bluuebunny/crossref_metadata_2025 huggingface dataset:
Giant photovoltage of semiconductor heterostructures
Authors: Paget D. , Vinter B. , Rondi D.
Published: July 2002

We have found that a nonquantizing weakly p-doped InP/Ga0.47In0.53As/InP heterostructure exhibits a photovoltage as high as 2 V at 120 K for moderate light excitation power densities of a few mW/cm2. The back electrical contact is ohmic and the front rectifying contact is established through a thin silver layer. We have monitored as a function of reverse bias applied to the structure the internal photoemission current and also the external photoemission current, due to electrons emitted into vacuum after lowering the surface work function by cesium and oxygen adsorption. Both of these dependences exhibit strong effects of the excitation power density. The dependence of the photovoltage as a function of external bias is obtained using photoreflectance. As shown by a simple model, this gigantic photovoltage arises from accumulation of photoexcited carriers in the Ga0.47In0.53As layer because of the existence of energy barriers with the neighboring InP layers. The different electron and hole transfer probabilities across these barriers result in a strong change of the potential of the Ga0.47In0.53As layer under light excitation.
Implantation temperature effect on polycrystalline silicon by ion shower doping
Authors: Mishima Y. , Takei M. , Matsumoto N. , Uematsu T.
Published: July 2002

We present a new doping technique using an ion shower doping system with a bucket ion source. Phosphorus atoms were implanted in polycrystalline silicon from room temperature to 300 °C. Sheet resistances were significantly reduced by raising the implantation temperature. With a crystal fraction of 85%, sheet resistance was 5×102 S−1/⧠ as implanted. These effects were not due to pure thermal annealing by ion beam heating. A significant improvement was found in sheet resistance as a result of averaging the impurity profile by radiation enhanced diffusion and low temperature recrystallization of the implanted region by collision of atoms.
The effect of coimplantation on the electrical activity of implanted carbon in GaAs
Authors: Moll A. J. , Ager J. W. , Yu Kin Man , Walukiewicz W. , Haller E. E.
Published: July 2002

The effects of radiation damage and stoichiometry on the electrical activity of carbon implanted in GaAs are studied. Damage due to implantation of an ion heavier than C increases the number of C atoms which substitute for As (CAs). Creation of an amorphous layer by implantation and the subsequent solid phase epitaxy during annealing further enhances the concentration of CAs. However, the free carrier concentration does not increase linearly with increasing concentration of CAs due to compensating defects. Activation of implanted C is maximized by maintaining the stoichiometry of the substrate which reduces the number of compensating defects in the crystal. Under optimum conditions for carbon implanted at a dose of 5×1014 cm−2, the carbon acceptor activity can be increased from 2% to 65% of the total implanted carbon.
5-THz bandwidth from a GaAs-on-silicon photoconductive receiver
Authors: Pedersen J. Engholm , Keiding S. Rud , So/rensen C. B. , Lindelof P. E. , Rühle W. W. , Zhou X. Q.
Published: July 2002

We demonstrate that GaAs grown by molecular beam epitaxy on silicon has ideal characteristics for THz receiver applications. The lattice mismatch between silicon and GaAs causes a disordered growth of GaAs, reducing the carrier lifetime to 1.8 ps. This is similar to the characteristics observed in low temperature grown GaAs. Furthermore, the high resistivity silicon substrate has a very low absorption and dispersion in the far infrared. This makes it an ideal material in THz system applications, and we show that a maximum frequency of 5 THz and a sixfold increase in sensitivity can be obtained using a GaAs-on-silicon based THz detector.
Condition for no thermal runaway in cw semiconductor lasers
Authors: Yoo Jay S. , Fang Sychi , Lee Hong H.
Published: July 2002

A necessary and sufficient condition for no thermal runaway is given for cw double-heterostructure semiconductor lasers. No catastrophic damage at the mirror facet should occur when the condition is satisfied. The condition for no thermal runaway contains the dimension, operating conditions, and material properties of the double-heterostructure laser. As such, it can be used to systematically optimize the laser structure. Use of the condition is illustrated and a typical case analyzed.
Comparison of propagation loss of sine-generated and constant radius S bends in Al(Ga)As waveguides
Authors: Lee T. C. , Vernstrom G. D. , Mohapatra S. K. , Misemer D. K.
Published: July 2002

Constant radius and sine-generated S bends were fabricated from double heterostructure Al(Ga)As waveguides. No significant difference in the loss characteristics between the two structures was observed. These results are within the bounds of our beam propagation method calculation.
X-ray photoelectron spectroscopic study of the chemical vapor deposited W/Al interface
Authors: Ohshima H. , Katayama M. , Onoda K. , Hattori T. , Suzuki H. , Tokuda Y.
Published: July 2002

The dependence of the amount of aluminum trifluoride (AlF3) piled up at the interface of chemical vapor deposited tungsten and the aluminum under layer on the deposition time and subsequent annealing in ultrahigh vacuum (UHV) or in monosilane (SiH4) gas has been studied. AlF3 is formed by the reaction of the aluminum under layer with tungsten hexafluoride (WF6) during the initial state of tungsten chemical vapor deposition. Tungsten was deposited on an Al layer under selective deposition conditions by SiH4 reduction at 250 °C. X-ray photoelectron spectroscopy measurement reveals that the amount of AlF3 decreases with an increase in the tungsten deposition time and that the reduction of AlF3 by volatilization of aluminum fluorides, which occurs at higher temperatures (≳400 °C) is not observed at low temperature (270 °C). Annealing in SiH4 gas after the tungsten deposition was effective to reduce the amount of AlF3 compared with annealing in UHV. This result and thermochemical data would suggest that the dependence of the amount of AlF3 on the tungsten deposition time is explained by the reduction of AlF3 with hydrogen atoms supplied from the dissociation of SiH4.
Dynamics of the detonation products of lead azide: III. Laser-induced hole burning and flow visualization
Authors: Tzuk Y. , Barmashenko B. , Bar I. , Rosenwaks S.
Published: July 2002

The cloud of products formed following the detonation of lead azide (LA) contains solid particles. Utilizing a pulsed beam of a neodymium: yttrium aluminum garnet (Nd:YAG) laser, the particles are evaporated and hole burning through the opaque cloud is demonstrated. The characteristics of the hole and of the expanding cloud are monitored in real time by a HeNe beam, high-speed framing photography and emission of excited Pb atoms. The hole is carried with the cloud and propagates at a constant velocity of 0.5–2.8 km/s, depending on the time and location of burning and given by d(h)/t(h), where d(h) is the distance from the LA sample to the center of the Nd:YAG beam and t(h) is the time from detonation to hole burning. The reduction in the number and size of the particles is monitored by scanning electron microscopy of the deposits formed on a substrate following the detonation. The propagation of the Nd:YAG laser pulse through the cloud is numerically modeled and provides an estimate of the increase in the temperature and the decrease of the size of the particles as a result of the interaction with the laser beam.
Resonance effects in Josephson tunnel junctions with integrated tuning structures
Authors: Lehnert T. , Schäfer F. , Gundlach K. H.
Published: July 2002

Large-current steps have been found in the I/V characteristics of superconducting tunnel elements that are integrated within fixed tuning structures. The Josephson frequency at the steps corresponds to the operation frequencies of the different tuning structures at 345, 460, or 600 GHz. Therefore, these current steps are interpreted as resonance effects generated by an internal interaction of the Josephson oscillation with the tuning structure. The result of a spectrometer measurement around 350 GHz is in very good agreement with the resonance frequency obtained from the I/V characteristic. This confirms the interpretation of the current steps. A simple dc measurement is therefore sufficient to determine the actual resonance frequency of the tuning structure. It may be shifted with respect to the expected frequency, due to deviations of the junction size or other parameters from their required values. The exact knowledge of the resonance frequency is important for the application of these integrated tunnel elements as mixers in radioastronomical receivers. In single junctions a splitting of the resonance step into several branches was observed, whereas in two-junction arrays a splitting into two distinct states was found. Irregular switching appeared between these two states. The temperature and magnetic-field dependence of the current steps was investigated.
Experimental determination of the surface acoustic wave properties of new fine grain piezoelectric ceramics
Authors: Feuillard G. , Lethiecq M. , Amazit Y. , Certon D. , Millar C. , Patat F.
Published: July 2002

The surface acoustic wave (SAW) properties, i.e., free surface wave velocity, surface coupling coefficient, and static surface permittivity, of a lead titanate composition modified with an additive of samarium and processed by hydrothermal synthesis are determined. The effective permittivity of the piezoelectric ceramic was calculated, and the SAW properties were extracted from the analysis of the curve. In particular, the relations between the square coupling coefficient, the effective permittivity, and the usual definition k2s=2ΔV/V are discussed. In parallel, experimental measurements of the SAW properties were carried out by developing a curve-fitting algorithm on the real and imaginary parts of a unapodized single electrode SAW transducer. A free surface wave velocity of 2595 m/s, a coupling coefficient of 1.8%, and a static permittivity of 196 are found which were predicted by the analysis of the effective permittivity curves. The SAW properties of a Y+128° cut lithium niobate single crystal are also presented and are in agreement with those found in literature. These results are discussed and suggest that the present ceramic has the potential as a substrate for SAW devices.
Experimental investigation of the magnetic circular dichroism sum rules (abstract)
Authors: Chen C. T. , Idzerda Y. U. , Lin H.-J. , Meigs G. , Ho G. , Smith N. V.
Published: July 2002

High quality L2,3 edges magnetic circular dichroism (MCD) data of in situ grown Fe, Co, and Ni ferromagnetic thin films were measured using transmission x-ray absorption technique. These data were utilized to investigate the validity of the recently proposed x-ray MCD sum-rules that offer a new means for deducing orbital- and spin-magnetic moments from MCD data. We find that the orbital to spin magnetic moment ratios of Fe, Co, and Ni deduced from MCD data according to the sum-rules are at ±30% discrepancy with those deduced from neutron scattering data. This inconsistency may be attributed to the neglecting of multi-electron excitations and band structure effects in the derivation of the sum-rules or due to uncertainties in the neutron scattering results. Caveats for MCD data taken with the fluorescence yield x-ray absorption technique will also be discussed.
Local magnetoresistance and point-source excitation of Ni-Fe thin films (abstract)
Authors: Cross R. W. , Kos A. B.
Published: July 2002

The magnetoresistive (MR) response was measured in Ni-Fe thin films, representative of the films used in magnetic recording read heads, with sense areas as small as 6×6 μm. For the bulk, central, and edge regions of the film, the MR response was measured as a function of magnitude and angle of a uniform in-plane applied magnetic field. Measurements were made using a four-contact technique which included two scanning microprobes and two orthogonal field sources. The microprobes could be scanned with a resolution of 0.1 μm and positioned separately. The field sources produced a maximum field of 24 kA/m (300 Oe) that could be rotated up to ±15°. From the local MR response, the local magnetic behavior was obtained and compared to micromagnetic theory. The bulk MR response was also measured as a function of position on the film of a microfield source used for point-source excitation. The microfield source was a Fe wire electrochemically etched to a 0.1 μm tip diameter. From these results the local MR sensitivity was determined for the central and edge regions. The sensitivity profile of the film is important in optimizing the design of the device. The large variations observed in the MR response between the central and edge regions as a function of uniform field and point source excitations are indicative of the fact that magnetostatic fields dominate the response in these small structures.
Band structure calculations of heavy fermion YbSbPd and YbSbNi
Authors: Solanki A. K. , Kashyap Arti , Auluck S. , Brooks M. S. S.
Published: July 2002

Dhar et al. [J. Phys. F 18, L41 (1988); and Proceedings of the International Conference on Strongly Correlated Electron Systems Sendai, Japan, 1992 (Plenum, New York, 1987)] have recently measured the low-temperature specific heat of YbSbPd and YbSbNi. Their measurements yield large values for the specific heat coefficient (1384 states/Ry cell for YbSbPd and 865 states/Ry cell for YbSbNi), and suggest a magnetic transition at low temperature. With a view to understand the ground state of these compounds, we have performed self-consistent scalar relativistic linear muffin-tin orbital band structure calculations. Our paramagnetic calculations for YbSbPd and YbSbNi give the density of the states at Fermi level to be 82.94 and 27.96 states/Ry cell, respectively. These give enhancement factors of 16.7 and 30.1 for YbSbPd and YbSbNi. We present results of our calculations of the band structure as well as the Stoner I parameter for these compounds.
Magnetic properties and crystallization of amorphous Fe-Nd-B alloys at constant Nd concentration
Authors: Shen Bao-gen , Yang Lin-yuan , Guo Hui-qun , Zhao Jian-gao
Published: July 2002

The B-content dependence of magnetization, Curie temperature, and crystallization temperature for amorphous (Fe1−xBx)100−yNdy alloys with y=4, 7, and 12 were studied. Spontaneous magnetization shows a monotonic decrease with x, and the noncollinear spin structures have been proposed to explain the observed results. It is found that the Curie temperature of the samples increases at first with increasing B concentration x, and shows a maximum value at a certain B concentration, then decreases monotonically with x. The composition dependence of Tc is explained by the average molecular-field model. An exceptionally strong rise of crystallization temperature with x is found, and demonstrates that the thermal stability of amorphous Fe-Nd-B alloys has a remarkable enhancement by the substitution of B for Fe.
Magnetic properties of Er2Fe17−xAlxNy compounds
Authors: Yang F. M. , Tang N. , Wang J. L. , Zhong X. P. , Zhao R. W. , Lin W. G.
Published: July 2002

Structural and magnetic properties of the Er2Fe17−xAlxNy compounds (0≤x≤3) have been investigated. All nitrides and parent compounds crystallize in the Th2Ni17 structure. Al substituted for Fe leads to an increase in lattice constants a and c. Introduction of nitrogen results in a further increase of lattice constants, but the magnitude of this increase is smaller for increasing x. As Al content increases, the Curie temperature of the parent compound increases, whereas the Curie temperature of the nitride decreases. The substitution of Al for Fe results in a decrease of Fe moment in both nitrides and parent compounds. Introduction of nitrogen leads to an increase in the uniaxial anisotropy of the Er sublattice and a spin reorientation. A tentative spin phase diagram has been constructed.
Modeling of thin-film media with advanced microstructure for ultrahigh density recording
Authors: Ye Xiao-Guang , Zhu Jian-Gang
Published: July 2002

Magnetic thin films with subgrain structure, or nanocrytalline films are studied via micromagnetic modeling. The subgrain nanocrystallites form a bicrystal structure inside a normal grain, due to proper epitaxial growth. It is shown that a relatively small but nonzero exchange coupling through normal grain boundaries is critical for obtaining high coercive squareness. Maintaining low exchange coupling between subgrains in a normal grain is important for achieving low transition noise. The calculation shows that films with this microstructure can have S*≊0.95 and a signal-to-noise ratio of 36 dB at 385 KFCI with 1-μm track width. Such film microstructure is practically achievable in principle and is suited for future high recording density applications.
Process temperature dependence of ∂M plots on Co alloy media on amorphous carbon substrates
Authors: Kuwabara Masago , Saffari Haydee , Visokay Mark R. , Hayashi Hidetaka , Sato Motoharu
Published: July 2002

The static magnetic properties and the film structure of Co alloy recording media made under different deposition and annealing temperatures were investigated. With increasing film coercivity an increase of the grain size and a reduction of the positive peak in the ∂M plots were observed. It is believed that reduced exchange coupling was achieved by preferential Cr segregation at the grain boundaries during high-temperature processing.
Friction and wear of ion-implanted diamondlike carbon and fullerene films for thin-film rigid disks
Authors: Bhushan Bharat , Gupta B. K.
Published: July 2002

In this paper, DLC coatings on a rigid magnetic disk were ion implanted with nitrogen and carbon ions to improve their wear lives. Nitrogen and carbon ion implantation with a dose of 5×1015 ions cm−2 at 200 keV have shown significant improvements in the coefficient of friction and sliding wear life which suggests that ion-implanted DLCs may be more desirable overcoats. Microstructural examinations of implanted films show that these films are still amorphous with no long range order. Implanted DLC films also may be attractive as an overcoat for the slider surface. An approximately 20-nm-thick fullerene film, a new solid lubricant, was also deposited on the disk surface to reduce its friction and wear. Fullerene films exhibited lower friction, however, these readily formed a transfer film on the mating slider surface. Since any transfer and movement of the material at the head-disk interface is undesirable, fullerene films are not expected to be potential overcoats. Coefficient of friction of implanted DLC and fullerene films on a microscale was also measured and was found to be lower than that on macroscale. Microfriction values of unimplanted and implanted DLC films were comparable.
Growth temperature dependence of biquadratic coupling in Fe/Cr(100) superlattices studied by polarized neutron reflectivity and x-ray diffraction (abstract)
Authors: Schäfer M. , Wolf J. A. , Grünberg P. , Ankner J. F. , Schreyer A. , Zabel H. , Majkrzak C. F.
Published: July 2002

We have measured the polarized neutron specular reflectivity of superlattices of nominal composition (5.0 nm Fe/1.7 nm Cr) grown by molecular-beam epitaxy. This chromium thickness lies at a minimum of the oscillatory bilinear (180°) coupling parameter, so these films are especially sensitive to biquadratic (90°) terms. One set of films was grown at a substrate temperature of 293 K and another at 593 K. Using neutron reflection, we find that the films grown at 523 K exhibit a 90° magnetic moment rotation between successive Fe layers, while the 293 K films are remanently ferromagnetically ordered in small applied fields (H=1.7 mT). Furthermore, we have observed that films grown at elevated temperature exhibit a larger amount of diffuse x-ray scattering due to conformal roughness than those grown at room temperature. These results suggest that the biquadratic coupling could be induced by the structure of the interfaces. We will also present the field and temperature dependence of the neutron reflectivity from the biquadratic films.
Studies of stoichiometric variations of epitaxially grown Fe3−δO4 (abstract)
Authors: Lochner E. , Shaw K. A. , DiBari R. C. , Hilton D. , Lind D. M. , Berry S. D.
Published: July 2002

Using plasma-assisted molecular beam epitaxy, films of iron oxide cubic spinel phases have been prepared on single crystal MgO (100). Preparation was by deposition of Fe from an elemental e− gun in a reactive oxygen plasma (primarily O+) from an ECR source. Sample stoichiometry during synthesis was controlled by variation of growth parameters, including substrate temperature, oxygen flux, plasma power, and deposition rate. We present the results of structural and magnetic studies of these materials using electron and x-ray diffraction, as well as SQUID magnetometry. Lattice spacing, saturation magnetization, and magnetic anisotropy all provide strong evidence that the variation of growth parameters does indeed produce a range of ‘‘cubic’’ defect spinel structures ranging from Fe3O4 to one approximating γ-Fe2O3. Both structural and magnetic probes indicate that strong ordering changes occur in these systems as they are cooled through the ∼119 K Verwey transition. The behavior of the Verwey transition as a function of growth parameters indicates that Fe vacancies in these defect spinels have a profound effect on the structural distortion related to the Verwey transition. Epitaxial strain due to lattice mismatch further contributes to structural distortion, and thus to the Verwey transition. The relative contributions of these stoichiometric variations and epitaxial strain on the Verwey transition will be discussed.
The effects of various magnetic materials on lamination design for stator–rotor diecasting of induction motors for electric vehicle applications
Authors: Elkasabgy N. M. , Di Pietro C.
Published: July 2002

In this paper we describe a novel technique to model induction motors with a diecast stator and rotor and to examine the effects of various magnetic materials on the electrical performance of the motor. For electric vehicle applications, a high volume production operation of the electric motor requires the motor to be small and inexpensive. The expensive labor and material used to manufacture the motor encouraged the researchers to find new methods and techniques to reduce the cost and improve the performance. Diecast rotor and stator windings reduce motor cost and size. For diecasting induction motors, the motor laminations should be designed to optimize the electromagnetic field distribution over the cross section and along the axial direction. The magnetic material used for the laminations should also reduce losses and improve the overall efficiency. A 100 hp four-pole induction motor was modeled with finite elements, the field distribution, the magnetic flux density, and the mechanical performance of the motor were computed using nonlinear magnetostatic and complex steady-state eddy current techniques. The difference in the electrical and mechanical performance of the motor were evaluated for copper and aluminum diecasting. The results show that copper diecasting of the rotor and the stator of the induction motor with magnetic material properties and identified slotting shape is the way to achieve better motor performance and low cost operation.
Dynamical properties of quantum spin systems in magnetically ordered product ground states
Authors: Viswanath V. S. , Stolze Joachim , Müller Gerhard
Published: July 2002

The one-dimensional spin-s XYZ model in a magnetic field of particular strength has a ferro- or antiferromagnetically ordered product ground state. The recursion method is employed to determine T=0 dynamic structure factors for systems with s=1/2, 1, 3/2. The line shapes and peak positions differ significantly from the corresponding spin-wave results, but their development for increasing values of s suggests a smooth extrapolation to the spin-wave picture.
Measurement of Young’s moduli for film and substrate by the mechanical resonance method
Authors: Lee Y. H. , Shin Y. D. , Lee K. H. , Rhee J. R.
Published: July 2002

Young’s moduli for films and substrates are obtained by measurement and theoretical analysis of the resonance frequencies for cantilevered substrates with and without films in the flexural vibration mode. Young’s moduli of 7.1, 19.2, and 21.3×1010 Pa obtained for the glass substrate, Ni, and Ni53Fe47 films agree with the published values for bulk material within 10%. Decrease of the resonance curve Q value is observed for substrates with films, which implies an increase of internal friction.
Ferromagnetism of single crystal Fe[S2CN(C2D5)2]2Cl
Authors: DeFotis G. C. , Brubaker W. W. , Chandarlapaty S. , Beers K. L. , Coffey G. A .
Published: July 2002

The fully deuterated form of previously studied Fe[S2CN(C2H5)2]2Cl, needed for neutron diffraction and scattering measurements, has been prepared for the first time and its magnetic behavior in single crystal form studied at low temperatures. Susceptibility and magnetization data show that Fe[S2CN(C2D5)2]2Cl has extremely similar magnetic anisotropy to the normal material: the monoclinic [101] direction is the only easy axis of ferromagnetism, with the orthogonal [010] and (1̄01)⊥ axes even showing antiferromagnetic-like maxima in their χ(T) near Tc. Only along [101] does M approach saturation at low fields. Analysis of χ(T) in the paramagnetic regime, assuming axial and rhombic crystal field distortions described by H= D[Ŝ32z−S(S+1)/3]+E[Ŝ32x −Ŝ32y] and including exchange interactions in a mean field approximation, leads to D/k=−3.03(5) K, E/k=−0.49(4) K, and zJ/k=0.99(3) K along with gx=2.058(20), gy=2.060(20), and gz=2.080(20). These parameters are rather similar to those of the normal material, though zJ/k is significantly larger. The ordering temperature, obtained from a critical law fit to [101] data in a small field, i.e., χ0=Γt−γ, is Tc=2.486(2) K, with γ=1.16(1) and Γ=1.07(5) emu/mol. The critical exponent γ is the same as in the normal material and corresponds to the theoretical value in Kawamura’s Z2×S1 model. An ∼1.2% enhancement in Tc over that of the normal material occurs, which may be due to slightly closer molecular packing. 75.30.Kz, 75.30.Cr, 75.30.Gw, 75.40.Cx
Simulation of magnetization reversal in two-phase exchange coupled nanocrystalline materials
Authors: Feutrill E. H. , McCormick P. G. , Street R.
Published: July 2002

A nanoscale two-phase uniaxially anisotropic material has been numerically modeled using a two-dimensional array of micromagnetic moments to represent the material on an atomic scale. Demagnetization curves are calculated by minimizing the total energy of the system which includes a component due to exchange interactions between nearest neighbors, as well as magnetocrystalline and magnetostatic energies. Magnetization reversal is shown to be initiated in the soft magnetic phase and to proceed by reversible rotation until a critical field, coercivity, at which the magnetization of the system switches irreversibly. As the dimension of the soft magnetic phase increases, coercivity approaches a lower limit and there is a transition from single- to two-phase magnetic behavior.
Magnetostriction of polycrystalline Co-Pd alloys
Authors: Jen S. U. , Chao B. L.
Published: July 2002

Magnetostriction of polycrystalline Co100−xPdx alloys was measured by the strain gauge method from 4 to 300 K. The saturation magnetostriction λs=(2/3)[(ΔL/L)s∥−(ΔL/L)s⊥], where (ΔL/L)s∥ and (ΔL/L)s⊥ are the saturated values (when HE≳5 kG) of ΔL/L in fields parallel and perpendicular to sample’s length (L). λs at 4 K is found to change sign from positive to negative value as x is increased from below x0=50 at. % Pd to above. This phenomenon can be understood from the split-band theory for Co-Pd alloy. However, since some experimental facts indicate that unquenched orbital moments may exist in the x≳50 at. % Pd alloys it is necessary to consider λs = λsband+ λsion, where λsband is due to the split-band theory and λsion is from the one-ion mechanism. Under this proposal, it is possible to explain why λs(4 K) is not antisymmetric with respect to x0. Finally, two different origins of temperature dependence of λs are discussed.
X-ray photoelectron spectroscopy study of substrate surface pretreatments for diamond nucleation
Authors: Arezzo F. , Zacchetti N. , Zhu W.
Published: July 2002

The effects of surface pretreatments on the nucleation of diamond on silicon substrates have been studied by quantitative x-ray photoelectron spectroscopy measurements. It was found that methods of surface pretreatments including ultrasonic abrasion, scratching, and dc biasing all introduced a substantial amount of carbon species to the substrate surface which was the primary reason for the enhancement of diamond nucleation. Both the scratching and biasing processes formed carbide on the Si surface which also facilitated diamond nucleation. In addition, the biasing process reduced and suppressed the formation of oxide which further contributed to the enhanced nucleation density of diamond. This analysis is consistent with the experimental data of nucleation densities of diamond on the differently pretreated substrate surfaces both observed in this study and found in the literature.
Strong interaction of arbitrary fields of sound and light: Application to higher-order Bragg imaging
Authors: Van Den Abeele K. , Breazeale M. A. , Leroy O. , Na J. K.
Published: July 2002

Small objects positioned in a high-frequency ultrasonic beam can be imaged by Bragg diffraction of light. The first order contains one image. Using a light beam with a considerable convergence angle and reducing the ultrasonic frequency, one observes that the second diffraction order contains two adjoining images, the third order three, etc., and that the positive orders are the mirror images of the negative ones. These experimental observations are explained by the present theory and general expressions for the angular distribution of the light in the different diffraction orders are presented in the form of a series expansion. Evidence for the multiple images in the higher diffraction orders is found by analyzing the first term in this expansion. The center-to-center separation of the images within the higher orders is found to be proportional to the ultrasonic frequency and the interaction width.
Carrier compensation induced by rapid thermal annealing in undoped InP
Authors: Kadoun A. , Brémond G. , Barbier D. , Laugier A. , Tardy J.
Published: July 2002

The region beneath the interface of an InGaAs layer grown onto an undoped InP substrate by molecular beam epitaxy was investigated before and after rapid thermal annealing. Capacitance-voltage measurements revealed a depletion region in the underlying InP due to donor compensation that is mainly caused by the Fe-related Ec−0.63 eV-deep level observed by deep level transient spectroscopy.
Sources of errors in nonlinear constants of crystals and their assessment
Authors: Hruska Carl K.
Published: July 2002

Standard errors of third-order nonlinear material constants of a crystal, obtained by the least-squares fit, reflect only the errors from a single source. The source is the random errors in the experimental data used to determine the nonlinear constants. Other, hitherto disregarded, sources of errors are pointed out, namely the linear material constants of the crystal and the orientations of the crystal specimens used to produce the experimental data, and a method to assess their effect is suggested. The case investigated numerically concerns the third-order nonlinear electromechanical constants of α-quartz determined by the transit-time method. To minimize the effect of the errors mentioned, attention must be focused on the linear elastic constants. Standard errors of 1%–2% in the linear constants produce nontrivial errors in the nonlinear constants comparable in size to those due to experimental errors. The standard errors increase the traditionally calculated errors of the nonlinear constants by about 10%–40%, respectively. The errors caused by the remaining linear constants and by the orientation angles seem to be substantially less important.
Electrodeposition and characterization of GaAs polycrystalline thin films
Authors: Gao Yuankai , Han Aizhen , Lin Yiqing , Zhao Yongchun , Zhang Jingdong
Published: July 2002

The preparation of polycrystalline GaAs films by using electrodeposition technology is described. Using scanning electron microscopy, x-ray diffraction, spectrophotometry, and a CG-1 HF C-V tester, the characteristics of the films prepared have been measured. The results show that the stoichiometry of the film approximates to GaAs. On the basis of Mott–Schottky plot, the position of energy band edges of film is calculated. Finally, the photoelectrochemical characteristic of the electrodeposited film/electrolyte junction is measured.
Slow decay of space-charge-limited current in CdS
Authors: Wang Yicheng
Published: July 2002

Extra electrons forced into polycrystalline CdS from ohmic indium electrodes result in space-charge-limited current. The transient current resulting from a step voltage is measured and found to decay in a dispersive form of t−(1−α) over several orders of magnitude in time. This dispersive decay is attributed to extensive trapping and detrapping of the electrons and is analyzed in terms of the stochastic transport theory of Scher and Montroll [Phys. Rev. B 12, 2455 (1975)].
Pseudomorphic high electron mobility heterostructures with extremely high conductivity using Te as n-type dopant by low-pressure metal organic chemical vapor deposition
Authors: Blumina M. , Lelong I. O. , Sarfaty R. , Fekete D.
Published: July 2002

Modulation-doped AlxGa1−xAs/InyGa1−yAs/GaAs single-quantum-well structures have been grown by low-pressure metal organic vapor phase epitaxy and characterized by Hall, C-V measurements, and photoluminescence spectroscopy. The use of tellurium instead of silicon as an n-type dopant for AlxGa1−xAs increases the electron concentration without decreasing the electron mobility. High free-electron concentrations of ns=7.5×1012 cm−2 (300 K) and ns=3.7×1012 cm−2 (77 K), and Hall mobilities of μ=5470 cm2 (V s)−1 (300 K) and μ=24 600 cm2 (V s)−1 (77 K) were obtained. The high concentration and mobility product of the channel: nsμ=4.1×1016 (V s)−1 at 300 K and nsμ=9.1×1016 (V s)−1 at 77 K, makes it a preferred choice for high-speed applications.
Enhancement of magnetoresistance sensitivity in a Co/Cu artificial superlattice
Authors: Min Kyeong-Ik , Joo Seung-Ki
Published: July 2002

Co/Cu artificial superlattices were fabricated with an rf-magnetron sputtering system. Cu deposited on silicon substrate was used as an underlayer. The Co/Cu artificial superlattice was not only textured but also rotationally aligned to the Si substrate, which presumably rendered the Si[100] an easy axis in plane direction. A strong (100) preferred orientation was developed as the thickness of the cobalt decreased and the thickness of the copper underlayer increased. This strong preferred orientation turned out to be closely related to the reduction of the saturation field as well as the value of the magnetoresistance. By addition of 6 at. % nickel to the copper underlayer, electrical shunting through the thick underlayer could be effectively depressed. In [Cu(20 Å)/Co(30 Å)]20Cu-6 at. % Ni(200 Å)‖Si, an 18.5% magnetoresistance could be obtained within a ±100 Oe field range at room temperature.
Amplification studies of a two-cavity second harmonic gyroklystron with a mixed-mode output cavity
Authors: Calame J. P. , Cheng J. , Latham P. E. , Lawson W. , Hogan B. , Matthews H. W. , Flaherty M. K. E. , Striffler C. D.
Published: July 2002

The performance of a two-cavity second harmonic gyroklystron employing a short, mixed-mode output cavity with stepped radial transitions is described. The short cavity was employed to prevent low frequency spurious oscillations that can compete with the harmonic signal. The radial rf field profile in the cavity and the output radiation consisted of both the TE01 and TE02 circular waveguide modes. This device produced a peak output power of 20 MW at 19.782 GHz, with an efficiency of 23% and a gain of 26 dB. The nominal mode mixture of the radiated power during optimal operation was found to be about 60% TE02 and 40% TE01. Variations from this ratio are observed at lower powers and are attributed to shifts in the cavity rf field profiles. Systematic studies of amplifier performance as a function of beam parameters and magnetic field profile are described. The sensitivities of output power production to changes in operating parameters are compared to results from earlier harmonic and fundamental gyroklystrons. The present device is found to be more stable to parasitic oscillations and less sensitive to variations in beam current and output cavity magnetic field than previous harmonic gyroklystrons that employed longer, smoothly transitioned cavities. However, both the peak power and efficiency in the present device are lower than the 30 MW at 28% efficiency obtained with the final smooth-cavity tube. The tradeoffs between the two output cavity concepts will be discussed.
The observation of silicon nanocrystals in siloxene
Authors: Pinizzotto R. F. , Yang H. , Perez J. M. , Coffer J. L.
Published: July 2002

We report the direct observation of silicon nanocrystals in unannealed siloxene using high resolution transmission electron microscopy. The microstructure consists of an amorphous matrix plus silicon crystallites with dimensions of a few nanometers. This is additional evidence that the photoluminescence of silicon-based materials is due to quantum confinement.
A simplified procedure for obtaining relative x-ray intensities when a texture and atomic displacements are present
Authors: He Baoping , Rao Satish , Houska C. R.
Published: July 2002

The orientation problem in polycrystalline cubic materials has been simplified, using fundamental relationships, so that the determination of a quantitative interrelationship between the various Bragg peak intensities is no longer a formidable task. This is demonstrated with a cubic Cu-Be-Co alloy having a fiber texture, and a conventional focusing diffractometer. Because data are required which extend over a larger range in d spacings, extinction, thermal, and static atomic displacements must be included into the analysis of intensities. The displacement terms and the extinction parameters may be of primary interest or used as a correction. Seventeen diffraction peaks are used in the example. These must be internally consistent with a crystallite orientation function, the cubic symmetry of the sample, extinction effects influencing the two strongest peaks, and attenuation due to atomic displacements. Tabulated coefficients are presented which greatly reduce the task of calculating the orientation function. A correction is given for instrumental smearing which should be considered for stronger textures than the intermediate case examined or for intermediate textures and nonfocusing instrumental conditions.
Surface resistance, residual losses, and granularity in Ag-doped YBa2Cu3O7−δ thin films
Authors: Apte P. R. , Pinto R. , Chourey A. G. , Pai S. P.
Published: July 2002

We have studied microwave surface resistance Rs and residual resistance Rres in undoped and Ag-doped laser ablated thin-film YBa2Cu3O7−δ microstrip resonators on LaAlO3 substrates. While the undoped films showed a frequency dependence Rs∝fp, where p=1.9±1, Ag-doped films showed p=1.6±1 and 1.4±1 for 5 and 10 wt % Ag doping, respectively. Lower p values and higher Rres observed in Ag-doped films indicate a metallic contribution. However, the advantage of Ag-doped films has been shown to be at 77 K at which they not only have a lower Rs but also a low dRs/dT, thus making them superior to undoped films for microwave devices operating at 77 K.
Local stoichiometry measurement of Y-Ba-Cu-O thin layers grown by metal organic chemical vapor deposition
Authors: Waffenschmidt E. , Waffenschmidt K. H. , Arndt F. , Boeke E. , Musolf J. , He X. , Heuken M. , Heime K.
Published: July 2002

Y-Ba-Cu-O thin films with different stoichiometry were grown by metal organic chemical vapor deposition on MgO and SrTiO3. The samples showed superconducting behavior in a wide range of average stoichiometry. However, energy dispersive x-ray spectroscopy (EDX) measurements show that best results can be obtained only in a small stoichiometry range. Critical temperatures of Tc≳89 K and critical current densities of jc (77 K)≳2×106 A/cm2 could be obtained with optimized stoichiometry. Spatially resolved EDX measurements show that copper tends to form precipitates on the layers if its average content exceeds 50 mol %, while yttrium is incorporated into the matrix if offered in excess.
Formation of plasma working fluids for compression by liner implosions
Authors: Lehr F. M. , Alaniz A. , Beason J. D. , Carswell L. C. , Degnan J. H. , Crawford J. F. , Englert S. E. , Englert T. J. , Gahl J. M. , Holmes J. H. , Hussey T. W. , Kiuttu G. F. , Mullins B. W. , Peterkin R. E. , Roderick N. F. , Turchi P. J. , Graham J. D.
Published: July 2002

Research on the formation of a hot hydrogen working fluid, which may be used in multiple concentric solid-density liner implosions, is reported. In such implosions, an axisymmetric outer liner is driven by a multi-megamp axial discharge, and a coaxial inner liner is driven by a working fluid contained between the liners. The fluid is shocklessly compressed to high pressure as the outer liner implodes around it. In the work reported here a 10 to 100 Torr pressure, hydrogen filled coaxial gun discharge was used to inject plasma into a diagnostic chamber simulating an interliner volume. Spectroscopically determined electron densities of between 1017 and 1018 cm−3 and electron temperatures in the 0.5–2.0 eV range were obtained with a fair degree of reproducibility and symmetry. Two-dimensional, time-dependent magnetohydrodyna- mic computer simulations of the working fluid formation experiment have been performed, and the computations suggest that the present experiment achieves electron number densities and temperatures at the lower extreme of these limits, and neutral densities ∼ 0.3–1.0 ×1019 cm−3. The simulations further suggest that the upper range, and beyond, can be achieved in a more energetic version of the present experiment.
Electro-optical measurements in a semiconductor: The case of CdIn2Te4
Authors: Jean B. , Couturier G. , Joffre P.
Published: July 2002

The precautions which have to be taken in measuring electro-optical coefficients of some semiconductors are emphasized. It is shown that classical measurements using a lock-in amplifier may lead to erroneous results if ohmic contacts are not obtained. In presence of Schottky contacts, electro-optical coefficients may still be determined provided that measurements are performed in dc fields and that also an adequate theoretical model based on a linear distribution of the electric field at the interfaces is used. The model is tested with the electro-optical semiconductor CdIn2Te4. Electrical properties of contacts were investigated by using I-V and C-V measurements. Then electro-optical measurements in ac and dc fields are compared. Special attention is paid to dc measurements, and results are in very good agreement with those predicted by the model. Finally, a value of the electro-optical coefficient r41 of CdIn2Te4 close to 3 pm V−1, and not 50 pm V−1 as already announced, is found.
Effects of finite junction length on the vortex-flow transistor
Authors: Thompson James H. , Beyer James B. , Nordman James E.
Published: July 2002

Volt-ampere characteristics of the Josephson junction vortex-flow transistor were studied through comparison of experiment and numerical simulation. Fine structure in the flux flow branch, which is not predicted by a simple particle model for flux flow, is shown to be quantized in voltage. The quantization results from the interaction of the flux wave with the junction’s cavity resonances. It is shown that the separation of the voltage states is proportional to the maximum operating frequency of the device. In an amplifier circuit, quantization in the output voltage will reduce the dynamic range of the device by adding quantization noise. Hysteretic switching between states produces distortion. Possible device modifications for removing the quantization are discussed.
A structural investigation of a Fe73.5Cu1Nb3Si13.5B9 nanocrystalline soft magnetic material
Authors: He K. Y. , Sui M. L. , Liu Y. , Zhao B. F.
Published: July 2002

Structural characteristics of Fe73.5Cu1Nb3Si13.5B9 soft magnetic alloys that were rapidly solidified and then annealed at various temperatures between 400 and 600 °C have been studied. Variations of the Si content in the nanocrystalline α-Fe(Si) phase for the alloys with the annealing temperatures are determined. A maximum volume fraction, less than 70%, of the α-Fe(Si) phase is given by the Si-content results. The relationship between the structural characteristics and the magnetic properties for the alloys is discussed.
Nonlinear regime of laser-induced piezoexcitation of the Rayleigh acoustic wave in CdS1−xSex crystal
Authors: Telenkov Sergei A. , Gusev Vitalyi E. , Avanesyan Sergei M.
Published: July 2002

The Rayleigh-type surface acoustic wave piezoexcitation induced by the interband absorption of laser pulses in CdS1−xSex crystal placed in a dc electric field was investigated. We detected the surface acoustic wave (SAW) pulses with a profile of the particles’ vibrational velocity consisting of three consequent phases and we observed nonlinear (logarithmic) increase of the SAW amplitude with the increase of laser intensity. Our experiments directly demonstrated that the efficiency of SAW laser-induced piezoexcitation is more than 4 orders of magnitude higher than the efficiency of SAW laser-induced thermoelastic generation.
Magnetic stray fields of Co-Cr microstrips measured by Lorentz microscopy
Authors: te Lintelo J. G. Th. , Lodder J. C. , McVitie S. , Chapman J. N.
Published: July 2002

Magnetic stray fields of Co-Cr microstrips are investigated for bit stabilization in a vertical Bloch line memory (VBLM). The stray fields were revealed using Lorentz force based Foucault and differential phase contrast (DPC) techniques in a transmission electron microscope. The assumed shape of the stray fields for VBLM use has been experimentally verified. Agreement between experiment and simulation is obtained.
Low-temperature thermoluminescence of cuprate high-temperature superconductors
Authors: Katz S. , Roth M. , Golben J. , Vlasse M.
Published: July 2002

The thermoluminescence (TL) of three different high-temperature superconducting materials, namely ErBaCuO, YbBaCuO, and (Bi,Pb)SrCaCuO, has been measured after x irradiation at 20 K. This comparative low-temperature TL investigation has revealed a close similarity in the structure of the glow curves for all three compounds in the 20–300 K temperature range. Strongest glow peaks are shown to appear below the superconducting transition temperature. The origin of the various glow peaks is discussed in terms of radiative recombination of thermally released holes with trapped electron centers. The model is supported by further TL measurements of the ErBaCuO compound, thermally treated, in reducing and oxidizing atmospheres. It is demonstrated that the TL intensity is closely related to the oxygen stoichiometry of the material, namely, the oxygen vacancies.