bluuebunny/crossref_metadata_2025 huggingface dataset:
Internal Lifshitz tails for Schrödinger operators with random potentials
Authors: Klopp Frédéric
Published: July 2002

In this short note, we prove that, for periodic Schrödinger operators perturbed by an Anderson-type random potential with long-range single site potential, the density of states always show a Lifshitz tail at a band edge. Thus, we correct a mistake made in an earlier paper [F. Klopp, Duke Math. J. 98, 335–396 (1999)].
Optical gain and loss in 3 μm diode “W” quantum-well lasers
Authors: Suchalkin Sergey , Westerfeld David , Donetski Dmitrii , Luryi S. , Belenky G. , Martinelli Ramon , Vurgaftman Igor , Meyer Jerry
Published: July 2002

Gain in broad-area midinfrared diode “W” lasers (λ=3–3.1 μm) has been measured using lateral mode spatial filtering combined with the Hakki–Paoli approach. The internal optical loss of ≈19 cm−1 determined from the gain spectra was the same for devices with either ten or five period active regions and nearly constant in the temperature range between 80 and 160 K. Analysis of the differential gain and spontaneous emission spectra shows that the main contribution to the temperature dependence of the threshold current is Auger recombination, which dominates within almost the entire temperature range studied (80–160 K).
Effect of compression on the molecular shape of polymer mushrooms with variable stiffness
Authors: Edvinsson Tomas , Elvingson Christer , Arteca Gustavo A.
Published: July 2002

Under confinement, the average shape of a polymer chain is modified in interesting ways. In this work, we discuss how confinement affects the mean geometrical properties of wormlike polymers with variable flexibility and monomer–monomer interaction. Here, we consider a polymer mushroom, i.e., a single chain that is permanently anchored to a flat surface by an end point. Compression is introduced by confining the chains inside an infinite slab with parallel hard walls. Regarding polymer shape, we focus on two large-scale geometrical properties that are not correlated a priori: the chain’s size and its entanglement complexity. Using Monte Carlo simulations, we have analyzed the behavior of these two properties under confinement for a range of potential energy functions. A recurrent pattern of shape transitions emerges, as indicated by changes in the correlation between mean size and entanglements. Our results show that, whereas a flexible polymer with strong self-attraction sustains high compression without deforming, polymers that are either too rigid or too weakly self-attracting are “flattened” by slight compression. Furthermore, we find a general relation between molecular size and entanglements that is valid over a range of polymer models and levels of confinement. We conclude that chain stiffness influences less the compressive behavior of a polymer than chain self-interactions.
Ordering of Ge quantum dots with buried Si dislocation networks
Authors: Leroy F. , Eymery J. , Gentile P. , Fournel F.
Published: July 2002

Buried dislocation networks obtained by Si(001) wafer bonding pattern the free surface of the sample, giving rise to long-range undulations and short-range embossing, respectively, for flexion and rotation misalignement. Comparison with continuum-elasticity calculations reveals that this patterning is enhanced by strain-driven overetching. These surfaces are a template for growth, and we show that Ge quantum dots can be ordered with a fourfold symmetry by proceeding a postgrowth annealing.
Electrically isolated SiGe quantum dots
Authors: Tevaarwerk Emma , Rugheimer P. , Castellini O. M. , Keppel D. G. , Utley S. T. , Savage D. E. , Lagally M. G. , Eriksson M. A.
Published: July 2002

A variation of electric force microscopy (EFM) is used to measure the electrical isolation of SiGe quantum dots (QDs). The SiGe QDs are grown on mesas of ultrathin silicon on insulator. Near the mesa edges, the thin silicon layer has been incorporated into the QDs, resulting in electrically isolated QDs. Away from the edges, the silicon layer is not incorporated and has a two-dimensional resistivity of less than 800 TΩ per sq, resulting in relatively short RC times for charge flow on the mesa. The EFM technique we use here is a powerful probe of samples and devices with floating-gate geometries.
Local Lyapunov exponents for spatiotemporal chaos
Authors: Pikovsky Arkady S.
Published: July 2002

Local Lyapunov exponents are proposed for characterization of perturbations in distributed dynamical systems with chaotic behavior. Their relation to usual and velocity–dependent exponents is discussed. Local Lyapunov exponents are analytically calculated for coupled map lattices using random field approximation. Boundary Lyapunov exponents describing reflection of perturbations at boundaries are also introduced and calculated.
Quantification of scaling exponents and crossover phenomena in nonstationary heartbeat time series
Authors: Peng C.-K. , Havlin Shlomo , Stanley H. Eugene , Goldberger Ary L.
Published: July 2002

The healthy heartbeat is traditionally thought to be regulated according to the classical principle of homeostasis whereby physiologic systems operate to reduce variability and achieve an equilibrium-like state [Physiol. Rev. 9, 399–431 (1929)]. However, recent studies [Phys. Rev. Lett. 70, 1343–1346 (1993); Fractals in Biology and Medicine (Birkhauser-Verlag, Basel, 1994), pp. 55–65] reveal that under normal conditions, beat-to-beat fluctuations in heart rate display the kind of long-range correlations typically exhibited by dynamical systems far from equilibrium [Phys. Rev. Lett. 59, 381–384 (1987)]. In contrast, heart rate time series from patients with severe congestive heart failure show a breakdown of this long-range correlation behavior. We describe a new method—detrended fluctuation analysis (DFA)—for quantifying this correlation property in non-stationary physiological time series. Application of this technique shows evidence for a crossover phenomenon associated with a change in short and long-range scaling exponents. This method may be of use in distinguishing healthy from pathologic data sets based on differences in these scaling properties.
(Global and local) fluctuations of phase space contraction in deterministic stationary nonequilibrium
Authors: Bonetto F. , Chernov N. I. , Lebowitz J. L.
Published: July 2002

We studied numerically the validity of the fluctuation relation introduced in Evans et al. [Phys. Rev. Lett. 71, 2401–2404 (1993)] and proved under suitable conditions by Gallavotti and Cohen [J. Stat. Phys. 80, 931–970 (1995)] for a two-dimensional system of particles maintained in a steady shear flow by Maxwell demon boundary conditions [Chernov and Lebowitz, J. Stat. Phys. 86, 953–990 (1997)]. The theorem was found to hold if one considers the total phase space contraction σ occurring at collisions with both walls: σ=σ↑+σ↓. An attempt to extend it to more local quantities σ↑ and σ↓, corresponding to the collisions with the top or bottom wall only, gave negative results. The time decay of the correlations in σ↑,↓ was very slow compared to that of σ.
Monitoring the growth of nonuniform gratings written holographically by Gaussian laser beams
Authors: Bjorkholm J. E. , Eichner L.
Published: July 2002

Interfering Gaussian laser beams are sometimes used to photochemically etch gratings into materials; the gratings which result are nonuniform since the groove depth varies over the grating cross section. The grating growth can be monitored in real time by observing the diffraction of the writing beams into their various orders. In order to relate the maximum groove depth to the observed diffraction efficiency, the grating nonuniformity must be accounted for. We present a short calculation which does this. The results are checked with measurements on actual gratings and good agreement is obtained. The results can help to interpret previously published measurements.
Pressure-induced effects and phase relations in Mg2NiH4
Authors: Gavra Z. , Kimmel G. , Gefen Y. , Mintz Moshe H.
Published: July 2002

The low-temperature (<210 °C) crystallographic structure, electrical conductivity, and thermal stability of Mg2NiH4 powders compacted under isostatic pressures of up to 10 kbar were studied. A comparison is made with the corresponding properties of the noncompressed material. It has been concluded that under stress-free hydriding conditions performed below 210 °C, a two-phase hydride mixture is formed. Each of the hydride particles consists of an inner core composed of an hydrogen-deficient monoclinic phase coated by a layer of a stoichiometric orthorhombic phase. The monoclinic phase has a metalliclike electrical conductivity while the orthorhombic phase is insulating. High compaction pressures cause the transformation of the orthorhombic structure into the monoclinic one, thereby resulting in a pressure-induced insulator-to-conductor transition. Reduced decomposition temperatures are obtained for the compressed hydrides. This reduction is attributed to kinetic factors rather than to a reduced thermodynamic stability.
Propagation of a 3-ns relativistic electron beam in air
Authors: Greenspan M. A. , Juhala R. E.
Published: July 2002

Experiments were performed measuring beam current, magnetic field, and energy of a 400-keV relativistic electron beam propagation in air in a 7.6-cm-diam glass guide tube, the same covered with a conducting screen, and in a 3.4-m-diam chamber. Nose-erosion rates, current neutralization, and stability data are given at various pressures. A propagation window exists between pressures of 270–1070 Pa. At the lower pressures, propagation is limited by nose erosion, whereas at higher pressures, propagation is limited by instability of the tail. The conducting screen stabilizes the tail of the beam, extending the high-pressure end of the window to ∼6000 Pa. Rectilinear propagation within 5 mrad occurs in the large chamber at 270–800 Pa.
GaAs, AlAs, and AlxGa1−xAs: Material parameters for use in research and device applications
Authors: Adachi Sadao
Published: July 2002

The AlxGa1−xAs/GaAs heterostructure system is potentially useful material for high-speed digital, high-frequency microwave, and electro-optic device applications. Even though the basic AlxGa1−xAs/GaAs heterostructure concepts are understood at this time, some practical device parameters in this system have been hampered by a lack of definite knowledge of many material parameters. Recently, Blakemore has presented numerical and graphical information about many of the physical and electronic properties of GaAs [J. S. Blakemore, J. Appl. Phys. 53, R123 (1982)]. The purpose of this review is (i) to obtain and clarify all the various material parameters of AlxGa1−xAs alloy from a systematic point of view, and (ii) to present key properties of the material parameters for a variety of research works and device applications. A complete set of material parameters are considered in this review for GaAs, AlAs, and AlxGa1−xAs alloys. The model used is based on an interpolation scheme and, therefore, necessitates known values of the parameters for the related binaries (GaAs and AlAs). The material parameters and properties considered in the present review can be classified into sixteen groups: (1) lattice constant and crystal density, (2) melting point, (3) thermal expansion coefficient, (4) lattice dynamic properties, (5) lattice thermal properties, (6) electronic-band structure, (7) external perturbation effects on the band-gap energy, (8) effective mass, (9) deformation potential, (10) static and high-frequency dielectric constants, (11) magnetic susceptibility, (12) piezoelectric constant, (13) Fröhlich coupling parameter, (14) electron transport properties, (15) optical properties, and (16) photoelastic properties.

Of particular interest is the deviation of material parameters from linearity with respect to the AlAs mole fraction x. Some material parameters, such as lattice constant, crystal density, thermal expansion coefficient, dielectric constant, and elastic constant, obey Vegard’s rule well. Other parameters, e.g., electronic-band energy, lattice vibration (phonon) energy, Debye temperature, and impurity ionization energy, exhibit quadratic dependence upon the AlAs mole fraction. However, some kinds of the material parameters, e.g., lattice thermal conductivity, exhibit very strong nonlinearity with respect to x, which arises from the effects of alloy disorder. It is found that the present model provides generally acceptable parameters in good agreement with the existing experimental data. A detailed discussion is also given of the acceptability of such interpolated parameters from an aspect of solid-state physics. Key properties of the material parameters for use in research work and a variety of AlxGa1−xAs/GaAs device applications are also discussed in detail.
Attenuation effects in accelerated cluster-ion beams
Authors: Moser H. O. , Krevet B.
Published: July 2002

Intense energetic beams of hydrogen cluster ions characterized by an atom flux density of several A0/cm2, a kinetic energy per atom of several eV, and a number of atoms per charge in the cluster ions of about 105 are markedly influenced by collisions of the cluster ions among themselves and with background gas particles. This is demonstrated by acceleration of a partially ionized cluster beam with high voltages in the range of 75–350 kV and measurement of the attenuation of the neutral component. The attenuation varies exponentially with the ionizing electron current; the attenuation constant b is proportional to U1.7a , where Ua is the acceleration voltage. Straightforward extrapolation of  b to the conditions prevailing in fully ionized cluster beams leads to attenuations down to about 20% which is not too far from the measured value scattering around 40%.
Impurity bands and band tailing in moderately doped silicon
Authors: Lowney Jeremiah R.
Published: July 2002

The density of states of the valence and conduction bands in silicon has been calculated at room temperature for dopant densities near the transition between the existence of a distinct impurity band and its coalescence with the continuum band to form a band tail. The dopant densities for the three cases considered are (1) 1.5×1018 cm−3 acceptors; (2) 6.2×1018 cm−3 acceptors; and (3) 1.2×1019 cm−3 donors compensated by 6.2×1018 cm−3 acceptors. The calculation is based on multiple-scattering theory with the self-energy calculated self-consistently to all orders of the interaction. The results show a small but significant amount of effective band-gap narrowing.
Structural characterization of proton exchanged LiNbO3 optical waveguides
Authors: Canali C. , Carnera A. , Della Mea G. , Mazzoldi P. , Al Shukri S. M. , Nutt A. C. G. , De La Rue R. M.
Published: July 2002

This paper reports the results of structural analysis of proton-exchanged lithium niobate optical waveguides fabricated in Z-, X-, and Y-cut substrates immersed in pure benzoic acid. Rutherford backscattering spectrometry, nuclear reactions, secondary ion mass spectrometry, scanning electron microscopy, and x-ray diffraction were used to measure atomic composition profiles and the marked lattice distortion induced by the proton exchange process in the waveguiding layer. H and Li concentration measurements indicate an exchange of about 70% of the Li atoms are present in the virgin LiNbO3 crystal.
Optical properties of AlxGa1−x As
Authors: Aspnes D. E. , Kelso S. M. , Logan R. A. , Bhat R.
Published: July 2002

We report pseudodielectric function 〈ε〉 data for AlxGa1−xAs alloys of target compositions x=0.00–0.80 in steps of 0.10 grown by liquid-phase epitaxy and measured by spectroellipsometry. Cleaning procedures that produce abrupt interfaces between the technologically relevant alloys x≤0.5 and the ambient are described. The 〈ε2〉 data are corrected near the fundamental direct absorption edge by a Kramers–Kronig analysis of the 〈ε1〉 data to circumvent a limitation of the rotating-analyzer ellipsometric technique. The results and the associated pseudooptical functions 〈n〉, 〈R〉, and 〈α〉 are listed in tabular form. Accurate values of the E0 and E1 threshold energies are determined from these spectra by Fourier methods. From these values, and from similar values for a GaAs-capped AlAs sample grown by organometallic chemical vapor deposition, the dependencies of the E0 and E1 interband critical point energies on nominal composition are obtained. Cubic polynomial representations of these dependences are determined to allow nominal Al fractions to be calculated analytically from optical threshold data. The systematic behavior of 〈ε1〉 at 1.5 eV and of the E2 peak in 〈ε2〉 near 5 eV show that scatter in these data is less than 1% of the peak values of the spectra for x≤0.5. For x≥0.6 the peak data appear to show systematic discrepancies indicating that chemical cleaning cannot completely remove surface overlayers on high-Al-content samples. Optical measurements for a sample with x=0.9 also reveal the oxidation of high-Al samples proceeds irregularly and not along a uniform spatial front. Interpolation procedures to obtain approximate representations of dielectric function spectra at compositions other than those measured are discussed, and suggestions for improving accuracy in future optical measurements on these and related materials are also given.
Temperature dependence of the specific heat and entropy of CeAl3
Authors: Edelstein A. S. , Fisher R. A. , Phillips Norman E.
Published: July 2002

It is thought that with decreasing temperature CeAl3 first condenses into a crystal-field JZ=±3/2 doublet ground state and then further condenses into a Kondo singlet state. To test this description, we use it to calculate the specific heat and entropy of CeAl3. We calculate the specific heat contribution of the JZ=±3/2 doublet using the resonant level model. The contributions from the JZ=±5/2 and ±1/2 doublets are computed using the known crystal-field energies but allowing for a broadening of the levels. If it is assumed that the excited crystal-field states have Lorentzian distributions with a width of the order of 50 K, the calculation is in generally good agreement with experimental data for the f-electron contribution. (The specific heat of LaAl3, which is reported here, was subtracted from the total to obtain the f-electron contribution.)
Application of a particle simulation to modeling commutation in a linear thyratron
Authors: Kushner Mark J.
Published: July 2002

Commutation is the period during which a thyratron makes the transition between an open state and a conducting state. During commutation the voltage across the thyratron decreases from the holdoff voltage to the conduction value; 10’s of kV to <100 V. The time for commutation, as measured by the anode voltage fall time, is usually 10–100 ns, a value which depends on the holdoff voltage, internal gas pressure, and grid geometry. In this paper, a model for commutation in a thyratron is described and its results are compared to experiment for a thyratron having a linear geometry. The model uses a Monte Carlo particle simulation for electrons and a continuum fluid representation for ions. A particle multiplication and renormalization scheme is used in the model to simulate electron avalanche so that only a moderate number of particles (4000–12000) need to be used. A modified null cross-section technique is used to account for large changes in the density of electron collision partners as a function of position or time. A model for the external circuit enables simulation of current and voltage. Results from the model for these quantities agree well with experiment, and indicate that commutation occurs in two stages. A survey study contrasts the tradeoff between high-voltage holdoff and switching speed.
Parametric studies of an electron-beam-pumped krypton-rich KrF laser
Authors: Kannari F. , Shaw M. J. , O’Neill F.
Published: July 2002

This paper describes the results of a detailed experimental study of an electron-beam-pumped, high Kr concentration KrF laser. The excitation rate is 1.4 MW/cm3 for 1 atm of Kr gas. The formation efficiency of KrF* and extraction efficiency are estimated using calculated values of saturation intensity and g0/α0, the ratio of small-signal gain to saturable absorption, together with measured values of g0 and the ratio of g0 to nonsaturable absorption (αn). Although the highest formation efficiency of 24% is observed at 99.7% Kr concentration, the effect of finite vibrational-relaxation rate significantly decreases the KrF* density accessible to lasing at high Kr concentration due to the shorter lifetime of KrF*. KrF* vibrational-relaxation rates of 4×10−11 and 5×10−11 cm3 s−1 are determined for Ar gas and Kr gas, respectively. A decrease of g0/α0 and g0/αn resulting in low extraction efficiency is observed at high Kr concentration due to the relatively high α0 and αn. The intrinsic efficiencies are 11, 11.8, and 9% for 1 atm mixtures at 10, 50, and 99.7% Kr, respectively.
Formation of the oxygen precipitate-free zone in silicon
Authors: Yang K. , Carle J. , Kleinhenz R.
Published: July 2002

A model for the formation of the oxygen precipitate-free zone (PFZ) has been developed for silicon subjected to ‘‘high–low–high’’ anneals. This model uses a time-dependent nucleation rate for the calculation of the nuclei density, and the stability of the precipitate nuclei at the temperature of the third anneal for the calculation of the PFZ depth. The incubation time for nucleation and the interfacial energy between the oxygen precipitates and the silicon matrix are obtained by fitting experimental data. Using the incubation time and the interfacial energy so obtained, the PFZ depth, the precipitate density profiles, and the oxygen concentration profiles calculated from this model are in good agreement with experimental data.
Physics of ferromagnetic amorphous alloys
Authors: O’Handley R. C.
Published: July 2002

After some introductory comments on materials classification and a brief historical outline, this review seeks to identify those fundamental physical phenomena that underlie the major technical properties of ferromagnetic amorphous alloys. Those phenomena are reviewed and an attempt is made to compare existing data and, where possible, to synthesize new perspectives. A fundamental approach is taken in the sense that we move from consideration of the local atomic structure to its consequences for the electronic structure and from the electronic structure finally to the physical properties it determines. We focus on the aspects of the structure-property sequence that set amorphous metallic alloys apart from their crystalline counterparts. Such a review would be incomplete without addressing the new issues and insights raised by the discovery of the quasicrystalline state. The very existence and better understood atomic arrangements of quasicrystals help to define and illuminate their amorphous cousins.
IBEX magnetic field extraction and propagation experiments of intense high-energy electron beams
Authors: Mazarakis Michael G. , Miller R. Bruce , Poukey James W. , Adler Richard J.
Published: July 2002

We have investigated the extraction and propagation of intense relativistic electron beams from an immersed foilless diode into a magnetic field-free region. It was established experimentally that under matching conditions, the extracted beam propagates into and through the axially varying magnetic field region with minor perturbation of the equilibrium. The independent variables of the experiment were beam current, beam radius, magnetic field strength, and gas pressure in the field-free region. The accelerator used was IBEX. [J. J. Ramirez, J. P. Corley, and M. G. Mazarakis, in Proceedings of the Fifth International Conference on High-Power Particle Beams, San Francisco (Physics International, San Leandro, CA, 1983), p. 256.] The propagation of the extracted beam was studied up to 60 cm downstream from the extraction foil. A strong, fast growing filamentation instability was observed after extraction. Time-resolved measurements of the beam current, net current, and current distribution were performed by using segmented Faraday cups. Time-integrated measurements of beam rotation and emittance were also recorded. The observed beam parameters and equilibrium radii before and after extraction are compared with theory and numerical calculations.
Studies of the 1.35-eV photoluminescence band in InP
Authors: Kim T. S. , Lester S. D. , Streetman B. G.
Published: July 2002

A commonly observed luminescence band in InP near 1.35 eV has been studied in detail. The dependence of the transition energy on sample temperature and excitation power density indicates the band results from a donor-to-acceptor pair transition involving a donor level with an activation energy of ∼33 meV. Luminescence spectra from samples implanted with Si, Al, or P show that the donors responsible for the band are native defects or complexes that result from radiation damage. These results do not support previous assignments of the 1.35-eV band to transitions involving various impurities.
Effective cross section of the Nd:YAG 1.0641-μm laser transition
Authors: Fuhrmann K. , Hodgson N. , Hollinger F. , Weber H.
Published: July 2002

The cross section of a laser transition is one of the most important parameters, because via the saturation intensity, Is=hν/(στ), the output power depends on it. For the Nd:YAG 1.0641-μm laser transition, the published values vary between 4×10−19 and 8.8×10−19 cm2, as obtained by spectroscopic methods. This paper deals with a new method, which determines σ from the absolute value of the output power, the small-signal gain, and the losses. Moreover, the extraction efficiency is evaluated, taking into account the mode structure.
Exchange interaction between electric current and magnetic domain wall containing Bloch lines
Authors: Berger L.
Published: July 2002

Bloch lines are boundaries between regions of a magnetic domain wall with opposite chiralities. An electric current exerts a force on Bloch lines through the s-d exchange interaction, in metallic ferromagnets. This large ‘‘s-d gyroscopic force’’ is normal to the drift velocity ve of the electron gas and to the Bloch line itself. We consider a current crossing a plane domain wall which contains Bloch lines, all of the same sense of twist. At a critical value of ‖ve‖, the Bloch lines start to move along the wall. At a larger critical value, the wall itself starts to move, in the direction of ve. This should happen at current densities ≂106 A/cm2, for Bloch walls in Ni-Fe films. The effective viscous coupling between electron gas and a Bloch wall is ≂100 times larger than the coupling arising from s-d exchange in the absence of Bloch lines. Small magnetic bubble domains move at right angle to the direction of a uniform current.
Open-tube Zn diffusion in GaAs using diethylzinc and trimethylarsenic: Experiment and model
Authors: Reynolds S. , Vook D. W. , Gibbons J. F.
Published: July 2002

We have characterized the diffusion of Zn into GaAs from the organometallic sources diethylzinc and trimethylarsenic. This method produces surface hole concentrations in excess of 1020 cm−3 with good control of junction depths as shallow as 0.1 μm. Smooth surface morphology is retained. The profile shape is much more complex than the accepted interstitial-substitutional Zn-diffusion model would predict. To explain the observed profiles, a new model for Zn diffusion is proposed and implemented in a computer simulation.
Electronic structure and spin density of Gd2Fe14B
Authors: Ching W. Y. , Gu Zong-Quan
Published: July 2002

The electronic structure of Gd2Fe14B has been calculated using the spin-polarized orthogonalized linear combination of atomic orbitals method. The use of the band approach to study the magnetic properties of the rare-earth iron-boron compounds should be more valid in the case of Gd2Fe14B because of the exactly half-filled f shell of the Gd atom, which has a zero orbital angular momentum. The calculated total spin magnetic moment of 18.41 μB per formula unit is in good agreement with experiment, and the site-decomposed Fe moments show that the j2 site has the highest and the e site has the smallest moment. Other results presented include total and partial density of states and the spin density distributions on the basal and [110] plane. The positive spin density from the Fe sites shows a network type of structure parallel to the c axis. These and other results are compared with those calculated for Nd2Fe14B.
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u spatially resolved surface characterization of realistic semiconductor structure after reactive ion etching process
Authors: Oehrlein Gottlieb S. , Chan Kevin K. , Jaso Mark A.
Published: July 2002

The properties of a patterned semiconductor structure have been utilized to enable spatially resolved analysis of the surface chemistry of a contact hole reactive ion etching process by x-ray photoemission spectroscopy. The topography of the semiconductor structure in combination with angle resolved analysis has been used to cause geometrical shadowing and to enable selective area analysis. Differences in the conduction characteristics of silicon and photoresist and concomitant electrostatic charging of the insulating photoresist layer made fluorocarbon films on photoresist and silicon nonequivalent and allowed to unambiguously assign their spatial origin.
Transient-grating study of amorphous As2S3 films
Authors: Tanaka Keiji
Published: July 2002

Dynamics of the photoinduced refractive-index change in glassy As2S3 excited by pulsed light have been studied using a novel transient-grating technique, in which the grating is produced by projecting comb-filter images. Monotonic relaxations in the μs region are observed at room temperature and at 80 K. The results are discussed on the basis of the single-and-double well model proposed for the photodarkening phenomenon.
Parametric investigation of the dirt spike generation in a pulsed metal vapor laser discharge
Authors: Lin C. E. , Yang C. Y. , Wang T. C. , Huang C. L.
Published: July 2002

The generation of dirt spikes in the discharge of a clean pulsed metal vapor laser is measured under various operating conditions, such as a change in pulse repetition rates, laser tube temperatures, buffer gas pressures, and charging voltages. It is shown that the dirt spikes will increase in magnitude for such conditions that the pulse repetition rate decreases, the laser tube temperature decreases, and the buffer gas pressure increases. The ratio of the dirt spike to the charging voltage will also increase as the charging voltage decreases. All experimental results are well explained by theoretical analyses. These results lead to a number of useful suggestions for the operation of a pulsed metal vapor laser.
A new sputtering-type electron cyclotron resonance microwave plasma using an electric mirror and high-rate deposition
Authors: Matsuoka Morito , Ono Ken’ichi
Published: July 2002

Film deposition is performed by means of a new electron cyclotron resonance microwave plasma employing a high-rate sputtering system using an electric mirror. This apparatus consists of both planar and cylindrical targets. The magnetic flux penetrates both target surfaces. Microwave power is perpendicularly or obliquely introduced into the resonance cavity. High-density plasma, exceeding 1012 cm−3, much denser than the cutoff density 7×1010 cm−3, is generated. The electron beam oscillating between the two targets plays a major role in generating the dense plasma, i.e., as a beam plasma interaction. Both insulator and conductor films can be deposited continuously by this new sputtering method at high rates under low gas pressures of 10−2 . Al, Mo, and Fe films are deposited at rates above 2000 Å/min. Target utility reaches higher than 55% for nonmagnetic materials including Mo and Al, and 40% for magnetic materials including Fe. Film thickness uniformity over 4 in. in diameter with a 10% distribution is realized.
Luminescence, level saturation, and optical gain in a single InGaAs/GaAs quantum well
Authors: Fortin E. , Hua B. Y. , Roth A. P. , Charlebois A. , Fafard S. , Lacelle C.
Published: July 2002

Low-temperature photo- and electroluminescence spectra were performed on InxGa1−xAs/GaAs single quantum wells (x=0.13) under varying excitation conditions. Both types of spectra display strong 11H-associated emission, as well as impurity-related features. Saturation effects are observed for both the intrinsic and impurity emission under high excitation conditions. When optically pumped at energies higher than the GaAs band gap, the InGaAs single quantum well gave optical gains in the 10-cm−1 range, saturating at a pumping intensity of 104 W/cm2.
Theoretical and experimental investigations of subpicosecond photoconductivity
Authors: Chamoun S. N. , Joshi R. , Arnold E. N. , Grondin R. O. , Meyer K. E. , Pessot M. , Mourou G. A.
Published: July 2002

Monte Carlo methods are used to study photoconductive transients in gallium arsenide. It is demonstrated that working with presently established ranges for the Γ-L coupling coefficient, the existence of a velocity overshoot at moderate fields cannot be exactly predicted. The role of negative velocity electrons in the initial transient for short wavelength excitation is also demonstrated. Details of an actual experiment are described and evaluated against a model which incorporates the Monte Carlo simulation into a transmission line structure with a frequency-dependent characteristic impedance. The results demonstrate that an appropriately designed experiment can observe subpicosecond carrier transport transients.
A relation between EL2 (E
c−0.81 eV) and EL6 (E
c−0.35 eV) in annealed HB-GaAs by hydrogen plasma exposure
Authors: Cho Hoon Young , Kim Eun Kyu , Min Suk-Ki
Published: July 2002

We present annealing and hydrogenation behaviors for EL2 (Ec−0.81 eV) and EL6 (Ec−0.35 eV) as dominant deep levels in GaAs. During rapid thermal annealing and the hydrogenation process, a relation has been identified between a midgap level group (the EL2 group) at 0.73, 0.81, and 0.87 eV, and a deep-level group (the EL6 group) at 0.27, 0.18, and 0.22 eV below the conduction band. We then discuss a relation between the two groups and their origins.
The study of the thermal oxide films on silicon wafers by Fourier transform infrared attenuated total reflection spectroscopy
Authors: Nagasawa Yoshikatsu , Yoshii Ichirou , Naruke Kiyomi , Yamamoto Kazuhiko , Ishida Hideyuki , Ishitani Akira
Published: July 2002

Fourier transform infrared attenuated total reflectance technique was used to measure the SiOH and SiH contents in the thermal oxide films grown on Si wafers. It was found that the SiOH groups in the bulk could be eliminated by annealing at 850 °C, whereas SiOH at the Si/SiO2 interface could only be removed by annealing at 1000 °C. It was also found that SiOH and SiH groups were generated in the thin oxide film by γ-ray irradiation. The presence of H or H2 in SiO2 is necessary to explain the result.
Preparation and electrical properties of MOCVD-deposited PZT thin films
Authors: Sakashita Yukio , Ono Toshiyuki , Segawa Hideo , Tominaga Kouji , Okada Masaru
Published: July 2002

Strongly [001] oriented lead zirconate-titanate [Pb(ZrxTi1−x)O3] thin films with tetragonal structure (0<x<0.52) have been successfully grown on (100)Pt/(100)MgO substrates by using metalorganic chemical vapor deposition (MOCVD). The metalorganic precursors were Pb(C2H5)4, Zr(DPM)4 and Ti(i-OC3H7)4. Scanning electron micrographs showed dense and noncolumnar growth with good surface morphology. The relative dielectric constants at room temperature were 200–350, and appeared to have less dependence on composition x than for PZT bulk ceramics. Typical D-E hysteresis loops which occur with PZT bulk ceramics were observed. Remanent polarizations were 30–40 μC/cm2. The coercive field decreased from 65 to 40 kV/cm with increases in Zr content. The pyroelectric coefficients without poling treatment were about 3×10−8 C/cm2 K, showing almost the same value as that of poled PZT bulk ceramics.
Imaging high-temperature superconducting films
Authors: Batalla E. , Zwartz E. G. , Wright L. S. , Raider S. I. , Gupta A.
Published: July 2002

A magneto-optically active glass, Ce(PO3)3, was used to image field penetration into three superconducting films of YBa2Cu3O7 that were laser ablated on (100)-oriented SrTiO3 substrates. The magnetic-field profile in these films was mapped using the Faraday effect in an external field of 92 mT for two of the films and 181 mT for the third film. These contours show regions where flux had easily penetrated, indicating weak pinning, and other regions that were strongly pinning. From the measured field gradients, it was determined that Jc varies by at least an order of magnitude across the surface of the films.
Characterization of Er3+-doped glasses by fluorescence line narrowing
Authors: Zemon S. , Lambert G. , Andrews L. J. , Miniscalco W. J. , Hall B. T. , Wei T. , Folweiler R. C.
Published: July 2002

The Stark levels of the 4I15/2 ground state manifold have been determined for Er3+-doped fluorozirconate, fluorophosphate, phosphate, and silicate bulk glasses from fluorescence-line-narrowing (FLN) measurements at 4.2 K. Splittings between adjacent Stark levels were observed to be 10–140 cm−1 and the total energy spread of the manifold was found to range from 335 to 400 cm−1. The position of a given Stark level varies up to 60 cm−1 depending on the particular Er3+ sites excited. Using the 4.2-K results, homogeneous broadening is found to be a reasonable approximation for the 300-K luminescence band of the glasses examined. Results are also presented for silica preforms as well as for a barium-zinc-lutetium-thorium fluoride composition. The FLN studies together with a Judd–Ofelt [Phys. Rev. 127, 750 (1962); J. Chem. Phys. 37, 511 (1962)] analysis of the absorption data suggest similarities in the local environment between the fluorozirconates and the high-fluorine fluorophosphates.
Neutron diffraction study of YFe10−xCoxMo2
Authors: Lin Chin , Sun Yun-Xi , Liu Zun-Xiao , Li Gang , Yang Ji-Lian , Zhang Bai-Shen , Ding Yong-Fan , Jin Lan
Published: July 2002

YFe10−xCoxMo2(0 ≤ x ≤ 10) compounds were synthesized and studied by x-ray and neutron diffraction. Single phase samples with ThMn12-type structure can be formed in the entire range of composition. Magnetic properties were studied at fields up to 70 kOe in the temperature range of 1.5 K to room temperature. X-ray diffraction analyses of aligned powders indicate that the easy magnetization direction is parallel to the c axis when x≤6, and deviates from the c axis when x≥8. Neutron diffraction experiments show that the molybdenum atoms exhibit a strong preference for occupying the 8i sites, and cobalt atoms prefer to occupy the 8f and 8j sites.
The role of spin-dependent impurity scattering in Fe/Cr giant magnetoresistance multilayers
Authors: Baumgart Peter , Gurney Bruce A. , Wilhoit Dennis R. , Nguyen Thao , Dieny Bernard , Speriosu Virgil S.
Published: July 2002

To probe the mechanism of giant magnetoresistance (GMR) observed in Fe/Cr multilayers, we have sputter deposited at the interfaces of Fe(15 Å)/Cr(12 Å) multilayers an additional, ultrathin (0–4 Å) layer of a variety of third elements (V, Mn, Ge, Ir, and Al). When alloyed with Fe in dilute concentrations, the elements chosen have known resistivities for spin-up (ρ↑) and spin-down (ρ↓) currents arising from spin-dependent impurity scattering. The results show a clear correlation between α=ρ↓/ρ↑ of the respective element and the way in which GMR varies with the ultrathin layer thickness. In addition, little difference in GMR is observed between multilayers where the ultrathin layer thickness t/2 is deposited on every Fe/Cr interface and those with a thickness t deposited on alternate interfaces. This investigation demonstrates the importance of the type and total number of scattering centers per multilayer period to the GMR effect.
Beyond discrete tracks: Other aspects of patterned media
Authors: Lambert S. E. , Sanders I. L. , Patlach A. M. , Krounbi M. T. , Hetzler S. R.
Published: July 2002

The surface of a thin-film disk can be patterned using standard lithographic techniques to form discrete tracks as narrow as 0.5 μm. These studies have been extended to patterns formed when an etched track is broken into discrete segments by etching away some portions of a discrete track. Abrupt changes in the magnetization can be obtained by dc erasing the medium, giving readback signals with ∼50% of the amplitude of conventional transitions when the gap of the readback head is aligned with the edge of the media pattern. The implications of these results for servo and read-only applications are discussed.
Quantum-well structures of InAlP/InGaP grown by gas-source molecular-beam epitaxy
Authors: Hafich M. J. , Lee H. Y. , Robinson G. Y. , Li D. , Otsuka N.
Published: July 2002

Both single quantum-well (SQW) and multiple quantum-well (MQW) structures have been produced using the technique of gas-source molecular-beam epitaxy to grow the two wide band-gap ternary alloys, InAlP and InGaP. SQWs as narrow as two monolayers observed by bright field Transmission Electron Microscopy were found to be laterally uniform with abrupt InAlP/InGaP interfaces. Photoluminescence of SQWs of differing thickness produced a larger quantum confinement energy shift than expected, with emission at 570 nm for an InGaP well of 3.0 nm in thickness. The number and amplitude of peaks detected in double-crystal x-ray diffraction (DCXR) measurements of the MQW samples matched, to within the limit of the dynamic range of the DCXR system, the peaks calculated in a periodic two-layer dynamical simulation of the x-ray rocking curve.
Calculation of spin-reorientation temperature in Nd2Fe14B
Authors: Zhong Xue-Fu , Ching W. Y. , Lai Wuyan
Published: July 2002

The spin-reorientation phenomenon in Nd2Fe14B has been investigated using an angular dependent free energy approach. A magnetic Hamiltonian which includes the crystal electric field term and the exchange term has been established using realistic band structure results. The temperature dependence of the molecular field is accounted for by introducing the Brillouin function and the magnetic Hamiltonian is diagonalized within the ground state multiplet of the Nd ion. The eigenstates are then used to form the partition function for the free energy. At each temperature, the direction of the molecular field is obtained by searching for the minimum in the angular parameter space of the free energy. Our calculations show that for Nd2Fe14B, the net magnetic anisotropy direction is canted away from the c axis at a temperature close to the experimentally reported spin-reorientation temperature of 150 K. The temperature dependence of the magnetic structure is found to be very sensitive to the size of the second order crystal field parameter B20.
Magnetic anisotropy in Dy(Fe,Co)10V2
Authors: Jurczyk M. , Nicolaides G. K. , Rao K. V.
Published: July 2002

We have studied random as well as field-aligned powders of DyFe10−xCoxV2 alloys, (0≤x≤10), to investigate, by Co substitution for Fe, the effects on the saturation magnetization, anisotropy field, Curie and spin reorientation temperatures. In this system, which crystallizes with a ThMn12 structure, Co readily substitutes for iron in the whole composition range. X-ray diffraction analyses on aligned powders indicate uniaxial anisotropy at 298 K. A phase diagram for the spin arrangements in Dy(Fe,Co)10V2 system is presented. A distinctive feature we observe is that with Co substitution the axial-to-cone spin reorientation is found to shift to higher temperatures, while at the same time the cone-to-plane spin reorientation is suppressed to lower temperatures. At 290 K, the anisotropy field, HA initially increases in Dy(Fe,Co)10V2, i.e., from HA = 25 kOe (x=0) to HA = 48 kOe (x=5) and for x≥ (R18)7.5 the anisotropy becomes conical. The above results obtained from x-ray and magnetization measurements are consistent with ac susceptibility data at low temperatures. The effects of Co substitution on the anisotropic behavior in Dy(Fe,Co)10V2 system will be discussed.
Quantitative emission microscopy
Authors: Kölzer J. , Boit C. , Dallmann A. , Deboy G. , Otto J. , Weinmann D.
Published: July 2002

Emission microscopy has now become established as an effective technique in terms of reliability physics of industrial semiconductors. This convenient method allows chip verification and failure analysis to be carried out in many applications. Besides this, emission microscopy provides a technique for use in device engineering and the optimization of test structures. The key to using this technique to permit a more sophisticated quantitative analysis lies in a unique assignment of the light emission to the defect mechanism. Since the corresponding phenomena are numerous and their details are not fully clarified in all cases, further investigation is still required before this technique can be used routinely in a quantitative rather than qualitative approach. Some quantitative aspects of emission microscopy with respect to fundamental studies will therefore be outlined in this article, and the applicability of such practical guidelines will be illustrated. This provides the fundamentals for a comprehensive evaluation of the potential applications and degree of informativeness of this advanced method of failure analysis.
Dielectric–base transistor using YBa2Cu3O7−x/NdGaO3/SrTiO3 heterostructures
Authors: Yoshida Akira , Tamura Hirotaka , Takauchi Hideki , Imamura Takeshi , Hasuo Shinya
Published: July 2002

This paper describes the fabrication and evaluation of dielectric-base transistors having high-Tc YBa2Cu3O7−x electrodes with NdGaO3 low-permittivity barriers on SrTiO3 high-permittivity substrates. The YBa2Cu3O7−x/NdGaO3/SrTiO3 heterostructures were made by laser ablation. Nb base electrodes were sputtered on the back of the SrTiO3 substrate. The device showed transistor characteristics with voltage and current gains exceeding unity at 4.2 K. The collector current density was about 10 A/cm2 at a collector voltage of 20 V, four orders of magnitude larger than that obtained for devices having no artificial barriers.
Effects of nitrogen on oxygen precipitation in silicon
Authors: Sun Q. , Yao K. H. , Gatos H. C. , Lagowski J.
Published: July 2002

Defect interactions among oxygen, carbon, and nitrogen during a three-step high-low-high intrinsic gettering process (1100 °C+750 °C+1000 °C) were studied using differential analysis of Fourier transform infrared (FTIR) absorption spectra of Czochralski-Si crystals intentionally doped with carbon and nitrogen. Two phenomena related to nitrogen were observed: (1) Nitrogen-enhanced oxide nucleation in the temperature range from 750 to 1100 °C, thus having a negative effect on the denuding step; and (2) defect interaction associated with carbon during oxygen precipitation was significantly affected by the co-existence of nitrogen. For the latter effect the first-step annealing at 1100 °C was crucial. The results presented are consistently interpreted assuming that nitrogen participates in creation of nucleation sites for heterogeneous oxygen precipitation, and also assuming that nitrogen aggregates at the strain regions surrounding precipitates and thus retards Si self-interstitial migration. This explanation was supported by observed differences in oxygen-precipitate-related FTIR absorption and by the behavior of stress-related photoluminescence D lines.
The effect of oxygen on diamond synthesis in a microwave plasma jet
Authors: Takeuchi Ken , Yoshida Toyonobu
Published: July 2002

Although the effect of oxygen on diamond synthesis has been reported in many papers, the exact role of oxygen has not been clarified yet. The effect of oxygen on diamond synthesis in a microwave plasma jet is investigated and an attempt is made to find out the exact role of oxygen by using optical emission spectroscopy and quadrupole mass spectroscopy. The results reveal that oxygen removes C2H2 selectively in a boundary layer by producing CO, and clarify the importance of the CHx to C2H2 ratio at the place. Therefore, oxygen seems to form an advantageous environment for diamond synthesis rather than accelerate the removal of nondiamond carbons.