bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetization and magnetic susceptibility of the diluted magnetic semiconductor Cd1−xMnxS
Authors: Chen Chen-jia , Qu Ming , Hu Wei , Zhang Xin , Lin Feng , Hu Hong-bing , Ma Ke-jun , Giriat W.
Published: July 2002

Results of experiments done to measure the magnetization and magnetic susceptibility in Cd1−xMnxS are given. The measurements were performed on the samples with x=0.03, 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, and 0.45 in the temperature range 1.5 K≤T≤300 K and with magnetic fields up to 7 T by using a vibrating-sample magnetometer and the extraction method. A modified Brillouin function fits the magnetization data and the fitting parameters T0 and xeff are obtained at T=1.5 K for different compositions. The susceptibility displays a high-temperature Curie–Weiss behavior. From quantitative analysis we obtain the value of the exchange integral constant 2J/kB to be −25.9 K. By using our results in conjunction with a direct measurement of the nearest-neighbor exchange JNN from high-field magnetization steps and Raman scattering, we obtain an estimate of the next-nearest-neighbor exchange constant J2/kB = −4.7 K.
Bonded anisotropic Nd-Fe-B magnets from rapidly solidified powders
Authors: Doser M. , Ribitch R. W. , Croat J. J. , Panchanathan V.
Published: July 2002

There has been great interest in using Nd-Fe-B material for bonded magnets. Bonded magnets made using rapidly solidified powders are limited to maximum energy products of ∼10 MGOe. Anisotropic Nd-Fe-B magnets having high-energy products can be prepared by hot deformation of rapidly solidified material. They can be converted into stable powders for processing into bonded anisotropic magnets. The stability of this powder is better than that prepared by grinding sintered magnets. The stability data at 80, 100, and 125 °C for coated and uncoated anisotropic powders prepared by converting hot deformed anisotropic magnets into powder are given. The data indicate the need for additional protection for higher operating temperatures. Bonded magnets having maximum energy product of 15.8 MGOe with intrinsic coercivity of 14.5 kOe have been made. Data will be given showing the effect of particle size on the magnetic characteristics. Long-term thermal stability data for bonded magnets are given. Coating of particles reduces the structural losses during long-term thermal aging.
Properties of ferromagnetic MnAl thin films with additives
Authors: Matsumoto M. , Morisako A. , Ohshima J.
Published: July 2002

MnAl thin films with additives were prepared by dc magnetron sputtering. The ferromagnetic τ phase was obtained in the composition of Mn60Al40, which is Mn rich by 6 at. % as compared with the τ-phase bulk one. Excess Mn atoms are considered to occupy the Al site and cause the reduction in saturation magnetization Ms to one-fourth of the bulk one because of their antiparallel spin orientation. We tried to add Fe, Co, Ni, Cu, Zn, and Ag separately to replace the antiparallelly oriented Mn atoms in order to increase Ms. A few atomic percent additions of Fe, Co, Ni, and Cu brought 1.7–2.5 times the increase in Ms (i.e., 200–300 G), with the increase of Hc as well except that with the Cu addition. Further addition brought a sharp decrease in Hc. Different types of crystal orientation were observed regarding the film thickness and the kind of additives. For a τ-phase film thinner than 0.3 μm, (111) orientation was observed in every additive. In this case the easy magnetization axis, which is the c axis in the tetragonal structure, is neither in the film plane nor normal to the film plane. Consequently, magnetically isotropic films were obtained. For thicker ones than 0.3 μm, the addition of elements with an atomic radius smaller than that of Mn (i.e., Ni, Co, Fe) directed (110) to the normal plane, and therefore longitudinally magnetically oriented films were obtained. The crystallographic and magnetic properties as a function of anneal temperature were also evaluated and found practically to be invariable with the temperature under 250 °C.
An isotropic description of the new-found gradient-related magneto-optical effect (invited)
Authors: Thiaville André , Hubert Alex , Schäfer Rudolf
Published: July 2002

The recent observation of a magnetization-gradient-related birefringence in ferromagnetic materials is reviewed. A new phenomenological description using an isotropic dielectric material law in which the dielectric tensor is a linear function of the components of the propagation vector of the light wave and of the symmetric part of the magnetization gradient tensor is proposed. The symmetry of this interaction is derived in terms of space and time inversion invariance requirements, adding information from perpendicular incidence experiments. The dielectric law contains only one material parameter and displays additional unexpected symmetries. It is compatible with all observations for the perpendicular incidence, in-plane magnetization case. Its predictions for the case of oblique incidence and a gradient in the polar component of magnetization are found not to be in contradiction with experiments when precautions are taken to avoid asymmetric diffraction due to the polar Kerr effect.
Deformation-induced defects in GaAs
Authors: Dannefaer S. , Mascher P. , Kerr D.
Published: July 2002

Semi-insulating undoped GaAs was plastically deformed and then investigated by positron lifetime spectroscopy. Strains between 0% and 40% and temperatures of deformation of 450, 500, and 600 °C were investigated, with detailed investigations carried out for the lowest temperature of deformation. Between 0% and 4% strain a reduction of the grown-in vacancy response takes place simultaneously with a slight increase in vacancy cluster size to 2 or 3 vacancies. Between 4% and 6% strain a very substantial increase in vacancy production occurs but nearly all of these vacancies are clustered into voids with a radius of about 50 Å and density of the order of 1013–1014 cm−3. The total concentration of vacancies necessary to produce these voids is 1017–1018 cm−3. This clearly shows that vacancies are formed upon deformation and that they are mobile at 450 °C. The small vacancy clusters (2 or 3 vacancies) are present at a concentration of about 5×1016 cm−3, the same as for the 4% strained samples. Upon further deformation to 20% strain the overall defect concentration becomes so high that all positrons become trapped for which reason no absolute defect concentrations can be deduced. The dominant defect types can nevertheless be identified as voids (with average size of 20 Å), two- or three-vacancy clusters, and shallow traps. These shallow traps have a positron binding energy of about 40 meV. Isochronal and isothermal annealing of 40% strained samples shows that heat treatment reduces the void concentration but increases the average void size, reduces the small vacancy cluster concentration, but results only in a small decrease in shallow trap concentration. The shallow traps are likely the dislocation lines themselves and the small vacancy clusters appear to be associated with the dislocation lines.
Decay widths for double-barrier resonant tunneling
Authors: García-Calderón Gastón , Rubio Alberto , Romo Roberto
Published: July 2002

Calculations of the decay width and the partial decay widths for double-barrier resonant tunneling structures are discussed using a description of resonances in terms of the complex energy poles of the transmission amplitude of the system and comparing it with the corresponding Wentzel–Kramers–Brillouin approximations. The effect of the asymmetry of the potential profile is emphasized.
Photoluminescence studies of hydrogen passivation of GaAs grown on InP substrates by molecular-beam epitaxy
Authors: Chen Y. F. , Chen W. S. , Huang S. H. , Juang F. Y.
Published: July 2002

Hydrogen passivation of GaAs grown on InP substrates by molecular-beam epitaxy has been performed. Photoluminescence studies show that two peaks at 1.503 and 1.462 eV, which have the luminescence intensities in heteroepitaxial GaAs stronger than that in homoepitaxial GaAs, are effectively passivated by atomic hydrogen. The copper-arsenic vacancy complex associated recombination is also eliminated after hydrogenation. However, hydrogenation can enhance the intensity of donor to C(As) acceptor transition. In addition, we show that the damaged surface during hydrogenation using rf glow-discharge method can be passivated by the hydrogenation using photochemical vapor deposition system.
Reverse temperature dependence of Ge surface segregation during Si-molecular beam epitaxy
Authors: Nakagawa Kiyokazu , Miyao Masanobu
Published: July 2002

Ge surface segregation on Si(100) and Si(111) substrates during silicon molecular beam epitaxy was studied using x-ray photoelectron spectroscopy. During growth, the Ge atoms were only partly incorporated into the growing layer and the residuals segregated on the grown surface. The Ge segregation phenomena increased to a maxima at around 450 °C in the case of the Si(100) substrates and at around 650 °C in the case of the Si(111) substrates. Segregation decreased above these temperatures. These reverse temperature dependencies enable not only good crystallinity of the heteroepitaxial layer, but also abrupt heterointerfaces. The incorporation coefficients for Si(111) were much larger than those for Si(100), which is well explained by a model based on surface migration.
Theory of electron-plasmon-scattering rate in highly doped bulk semiconductors
Authors: Diff Karim , Brennan Kevin F.
Published: July 2002

We compared two different formulations, the electron-field and electron-electron models, for electron-plasmon scattering in bulk semiconducting materials. The calculations employ three different expressions for the plasmon dispersion relation and are made at two different temperatures. It is found that the functional form of the dispersion relation greatly affects the electron-plasmon-scattering rate. The electron-field model is found to predict a higher scattering rate than the electron-electron model, independent of the form of the dispersion relation. Either model predicts the same order-of-magnitude scattering rate, which is found, in the case of bulk degenerate GaAs, to be comparable to the polar optical-phonon-scattering rate. Based on these calculations, plasmon scattering appears to be an important mechanism limiting electron transport in degenerate semiconductors and related semiconductor devices.
A boundary-layer model for a plane free-burning high-pressure gas-discharge arc
Authors: Kuiken H. K.
Published: July 2002

A boundary-layer model for a plane free-burning high-pressure gas-discharge arc is given. For the dependence on the temperature, a rule given by Elenbaas [The High Pressure Mercury Vapour Discharge (North-Holland, Amsterdam, 1951)]is used for the electrical conductivity and power-law rules for the dynamic viscosity and the thermal conductivity. The specific heat is assumed to be constant. It is shown that a similarity transformation can be applied. The upward velocity increases with the square root of the core temperature. Graphs are given which show how the temperature rise in the arc depends upon the applied current.
A new method to determine the switching field distribution with application to barium ferrite powder
Authors: Schumacher F.
Published: July 2002

A method to determine the switching field distribution Hs(■cr>gc0) of powder assemblies of magnetically hard materials with a random orientation of the easy axes is described. The method is based on the ferromagnetic resonance absorption and the measurements of remanence curves. Direct information about the switching field distribution is obtained from major and minor loops of the hysteresis of the microwave absorption loss. By fitting calculated remanence curves and measured remanence curves the switching field distribution and its distribution at each orientation angle ■cr>gc0 is obtained. The application of this method leads to switching field distributions for coprecipitated barium ferrite, which are strongly correlated to the predictions of the theory of coherent rotation. The distribution of Hs for this sample is made narrower by an etching process or by magnetic dilution. For barium ferrite prepared by the conventional oxid ceramic method with additional milling, a monotonic increase of the switching field with increasing orientation angle is found. This increase is much smoother than the Kondorsky function provides.
A Monte Carlo model of hot electron trapping and detrapping in SiO2
Authors: Kamocsai R. L. , Porod W.
Published: July 2002

High-field stressing and oxide degradation of SiO2 are studied using a microscopic model of electron heating and charge trapping and detrapping. Hot electrons lead to a charge buildup in the oxide according to the dynamic trapping-detrapping model by Nissan-Cohen and co-workers [Y. Nissan-Cohen, J. Shappir, D. Frohman-Bentchkowsky, J. Appl. Phys. 58, 2252 (1985)]. Detrapping events are modeled as trap-to-band impact ionization processes initiated by high energy conduction electrons. The detailed electronic distribution function obtained from Monte Carlo transport simulations is utilized for the determination of the detrapping rates. We apply our microscopic model to the calculation of the flat-band voltage shift in silicon dioxide as a function of the electric field, and we show that our model is able to reproduce the experimental results. We also compare these results to the predictions of the empirical trapping-detrapping model which assumes a heuristic detrapping cross section. Our microscopic theory accounts for the nonlocal nature of impact ionization which leads to a dark space close to the injecting cathode, which is unaccounted for in the empirical model.
Growth-induced surface state in hydrogenated and fluorinated amorphous silicon
Authors: Maruyama A. , Liu J. Z. , Chu V. , Shen D. S. , Wagner S.
Published: July 2002

The steady-state density of surface states during the deposition of hydrogenated and fluorinated amorphous silicon (a-Si:H,F) can be adjusted via the deposition parameters, particularly the growth pressure. The density of surface states can be frozen in if the sample is cooled immediately after the termination of growth. We have measured frozen in densities of surface states between 1.5×1012 cm−2 and 4×1014 cm−2. a-Si:H,F grown at high density of surface states exhibits a small Urbach energy and a low bulk defect density.
Characterization of interdiffusion coefficients in GaAs-AlAs superlattices with laser Raman spectroscopy
Authors: Hara Naoki , Katoda Takashi
Published: July 2002

A new method to estimate interdiffusion coefficients in superlattices (SLs) is proposed. The method is based on measurement of thicknesses of layers which remain without forming an alloy after an annealing that induced interdiffusion. The measurement was done from the frequency of phonons based on the Raman spectra. Values of interdiffusion coefficients obtained by the method were almost in the same order as those reported previously. It is also shown that the gallium atoms in GaAs-AlAs SLs diffuse more rapidly into AlAs layers than aluminum atoms which diffuse into GaAs layers. Interdiffusion coefficients decreased at first with the annealing time and increased slightly when the annealing was done for more than 1.5 h at 860 °C.
III-V ternary semiconductor heterostructures: The choice of an appropriate compositional analysis technique
Authors: Bithell E. G. , Stobbs W. M.
Published: July 2002

The composition of ternary III-V semiconductor heterostructures can now be measured in a number of ways. Conventional spectroscopic probe techniques are inappropriate for fine (nanometer scale) heterostructures: Here, those transmission electron microscopy techniques which are appropriate, are compared emphasizing that different alloy systems often require different approaches. The three representative methods discussed in detail are kinematic convergent beam diffraction, 200 dark field intensity measurement, and [001] bright field thickness fringe matching. Dark field intensity measurement is found to be the most sensitive analytical method for many alloys, but the accuracy that may be achieved by thickness fringe matching is generally little worse, and sometimes better. Those convergent beam diffraction techniques which rely on lattice parameter measurement would not appear to be particularly useful except for the purposes of distinguishing nonunique interpretations of other measurements. It is also noted that no technique currently available is capable of measuring the composition of AlxGa1−xSb alloys to an accuracy of better than ±0.05 in x, so that further technique development will be required if heterostructures in this alloy system are to be studied seriously.
Distributive deflection of Rayleigh waves
Authors: Seshadri S. R.
Published: July 2002

Asymptotically exact coupled-mode equations which govern the characteristics of distributive deflection of Rayleigh waves caused by a weak periodic corrugation of the free surface of an elastically isotropic half-space are deduced for the general case in which the wave vectors are not aligned with the grating vector. The theory is applied to obtain the characteristics of the selective deflection of a Rayleigh wave incident obliquely on a moderately long periodic array of shallow grooves etched on the free surface. The Brewster phenomenon of total transmission exists, with the Brewster angle depending only on the Poisson ratio. For angles of incidence sufficiently greater than the Brewster angle, the reflection coefficient is considerably larger than for normal incidence. For the special case of a 90° deflection caused by a grating whose length is sufficiently small, the experimental observations available in the literature are in good agreement with the present theoretical predictions. The dephasing effects caused by the wave frequency being different from the Bragg frequency and by the angle of incidence being different from the Bragg angle have also been examined.
Comparison of different formulations of the electron-plasmon scattering rate and the dispersion relation on bulk semiconductor transport
Authors: Mansour Nabil S. , Diff Karim , Brennan Kevin F.
Published: July 2002

We compare the effect of two different formulations of the electron-plasmon scattering rate, the electron-field and electron-electron models, as well as different formulations of the dispersion relationship on the calculated bulk transport properties of degenerate GaAs. The calculations are performed using an ensemble Monte Carlo simulation which includes an analytical nonparabolic model of the principle valleys in the conduction band, and all of the dominant scattering mechanisms. It was previously found that the functional form of the dispersion relationship significantly alters the magnitude of the electron-plasmon scattering rate. As a consequence, the steady-state velocity-field characteristics are also significantly altered by as much as ∼40% by the choice of the dispersion relation. It is further found that the choice of either the electron-electron or electron-field model does not by itself significantly alter the calculated results. Therefore, either model can be used to describe the effects of electron-plasmon scattering in degenerate bulk materials.
Strain-induced carrier confinement in a buried stressor structure
Authors: Xu Z. , Petroff P. M.
Published: July 2002

The possibility of strain-induced confinement of carrier into wires and boxes in a buried stressor structure is theoretically investigated. The strain distribution and the corresponding strain induced modulation of the band gap is dependent not only on the material properties but also on the geometrical parameter of the structure. A potential well of 30 meV is available for both electron and light hole. For a box stressor, up to 60 meV modulation in the band gap is estimated for a GaAs QW parallel to the In0.35Ga0.65As stressor.
Study of hydrogen interaction with SiO2/Si(100) system using positrons
Authors: Asoka-Kumar P. , Lynn K. G. , Leung T. C. , Nielsen B. , Wu X. Y.
Published: July 2002

We describe positron annihilation studies of SiO2/Si(100) structures having 100-nm-thick oxide grown by plasma enhanced chemical vapor deposition. A normalized shape parameter is used to characterize the positron annihilation spectra. Activation and passivation of interface states by atomic hydrogen are demonstrated by repeated vacuum anneal and atomic hydrogen exposure. Hydrogen activation energy is derived for one of the samples as ■=2.02±0.07 eV.
Two-stage photoquenching in semi-insulating GaAs:EL2
Authors: Pandian V. , Kumar V.
Published: July 2002

The photoquenching of EL2 in semi-insulating gallium arsenide is seen to be a complex process, where at low temperatures the initial slow quenching is followed by a switch to fast quenching. A possible explanation involving lattice strain mediated cooperative structural relaxation arising out of transition to the metastable state is proposed.
Phase-locked sustainment of photorefractive holograms using phase conjugation
Authors: Qiao Yong , Psaltis Demetri , Gu Claire , Hong John , Yeh Pochi , Neurgaonkar R. R.
Published: July 2002

A method for sustaining multiply exposed photorefractive holograms, in a phase-locked fashion, by using a pair of phase-conjugating mirrors is described. It is shown that a steady state exists where the overall diffraction efficiency is independent of the number of holographic exposures and the final holograms are exactly in phase with the initial ones. Both analytical and experimental results are presented.
High corrosion resistance FeSi multilayered films
Authors: Ishiwata Nobuyuki , Wakabayashi Chizuko , Matsumoto Takayuki
Published: July 2002

FeSi multilayered films (MLFs) with intermediate SiO2 or Ni80Fe20 layers have been found to have superior corrosion resistance, as well as excellent soft magnetic properties. Corrosion resistance for the MLFs depends on the intermediate layer material, intermediate layer thickness, and FeSi layer thickness. In the MLFs with appropriate intermediate layers, oxygen diffusion is restricted to only 20 nm depth from the surface, which is less than the FeSi layer thickness, and no rust is observed after 600 h exposure in 60 °C and 90% relative humidity conditions. In contrast, in FeSi single-layered films, oxygen spreads throughout the entire film, and a reddish brown rust of Fe2O3 was observed. Due to the high saturation magnetization and high corrosion resistance, the FeSi MLFs are forseen to be soft magnetic materials applicable for higher density magnetic recording heads.
Coupled broad-area mode theory of gain-guided laser arrays
Authors: Cherng Chung-Pin , Osiński Marek
Published: July 2002

Multiple-stripe semiconductor laser arrays are analyzed using a broad-area mode coupling approach. Rather than considering coupling between individual waveguide modes as in the conventional supermode theory, a basis of broad-area modes is chosen. These modes are coupled through a perturbation of refractive index and gain profiles caused by nonuniform carrier injection, thermal effects, and/or built-in weakly guiding or antiguiding profiles. Present theory reveals that earlier simplified analysis involving broad-area mode-coupling may lead to significant errors in modal gains of high-order array modes.
Skin effect in a high-T
c flux-flow superconducting wire
Authors: Ando Yoichi , Akita Shirabe
Published: July 2002

As a candidate for a low ac-loss bulk power transmission cable, a high-Tc superconducting wire in a flux-flow state, which is called a flux-flow superconductor here, is theoretically studied. The electrodynamics of such a wire in a self-excited ac field is formulated, where the governing equation is nonlinear because of the magnetic field dependence of the flux-flow resistivity. The current distribution inside the wire and the ac loss are numerically calculated to investigate the influence of the skin effect in such a nonlinear system. The ac loss is enhanced by the skin effect, and it is found that the amount of this enhancement can be scaled by a nondimensional parameter which depends not only on the frequency and the radius of the wire but also on the peak current. As a means to reduce the ac loss in the presence of the skin effect, it is shown to be effective to divide the wire into many coaxial layers and to set the current distribution between the layers artificially. It is also shown that, if an optimized current distribution is settled between the layers, the ac loss can be reduced to a smaller value than that for a nondivided wire neglecting the skin effect.
Plasma structures in an electron cyclotron resonance plasma processing device
Authors: Iizuka Satoru , Sato Noriyoshi
Published: July 2002

Plasma parameters are measured in a low-pressure discharge plasma produced by the 2.45-GHz electron cyclotron resonance. Radial plasma profiles, which are important for homogeneous plasma processings, are found to be very sensitive to the resonance position in a plasma production chamber. Quite inhomogeneous plasmas are obtained when the resonance position is set in the narrow production chamber (cavity) while uniform plasmas are produced when the resonance position is in a wide space chamber following the production chamber. Plasma potentials determining the ion flow speed toward the substrate decrease gradually along the diverging magnetic field lines up to the ion sheath region in front of the substrate. The plasma structures observed are well consistent with theoretical results.
X-ray diffraction study of silver–nickel superlattices
Authors: Rodmacq Bernard
Published: July 2002

Silver–nickel multilayers, with elementary layers comprising a few to a few ten atomic planes, have been prepared by cathodic sputtering on glass substrates. X-ray diffraction experiments show that highly textured, polycrystalline superlattices are formed. For a deposition temperature of 100 K, there exists a critical number of atomic planes nc = 3, below which noncrystalline samples are obtained. This critical number can even be lowered in samples with nonequal numbers of Ag and Ni atomic planes. Transmission x-ray and electron diffraction experiments show that equivalent crystallographic directions are aligned in the Ag and Ni (111) planes, with a noticeable relaxation of the in-plane distances at the interfaces. The simulation of the periodic structure assuming a rectangular composition profile with interplanar distances slightly larger than the bulk values leads to a very good agreement with the experimental diffraction spectra.
Reversed magnetic anisotropy of (100) Pd/Ni/Cu structures
Authors: Chang Chin-An
Published: July 2002

(100) Ni films with an asymmetrical stress have been made by depositing Pd/Ni/Cu structures on Si. A completely reversed magnetic anisotropy is observed for the Ni layers of 50 Å and thinner in such structures, with the normal-to-plane magnetization being easier than the in-plane one. The results are compared with those of (100) Ni layers in symmetrical structures, where similarly reversed magnetic anisotropy is also observed, to assess the role of stress on such magnetic properties of (100) Ni.
Influence of thermal history on the growth of two-phase layered films or scales
Authors: Wautelet M.
Published: July 2002

The kinetic equations for the growth of two-phase layered films or scales are solved numerically. Emphasis is laid on the effects of changing the thermal history of the system. Sudden heating, linear, parabolic, and quadratic evolution of temperature with time are considered. The time constants of heating are also varied. It is shown how the thickness ratio obtained at the end of heating depends on the thermal history. In particular, for low heating rate, the oxide growth is paraboliclike. But the value of the parabolic constant depends on the type of thermal history (linear, parabolic, or quadratic heating).
Formation of the 110-K superconducting phase in Pb-doped Bi-Sr-Ca-Cu-O thin films
Authors: Kula Witold , Sobolewski Roman , Górecka Joanna , Lewandowski Stanisl/aw J.
Published: July 2002

Investigation of the 110-K Bi2Sr2Ca2Cu3Ox phase formation in superconducting thin films of Bi-based cuprates is reported. The films were dc magnetron sputtered from single Bi(Pb)-Sr-Ca-Cu-O targets of various stoichiometries, and subsequently annealed in air at high temperatures. The influence of the initial Pb content, annealing conditions, as well as the substrate material on the growth of the 110-K phase was investigated. We found that the films, fully superconducting above 100 K could be reproducibly fabricated on various dielectric substrates from Pb-rich targets by optimizing annealing conditions for each initial Pb/Bi ratio. Heavy Pb doping considerably accelerated formation of the 110-K phase, reducing the film annealing time to less than 1 h. Films containing, according to the x-ray measurement, more than 90% of the 110-K phase were obtained on MgO substrates, after sputtering from the Bi2Pb2.5Sr2Ca2.15Cu3.3Ox target and annealing in air for 1 h at 870 °C. The films were c-axis oriented, with 4.5-K-wide superconducting transition, and zero resistivity at 106 K. Their critical current density was 2 × 102 A/cm2 at 90 K, and above 104 A/cm2 below 60 K. The growth of the 110-K phase on epitaxial substrates, such as CaNdAlO4 and SrTiO3, was considerably deteriorated, and the presence of the 80- and 10-K phases was detected. Nevertheless, the best films deposited on these substrates were fully superconducting at 104 K and exhibited critical current densities above 2 × 105 A/cm2 below 60 K−one order of magnitude greater than the films deposited on MgO. We associate the presence of low-Tc phases in the films grown on epitaxial substrates with the intrinsic mechanism of the 110-K phase growth during the high temperature annealing process.
Strontium barium niobate single-crystal fibers: Optical and electro-optic properties
Authors: Yamamoto Joyce K. , McHenry Dean A. , Bhalla Amar S.
Published: July 2002

The room-temperature transverse electro-optic, rc, coefficient, halfwave voltage, Vπ, and temperature dependence of the birefringence, Δn0(T), were determined for Sr0.61Ba0.39Nb2O6 single-crystal fibers produced by the laser-heated pedestal growth technique. The effect cerium doping, 0.034 at. %, had on the measured properties is also reported. Concurrent measurements on a Czochralski-grown Sr0.61Ba0.39Nb2O6 single crystal enabled comparison of the single-crystal fibers to a bulk-grown single crystal. The growth rate of the Sr0.61Ba0.39Nb2O6 single-crystal fibers was approximately an order of magnitude greater than the Czochralski-grown Sr0.61Ba0.39Nb2O6 single crystal. The effect the rapid growth rate had on the optical properties is also discussed.
On the period of reflection high-energy electron diffraction intensity oscillations during Si molecular-beam epitaxy on vicinal Si(001)
Authors: Zandvliet H. J. W. , Elswijk H. B. , Dijkkamp D. , van Loenen E. J. , Dieleman J.
Published: July 2002

We report the observation of reflection high-energy electron diffraction intensity oscillations with a period different from an integer number of atomic layers. These oscillations, which arise from the periodic nucleation, growth, and coalescence of two-dimensional islands, are recorded during Si molecular-beam epitaxial (MBE) growth on vicinal Si(001) at growth conditions near step flow. We explain the deviation of the period from an integer number of atomic layers by the diffusive loss of Si atoms from the terraces where the islands grow to the surface steps. This explanation will be elucidated by comparison with Monte Carlo computer simulations of Si MBE.
Stability of C49 and C54 phases of TiSi2 under ion bombardment
Authors: Motakef S. , Harper J. M. E. , d’Heurle F. M. , Gallo T. A. , Herbots N.
Published: July 2002

The transformation of C49 phase TiSi2 to the low resistivity C54 phase is necessary for many microelectronic applications. Here, we report on attempts to decrease this transformation temperature by low-energy ion bombardment at elevated temperature. Ion irradiation was performed using a broad beam Kaufman ion source operated in N2 or Ar gas between 0.1 and 2 keV beam energy, with ion doses ranging from 2.0×1016 to 1.9×1018 ions/cm2, and sample temperatures from 480 °C to 735 °C. For comparison, room-temperature Ar+ implantation at higher energy (105–210 keV) was performed with a dose of 1016 ions/cm2 with projected ranges within and beyond the TiSi2 layer thickness. Resistivity measurements as a function of temperature, x-ray diffraction, and Rutherford backscattering spectrometry were used to determine the composition and phases. Results show that low-energy ion bombardment does not promote the C49-C54 transformation at the temperatures studied, while ion implantation actually raises the temperature for the transformation. In addition, bombardment of C54 TiSi2 does not cause it to revert to the C49 phase, indicating that both phases appear to be surprisingly stable under ion bombardment. Simulations of defect production using the trim code indicate the formation of a higher number of displaced atoms than are usually required to initiate a transformation. We conclude that the defects introduced into C49 TiSi2 by ion bombardment at energies up to 2 keV are either not sufficient to nucleate the C54 phase or they are annealed out too quickly at the temperature needed for C54 phase growth.
Polarization control by a twist reflector
Authors: Seshadri S. R.
Published: July 2002

A twist reflector is idealized by a surface which supports electric current in one direction only. When a transverse electric mode or a transverse magnetic mode is incident on a twist reflector, both types of modes are reflected. This property of the twist reflector to generate the cross-polarized mode is used in the development of a device that can rotate the plane of polarization of the incident electromagnetic wave by the rotation of the twist reflector about an axis normal to its surface. A ray-tracing technique is used to deduce the angle of rotation of the plane of polarization as a function of the orientation angle of the twist reflector. Numerical results are provided to illustrate the characteristics of the polarizer.
Achievable pump power and gain in the Al x
i-Mg i
x photoresonant x-ray laser
Authors: Apruzese J. P. , Buie M.
Published: July 2002

The aluminum-magnesium photoresonant x-ray laser scheme is investigated using detailed atomic models for both elements. The aluminum pump source is assumed to be a Z pinch driven by a current of several MA. It is found that monochromatic pump powers of 100 GW/eV are obtainable within the 48-Å aluminum pump line over a broad range (125–400 eV) of pump plasma temperatures. The gain in Mg ix is calculated assuming separations of 1 or 2 cm from the pump plasma. The highest gain appears in the 2s3d 1D2-2s4f 1F3 line at 228 Å. However, photoionization as well as resonant photoexcitation appears to be crucial to the success of this scheme. If photoionization by lines other than the pump line is neglected, Mg ix does not exist below∼60 eV. In the 60–100-eV Mg plasma temperature range, collisional excitation from low-lying states to the lower laser level severely degrades the gain. However, when photoionization of Mg by all of the strong Al xi lines is taken into account, Mg ix is found to exist at much lower temperatures, leading to respectable gain of ∼3 cm−1 at 1-cm Al-Mg separation.
Stability of high-quality Nb/AlOx/Nb Josephson junctions
Authors: Morohashi Shin’ichi , Yoshida Akira , Hasuo Shinya
Published: July 2002

We fabricated Nb/AlOx/Nb Josephson junctions which showed excellent I-V characteristics (Vm = 80 mV at the critical-current density of 1500 A/cm2). We attribute these characteristics to the clear junction interface, obtained by depositing Nb and Al layers with a minimum of thermal and physical damage. We fabricated 104 junctions connected in series on a single chip with an area of 5×5 mm2. Each junction is 10×10 μm2. These junctions have excellent uniform critical currents, have not failed, and have not changed after room-temperature storage for 4 years. These results indicate that Nb/AlOx/Nb junctions are excellent for use in Josephson LSI circuits. However, it may be further necessary to improve the uniformity of Al and Al-oxide layers if they are used in an actual large-scale integrated circuit, where more than 105 junctions are contained. The influence of the flux trap on current uniformity and deterioration of the I-V characteristics by annealing may be critical for large-scale integration.
Interaction of a screw dislocation with an interface crack
Authors: Zhang Tong-Yi , Li J. C. M.
Published: July 2002

The interaction between a screw dislocation and an interface cylindrical hole is found to depend on the source and location of the screw dislocation. When a screw dislocation is inside one of the media it has one image in the other medium. If the real dislocation is emitted from the hole which is originally stress free, it has only two images inside the hole. However, if the real dislocation is emitted from elsewhere and moves to the vicinity of the hole, there is a third image at the center of the hole to keep the total Burgers vector of the images in the hole zero. These considerations were used to study the interaction of a screw dislocation with an interface crack (or elliptical hole) by means of conformal mapping. The effect of the screw dislocation on the stress intensity factor at the crack tip is continuous when the screw dislocation moves from one medium across the interface to the other medium. The image force can be divided into two parts. One part is due to the interface and the other is due to the interface crack. The composite solid behaves like a homogeneous solid with an effective shear modulus when the dislocation is in the interface. The interaction between two or more screw dislocations in the presence of an interface crack is studied also. The latter result can be used to study the emission of an array of screw dislocations from an interface crack.
The surface morphology of selectively grown epitaxial silicon
Authors: Lou Jen-Chung , Oldham William G. , Kawayoshi Harry , Ling Peiching
Published: July 2002

The low-temperature epitaxial growth of Si under conditions in which no nucleation occurs on SiO2 (selective growth) results in interesting new surface morphology. For substrates free of nonvolatile surface contaminants, specular defect-free films are obtained at 850 °C. Surprisingly, small residual oxide islands can also be tolerated because of epitaxial lateral overgrowth. However, for islands greater than about 50 nm, shallow surface pits on an otherwise specular surface are observed. Based on experiments that show a reduction in growth rate in oxygen-implanted regions, these surface depressions are attributed to an oxygen effect. If the interfacial oxide islands are of such high density that they merge into a semicontinuous film, a textured surface morphology is observed, although the film is epitaxial and can be defect free. At even higher levels of interfacial contamination, threading dislocations and other defects are observed.
Stress-induced rearrangement of oxygen atoms in Si investigated by a monoenergetic positron beam
Authors: Wei L. , Tabuki Y. , Kondo H. , Tanigawa S. , Nagai R. , Takeda E.
Published: July 2002

A monoenergetic positron beam has been used to investigate the state of interstitial oxygen in Czochralski-grown Si with coverage of SiO2 (100 nm) and poly-Si (200 nm)/SiO2 (100 nm), respectively. It was found that (i) the growth of SiO2 gives rise to a strong Doppler broadening of positrons in the bulk of Si and (ii) such a broadening can be recovered to the original level by annealing at 450 °C, by the removal of overlayers using chemical etching and by long-term aging at room temperature. This broadening was assigned to arise from the positron trapping by oxygen interstitial clusters. It was concluded that film stress is responsible for the rearrangement of oxygen atoms in Czochralski-grown Si.
Infrared transmission and photocurrent study of intersubband transitions in a coupled asymmetrical quantum well structure
Authors: Liu H. C. , Steele A. G. , Buchanan M. , Wasilewski Z. R.
Published: July 2002

We report the results of an experimental study of intersubband transitions in a coupled asymmetrical double quantum well structure. Infrared transmission and photocurrent spectra are measured at 80 K. One period of the 40-repeat quantum well structure consists of a wide Si-doped GaAs well and a narrow undoped GaAs well separated by a thin AlGaAs barrier. The intersubband transition in the wide well occurs at about 9.5 μm, and, under appropriate bias, an intersubband absorption feature in the narrow well appears at 6.2 μm. The switching between intersubband transitions at 9.5 and 6.2 μm relies on electron transfer between the wells. Our absorption measurements provide direct evidence that up to 35% of the 9.2×1011 cm−2 electrons in the wide well can be transferred into the narrow well. These transferred electrons give rise to a photocurrent peaked at 6.2 μm.
Metallurgical study of Ni/(Ga,Al) As contacts. III. Transmission electron microscopy characterization of ternary superstructured phases in the reacted layers
Authors: Poudoulec A. , Guenais B. , Guivarc’h A. , Caulet J. , Guérin R.
Published: July 2002

Solid-state interactions of Ni thin films on (111) GaAs and (111) AlAs were investigated using transmission electron microscopy. We show that the experimental determination of the Ni-Ga-As and Ni-Al-As ternary phase diagrams, and the accurate determination of the atomic composition and crystalline structure of the various ternary solid solutions are absolutely required to understand the x-ray and electron diffraction patterns, and thus identify the compounds in the reacted layers and explain the different steps of the reactions. For this purpose, we report the results obtained on three typical samples, where hexagonal superstructured ternary phases have been observed.
Switching speeds in double-barrier resonant-tunneling diode structures
Authors: Mains R. K. , Haddad G. I.
Published: July 2002

Switching speeds are calculated for GaAs-AlGaAs resonant-tunneling diode structures with different barrier widths from the time-dependent Schrödinger equation. The speed is determined by monitoring the device current as the bias voltage is instantaneously switched. Effective mass discontinuities at the barrier and quantum well edges are included. Comparisons with previously published results using the wave packet approach are given. It is found that the turn-off transient is dominated by the lifetime of the quasibound state; however, care must be used in calculating the lifetime.
Chemical plasma etching of Y-Ba-Cu-oxide thin films
Authors: Poor M. R. , Fleddermann C. B.
Published: July 2002

The use of chemical plasma etching for patterning thin films of superconducting Y-Ba-Cu-oxide thin films is reported. Etch rates as high as 10 μm/min were measured, and were found to be highly dependent on substrate temperature and annealing of the film. Energy dispersive spectroscopy measurements showed significant variations in film stoichiometry as substrate temperatures increased, with copper being the most volatile element, followed by barium and yttrium. Although the etching is isotropic, this study indicates that chemical plasma etching can be a viable technology for high-Tc superconducting thin-film patterning.
Fabrication of SnO2:As/SiO2/n-Si (textured) (semiconductor/insulator/semiconductor) solar cells by chemical vapor deposition
Authors: Vishwakarma S. R. , Rahmatullah  , Prasad H. C.
Published: July 2002

Semiconductor/insulator/semiconductor solar cells having AM 1 efficiency of 14.5% on single silicon crystal were fabricated. The arsenic-doped tin oxide films were deposited by the chemical vapor deposition technique on heated n-Si substrate with 〈100〉 orientation having a resistivity of 0.1 Ω cm. Before the deposition of SnO2:As the wafers were made textured and the SiO2 layer was chemically grown on the Si surface. The capacitance-voltage measurement at 1-kHz frequency shows the abrupt nature of the junction with built-in voltage Vd = 0.77 V. The variation of dark current density–voltage characteristics with temperatures was also studied.
Annealing behavior of Ga and Ge antisite defects in neutron-transmutation-doped semi-insulating GaAs
Authors: Kuriyama K. , Yokoyama K. , Tomizawa K.
Published: July 2002

The evaluation of GaAs and GeAs antisite defects in neutron-transmutation-doped semi-insulating GaAs was studied by the photoluminescence measurements at temperatures ranging from 15 to 80 K. The annealing behavior of both the GeAs acceptors and the band-edge distortion, induced by the neutron irradiation, plays an important role in the detection of GaAs double acceptors. The 200-meV level of the GaAs double acceptor cannot be observed unless the 30-meV GeAs and 78-meV GaAs levels are partially or completely filled with electrons.
10–20 MeV energy range Si implantations into InP:Fe
Authors: Nadella Ravi K. , Rao Mulpuri V. , Simons David S. , Chi Peter H. , Dietrich Harry B.
Published: July 2002

Si implantations in the energy range 10–20 MeV were performed into InP:Fe with a dose of 4×1014 cm−2. The secondary-ion mass spectrometry profiles for the as-implanted samples were used to calculate the first four statistical moments of the Si implant distribution. Either 875 °C/10 s rapid thermal annealing or 735 °C/10 min furnace annealing was used to activate the Si implants. No redistribution of Si was observed after annealing. Electrochemical capacitance-voltage profiling was performed on the annealed samples to obtain the carrier concentration depth profiles. Activations of 90%–100% and peak carrier concentrations of 3–4×1018 cm−3 were measured for 10–20 MeV Si implants after 875 °C/10 s rapid thermal annealing.
Far-infrared reflectivity−A novel tool in the investigation of the relaxation process of excess carriers in HgCdTe
Authors: Dingrong Qian
Published: July 2002

The far-infrared reflectivity spectrum of HgCdTe measured at 77 K has been studied in the region 40–220 cm−1. A new measurement has been proposed to investigate the relaxation process of excess carriers, it offers a new way of noncontact and nondestructive characterization of materials. There are no requirements for the shape, nor for the thickness of sample.
Laser-induced optical index gratings on superconducting thin film structures
Authors: Glass N. E. , Rogovin D.
Published: July 2002

A theory is presented that demonstrates that a superconducting thin film under laser illumination can form an optical index grating similar to those created in nonlinear dielectric media. The grating consists of a spatially varying quasiparticle density in accordance with the intensity of a laser interference pattern. The analysis shows that such laser-induced optical index gratings form rapidly, on the order of 0.5 nsec, and can be detected via the diffraction of millimeter waves.