bluuebunny/crossref_metadata_2025 huggingface dataset:
A flexible two-dimensional phase correction for interleaved echo-planar imaging reconstruction
Authors: Liu Haiying
Published: July 2002

Interleaved echo-planar imaging (EPI) is a fast clinical magnetic resonance imaging (MRI) scheme that obtains multiple echoes with a proper phase encoding (PE) strategy to generate multiple k-space PE lines. Since these PE data lines are from different echoes that may carry different phase and amplitude errors originating from the static magnetic field inhomogeneity and nuclear spin relaxation, to form an image free of artifacts, both phase and amplitude errors need to be compensated properly. To address this issue, we have developed a general image reconstruction technique which is capable of accomplishing two-dimensional (2D) phase correction for image reconstruction of interleaved EPI data. In this technique we formulated the reconstruction as a problem of finding an optimal solution to a set of linear algebraic equations corresponding to an imaging measurement. The phase errors, as well as other constraints, can be incorporated into these equations. The final solution can be obtained by inverting the coefficient matrix of the equation via a complex singular value decomposition (SVD) procedure, free of k-space data gridding. 2D phase corrected images have been successfully reconstructed using a set of imaging data acquired on a clinical MRI scanner. The significance of the work is that it has demonstrated that the 2D spatial phase correction can be accomplished for a set of interleaved EPI acquisition. Also, this is a flexible image reconstruction method for further improving the resulting image quality.
Magnetic dissipation force microscopy studies of magnetic materials (invited)
Authors: Liu Y. , Grütter P.
Published: July 2002

We describe the principles of dissipation measurements, discuss various eddy current damping mechanisms, give a brief review of a model for magnetoelastic dissipation due to domain-wall width oscillations, and present some applications of magnetic dissipation force microscopy to magnetic materials. Energy dissipation is measured by simultaneous monitoring of the damping of an oscillating cantilever and the shift in resonant frequency in a magnetic force microscope. Magnetoelastic dissipation is caused by tip-field-induced domain-wall width oscillations through magnetostriction effects. Magnetoelastic damping is strongly correlated with micromagnetic structures and allows different domain walls (such as Bloch and Néel walls) to be distinguished.
Local strain relaxation in Si0.7Ge0.3 on Si(001) induced by Ga+ irradiation
Authors: Kim Chinkyo , Robinson I. K. , Spila T. , Greene J. E.
Published: July 2002

A strained pseudomorphic Si0.7Ge0.3 film grown by gas-source molecular-beam epitaxy on Si(001) was irradiated at room temperature with 25 keV Ga+ ions. The gradual strain relaxation of the metastable Si0.7Ge0.3 film was monitored using in situ x-ray diffraction as a function of dose. Based on a dimensional argument, the ion-induced damage scales as extended defects. The Hendricks-Teller model was successfully applied to explain the shifting and broadening of the additional diffuse scattering.
Degradation of commercial high-brightness GaP:N green light emitting diodes
Authors: Z̆dánský K. , Zavadil J. , Nohavica D. , Kugler S.
Published: July 2002

Deep level transient spectra, electroluminescence spectra, and light output versus current were measured on diodes degraded by a current stress. It has been shown that the drop in electroluminescence efficiency can be related to a new deep level formed by recombination enhanced reaction from the electron trap attributed to the nitrogen pair in the phosphorus site with silicon in the nearest gallium site.
Behavior of excitonic levels in symmetric and asymmetric double quantum wells in a magnetic field
Authors: Vera Francisco , Barticevic Zdenka
Published: July 2002

We studied, theoretically, the excitonic energy levels and the optical absorption spectra for double quantum wells, both symmetric and asymmetric, in the presence of a homogeneous magnetic field. Within the effective-mass approach, we expanded the excitonic wave function, in an orthogonal basis formed by the products of electron and hole wave functions in growth direction z, and one-particle solutions of the magnetic Hamiltonian in the x–y plane. We applied our method to the case of AlxGa1−xAs, for which we showed how the exciton wave functions vary, and how the basis functions are mixed in a nontrivial way by the effect of the Coulomb potential. By taking into account all the mixing between the elements in our base, we get anticrossings between excited excitonic states (to the best of our knowledge) not reported previously. The behavior in the excitonic energies and wave functions for different wells and barrier geometries is of importance in double quantum well devices.
A study of oxygen diffusion in and out of YBa2Cu3O7−δ thin films
Authors: Michaelis A. , Irene E. A. , Auciello O. , Krauss A. R.
Published: July 2002

The c-axis oriented YBa2Cu3O7−δ (YBCO) films with superconducting transition temperatures up to 89 K were prepared by ion beam sputter deposition on single crystal (100) MgO and (100) SrTiO3 substrates. The variation of the oxygen concentration δ during annealing in vacuum and in oxygen was measured in situ and in real time by means of spectroscopic ellipsometry. The ellipsometric measurables Δ and Ψ were quantitatively correlated with δ at a photon energy of 4.1 eV. Changes of the oxygen concentration below 1% were resolved. Measurements for different film thicknesses in the range from 15 to 100 nm provided information to elucidate the mechanisms for oxygen out- and in-diffusion. The oxygen out-diffusion rate depends on the layer thickness confirming a bulk diffusion mechanism. The oxygen in-diffusion is relatively independent of layer thickness suggesting that a surface/grain boundary diffusion mechanism is dominant in this case. Additionally, the effect of H2O on the oxygen diffusion was studied. It was found that H2O enhances the oxygen out-diffusion while the in-diffusion remains unchanged or even decreases. The present study shows that ellipsometry provides a powerful tool for the in situ, noninvasive, on-line control of the oxygen content of thin YBCO films.
The coupled influence of sample heating and diffraction on thermal diffusivity estimate with infrared photothermal microscopy
Authors: Bisson J. F. , Fournier D.
Published: July 2002

We consider the influence of sample heating on spatially resolved thermal diffusivity measurements with a photothermal microscope using infrared detection. The continuous component of temperature induced by an intensity modulated focused laser beam results in a sensitivity amplification in the laser beam area and contributes to enhance the effect of diffraction on the phase profile, yielding a thermal diffusivity overestimate if it is not considered. A model including diffraction and nonlinear infrared emission is presented. For moderate heating, the influence of sample heating on the phase shift and on the amplitude of the infrared signal as seen by the detector is calculated. By using this model for fitting successively the amplitude and the phase data, no significant change in thermal diffusivity value is found on a homogeneous Y2O3-doped ZrO2 sample when the modulation frequency is changed. Validation of our model is done by comparing experimental amplitude data with the expected profiles obtained with the experimental absorbed power and with the reference thermal conductivity estimate for cubic zirconia.
Sputter-deposited yttria–alumina thin films for optical waveguiding
Authors: Stadler Bethanie J. H. , Oliver Manuel
Published: July 2002

Yttria–alumina planar waveguides were fabricated by reactive codeposition from yttrium and aluminum targets. These waveguides were verified to be amorphous with yttria contents as high as 23.4% by x-ray diffraction, both conventional and glancing angle, and by transmission electron microscopy. Above 41.8% yttria, the waveguides had mixed crystallinity and contained microcrystallites (0.5–0.9 nm) dispersed throughout an amorphous matrix. These microstructures appeared to be unaffected by the oxygen content in the sputtering gas. The index of refraction was found to increase strongly as a function of yttria content, but remain constant with oxygen content. Although the waveguides had wide transmission windows, the infrared edges were observed to shift with composition toward the values of the end member edges of 11 (alumina) to ⩾15 μm (yttria). In general, the waveguides had optical losses of 10–20 dB/cm. However, films with compositions roughly equivalent to that of yttrium iron garnet had lower losses (1–5 dB/cm). These losses are the lowest reported to date for yttria–alumina waveguides, and combined with the extended infrared transparencies, make these films very promising hosts for waveguide amplifiers.
Interpulse plasma of a high-power narrow-bandwidth pulsed microwave discharge
Authors: Bhattacharjee Sudeep , Amemiya Hiroshi
Published: July 2002

The plasma produced by high-power (60–100 kW), narrow-pulse-width (0.5–1 μs) microwaves with a repetition frequency of 0.3–1 kHz has been studied experimentally. Particular attention is paid to the plasma between pulses (interpulse plasma). The plasma was created by launching microwave pulses from a magnetron operating at 3 GHz into a magnetic confinement device in a vacuum chamber. The gas used was a rare gas (Ar), a molecular gas (N2), and a molecular gaseous mixture (O2+N2), with a volume mixing ratio of 1:4. The temporally decaying ion current measured with a Langmuir probe showed different features for the three kinds of gases, which are attributed not only to the effects of recombination and diffusion but also those of metastables and negative ions. The plasma density at the end of each microwave pulse was of the order 1010 cm−3 and the electron temperature was 6–8 eV, much higher than that of the usual afterglow. Numerical simulation of the decay characteristics showed a fair agreement with the experimental results.
Direct imaging of submicron-scale defect-induced birefringence in SrTiO3 bicrystals
Authors: McDaniel E. B. , Hsu J. W. P.
Published: July 2002

Using a near-field scanning optical microscope capable of quantitative polarimetry, we map the anisotropic strain fields associated with individual submicron defects near the fusion boundaries of SrTiO3 bicrystals. Many defects exhibit unexpected spiral-shape strain patterns, whose handedness is believed to be linked to the bicrystal synthesis process. Direct observation of these defect-induced strain fields helps explain previously reported nonuniformity in the characteristics of hightemperature superconductor grain-boundary junctions fabricated on SrTiO3 bicrystals.
Selective epitaxial growth of silicon carbide on SiO2 masked Si(100): The effects of temperature
Authors: Edgar J. H. , Gao Y. , Chaudhuri J. , Cheema S. , Casalnuovo S. A. , Yip P. W. , Sidorov M. V.
Published: July 2002

The effect of substrate temperature on the growth rate, crystal grain size, and SiO2 mask stability in the selective epitaxial growth of silicon carbide deposited from SiH4, C2H4, and HCl1 on silicon dioxide masked silicon (100) was examined. Depositing at atmospheric pressure and a Cl/Si input ratio of 50 to achieve good selectivity, increasing the substrate temperature from 950 to 1000 °C increased the growth rate and the crystal size, and improved the film’s surface morphology, but also enhanced the SiO2 mask degradation rate, causing a loss of selectivity for long deposition times. For prolonged deposition times at 1000 °C, SiC nucleation occurred at both voids formed in the mask from its reaction with the silicon substrate and on the SiO2 mask itself—a consequence of increasing oxide surface roughness.
Solitary wave equation for steady-state propagation of an extended defect in a solid
Authors: March N. H. , Razavy M. , Paranjape B. V.
Published: July 2002

Lattice models to describe the steady-state propagation of (i) a screw dislocation and (ii) a crack as a pileup of screw dislocations appear to be useful. This prompts us to exhibit a solitary wave equation which describes the continuum limit of the lattice model of Celli and Flytzanis for a screw dislocation. Some numerical consequences of this continuum equation are also presented.
Structural and magnetic transformations of annealed Tb/Fe multilayers
Authors: Juraszek J. , Fnidiki A. , Teillet J.
Published: July 2002

Amorphous and crystalline sputtered Tb/Fe multilayers were annealed at different temperatures in a high-vacuum furnace and investigated at 300 K by x-ray diffraction and conversion electron Mössbauer spectrometry in order to study the effect of annealing on the structural and magnetic properties. At low annealing temperature, we have evidenced an enhancement of the perpendicular magnetic anisotropy due to a demixing process which sharpens the interfaces. At intermediate annealing temperatures, the mixing of layers progressively destroys the layered structure and, finally, the sample exhibits magnetic properties of the corresponding amorphous alloy. At higher temperatures, the crystallization of bcc-Fe and hcp-Tb is observed.
Effect of competing interactions on the critical behavior of FeCl2
Authors: Hernández Laura , Diep H. T.
Published: July 2002

In order to search for the origin of the deviation of the critical exponents of a FeCl2 model from the three-dimensional (3D) Ising universality class, we have systematically studied by standard and histogram Monte Carlo simulations the influence of different features of that model such as the frustrating in-plane interaction, the super-exchange interaction and the layered character of the lattice on the critical behavior of the system. We show that it is the layered character of this structure which is responsible for the shift of critical exponents with respect to the 3D Ising values.
Quantum tunneling of magnetization in a general magnetic field
Authors: Kim Gwang-Hee
Published: July 2002

We study macroscopic quantum tunneling and coherence in small ferromagnetic particles in the presence of magnetic fields with a general direction. Different structures of the tunnel barriers can be generated by the magnitude and direction of the magnetic field. We calculate the tunneling rate via instanton method and give the approximate analytic forms of the rate for the hexagonal and cubic symmetries. We also present the numerical results of the WKB exponent for cubic symmetry in a wide range of angles, and discuss their different features.
Optical intensity of light in layers of silicon with rear diffuse reflectors
Authors: Cotter Jeffrey E.
Published: July 2002

Light trapping is essential to the performance of thin-layer polycrystalline silicon solar cells. One relatively new method of light trapping is the use of textured or pigmented dielectric layers on the rear surface which diffuse and reflect light reaching the rear surface. This article presents a one-dimensional optical model of thin silicon solar cells with such rear diffuse dielectric reflectors. Experimental front reflectance measurements and ray tracing simulations of thin, planar silicon layers with rear diffuse dielectric rear reflectors are presented and compared to the model with good agreement. Finally, an expression for the upper limit of the optical enhancement factor is developed for this type of light trapping.
Phonon spectra of metastable C60 systems obtained under high-energy impacts
Authors: Belogorokhov Alexander I. , Afanasyeva Natalia I. , Blank Vladimir D.
Published: July 2002

Low-frequency infrared (IR) spectra of fullerene and metastable forms of C60 obtained at high pressures and temperatures have been investigated along with the spectra of natural diamond and graphite in the range from 8 to 170 cm−1. Several bands of C60 and the diamond-like phase exist in the reflection IR spectra of the low-temperature phase at comparatively low pressures. In the new solid phase, most bands shift with an increase in pressure. The bands corresponding to the diamond-like structures with sp3 hybridization were only observed in the high-pressure high-temperature phase. These low-frequency modes can be presumably attributed to zone- and space-folded phonons.
Photoreflectance spectroscopy of strained-layer (111)B InGaAs/GaAs quantum well diodes
Authors: Chan C. H. , Chen Y. F. , Chen M. C. , Lin H. H. , Jan G. J. , Chen Y. H.
Published: July 2002

InGaAs/GaAs (111)B quantum well p-i-n structures grown by gas source molecular beam epitaxy have been investigated with a photoreflectance technique. Using the reduced mass deduced from experiments, the built-in electric field is obtained from the above band-gap Franz–Keldysh oscillations (FKOs). The strain-induced piezoelectric field is then determined directly from the comparison of the periods of FKOs in different samples. Numerical solutions for exciton transition energies with the experimentally derived potentials are in good agreement with experimental results. Hence, the piezoelectric constant can be determined using the piezoelectric field. The temperature dependences of the quantized energy levels indicate that the influence of temperature on exciton transitions is essentially the same as that of the gaps of the relevant bulk constituent materials.
Measurements of charge accumulation induced by monochromatic low-energy electrons at the surface of insulating samples
Authors: Bass A. D. , Cloutier P. , Sanche L.
Published: July 2002

We investigate charging of insulators with an apparatus that allows measurements of trapped charges resulting from the impact of monoenergetic electrons of 0.1–28 eV. Details are given on the construction and operation of this instrument. A high-resolution electron monochromator provides a pulsed electron beam of variable energy and current. Accumulated surface charge is monitored using a Kelvin probe and a high-sensitivity electrometer. An ultraviolet source of adjustable maximum frequency allows the sample to be discharged for multiple measurements on the same sample. We illustrate the use of the instrument with preliminary measurements for ∼100 μm thick samples cut from an industrial polyethylene cable. The incident electron-energy dependence of the trapping probability exhibits large variation and indicates that electrons with energies <5 eV are the most efficiently trapped; charging near 10 eV is attributed to dissociative electron attachment to polyethylene molecules.
Particle-induced conductivity and photoconductivity of silicon under 17 MeV proton irradiation
Authors: Amekura Hiroshi , Kishimoto Naoki , Kono Kenichiro
Published: July 2002

Particle irradiation, as well as light illumination, to semiconductors increases electric conductivity. The particle-induced conductivity (PIC) of Si, under 17 MeV proton irradiation, has been studied measuring the dependence on proton fluence and flux. While the PIC of undoped Si rapidly deteriorates with proton fluence, that of doped Si does not greatly decrease below a certain fluence φC and steeply decreases above the fluence. The results are compared with photoconductivity (PC) in response to near-infrared light. The fluence dependence of the PIC is similar to that of the PC. The specific fluence φC coincides with the critical fluence in the PC evolution which we previously reported. The PIC is proportional to the square root of proton flux, while the PC follows a linear relation to the photon flux. Although the proton irradiation causes high-energy synergistic processes, the PIC is dominated by electron–hole production due to proton excitation. The PIC processes are elucidated in a similar manner to the PC processes, taking into account the stronger electronic excitation of the protons than that of the photons.
Two-dimensional simulation of plasma-based ion implantation
Authors: Paulus M. , Stals L. , Rüde U. , Rauschenbach B.
Published: July 2002

A particle-in-cell simulation is used to study the time-dependent evolution of the potential and the electrical field surrounding two-dimensional objects during a high voltage pulse in the context of plasma immersion ion implantation. The numerical procedure is based on the solution of Poisson’s equation on a grid and the determination of the movement of the particles through the grid. Ion current density, implanted concentration, average impact energy, and impact angle of the ions were calculated using this method for two geometrical shapes, a square and an L-shaped object. The nonuniformity of the sheath potential near convex and concave corners is shown. The divergence of the electrical field in the vicinity of corners leads to dramatically reduced concentration of the incident ions. The simulation also shows that a large ion flux hits the surface during the rise time of the pulse. Directly after the rise time, more than 40% of the whole concentration is implanted. Hence, the average impact energy of the ions is reduced during the rise time of the pulse. In the vicinity of corners the incident ions strike the surface under oblique angles. The interior sides of the objects are characterized by smaller average impact angles than the exterior sides. In addition, the dependence of the impact angle and the energy distribution on the pulse time is presented. The influence of the shape of the objects on the average energy of the ions turns out to be slight for both geometries. The results of the particle-in-cell simulation are in good agreement with the published measurements.
Sulfur doping of GaAs with (NH4)2Sx solution
Authors: Lee Jong-Lam
Published: July 2002

A novel technique for sulfur doping to GaAs was demonstrated. The surface of GaAs was treated with (NH4)2Sx solution, subsequent to annealing using either furnace or rapid thermal processing. Sulfur atoms adsorbed at the surface of GaAs during the (NH4)2Sx treatment diffuse into GaAs during the annealing. The diffusion profiles of sulfur in both types of annealing treatments show a concave shape from the GaAs surface. Diffusion constants of sulfur determined using the Boltzmann–Matano technique increase with the decrease of sulfur concentration via the depth from the surface of GaAs. This suggests that immobile sulfur donor SAs+ forms at the near surface interacts with a Ga divacancy, and results in the production of mobile As interstitials, IAs. The IAs moves fast toward the inside of GaAs and kickout the SAs+ donor, producing a fast diffusing species of interstitial S atoms. The diffusion coefficients of sulfur determined are 2.5×10−14 cm2/s at 840 °C and 5×10−12 cm2/s at 900 °C. The sulfur doping technique is applied to the fabrication of metal-semiconductor field-effect transistors (MESFETs). The MESFETs with 1.0 μm gate length exhibit transconductance of 190 mS/mm, demonstrating the applicability of this technique to the formation of active channel layer of MESFETs.
Behavior of strained Si1−yCy (0⩽y⩽0.02) layers grown on silicon during wet oxidation
Authors: Garrido B. , Morante J. R. , Franz M. , Pressel K. , Krüger D. , Zaumseil P. , Osten H. J.
Published: July 2002

We have investigated the properties of strained Si1−yCy(0⩽y⩽0.02) alloy layers grown on silicon after wet oxidation between 750 and 1100 °C. Both secondary ion mass spectrometry and x-ray photoelectron spectroscopy prove the presence of carbon in the oxide. The growth rates and refractive indices of the oxides obtained from ellipsometry show no significant differences compared with oxides grown on silicon. Infrared absorption measurements reveal decreasing stress in the oxides with rising oxidation temperature and a slight dependence of the stress in the oxide upon the carbon concentration. For the Si1−yCy layer, x-ray diffraction measurements show a decrease of the substitutional carbon concentration with increasing oxidation temperature and duration. This loss of substitutional carbon is enhanced near the SiO2/Si1−yCy interface. The formation of silicon carbide precipitates in the Si1−yCy layer is demonstrated by infrared absorption. For short oxidation times, we find an increase of the intensity of the local vibrational absorption mode of substitutional carbon. We observe discrepancies between the determination of the substitutional carbon concentration in the x-ray diffraction and infrared absorption measurements.
High field nonlinearities and current density profiles in off-axis silicon
Authors: Evans H. B. , Mawbry P. A. , Aubrey J. E.
Published: July 2002

An off-axis device simulator is developed and used to model the distribution of electrons in a thin off-axis sample of p-type silicon. The results from the simulator are validated by matching with the results from an existing analytical model in the low field limit. At high fields, accumulation of electrons can be observed at both sample surfaces causing surface inversion layers there. The individual electron valley current densities are also calculated. It is found that at low values of applied field, the diffusion components govern the current density trends, whereas at high fields the drift components dominate.
Magnetic cluster and medium noise in CoCrTa/Cr longitudinal film media studied by magnetic force microscopy
Authors: Chen J. , Saito H. , Ishio S. , Kobayashi K.
Published: July 2002

The two-dimensional analysis method of magnetic force microscopy is proposed and applied to investigate magnetic cluster and medium noise in CoCrTa/Cr longitudinal film media. It is found that both the magnetic cluster size and root mean square (rms) noise intensity are dependent on recording density and the rms noise intensity strongly enhances with the increase of magnetic cluster size. To understand the factors that influence magnetic cluster formation, the magnetic cluster size, rms noise intensity and half-amplitude pulse width are plotted against tBS/Hc and δM/MS, respectively. It reveals that the increase of coercive force Hc and the reduction of intergranular magnetic interaction could control magnetic cluster size and decrease medium noise. The relationship between medium noise and residual magnetization fluctuation has been discussed.
Domain structure dynamics of amorphous Fe64Co21B15 and Co77B23 ribbons studied by three-dimensional neutron depolarization
Authors: Sinnecker J. P. , Turtelli R. Sato , Grössinger R. , Badurek G. , Riedler P. , Menhart S.
Published: July 2002

Relaxation phenomena related to domain structure dynamics in amorphous ferromagnetic Fe64Co21B15, and Co77B23 samples were studied by time-resolved three-dimensional neutron depolarization and a conventional magnetic induction technique. Different initial domain structures were induced either by applying external stresses or by stress annealing. A theoretical model was developed to describe the observed time dependence of neutron depolarization upon passage through such samples. It is shown that the domain structure approaches the equilibrium state with stable domain wall positions at a rate that depends essentially both on the sample composition and on the induced magnetic anisotropy.
Role of silicon impurities in the trapping of holes in KTiOPO4 crystals
Authors: Stevens K. T. , Setzler S. D. , Halliburton L. E. , Scripsick M. P. , Rottenberg J.
Published: July 2002

Electron paramagnetic resonance (EPR) has been used to characterize a new hole trap in flux-grown KTiOPO4 crystals. This center is formed at room temperature when the crystals are exposed to either 60 kV x rays or a pulsed 355 nm laser beam. Principal g values measured at room temperature are 2.0030, 2.0102, and 2.0320. The intensity of the EPR spectrum is considerably larger in a silicon-doped sample, thus suggesting that the responsible defect consists of a hole trapped on an oxygen ion adjacent to a silicon impurity located on a phosphorus site. Also, a broad optical absorption band peaking near 500 nm has been observed in the irradiated samples. The silicon-associated hole centers thermally decay over a period of several days at room temperature as electrons are released from Ti3+ traps. Analysis of hole-center decay curves obtained at three temperatures (291, 300, and 311 K) has shown that the kinetics of this electron-release process are primarily second order. The activation energy is approximately 0.80 eV and the “frequency” factor is approximately 4.1×109 s−1.
Post-annealing effects on antireduction characteristics of IrO2/Pb(ZrxTi1−x)O3/Pt ferroelectric capacitors
Authors: Kushida-Abdelghafar Keiko , Hiratani Masahiko , Fujisaki Yoshihisa
Published: July 2002

Antireduction characteristics of IrO2/Pb(ZrxTi1−x)O3(PZT)/Pt ferroelectric capacitors are improved by post annealing. When an as-processed capacitor receives a 3% hydrogen annealing at 300 °C (a process condition for fabricating the interlayer dielectric), capacitor characteristics are heavily degraded. This is because Ir that is produced by IrO2 reduction plays a catalytic role in PZT reduction. By contrast, if the IrO2/PZT/Pt capacitor is post annealed in O2 atmosphere at 600 °C for 1 h, the capacitor characteristics can be maintained even if it undergoes the hydrogen annealing. The O2 annealing improves the crystallinity of the IrO2 top electrode and excess PbOx in sol-gel derived PZT diffuses into the IrO2 film. As a result, antireduction characteristics of the IrO2 top electrode itself are drastically improved and the PZT film becomes stoichiometric at the same time. Exclusion of excess PbOx in PZT results in an increase in spontaneous polarization of the IrO2/PZT/Pt ferroelectric capacitor. Furthermore, the polarization hysteresis characteristics can be preserved after the hydrogen annealing because the reduction of the top IrO2 electrode does not occur and there is no material which causes the PZT reduction.
Capacitance transient spectroscopy in metal-insulator-metal systems and its application to the determination of trap parameters in polyimide films
Authors: Liufu D. , Kao K. C.
Published: July 2002

The capacitance of a metal-insulator-metal system with the presence of a space charge in the insulator has been derived under various conditions. On the basis of the transient behavior of the capacitance as a function of the applied voltage and temperature, trap parameters in an insulator can be determined. Polyimide films were used to demonstrate the use of this capacitance transient spectroscopy for the determination of the concentrations of the originally existing traps as well as the new traps created by dissociative trapping of carriers injected from the electrical contact at high fields.
Retention time in multiple-tunnel junction memory device
Authors: Jalil M. B. A. , Wagner M. , Ahmed H.
Published: July 2002

A computationally inexpensive approximation is obtained for the retention time of charges stored on a memory node of a multiple-tunnel junction (MTJ) memory device, based on previous simplifying assumptions by Jensen and Martinis. The approximation takes into account both thermally assisted single electron tunneling and higher order processes, or cotunneling and is in good agreement with a full master equation simulation of the device up to a temperature T≈T0/10, where T0=e2/kBC. For the case of a memory device formed within a δ-doped layer in GaAs, it is predicted that leakage due to single tunneling starts to dominate over cotunneling at temperatures above T≈T0/60, and that a sharp reduction in retention time occurs above T≈T0/100. Our analysis also shows that with the typical dimensions of present devices, a memory lifetime of a year requires the stringent condition of an 11-junction MTJ operated at below 1 K.
Temperature investigation of dark current and its electrical noise in GaAs/AlGaAs multiquantum well photodiodes
Authors: Wintrebert-Fouquet M. , Orsal B.
Published: July 2002

Dark current fluctuations in three types of multiquantum well (MQW) GaAs/AlGaAs avalanche photodiodes have been investigated. This work investigated both forward and reverse biases and furthered the understanding of the physics of noise in MQW structures used in photodetection (avalanche photodiodes) and emitters (semiconductor lasers). Under reverse bias, the increase of dark current and flicker noise compared with a classical PIN junction or Schottky junction is caused by thermionic field effect (TFE) conduction at the MQWs barriers. A method is developed as a function of temperature to detect the TFE at each barrier of the MQW before the onset of multiplication. Decreasing temperature is known to produce an increased resistance limit across an MQW emitter photodiode. Under forward bias, white and flicker noises are governed by the increase of resistance limit.
Structure and photoluminescence of InGaAs self-assembled quantum dots grown on InP(001)
Authors: Liu Feng-Qi , Wang Zhan-Guo , Wu Ju , Xu Bo , Gong Qian , Liang Ji-Ben
Published: July 2002

Molecular beam epitaxy has been used for growing InGaAs self-assembled quantum dots (QDs) in InAlAs on an InP(001) substrate. Nominal deposition of 9.6 monolayers of In0.9Ga0.1As results in QDs of ∼6.5 nm high with an areal density of 3.3×1011 cm−2. Conspicuous bimodal size distribution is identified, and is responsible for the observed QDs photoluminescence (PL) emission with two peaks at 0.627 and 0.657 eV. Good agreement is achieved between the observed PL peak energies and calculated results.
A theoretical investigation of field induced switching in a disordered electron wave coupler
Authors: Steinberg Michal , Peskin Uri
Published: July 2002

A theoretical study of field induced switching in a disordered dual electron wave coupler [Eugster and del Alamo, Appl. Phys. Lett. 64, 3157 (1994)] is presented. A far-microwave field is applied in order to control the lateral tunneling of ballistic electrons, represented as time-dependent wave packets. Coherent suppression of the tunneling oscillations [Hanggi et al., Phys. Rev. Lett. 67, 516 (1991)] is demonstrated within a disordered wave coupler, represented by a two dimensional stochastic model. The longitudinal propagation of the electron wave packet is shown to be sensitive to weak disorder in the wave coupler only when the maximal elastic scattering range exceeds roughly half the De-Broglie (Fermi) wavelength of the electron.
On the mechanism of aluminum via fill by reflow and forcefill as studied by transmission electron microscopy
Authors: Dirks A. G. , Webster M. N. , Turner P. , Rich P. , Butler D. C.
Published: July 2002

A comparison has been made between the Al via fill mechanisms in both reflow and forcefill processes. Cross-sectional transmission electron microscopy has been used to study the Al transport into the vias as a function of time. Our analysis shows that reflow and forcefill results can be explained by a stress relaxation model. We propose that the transport of aluminum into the vias as a function of time is described by both diffusion and dislocation movement. In the case of reflow at high temperature, the vias may be filled completely, after closure, by high-temperature creep of Al. In the case of forcefill, an additional high stress has been applied which raises the strain levels such to activate the dislocation glide and climb mechanism. The results from detailed investigations of the microstructure by cross-sectional transmission electron microscopy support these new insights.
Electromigration proximity effects of two neighboring fast-diffusion segments in single-crystal aluminum lines
Authors: Joo Y.-C. , Thompson C. V. , Baker S. P. , Arzt E.
Published: July 2002

In near-bamboo lines, electromigration-induced damage initiates at polygranular clusters which are longer than a critical length and which act as fast-diffusion segments. It has been proposed that two neighboring subcritical clusters can also lead to damage through the interaction of their stress fields. In order to prove the existence of, and to study, such proximity effects, artificial clusters were generated by creating continuous segments of plastic deformation in single-crystal aluminum lines using nanoindentation. Pairs of segments having different separation distances and lengths were made. In situ electromigration tests showed that these segments generated damage in the form of voids and hillocks even when the individual segments were shorter than the critical length. The void growth rate was found to be a function of the separation distance and segment length. A simple analytical model for the electromigration flux in these structures is shown to be consistent with the measured void growth rates. Electromigration characteristics such as the diffusivity, the effective charge, and the critical stress for void formation can be extracted from a comparison between experimental results and model predictions.
Ultraviolet-photosensitive effect of sol–gel-derived GeO2–SiO2 glasses
Authors: Shigemura Hikari , Kawamoto Yoji , Nishii Junji , Takahashi Masahide
Published: July 2002

Germanosilicate glasses are prepared by a sol–gel method and the ultraviolet (UV) photosensitivity of the glasses is investigated by optical absorption, electron spin resonance, and photoluminescence measurements. A KrF pulsed laser and a Hg lamp are used as UV light sources. The concentrations of intrinsic germanium-related oxygen-deficient centers in the glasses are successfully controlled by sintering conditions; in air or under reduced pressure. One-order larger intensity of the 5 eV absorption band is observed in the sol–gel glass sintered under the latter condition, as compared to a fiber preform of almost the same composition, which is formed by the vapor-phase axial deposition method. The effect of irradiation with KrF laser pulses on sol–gel glass is different from that on preform glass. On the other hand, the Hg-lamp illumination has the same effect on both sol–gel glass and preform glass. Based on these results, we discuss the defect states in sol–gel-derived glass and fiber preform glass and also the mechanisms of photochemical reactions under these two UV light sources.
Direct correlation between mechanical failure and metallurgical reaction in flip chip solder joints
Authors: Liu C. Y. , Chen Chih , Mal A. K. , Tu K. N.
Published: July 2002

We tested flip chip solder bonded Si samples under tensile and shear loading as a function of annealing time at 200 °C. The solder bump was eutectic SnPb and the underbump thin film metallization was Cu/Cr deposited on oxidized Si. We found that the failure mode is interfacial fracture and the fracture strength decreases rapidly with annealing time. From scanning electric microscope observations, the fracture occurs at the Cu–Sn/Cr interface. We conclude that it is the metallurgical reaction that has brought the solder into direct contact with the Cr surface. The weak joint is due to the spalling of Cu–Sn compound grains from the Cr surface, especially near the edges and corners of the joint.
Cathode fall-dominated Ar discharge: Transient and steady-state experiments
Authors: Jelenković B. M. , Phelps A. V.
Published: July 2002

The time-dependent transition of an Ar discharge from a low-current diffuse or Townsend discharge to a moderately high-current diffuse or abnormal discharge is investigated. We measure the current, voltage, and optical emission transients after a high-voltage pulse is superimposed on the direct current voltage of the low-current discharge. Emission transients are obtained near the cathode, at the end of the steady-state cathode fall, and near the anode. Spatial scans of absolute optical emission at the 750 and 811 nm lines are taken during the development of the cathode fall. These data show the initial growth of current and emission while the electric field is essentially uniform; the early minimum in emission near the anode marking the collapse of the electric field; the motion toward the cathode of the peak of emission; the drop in the discharge voltage, current, and emission during the approach to the steady-state; and the spatial distribution of emission from the steady-state discharge. Measurements are for pressure times electrode separations from 0.5 to 2 Torr cm and steady-state current densities of 500–100 μA/cm2, respectively. The initial rate of rise of the discharge voltage is roughly 100 V/μs and the times required to reach steady state are about 10 μs.
Criteria for formation of interface dislocations in a finite thickness epilayer deposited on a substrate
Authors: Zhang Tong-Yi , Lee Sanboh , Guido L. J. , Hsueh Chun-Hway
Published: July 2002

The critical epilayer thickness for the formation of misfit dislocations at the interface between an epilayer and a substrate with a finite thickness is derived in the present study. The analysis is based on the energy approach, in which the self-energy of dislocation, the interaction energy between the dislocation and free surfaces, and the lattice mismatch energy of substrate and epilayer are calculated. To satisfy the free surface condition, the methodology of superposition principle and Fourier transformation are used in analyzing the stress field due to the interface dislocation. The critical epilayer thickness is compared with those reported in the literature.
Wavelength dependence of the indices of refraction of molecular beam epitaxy-grown ZnMgSe and ZnCdSe thin films measured by two complementary techniques
Authors: Peiris F. C. , Lee S. , Bindley U. , Furdyna J. K.
Published: July 2002

We have measured the wavelength dependence of the indices of refraction n of epitaxial Zn1−xMgxSe and Zn1−xCdxSe films for a series of alloy compositions x, at wavelengths below the energy gaps of these semiconductor alloys. The measurements were performed using a combination of the prism coupler method and reflectivity. The prism coupler technique was capable of measuring n with an accuracy of at least 0.1% at four discrete wavelengths, and simultaneously to determine the thickness of the layers with an uncertainty of less than 0.5%. Using these discrete, highly precise values of n, the Fabry–Perot oscillations of the reflectivity spectra were then analyzed to obtain the continuous variation of the indices of refraction as a function of wavelength in the transparency region of the alloys.
Formation energy of self-interstitials in carbon-doped Si determined by optical absorption due to hydrogen bound to self-interstitials
Authors: Fukata Naoki , Suezawa Masashi
Published: July 2002

We determined the formation energy of self-interstitials in carbon (C)-doped Si from measurements of optical absorption due to hydrogen (H) bound to isolated self-interstitials. Specimens of C-doped Si were sealed in quartz capsules together with hydrogen (H) gas, with pressure being 1 atm at high temperature, and were annealed at high temperature for 1 h followed by quenching in water. We measured their optical absorption spectra at about 7 K with an FT-IR spectrometer. Several peaks coincided with those observed in proton-implanted Si. Hence, we conclude that complexes of simple point defects such as vacancies and self-interstitials with hydrogen atoms existed in those specimens. From the quenching temperature dependence of the peaks identified to be H bound to self-interstitials, the formation energy of self-interstitials in C-doped Si was estimated to be about 3 eV.
Global modeling of a dielectric barrier discharge in Ne–Xe mixtures for an alternating current plasma display panel
Authors: Ikeda Y. , Verboncoeur J. P. , Christenson P. J. , Birdsall C. K.
Published: July 2002

A global model of a dielectric barrier discharge in Ne–Xe mixtures for an alternating current plasma display panel was developed. This model was used to evaluate electron temperature, plasma density, densities of excited state atoms, wall charge density, current density, excimer density, and vacuum ultraviolet (VUV) intensity, and their gas composition-pressure dependencies, in order to analyze the mechanism of VUV radiation and discharge efficiency. The results show that the intensity ratio of 173 to 147 nm VUV is about a few percent. This means that the contribution of excimers is small in terms of VUV radiation. The maximum discharge efficiency was about 9% for Xe fraction in the range of 2%–12% and gas pressure in the range of 100–600 Torr. Discharge efficiency increases in the high Xe fraction and gas pressure region. The increase of the discharge efficiency is attributed to a decrease of discharge current and an increase of Xer*(3P1) excited state atom, due to the low electron temperature in the high Xe fraction and gas pressure region.
Effect of substrate hot-carrier injection on quasibreakdown of ultrathin gate oxide
Authors: Cho Byung Jin , Xu Zhen , Guan Hao , Li M. F.
Published: July 2002

The quasibreakdown (QB) of ultrathin gate oxide under substrate hot-hole and -electron injection was investigated. It has been found that hot-carrier injection greatly degrades the immunity to the QB and the hot hole is more effective than the hot electron in the degradation. The phenomenon was explained by an interface damage-controlled mechanism and verified again by monitoring the interface state densities at the onset point of QB. It also has been found that QB occurs when the interface state density reaches a critical value, regardless of the stress current density and stressing carrier type.
Switching in ferroelectric polycrystals
Authors: Hwang Stephen C. , Arlt G.
Published: July 2002

The Rayleigh law and a propagating switching region of a ferroelectric polycrystal are studied with a finite element model. Each crystallite, represented by a cubic element in a finite element mesh, is a single domain that switches completely without a simulated domain wall motion. The model involves only electric field induced (i.e., ferroelectric) switching. Under a low applied field, the model reproduces the Rayleigh law. The model predicts that a switching crystallite and its follow-up switching crystallite are likely to be the nearest neighbors and that the switching sequence of the crystallites forms the shape of an ellipsoid the major axis of which is parallel with the applied field direction. A spontaneous polarization reverses by direct 180° reorientation if only one layer of the finite elements between two electrodes is simulated but reverses by two consecutive 90° domain reorientations if the number of stacked layers between the electrodes is equal to two or greater.
Si/SiO
2
interface roughness study using Fowler–Nordheim tunneling current oscillations
Authors: Lai L. , Irene E. A.
Published: July 2002

A decrease in the amplitude of Fowler–Nordheim current oscillations (FNCOs) is reported for metal–oxide–semiconductor devices made using Si surfaces that have high spatial complexity roughness. A model based on nonuniform Si reactivity which yields SiO2 thickness fluctuations is used to explain the observations. Previous studies using lower spatial complexity roughness have shown no measurable changes in FNCOs resulting from the oxidation of purposely roughened Si surfaces. The spatial complexity of the purposely roughened Si surfaces was compared using the fractal dimension (DF) as obtained from atomic force microscopy measurements.
Wavelength shifting of adjacent quantum wells in V-groove quantum wire structure by selective implantation and annealing
Authors: Liu Xingquan , Lu Wei , Chen Xiaoshuang , Shen S. C. , Tan H. H. , Yuan S. , Jagadish C. , Johnston M. B. , Dao L. V. , Gal M. , Zou J. , Cockayne D. J. H.
Published: July 2002

Intermixing induced by selective implantation was used to modify the two-dimensional (2D) quantum wells in the V-grooved quantum wire structure. Photoluminescence measurement of the implanted samples shows the obvious blueshift of the interband transition energy while quantum wire is not influenced by implantation. So the selective implantation method has been demonstrated in this article as a useful technique to isolate the energy levels of quantum wire structure from its neighbor 2D structures, which is preferred for the optoelectronic device application of quantum wire.