bluuebunny/crossref_metadata_2025 huggingface dataset:
Third-order nonlinear optical interactions of C60 and C70
Authors: Aranda Francisco J. , Rao D. V. G. L. N. , Roach Joseph F. , Tayebati P.
Published: July 2002

We measured the third-order nonlinear optical susceptibility χ(3) for C60 and C70 solutions as a function of concentration using degenerate four-wave mixing with picosecond pulses at 532 nm. From the observed minimum we were able to obtain the real and imaginary parts of χ(3). The real part is negative at this wavelength. Values of the real and imaginary components of the molecular hyperpolarizability (γ) calculated are in the range 10−31 esu.
Quantum confinement effects on low-dimensional electron mobility
Authors: Wang Tahui , Hsieh T. H. , Chen T. W.
Published: July 2002

A study of quantum confinement effects on the low-dimensional electron mobility in various AlGaAs/GaAs quantum well/wire structures has been performed. The influence of the electron envelop wave function and the subband structure on the low-dimensional electron scattering rates is evaluated. The electron transport behavior is studied through a Monte Carlo simulation. The result shows that the low-dimensional electron mobility varies significantly with the quantum well/wire geometry. The one-dimensional electron mobility of 9200 cm2/V s is obtained in a rectangular quantum wire with a geometry of 110 Å×110 Å. This value is much improved in comparison with the bulk electron mobility of 8000 cm2/V s in intrinsic GaAs and the maximum two-dimensional electron mobility of 8600 cm2/V s in a 120 Å GaAs quantum well. It is also noticed that the highest low-dimensional electron mobility is achieved in a quantum well/wire structure where the energy separation between the first subband and the second subband is about two polar optical phonon energy.
Examination of the multilevel diffraction model for interface roughness characterization by scanning tunneling microscopy
Authors: Yang H.-N. , Chan A. , Wang G.-C.
Published: July 2002

Scanning tunneling microscopy (STM) has been used to investigate rough Au:Pd thin films. The Au:Pd surface is best described by the self-affine scaling model, with the roughness exponent α=0.79±0.06 and the interface width w=15.0±0.5 Å measured directly from the STM images. We further show how α and w may be extracted from diffraction techniques by utilizing the multilevel diffraction theory, using the STM images as a model self-affine surface.
Measurement of aluminum concentration in epitaxial films of AlxGa1−xAs on (110)- and (111)-oriented GaAs by double axis x-ray diffractometry
Authors: Lind M. D. , Farley C. W. , Sullivan G. J. , Grant R. W.
Published: July 2002

The relationship between the Al mole fraction (x) and the angular separation (Δθ) of film and substrate maxima in double axis x-ray diffraction rocking curves for strained epitaxial AlxGa1−xAs films on (110)- and (111)-oriented GaAs substrates was determined. It was derived from measured Δθ’s for 5000-Å-thick strained epitaxial AlAs films grown by molecular beam epitaxy on (110)- and (111)-oriented GaAs substrates and published values of the AlAs and GaAs lattice parameters and GaAs elastic constants. The critical thickness for relaxation appears to be significantly less for (111)- than for (100)- and (110)-oriented films.
Nonlinear photothermal radiometrical material inspection technique
Authors: Wang Chinhua , Li Peizan
Published: July 2002

A new technique called nonlinear photothermal radiometry that applies the second-harmonic thermal waves to material inspection and nondestructive evaluation is described. The measurement results of the second-harmonic signal show more sensitivity and higher resolution than those of fundamental signal. A theoretical model is developed and some characteristics are discussed to aid in understanding the experiment results.
The role of hydrogen dilution and radio frequency power in the formation of microcrystallinity of n-type Si:H thin film
Authors: Saha S. C. , Barua A. K. , Ray Swati
Published: July 2002

Phosphorus doped n-type hydrogenated microcrystalline silicon (μc-Si:H) films have been prepared at low power densities suitable for application in solar cells by the usual radio-frequency plasma enhanced chemical vapor deposition method (rf-PECVD, 13.56 MHz). For this purpose hydrogen (H2) dilution in the silane (SiH4) and phosphine (PH3) gas mixture and rf power densities have been varied carefully to produce a plasma condition conducive to the growth of microcrystallinity. The structural properties of the films have been studied by Raman spectroscopy, x-ray diffractometry, transmission electron microscopy, and infrared vibrational spectroscopy. The electrical and optical characterizations have been done by dark conductivity, dark conductivity activation energy, and optical absorption measurements, respectively. Effects of variations of hydrogen dilution and rf power density on the electrical and structural properties of the films have been investigated thoroughly. Film with highest conductivity (32.6 S cm−1) has been obtained with a H2/SiH4 ratio of 90 and rf power density 30 mW/cm2. At lower hydrogen dilution (H2/SiH4=20), higher power density (180 mW/cm2) is required to produce the desired microcrystallinity. Attempt has been made to explain the results in terms of growth kinetics.
Study of Schottky contacts on n-Ga0.51In0.49P by low-pressure metal-organic chemical-vapor deposition
Authors: Chang Edward Y. , Lai Yeong-Lin , Lin Kun-Chuan , Chang Chun-Yen
Published: July 2002

A comprehensive study of the Schottky contacts on Ga0.51In0.49P has been made. The Ga0.51In0.49P epitaxial layer was successfully grown on the GaAs substrate by low-pressure metal-organic chemical-vapor deposition to form a lattice-matched heterostructure. Three different types of films, including single-layer metal (Pt, Ni, Pd, Au, Co, Mo, W, Cr, Ti, Al, Ta, and In), metal silicides (WSi2, W5Si3 PtSi, and Pt2Si), and TiW nitrides (TiWNX) as the Schottky contacts metals on Ga0.51In0.49P were studied. Due to the high-band-gap nature of Ga0.51In0.49P, the Schottky contacts on Ga0.51In0.49P demonstrate good characteristics. The barrier heights range from 0.79 to 1.19 eV depending on the selection of the metals and the annealing conditions. Among single-metal films, Pt film demonstrates the best thermal stability. A barrier height of 1.09 eV and an ideality factor of 1.06 were obtained even after the Pt Schottky diode was furnace annealed at 500 °C for 30 min. For refractory compounds, the TiWNX film with the highest nitrogen content shows the best thermal stability with a barrier height of 1.00 eV and an ideality factor of 1.04 even after high-temperature annealing at 850 °C.
Dynamics of the detonation products of lead azide. IV. Laser shadowgraphy of expanding species
Authors: Tzuk Y. , Bar I. , Rosenwaks S.
Published: July 2002

Laser resonant shadowgraphy (LRS) and laser nonresonant shadowgraphy (LNRS) are used to monitor the detonation products of lead azide. Photographs of the cloud of products are obtained via illumination with a doubled dye laser tuned on-resonance to the 3P1o-3P0 transition of the Pb atom at 283.31 nm, and off-resonance at 284.31 nm. The versatility of the diagnostics and its applicability to detonation products expanding into vacuum and into atmospheric pressure air are demonstrated. The LRS monitors the density gradients of both lead atoms and solid particles formed in the detonation, whereas the LNRS detects only the latter. Expansion into vacuum through a nozzle leads to an increase in the velocity (from ∼4.5 to ≳5 km/s) and density of the atoms and to a decrease in the density of the particles. The LRS measurements show that the expansion of both products in air is relatively slow (∼0.75 km/s) and leads to production of shock waves. From the shape of the shock waves created by an obstacle when the products expand into vacuum, the Mach number is estimated to be ≳20 in the outer parts and around 3 in the inner parts of the cloud.
Resistive transition of Bi(2223) silver clamped thick film
Authors: Han G. C. , Wang Y. G. , Han H. M. , Wang Z. H. , Wang S. X. , Yuan W. F. , Liu Z. M. , Huang Q. L. , Chen J. L.
Published: July 2002

Detailed measurements of voltage-current (V-I) curves and magnetoresistance (R-H) for Bi(2223) thick film were carried out for various temperatures and magnetic fields. The results indicate that a flux lattice melting transition takes place as the temperature and the field are raised. This transition boundary in the (H,T) phase diagram was found to follow the irreversibility line described by the function of H=H0(1−T/Tc)3/2. Above this line, the V-I curves display a flux-flow-like character. Temperature and magnetic field dependencies of flow resistance Rf-T and Rf-H show a varied viscosity in different temperature and field ranges. Below this line, V-I curves in the low voltage region present a thermally activated flux creep property. The R-H measurements indicate that the fields at the onset and the midpoint of the magnetoresistive transition also follow a (1−T/Tc)3/2 dependence.
Crystallization of coevaporated and ion-irradiated amorphous CoSi2
Authors: Hong Q. Z. , Barmak K. , Hong Stella Q. , Clevenger L. A.
Published: July 2002

The crystallization of coevaporated, amorphous CoSi2 with and without ion irradiation has been studied. Without ion irradiation, the crystallization of amorphous CoSi2 is characterized by three-dimensional growth from preexisting nuclei. The crystallization kinetics, described by the Avrami equation, are retarded by irradiating the as-deposited CoSi2 with either Si or Kr ions at liquid nitrogen temperature. The dose dependence of the crystallization kinetics can be divided into two regions. In the low dose regime, the crystallization kinetics decrease sharply with increasing dose, while the mode of crystal growth changes continuously from three-dimensional to two-dimensional growth. In the high dose regime, the crystallization kinetics are only slightly dependent on the irradiation dose. Nucleation occurs throughout the crystallization process and two-dimensional growth dominates.
A geometrical rationalization of the special properties of the 14° [001] grain boundary in YBa2Cu3O7−δ
Authors: King A. H. , Singh Abha
Published: July 2002

14° [001] tilt grain boundaries in YBa2Cu3O7−δ have been found to exhibit anomalously good superconducting critical currents, associated with magnetic flux pinning, although no special interfacial structure has heretofore been associated with this misorientation. We present an analysis of the geometry of the grain boundary in question and show that it can correspond to a special interface, within the definition of constrained lattice coincidence, which may lead to new understanding of the superconducting behavior of grain boundaries. Our analysis shows that the tetragonal-to-orthorhombic phase transformation may have important effects upon grain boundary structure and properties, indicating new approaches to producing high-current superconductors.
Wannier–Stark localization in InGaAs/GaAs superlattices and its application to electro-optical devices
Authors: Liu Wei , Zhang Yaohui , Jiang Desheng , Wang Ruozhen , Zhou Junming , Mei Xiaobing
Published: July 2002

We have observed Wannier–Stark localization in strained In0.2Ga0.8As/GaAs superlattices by low- and room-temperature photocurrent spectra measurements. The experimental results are well in agreement with the theoretical predictions. A large field-induced modulation response of the absorption edge of the superlattices at room temperature suggests the possibilities of the application to the design of various kinds of electro-optical devices operating at a wavelength of 0.98 μm, based on Wannier–Stark localization effects.
Electrical characterization of neutron irradiation induced defects in undoped epitaxially grown n-GaAs
Authors: Auret F. D. , Goodman S. A. , Myburg G. , Barnard W. O. , Jones D. T. L.
Published: July 2002

Undoped n-GaAs, grown by organometallic vapor phase epitaxy, was irradiated with neutrons from a clinical p(66)/Be(40) source for a range of fluences. Deep level transient spectroscopy (DLTS), employing Pd Schottky barrier diodes, indicated that four electron traps, En1, En2, En4, and En5, with energy levels at 0.04, 0.14, 0.36, and 0.66 eV, respectively, below the conduction band were created during neutron radiation. Their introduction rates varied from 1 cm−1 for the En1 to 11 cm−1 for the En5. It was found that the En1, En2, and En4 defects have DLTS ‘‘signatures’’ similar to the E1, E2, and E3 point defects introduced during high energy electron irradiation, indicating their point defect nature. The En5 has a very large capture cross section, its emission rate exhibits a strong electric field dependence, and there are indications that it has a band-like energy distribution, that results in a broad DLTS peak. We speculate that this trap is related to the presence of extended defects in the neutron irradiated GaAs.
Fabrication and properties of textured YBa2Cu3O7 thick films on polycrystalline Ag0.9Pd0.1 and silver substrates
Authors: Wang Y.-L. , Wiesmann H. J. , Liu C. F. , Zhu Y. , Sabatini R. L. , Suenaga M.
Published: July 2002

Highly textured (c axis perpendicular to the plane of the substrate tape) thick films of YBa2Cu3O7 grown on Ag0.9Pd0.1 and pure silver substrates have been made by a traveling heated zone method. The speed of the traveling zone can be as fast as ∼5 cm/h and the temperatures of the zone, 930–975 °C, were well below the peritectic temperature of YBa2Cu3O7. A precursor layer, which consisted of a nitrate solution of yttrium, barium, and copper cations, was deposited by spray pyrolysis directly onto a heated substrate. The values of the resistively measured Tc were 83–91 K. The transport critical current density of these thick films was in the range of 2–8×103 A/cm2 at 77 K and 0 T.
InxGa(1−x)N/InyGa(1−y)N superlattices grown on GaN films
Authors: Nakamura Shuji , Mukai Takashi , Senoh Masayuki , Nagahama Shin-ichi , Iwasa Naruhito
Published: July 2002

High-quality In0.22Ga0.78N/In0.06Ga0.94N superlattices were grown on GaN films with periods of 60 and 200 Å by the two-flow metalorganic chemical-vapor deposition method. The double-crystal x-ray rocking curve measurements showed satellite peaks which indicated the existence of the In0.22Ga0.78N/In0.06Ga0.94N superlattices. The quantum effects were observed through room-temperature photoluminescence (PL) measurements. These PL spectra were compared to theoretical solutions for the In0.22Ga0.78N/In0.06Ga0.94N superlattices.
Optical properties of polycrystalline Cd1−xMnxTe
Authors: Guerrero H. , Escudero J. L. , Bernabeu E. , Hernández-Rojas J. L. , González-Díaz G.
Published: July 2002

Bulk polycrystalline cadmium manganese telluride, Cd1−xMnxTe, was manufactured in several compositions by a synthesis process. The structure of the obtained compounds was the characteristic zinc-blende polycrystalline pattern being the grain size 100±20 nm. These materials are manufactured to replace single-crystal compounds in some magneto-optical devices. The cut-off wavelength and the Verdet constant are the same as the single-crystals with identical composition. A polarized laser beam, after having passed through a sample of 0.76 mm thickness, was depolarized less than 2.5%, and 90% of its energy was spread into a 2° cone. Scattering of light is produced because of the polycrystalline structure of these compounds. Some scattering diagrams, due to the diffraction and Mie scattering in the polycrystalline grains are shown.
Sb as an indium-absorptive barrier in ZnSe/InP(100) heterostructures
Authors: Rioux Dennis , Höchst Hartmut
Published: July 2002

Antimony layers, sandwiched between a ZnSe/InP(100) heterostructure interface, can be used as a barrier preventing outdiffusion of In into ZnSe epilayers. Through core level photoemission spectroscopy and reflection high-energy electron diffraction investigations, we found that the Sb layer must be annealed in order to prevent In outdiffusion. Barrier action occurs by means of InSb formation. A single pseudomorphic monolayer was insufficient to prevent In from outdiffusing. A thicker Sb layer greatly reduced In outdiffusion but through misfit dislocation the initially strained InSb film relaxed to its bulk lattice constant and did not allow for subsequent pseudomorphic epitaxy of strained ZnSe overlayers.
Accurate measurements of the silicon intrinsic carrier density from 78 to 340 K
Authors: Misiakos Konstantinos , Tsamakis Dimitris
Published: July 2002

The intrinsic carrier density in silicon has been measured by a novel technique based on low-frequency capacitance measurements of a p+-i-n+ diode biased in high injection. The major advantage of the method is its insensitivity to uncertainties regarding the exact values of the carrier mobilities, the recombination parameters, and the doping density. The intrinsic carrier density was measured in the temperature range from 78 to 340 K. At 300 K the value of ni was found to be (9.7±0.1)×109 cm−3.
Characterization of the buried oxide in SOI structures by a rate window method
Authors: Ioannou-Sougleridis V. , Papaioannou G. J. , Dimitrakis P. , Cristoloveanu S.
Published: July 2002

A new method for the characterization of the SOI separation by implanted oxygen (SIMOX) oxide is presented. It is based on the fact that the buried oxide can be polarized by applying a bias in the substrate of the structure. In the process of relaxation, current transients are induced in the Si film, which can be monitored by the rate window technique. The experiment reveals that the relaxation process is thermally activated with one or more time constants. These properties of the SIMOX oxide are attributed to the high metal concentration of the oxide.
Resistive transitions and the origin of the n value in superconductors with a Gaussian critical-current distribution
Authors: Edelman H. S. , Larbalestier D. C.
Published: July 2002

The resistive transition of a superconductor with a Gaussian distribution of critical currents is analyzed and exact relations for the voltage-current characteristic and the resistive transition index (n value) in such a superconductor are developed. Excellent fits are found to the experimental transitions in two very different types of superconductor; a Nb-Ti monofilament and a Bi2Sr2Ca2Cu3O10 tape.
Calculations and modeling of grain-boundary acceptor states for (Ba,Pb)TiO3 positive temperature coefficient ceramics
Authors: Lai Chun-Hung , Lu Yuh-Yih , Tseng Tseung-Yuen
Published: July 2002

The electrical properties of high-Curie-point positive temperature coefficient of resistance ceramics of composition Ba0.497Pb0.5La0.003Ca0.005Ti0.995O3 prepared from commercial BaTiO3 powder were studied. The acceptor-state energy and acceptor-state density were determined from the calculated ρmax vs Tmax plot, where ρmax and Tmax are the resistivity and temperature corresponding to the maximum in resistivity. These two parameters, combined with the effect of nonvanishing spontaneous polarization below the Curie point, were treated quantitatively to demonstrate the dependence of measured resistivity ρdc on the measured permittivity εm. The obtained values of potential barrier height and acceptor-state density based on the procedure above were found to be in excellent agreement with those extracted from the slope in the Arrhenius plots of resistivity versus 1/(Tεm), where T is the absolute temperature. Also, the deviation of the measured dielectric constant εm from the Curie–Weiss law’s prediction was explained by the narrowing of the grain-boundary barrier layers.
Optical probing of intermixing in GaAs-AlGaAs multiquantum wells
Authors: Seidel W. , Lugagne-Delpon E. , Voisin P. , Rao E. V. K. , Krauz Ph. , Alexandre F.
Published: July 2002

It is shown that a combination of low-temperature photoluminescence and luminescence excitation spectroscopies together with appropriate modelization can provide the precise information needed for a thorough control of interdiffusion in quantum well structures. A fit of observed and calculated transition energies up to five energy levels, using the interdiffusion length as a unique parameter, is considered. The potentiality of this procedure to fully characterize the interdiffusion process is illustrated by considering the examples of lightly and heavily intermixed GaAs-AlGaAs multiquantum wells.
Retracing behavior of the phase-matching angle of nonlinear crystals in optical parametric oscillators
Authors: Liu Xiang , Deng Daoqun , Li Ming , Guo Dongsheng , Xu Zuyan
Published: July 2002

The retracing behavior of the phase-matching angle (RBPA) of many nonlinear optical crystals in optical parametric oscillators (OPO) is reported here. The wavelength range of the pump wave and the tuning angle range over which RBPA can occur are obtained. Furthermore, the generality of this novel and interesting phenomenon is successfully explained by theoretical analysis. We point out that RBPA exists generally in both type I and type II OPO’s by using either uniaxial or biaxial crystals.
High quality undoped n-type GaSb epilayers by low-temperature metalorganic chemical vapor deposition
Authors: Chen S. M. , Su Y. K.
Published: July 2002

We obtain undoped n-type GaSb epilayers by low-temperature metalorganic chemical vapor deposition at a low growth temperature of 450 °C reproducibly. Different conduction types of GaSb and different energy levels are compared by photoluminescence spectra. For n-type undoped GaSb, the FWHM of dominant peak and bound exciton are 11 and 1.3 meV, respectively. Because semi-insulating GaSb substrates cannot be obtained, we cannot use the Hall effect to determine the carrier concentration and mobility of the homoepilayer. In order to identify the conduction types of GaSb, ohmic contact and Schottky barrier are made by Au/Ge/Ni and Au, respectively. The concentrations of undoped n-type GaSb homoepilayers obtained from I-V and C-V measurements are 1.44×1017–3.0×1017 cm−3, respectively. The mobility and concentration of undoped p-type GaSb heteroepilayers are 758 cm2/V s and 9.0×1015 cm−3 at 300 K, respectively.
The Ag/As2S3 photodoping mechanism: Photon absorption
Authors: Dumford S. A. , Lavine J. M. , Lis S. A.
Published: July 2002

The sensitivity of the Ag-photodoping process has been measured as a function of photon energy between 1.9 and 6.4 eV. The sensitivity increases with increasing photon energy except at 3.8 eV (325 nm) where Ag exhibits an anomalous window. At this energy there is an abrupt and large decrease of sensitivity. In a second measurement, the transmission as a function of wavelength between 200 and 900 nm of a 2000-Å-thick film of As2S3 doped with an imaging dose of Ag and a second sample doped with a larger than imaging dose are compared with an undoped sample. Band-gap shrinkage is different for the two doses. Both measurements suggest that under certain conditions, photon absorption in the Ag-photodoping process occurs in the Ag.
Investigation of the enhanced efficiencies of small superconducting loop antenna elements
Authors: Khamas S. K. , Cook G. G. , Kingsley S. P. , Woods R. C. , Alford N. McN.
Published: July 2002

The fields backscattered from arrays of electrically small copper and YBCO superconducting loops are measured and compared with moment method predictions to confirm the gain enhancements and changes in Q factors due to increasing the efficiencies of the antenna elements alone, without the influence of feed and matching networks. Measurements on coplanar and parallel loop arrays show only small increases in the backscattered fields of the YBCO scatterers, with the largest increase in efficiency being for the single loop. The mutual resistance between elements reduces the benefit of adding more elements to a YBCO loop, to a greater extent than when copper elements are added to a copper loop.
Optimization of charge transfer to the active channel in δ-doped heterostructures
Authors: Lazzouni M. E. , Einevoll G. T. , Sham L. J.
Published: July 2002

An accurate theoretical model based on the two-band effective-mass-approximation that includes nonparabolic, strain, finite temperature, many-body, and deep donor (DX) center effects is used to investigate the electronic properties of δ-modulation-doped semiconductor heterostructures with the aim of optimizing the active channel density. Inclusion of the DX centers in the model leads to the saturation of the electronic density with increasing δ-doping concentration for both structures doped on one side and structures doped on both sides of the channel. The saturation value in the latter case is almost twice as high as in the former. The self-consistent calculations show that by using a superlattices of superlattices configuration with an appropriately chosen superlattice barrier one can achieve a 50% increase in the maximum charge transfer compared to conventional heterostructures of similar design, without increasing impurity scattering in the channel.
Electrical conduction in CaF2 and CaF2-Al2O3 nanocomposite films on Al2O3 substrates
Authors: Modine F. A. , Lubben D. , Bates J. B.
Published: July 2002

Thin films of pure CaF2 and nanocomposite mixtures of Al2O3 with CaF2 were evaporated on Al2O3 substrates. Interdigital electrodes on some of the substrates allowed in situ measurements of the electrical conduction in the films during and subsequent to film growth. Electrical conduction was studied as a function of film thickness, film deposition rate, composition, time, and temperature. The electrical conductivity in pure CaF2 adjacent to an Al2O3 interface sometimes exceeded the bulk CaF2 conductivity (i.e., value at more than 50 nm distance) by as much as a factor of 6700 at 200 °C. The high conductivity is characterized by an activation energy of 0.6±0.1 eV, which is significantly lower than the activation energy of about 1.0 eV for conduction in the bulk. However, this high conductivity is thermally unstable and diminishes in time. A high but stable conductivity was obtained in CaF2 films containing about 10 mol % Al2O3 as a dispersed second phase. At 200 °C, a two-phase film gave a factor of 360 enhancement over the measured bulk CaF2 conductivity and a factor of 7 improvement over the best previously reported conductivity for CaF2-Al2O3 composite materials. The origin of enhanced conduction in CaF2 is attributed to ion transport along dislocations. Dislocations anneal with a characteristic log of time dependence that is recognizable in the annealing behavior of the electrical conductivity. Presumably, the addition of a dispersed second phase of Al2O3 to CaF2 serves both to generate and to pin dislocations; the electrical conductance is thereby enhanced and stabilized.
Magnetization reversal processes in Co-Re antiferromagnetically coupled multilayers: A magneto-optic and Monte Carlo study
Authors: Trindade I. G. , Freitas P. P.
Published: July 2002

A study of magnetization reversal processes in sputtered antiferromagnetically coupled (CotCoRe5 Å)×n multilayers, with n=2,3,5 is reported. The two components of the magnetization, parallel and perpendicular to the applied field are analyzed using a suitable transverse Kerr effect differential magneto-optical setup. At the remanent state, and for n=3, and 5, we obtain a magnetization of 1/3 and 1/5 of the saturation magnetization, respectively. This means that the magnetization in each layer is aligned parallel or antiparallel to the applied field direction. The observed perpendicular magnetization component is as expected, much smaller than the parallel magnetization component over the entire length of the hysteresis cycle. A Monte Carlo simulation was used to study the spin configurations in the individual layers as well as the type of magnetization hysteresis cycles. We find that the introduction of a small uniaxial anisotropy is needed to explain the observed multiloop structure in the n=3 multilayers. Within our model, spin-canting may occur within the ferromagnetic layers leading to particular remanent-state spin configurations.
Analysis of thin-film solid solutions on single-crystal silicon by simulation of x-ray rocking curves: B-Si and Ge-Si binary alloys
Authors: Fabbri R. , Cembali F. , Servidori M. , Zani A.
Published: July 2002

B-Si and Ge-Si thin-film solid solutions on silicon at different compositions are analyzed by multiple-crystal x-ray diffraction. Computer simulations of the rocking curves are made with a diffraction model which, for dilute alloys, does not differ from that commonly reported in the literature. For sufficiently high solute atomic fractions, modifications are introduced to the Fourier coefficients of the crystal polarizability and to the parameters depending on the lattice strain. In the B-Si case, the comparison between strain and carrier profiles resulting from the simulations and electrical measurements, respectively, gives information on the fraction of substitutional B, the presence of precipitates, and their coherent or incoherent nature. In the Ge-Si case, the solute fraction, its depth gradient, and the static atomic disorder in the alloy are determined by means of the modified diffraction model. In particular, the determination of the atomic displacements around the lattice points in fully strained thin-film Ge-Si alloys give results larger than those evaluated by Monte Carlo calculations for relaxed solid solutions.
Ion channeling in textured polycrystalline diamond films
Authors: Samlenski R. , Flemig G. , Brenn R. , Wild C. , Müller-Sebert W. , Koidl P.
Published: July 2002

Channeling of H+ and H2+ ions of energies between 1.0 and 2.0 MeV in 〈100〉-textured polycrystalline diamond films grown by microwave plasma-assisted chemical-vapor deposition has been observed with Rutherford backscattering. The width of the orientational distribution of the diamond crystallites as deduced from the measured projectile velocity dependence of the observed channeling angular scans amounted to about 1°.
A high efficiency double 45°-cut mutually pumped phase conjugate mirror
Authors: Zhang Zhiguo , Zhu Yong , Yang Changxi , Fu Panming
Published: July 2002

We report for the first time a double 45°-cut mutually pumped phase conjugate mirror, which has high phase conjugate reflectivities and is highly insensitive to the alignment of the two incident beams. For example, two mutually incoherent incident beams can produce their own phase conjugate outputs when the angle between the incident beams is varied from as much as 7° to 140° and over 60% conjugate reflectivity can be obtained. Furthermore, the phase conjugate outputs are stable because the competition from the self-pumped phase conjugation can be avoided easily.
High field effective linewidth due to conductivity losses in Zn2Y hexagonal ferrite at 10, 20, and 35 GHz (abstract)
Authors: Truedson J. R. , McKinstry K. D. , Kabos P. , Patton C. E.
Published: July 2002

A simple technique to analyze the effective linewidth at high field, corresponding to the far field tail of ferromagnetic resonance (FMR) absorption, was recently reported. This technique has now been applied at 10, 20, and 35 GHz to single crystal Zn2Y hexagonal ferrite with planar anisotropy. Far field effective linewidth (ΔHeffFF) measurements were made for a series of 2–3 mm-diam, 0.08–1.33-mm-thick c-plane disks. The ΔHeffFF is taken to represent the intrinsic linewidth, in the sense that there are no two magnon or inhomogeneous linebroadening contributions to the losses on the far-field FMR tail. ΔHeffFF at each frequency increases with the square of the disk thickness. This increase is consistent with an eddy current loss process. A fit of the data to a simple eddy current model yields resistivities of 10.3, 9.7, and 8.3 Ω cm at 10, 20, and 35 GHz, respectively. These values are consistent with a resistivity of 2 Ω cm from 10 GHz dielectric measurements and 20 Ω cm from the resistivity measurements.

These results are similar to previous results for barium ferrite. However, the microwave response in these Zn2Y materials also shows many anomalies. First, ΔHeffFF is larger, not smaller, than the corresponding FMR linewidth. Second, ΔHeffFF also depends on the orientation of the microwave field relative to the crystallographic c plane. The losses for out-of-plane microwave pumping are larger by a factor of 2–3 than for in-plane pumping. Research sponsored by the United States Office of Naval Research, Contract N00014-90-J-4078. The single crystal samples were kindly provided by M. A. Wittenauer, Purdue University.
Frequency dependence of the ferromagnetic resonance and effective linewidth in single crystal manganese doped barium ferrite (abstract)
Authors: Karim R. , Patton C. E. , Ball S. D.
Published: July 2002

The frequency dependence of the ferromagnetic resonance (FMR) linewidth and effective linewidth has been measured in Mn doped single crystal barium hexaferrite (BaFe12−xMnxO19) with x=0.1. Mn doped samples were used to minimize conductivity losses. Measurements were made on c-plane thin disks magnetized to saturation along the disk axis and c direction. A shorted waveguide technique was used to measure the FMR profiles in the range of 55–90 GHz. The FMR field position increased linearly at 0.35 kOe/GHz, with a zero field extrapolation of 34.7 GHz as expected for uniform mode FMR in barium ferrite. The linewidth ΔH increased linearly with frequency at 0.29 Oe/GHz with a zero frequency extrapolation of 18 Oe. A high-Q cavity method was used to measure the high field effective linewidth, ΔHeffFF at 10, 20, 35, and 60 GHz. The effective linewidth increased linearly with frequency at 0.4 Oe/GHz, with a zero frequency extrapolation of 4 Oe. There were no dependencies of ΔH or ΔHeffFF on sample thickness. These results indicate that (1) eddy current contributions to ΔH and ΔHeffFF in these Mn doped barium ferrite materials are absent, (2) ΔHeffFF is significantly lower than ΔH and appears to be a good measure of the intrinsic losses, and (3) both linewidths increase linearly with frequency at about the same rate.

These intrinsic linewidths in barium ferrite are still significantly greater than linewidths in yttrium iron garnet. Research sponsored in part by the United States Office of Naval Research, Contract No. N00014-90-J-4078. The single crystal samples were kindly provided by M. A. Wittenauer, Purdue University.
Cathodoluminescence and photoluminescence studies of dislocations in GaAs/AlGaAs quantum wells
Authors: Araújo D. , Oelgart G. , Ganière J.-D. , Reinhart F. K.
Published: July 2002

The optical properties of low pressure metal organic vapor deposition grown GaAs/AlxGa1−xAs (x=0.5) single quantum well structures (SQW) with grown-in dislocations (GD) were studied by low temperature cathodoluminescence (CL) and photoluminescence (PL). High luminescence efficiency around the GD was observed and attributed to impurity decoration. CL spectra show a region surrounding the GD that consists of Si impurities and native defects in the SQW and barrier layers. The diameter of this region was found to be in the order of 1 μm using spectrally resolved CL micrographs.
Homoepitaxial growth of diamond by an advanced hot-filament chemical vapor deposition method
Authors: Kondoh Eiichi , Tanaka Kenji , Ohta Tomohiro
Published: July 2002

Homoepitaxial (111), (110), and (100) diamond films were grown by an advanced hot-filament chemical vapor deposition method that enables accurate control of the substrate temperature independently of the other chemical vapor deposition parameters. The obtained films were examined mainly by optical microscopy and reflection high energy electron diffraction (RHEED). The surface morphology of the films depended on the deposition pressure, methane concentration in the feed gas, and substrate temperature. Very streaky RHEED patterns, indicative of atomically smooth surfaces, were obtained from the samples deposited on the (111) substrates at a pressure of 100–500 Torr and methane concentration of 0.5%, and also from the samples deposited on the (100) substrates at 300–500 Torr and 1%–2%. These conditions, which we call ‘‘window’’ conditions, are remarkable, since such deposition pressures as 100–500 Torr are much higher than the few tens of Torr normally required for polycrystalline growth. However, the films on the (110) substrates exhibited spotty patterns due to three-dimensional growth, although optical microscopically smoothness was achieved by the 500 Torr and 0.5% deposition. Regarding the pressure effects, a reduction of H radicals and concurrent increase of the C2Hx(x=1–2) species are characteristic of the gas-phase chemistry under these window conditions. We speculate that the success of epitaxial deposition under these window conditions was due to surface reconstruction arising from the lack of H radicals and/or from the surface reactions in which C2Hx mediates.
A noise-tolerant solution to the magnetostatic inverse problem for nondestructive evaluation
Authors: McFall Gregory D. , Miracky Robert
Published: July 2002

We present a probabilistic analysis which, given a finite set of magnetic induction measurements, yields the ‘‘most likely’’ source current density. The need for a probabilistic analysis stems from the presence of noise in the measurements. In the noise-free limit, our algorithm reduces to the so-called minimum-norm estimate for the source current density. Our analysis differs from the work of previous investigators in its simplicity and completeness; the previous work drew substantially from measure theory and left the variance in a prior probability measure undetermined—whereas our analysis uses elementary probability theory and contains no free parameters. In numerical studies, we have applied our algorithm to the problem of identifying a crack at the edge of a thin metal plate. Simulating an impressed current in the plate, we computed the resulting magnetic induction and used our algorithm to obtain an estimated current density. Graphical images of the estimated current accurately reveal the position and size of the crack, and confirm that optimal estimates are obtained in the presence of noise.
An envelope function description of the quantum well formed in strained layer SiGe/Si modulation doped field effect transistors
Authors: Anwar A. F. M. , Liu K.-W. , Carroll R. D.
Published: July 2002

Schrödinger and Poisson equations are solved self-consistently to calculate the quantum mechanical properties of the quantum well (QW) formed in SiGe/Si/SiGe strained layer modulation doped field effect transistors. The strain produces an electron quantum well in Si. The two-dimensional electron gas distribution is calculated to show excellent confinement at low temperature. The confinement is poor at very low electron concentration at room temperature. However, it improves with increasing number of channel electrons. Moreover, a large electron concentration in a wide QW may result in the loss of confinement.
Electrical properties of silicon under nonuniform stress
Authors: Manku T. , Nathan A.
Published: July 2002

We present a detailed analysis of the electronic carrier transport in silicon when subject to a nonuniform stress distribution. Such a distribution gives rise to two independent current components which can be viewed in terms of carrier generation-recombination. One component arises as a result of the nonuniform stress induced position dependent density of states, and the other due to stress induced shifts in the band edges. The various parameters and coefficients describing these phenomena are presented.
A macroscopic model for focused-ion-beam-induced deposition
Authors: Overwijk M. H. F. , van den Heuvel F. C.
Published: July 2002

A time-dependent model for focused-ion-beam-induced deposition is presented which explicitly takes the scanning strategy of the beam during deposition into account. The model differentiates between the contribution of the beam center and that of the beam wings, and contains all major experimental variables such as current density, focus size, scan speed, and frame time. The deposition rate has been measured for tungsten as a function of the major experimental variables. The model has been fitted to these data and is found to describe the various dependences very well. By use of the model inclusive of the parameters obtained from the fit, we can predict optimum deposition conditions. Furthermore, the model clarifies effects observed during deposition on the structured surface of an integrated circuit, such as redeposition of sputtered material and poor step coverage due to an impeded gas flow.
Ion implantation and dry etching characteristics of InGaAsP (λ=1.3 μm)
Authors: Pearton S. J. , Abernathy C. R. , Wisk P. W. , Ren F.
Published: July 2002

The electrical activation characteristics of Si+ and Be+ ions implanted into InGaAsP (λ=1.3 μm) grown lattice matched to InP by metalorganic molecular beam epitaxy were studied as a function of ion dose (5×1012–5×1014 cm−2), annealing time (3–60 s) and annealing temperature (575–750 °C). Maximum doping concentrations of ∼2×1019 cm−3 were obtained for both Si+ and Be+, with activation energies for electrical activation of 0.58 and 0.39 eV, respectively. Multiple energy F+ or H+ implants can be used to produce high resistance layers for isolation purposes—maximum sheet resistances of ∼8×106 Ω/⧠ or ∼106 Ω/⧠ for initially p+ or n+ InGaAsP, respectively, were obtained for F+ implants followed by annealing near 450 °C. Smooth, anisotropic dry etching of the InGaAsP is obtained with electron cyclotron resonance CH4/H2/Ar discharges at low dc biases. The etch rates are the same for both n+ and p+ quaternary layers and are independent of the doping level.
X-ray analysis of compositional modulation in Co/Pt multilayer films for magneto-optic recording
Authors: Bain J. A. , Clemens B. M. , Notarys H. , Marinero E. E. , Brennan S.
Published: July 2002

The compositional modulation in Co/Pt multilayer films was studied through the use of asymmetric Bragg diffraction. The angle between the scattering vector and the surface normal was varied in order to interrogate different components of the in-plane strain. In-plane strain values and unstrained lattice parameters, which reveal the intermixing of the two metals, were extracted from these measurements. The films displayed strains which varied with bilayer period and showed substantial intermixing at the smaller bilayer periods. These small bilayer period films showed perpendicular anisotropy as measured by Kerr rotation.
Measurement of the optical properties of an asymmetric Einzel lens using the two-grid method
Authors: Colman R. A. , Legge G. J. F.
Published: July 2002

A method is described by which the optical properties of asymmetric Einzel lenses may be measured. This method uses the technique of grid shadows. For the measurement of cardinal elements as well as spherical aberration coefficients, two independent measurements are required. For chromatic aberration coefficients, measurements are required as a function of lens voltage ratio. No extra lens is required for the measurements. An experiment is described in which the optical properties of an asymmetric lens are measured. Within the errors of the measurement, the technique is demonstrated to produce good agreement with theoretical calculations.
Thermally stable ternary titanium-tantalum silicide formation on polycrystalline silicon
Authors: Choi J. S. , Paek S. H. , Hwang Y. S. , Kang S. G. , Cho H. C. , Oh J. E. , Shim T. E. , Lee S. I. , Lee J. K. , Lee J. G.
Published: July 2002

A material for thermally stable self-aligned silicide technologies has been developed using sequentially deposited Ti/Ta on polycrystalline silicon. At lower annealing temperatures below 1000 °C two separate phases were found by cross-sectional transmission electron microscopy to exist in the form of bilayer TiSi2/TaSi2. The formation of a ternary phase (TiTa)Si2 has been observed at a higher temperature of 1000 °C. Consequently, the ternary (TiTa)Si2 layer could be kept extremely flat, with a sheet resistance of 5 Ω/⧠, even after 1000 °C, 30 min annealing. Cross-sectional transmission electron micrographs of the structure clearly reveal that no agglomeration occurs during the heat treatment.
Epitaxial growth of oxides on semiconductors using fluorides as a buffer layer
Authors: Hung L. S. , Mason G. M. , Paz-Pujalt G. R. , Agostinelli J. A. , Mir J. M. , Lee S. T. , Blanton T. N. , Ding G.
Published: July 2002

The success in epitaxial growth of oxides on Si using an intermediate fluoride layer largely depends on the reactivity of the fluoride with the oxide and the stability of the fluoride against oxidation. The fluoride-oxide reaction was studied by Rutherford backscattering spectrometry and x-ray diffractometry. It is found that a large number of oxides are stable on CaF2, while some containing K, Li, and Ba react with CaF2. The results are consistent with thermodynamic predictions, and correlate well with the equalized electronegativity of the oxides. The stability of bare CaF2 on Si is found to be strongly related to the ambient. The CaF2 surface remains intact after annealing at 650 °C in 25% O2/N2, although Ca-silicate formation takes place at the Si-CaF2 interface. When annealing is conducted in air, Ca-carbonate is readily formed at the surface. The results provide guidelines for epitaxial growth of oxides on semiconductor/fluoride structures. The potential application of using fluorides as buffer layers is demonstrated in epitaxial growth of SrTiO3 on (100)Si/CaF2.
An investigation of anomalous current-voltage characteristics in silicon-on-insulator metal-oxide-semiconductor transistors
Authors: Liu Patrick S. , Liu George T.
Published: July 2002

Floating-body effects such as hysteresis, a single-transistor latch, and steep subthreshold slopes in n-channel silicon-on-insulator metal-oxide-semiconductor transistors are investigated. It is shown that the existence of multistable floating-body potentials is responsible for hysteresis and a single-transistor latch. Hysteresis denotes the presence of three floating-body potentials, while a single-transistor latch could reveal as many as five. Furthermore, a sharp rise (fall) in floating-body potentials, which triggers an abrupt device transition from subthreshold (saturation) to saturation (subthreshold), produces the steep subthreshold ID-VG characteristics observed at high drain biases.
Finite element analysis of thermal residual stresses at graded ceramic-metal interfaces. Part II. Interface optimization for residual stress reduction
Authors: Drake J. T. , Williamson R. L. , Rabin B. H.
Published: July 2002

An elastic-plastic finite element method numerical model previously developed (see Part I of this article) for predicting thermal residual stresses at graded ceramic-metal interfaces has been applied to determine interface conditions favorable for achieving residual stress reductions. Using Al2O3-Ni as a model system, and for a fixed specimen geometry, a study was performed to investigate the effects of different interlayer thicknesses and nonlinear composition profiles on strain and stress distributions established during cooling from an assumed elevated bonding temperature. For each interface condition, relative stress reductions were evaluated by comparing the magnitude of specific stress and strain components important for controlling interface failure with those predicted for a sharp (nongraded) interface. For the geometry considered, stress was reduced by thick graded interlayers and nonlinear composition profiles that distributed the largest property changes over the interlayer region having low elastic modulus and high plasticity. In contrast to the Part I results for a linear composition profile, the optimized interlayer condition effectively reduced the peak near-surface axial stress component.