bluuebunny/crossref_metadata_2025 huggingface dataset:
Removal of chlorofluorocarbons from the Earth’s atmosphere
Authors: Stix Thomas H.
Published: July 2002

This work addresses the possibility of processing the Earth’s atmosphere (5×1015 metric tons) to remove the chlorofluorocarbons (CFCs). It is the chlorine atoms, from the ultraviolet photolysis of CFCs in the stratosphere, that are held responsible for catalyzing the thinning of the Earth’s protective ozone layer. In addition, it is estimated that the contribution of CFCs to the ‘‘greenhouse effect’’ and global warming is already 40% that of carbon dioxide and the figure is estimated to rise to 60% in the next four decades. This study surveys the use of powerful lasers to break up CFCs, while still in the troposphere, by infrared multiphoton dissociation. The reaction products would be expected to dissolve in rain droplets. One major limitation to this highly speculative scheme is posed by stimulated rotational Raman scattering of the laser beams. As presently perceived, the cost of installation and operation of the elaborate laser facilities would be certainly prohibitive unless a factor of 5 or 10 improvement in overall efficiency can be found.
Discovery of a new photoinduced electron trap state shallower than the DX center in Si doped AlxGa1−xAs
Authors: Jia Y. B. , Li M. F. , Zhou J. , Gao J. L. , Kong M. Y. , Yu P. Y. , Chan K. T.
Published: July 2002

We have found a new electron trap state in Si-doped AlxGa1−xAs by deep level transient spectroscopy and constant temperature capacitance transient measurements under strong light illumination. This new trap is shallower than the DX center associated with Si impurity in that its emission and capture activation energies are equal to 0.20±0.05 and 0.17±0.05 eV, respectively. Its maximum concentration is comparable to the concentration of the DX center. Possible origins of this new trap and its relationship to the DX center are discussed.
Charge transfer between paramagnetic photoquenchable anion antisites and electron-induced acceptors in GaAs
Authors: Christoffel E. , Goltzene A. , Schwab C.
Published: July 2002

The variation of As+Ga content during illumination in weakly electron-irradiated semi-insulating GaAs is analyzed in terms of the pertinent parameters of the midgap donor EL2, leading to a determination of the total content of photoquenchable anion antisites independent of initial paramagnetic fraction. The associated photocarrier release is used for modeling the corresponding variation of the concentration of neutralized ST1 acceptors in a scheme involving one donor and two competing acceptor levels.
Fine crystals of zinc oxide formed by a conically converging shock-wave technique
Authors: Yamada Kenjiro , Tobisawa Shotaro
Published: July 2002

ZnO fine crystals with various growth forms were developed by condensation of the high-temperature ultrasupersaturated gas generated from ZnO powder by means of the conically converging shock-wave technique utilizing detonation of explosive charge. The morphology and structure of ZnO fine crystals were investigated by electron microscopy. They were conveniently classified into plates, columns, pyramids, hollow crystals, stellar-shaped crystals, spheres, whiskers, and dendrites. Most of them have the hexagonal structure, while small number of crystals which apparently have the cubic structure also were obtained.
Synthesis of electrostatic lenses by simulated annealing
Authors: Szilagyi M.
Published: July 2002

The use of simulated annealing is proposed for automatic design of electrostatic lenses with given first-order properties and minimum aberrations. The synthesis of a high-quality lens for focusing an ion beam produced by a liquid-metal source is shown as an example.
Noncollinear third harmonic generation and tunable second harmonic generation in barium borate
Authors: Bhar G. C. , Chatterjee U. , Das S.
Published: July 2002

The third harmonic of a Nd:YAG laser is generated in a beta barium borate crystal by noncollinear sum frequency mixing of the second harmonic with the fundamental beam from a Nd:YAG laser. Tunable ultraviolet radiation is also generated by the second harmonic of different dye lasers in this crystal.
Device physics of the soft-mode electro-optic effect
Authors: Andersson G. , Dahl I. , Komitov L. , Lagerwall S. T. , Skarp K. , Stebler B.
Published: July 2002

The soft-mode ferroelectric liquid-crystal (SMFLC) effects utilize the electroclinic response of chiral orthogonal smectic phases (A*,B*,E*) in bookshelf geometry. The SMFLC cell may be considered a retardation plate with a field controllable optic axis, with a submicrosecond response time, and a wide continuous dynamic range. A great variety of electro-optic components and devices can be constructed based on the SMFLC effect, many of them adding novel possibilities and challenges for optical design. We discuss in the present paper different combinations of SMFLC cells with retarders and polarizers, giving optical components capable of light and color modulation. Particularly, multiple electroclinic cells in a special constellation have the potentiality to give nearly achromatic full-modulation light valves, as well as electrically controlled high-speed color filters, which can be used for simple and compact TV cameras. Reflective single-cell electroclinic devices are suitable for integration with semiconductors to give high-speed spatial light modulators and general optical processing components with high contrast and full grey-scale capability.
Pressure dependence of i
n s
i
t
u boron-doped silicon films prepared by low-pressure chemical vapor deposition. I. Microstructure
Authors: Joubert P. , Sarret M. , Haji L. , Hamedi L. , Loisel B.
Published: July 2002

I n situ boron-doped silicon films have been deposited by the low-pressure chemical vapor deposition technique in the pressure and temperature ranges of 1–2.5×10−3 Torr and 515–700 °C, respectively. These films have been investigated by means of x-ray diffraction and transmission electron microscopy in order to study the influence of the silane partial pressure and deposition temperature on the microstructure of the doped films. X-ray experiments combined with gradual etching were performed in order to check the in-depth distribution of the crystallite textures. The microstructure of the boron-doped and undoped polysilicon films are compared.
Effects of annealing on resistivity and on Schottky barrier heights of sputter-deposited MoSi2 films
Authors: Koshy J.
Published: July 2002

MoSi2 films were deposited by rf sputtering from MoSi2 grains. The stoichiometry of the film was verified by the backscattering method. The effect of heat treatment on the resistivity of the film was studied by annealing the film up to 1000 °C in nitrogen atmosphere. After a 1000 °C anneal, resistivity of 90 μΩ cm can be achieved reproducibly. Measurements of hole and electron barriers of junctions between sputter-deposited MoSi2 films and either p- or n-Si are reported. For an as-deposited contact, the hole and electron barriers on p- and n-Si were 0.75 and 0.38 eV, respectively, for chemically etched surfaces. For sputter-etched surfaces, the hole barrier increased further to 0.83 eV and the electron barrier reduced to 0.32 eV. By annealing the diodes in nitrogen at 400 °C for 30 min, the hole barrier was lowered to 0.56 eV and the electron barrier was increased to 0.58 eV for both chemically etched and sputter-etched surfaces.
Deviations from bulk transport measurements in semi-insulating GaAs
Authors: Halder N. C. , Look D. C.
Published: July 2002

Because of the high bulk resistivity of semi-insulating GaAs, surface or near-surface effects can change the apparent magnitudes of resistivity, mobility, and carrier concentration. We consider the following causes: (1) above-surface conduction, such as that due to impurities in a porous oxide; (2) subsurface conduction, due to sawing and polishing damage; (3) tunneling conduction in surface states; and (4) changes in near-surface conduction due to the modification of surface potential by surface states or absorbates. The most important of these effects appear to be subsurface damage and surface potential changes.
Theory of a metal-semiconductor photodiode with grating coupling of the incident light to surface plasma waves
Authors: Rahman M. , Karakashian A. S. , Broude S.
Published: July 2002

A theoretical model has been developed to design a metal-semiconductor (Schottky barrier) narrow-band photodiode with grating coupling of the incident light to surface plasma waves. With optimal choice of grating parameters and the right combination of materials, the quantum efficiency can be increased over the flat surface geometry. The results of this model are in good agreement with the experimental results found in the literature.
Hydrogenated amorphous carbon films deposited by low-frequency plasma chemical vapor deposition at room temperature
Authors: Shimozuma M. , Tochitani G. , Ohno H. , Tagashira H. , Nakahara J.
Published: July 2002

Hydrogenated amorphous carbon (a-C:H) films were prepared at room temperature by low-frequency (50-Hz) plasma chemical vapor deposition using CH4 and H2 . The a-C:H films were transparent, highly resistive, and very uniform. Infrared absorption measurements, as well as Raman spectroscopy, indicated that the C bonding in the a-C:H films was predominantly sp3 . Moreover, the optical band gap of the a-C:H films was measured.
Multistep stress-relaxation study of a single crystal of n-eicosane (C2H42) in torsion
Authors: Crissman J. M.
Published: July 2002

Multistep stress-relaxation experiments in torsion have been done on a single crystal of the long-chain hydrocarbon compound n-eicosane. It was found that at very small strains the behavior approaches that of a linear viscoelastic material, whereas at larger strains the behavior becomes increasingly nonlinear and time dependent. In the region where the stress-strain behavior becomes nonlinear, it is shown that the second-step response, in an experiment in which the magnitude of the second step is one half that of the first step, can be described very well using a recent constitutive equation proposed by Zapas.
Implantation-induced diffusion of Zn and Be in GaAs/AlGaAs heterostructures
Authors: Humer-Hager T. , Treichler R. , Wurzinger P. , Tews H. , Zwicknagl P.
Published: July 2002

A combined Be/O implantation was performed into GaAs/Al0.3Ga0.7As heterostructures containing Zn and Se as intrinsic p and n dopants. Subsequent rapid thermal annealing resulted in an enhanced out-diffusion of Zn and a redistribution of Be, whereas the Se dopant profile remained essentially unchanged. Atomic profiles of Zn and Be could be correlated with the microscopic defect distribution. A change in the photoluminescence spectrum due to the overcompensation of the n-doped GaAs and AlGaAs layers was observed and corresponding signals associated with Be were identified. Annealing without a preceding implantation was shown to have no influence on the Zn atomic profile.
Subnanosecond pulse train generation from a dye laser using two interfering pump beams
Authors: Martorell Jordi , Lawandy N. M.
Published: July 2002

We have generated in a dye laser operating at 670-nm, 350-ps pulses at a 236.6-MHz repetition rate using a new gain modulation technique. The method utilizes the coherent superposition of two frequency shifted continuous wave argon laser pump beams.
A study of the AgBr(111) and AgBr(100) surface by means of atomic force microscopy
Authors: Meyer E. , Heinzelmann H. , Grütter P. , Hidber H.-R. , Güntherodt H.-J. , Steiger R.
Published: July 2002

For the first time, atomic force microscope measurements on the (111) and (100) surfaces of AgBr crystals are reported. We could image steps of varying sizes ranging from 0.9 nm to several nm. The lateral orientation of these steps could be determined by comparison with x-ray measurements. On the (100) surface, steps with the low index orientations 〈011̄〉 and 〈011〉 were observed. On the (111), surface steps were mainly oriented in the 〈12̄1〉 and 〈11̄0〉 directions. The most evident difference between these surfaces was that on the (111) surface no crossing steps occurred. This observation will be discussed in relation to the adsorption of dye aggregates on these crystals, which is of great importance for photographic emulsion technology.
Investigation of the probabilistic behavior of laser-induced breakdown in pure water and in aqueous solutions of different concentrations
Authors: Schmidt-Kloiber H. , Paltauf G. , Reichel E.
Published: July 2002

In this paper we report on experiments to investigate the laser-induced breakdown properties of saline solutions of different concentrations and of highly deionized water, using a Q-switched Nd:YAG laser. The observation of the dependence of the breakdown probability on the pulse energy gives information about the influence of the ion concentration on the breakdown occurrence. It has turned out that the generation of initial electrons for the avalanche by the ions determines the breakdown threshold in saline solutions. In extremely pure water, with no ions as electron donors, the first free electrons have to be produced by multiphoton ionization of the water molecules, which leads to a very sharp threshold. The region of pulse energies, where breakdown occurs only with a certain probability, has its minimum width in pure water, shows its maximum extension in low concentrated solutions and is again getting narrower with increasing concentrations.
Temporal distortion of a short laser pulse in an absorbing amplifier
Authors: Tilleman Michael M.
Published: July 2002

Temporal laser pulse distortion during amplification in the presence of nonsaturable absorbers is analyzed. The laser pulse duration ranges between the inverse of the laser bandwidth and the lasing state lifetime. It is found that nonsaturable absorption in the amplifying medium has two effects: (i) it limits the maximum pulse fluence and (ii) it reduces the pulse-width growth.
Optical and electrochemical studies of passive film formation in amorphous Ni-Cr-P-C alloys
Authors: Hagan D. B. , Sloope B. W. , Niculescu V. A.
Published: July 2002

The investigation of passivation of an amorphous Ni-l4Cr-17P-0.5C alloy in lN H2 SO4 through anodic polarization and near-normal optical reflectance is reported. It was found that the alloy passivates with a current density of 10−1 A/m2 extending to 1.0 V with current density dependent upon surface morphology. In the transpassive region under constant current density conditions the reflectance of the film exhibits strong interference phenomena and overall exponential decay in intensity. The behavior of the system in this region is described with a single thin-film optical model consistent with the formation of a chromium phosphate deposit layer which increases in thickness at a rate of 7 nm/s at a 1.67 mV/s sweep rate.
Deep-level admittance spectroscopy of D
X centers in AlGaAs:Sn
Authors: Chakravarty S. , Subramanian S. , Sharma D. K. , Arora B. M.
Published: July 2002

Deep-level admittance spectroscopy (DLAS) of DX centers in AlxGa1−xAs:Sn (0.2<x<0.6) reveals the presence of three levels SN1, SN2, and SN3 related to the Sn donor. While SN1 and SN3 are observed in all the samples, SN2 is prominently seen only in the indirect band-gap samples. The conventional capacitance deep-level transient spectroscopy (DLTS) is found to be unsuitable for the study of the DX center in AlxGa1−xAs:Sn with x>0.35 because of the strong freeze-out of free carriers in these samples. Even in the case of low AlAs mole fraction samples (x<0.35), the DLTS technique fails to reveal all the levels observed by DLAS and provides information only on the SN3 level.
Intense microwave radiation from a repetitive backward-wave oscillator driven by a relativistic electron beam
Authors: Bromborsky A. , Still G. W. , Kehs R. A. , Clark C. , Early L. , Rohwein G. , Poukey J.
Published: July 2002

High-power microwaves (20–50 MW, 8.8 GHz) have been produced in repetitive pulses at a rate of 10 Hz in a joint experiment by Harry Diamond Laboratories and Sandia National Laboratories. These microwaves were produced with Harry Diamond Laboratories’ backward-wave oscillator (BWO), driven by a 600 to 800-kV, 2-kA electron beam, which was guided by a magnetic field of variable strength from 0.75 to 1.05 T. The beam was produced with Sandia National Laboratories’ repetitive high-voltage pulser, RAVEN. Microwave diagnostic instrumentation included a directional coupler, heterodyne receiver, dispersive waveguide delay line, and calorimeter. In a train of 10 pulses, the shape, duration, and amplitude of the injection voltage and beam current remained unchanged for each individual pulse. The intensity of the final microwave pulse was 40% of the first pulse, and the final pulse was 80% as long as the first. The basic pulse shape remained unchanged. More intense microwave radiation should be obtained with a higher magnetic field. Computer simulations using the code magic predicted the characteristic dip in the magnetic field strength versus microwave power output curve. Code predictions of microwave power output with a warm beam agree very well with experimental results. Finally, cyclotron resonance is presented in a descriptive fashion to account for the power output dip. This is the first experiment with a repetitively pulsed high-power BWO driven by a relativistic electron beam performed outside the USSR.
Silicon atom migration along grain boundaries in electron-beam-annealed silicon-on-insulator islands
Authors: Hayafuji Y. , Yanada T. , Shibata A. , Kawado S.
Published: July 2002

We have observed very rapid migration of silicon atoms along the grain boundaries of electron-beam-annealed polycrystalline silicon film in a silicon-on-insulator (SOI) island structure with a capped layer consisting of Si3N4 and SiO2 films. A considerable amount of mass transport was observed in the SOI structure at a temperature high enough to melt grain boundaries but not high enough to melt the entire polycrystalline silicon film. Our results support the notion that electromigration of Si+4 ions in molten silicon at the grain boundaries is responsible for the rapid migration of silicon atoms.
Structural perfection of InGaAs/InP strained-layer superlattices grown by gas source molecular-beam epitaxy: A high-resolution x-ray diffraction study
Authors: Vandenberg J. M. , Gershoni D. , Hamm R. A. , Panish M. B. , Temkin H.
Published: July 2002

High-resolution x-ray diffraction (HRXRD) studies have been carried out to determine the structural perfection and periodicity for a number of high-quality InGaAs/InP strained-layer superlattices grown by gas source molecular-beam epitaxy. X-ray scans were carried out with a compact four-crystal monochromator resulting in a resolution of one molecular layer (∼3 Å), which enables one to observe very small variations in the periodic structure. Sharp and strong higher-order satellite reflections in the XRD profiles were observed indicating smooth interfaces with well-defined modulated structures. Excellent computer simulated fits of the x-ray satellite pattern could be generated based on a kinematical XRD step model which assumes ideally sharp interfaces. Our results demonstrate that HRXRD in conjunction with the kinematical step model provides a powerful tool to evaluate the structural perfection of InGaAs/InP strained-layer superlattices.
Activation uniformity improvement of undoped semi-insulating GaAs with an improved post-implant anneal furnace
Authors: Lanzieri C. , Ciceroni S. , Cetronio A.
Published: July 2002

In this article we illustrate how by suitable furnace design, the radial thermal gradients generated on a GaAs substrate during the post-implant anneal cycle can be virtually eliminated, and how such a technique can result in appreciable improvements in on-wafer activation uniformity with improved activation efficiency uniformity in going from the seed to the tail-end wafer of an ingot.
Numerical analysis of infrared laser heating in thermoluminescent material layers: The focused laser case
Authors: Grupen-Shemansky M. E. , Kearfott K. J. , Hirleman E. D.
Published: July 2002

It may be possible to extract spatially resolved quantitative radiological information from thermoluminescent detectors (TLD) upon infrared laser stimulation. Acceptable spatial resolution for the application of this TLD imaging procedure may be attained by focusing the laser beam. A two-dimensional, transient model has been derived to determine the presently immeasurable axial and radial temperature profiles in a LiF layer heated with a focused CO2 Gaussian laser beam. It is found that focused laser heating is a strong function of axial position despite the fact that LiF is a relatively weak absorber.
Surface-wave reflection and refraction at an impedance discontinuity
Authors: Lam John
Published: July 2002

The general problem of surface-wave reflection and refraction at an impedance discontinuity, for both transverse-magnetic and transverse-electric polarizations, oblique incidence and lossy surfaces, is solved exactly by the Wiener–Hopf technique. General formulas are obtained for the reflected surface wave, the transmitted surface wave, and the radiation at the discontinuity. The solution is shown to become unphysical for certain ranges of the problem parameters. The source of the unphysicality is the approximate nature of the impedance formulation of the surface-wave scattering problem.
WKB solution for wave propagation in a decaying plasma medium
Authors: Kalluri Dikshitulu K. , Goteti Venkata R.
Published: July 2002

The problem of wave propagation in a slowly decaying plasma medium is considered. The appropriate Riccati equation for the instantaneous frequency is derived and an approximate WKB solution is obtained for the amplitudes and frequencies of the reflected and transmitted waves.
X-ray photoelectron spectroscopy studies on modified polyimide surfaces after ablation with a KrF excimer laser
Authors: Kokai F. , Saito H. , Fujioka T.
Published: July 2002

The chemical properties of modified polyimide (PI) surfaces after ablation with a single laser pulse from a KrF excimer laser are studied by x-ray photoelectron spectroscopy (XPS). Significant decreases in the atomic ratios (both oxygen to carbon and nitrogen to carbon) and bonding environment change are observed at the top ∼100 Å surfaces irradiated at laser fluences greater than 30 mJ/cm2 . The mechanism of formation of these modified surfaces is discussed in terms of the etching process based on the principal decomposition of imide groups of PI molecules, followed by rearrangement and recombination reactions. Furthermore, as a result of angular-dependent XPS studies, an atomic concentration gradient is found to exist along the depth of the surfaces remaining after ablation. The possibility of surface oxidation after ablation is discussed.
Effect of InGaAsP surface treatment for indium-tin-oxide/InGaAsP/GaAs solar cells
Authors: Matsubara Shuichi , Narui Hironobu , Tsuchiya Naoki , Takahashi N. Shin-ichi , Kurita Shoichi
Published: July 2002

The performances of n-indium-tin-oxide (ITO)/n-InGaAsP/p-GaAs solar cells in which the chemical treatment at the ITO/InGaAsP heterointerface is varied are compared: HNO3 treatment, HCl treatment, and nontreatment. The cells with HNO3 treatment show good solar-cell performance in spite of large lattice mismatch between ITO and InGaAsP. Others do not show even rectifying behavior. The structure of the cells with HNO3 treatment is thought to be a semiconductor-insulator-semiconductor structure, and its current model follows the tunneling model. By Auger analysis the oxide layer, which is thought to be formed by HNO3 treatment, was ascertained. Using the heterostructure back-surface field for the cells with HNO3 treatment, the highest efficiency attained so far is 10.9% (total area) under AM1 illumination normalized to 100 mW/cm2; the corresponding open-circuit voltage, short-circuit current density, and fill factor are 0.56 V, 28.8 mA/cm2, and 0.677, respectively.
Enhancement of the critical current by grain size refinement in Ta-cosputtered NbN thin films
Authors: Juang J. Y. , Barmak K. , Rudman D. A. , van Dover R. B.
Published: July 2002

NbN thin films cosputtered with Ta show approximately an order of magnitude enhancement in critical current density over a wide range of applied magnetic fields, while the critical fields and transition temperatures are essentially unchanged by the Ta addition. Both thin-film x-ray diffraction and cross-sectional transmission electron microscopy analyses show a highly textured structure with a second phase (also highly textured) present in these films at the grain boundaries. The Ta acts to refine the grain size of the NbN, increasing the effective pinning strength and hence the critical current density. Comparison of the global pinning force to current models of flux pinning supports individual pin breaking as the limiting mechanism for critical current in NbN films.
Variation of photoconductivity with doping and optical degradation in hydrogenated amorphous silicon
Authors: Bube Richard H. , Redfield David
Published: July 2002

A simple model for photoconductivity in a-Si:H is shown to be capable of describing the variations of photoconductivity observed both with doping and with optical degradation. The model consists of a trivalent recombination center with consideration only of transitions connecting the centers and extended states, and of exponential conduction and valence-edge tail states with occupancy described simply by the locations of the dark or quasi-Fermi levels. The model describes the changes in the magnitude of photoconductivity with doping or optical degradation as arising primarily from changes in the density of effective recombination centers caused by shifts in the location of the dark Fermi level, and only secondarily from changes in the total density of dangling bonds. The model also describes the change in the exponent for the variation of photoconductivity as a power of the excitation rate; this exponent changes from a value of 0.50, when the density of electrons trapped in conduction tail states is proportional to the density of neutral recombination centers, to a value of 1.0 when an appreciable density of neutral recombination centers exists in thermal equilibrium. Both qualitative and semiquantitative agreement are demonstrated between the predictions of the model and published experimental data on doping and optical degradation.
Magnetic effects on optical energy gap values of (CuIn)1−z Mn2z Te2 alloys
Authors: Quintero M. , Marks B. D. , Woolley J. C.
Published: July 2002

Measurements of optical absorption were made as a function of temperature in the range 15–300 K to give optical energy gap E0 values for polycrystalline samples of (CuIn)1−z Mn2z Te2 alloys with z=0.4 and 0.5. Absorption edges were observed for both the ordered and disordered zinc-blende phases and also for a lower energy transition assumed to be an internal Mn2+ transition. As confirmed by magnetic susceptibility data, the dominant phase in these alloys was the ordered zinc blende. For this phase, the variation of E0 with temperature in the vicinity of the magnetic transition temperature Tg was analyzed to give the magnetic contribution ΔE, which increases the value of E0. ΔE was determined as the difference between the experimental values of E0 and an extrapolation from higher temperatures where the magnetic contribution is negligible. These values of ΔE were fitted to the relation d/dt(ΔE)=−Pt−μ, where t=‖T−Tg ‖/Tg , and good agreement was found with previous theoretical predictions for the effect on the band gap of a critical point such as Tg . As predicted, different behavior was observed close to Tg and at temperatures outside the critical range, μ having a value close to zero in the first range and close to 0.5 in the second.
Electron energy levels in a quantum well within an in-plane magnetic field
Authors: Lee H. R. , Oh H. G. , George Thomas F. , Um C. I.
Published: July 2002

The exact eigenenergy spectrum of an electron is calculated in a quantum well within an in-plane magnetic field. The numerical solutions for the excited energy states as well as the ground-state energy are found for various quantum-well widths and barrier heights. The cyclotron orbits are considerably affected by the quantum well. The energy levels higher than the potential height of the quantum well and the energy levels lower than the potential height of the quantum well show quite different behaviors. These are explained with the properties of the combined potential and the wave function inherent to the system.
A simple process to generate deeply modulated and large dimension submicron gratings on reflecting surfaces
Authors: Chi Wei Dong , Carton Michel , Paraire Nicole
Published: July 2002

By using laser lithographic holography and argon-ion etching techniques, we have produced high-quality 300-nm gratings on 1×1 cm2 polished bulk silicon (100) or silicon-on-sapphire substrates. Obtaining large modulation depth (>100 nm) becomes possible by making use of a new photoresist which attenuates standing-wave effects appearing in photoresist layers deposited on a reflecting surface.
Gradual bulk degradation in (AlGa)As laser diodes during − 20 °C tests due to arsenic out-diffusion
Authors: Fritz William J.
Published: July 2002

AlxGa1−xAs laser diodes tested in vacuum (10−6 Torr) at a −20 °C heat sink temperature (Tj ∼0 °C) and with an average drive current of 160 mA for one set of diodes (test 1), and 190 mA for another set (test 2), were found to have small decreases in output power due to facet degradation, heat sink degradation, and bulk degradation. Analyses described in this paper show that the degradation mechanism causing the largest decrease in output power was gradual bulk degradation due to arsenic (As) out-diffusion from the active region. The arsenic out-diffusion was most likely caused by a processing anomaly. The data further indicate that the As out-diffusion increases with current. The results from this research can be used to identify a possible cause and accelerating stress of long-term gradual degradation. It was also observed that defects created by this degradation mechanism (suspected to be As vacancies) caused little change in the forward voltage at 1 mA.
Averaging fourth-rank elastic tensors for textured polycrystalline aggregates without physical symmetry
Authors: Zuo Liang , Xu Jiazheng , Liang Zhide
Published: July 2002

The fourth-rank tensor averaging method due to Morris [J. Appl. Phys. 40, 447 (1969)] is further extended to textured cubic materials with no physical symmetry. The coefficients of the nine linearly independent elements of the transformation matrix [Tijkl], as well as the relevant fifty-four relations for the calculation of the remaining Tijkl, are derived and presented in tabular form. It is also noted that for orthotropic physical symmetry and cubic crystal symmetry, the number of the linearly independent elements Tijkl is three instead of 15. The applicability of the present analysis is demonstrated by a comparative study.
State equation for shape-memory alloys: Application to Cu-Zn-Al
Authors: Planes Antoni , Castán Teresa , Ortín Jordi , Delaey Luc
Published: July 2002

We deal with the hysteretic behavior of partial cycles in the two-phase region associated with the martensitic transformation of shape-memory alloys. We consider the problem from a thermodynamic point of view and adopt a local equilibrium formalism, based on the idea of thermoelastic balance, from which a formal writing follows a state equation for the material in terms of its temperature T, external applied stress σ, and transformed volume fraction x. To describe the striking memory properties exhibited by partial transformation cycles, state variables (x,σ,T) corresponding to the current state of the system have to be supplemented with variables (x,σ,T) corresponding to points where the transformation control parameter (−σ and/or T) had reached a maximum or a minimum in the previous thermodynamic history of the system. We restrict our study to simple partial cycles resulting from a single maximum or minimum of the control parameter. Several common features displayed by such partial cycles and repeatedly observed in experiments lead to a set of analytic restrictions, listed explicitly in the paper, to be verified by the dissipative term of the state equation, responsible for hysteresis. Finally, using calorimetric data of thermally induced partial cycles through the martensitic transformation in a Cu-Zn-Al alloy, we have fitted a given functional form of the dissipative term consistent with the analytic restrictions mentioned above.
Effect of oxygen stoichiometry on superconducting transition broadening under a magnetic field in YBa2Cu3Ox
Authors: Shi Donglu , Boley Mark S. , Patel Mita , Kalia Rajiv K. , Vashishta P.
Published: July 2002

Resistivity as a function of temperature has been measured in magnetic fields up to 12 T for YBa2Cu3Ox samples with oxygen concentration ranging from x=6.55 to 6.98. It has been observed that the oxygen concentration has a strong effect on the broadening behavior of the resistive transition in the magnetic field. The smearing of the transition region is due to a superconductive glassy state which arises from weakly coupled semiconductor-insulator-semiconductor junctions in a magnetic field, where the insulating region is a few angstroms thick twin boundary, and the flux creep model can be used to interpret the shape and the width of the resistive transition. For the well-oxygenated sample (x=6.98), the data yield (dHc2/dT)T=Tc =−25.00 T/K for 90% transition resistivities at different fields, and −0.80 T/K for 10% transition curves. The broadening effect in field is decreased when the oxygen content is lowered to x=6.55 due to reduced thermally activated flux creep effects.
High-temperature deformation of YBa2Cu3O7−δ
Authors: von Stumberg A. W. , Chen Nan , Goretta K. C. , Routbort J. L.
Published: July 2002

Steady-state flow stress of dense (99% of theoretical) polycrystalline YBa2Cu3O7−δ has been measured in direct compression at temperatures between 870 and 980 °C in oxygen partial pressures of 0.03, 0.18, and 1.0×105 Pa for strain rates between 5×10−6 and 4×10−5 s−1. The stress exponent was close to one, indicating that diffusional flow was the dominant deformation mechanism. The flow stress decreased with decreasing oxygen partial pressure, obeying a power law with an exponent of approximately 1/2 . The activation energy was about 800 kJ/mol at an oxygen partial pressure 1×105 Pa, but decreased to 600 kJ/mol at a pressure of 3×103 Pa.
A new integrable optical modulator-switch optimized for speed and power consumption
Authors: Ching So Lai , Lee Charles A.
Published: July 2002

A new structure of planar waveguide directional coupler/switch composed of layered GaAs/AlGaAs is proposed and analyzed. This new configuration maximizes the change of coupling between adjacent guides while retaining their phase synchronism. This scheme provides, theoretically, a depth of modulation of 100%, a smaller device length with low drive power requirement, and an ability to compensate for dimensional offset by simple voltage tuning. Most importantly, this design is monolithically integrable with heterojunction laser sources. Projected operation limited by phase mismatch of the electrical and optical signals is above 12 GHz and a power per unit bandwidth of 280 μW/MHz is expected.
Energy exchange between heterostructure layers by real-space electron transfer
Authors: Moško Martin , Novák Ivo
Published: July 2002

Using Monte Carlo simulation we investigate electron transport in GaAs-n-AlxGa1−xAs heterostructure with high electric field applied parallel to the layer interface. Within a three-dimensional electron gas model we study the energy exchange between adjacent layers caused by real-space electron transfer (RSET). We have calculated an x-dependent electron temperature Te(x), with x being the distance from the interface, and distribution function f(kx,x), where kx is a wave-vector component perpendicular to the interface. Te(x) behavior clearly shows that the energy exchange between layers occurs: the electron temperature in the GaAs layer (high mobility—strong heating by field) is lower and that in the n-AlxGa1−xAs layer (low mobility—weak heating by field) is greater than the corresponding bulk values. A peculiar feature of the electron temperature x dependence is its abrupt change at the interface. We have shown that the presence of temperature step is necessary for the energy exchange due to RSET and it should be present in parallel transport simulations of three-dimensional electron gas where modulation doping of layers and smooth interfaces with abrupt potential barriers are considered. Compared to bulk distributions, the results for f(kx,x) are visibly influenced both by RSET and energy exchange. All numerical results are interpreted using simple general considerations. Finally, it is discussed that increased electron temperature in the n-AlxGa1−xAs layer can lead to more effective thermionic emission back to the GaAs layer, and thus increases the speed of the RSET oscillator.
1/f noise of indium near the melting transition
Authors: Scofield John H. , Epworth R. W. , Tennant D. M.
Published: July 2002

Measurements of the resistance and 1/f noise of continuous thin-film indium conductors in the temperature range 140–160 °C for frequencies 0.1–256 Hz are reported. The 250-nm-thick, 500-nm-wide, 5.0-μm-long, six-probe conductors were fabricated on an oxidized silicon wafer using e-beam lithography, and were encapsulated with a 500-nm-thick layer of Si3 Ni4 . Upon heating, melting occurred at (156±1) °C, whereas upon cooling, solidification occurred at (152±1) °C. The band-limited variance 〈δr2〉 of the resistance fluctuations was a factor of 10 lower for the liquid than for the solid, while the resistance of the liquid was nearly twice that of the solid. Hence, the relative 1/f noise of the liquid was nearly 40 times lower than that of the solid, in conflict with the results of two-probe measurements on liquid gallium found in the literature. These new results are consistent with models that attribute the 1/f noise of metals to defects and inconsistent with models that relate the noise to intrinsic mechanisms like phonon scattering or infrared divergences.
Effects of background Fe concentrations in the annealing of ion-implanted Si into InP substrates for InP metal-insulator-semiconductor field-effect transistor applications
Authors: Duhamel N. , Krauz P. , Gao Y.
Published: July 2002

Carrier activation for Si implants typical of metal-insulator-semiconductor field-effect transistors (MISFET) channels has been investigated as a function of background Fe doping in semi-insulating InP substrates, and different implantation temperatures and annealing procedures. A dramatic dependence of dose threshold for carrier activation on the Fe doping and on the annealing technique has been observed for the first time. A study of carrier and atomic distributions indicates that Fe redistribution is more pronounced under rapid thermal anneal (RTA) than under conventional furnace anneal (CFA). The redistribution of Fe is shown to influence the electrical characteristics of the channel-type implants. From these results and because RTA is more suitable for integrated devices we propose an implant sequence consisting of hot implants followed by RTA to realize device-quality layers for integrated devices. On the other hand, for discrete devices a classical furnace annealing after room-temperature implants gives very satisfactory results.
Suppression of acceptor deactivation in silicon by argon-ion implantation damage
Authors: Ashok S. , Srikanth K.
Published: July 2002

Permeation of atomic hydrogen in Si damaged with Ar implantation has been studied. Ar was implanted at two distinct doses so as to straggle the amorphization threshold, and atomic hydrogen was subsequently introduced by low-energy ion implantation. The deactivation of dopant boron atoms by atomic hydrogen is drastically reduced in silicon wafers subjected to low-energy argon-ion implantation. Trapping of hydrogen in defect sites generated by argon implant and possibly the formation of molecular hydrogen in the implanted region hinders hydrogen permeation into the Si bulk.
The limits of resonant tunneling diode subharmonic mixer performance
Authors: Smith P. M. , Conn D. R. , Xu J.
Published: July 2002

A theoretical analysis of the performance of subharmonically pumped mixers using resonant tunneling diodes is given based on the I-V curve of the latter. It is found that, in addition to the usual symmetry requirement, there are optimum positive and negative differential resistance values, as well as optimum current peak-to-valley ratios in this application. It is shown that, by carefully designing the diode, mixers can be built that will show positive conversion gain while operating in a harmonic mode.
Spectroscopic study of CdTe layers grown by molecular-beam epitaxy on (001) and (111) Cd0.96Zn0.04Te substrates
Authors: Dal’Bo F. , Lentz G. , Magnea N. , Mariette H. , Dang Le Si , Pautrat J. L.
Published: July 2002

The optical properties of CdTe grown by molecular-beam epitaxy are investigated by means of high-resolution photoluminescence, reflectivity, transmission, and resonant excitation spectroscopy. The CdTe epilayers are grown on (001)- and (111) B-oriented Cd0.96Zn0.04Te substrates. Sharp and strong lines associated with impurity bound exciton recombination dominate the spectra and indicate a good crystalline quality as well as a low level of impurity contamination. For the donor bound exciton lines, two electron transitions are observed which allow an identification of the chemical nature of the donors (probably Ga) by comparison with the data previously obtained on bulk material. For the acceptor lines, however, the shallow states which contribute to the spectra are different from those reported in the bulk and seem correlated with more complex centers. This study also reveals the importance of the residual strain contribution. Moreover, the marked difference observed for the optical properties between the (001) and the (111) epilayers spectra clearly evidence the change in the incorporation rate of impurities and/or grown-in defects density with the growth direction. The best spectra are obtained for the (001)-oriented CdTe layers.
High-temperature interaction studies of C/Cu/SiO2/Si and related structures
Authors: Chang Chin-An
Published: July 2002

Thermal stability of the C/Cu bilayer structure is studied up to 800 °C. Using electron-beam-evaporated Cu and amorphous C (700 Å) films on SiO2-coated Si substrates, no out-diffusion or oxidation of Cu is observed up to a heating of 72 h at 700 °C, or 6 h at 750 °C in a N2-H2 ambient. Reaction between Cu and the SiO2 layer is, however, observed under such conditions. Concerns such as adhesion are addressed by peeling the films at different stages of heat treatment and analyzing the surfaces exposed. Application of the carbon barrier to the reaction between Cu and other materials is studied using the Au/C/Cu structure. An enhanced out-diffusion of Cu through C is observed due to the presence of Au, which acts as a receiving layer for Cu. The out-diffused flux of Cu is enhanced by many orders of magnitude. The resulted dilution of the Au layer, however, is much less than that using Ni as a barrier in the Au/Ni/Cu structure. The mechanisms involved are discussed by considering the structural, chemical, and mechanical effects. Both the advantage and concerns using carbon as a barrier are also discussed.
The stability of a current-carrying hollow liquid-metal cylinder
Authors: MacDonald Rosemary A.
Published: July 2002

An investigation of the factors that influence the stability of a conducting hollow liquid-metal cylinder in a microgravity environment is carried out for the particular configuration in which a fraction of the current in the cylinder is returned down a central conducting rod. The analysis assumes that axial symmetry is maintained, that at any instant the cylinder is at a uniform temperature, and that the liquid metal is incompressible and inviscid. Vibrations in which the inner and outer boundaries of the cylinder move in phase are found to be always stable. The out-of-phase modes are unstable for long wavelengths, but these unstable modes can be excluded by a suitable choice of the length and thickness of the cylinder. The relationship of this analysis to the recent results of Chow and Harvanek [in Proceedings of the 1st National Fluid Dynamics Congress, Cincinnati, July, 1988 (American Institute of Aeronautics and Astronautics, New York, 1988), Part 3, p. 1805] on electromagnetic capillary instabilities in a hollow liquid-metal cylinder is discussed.
Improved electrochromic performance of iridium-oxide films prepared by thermal oxidation of iridium-carbon composite films
Authors: Sato Yoshiyuki
Published: July 2002

Thermally oxidized iridium-oxide films have exhibited a residual coloration in the as-prepared state. This residual coloration has been found to be much improved by potential cycling in a range from −0.25 to 1.25 V versus a saturated calomel electrode (SCE) in a 0.5M H2 SO4 electrolyte. In order to optimize the conditions for improving the electrochromic performance of the films, the anodic oxidation growth on sputtered-Ir films and changes of the electrochemical properties of the oxidized films have been investigated by applying various waveform voltages (triangular, sine, and square waves) at a frequency range from 0.033 to 0.5 Hz. Appreciable film dissolution has been observed for the Ir/SnO2 electrodes. On the other hand, the dissolution of the films during the electrochemical treatment has been less than 2% of the total Ir in the oxidized films at the optimum conditions: triangular wave at 0.067 Hz. 5×105 cycles have been obtained with less than 5% decrease in the charge for the film, when applying a square-wave voltage from −0.2 to 1.0 V vs SCE at 1 Hz in a 0.5M H2 SO4 electrolyte.
Microstructure and mechanical properties of ion-beam-produced Fe-Ti-(N), Fe-Ti-(C), and Fe-Ti-(C,N) surface films
Authors: Hirvonen J-P. , Nastasi M. , Zocco T. G. , Jervis T. R.
Published: July 2002

Ion-mixed films of Fe53 Ti47 were produced by ion irradiating a Fe-Ti multilayer structure on AISI 304 stainless steel. The ion-mixed films were subsequently implanted with nitrogen, carbon, or both carbon and nitrogen. The microstructure following nitrogen implantation consisted of a bcc solid solution of iron and titanium and finely dispersed TiN precipitates. In the cases of carbon or carbon and nitrogen implantation, a two-phase structure consisting of an amorphous matrix with TiC or Ti(C,N) precipitates was found. All these films initially possessed improved tribological properties as revealed by lowered friction and increased wear resistance. However, after an extended test of 1000 wear cycles, a reduced friction was only observed for the carbon or carbon and nitrogen implanted samples. The wear track on the dual implanted surface was extremely smooth, while the surface of the nitrogen-implanted sample was partly worn through, causing the friction to increase to the level of the untreated sample. The improved tribological properties of the implanted films are attributed to an increase in surface hardness. However, the surface hardness is unable to explain differences between different implantations. In the case of the dual carbon and nitrogen implantation, improvements appear to be in part the result from an increased capability to accommodate plastic deformation. These conclusions are supported by transmission electron microscope studies of the wear tracks as well as by nanoindentation measurements.
Hugoniot of amorphous metallic ribbon Metglas 2605CO for stresses of 0–38 kbars
Authors: Lemar E. R. , Forbes J. W.
Published: July 2002

A light gas gun has been used to measure the Hugoniot of Metglass 2605CO ribbon. Quartz gauges were used to measure stress. Both front- and rear-surface measurements were done. Front-surface experiments impacted the ribbon onto quartz gauges, while back- surface experiments impacted an aluminum plate into the ribbon which was backed by a quartz gauge. Single layers and composite layers of the ribbon were used. Two single-layer front-surface experiments provided the most accurate data.