bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlation of magnetic and mechanical properties of hydrogenated, compositionally modulated, amorphous Fe80Zr20 films (abstract)
Authors: Rengarajan S. , Yun E. J. , Lee B. H. , Cho B. I. , Walser R. M.
Published: July 2002

Recent research has demonstrated that large amounts of hydrogen can be electrolytically incorporated in amorphous, compositionally modulated (CM) FeZr films. The first irreversible changes in the magnetic state of an electrolytically hydrogenated iron-rich amorphous alloy were observed. The hydrogen-induced changes in the magnetization were interpreted in terms of specific structural rearrangements. In this work, simultaneous measurements of the variations in the magnetization and mechanical properties of these films were measured as a function of hydrogen charging to further clarify the hydrogen-induced structure changes. The Young’s moduli E and internal friction d of as-deposited, and as-hydrogenated CM Fe80Zr20 thin films were calculated from the displacements of a vibrating composite cantilever, measured using a laser heterodyne interferometer (LHI) having a displacement sensitivity of ∼0.01 Å. E and d were measured using the resonant frequency method. CM films with thickness 1390 Å and modulation wavelength ∼10 Å were deposited on glass cantilevers (5 mm long, 2 mm wide, and 150 μm thick) by sequentially sputtering (rf diode) elemental Fe and Zr targets.

The samples were electrolytically hydrogenated for various times in 2 N phosphoric acid with a current density of 26.3 mA/cm2. The maximum change in magnetization of the film (from 71.5 to 551 emu/cm3) was observed after 5 min. During this time, E increased 18-fold from 535 GPa to 9.63 TPa. The unusually high Young’s modulus of the as-deposited CM film is comparable to those previously observed in other CM films. The change is three times larger than the change in the E of carbon steel at the martensitic transformation, and nine times larger than the hydrogen induced increase in E of pure single crystals of iron. The d of the cantilever resonance decreased with hydrogenation, indicating that the incorporated H reduced the internal friction of the CM film. Preliminary analysis of the results indicates that the mechanical and magnetic changes can be interpreted in terms of similar atomic scale changes. Measurements on films with different CM wavelengths are in progress.
Magnetocrystalline anisotropy and spin reorientation in Gd1−xDyxCo4B
Authors: Ito T. , Asano H. , Ido H. , Yamada M.
Published: July 2002

Magnetic measurements at various temperatures have been performed for loose powder and field-oriented samples of Gd1−xDyxCo4B with x=0, 0.05, and 0.1. The temperature dependences of spontaneous magnetization in these compounds are determined. It is found that a spin reorientation occurs at around T=162 K for Gd0.95Dy0.05Co4B and at around 225 K for Gd0.9Dy0.1Co4B. The temperature dependences of magnetic anisotropy constants, K1(Gd1−xDyxCo4B), of Gd1−xDyxCo4B with x=0 and 0.1 are determined. The anomalous temperature dependence of K1 (GdCo4B) is well explained by taking account of the Gd sublattice magnetic anisotropy due to the dipole–dipole interaction and the Co sublattice magnetic anisotropy similar to that in YCo4B. The temperature dependence of the Dy sublattice magnetic anisotropy constant, K1(Dy), has also been determined by making use of K1(GdCo4B) and K1(Gd0.9Dy0.1Co4B).
Driven spin-wave dynamics in yttrium–iron–garnet films (abstract)
Authors: Mar D. J. , Carroll T. L. , Pecora L. M. , Heagy J. F. , Rachford F. J.
Published: July 2002

Yttrium–iron–garnet (YIG) is an important component used in filters and other microwave devices. In this work we investigate the behavior of driven magnetostatic wave modes in rectangular YIG films subject to an in-plane magnetic field. Patterned slotlines and coplanar waveguides are used to drive the film at separate spatial locations with microwave (2–4 GHz) excitations corresponding to the magnetostatic wave modes. For a single excitation with sufficient power above the Suhl instability, the transmitted power through the film displays periodic low-frequency (10 kHz) auto-oscillations. As the drive amplitude is increased, these oscillations may display period-doubling, intermittency, and high-dimensional behavior, including chaos. A second microwave drive applied to the sample excites additional spin-wave modes that interact with those arising from the original excitation. These interactions result in additional low-frequency components in the observed auto-oscillations.
Synchronization of chaos in circular yttrium iron garnet films
Authors: Peterman D. W. , Ye M. , Wigen P. E.
Published: July 2002

The results of the synchronization of two ferromagnetic resonance signals are presented. In the experiment, a thin yttrium iron garnet (YIG) film was placed in the perpendicular resonance configuration and the bias field, rf power, and frequency were chosen so that the rf absorption of the YIG sample was chaotic. A segment of this chaotic signal was stored into memory. The goal was to induce the sample to synchronize to its prerecorded output through a perturbation applied to a system parameter. The results of these synchronization experiments were predicted by a numerical model.
Finite temperature effects in the S=1/2 Heisenberg chain Cu(C6D5COO)2⋅3D2O (abstract)
Authors: Dender D. , Reich D. H. , Broholm C. , Lefmann K. , Aeppli G.
Published: July 2002

Quasi-one-dimensional magnetic materials provide important test beds for rigorous models of interacting many-body systems. Nevertheless, there have been few studies of finite temperature effects on spin correlations in low-spin systems, though these are most likely to exhibit quantum effects. Copper benzoate, Cu(C6D5COO)2⋅3D2O, is a good realization of the S=1/2 Heisenberg antiferromagnetic chain (HAFC). We have performed ac susceptibility and inelastic neutron scattering experiments on this material which establish the Hamiltonian and an excitation spectrum which is consistent with the spinon continuum ansatz of Müller et al. We present inelastic neutron scattering measurements of the temperature evolution of the dynamic spin–spin correlation function Szz(π,ω). Comparison will be made to the classical prediction and to a finite temperature field theory of Schulz as applied to this S=1/2 HAFC.
Cu2(1,4-diazacycloheptane)2Cl4: A quasi-one-dimensional S=1/2 spin liquid system
Authors: Hammar Philip R. , Reich Daniel H.
Published: July 2002

The structure of Cu2(1,4-diazacycloheptane)2Cl4 consists of well-separated zig-zag chains of Cu atoms, suggesting the possibility of significant antiferromagnetic near-neighbor and next-nearest-neighbor interactions. We report on measurements of magnetic susceptibility χ(H,T) and heat capacity Cp(T) that show that this material does not behave as a simple linear antiferromagnetic chain with spin S=1/2. χ(H=0,T) shows a broad peak at 8 K indicative of one-dimensional antiferromagnetic correlations, but below the peak, χ drops dramatically toward zero instead of remaining finite as T→0. For T≪Tpeak, χ(H) is independent of field below a critical field Hc≊6.6 T, and rises sharply above Hc to a plateau at 8 T. Below Tpeak, Cp(T)∝exp(−Δ/T) with an activation energy Δ=6.8 K. These data indicate the presence of a gap between the ground state and the lowest-lying excited states. This material is thus a candidate for a model quasi-one-dimensional S=1/2 system with a disordered ground state that is significantly affected by competing interactions.
Hydrogen charging in nickel and iron and its effect on their magnetic properties
Authors: Ramesh A. , Govindaraju M. R. , Jiles D. C. , Biner S. B. , Roderick J. M.
Published: July 2002

The current study was undertaken to explore the possibility of detecting hydrogen cavitation in magnetic materials through magnetic property measurements. It is known that dissolved hydrogen in a material causes microvoids. These voids may affect the structure-sensitive magnetic properties such as coercivity and remanence. In this study, hydrogen was introduced into nickel and iron by two processes, namely thermal charging and cathodic charging. The effect on the magnetic properties was measured. In addition, the variation of the magnetic properties with porosity was studied.
Transmission electron microscopy study of SiF/BF2 implanted and annealed (100)Si: Amorphization and residual effects
Authors: Kim J. H. , Lee J. Y. , Paik J. C. , Kim H. J.
Published: July 2002

Formation of amorphous layers and residual defects in SiF+/BF2+ implanted and annealed (100)Si was investigated on an atomic level by using a high-resolution transmission electron microscope. Amorphous layers, of which depths were about 70% of those of amorphous layers formed by Si+ preamorphization at the same implantation energies, could be formed by SiF+ preamorphization. Two distinct layers of defects were formed in SiF+/BF2+ implanted wafers annealed at 600 °C for 1 h and then rapidly thermally annealed at 950 °C for 30 s. One layer, observed near the surface regions, consisted of intrinsic stacking faults bounded by 30° Shockley partial dislocations, twins, amorphous regions, and fine clusters. The other layer, observed near the original amorphous/crystalline interface, consisted of Frank partial dislocations of which Burgers vector is 1/3a〈111〉 and 60° perfect dislocations of which Burgers vector is 1/2a〈110〉. These defects were formed by retarding growth rate by fluorine atoms; outdiffusion of fluorine atoms; lattice misorientation between the substrate and crystalline pockets; and the introduction of an extra half- plane during the preamorphization process.
Resonant tunneling times in superlattice structures
Authors: Choe J.-W. , Hwang H.-J. , Perera A. G. U. , Matsik S. G. , Francombe M. H.
Published: July 2002

We present a rigorous and convenient approach for estimating the resonant states from the pole of the scattering matrix (reflection coefficient) in the complex energy plane and for determining the resonant tunneling time from the spacing of the energy doublets arising at resonance. The numerical calculation is much faster than numerical integration of the Schrödinger equation. When we apply this method to the coupling of two identical quantum wells, it is shown that the usual and naive estimation of resonant tunneling time through the Wentzel-Kramers-Brillouin method is invalid.
Structural and optical studies in a-CdTe:O annealed films
Authors: Ramírez-Bon R. , Espinoza-Beltrán F. J. , Arizpe-Chávez H. , Zelaya-Angel O. , Sánchez-Sinencio F.
Published: July 2002

Thin films of stable crystalline phases of the Cd–Te–O ternary system were prepared by thermal annealing in an Ar flux of amorphous CdTe:O films. The composition of the annealed films depended on the initial oxygen content in the film, the temperature and duration of the annealing process. The annealed films were characterized by means of x-ray diffraction spectroscopy and by optical absorption spectroscopy. The results show that for low oxygen content in the as grown film and high annealing temperature, the CdTe cubic phase is the predominant crystalline phase in the annealed film. For intermediate oxygen content in the as grown film, the result obtained after the annealing process is a composite material consisting in the mixture of both CdTe and CdTeO3 crystallites. The variation of the annealing temperature produces changes in the size of the crystallites of both crystalline phases. It also can change the CdTe to CdTeO3 proportion in the films. For low annealing temperature, the size of the CdTe crystallites in the film is <14 nm, the exciton Bohr diameter in CdTe. The optical characterization of the CdTe–CdTeO3 composite material shows that this system is very suitable for the study of optical transitions in the electronic band structure of CdTe. Furthermore, for the films with the smallest CdTe crystallites it is possible to observe the effects in the CdTe band structure produced by the reduction in the size of the CdTe crystallites to a dimension comparable to the exciton Bohr diameter. The annealing process in the as grown films with high oxygen content produces films composed by a mixture of the oxide insulating phases CdTeO3 and CdTe2O5.
Interlayer thickness dependence of the strong 90° coupling in epitaxial CoFe/Mn/CoFe trilayers
Authors: Krebs J. J. , Prinz G. A. , Filipkowski M. E. , Gutierrez C. J.
Published: July 2002

Trilayers of CoFe/Mn/CoFe(001) have been prepared by molecular beam epitaxy and their magnetic properties measured by magnetometry and ferromagnetic resonance. Very strong near-90° coupling between the CoFe layers, with no evidence for 180° coupling, was found in all but the thickest Mn-layer samples. The coupling energy has the form suggested recently for the case when the interlayer itself is antiferromagnetic. An analysis of the ferromagnetic resonance data indicates that the magnitude of the coupling oscillates with the Mn thickness.
Permanent spectral hole-burning in semiconductor quantum dots
Authors: Gaponenko S. V. , Germanenko I. N. , Kapitonov A. M. , Artemyev M. V.
Published: July 2002

Permanent spectral hole-burning under prolonged laser illumination was found in an ensemble of CdS quantum dots of a size less than the exciton Bohr radius embedded in a polymer film. The effect is attributed to a two-stage process stimulated by resonant optical excitation. At the first stage selective photoionization of the crystallites gives rise to a broadening of the relevant components in the integral absorption spectrum due to the local electric field effect. At the second stage a continuous photolytic process occurs providing an irreversible destruction of the crystallites and a characteristic dip in the absorption spectrum. In addition to various other techniques the observed phenomenon is an effective complementary tool for the analysis of quantum dot ensembles with an inhomogeneously broadened spectrum.
Langmuir probe measurements of discharge parameters in a Cs–Ba tacitron
Authors: Luke James R. , El-Genk Mohamed S.
Published: July 2002

Experimental measurements of steady-state discharge parameters are performed in a Cs–Ba tacitron equipped with Langmuir probes. Measured quantities include electron temperature, plasma density, and plasma potential, in both the emitter-grid and grid-collector regions. The effects of Cs pressure and electrode arrangements on the measured parameters are investigated. Measurements indicate that the electron energy distribution function in the emitter-grid gap is Maxwellian, and that there is an electron beam in the grid-collector gap, which relaxes to Maxwellian at high cesium pressure. Placing the grid closer to the collector not only increases the ion loss rate, but also makes ionization inefficient, lowering the plasma density in the grid-collector gap. The low plasma density makes it easier to extinguish the discharge during current modulation.
Plasma impedance and electron density in a pulsed laser channel
Authors: Tsui K. H. , Cavalcanti G. H. , Farias A. S. , Marinha M. D. S. , Soares L. M. , Massone C. A.
Published: July 2002

The representation of plasma impedance of gas laser discharge and spark gap channels by an inductance–capacitance (Lp−Cp) tank circuit has been useful in describing the frequency response of a pulsed superradiant laser charging circuit. The impedance matching of these plasma channels can lead to resonant narrowing of the laser pulsewidth in superradiant nitrogen lasers. Using fluid equations to model the electron and ion plasmas, the impedance of plasma channels is formulated. This derived impedance supports the phenomenological Lp−Cp tank circuit configuration, and provides the means to calculate the inductance and capacitance in terms of the plasma density and discharge dimensions. Conjugating this model with the pulse width narrowing via plasma impedance matching, the electron density at the very moment of lasing in a superradiant gas laser channel can be estimated by using the measured Lp and Cp.
Luminescence and deep-level characteristics of GaAs/Si with atomic layer epitaxy grown predeposition layers
Authors: Mazumdar Mousumi , Dhar S. , Das Utpal
Published: July 2002

A relatively simple scheme for the growth of high optical quality GaAs layers on Si substrates by metalorganic chemical vapor deposition (MOCVD) technique is reported. The process is analogous to the conventional two-step growth procedure where the initial thin nucleating layer growth is done by atomic layer epitaxy (ALE) technique, implemented into the MOCVD reactor itself. The photoluminescence from the layer is increased to about sixfold by replacing the normal predeposition growth by the proposed ALE growth technique. Magnitude of luminescence is comparable to that obtained from layers grown with strained layer superlattice buffers. A number of electron and hole traps are detected in the material by deep-level transient spectroscopy and photocapacitance experiments. A particular electron trap with an activation energy of 0.76 eV is identified as the main nonradiative center by virtue of the decrease of its density in the same proportion as that of the increase in luminescence intensity. Density of some other electron traps are also reduced as a consequence of ALE predeposition.
The effect of linear and non-linear diffusion on exciton energies in quantum wells
Authors: Harrison P. , Hagston W. E.
Published: July 2002

This paper considers the technique of investigating diffusion processes via monitoring spectroscopically the ground state energy of an exciton confined in a quantum well. It is shown that the change in the exciton energy E−E0 during linear diffusion, can be described by an empirical relationship E−E0=(Ebg−E0)(1−exp{−γ√Dt/lw}), where Ebg is the band gap of the initial barrier material, D the diffusion constant and t the time. Detailed calculations accounting for the changes in the exciton binding energy have shown that the parameter γ∼1.5 for all wells of width lw≳40 Å regardless of the material system. It is proposed that this relationship could be used to determine the linear diffusion coefficient D. Once D has been determined the relationship could then be utilized as a predictive tool, e.g., to determine the annealing time necessary to produce a given energy shift for a particular quantum well width. The paper goes on to discuss the effects non-linear diffusion processes could have on exciton energies in quantum wells. In particular, it is shown how detailed spectroscopy and annealing experiments when coupled with accurate modelling could be used to distinguish between constant and concentration dependent diffusion coefficients.
Subband mixing in resonant magnetotunneling through double-barrier semiconductor nanostructures
Authors: Farinas Paulo F. , Marques Gilmar E. , Studart Nelson
Published: July 2002

We investigate subband mixing in the magnetotunneling of an electron through a double-barrier quantum dot. The fine structure in the current–voltage characteristics, observed in a device formed by a quantum-dot sandwiched by two quantum-wire contacts, is studied as a function of a magnetic field applied along the direction of the tunneling current. The increase of the magnetic field in this one-dimensional–zero-dimensional–one-dimensional tunneling process leads to a transition from a low-field regime dominated by lateral confinement to a high-field regime dominated by magnetic confinement. The fine structure is shifted due to the magnetic field. The main result is that, as the magnetic field increases, the effect of the subband mixing at the interfaces becomes negligible and the fine structure tends to disappear at strong fields. We provide a straightforward interpretation for the mechanism underlying this transition and conjecture that it has the same origin as the one recently observed in a different device.
Effect of post-pattern annealing on the grain structure and reliability of Al-based interconnects
Authors: Kang S. H. , Kim C. , Morris J. W. , Génin F. Y.
Published: July 2002

The possibility is addressed of improving the electromigration resistance of Al and Al–Cu thin-film conductors with ‘‘quasi-bamboo’’ structures by post-pattern anneals that decrease the maximum polygranular segment length. Pure Al, Al–2Cu, and Al–2Cu–1Si lines were patterned and annealed at temperatures high enough to stimulate grain growth. Appropriate anneals led to predominantly bamboo structures with short polygranular segments. These grain structures had a high median time to failure with a relatively low deviation of the time to failure. Metallographic analyses showed that polygranular segment length was a dominant factor in determining the failure site. Post-pattern annealing promotes a preferential shortening of the relatively long polygranular segments that cause early failures. However, even after annealing, failure occurred at the longest residual polygranular segments, even when these were significantly shorter than the ‘‘Blech length’’ under the test conditions. Statistical analysis of the failure of alloy lines revealed a simple exponential relation between the failure time and the longest polygranular segment length within a line, which is functionally identical to that previously found for lines tested in the as-patterned condition.
Crystallization of germanium–antimony–tellurium amorphous thin film sandwiched between various dielectric protective films
Authors: Ohshima Norikazu
Published: July 2002

Crystallization processes were studied for germanium–antimony–tellurium (Ge–Sb–Te) ternary amorphous thin film as a single layer or sandwiched between various dielectric films, such as silicon dioxide (SiO2), siricon nitride (Si3N4), tantalum oxide (Ta2O5), zinc sulfide (ZnS), and ZnS–20 mol % SiO2. The processes were analyzed quantitatively, based on transmittance changes in Ge–Sb–Te films heated either exothermally or isothermally. Both Kissinger equation and Johnson–Mehl–Avrami kinetic analysis were adopted to estimate activation energy and the reaction order of the processes. Ge–Sb–Te single-layer amorphous film crystallized in two stages, nucleation and crystal growth. These two processes can be distinguished by exothermal crystallization patterns. By sandwiching this film into dielectric films, crystallization activation energy increases and the nucleation processes are affected. The Si3N4 and Ta2O5 dielectric films accelerate the nucleation, while the SiO2 films inhibit it, and the ZnS and ZnS–20 mol % SiO2 films promote the nucleation even in the grain growth process. Wettability measurements indicate that surface reactivity and chemical affinity are the factors which produce this variation.
Experimental evidence of a crossover in the vortex dimensionality in high-T
c superconductors
Authors: García A. , Zhang X. X. , Tejada J.
Published: July 2002

Quantum motion of vortices in high-temperature superconductors (HTSCs) was studied via magnetic relaxation measurements performed with a commercial superconducting quantum interference device magnetometer. At a fixed temperature, the field dependence of the time-logarithmic magnetic relaxation rate normalized to the first magnetization value, R=‖d(M/M0)/d ln(t)‖, was investigated in different polycrystalline HTSCs: TlBaCaCuO (2212 and 2223 single phases), YBaCuO (123 phase), and (Hg,Tl)BaCaCuO (1223 phase). The results obtained for TlBaCaCuO 2223 phase and (Hg,Tl)BaCaCuO show a common trend: R increases linearly with magnetic field up to a certain value, the dimensional crossover field H3D-2D, above which it becomes field-independent. H3D-2D is a characteristic field which depends on the anisotropy parameter and the interlayer spacing of the material. The field dependence of R can be ascribed to a crossover in the dimensionality of the object involved in the quantum process: above H3D-2D, the longitudinal dimension of the tunneling object, Lc, is smaller than the interlayer distance, so the object is of two-dimensional (2D) nature (2D pancake vortices). Below H3D-2D, 2D vortices in neighboring layers become coupled, so the tunneling object becomes three-dimensional (3D) in nature (3D flux-lines). The field dependences of R obtained for TlBaCaCuO 2212 phase and YBaCuO show only the 2D and 3D vortex regimes, respectively. Well agreement between theoretical estimates and experimental values for the dimensional crossover field and normalized relaxation rates is achieved.
In-line phase modulators using coaxial thick lead zirconate titanate coated optical fibers
Authors: Barrow D. A. , Lisbôa O. , Jen C. K. , Sayer M.
Published: July 2002

Thick piezoelectric lead zirconate titanate (PZT) films (ceramic–ceramic 0–3 composite films), using a new sol-gel based process, have been produced and used to coaxially coat optical fibers. Coated PZT of up to 200 μm thick and 10 cm long have been achieved. Using thick PZT coated single mode optical fibers, in-line phase modulators are designed, built and tested. Theoretical and experimental investigations of such phase modulators are also presented. The measured phase modulation ranges from hundreds of kilohertz to several megahertz.
A new algorithm of quantitative texture analysis adapted to thin films
Authors: Wang Y. D. , Liu Y. D. , Xu J. Z. , Liang Z. D.
Published: July 2002

A new algorithm of quantitative texture analysis, i.e., a modified maximum entropy method, was applied to the texture analysis of polycrystalline thin films. The algorithm program suitable for determining the inverse pole figure of polycrystalline thin films with hexagonal structure was developed and is illustrated with an example of Zn film deposited on Fe substrate.
The influence of plastic properties of the probe tip/Si contact on spreading resistance analyses
Authors: Gaworzewski P. , Roos B. , Höppner K. , Höppner W.
Published: July 2002

Analyses of spreading resistance measurements in Si samples with dopant profiles of the dopant sequence lowly doped on highly doped yield unreliable results if the dopant profiles are extremely steep or ultra-shallow. Reasons for this behavior are seen in effects of penetration of the probe tips into the Si sample and in the presence of a zone of a metallically conducting Si phase beneath the probe tip. Atomic force microscopy has been used to investigate the geometry of probe tip indents and scanning electron microscopy to investigate the geometry of the probe tip itself. Results of loading–unloading experiments by means of nanoindentation with a conventional spreading resistance probe tip as indenter enable us to estimate the depth of the metallic Si phase zone. It ranges from about the fourfold up to the sevenfold of the residual depth after unloading the probe tip.
Ultrasonically facilitated two-dimensional crystallization of colloid particles
Authors: Sasaki Minoru , Hane Kazuhiro
Published: July 2002

A new ultrasonic radiation technique is described which facilitates the ordering of colloid particles into regular two-dimensional arrays. Ultrasonic radiation during the evaporation of the colloid solution enlarges the area of the particulate array and leads to a densely packed lattice reducing voids and random assemblies. Lattices of polystyrene particles (diameter: 64, 137, and 330 nm) and gold particles (diameter: 39 nm) were prepared under various ultrasonic powers. The arrays were imaged by the scanning electron microscope or the atomic force microscope.
Vaporization of aluminum by 50 ps KrF laser pulses
Authors: Tsui Y. Y. , Fedosejevs R. , Capjack C. E.
Published: July 2002

Removal of aluminum films, coated onto glass microscope cover plates, via evaporation by 50 ps krypton fluoride laser pulses has been experimentally and numerically investigated. At an energy density of 260±40 mJ cm−2, which is below that required for plasma formation, the material removal rate was measured to be 2.0±0.5 nm per laser shot. The results are in agreement with calculated evaporation rates if an increase in absorption is included upon melting.
Optical characteristics of LiNbO3 implanted with Au+ ions
Authors: Shang D. Y. , Matsuno H. , Saito Y. , Suganomata S.
Published: July 2002

Optical characteristics of LiNbO3 implanted with Au+ ions at energy of 23 keV were studied. The color of the surface of the LiNbO3 was changed to blue-green and a large absorption peak around 620 nm was observed. The surface morphology was also found to change with time. Metallic Au dots were observed on the surface after implantation and grew from day to day when the samples were held at room temperature. The absorption peak produced by Au+ implantation was relatively stable toward thermal treatment compared to that of Cu+ implantation into LiNbO3. But as the sample was heated at temperatures higher than about 500 °C, this peak gradually decreased and finally disappeared. These characteristics were explained fairly well by the behavior of Au colloids formed in the surface layer of LiNbO3.
Acceptor level determination by carrier freezeout in reverse-biased Hg0.8Cd0.2Te photodiodes
Authors: Ren J. , Nimtz G. , Wollrab R.
Published: July 2002

Carrier freezeout in reverse-biased Hg0.8Cd0.2Te photodiodes has been investigated to determine the relevant acceptor level. At temperatures between 12 and 21 K hole freezeout in the p region governs the interband tunneling, which dominates the current across the reverse-biased photodiode. The acceptor level was found to be ∼4 meV in the p-type Hg0.8Cd0.2Te substrate with NA−ND∼1016 cm −3. In comparison with Hall measurements, this new method avoids the uncertainty due to contact caused by surface inversion on p-Hg0.8Cd0.2Te.
Study on the electrical properties of single grain boundaries in BaTiO3 ceramics
Authors: Feng Zhang , Zechun Cao
Published: July 2002

In the article, the electrical properties of single grains and single grain boundaries in donor doped BaTiO3 ceramics have been investigated. The results show that the grains have no positive temperature coefficient of resistance effect (PTCR effect) if the influence of electrode was neglected. The results also show that different grain boundaries have various PTCR effect. The characteristics of current-voltage do not follow the Heywang model and accord with our modified model. The maximum barrier heights of single grain boundaries are also deduced experimentally.
Parametric aspects of electron–phonon temperature model for short pulse laser interactions with thin metallic films
Authors: Mitra Kunal , Kumar Sunil , Vedavarz Ali
Published: July 2002

This work studies one-dimensional and two-dimensional heat transfer for short pulse lasers (<1 ps in duration) applied on metals using a two-subsystem (i.e., electrons and phonons) temperature model. In this model laser energy is first deposited on the electrons, which then exchange energy with the lattice. Conduction of energy is by electron motion only and the lattice contributes to the scattering of electrons. The objectives of this study are (a) to analyze the effects of different parameters such as electron specific heat, lattice specific heat, electron–phonon coupling factor, and thermal relaxation time for the one-dimensional electron and lattice temperature distributions using both hyperbolic and Fourier heat conduction formulations; (b) to examine two-dimensional effects including the effects of laser beam radial variance, laser fluence, and laser power in addition to the above parameters; and (c) to solve the transient equation of radiative transfer to incorporate the wave nature of the radiative source for the one-dimensional case.
Electrical properties in arsenic-ion-implanted GaAs
Authors: Chen Wen-Chung , Chang C.-S.
Published: July 2002

A model of effective surface potential energy is proposed to explain unknown behavior of carrier transport in film and leakage currents in Schottky diodes. X-ray photoelectron spectroscopy is employed to investigate a series of band diagrams of arsenic-ion-implanted GaAs films. It is shown that the effective surface potential energies, affected by the shift of core levels, are due to different microstructures and atomic environments in these films at different annealing temperatures. Moreover, the effective barrier heights on the surfaces of these films are changed by the different effective surface potential energies which increase from 0.49 to 0.75 eV in films annealed from 200 to 600 °C, but slightly decrease to 0.7 eV in films annealed up to 800 °C.
Dielectric function and reflectivity of 3C–silicon carbide and the component perpendicular to the c axis of 6H–silicon carbide in the energy region 1.5–9.5 eV
Authors: Logothetidis S. , Petalas J.
Published: July 2002

The optical properties of commercially available 3C- and 6H-SiC single crystals were studied in the energy region 1.5–9.5 eV with conventional and synchrotron-radiation spectroscopic ellipsometry. The surface perfection of the materials was investigated by transmission electron and atomic force microscopies. The calculated values for the effective and static dielectric functions were higher than those found in the literature. This is consistent with the fine structure and absolute values of the corresponding reflectance spectra, which were higher than those reported in other studies. The dispersion of the refractive indices in the energy region below and above the indirect gap is determined and can be used as reference and for the design and analysis of semiconductor structures and devices.
Different reaction mechanisms during mechanical alloying Ti50C50 and Ti33B67
Authors: Ye L. L. , Liu Z. G. , Quan M. X. , Hu Z. Q.
Published: July 2002

Two different reaction mechanisms for Ti50C50 and Ti33B67 have been observed respectively during milling in a planetary ball mill. It is shown that a gradual reaction occurred during milling Ti50C50, while a self-sustained reaction was obtained during milling Ti33B67 under the same milling condition. Compared with the results of milling Ti50C50 in a spex mill, the difference in mechanism is suggested to be caused by the effect of plastic deformation on the changes of fine grains and internal strain during milling, and the different formation heat of TiC and TiB2, which is the driving force for the reactions.
Comment on ‘‘Line shape, line width, and configuration coordinate diagram of the Cu band (1.21 eV) in InP’’ [J. Appl. Phys. 78, 5206 (1995)]
Authors: Collan H. K. , Krustok J.
Published: July 2002

A recent article by Pal and Bose [J. Appl. Phys. 78, 5206 (1995)] reports a photoluminescence measurement of the Cu-related 1.2 eV optical emission band in InP. By applying the configuration coordinate (CC) model they concluded that the ground-state phonon energy of the recombination center involved with this band is exactly the same as the TO phonon energy 38 meV at the Γ point. Also, it was concluded that for the CC model to be consistent with other experimental data presented, one should assume that in the CC diagram the phonon energies for the ground state hνg and for the excited state hνe, respectively, are significantly different. We have reanalyzed part of their data and argue that the conclusions may not be warranted.
X-ray analysis of ZnSe/ZnSTe quantum structure
Authors: Mai Z. H. , Sou I. K. , Luo G. M.
Published: July 2002

A novel microstructure of an A1BA2-type ZnSTe/ZnSe quantum structure has been investigated by high-resolution x-ray two-axis diffraction, reflectivity, and x-ray topography which offer a nondestructive, high-strain-sensitive method for analyzing low-dimensional structures. The results show that the molecular-beam-epitaxy growth condition was well controlled to suppress dislocations extending from the substrate and the epitaxial layers have high crystalline quality. The ZnS0.665Te0.335 epilayer undergoes a tensile strain with εT∥=2.5633×10−2 and εT⊥=8.8254×10−2 while a compressed strain with εB∥=2.7864×10−3 and εB⊥=9.5061×10−3 exists in the first layer of ZnSe. The interfacial roughness is about 5 Å and the lateral correlation length ≥2000 Å.
Noncontact thickness and composition assessment of a strained AlGaAs/AlAs/InGaAs double barrier multiple quantum well structure
Authors: Chin V. W. L. , Egan R. J. , Osotchan T. , Vaughan M. R. , Anderson S. C.
Published: July 2002

By using a contactless double crystal x-ray diffraction technique with either photoluminescence or infrared intersubband absorption and theoretical calculations, it is possible to determine the dimensions and composition of a three layered multiple quantum well (MQW) structure accurately. A strained AlGaAs/AlAs/InGaAs double barrier (DB) three layered MQW structure was used to demonstrate this. Moreover, it is shown that this structure is well suited for infrared photodetection in the 3 μm wavelength region, based on intersubband absorption. The compositions and thicknesses evaluated are in good agreement, and transmission electron microscopy is utilized to confirm the thicknesses.
Reply to ‘‘Comment on ‘Temperature limits on infrared detectivities of InAs/InxGa1−xSb superlattices and bulk Hg1−xCdxTe’ ’’ [J. Appl. Phys. 80, 2542 (1996)]
Authors: Ehrenreich H. , Grein C. H. , Miles R. H. , Flatté M. E.
Published: July 2002

Despite the preceding Comment’s assertions, the maximum theoretical detectivities of LWIR InAs/InGaSb superlattices are greater than those of HgCdTe provided the comparison involves the same base layer thicknesses (greater than the minority carrier diffusion length). The higher optimal doping of the superlattices relative to HgCdTe results in noise suppression. It is desirable because Auger recombination is substantially depressed. Shockley–Van Roosbroeck optical recombination and hence photon recycling is of little consequence in realistic device structures.
The effect of the time dependent angular distribution of the intergrain magnetic field on the transport critical current in Ag-(Bi,Pb)2Sr2Ca2Cu3Ox tapes
Authors: Glowacki B. A. , Noji H. , Oota A.
Published: July 2002

Changes in the energy dissipation of the tape form Ag-(Bi,Pb)2Sr2Ca2Cu3Ox conductor have been interpreted in terms of magnetic flux movement from, or into, the intergrain regions of the highly textured plate like grain structure. The time dependent increase or decrease of the transport critical current (Ic), originates from time dependent angular superposition of the current induced self field (HSF), and external magnetic field [field cooling (HFC), and zero-field cooling (HZFC)] at the intergrain regions. The existence of time dependent changes of Ic can be explained in terms of the time dependent flux redistribution in grains and grain boundaries caused by thermal relaxation processes.
Raman investigation on thin-film electrodes of a-C:Li
Authors: Cazzanelli E. , Mariotto G. , Decker F. , Rosolen J. M.
Published: July 2002

Amorphous carbon films, deposited via radio frequency magnetron sputtering, have been electrochemically intercalated with lithium to study their possible application as anodes for rechargeable Li microbatteries. Various concentrations of intercalated lithium have been obtained, by using galvanostatic and potentiostatic methods. After preliminary examinations by optical microscopy and by optical absorption measurements, a comparative Raman spectroscopy characterization of the films has been performed with excitation wavelengths ranging from 676.4 to 457.9 nm, to follow resonance effects. A study is made on the Raman spectral shape and its excitation wavelength dependence for the film samples with different Li concentrations. A moderate graphitization process of a-C films after intercalation results from this analysis. The Raman spectral changes induced by Li insertion do not reverse after further deintercalation cycles, and this fact is discussed in connection to the observed electrochemical reversibility of the a-C:Li electrodes.
Ion-exchanged Fe doped KTiOPO4 optical waveguides
Authors: Pun E. Y. B. , Shi L. P. , Chung P. S.
Published: July 2002

Planar and channel waveguides were fabricated in Fe doped KTiOPO4 (KTP) using the Rb+:K+ ion-exchange process. These waveguides were characterized optically. It was found that the index change is smaller than that obtained using undoped KTP substrates. However, the diffusion depth is larger. The Fe ions appear to be an effective means to modify the properties of ion-exchanged KTP waveguides. The photorefractive effect (PRE) in Fe doped KTP channel waveguides was also investigated at wavelengths of 0.543, 0.6328, and 0.83 μm. PRE was not observed, indicating that unlike that in LiNbO3 or KNbO3, Fe ion is not a major contributing factor in KTP.
Improved linear prediction for deep level transient spectroscopy analysis
Authors: Ingham Edward A. , Scofield James D. , Pachter Meir
Published: July 2002

A novel linear prediction based parameter estimation algorithm is developed for analyzing deep level transient spectroscopy (DLTS) signals. The algorithm performs significantly better than a current linear prediction based algorithm used in DLTS because it accurately accounts for the effects of noise and any underlying baseline constant. The algorithm is developed for any digitized isothermal capacitance transient. It does not rely on overmodeling or require baseline nulling hardware. The superior performance of the algorithm is verified on synthesized, as well as challenging actual DLTS signals. It is shown to consistently extend the linear regions and resolve closely spaced activation energies on Arrhenius plots.
Magnetic and recording properties of amorphous TbFeCo–In thin films
Authors: Raasch D.
Published: July 2002

A disadvantage of rare-earth–transition-metal (TM) -based magneto-optical (MO) disks is the weak intrinsic chemical stability of the MO layer. This property can be improved by the addition of several elements, but elements with partly occupied d shells show a large influence on the magnetic and recording properties of the MO layer. Indium, as a 5p metal, is known to improve the long-term stability of TbFeCo layers. We investigated the magnetic and recording properties of TbFeCo–In layers as a function of In content. Only a small decrease of Curie temperature, compensation temperature, and anisotropy was observed. The carrier-to-noise ratio (CNR) of TbFeCo–In disks was determined as a function of In and TM content. A CNR≳53 dB was obtained for In contents up to 14 at. %. With 27 at. % In, the CNR is still larger than 50 dB. The aging stability of MO disks showed a significant improvement for In contents larger than 10 at. %. For MO recording, both requirements, high CNR and long-term stability, can be obtained with TbFeCo–In layers with an In content between 10 and 14 at. %.
Influences of damage and contamination from reactive ion etching on selective tungsten deposition in a low-pressure chemical-vapor-deposition reactor
Authors: Chang Kow-Ming , Yeh Ta-Hsun , Wang Shih-Wei , Li Chii-Horng
Published: July 2002

Reactive ion etching (RIE) used in contact hole formation can result in damage and contamination of the underlying silicon substrate. In this work, influences of these phenomena on selective tungsten deposition in a low-pressure chemical-vapor-deposition reactor have been studied. The damage was generated because of ion bombardment and radiation-induced bonding changes in silicon lattices. It causes large Si consumption, rough W/Si interface during tungsten deposition, and large leakage current of W/Si Schottky structure. Simultaneously, contamination occurred with two forms of residual layers and impurity permeation layers in fluorocarbon-based RIE chemistries. The CF4/CHF3/O2 RIE of oxide produces the SiFxCyOz complex layers deposited on the sidewall and on the Si surface as well as the embedding of impurities such as F and C in the Si substrate. The creep-up, selectivity loss, lateral encroachment, high W film resistivity, and rough W/Si interface have been observed in the contaminated samples. Accordingly, a post-RIE etching technique used to remove the damage and contaminants before tungsten growth has been developed. A CF4/O2 plasma etching followed with an O2 plasma ashing step exhibits the capability of efficient surface cleaning. The excellent characteristics of W films such as elimination of encroachment and creep-up, low selectivity loss (i.e., 0.25 pcs/cm2), low resistivity of W films, smooth W/Si interface, and very low leakage current of W/Si contacts are thus obtained.
Energy level effects during multiphoton dissociation and the laser separation of closely spaced isotopes
Authors: Andreou D.
Published: July 2002

A novel approach for enhancing the selectivity of the desired isotope in the molecular laser isotope separation (MLIS) process is presented. The scheme consists of simultaneously applying two laser beams with frequencies corresponding to those between the ground and the first energy excitation level and the ground and the second energy excitation level, respectively. Practical relations on the properties of the spherical-top molecules are derived and a semiclassical analysis of the electromagnetic interaction within the limits of the experimental conditions applied in actual MLIS experiments shows that the selectivity, defined as the ratio of the absorption cross sections of the two isotopes, increases by a factor of 10–20 times in the case of the uranium isotopes. In addition, it is demonstrated that during the multiphoton absorption process energy-level splittings due to induced magnetic dipoles and induced electric quadrupoles are by no means negligible. They become significant during multiphoton processes where two or more photons are lost during the interaction process. At high pumping powers they become dominant and inhibit selectivity. They cancel out during interaction processes where there is no change in the total number of photons, such as scattering. These effects can be avoided by applying the laser beams to the molecular gas in arrangements which in principle are equivalent to a Mach–Zehnder interferometer with the molecules substituted for the reuniting beam splitter. Moreover, the induced electric quadrupoles (E2) are fully exploited. The application of the results and the concepts described herein can render the MLIS process the most economic and practical method for the commercial separation of the uranium isotopes.
Pulse narrowing characteristics in traveling-wave optical parametric generation in KTiOPO4 crystals
Authors: Nishikawa Tadashi , Uesugi Naoshi
Published: July 2002

Pulse narrowing characteristics in traveling-wave optical parametric generation in KTiOPO4 crystals are investigated. By utilizing the pulse narrowing effect, output pulses with pulse duration of 250 fs can be obtained from 550 fs pump pulses in the experiment. It is also demonstrated that when the conversion efficiency becomes large by increasing the pump intensity or by changing the phase-matching angle, the pulse narrowing effect becomes small. These tendencies are confirmed by numerical calculations of the parametric propagation process, which include the effects of temporal pulse shape, group-velocity difference, transverse beam profile, walk-off, two-photon absorption, and depletion. The theoretical results indicate that when the conversion efficiency becomes greater than 1%, the back-conversion process becomes large at the high-intensity part of the signal and idler pulses. This causes the pulse width to increase and reduces the pulse narrowing effect.