bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogen-induced changes in TbNiAl
Authors: Bordallo H. N. , Nakotte H. , Eckert J. , Kolomiets A. V. , Havela L. , Andreev A. V. , Drulis H. , Iwasieczko W.
Published: July 2002

Neutron diffraction was used to determine the deuterium sites in TbNiAlD1.28 and TbNiAlD0.8. Both samples were found to crystallize in the orthorhombic Amm2 space group. Our analysis reveals that deuterium in TbNiAlD1.28 occupies positions at x=0 and x=1/2 only, while TbNiAlD0.8 shows the formation of two different phases. For TbNiAlD1.28, additional magnetic reflections are observed below 16 K indicating antiferromagnetic order. On the other hand, at 10 K, only one of the TbNiAlD0.8 phases was found to be magnetic. In addition, our study of the localized vibrations of hydrogen in TbNiAlH1.39 and in its non-magnetic analog YNiAlH1.35 using inelastic neutron scattering supports the existence of two different hydrogen sites in the saturated hydrides.
The magnetization study of melt-spun ribbons of B containing TbFe2 alloys
Authors: Kim K. S. , Yu S. C. , Kim S. R. , Lim S. H.
Published: July 2002

We have carried out the magnetization study of melt-spun ribbons of (Tb0.33Fe0.67)1−xBx (x=0, 0.02, 0.05, 0.1, and 0.15) alloys. The temperature dependence of magnetization was measured using a superconducting quantum interference device and a vibrating-sample magnetometer during heating from 5 to 800 K, with an applied field of either 10 or 50 kOe. The present study shows the existence of noncollinear magnetics structures. From an analysis of the approach to saturation magnetization, the average magnetic moment μa, random anisotropy field Hr, and local random anisotropy constant KL have been extracted. It is found that μa decreases from 1.68 (x=0) to 1.33 μB (x=0.15) and KL increases with increasing B concentration. This result suggests that the addition of B seems to increase the random anisotropy and hence to decrease the magnetic order, resulting a sperimagnet with large spread angle.
Magnetic x-ray investigation at the L2,3 edges of Nd in Nd2Fe14B
Authors: Bartolomé F. , Tonnerre J. M. , Sève L. , Raoux D. , Lorenzo J. E. , Chaboy J. , Garcı́a L. M. , Bartolomé J. , Krisch M. , Rogalev A. , Serimaa R. , Kao C-C. , Cibin G. , Marcelli A.
Published: July 2002

A systematic study of x-ray magnetic circular dichroism, x-ray resonant magnetic scattering, and resonant inelastic x-ray scattering at the L2,3 edges of Nd on Nd2Fe14B is presented. The combined information allows to assign a dipolar or quadrupolar origin to different features appearing in the experimental spectra and to study the thermal dependence of the Nd moment orientation below the spin reorientation transition which takes place at TSRT=135 K.
Field-emission current from diamond film deposited on molybdenum
Authors: Liao Meiyong , Zhang Zhengang , Wang Wanlu , Liao Kejun
Published: July 2002

Field-emission current from chemical vapor deposited diamond film on molybdenum wafer has been investigated experimentally and theoretically. The Fowler–Nordheim plot exhibits three linear regimes, corresponding to low, middle, and high electric field, respectively. A potential barrier model, based on a fact that metal carbide, Mo2C, exists at the interface between diamond and substrate, is presented. In terms of this model, the expression of field-emission current from diamond on Mo has been derived. The theoretical results agree qualitatively with the experimental observation and indicate that the emission current is related to the thickness of Mo2C and diamond under low and middle electric field, however, no similar relationship is found under high field.
X-ray crystal truncation rod scattering analysis of reactive ion etched silicon
Authors: Isomae Seiichi , Ohkura Makoto , Maki Michiyoshi , Matsuda Yasushi
Published: July 2002

We have investigated lattice damage in reactive ion etched silicon by using x-ray crystal truncation rod (CTR) scattering. The x-ray intensity associated with the rod in the reciprocal space depends on the etching-induced lattice distortion. To estimate the magnitude of the lattice distortion, we analyzed the obtained data with a kinematic x-ray diffraction model on the assumption that the lattice distortion decays exponentially with the depth. We found that the lattice distortion extends to a depth of about 9 nm. In addition, we propose a method for quantitatively evaluating lattice damage based on our analysis. This method allows us to compare lattice damage among samples etched under different conditions. This study indicates that x-ray CTR experiments provide a useful means of characterizing lattice distortions near processed surfaces.
Monomer-liquid crystal emulsions for switchable films
Authors: De Filpo G. , Lanzo J. , Nicoletta F. P. , Chidichimo G.
Published: July 2002

We have followed the phase separation process in mixtures of an organic monomer and nematic liquid crystals at different cooling rates. Systems form liquid crystal droplets in a liquid crystal-saturated monomer matrix and in some cases emulsions are stable over several months. Homogeneous droplet size distributions are obtained for faster cooling rates. We report the droplet size distribution, the behavior of the critical solution temperature as a function of liquid crystal content, and some electro-optical properties of different emulsions. The long stability and the electro-optical response show that such systems could be used as promising, low voltage, switchable films.
Interactive kinetics in thermally stimulated luminescence and conductivity and its effect on the trap depth determination
Authors: Opanowicz A.
Published: July 2002

Thermally stimulated luminescence (TSL) and conductivity (TSC) complex glow curves having overlapping peaks are calculated for a system with two kinds of interactive electron traps, one kind of inactive trap, and one kind of recombination center. The densities of electrons localized on the interactive traps and the rates of change of these densities during the TSL and TSC runs also are calculated. The calculation results show that electrons thermally released from the traps of one kind during the sample heating are partly trapped by the traps of another kind from which they are next released. These processes of transfer of electrons influence the properties (the peak-positions, shape, and intensity) of the complex TSL and TSC curves. Consequently, the accuracy of trap depths evaluated from the calculated TSL and TSC curves using eight methods known from literature is, in general, lowered. This is found, particularly, for the initial-rise and the peak-shape methods.
High resolution spectroscopy of free-standing GaAs films prepared by epitaxial liftoff
Authors: Harrison D. A. , Hu J. , Watkins S. P. , Thewalt M. L. W. , Beckett D. J. S. , SpringThorpe A. J.
Published: July 2002

Free-standing layers of high purity GaAs prepared by epitaxial liftoff are investigated using high resolution photoluminescence, optical transmission, and x-ray diffraction techniques. Low temperature (1.5 K) optical measurements of these thin, strain-free films yield spectra rich in structure, revealing much about the fundamental properties of the materials. X-ray diffraction analysis of layers as thin as 2000 Å produce well-resolved Pendellösung fringes, in excellent agreement with dynamical theory simulations. Once removed from their underlying substrates, these thin semiconductor cavities constitute unique systems for a variety of novel spectroscopic studies not possible in as-grown heterostructures.
Multiply charged ion transport in free boundary vacuum arc plasma jet
Authors: Keidar M. , Beilis I. I. , Brown I. G.
Published: July 2002

The free boundary plasma arc jet expansion was analyzed based on a two-dimensional hydrodynamic model. The plasma jet expansion was modeled using the sourceless steady-state hydrodynamic equations, where the plasma free boundary was determined self-consistently. Due to the existence of an electric field in the quasineutral plasma the different charged ion species can be spatially separated. It was found that the mean charge state distribution is strongly nonuniform with a tendency for the highly charged species to appear near the plasma jet boundary region. Along the center line the density of singly charged ions falls off by about four times while the density of fourfold charged ions drops by more than 100 times. The radial charge state distribution becomes more nonuniform with increasing magnetic field. Good qualitative agreement between calculated and experimental radial distributions of different charged species was obtained.
Laterally modulated composition profiles in AlAs/InAs short-period superlattices
Authors: Ahrenkiel S. P. , Norman A. G. , Al-Jassim M. M. , Mascarenhas A. , Mirecki-Millunchick J. , Twesten R. D. , Lee S. R. , Follstaedt D. M. , Jones E. D.
Published: July 2002

Laterally modulated composition profiles in AlAs/InAs short-period superlattices grown by molecular-beam epitaxy under tensile strain on (001) InP are examined by transmission electron microscopy (TEM) and x-ray diffraction K mapping. Weak, one-dimensional modulation with a wavelength of λm=110 Å is observed for a period of 1 ML. At 2 ML, the composition profile is irregular, while a two-dimensional network of wire and dot structures with λm=130 Å occurs at 3 ML. At a high growth rate, 4-ML samples exhibit smooth modulated profiles with λm=220 Å. When the growth rate is reduced with beam interrupts, sharp profiles develop that show strong alignment in the substrate plane with λm=270 Å. TEM dark-field image contrast of the modulated profiles is simulated using dynamical diffraction theory to reproduce features observed in experiment.
Direct tracing of the photocurrent multiplication process in an organic pigment film
Authors: Nakayama Ken-ichi , Hiramoto Masahiro , Yokoyama Masaaki
Published: July 2002

The transient response of the photocurrent multiplication phenomenon at an organic/metal interface was revealed to have two components, which were identified as the primary and the subsequent multiplied photocurrents. The transient photocurrent directly traced the multiplication process, that is, the accumulation of trapped holes near the interface, which is produced by the primary photocurrent and builds up a high electric field at the interface, and then tunneling electron injection from the metal electrode to the organic layer. The onset time for multiplication was observed at 43 ms under a light intensity of 0.19 mW cm−2. The amount of charge required for multiplication onset was found to have a specific value of 30 nC cm−2, implying that an increase of the carrier generation efficiency of the primary photocurrent is expected to be effective at achieving high speed multiplication.
Improved material properties of polycrystalline CuInSe2 prepared by rapid thermal treatment of metallic alloys in H2Se/Ar
Authors: Alberts V. , Schön J. H. , Bucher E.
Published: July 2002

In this study the material properties of metallic alloys were evaluated at different stages of reaction to H2Se/Ar. Precursors of identical composition (Cu/In atomic ratio=0.96) were considered and the temperature was rapidly (in 2 min) increased to the specific selenization temperature (i.e., 200, 300, 400, and 600 °C). The composition of the films remained virtually unchanged when selenized at low temperatures below 400 °C. The material properties of these films were dominated by the presence of binary phases and photoluminescence (PL) studies revealed the presence of only one broad transition around 0.83 eV. Structural analysis revealed a significant increase in the Cu/In atomic ratio with associated Cu-selenide secondary phases and inhomogeneous film morphologies in the case of samples selenized at temperatures around 400 °C. In this case, PL studies revealed relatively sharp and well-defined transitions which are typical for Cu-rich films. The most significant result that followed from this study is the vast improvement in the material quality of films rapidly heated and selenized at elevated temperatures above 400 °C. Scanning electron microscopy and x-ray diffraction studies revealed homogeneous and dense films with no evidence of secondary phases. Even more important, energy dispersive x-ray spectroscopy measurements indicated no change in the initial composition of samples selenized under these conditions (at temperatures above 400 °C while ramping the temperature in 2 min to the specific reaction temperature). The high material quality of these films was also confirmed by PL studies, revealing only one broad transition at 0.932 eV which is generally reported for device quality material. It is suggested that the rapid heating of samples and subsequent quick passage through the critical temperature range around 400 °C is responsible for the improved material properties of these selenized films.
Influence of surface charge on gas discharge characteristics
Authors: Ji-ting Ouyang , Chang-gen Feng , Hua-qing Huang , Ben-jiang Mao
Published: July 2002

The discharge current and the inception voltage of the surface discharge induced plasma chemical process (SPCP) element are measured to investigate the influence of surface charge on the surface discharge process in air at a dielectric surface. A ceramic-based surface discharge ozonizer is tested by applying a high frequency sinusoidal voltage. The results show that the inception voltage of the SPCP element is not constant but decreases linearly as the amplitude of applied voltage increases. An electrostatic equilibrium is reached along the surface when the microdischarge stops. The inception voltage and the current spikes are not symmetric for the two half cycles of the applied voltage. The microdischarges occur at a lower inception voltage in the negative half cycle than that in the positive one, while the current spikes have a larger amplitude in the negative half period. The microdischarge current is a short pulse with typical magnitude of 0.1–0.2 A and width of 10–20 ns for the SPCP element.
X-ray photoelectron spectroscopy of CdPS3
Authors: Curró G. M. , Grasso V. , Silipigni L.
Published: July 2002

Single CdPS3 crystals have been investigated at room temperature by means of x-ray photoemission spectroscopy (XPS) and x-ray induced Auger spectroscopy. Special attention has been paid to the Cd 3d and 4d and S and P 2p core levels and to the Cd Auger M4,5N4,5N4,5 transitions. As far as the XPS spectra are concerned, a single-peak structure has been observed for all the core levels investigated. Moreover, the Cd 4d levels are discrete and well localized, in good agreement with the transition–metal weakly interacting model according to which the transition metal–sulfur bond is weak. Further information about the nature of the cadmium–sulfur bond in CdPS3 was obtained from the calculated modified Auger parameter for Cd. A correlation has been observed between the change in the Cd modified Auger parameter in CdPS3 and the energy gap of this compound.
Diameter of As clusters in LT-GaAs by Raman spectroscopy
Authors: Toufella M. , Puech P. , Carles R. , Bedel E. , Fontaine C. , Claverie A. , Benassayag G.
Published: July 2002

Raman scattering measurements on low temperature GaAs layers are presented. Phonons in both GaAs and As are studied. The transition from diluted As in the GaAs matrix to the small As clusters formed after annealing is analyzed. This is performed by observing the reduction of the GaAs bound charge, i.e., the longitudinal optical GaAs frequency downshift, to the appearance of the crystalline As vibrational mode. From the phonon shifts of crystalline As, the diameter and the strain are derived, accordingly to transmission electron microscopy measurements.
Determination of the equivalent circuit of inductively coupled plasma sources
Authors: Colpo Pascal , Ernst Roland , Rossi F.
Published: July 2002

This article presents a new approach to investigate and model the electrical characteristics of inductive plasma sources. The technique is primarily based on the measurement of the total complex impedance of the plasma source. The measurements are subsequently numerically fitted to a generic and qualitative electrical model, predetermined by a classical Bode analysis of a circuit including a conductive dummy load of size comparable to the plasma itself. The match between the modeling and the experimental data using this new approach shows a drastic improvement compared to the usual inductively coupled plasma (ICP) electrical model, which is also detailed here as a comparison. We conclude the article on prospective benefits of an accurate electrical model for ICP plasma sources, showing in particular that the global electrical parameters of the discharge can be correlated with a good level of accuracy to the local electrical parameters of the plasma. Beyond the technological necessity to better understand the ICP plasma sources, these results also open many doors towards nonintrusive and accurate plasma monitoring technologies.
Magnetostrictive Sm1−xNdxFe2/Fe composites from melt-spun precursors
Authors: Pinkerton F. E. , Herbst J. F. , Capehart T. W. , Meyer M. S. , Fellberg W. A.
Published: July 2002

We have fabricated magnetostrictive composites containing Sm1−xNdxFe2 in an Fe matrix by hot pressing. The magnetostrictive component was prepared by heat treating melt-spun precursors, a method we find capable of producing the MgCu2-type phase for Nd concentrations as large as x=0.5. We report physical and magnetic properties of the rapidly solidified precursor materials, as well as the magnetostriction λ of Fe-based composites formed with them. The intrinsic coercivity Hci of the melt-spun ribbons decreases from 2.0 kOe for SmFe2 to 0.5 kOe for Sm0.5Nd0.5Fe2. As x increases from 0 to 0.5, λ of the composites decreases roughly linearly with x from 430 to 80 ppm.
Impluse response of a fiber optic probe hydrophone determined with shock waves in water
Authors: Wang Z. Q. , Lauxmann P. , Wurster C. , Köhler M. , Gompf B. , Eisenmenger W.
Published: July 2002

The impluse response of a fiber optic probe hydrophone (FOPH) is determined through it’s step response obtained by using a self-focusing electromagnetic shock wave excitation. The experimental transfer function agrees well with the theoretical calculation of the transient response by diffraction of the acoustic wave at the fiber end face. A rise time of about 5 ns has been obtained for the shock front of the self-focusing shock wave generator by the deconvolution of the output signal of the hydrophone with it’s impulse response. The FOPH can be used as a standard hydrophone for the absolute wideband measurement of shock waves of lithotripters and of acoustic waves in liquids in general.
Infrared and transmission electron microscopy studies of ion-implanted H in GaN
Authors: Seager C. H. , Myers S. M. , Petersen G. A. , Han J. , Headley T.
Published: July 2002

H and D have been implanted into undoped films of GaN heteroepitaxially grown on sapphire over a dose range from 5×1015 to 5×1017 ions/cm2. After a 600 °C post-implantation anneal, room temperature Fourier-transform-infrared spectroscopy reveals two major local vibrational modes at 3183 cm−1 (2364 cm−1) and 3219 cm−1 (2386 cm−1) for the H (D) material implanted at higher doses. The position and isotope shift (1.35) of these modes strongly suggest they are due to hydrogen bonded to nitrogen atoms; these atoms are located on the surfaces of seven sided cavities created by the H implant and thermal anneal cycle and identified by transmission electron microscopy. Nuclear reaction analyses of isochronally annealed D implanted films indicate that most of the deuterium remains bound within the implanted layer, and that the major release stage for D occurs near 900 °C. By contrast, the N–H (N–D) vibrational modes anneal out in the 750–800 °C temperature range. These findings indicate that the bound H exists in at least two major states, believed to be IR-active N–H on the cavity walls and IR-inactive H2 gas within the cavities.
Photocurrent and electroluminescence in vertical-cavity surface-emitting lasers
Authors: Georjon Laurent , Boucher Yann
Published: July 2002

We investigate both experimentally and theoretically the photocurrent and spontaneous emission spectra of vertical-cavity surface-emitting lasers below threshold. Special prominence is given to the spectral broadening due to finite numerical aperture. In the frame of a matrix formalism, photoresponsivity is determined as proportional to intracavity absorption, taking into account the angular dependence of the overlap factor, while an analytical approximation is proposed for the emitted flux as a function of the angle of collection.
ArF excimer laser irradiation effects in AlF3-based fluoride glasses for vacuum ultraviolet optics
Authors: Hosono Hideo , Mizuguchi Masafumi , Kawazoe Hiroshi , Ichimura Tomoaki , Watanabe Yuichi , Shinkuma Yoshikane , Ogawa Tohru
Published: July 2002

Color center formation in AlF3–YF3–RF2 (R=alkaline earth metal) glasses doped with PO2.5 (0–3 mol %) by irradiation with ArF excimer laser light was examined by optical absorption (vacuum ultraviolet–visible) and electron paramagnetic resonance (EPR) spectroscopies. Concentrations of impurity iron in all the glasses and oxygen in the P-free samples were ∼0.2 and ∼450 ppm, respectively. Optical absorption ranging from 2–8 eV was induced via one-photon absorption processes. The optical band dominating the transmission loss at 193 nm has a peak at 5 eV in the P-free glasses or a peak at 6.9 eV in the P-doped glasses. The origins of the 5 and 6.9 eV bands were tentatively ascribed to an oxygen-related hole center giving an EPR signal with a width of 7.2 mT at g=2.0097 and P E′ center giving a hyperfine doublet with a separation of ∼70 mT. Provided these correspondences, then the values of oscillator strength for the 5 and 6.9 eV bands were calculated as ∼0.15 and ∼0.1, respectively. No formation of color centers associated with intrinsic constituents such as Al, Y, R, and F ions, was observed. The present results suggest that the reduction of impurity oxygen content is a route to effectively suppress the solarization in the P-free AlF3-based glasses.
Resonant tunneling field-effect transistor based on wave function shape modulation in quantum wires
Authors: Khurgin Jacob B. , Yang D.
Published: July 2002

We propose a new type of three-terminal tunneling device with gating action provided by the external field inducing the changes in the symmetry of electron wave functions. We evaluate the current–voltage characteristics, transconductance, and speed of the proposed device.
New type of electric oscillations in bistable resonant tunneling diodes
Authors: Glavin B. A. , Kochelap V. A. , Mitin V. V.
Published: July 2002

We studied a resonant tunneling diode with intrinsic bistability when high and low current states simultaneously occur in a certain voltage range. We have found a novel type of electric oscillation in the bistable resonant tunneling diode. Under these oscillations one portion of the diode is in the high current state while the other is in the low current state. A periodic motion of the boundary between the high and low current regions gives rise to oscillations of the current in the external circuit.
From micromagnetics to quantum spin chains: Quantization of breathers
Authors: Braun Hans-Benjamin , Fettes Nadia
Published: July 2002

Classical bound states of solitons (“breathers”) in continuum spin chains are semiclassically quantized via Berry’s phase. Remarkably, our results at zone center and zone boundary as well as the whole continuum match the exact Bethe ansatz result of the discrete, XYZ spin-1/2 chain with arbitrary anisotropies.
Robust giant magnetoresistance material system for magnetic sensors
Authors: Lenssen K.-M. H. , Kuiper A. E. T. , Roozeboom F.
Published: July 2002

A new, robust giant magnetoresistance (GMR) material system is described that comprises an exchange-biased artificial antiferromagnet. For the exchange biasing Ir18Mn82 is used because of its high blocking temperature. Experiments have demonstrated that this material can withstand magnetic fields larger than 150 kA/m and annealing at temperatures above 275 °C without irreversible damage. At higher temperatures the GMR effect starts to decrease due to atomic diffusion; the exchange-biasing effect, however, does not disappear, which means that this is no longer the limiting factor. The excellent magnetic and thermal robustness, combined with the unambiguous asymmetric magnetoresistance curve, makes this GMR material system very suitable for application in (e.g., automotive) sensors.
Experiments towards realization of a recording medium capable of supporting near theoretical density
Authors: Carey R. , Newman D. M. , Holmes B.
Published: July 2002

A novel technique is reported for the preparation of dispersions of cobalt particles with a narrow distribution of diameters around an estimated mean of 8.5 nm. Particles of this size have blocking temperatures close to 220 °C and, dispersed to reduce mutual interaction, they constitute a near ideal ultrahigh density recording medium. Production of this medium requires a two-stage process: reactive sputtering to develop a precursor film of cobalt nitride followed by rapid thermal processing in vacuum. The precursor film disassociates leaving the required dispersion of cobalt particles. Varying thickness and density in the precursor films and the conditions attending the disassociation provides some control of the medium magnetic properties. Samples with saturation magnetisation (Ms) between 60% and 20% of bulk cobalt exhibit isotropic magnetic properties in-plane with high remanence and coercivities approaching 2 kOe.
Magnetoresistance of polycrystalline layered manganites La2−2xSr1+2xMn2O7
Authors: Dörr K. , Müller K.-H. , Ruck K. , Krabbes G. , Schultz L.
Published: July 2002

Polycrystalline bulk samples of the layered manganites La2−2xSr1+2xMn2O7 showing a colossal magnetoresistance (CMR) effect were prepared for doping levels of x=0.4 and 0.5 by a solid-state reaction route. Temperature and field dependences of magnetization and of electrical resistivity have been measured between 5 K and room temperature. Ferromagnetic behavior with a Curie temperature of TC=135 K and a high value of spontaneous magnetization (64 emu g−1) was found for x=0.4. The x=0.5 compound orders antiferromagnetically near TN=215 K, showing a resistivity enhancement there. The resistivity of the x=0.4 compound shows a field dependence at low temperatures similar to that found for polycrystalline La0.7Sr0.3MnO3. The resemblance includes the presence of both a low-field and a high-field contribution to the magnetoresistance, as well as the magnitude of the low-field MR (−23% at 20 K and −15% at 77 K for H=1 kOe). The low-field MR is attributed to the effect of grain boundaries. In contrast to the grain-boundary MR of La0.7Sr0.3MnO3, it was also observed at temperatures far above the TC of the layered manganite.
Magnetic and structural properties of Mg–Co nanostructures fabricated by chemical synthesis
Authors: Kirkpatrick E. M. , Leslie-Pelecky Diandra L. , Kim S.-H. , Rieke R. D.
Published: July 2002

Reductive chemical synthesis is a versatile tool for fabricating elemental nanostructures; however, less work has been completed on understanding and controlling alloy formation. Magnetic Mg–Co and Mg–Co–C nanocomposites have been fabricated using a reductive chemical synthesis designed to produce highly active metals. The as-synthesized powder was annealed at temperatures from 150 to 650 °C. Samples were investigated using x-ray diffraction, alternating gradient force magnetometry, and superconducting quantum interference device magnetometry. X-ray diffraction indicates that the resulting structures are multiphase with MgCo2, MgCo3C0.5, fcc Co, Mg, MgO, and Li2CO3 present depending on annealing temperature. The temperature-dependent magnetization of the as-synthesized sample indicates ferromagnetic and antiferromagnetic or ferrimagnetic contributions. Increases in coercivity and remanance ratio with increasing annealing temperature are consistent with the formation and growth of small Co grains.
Arrhenius–Néel thermal decay in polycrystalline thin film media
Authors: Bertram H. N. , Richter H. J.
Published: July 2002

A simple expression for the remanent coercivity versus field time duration has been developed for polycrystalline thin film media with two-dimensional random anisotropy axis orientation. Explicit averaging of the thermally induced reversal for random grains is shown to be well approximated by the thermal decay of one particle with anisotropy axis at an angle of ≈21° to the applied field. The expression has no adjustable parameters and two slightly different forms apply to noninteracting and weakly interacting grains. Applicability is shown to be for times greater than approximately 100 ns. Good agreement is shown with measurements on two series of thin films with varying coating thickness.
New CoPt/Ag films for high density recording media
Authors: Stavroyiannis S. , Panagiotopoulos I. , Niarchos D. , Christodoulides J. A. , Zhang Y. , Hadjipanayis G. C.
Published: July 2002

CoPt/Ag nanocomposite films have been prepared with magnetic properties promising for potential application in high density magnetic recording media. The films were initially deposited by sputtering, in a multilayer form and found to crystallize in the magnetically soft face centered cubic phase. Annealing leads to a microstructure consisting of the magnetically hard face centered tetragonal CoPt nanoparticles embedded in a Ag matrix. Microstructure and coercivity can be tailored by adjusting the annealing conditions and the relative CoPt/Ag composition. Values of coercivity in the range of 1–17 kOe with grain sizes in the range of 7–100 nm, respectively, have been obtained. Henkel plots of optimally annealed samples show only weak interactions of dipolar nature, characteristic of magnetically isolated single domain particles.
Structure and magnetic properties of Sm3(Fe, V)29NX
Authors: Kataoka M. , Satoh T. , Otsuki E.
Published: July 2002

The crystal structure and magnetic properties of Sm3(Fe, V)29NX compounds were investigated. It was found that the novel nitride, Sm3(Fe, V)29N2, is more stable than Sm3(Fe, V)29N4 in the atmosphere with low nitrogen pressure. The x-ray and electron diffraction studies show that the nitrides retain the same crystal structure as Sm3(Fe, V)29. The lattice parameters of Sm3(Fe, V)29N2 are a=1.084 nm, b=0.870 nm, c=0.985 nm, and β=97.06°.
Electron/ion emission from the plasma formed on the surface of ferroelectrics. II. Studies of electron diode operation with a ferroelectric plasma cathode
Authors: Dunaevsky A. , Krasik Ya. E. , Felsteiner J. , Dorfman S.
Published: July 2002

We present experimental results of electron diode operation with an active plasma cathode. The plasma was formed by a noncomplete discharge on the surface of different unpoled ferroelectric samples having the form of disks or tubes made of BaTiO3 or Pb(Zr,Ti)O3. To produce the discharge, a positive or a negative driving pulse was applied to the front or to the rear electrode of the sample. We studied the operation of planar and coaxial electron diodes under the application of an accelerating high-voltage pulse ⩽45 kV with repetition rate ⩽5 Hz or ⩽250 kV in a single-mode operation. Electron beams with a current density of several hundreds of A/cm2 and a time duration of several hundreds of ns were generated. It was shown that the parameters of the electron beam as well as the operation of the electron diode depend strongly on the method of the plasma formation and the time delay between the beginning of the plasma formation and the application of the high-voltage pulse.
Threshold stress behavior in thin film electromigration
Authors: Surh Michael P.
Published: July 2002

Thin film electromigration is simulated using simple models for constitutive relations. Inhomogeneities in the mass deposition and stress fields can explain many features of the phenomenon. They imply that the threshold stress depends on the thin film microstructure and texture. The vacancy Z* parameter derived from the Blech threshold is increased in magnitude, in better agreement with experiments than earlier estimates. The predicted transient vacancy flux displays shorter decay times than the commonly used stress model, possibly in better agreement with experiment below threshold. Finally, nonlinear stress–strain relations are shown to be consistent with the behavior that is seen above threshold in passivated and unpassivated interconnects.
Effects of plasma power on the epitaxial growth of (Ba0.48Sr0.52)TiO3 thin film
Authors: Oh U. C. , Kang T. S. , Park K. H. , Je Jung Ho
Published: July 2002

We studied the effects of plasma power on the epitaxial behavior of (Ba0.48Sr0.52)TiO3 (BST) film growth on MgO (001) substrates using synchrotron x-ray scattering experiments. The BST films were grown on MgO (001) by magnetron sputtering at sputtering powers up to 3 W/cm2. We found that stress in the epitaxial BST films grown at lower powers was mainly induced by lattice mismatch, but in films grown at higher powers, it was primarily intrinsic stress. The films grown at higher powers were much more strained and exhibited better epitaxial quality. This study suggests that it is feasible to control the epitaxial quality of BST films just by varying the plasma power in magnetron sputtering.
Second-harmonic generation in single-crystal thin films of 4-aminobenzophenone
Authors: Bhowmik Achintya K. , Wang Jianmin , Thakur Mrinal
Published: July 2002

Single-crystal thin films of 4-aminobenzophenone have been prepared by a modification of the shear method, and the significant elements of the second-order optical polarizability tensor have been measured by the transverse second-harmonic generation (SHG) technique. Films with thickness less than the coherence length allowed measurements without significant effects due to phase-mismatch. Detailed SHG experiments with different polarization conditions were performed to determine the d coefficients. The magnitudes of the d coefficients at the fundamental wavelength of 1064 nm were found to be d23=7.3±0.4 pm/V and d22=0.73±0.04 pm/V. Directions for both type-I and type-II phase-matched propagation parallel to the film were identified. The results showed that guided-wave phase-matched SHG (type I and type II) should be possible using the films.
Quantum-classical transition of the escape rate of a biaxial spin system in a general magnetic field
Authors: Kim Gwang-Hee
Published: July 2002

Using the method of mapping of a spin problem onto a particle one, we study phase transition between quantum and classical regimes for the escape rate of biaxial spin system in the presence of both a transverse and longitudinal field. It is found that the phase diagram separating the first- from the second-order transition and its crossover temperature are greatly influenced by the ratio of the anisotropy constants as well as the external magnetic field via the particle mass and the potential.
Modeling of gas-phase and surface reactions in liquid-source chemical-vapor deposition of (Ba,Sr)TiO3 films
Authors: Yamamuka Mikio , Kawahara Takaaki , Tarutani Masayoshi , Horikawa Tsuyoshi , Oomori Tatsuo , Ono Kouichi
Published: July 2002

Reaction mechanisms for chemical-vapor deposition (CVD) of (Ba,Sr)TiO3 (BST) films have been studied by modeling reactions that should occur in the gas phase and on the film surfaces. We considered a conventional model and two other kinds of models: a copolymerization and a surface reflection model. The conventional model consisted of thermal decomposition of dipivaloylmethanato (DPM) source materials in the gas phase, followed by deposition of the decomposition products on the film surfaces. In the copolymerization model, Ba(DPM)2 and Sr(DPM)2 were assumed to preferentially copolymerize with TiO(DPM)2 in the gas phase, and the resulting products behave as dominant film precursors. In the surface reflection model, moreover, each source material was assumed to thermally decompose in the gas phase, and the products from TiO(DPM)2 adsorbed on film surfaces prevent the other Ba and Sr precursors from sticking onto the surfaces. Numerical simulations were performed for CVD of SrTiO3 films, and the atomic incorporation rates of Sr and Ti into SrTiO3 films were calculated as a function of the titanium source flow rate. The conventional model gave numerical results that the Sr incorporation rate was independent of the titanium flow rate, while the experiments showed a decrease with increasing flow rate. This implies that the conventional model cannot explain the CVD-SrTiO3 reaction mechanisms. On the other hand, the incorporation rates of Sr obtained from the two experimental models decreased with increasing titanium flow rate, being in agreement with the experiments. Moreover, the overall sticking probabilities for SrTiO3 film deposition calculated using the experimental models also fitted the experiments, where the surface reflection model gave a better agreement. These results indicate that the experimental models, especially the surface reflection model is suitable to explain the CVD reaction mechanisms for SrTiO3, and thus, BST film deposition.
Experimental verification of the theory of multilayered Rayleigh waves
Authors: Potel Catherine , Devolder Stefaan , Ur-Rehman Aziz , de Belleval Jean-François , Gherbezza Jean-Marc , Leroy Oswald , Wevers Martine
Published: July 2002

A phenomenon which has been termed “multilayered Rayleigh modes” has been presented in previous papers. This study aims to prove experimentally the existence of these waves in anisotropic periodically multilayered media. These modes result from a combination of Floquet waves which propagate in a periodically multilayered medium when all the Floquet waves are inhomogeneous. The experimental verification was done using an acousto-optic technique and a measurement of the reflected field, which was obtained with a hydrophone measurement system, on a carbon/epoxy composite plate. The experimental and calculated dispersion curves of the multilayered Rayleigh modes were then drawn. The coincidence of the curves was found quite good, thus confirming our theory. However, two modes were found by the acousto-optic technique not to fit into the theory. One experimentally detected mode was found to correspond to the Lamb mode of the plate and the other was not experimentally detected by the acousto-optic technique. Measurement of the reflected field for this mode, which was obtained with a hydrophone measurement system, and its comparison with the predicted reflected field make it possible to verify the existence of the mode. The combination of both experiments permit a good coincidence to be found.
Optical properties and luminescence mechanism of oxidized free-standing porous silicon films
Authors: Xu Dongsheng , Guo Guolin , Gui Linlin , Tang Youqi , Zhang B. R. , Qin G. G.
Published: July 2002

We have systematically studied the evolution of the optical properties of free-standing porous silicon (PS) films during thermal oxidation at 200 °C in air by measuring of the PL, IR, optical absorption and Raman scattering spectra. After thermal oxidation for 200 h, the PL peak energies of free-standing PS films focus on a small energy range centered around 1.61 eV. In this case, a conclusion that the sizes of nanometer silicon particles (NSPs) decrease with increasing time of thermal oxidation is obtained by theoretical fitting for Raman scattering spectra. The evolution of transmission curve is quite complicated (which redshifts first and then blueshifts during thermal oxidation), and can be explained by a model including the quantum confinement effect in the NSPs and the influence of the Si–O bonds on the surface of NSPs. Meanwhile, no focusing of the optical absorption edge of free-standing PS films is found. Experimental results clearly indicate that there is no simple correlation between the PL energies and the sizes or the energy gaps of NSPs. These results can be explained by the quantum confinement/luminescence center model.
Lasers in dense gases pumped by low-energy electron beams
Authors: Ulrich A. , Nießl C. , Wieser J. , Tomizawa H. , Murnick D. E. , Salvermoser M.
Published: July 2002

The use of low-energy (≈15 keV) electron beams for pumping laser systems in dense gases with high specific power deposition is described. Thin (300 nm) SiNx ceramic foils used as entrance window in a transverse geometry for the electron beam allows pressure differentials of several atmospheres with low percentage energy loss in transmission. The 1.73 μm XeI (5d[3/2]1–6p[5/2]2) infrared laser was used for a first demonstration of this concept. The laser operated between 130 and 650 mbar. A threshold pumping power of 5.3 W and a maximum output power of 6 mW were observed. The system can be scaled to high pumping power (≈MW/cm3) and short wavelength.
Determining the permeability of a half space of linear magnetic material by magnetic force microscopy
Authors: Coffey Mark W.
Published: July 2002

A fundamental inversion problem for the magnetic force microscopy (MFM) of a semiinfinite linear magnetic material is formulated. The solution is developed for a general applied field in the upper half space. Static conditions are assumed so that a magnetic scalar potential can be employed. By specializing to a point-source model for the MFM tip, it is shown how the magnetic permeability μ(z) depending only upon the vertical coordinate can be recovered from one-dimensional force measurements. The inversion procedure uses a wave number-dependent kernel function K(k), which is analogous to a surface impedance ratio. A numerical example illustrates the process of obtaining μ(z) from the kernel function. The inversion results describe the use of MFM data to extract a material property as a function of depth.
1/f
noise in n-channel metal-oxide-semiconductor field-effect transistors under different hot-carrier stresses
Authors: Xu J. P. , Lai P. T. , Cheng Y. C.
Published: July 2002

Degradation mechanisms contributing to increased 1/f noise of n-channel metaloxide-semiconductor field-effect transistors (n-MOSFETs) after different hot-carrier stresses are investigated. It is demonstrated that for any hot-carrier stress, the stress-induced enhancement of 1/f noise is mainly attributed to increased carrier-number fluctuation arising from created oxide traps, while enhanced surface-mobility fluctuation associated with electron trapping at preexisting and generated fast interface states and near-interface oxide traps is also responsible under maximum substrate- and gate-current stresses. Besides thermal-oxide n-MOSFETs, nitrided-oxide devices are also used to further support the above analysis.
Modal gain and lasing states in InAs/GaAs self-organized quantum dot lasers
Authors: Fry P. W. , Harris L. , Parnell S. R. , Finley J. J. , Ashmore A. D. , Mowbray D. J. , Skolnick M. S. , Hopkinson M. , Hill G. , Clark J. C.
Published: July 2002

The modal gain of an InAs/GaAs self-organized quantum dot laser is determined from a measurement of the normal incidence, interband photocurrent. The maximum modal gain of the ground state transition is shown to have a value of (7±3) cm−1, considerably smaller than typical values for comparable quantum well lasers. The photocurrent technique is demonstrated to be a convenient and simple method for determining the spectral form of the gain and for comparing the modal gain of different devices. The consequences of the small modal gain for the laser characteristics are discussed.
Effect of annealing and replacement of vanadium by Cr(III) and Mn(IV) ions in (V2O5)0.8–(P2O5)0.2 glass on its magnetic susceptibility, electrical conductivity, and dielectric constant
Authors: El-Shaarawy M. G.
Published: July 2002

The effect of heat treatment and substitution of vanadium by other transition metal ions, such as Cr3+ or Mn4+ in (V2O5)0.8–(P2O5)0.2 glass on the electrical conductivity, dielectric constant, dielectric loss, and magnetic susceptibility has been studied over a temperature range of 80–400 K and frequencies of 102–106 Hz. The ac conductivity, σac, was found to be increased by annealing and decreased by the replacement of vanadium with Mn4+ or Cr3+ ions. The σac value increased with the measuring frequency ω according to σac(ω)=A(ω)s, where s has a value in the range of 0.33–0.48. Dielectric loss ε showed maxima at temperatures depending on the sample composition and the measuring frequency. The magnetic susceptibility χ was found to increase by annealing and by introducing Cr3+ or Mn4+ into glass materials. The results obtained were explained on the basis of a mutual interaction, which is exclusively occurring between double redox pairs during the sample preparation or during the annealing process, to produce a shift in redox ratios. The experimental results were correlated together and discussed.
Secondary ion mass spectrometry and x-ray analysis of superconducting Nb/Pd multilayers
Authors: Gerardi C. , Tagliente M. A. , Del Vecchio A. , Tapfer L. , Coccorese C. , Attanasio C. , Mercaldo L. V. , Maritato L. , Slaughter J. M. , Falco C. M.
Published: July 2002

We report on accurate structural investigations of sputtered Nb/Pd multilayers by means of high-resolution secondary ion mass spectrometry and x-ray reflectivity. The combined use of secondary ion mass spectrometry and x-ray specular reflectivity techniques allows us to study the chemical configuration of the interfaces and to relate it to the observed superconducting properties. Secondary ion mass spectrometry analyses reveal a distinct Nb and Pd modulation and very sharp profiles with abrupt interfaces indicating a negligible interdiffusion of Nb and Pd at the interfaces. Moreover, analyzing the features in the Nb and Pd profiles and correlating them to the oxygen distribution in the multilayers and to the low-angle x-ray patterns, thin layers (3–4 nm thick) of niobium oxide were noticed at the Nb/Pd interfaces, while no oxide layers at the Pd/Nb interfaces could be detected. The role of this oxide layer in the determination of the crossover between three- and two-dimensional superconducting behavior in parallel external magnetic field, is discussed.
Plasma charge-density ratios in a dusty plasma
Authors: Childs M. A. , Gallagher Alan
Published: July 2002

It is shown that particle diffusion in the afterglow of a dusty plasma can be used to establish several properties of the active plasma. Specifically, the ratio of the average mass of light negative and positive ions, and a limit for the ratio of electron to ion charge densities can be determined. From the afterglow decay of visible particles, with and without electrode bias, the charged fraction of particles can be measured. An afterglow ambipolar-diffusion model is developed to relate this neutral fraction to the densities and masses of electrons and light ions in the active plasma. We then use this technique to analyze a silane radio-frequency plasma. In the active plasma positive charge is dominated by small SiyHn+ cations, and the negative charge by small SixHm− anions, with x and y<100. This analysis establishes that the electron density is less than 10% of the ion density in the operating discharge and that the anion/cation average mass ratio (x/y) is ∼6.
Viscoelastic behavior of 80In15Pb5Ag and 50Sn50Pb alloys: Experiment and modeling
Authors: Edwards L. K. , Lakes R. S. , Nixon W. A.
Published: July 2002

Dynamic and creep behavior of 80In15Pb5Ag and 50Sn50Pb were studied isothermally over nine decades of time and frequency. 80In15Pb5Ag was examined at −6, 21, and 50 °C, and 50Sn50Pb was examined at 21 °C. Viscoelastic behavior was observed at strains less than 10−5 as a function of temperature and time/frequency. At the small strain used in the study, the alloys exhibit linear viscoelasticity rather than the viscoplasticity observed at larger strain. Viscoelasticity was subject to constitutive modeling. The creep followed a superposition of a stretched exponential and a power law in time, and an Arrhenius form in temperature. Behavior was thermorheologically simple over at least nine decades of true time and frequency.