method is categorized in two types. One is the formation of a GaNAs layer at the heterointerface which causes both increase of emission wavelength and degradation of crystal quality. The other is generation of nonradiative centers induced by incorporation of nitrogen (N). The insertion of a GaInAs layer to the GaInNAs/GaAs heterointerface is proposed to overcome these degradation mechanisms. A GaInAs intermediate layer is effective to suppress the GaNAs formation and to reduce the total GaInNAs thickness.
Microscopic aspects of pattern formation on surfaces
Authors: Wintterlin Joost
Published: July 2002

Recent scanning tunneling microscopy (STM) work gives insight into microscopic processes of surface reactions that play a role for spatio-temporal pattern formation. STM allows to resolve adsorbed particles, follow their surface motion, and monitor reactions with other particles on the atomic scale. The data reveal pronounced deviations from the implicite assumptions of the reaction-diffusion equations traditionally used to model spatio-temporal patterns. In contrast to these descriptions, particles are often not randomly distributed, but cluster in islands because of attractive interactions, and particle hopping can be highly correlated. It is shown that such phenomena can even affect the macroscopic kinetics. The article also discusses a case where the atomic processes inside propagating reaction fronts could be resolved. Here particular strong interaction effects were observed, caused by hydrogen bonds between the reacting species.
Spatially resolved derivative spectroscopy of vertical-cavity surface-emitting lasers using near-field scanning optical microscopy
Authors: Bradford W. C. , Beach J. D. , Collins R. T. , Kisker D. W. , Galt D.
Published: July 2002

A near-field scanning optical microscope was used in collection mode to generate spatially resolved maps of the first derivative with respect to operating current of power emission from vertical-cavity surface-emitting lasers (VCSELs). This technique is highly sensitive to the formation of new modes and can be used to identify mode cutoff points. An example of the usefulness of this technique is demonstrated as we estimate the index of refraction profile of the VCSEL under study at the single mode cutoff point. This profile is a primary feature of the waveguiding characteristics of such lasers.
Atomic image of hydrogen-terminated Si(001) surfaces after wet cleaning and its first-principles study
Authors: Endo Katsuyoshi , Arima Kenta , Hirose Kikuji , Kataoka Toshihiko , Mori Yuzo
Published: July 2002

Atomic arrangements of the hydrogen-terminated Si(001) surface after wet cleaning are investigated by scanning tunneling microscopy and by first-principles calculations. The hydrogen-terminated Si(001) surface after dilute HF cleaning is atomically rough with a structure of terraces and steps. In addition, it is confirmed that 1×1 dihydride structures are formed inside the terraces. First-principles calculations reveal that the maxima of the local density of states string parallel to the Si–H direction on the 1×1 dihydride structure, which makes it possible to determine the atomic arrangement of the observed atomic images. When the surface after HF cleaning is subsequently rinsed with ultrapure water, rows emerge along the 〈110〉 direction. Atomic images show that the rows are mainly formed by a 2×1 unit cell. To elucidate the atomic structure of the 2×1 unit cell, it is proposed that every other row of the ideal 1×1 dihydride surface is preferentially etched with ultrapure water. Total energy calculations are performed based on the first principles of quantum mechanics, which justify the proposed etching mechanism of the Si(001) surface with ultrapure water.
Influence of boron on radiation enhanced diffusion of antimony in delta-doped silicon
Authors: Lévêque P. , Christensen J. S. , Kuznetsov A. Yu. , Svensson B. G. , Larsen A. Nylandsted
Published: July 2002

The silicon samples used in this work contain a sequence of alternating boron and antimony spikes grown by molecular beam epitaxy. These samples were irradiated with 2.5 MeV protons at elevated temperatures ranging from 580 °C to 830 °C and characterized by secondary-ion mass spectrometry. The energy of the proton beam was chosen such that the generation rate of point defects can be considered as uniform throughout the delta-doped layers. For each sample the boron and the antimony diffusion coefficient are increased under irradiation as compared to their diffusivity in unirradiated areas. A measurable diffusion of antimony is observed in samples containing both boron and antimony spikes even at temperatures as low as 580 °C while a reference sample containing only an antimony spike do not exhibit any radiation enhanced diffusion, even at 830 °C. The boron diffusion coefficient increases as the irradiation temperature increases but the antimony diffusion coefficient decreases for the highest irradiation temperature investigated.
Anomaly of the temperature dependence of the diffusion of oxygen in supercritical water
Authors: Ohmori T. , Kimura Y.
Published: July 2002

We have determined the diffusion constants of oxygen molecule (DO2) in near- and supercritical water (the SPCE model) over the wide density region by molecular dynamics simulations. Anomalous temperature dependence of DO2 has been observed: DO2 decreases with increasing temperature from 647 to 773 K at the 115 and 217 kg m−3. The memory function for the friction on the diffusion shows that DO2 is mainly dominated by the binary part of the friction, which is closely related to the contact value of the radical distribution function between oxygen and water. This value decreases with decreasing the temperature from 773 to 647 K, which is a main reason of the peculiar temperature dependence of DO2.
Investigation of ultrafast spin dynamics in a Ni thin film
Authors: Wilks R. , Hughes N. D. , Hicken R. J.
Published: July 2002

Optically induced ultrafast demagnetization has been studied in a polycrystalline nickel thin film by means of a magneto-optical pump-probe technique. The time and magnetic field dependence of the effect have been explored by measuring changes in the reflectivity, and the rotation and ellipticity associated with the linear magneto-optical Kerr effect. We find that, contrary to an earlier report, there is no significant difference in the time dependence of the rotation and ellipticity signals. Furthermore, we observe dynamic hysteresis loops with strange shapes which we believe result from a slow magnetic reorientation induced by average heating effects. These observations emphasize the importance of studying ultrafast demagnetization at saturation.
Magnetic properties of layered oxysulfide Sr2Cu2(Co,Cu)O2S2 with Cu-doped CoO2 square planes
Authors: Okada S. , Matoba M. , Fukumoto S. , Soyano S. , Kamihara Y. , Takeuchi T. , Yoshida H. , Ohoyama K. , Yamaguchi Y.
Published: July 2002

We have studied the magnetic properties of layered oxysulfide Sr2Cu2(Co,Cu)O2S2 with the (Co,Cu)O2 planes. Magnetic susceptibility shows a broad maximum indicative of two-dimensional antiferromagnetic nature above 140 K. Below 80 K, the divergence between zero-field cooled and field cooled magnetizations is seen; long time decay is observed at 10 and 75 K, while it is not observed at 45 K. These feature is discussed from the viewpoint of the strongly and frustrated spin system which is different from the traditional spin glass.
Low temperature properties of spin valves with extremely thin IrMn
Authors: Eckert J. C. , Stern N. P. , Barton A. E. , Mann D. A. , Sparks P. D. , Carey M. J.
Published: July 2002

The properties of IrMn spin valves with tIrMn⩽26 Å are explored at temperatures down to 5 K. The structure is: Ti(50 Å)/NiFe(40 Å)/Co(8 Å)/Cu(30 Å)/Co(30 Å)/IrMn(t Å)/Ti(50 Å) on a Si substrate. The low temperature giant magnetoresistance(GMR) is not greatly affected by the thickness of the IrMn. The thinner the IrMn, the lower the temperature at which the GMR is adversely affected. This is consistent with a reduction in blocking temperature. A number of interesting features in the coercivity and field training are IrMn thickness dependent.
Structural and magnetic properties of (Sr2−xCax)FeReO6
Authors: Alamelu T. , Varadaraju U. V. , Venkatesan M. , Douvalis A. P. , Coey J. M. D.
Published: July 2002

The compounds (Sr2−xCax)FeReO6 (x=0, 0.2, 0.5, 1.0, 1.5, and 2.0) were synthesized by solid state reaction. The resistivity exhibits a metallic behavior for Sr2FeReO6 and insulating behavior for Ca2FeReO6. Structural transformation is observed from tetragonal (x⩽1) to monoclinic (x⩾1.5). The Curie temperature increases from 405 K for x=0 to 539 K for x=2. The saturation magnetic moment is always less than the 3 μB anticipated for a ferrimagnetic configuration of Fe3+ and Re5+, suggesting some antisite disorder. All compounds exhibit significant coercivity, which increases with increasing Ca content, from 0.2 T for x=0 to 1.1 T for x=2. The unexpectedly large coercivity in these compounds is attributed to intrinsic magnetic anisotropy of the Re5+ ions. Mössbauer spectra indicate a small admixture of 0.2–0.3 electrons in 3d↓(Fe)t2g orbitals.
Interfacial Co nanolayers for enhancing interlayer exchange coupling in antiferromagnetic interlayer exchange coupling media
Authors: Peng Yingguo , Zhu Jian-Gang , Laughlin David E.
Published: July 2002

Significant enhancement of the interlayer coupling strength has been achieved by depositing Co nanolayers on both sides of the Ru layer in a conventional CoCrPt/Ru/CoCrPt antiferromagnetic interlayer exchange coupling structure. The interlayer coupling increases nearly linearly from 0.13 to 0.8 erg/cm2 and then levels off with an increase in Co thickness. Substrate bias was found to be very harmful to the exchange coupling. The texture, structure and the growth of the grains and the crystal lattices were also studied with an x-ray diffractometer and a transmission electron microscope.
Concentration dependence of magnetic and electrical properties of gap-type antiferromagnetic MnPt alloys
Authors: Umetsu R. Y. , Fukamichi K. , Sakuma A.
Published: July 2002

Concentration dependence of the magnetic and electrical properties of MnPt alloy system with a AuCu-I type crystal structure has been investigated in order to discuss the electronic state. Temperature dependence of the electrical resistivity shows a characteristic behavior of gap-type antiferromagnets and the electronic specific heat coefficient γ is considerably small in consistent with the calculated band structure having a pseudo-gap around the Fermi level. In the vicinity of the equiatomic composition, the Néel temperature is highest, whereas the value of γ is smallest and increases with decreasing the Néel temperature. From the present experimental results, a close relationship between the electronic state and the antiferromagnetic stability in this alloy system is revealed, in accord with the band calculations.
Picosecond intersubband dynamics in p-Si/SiGe quantum-well emitter structures
Authors: Murzyn P. , Pidgeon C. R. , Wells J.-P. R. , Bradley I. V. , Ikonic Z. , Kelsall R. W. , Harrison P. , Lynch S. A. , Paul D. J. , Arnone D. D. , Robbins D. J. , Norris D. , Cullis A. G.
Published: July 2002

We report time-resolved (ps) studies of the dynamics of intersubband transitions in p-Si/SiGe multiquantum-well structures in the far-infrared (FIR) regime, ℏω<ℏωLO, utilizing the Dutch free electron laser, (entitled FELIX—free electron laser for infrared radiation). The calculated scattering rates for optic and acoustic phonon, and alloy scattering have been included in a rate equation model of the transient FIR intersubband absorption, and show excellent agreement with our degenerate pump-probe spectroscopy measurements where, after an initial rise time determined by the resolution of our measurement, we determine a decay time of ∼10 ps. This is found to be approximately constant in the temperature range from 4 to 100 K, in good agreement with the predictions of alloy scattering in the Si0.7Ge0.3 wells.
Structure and magnetic properties of Co–Pt alloy film deposited on Ru underlayer
Authors: Ohmori Hiroyuki , Maesaka Akihiro
Published: July 2002

In order to study the origin of high coercivity in a Co–Pt film deposited on an Ru underlayer we used a single-crystal MgO substrate to simplify the measurement of magnetic properties and transmission electron microscopy. The structure of the Ru layer on single-crystal MgO (110) is twin. MgO [001] and the c axes of Ru grains are arranged at an angle of about 60°. The Co–Pt layer grows epitaxially on the Ru layer. Although the initial Co–Pt layer is mostly a hcp structure, fcc structure grains are growing at the upper surface through the boundary of hcp grains. The MgO [001] direction is magnetically easy and the MgO [1-10] direction is normally hard axis. The anisotropy field increases when an Ru underlayer is used in the Pt-rich composition. Coercivity is enhanced by the increase in magnetic anisotropy originating from the hcp-Co–Pt alloy that is stabilized even in the Pt-rich composition by using the hcp-Ru underlayer. The Ru layer deposited at a high gas pressure forms a columnar structure, which is effective as well as hcp-Co–Pt with high magnetic anisotropy in the enhancement of coercivity.
Recording physics of perpendicular recording with single layered medium and ring head
Authors: Lee K. J. , Kim Y. S. , Kim E. S. , Im Y. H. , Lee K. M. , Kim J. W. , Lee B. K. , Oh H. S. , Kim K. Y. , Park N. Y. , Lee T. D.
Published: July 2002

In this article, the recording physics of a ring head with a single layered perpendicular medium (Ring/SL) is studied and the results are compared with a single pole head with a double layered perpendicular medium (SPT/DL) by using various simulations and experiments. The Ring/SL has much lower effective medium coercivity than the SPT/DL due to the substantial longitudinal field component of ring head and the incoherent rotation mode of medium magnetizations. Furthermore, switching time of the Ring/SL is estimated as only 10%∼30% of the SPT/DL. In the Ring/SL, the head field gradient of 40 Oe/nm is enough for maximizing SNR. The Ring/SL shows very low noise characteristics especially at high linear density. The signal output of the Ring/SL is smaller than the SPT/DL, but it is large enough to be detected. Therefore, it can be concluded that the combination of single layered perpendicular medium and ring head is highly promising for ultrahigh density recording.
Direct imaging of a biased p-n junction with conductance mapping
Authors: Park Jeong Young , Williams E. D. , Phaneuf R. J.
Published: July 2002

We report characterization of Si p-n junction arrays using simultaneous conductance imaging and constant current mode (topographical) scanning tunneling microscopy imaging over a range of reverse bias conditions. Both constant current and conductance imaging of the electrically different regions (n, p, and inverted region) show a pronounced dependence on applied p-n junction bias. Tunneling spectra measured across the p-n junction show that the conductance contrast agrees well with the expected variation due to tip-induced band bending. Taken in combination with the topographical image, conductance images can be used to characterize spatial variations of carrier densities across the device.
Initial convergence of the perturbation series expansion for vibrational nonlinear optical properties
Authors: Torrent-Sucarrat Miquel , Solà Miquel , Duran Miquel , Luis Josep M. , Kirtman Bernard
Published: July 2002

Ab initio Hartree–Fock and MP2 calculations of the longitudinal (hyper)polarizability—including the static electronic, static zero-point vibrational average (ZPVA), and pure vibrational (static and dynamic) contributions—have been carried out on a set of seven typical medium size conjugated nonlinear optical (NLO) molecules. The ZPVA is obtained through first-order in mechanical plus electrical anharmonicity. Based on physical “nuclear relaxation” considerations the individual (square bracket) terms that contribute to the pure vibrational (hyper)polarizability are then taken into account through third-, fourth-, or fifth-order depending upon the type of term. In order to carry out the correlated treatment, field-induced coordinates and a special finite field technique are utilized. Correlation leads to very substantial differences in the absolute and relative values of the various contributions. In comparison to the electronic term the ZPVA correction is usually small but in one case is over two-thirds as large. On the other hand, both static and dynamic pure vibrational contributions are commonly of a magnitude that is comparable to, or are larger than, the electronic term. The higher-order pure vibration terms are often large. For dynamic processes they can be almost as important as the lowest-order terms; for static (hyper)polarizabilities they can be more important. Thus, for typical NLO molecules, the initial convergence behavior of the perturbation series in mechanical and electrical anharmonicity requires further investigation.
Control of plasma parameters and wall sheath voltage in radio frequency magnetron discharge by grid bias
Authors: Sirghi L. , Hatanaka Y. , Popa G.
Published: July 2002

The plasma of a radio frequency (rf) magnetron discharge used for deposition of TiOx thin films was separated by a mesh grid into source (negative glow) and diffusion (deposition) plasmas. Langmuir probes were used to measure the potential, electron density, and electron temperature of both plasmas. While the change of the grid bias affected the diffusion plasma parameters, it did not change the source plasma parameters (except the potential). The use of the biased grid resulted in a decrease of temperature and an increase of density of plasma electrons in the film deposition region. With an increase of the grid biasing potential, the plasma potential increased in order to maintain a negative bias voltage across the grid sheath, the electron temperature increased, and the electron density decreased. The biased-grid-induced change of the plasma potential and the bias voltage across the wall sheath is explained based on the model of the asymmetric double probe, which is formed by the discharge chamber wall and the grid. The effect of the biased grid on the diffusion plasma parameters is discussed accounting for the particle transport phenomena in the system.
Molecular dynamics of glass-forming liquids: Structure and dynamics of liquid metatoluidine
Authors: Chelli Riccardo , Cardini Gianni , Procacci Piero , Righini Roberto , Califano Salvatore
Published: July 2002

A molecular dynamics simulation has been performed to investigate the structure and the dynamics of liquid and supercooled metatoluidine. H-bonding and clustering has been shown to dominate the structure of the liquid. An extensive analysis of the cluster formation and of its relation with the characteristic prepeak of the static structure factor is given. It is shown that molecular association is strongly driven not only by H-bonds, but also by methyl–methyl interactions which favor specific cluster configurations. The liquid–glass transition has been followed through a calculation of the temperature variation of the molar specific heat and a mechanism has been suggested for the structural changes occurring at the phase transition. The librational dynamics of the system has been studied and recent optical Kerr effect measurements have been perfectly reproduced in a wide time regime.
Abnormal dielectric relaxation phenomena in mixture of polar liquid and conductive particles
Authors: Miura Nobuhiro , Yagihara Shin , Mashimo Satoru
Published: July 2002

Dielectric measurements of water and methanol containing gold, graphite, silicon, silicon carbide, and silicon nitride powders were performed using the time domain reflectometry method. The relaxation process caused by orientation of the polar liquid molecules was observed in the frequency range of 100 MHz to 20 GHz, similar to the pure liquid. The relaxation strength shows an abnormal increase with volume fraction growth of the conductor or semiconductor, and it diverged at a certain fraction. The dependence on the concentration of Δεapp is experimentally given by Δεapp=δγΔεL/(φL−1+γ)+(1−δ)φLΔεL, where φL is the volume fraction of the liquid, ΔεL is the relaxation strength of the liquid, δ is the weighting parameter of the first term for the conductor property and the second term for the insulator property, and γ is a constant which expresses the degree of the shielding effect versus the applied electric field by the conductive particles. A divergence of Δεapp at φL=1−γ shown in the experimental results can be expected by this equation. This equation also expresses the properties of silicon carbide, which has a low conductivity, and also the insulator silicon nitride. These new findings in dielectric characteristics are applicable to a wide number of industrial purposes.
0.1-micron-wide sandwich flux guide and free layer for spin dependent tunneling head sensors
Authors: Pohm A. V. , Anderson J. M.
Published: July 2002

The performance of a 0.1-μm-wide, sandwich flux guide was analyzed for a 200-Å-thick media with a remnant magnetization of 400 emu/cm3 and a guide to media distance of 200 Å. The head was assumed to have a 0.08-μm gap, and the sensor was assumed to have 35% flux capture.1 For a near optimum 0.1×0.2 μm2 sensor beginning 500 Å into the gap, with 40% giant magnetoresistance, a resistance of 2500 Ω, and a 150 mV operating voltage, the calculated signal output is 8 mV. For a bandwidth of 1 GHz, the signal exceeds the Johnson noise by 31 dB.
Hyperfine fields at 3d impurities in ZrFe2 intermetallic compound: A theoretical study
Authors: de Oliveira A. L. , de Oliveira N. A. , Troper A.
Published: July 2002

In this article we study the systematics of the local magnetic moments and hyperfine fields of 3d impurities diluted in ZrFe2 intermetallic compound. In order to describe the magnetic properties of this intermetallic, we use a two coupled sublattice Hubbard Hamiltonian, treated in the mean field approximation. We include in the hopping the next neighbor perturbation, due to the transnational invariance breaking introduced by the 3d impurity. After determining the local charge potential by using an extended Friedel sum rule, we obtain the perturbed density of states and the local magnetic moments at the impurity site. The corresponding hyperfine fields are in good agreement with experimental data.
Production of Nd–Fe–B alloys by the glass slag method
Authors: Ozawa S. , Sato H. , Saito T. , Motegi T. , Yu J.
Published: July 2002

The microstructures of the Nd–Fe–B alloy with the stoichiometric composition of Nd2Fe14B produced by the glass slag method were investigated. The Nd–Fe–B melts in the molten slag materials such as lead silicate glass, soda-lime glass, and Pyrex glass experienced a large undercooling over 160 K below solidification. When the Nd–Fe–B melts were solidified either in the molten lead silicate glass or in the molten soda-lime glass, the resultant Nd–Fe–B alloys had coarse dendrites of α-Fe phase together with grains of Nd2F14B. On the other hand, the Nd–Fe–B alloys exhibited columnar dendrite grains of Nd2Fe14B phase when the Nd–Fe–B melts were solidified in the molten Pyrex glass.
Far infrared photovoltage effect in a blocked impurity band detector
Authors: Rylkov V. V. , Leotin J. , Asadauskas L. , Aronzon B. A. , Kovalev D. Yu.
Published: July 2002

A photovoltage was found across a silicon blocked impurity band detector when illuminated at low temperatures with photons of wavelengths up to about 30 μm. It appears as an open loop photovoltage, constant over a wide range of incident flux intensity, while the short circuit photocurrent changes linearly with photon flux. The device is a boron doped epitaxial structure, sandwiched between degenerately doped thin semitransparent contacts, consists of a pure layer next to a photoactive layer doped in the regime where impurity banding occurs. The short-circuit photocurrent is shown to originate from a ballistic transport across the micrometer thick pure layer of holes photoexcited at the degenerately doped contact with the pure layer. On the other hand, the open loop photovoltage drives across the pure layer a counter ballistic flow of holes thermally emitted over a barrier existing at the interface with the pure layer. The open loop photovoltage at 0 K limit is then a direct measure of the Fermi energy inside the impurity band of the doped photoactive layer.
Magnetic core characteristics for high rep-rate induction modulator
Authors: Watanabe M. , Nakajima M. , Shiho M. , Horioka K. , Takayama K. , Kishiro J.
Published: July 2002

Typical magnetic materials are experimentally characterized. Particularly our efforts are concentrated on deriving a core-loss scaling in operation region with minor B–H loops for highly repetitive voltage modulators. The core losses are evaluated as functions of magnetization rate and flux swing using semiempirical equations based on magnetization models. A prototype induction module has been successfully operated up to 1 MHz and the loss values are adapted well to the core-loss criterion.
Nonlinear dynamics of a noncontacting atomic force microscope cantilever actuated by a piezoelectric layer
Authors: Wolf K. , Gottlieb O.
Published: July 2002

The nonlinear equations of motion for a silicon cantilever beam, covered by a piezoelectric lead–zirconate–titanate layer, subjected to a Lennard-Jones type boundary condition, are derived for voltage excitation. The Lagrangian of the system is obtained from the electric enthalpy density, including the virtual work of the Lennard-Jones potential, assuming the beam undergoes only small displacements. By application of Hamilton’s principle, the nonlinear equations of motion are consistently derived and truncated to third order for perturbation analysis. The evolution equations are obtained by the multiple scales method and periodic solutions to the equations of motion are determined and discussed with respect to different tip to sample distances. An analytically obtained frequency response function enables determination of the frequency shift of individually piezoactuated microbeams, which are proposed as fundamental elements of parallel atomic force microscopy, undergoing forced vibration in a dissipative environment.
Theory of fluorescence decay of naphthalene: Was photoinduced cooling observed experimentally?
Authors: He Yong , Pollak Eli
Published: July 2002

A combination of an ab initio harmonic force field and experimentally determined frequencies is used to study the nascent energy distribution of naphthalene when photoexcited from the ground electronic state (S0) to the first excited electronic state (S1). We find extensive cooling of the nascent vibrational energy distribution for photoexcitation frequencies which are within 500 cm−1 to the blue and to the red of the transition frequency ω00 from the ground vibrational state of S0 to the ground vibrational state of S1. The experimentally measured pressure dependence of the internal conversion rates of naphthalene in the presence of argon gas are examined theoretically with an improved version of the Gaussian binary collision theory of Talkner, Berezhkovskii, and Pollak. We find, in agreement with experiment, that at low excitation energies, the lifetime of the excited state decreases with increasing pressure—a signature of vibrational cooling, while for high photoexcitation energies the lifetime increases, a signature of vibrational heating of the nascent distribution. The energy transfer per collision is found to be 25% of the excess (thermal) energy.
Electrical activation studies of GaN implanted with Si from low to high dose
Authors: Fellows James A. , Yeo Y. K. , Hengehold R. L. , Johnstone D. K.
Published: July 2002

Electrical activation studies of Si-implanted GaN grown on sapphire have been made as a function of ion dose and anneal temperature. Silicon was implanted at 200 keV with doses ranging from 1×1013 to 5×1015 cm−2 at room temperature. The samples were annealed from 1100 to 1350 °C with a 500-Å-thick AlN cap in a nitrogen environment. Samples implanted with high doses (⩾1×1015 cm−2) have optimum anneal temperatures of around 1350 °C, exhibiting a nearly 100% electrical activation efficiency, whereas low dose (⩽5×1014 cm−2) samples exhibited lower activation efficiencies, but efficiencies increase with anneal temperature even after annealing at 1350 °C.
Response to “Comment on ‘Self-diffusion near the liquid–vapor critical point’ ” [J. Chem. Phys. 116, 6379 (2002)]
Authors: Drozdov Alexander N. , Tucker Susan C.
Published: July 2002

It was predicted by us [J. Chem. Phys. 114, 4912 (2001)] that the presence of local density enhancements in a neat supercritical fluid near its liquid–vapor critical point should generate a weak anomaly in the fluid's self-diffusion constant. Herein, we examine possible reasons why the limited number of experimental studies conducted to date on diffusion constants in near-critical supercritical fluids do not provide clear evidence of this predicted weak anomaly.