bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphology and transport of YBa2Cu3O7−x sputtered in argon, oxygen, and hydrogen: Dependence on deposition temperature
Authors: Cukauskas E. J. , Allen L. H. , Sherrill G. K. , Holm R. T. , Vold C.
Published: July 2002

YBa2Cu3O7−x films have been deposited on MgO by reactive, off-axis magnetron sputtering in an argon, oxygen, and hydrogen gas mixture. The material and electrical properties of the films were studied for deposition temperatures from 600 to 760 °C. The films, all approximately 300 nm thick, were predominantly a-axis oriented when deposited at or below 620 °C but were c-axis oriented when deposited at temperatures above 640 °C. The surfaces of films deposited between 640 and 710 °C were partially covered with a-axis grains. Surface roughness measurements indicated the smoothest films occurred for deposition temperatures below 680 °C. Resistance ratios as great as 3.1 were observed for some films. Transition temperatures exceeded 89 K and resistivities at 100 K were less than 150 μΩ cm for the best films. Low-temperature critical current densities exceeded 107 A/cm2 for films deposited from 640 to 720 °C. The temperature dependence of the critical current density near the transition temperature had a power law dependence of nearly 3/2 for deposition temperatures below 690 °C. The power law dependence decreased for increasing deposition temperatures, dropping to nearly 1.1 in the film deposited at 750 °C.
Magneto-optical properties and magnetic anisotropies for Au/Cu/Au/Co and Cu/Au/Cu/Co multilayers
Authors: Sakurai Makoto , Shinjo Teruya
Published: July 2002

Kerr spectra and magnetic properties for multilayers of ultrathin Co and Cu/Au composite layers were systematically investigated. A Kerr enhancement was observed for the multilayers. The peak position of Kerr rotation shifts from the Cu plasma edge (560 nm) to the Au plasma edge (480 nm) by varying the constitution of Au/Cu/Au and Cu/Au/Cu parts. Magnetic anisotropies for the multilayers strongly depend on the constitution of Cu/Au composite layers. For [Cu(tÅ)/Au(25−2tÅ)/Cu(tÅ)/Co(8 Å)]15 multilayers, the easy axis changes from perpendicular to parallel along the film plane at a Cu layer thickness of around 2.5 Å. The anisotropy for the [Au(tÅ)/Cu(25−2tÅ)/Au(tÅ)/Co(8 Å)]15 multilayer remains unchanged below a Au layer thickness of 3 Å and increases above that thickness. The change of easy axis is mainly due to the change of interface anisotropy.
Temperature dependence of Auger lifetime in heavily doped Hg1−xCdxTe
Authors: De S. S. , Ghosh A. K. , Halder J. C. , Bera M. , Hazra A. K.
Published: July 2002

An expression for Auger lifetime as a function of temperature has been derived for a heavily doped Hg1−xCdxTe in the presence of a nonparabolicity of band structure, band gap narrowing, and carrier degeneracy. It is utilized to study the variation of Auger lifetime with temperature through numerical analysis.
Deposition behavior of Pb(ZrxTi1−x)O3 thin films by metalorganic chemical vapor deposition
Authors: Choi Joon-Hoo , Kim Ho-Gi
Published: July 2002

Polycrystalline Pb(ZrxTi1−x)O3 (PZT) thin films with a well-developed perovskite structure have been prepared on p-type (100) Si wafers by the metalorganic chemical vapor deposition process. Bisdipivalomethanato lead {Pb(DPM)2}, zirconium tetra-t-butoxide {Zr(O-t-C4H9)4}, titanium tetra-i-propoxide {Ti(O-i-C3H7)4}, and oxygen were used as source materials. The film composition could be controlled easily by simply adjusting each source temperature and the carrier gas-flow rates. A perovskite PZT phase was obtained at substrate temperatures above 550 °C. Scanning electron micrographs showed dense and noncolumnar growth with good surface morphologies. We investigated the effect of each element on the sticking of other elements, and the structural changes of the PZT thin films with composition variation. At the initial stage of deposition, the sticking of Pb was strongly restricted by Zr, therefore, the films were lead deficient and the pyrochlore phase was formed. With increasing Zr/Ti ratio, the structure of PZT thin films transformed from the tetragonal phase, and tetragonal and rhombohedral mixed phase, to the rhombohedral phase. The oxygen partial pressure also played an important role in the formation of perovskite PZT. With increasing oxygen partial pressure, the sticking of Pb was promoted so the perovskite PZT phase was easily formed. For the formation of perovskite PZT thin films, the most important step was the sticking of the Pb-containing radical.
Charged particle activation analysis study of the oxygen outdiffusion from Czochralski-grown silicon during classical and rapid thermal annealing in various gas ambient
Authors: Maddalon-Vinante C. , Barbier D. , Erramli H. , Blondiaux G.
Published: July 2002

Oxygen outdiffusion from Czochralski silicon has been studied under various atmospheres, such as oxygen, nitrogen, and argon/hydrogen (10%). The enhancement of the oxygen diffusion coefficient by hydrogen has been confirmed. Besides, thermal treatments in a halogen lamp furnace has led to a 100-fold higher oxygen diffusion coefficient under a neutral atmosphere, and to a 1000-fold enhancement under a hydrogenated atmosphere. Moreover, in this latter case, a level at 6.5×1017 atoms cm−3 in the oxygen profile has been observed at the surface of the sample. Electron-hole pair generation under intense ultraviolet radiation eventually combined with the presence of hydrogen is likely responsible for the anomalously high oxygen diffusion during rapid thermal processing.
Equivalent noise source for Boltzmann transport equation with relaxation-time approximation in nondegenerate semiconductors
Authors: Moh K. G. , Min H. S. , Park Y. J.
Published: July 2002

An equivalent noise source with a useful functional form, which enables easy calculation of noise in semiconductor devices, is derived in a unified way for Boltzmann transport equations from the classical expression of the noise source. Since the derivation is carried out within the framework of the relaxation-time approximation, the equivalent noise source is good for elastic or randomizing collisions and is valid when the carrier distributions are not far from the local equilibrium distributions. The derived functional form of the equivalent noise source is shown to be the same as the one used during derivation of the steady-state Nyquist theorem. Also, the recent controversy over correctness of the classical expression of the noise source is discussed.
Numerical analysis of higher-order geometric aberrations for a two-tube electrostatic lens
Authors: Liu Zhixiong , Ximen Jiye
Published: July 2002

Based on the electron optical canonical aberration theory, up to the fifth-order geometric aberrations have been analyzed for an equal diameter two-tube electrostatic lens with the gap of 0.1 diameter and accelerating voltage ratio ranging from 5 to 40. The precisions are controlled rigorously at every step. For the computational results presented the computed first- and third-order electron optical properties agree with the accurate values published in the literature of about 0.2%, and thus the fifth-order aberration is believed to be acquired in a precision of about 1%. The contributions of third- and fifth-order aberrations to the total aberration with respect to the filling factor or the accelerating voltage ratio have been first calculated numerically in the above-mentioned electrostatic lens. The method of accurate numerical differentiation of an analytical or a digital function up to the sixth order would be expected to make a contribution to the development of computational electron optics.
Hydrogenated amorphous silicon films by 60 Hz glow-discharge deposition
Authors: Fragalli J. F. , Misoguti L. , Nakagaito A. N. , Grivickas V. , Bagnato V. S. , Branz H. M.
Published: July 2002

We deposit hydrogenated amorphous silicon (a-Si:H) in a low-frequency (60 Hz) glow-discharge deposition system. The films show electronic and optical properties nearly equivalent to those of films produced by the conventional radio-frequency (13.56-MHz) glow-discharge technique. The optimal substrate temperature for the low-frequency glow-discharge technique is 150–170 °C, about 100 °C lower than at radio frequency. We report measurements of film properties including dark conductivity, photoconductivity, ambipolar diffusion length, infrared absorption, optical band gap, and deep defect density.
Realistic structures for electron interferometers constituted by the control of the wavefunctions in double quantum wire structures
Authors: Okuda Masahiro , Fujii Kazuhito , Shimizu Akira
Published: July 2002

To constitute Aharonov–Bohm type electron interferometers, we propose a double-quantum-wire array with Schottky gates fabricated from modulation-doped asymmetric double quantum well structures. Self-consistent calculation of the electron wave functions and calculation of the electron wave propagation by scattering matrix formalism with two-dimensional assumption have been performed in the proposed structure. It is shown that an exact 1:1 beam splitter can be realized by a properly designed barrier between the two quantum wires.
Switch simulations of a double-barrier resonant-tunnel diode based circuit
Authors: Joosten H. P. , Noteborn H. J. M. F. , Kaski K.
Published: July 2002

Along with double barrier resonant tunneling devices becoming high speed engineering devices, there is a need for relatively simple and robust models for the dynamics of these devices. In this study a model for the device dynamics and numerical simulations of the switching process are presented. The model incorporates both the RC time due to the capacitorlike structure of the leads, and the loading/unloading time of the quantum well. During the simulation the local current densities, charge densities, the change in electron potential, and related changes in transmission probabilities are followed.
Persistent decrease of dark conductivity due to illumination in AlGaAs/GaAs modulation-doped heterostructures
Authors: Pettersson H. , Grimmeiss H. G. , Powell A. L. , Button C. C. , Roberts J. S. , Rockett P. I.
Published: July 2002

We report on a persistent decrease of the dark conductivity in AlGaAs/GaAs heterostructures due to illumination. The decrease was observed for photon energies between 0.7 and 1.15 eV and larger than 1.4 eV in the temperature range 170<T<300 K. Using proper bias conditions the dark conductivity after illumination can be 20% smaller than the dark conductivity in thermal equilibrium. The studies have been performed on samples with different doping species and compositions. A possible model for the observed behavior is discussed.
A low drive voltage electroabsorption modulator using an InGaAs/InP superlattice
Authors: Chen C. W. , Kim J. W. , Silvestre P. , Hafich M. J. , Woods L. M. , Robinson G. Y. , Lile D. L.
Published: July 2002

Spectral transmission, reflection, and photocurrent absorption data obtained on gas-source molecular beam epitaxy grown InGaAs/InP multiple quantum well (MQW) and superlattice p-i-n diode structures demonstrate, for the first time in this materials system, that similar modulation to MQW structures can be achieved using superlattices, but at significantly lower operating voltages. Specifically, we have observed photocurrent absorption changes of as much as 58%, transmission changes of 8.2%, and reflection changes of 32% for applied biases of only 4 V, in nonresonant modulators operating at a wavelength ∼1.5 μm. These results encourage the possibility of employing such devices in fast, high density optical modulator arrays operating over the 1.3–1.6 μm range.
Schottky diodes using poly(3-hexylthiophene)
Authors: Kuo C. S. , Wakim F. G. , Sengupta S. K. , Tripathy S. K.
Published: July 2002

Schottky barrier diodes have been fabricated using poly(3-hexylthiophene)(P3HT) as the semiconductor and indium as the metal. P3HT was doped with FeCl3 at room temperature to form a p-type semiconductor. The Schottky junctions of In on FeCl3-doped P3HT using pressure contact exhibit rectification ratios ranging from 104:1 to 106:1 at a bias of ±1 V.
Interface and growth-mode characterization of Ce/Fe and CeH≊2/Fe multilayers by x-ray diffraction and Rutherford backscattering spectroscopy
Authors: Klose F. , Steins M. , Kacsich T. , Felsch W.
Published: July 2002

The detailed structural characterization of ion beam sputtered Ce/Fe and CeH≊2/Fe multilayers offers the possibility for a better understanding of their magnetic properties. In the case of the Ce/Fe multilayers the extension of the interface, as one of the most important features, is determined to 5–7 Å by means of Monte Carlo simulations of the small-angle x-ray scattering diagrams. Below a critical thickness of ≊24 Å Fe grows in an amorphous structure. Here the interface extension is enhanced. In contrast all CeH≊2/Fe multilayers show nearly abrupt interfaces. X-ray scattering experiments at higher angles in reflection and transmission mode provide information about the crystal structure, the texture, and the lateral dimensions of the grains in the samples. Depths profiles of the multilayers are generated by Rutherford backscattering spectroscopy, which confirm the well-ordered periodic structures. Surprisingly indications of an island-like growth mode of the Fe layers onto the Ce and CeH≊2 layers could be resolved by using this procedure.
Anisotropic screening and ionized impurity scattering in semiconductor superlattices and multiple quantum wells
Authors: Meyer J. R. , Arnold D. J. , Hoffman C. A. , Bartoli F. J.
Published: July 2002

We present a general theoretical treatment of ionized impurity scattering in semiconductor superlattices. Employing an extension of the quasi-two-dimensional calculations of Stern and Howard to multi-well structures, we explicitly account for nonuniformity of the wavefunction distribution function, arbitrary dispersion relations, scattering by impurities in neighboring periods, and screening by electrons in neighboring wells. Interperiod phenomena are found to be quite significant whenever the screening length is comparable to or longer than the distance between the quantum wells. Calculated results are compared with recent data for modulation-doped and setback-modulation-doped HgTe-CdTe superlattices. However, the discussion emphasizes general aspects of the problem rather than features specific to a particular system.
Study on surface photovoltage measurement of long diffusion length silicon: Simulation results
Authors: Anttila O. J. , Hahn S. K.
Published: July 2002

The limitations of surface photovoltage method (SPV), using the analytical solution for the minority-carrier distribution, are studied in detail. The principal source of error in thin wafers of long diffusion length material is the back surface recombination. The possibility of measuring large diffusion lengths in a reliable manner is discussed. With proper back surface passivation, diffusion lengths as long as several times the sample thickness can be measured. Evaluation of minor amounts of iron contamination in p-type material is possible even if the back surface recombination velocity is high, but a correction factor is required for the traditionally used relationship to convert the observed diffusion length change to iron concentration. The value of the correction factor varies between 1 and 1.5 for high back surface recombination velocity; the magnitude depends on the ratio between wafer thickness and the diffusion length of the minority carriers. The detection limit for iron is in the 109–1011 at/cm3 range, depending on the quality of the instrumentation and on the sample preparation; low back surface recombination gives better sensitivity. The use of SPV to measure the denuded zone width in precipitated material is briefly analyzed. It is shown that in heavily precipitated material an SPV measurement underestimates the denuded zone width, and the result will be very sensitive to the diffusion length in the bulk of the sample. Finally, the sensitivity of the measured diffusion length to different sources of errors and requirements for the sample preparation are discussed. The use of constant-flux method introduces some potential errors, which can be avoided through the use of constant bias illumination during the measurement.
Sensitivity distribution asymmetries in magnetoresistive heads with domain control films (abstract)
Authors: Koyama N. , Ishikawa C. , Suzuki Y. , Aoi H. , Yoshida K.
Published: July 2002

Suppression of the sidetrack reading behavior is important in achieving⋅high track-density recording with a magnetoresistive head. In the present work, we investigate the sensitivity distribution profiles of MR heads through experimentation using a microtrack technique1 and computer simulation. Shielded, soft, adjacent-layer-biased MR heads with 3∼6−μm-wide tracks are used. The ends of the MR elements are coupled to antiferromagnetic or hard ferromagnetic films for domain control. In the simulation based on the Landau–Lifshitz–Gilbert equation,2 the magnetization configurations in the MR elements of the domain stabilizing films are calculated to analyze the sensitivity distribution. The measured sensitivity profiles in all cases have asymmetries that are reversed when the sensing current direction or the magnetization direction of the MR element is reversed. These results agree with the simulation. The asymmetries of sensitivity profiles are explained by the magnetic poles at the domain control film edges and at the transverse edges of the element which generate a diagonal demagnetizing field distribution in the sensing region.
Magnetic anisotropy in ultrathin films grown on vicinal surfaces (abstract)
Authors: Chuang D. S. , Ballentine C. A. , O’Handley R. C.
Published: July 2002

Growth of thin epitaxial magnetic films on terraced substrates, such as Co/Cu(1 1 13) vicinal to (001), leads to unexpected magnetic anisotropy associated with the surface steps. This anisotropy remains largely unexplained and is of potential technological importance. We have studied the anisotropy of fcc Co/Cu(1 1 13) films of 3–20 ML thicknesses using in situ MOKE. The presence of monoatomic steps on the Cu(1 1 13) surface induces a uniaxial anisotropy favoring magnetization parallel to the steps. The strength of this anisotropy decreases with increasing film thickness. In this paper we focus on the interpretation of this anisotropy in terms of the Néel model.1,2 Vicinal surfaces are characterized by (001) terraces separated by monoatomic steps. The Néel anisotropy energy for such a surface has the form EtotalN= Ebulk atoms+(Esurface atoms /t) + Estep-edge atoms /td), where t and d are film thickness and terrace width, respectively. The last term includes contributions from sites at both the top and bottom of the step and is responsible for the step-induced anisotropy. For 10 ML of Co on Cu(1 1 13), the magnitude of this term is approximately 0.3 erg/cm2, favoring M parallel to the steps, as we have observed. Fe/W vicinal to (001) films show a preference for in-plane magnetization perpendicular to the steps.3 The Néel model predicts this anisotropy for a bcc Fe film provided the magnetization lies in the film plane, not in the (001) plane.
Theoretical predictions for magnetic anisotropy of superlattice defects (abstract)
Authors: Victora R. H. , MacLaren J. M.
Published: July 2002

Most experimental superlattices contain numerous defects that substantially affect the anisotropy. Calculations based on two different theoretical approaches are presented for a variety of substitutional defects at the interface. The first method involves electronic structure calculations employing the local density approximation within the layer Korringa–Kohn–Rostoker technique. Defects are treated as periodic at a third nearest-neighbor spacing. Large in-plane contributions to the anisotropy are found for a substituted atom within the (111) Co layer of both the Co/Pd and Co/Pt systems. For example, −203 uRy is obtained for a single defect in the 1Co/1Pt superlattice: this is −4.2 times the interface anisotropy. This is believed to be the first ab initio prediction of the anisotropy energy of defects. The second method sums pair interactions using the potential (M⋅R)2, where M is the magnetization and R is the vector connecting the two atoms. This method has been previously demonstrated1 to be accurate in comparison both to electronic structure calculation and to experiment. For the fcc (111) interface, it is predicted that the anisotropy (in units of interface anisotropy) of a substitution in a monolayer is −4, the anisotropy of an adatom is −2, and the anisotropy of a one-atom recess that does not penetrate the magnetic layer is −2. These predictions are found to aproximately match the electronic structure theory in those cases we have tested. Finally, the summation of a variety of randomly chosen defects to form a diffuse interface yields an anisotropy equal to that of a perfect interface times the sum over all layers i of [P(i)−P(i+1)]2, where P(i) is the probability of a magnetic atom in layer i. This suggests that the highest anisotropy is obtained at the sharpest interface.
Electronic structure and the Stoner I parameter for RPd3 compounds (R=La, Ce, Pr, and Nd)
Authors: Nautiyal T. , Kashyap A. , Auluck S. , Brooks M. S. S.
Published: July 2002

Gardner et al. have made measurements of the magnetic susceptibility in a large range of temperature for a complete series of RPd3 compounds (R=rare earths). Some band structure calculations exist on LaPd3 and CePd3. However, the question of magnetic ordering has not been addressed in existing theoretical work. With a view to understand the magnetic behavior of these compounds we have performed self-consistent band structure calculations for LaPd3, CePd3, PrPd3, and NdPd3. Our calculations predict magnetic ordering only in PrPd3 and NdPd3 and hence are consistent with the experimental findings.
Unusual transport and magnetic properties of Tb-doped YBa2Cu3O7 single crystals and epitaxial thin films
Authors: Cao G. , O’Reilly J. W. , Crow J. E. , Kennedy R. J. , Nichols D. H.
Published: July 2002

The electrical resistivity ρ(T) and magnetic susceptibility χ(T,H) (1.8≤T≤350 K and 0≤H≤5.5 T) have been measured on single crystals and epitaxial thin films of Y1−xTbxBa2Cu3O7. The Tc is 92 K and irrespective of Tb doping up to x=0.50. For T≳Tc, ρ(T) has a linear dependence, i.e., ρ(T)≊A+BT, with the reduced resistivity ρ(T)/ρ(250 K) for x=0.10, 0.25, and 0.50, being independent of Tb doping. The results of magnetic susceptibility along with the computation of effective moment of Tb in the presence of crystal electric fields (CEF) tend to suggest that the Tb is mixed valent. The insensitivity of Tc to the Tb doping and the possibility that Tb may be mixed valent are in sharp contrast to the case of Pr and Ce doping which have been shown to be very deleterious to superconductivity. The magnetic susceptibility χ(T) is extremely anisotropic, and this anisotropy cannot be explained by simple models with CEF effects.
Magnetic and optical characteristics of bilayered films composed of Tb-Fe-Co layer with overlayers of Co-Cr, Ni-Fe, Ta, and C
Authors: Song Kibong , Naoe Masahiko
Published: July 2002

Amorphous Tb-Fe-Co single layers and Tb-Fe-Co/M (M: Ta, C, Co82Cr18, Ni81Fe19) bilayers have been prepared by using a facing targets sputtering apparatus. The Tb-Fe-Co films deposited by Kr sputtering exhibited internal stress as low as 1×109 dyn/cm2 even at a pressure as low as 0.2 mTorr. The Tb-Fe-Co/Ta bilayers showed a Kerr rotation angle as large as 0.85° at the thickness of Tb-Fe-Co layer of about 30 nm. The direction of magnetic moments in Tb-Fe-Co layers were arranged antiparallel by a soft magnetic Ni81Fe19 overlayer.
In situ and dynamic observation of NdFeCoB magnet by high voltage transmission electron microscope (abstract)
Authors: Shuming Pan , Jinfang Liu , Yinfan Xu
Published: July 2002

In situ and dynamic observation of microstructural characteristics of sintered Nd-Fe-Co-B magnet has been carried out using JEM-1000X high voltage transmission electron microscope (HVTEM). Magnetic properties of the sample studied are as follows: Br=1.28 T, Hc=589 kA/m, (BH)max=302.4 kJ/m3. HVTEM observation results are as follows: (1) At room temperature, the grains of the matrix phase are found to be nearly perfect crystals. In some grains, there exist some spherical inclusions that are embedded in the matrix. Structural analysis of these inclusions has been made by electron diffraction. (2) When the temperature is lower than 400 °C, we found no obvious changes. (3) When the temperature is higher than 400 °C, some small precipitates began to occur in the matrix. (4) When the temperature reaches 500 °C, the precipitates grow and become needlelike and perpendicular to each other. (5) When the temperature reaches 700 °C, the tetragonal symmetry of the matrix phase is completely damaged. (6) No remarkable changes were found for the Nd-rich grain boundary phase when the temperature increases from 25 to 600 °C. (7) Temperature dependence of coercivities of the sample has been explained by the structure changes.
Effect of Er2O3 addition on microstructure and physical properties of Mn–Zn ferrites for high-power use
Authors: Liu C. S. , Wu J. M. , Chen C. J. , Tung M. J.
Published: July 2002

The present authors found that Mn–Zn ferrites containing Er2O3 had improved values of σs (specific magnetization) and amplitude permeability. Samples with different addition amount of Er2O3 were sintered at 1180 °C. The results show that Er2O3 addition from 0.02 to 0.1 wt % causes the amplitude permeability to increase from 1070 to 2180. The magnetization can be increased from 91.6 to 92.8 emu/g within the range 0.02–0.1 wt %. Furthermore, the effect of Er2O3 addition was investigated in detail by power-loss analysis and scanning electron microscopy examination of microstructure. We found that samples with Er2O3 less than 0.04 wt % exhibit power loss similar to the sample without Er2O3 addition and with SiO2–CaO contents. Thus we conclude that the amplitude permeability and specific magnetization of Mn–Zn ferrites for high-frequency and high-power use were improved by a small Er2O3 addition (<0.04 wt %).
Magnetization in current carrying iron whiskers (abstract)
Authors: Arrott A. S. , Lee J.-G.
Published: July 2002

The structure deduced for a 〈100 〉 iron whisker carrying a current along its axis in the presence of a magnetic field is shown in Fig. 1. An analytic model of the ac response is obtained by considering the competition of exchange, anisotropy and magnetostatic energies. For the analytic model the magnetization is assumed to point either along an easy axis in the plane or out of the plane everywhere except in the walls where the energies of the walls per unit area are assumed to be independent of field. It is argued that the energy scales with that of the central cross section subjected to demagnetizing fields that depend on the magnetization along the axis in that cross section. The model is shown to account for the ac susceptibility of a current carrying whisker. The calculation is refined by considering a pattern that is divergenceless. The pattern is generated by taking the curl of a vector potential to produce the components in the plane and adding a component perpendicular to the plane to conserve the magnitude. The vector potential has a single component given by Az = Msq cothB/q[(1/√2) (q/{a ln [cosh(x/a)cosh (y/a)] })q/B − Ac[(x/a), (y/a)], where the parameter q determines the size of the central region of Fig. 1, the constant a sets the scale for the 90° domain walls between the four outer domains, and B sets the scale for the 90° domain wall between the central region and the outer domains. The term Ac is added to turn the magnetization along the axis of the whisker in each corner of the central cross section. The only parameter in Ac is a. The total energy is minimized for parameters q, B, and a. The field dependence of q accounts for the magnetic behavior.
Ferromagnetic resonance spectra of oriented barium ferrite tapes
Authors: Yu Yuwu , Harrell J. W. , Doyle W. D.
Published: July 2002

Ferromagnetic resonance spectra have been measured for three barium ferrite tapes at 34.5 GHz for two different orientations of the tapes with respect to the static and microwave fields. The orientation distributions in the tapes have been measured using x-ray diffraction, and these distributions have been used to calculate the spectra using the Landau–Lifshitz equation. The anisotropy energy, damping constant, and volume packing fraction have been used as adjustable parameters in the calculations. Calculated spectra were in good agreement with measurements. Anisotropy constants and damping constants determined from the fits are consistent with results reported for fine particle assemblies.
Photoresist stripping in afterglow of Ar-O2 microwave plasma
Authors: Metselaar J. W. , Kuznetsov V. I. , Zhidkov A. G.
Published: July 2002

The experimental investigation of the photoresist etching rate in the afterglow of Ar-O2 microwave plasma has been performed. It was found that up to 50% Ar can be added to O2 without etching rate decrease. A high photoresist etching rate of 2.9 μm/min has been achieved. A mathematical model based on the one-dimensional mass continuity equation for atomic oxygen, taken to be responsible for the etching process, has been proposed. Modeling of the Ar-O2 afterglow microwave photoresist stripping process was performed. The simulated behavior of the atomic oxygen flux shows a similar dependence with Ar dilution and pressure as the experimentally observed photoresist etching rate. It indicates that the photoresist etching rate is determined by the atomic oxygen flux to the substrate. The proposed model explains the measured dependencies.
Normal state YBa2Cu3Ox films: A new fast thermal detector for far infrared laser radiation with a uniform wavelength response
Authors: Huggard P. G. , Zeuner S. , Goller K. , Lengfellner H. , Prettl W.
Published: July 2002

Room temperature YBa2Cu3Ox films, epitaxially grown on oriented substrates, are shown to be effective detectors of far infrared laser pulses. The photovoltage arises due to an anisotropic material thermopower subject to the thermal gradient arising from the radiation heating. For a 40 nm thick film we have measured a responsivity of (5±2)×10−7 V/W, independent of frequency in the range from 20 to 110 cm−1. The response time is limited by thermal diffusion, giving a 200 MHz detector bandwidth and a noise equivalent power of 3.6×10−3 W(Hz)−1/2 for this film thickness. Due to their large area (1 cm2) and uniform spectral response, such films may be useful replacements for pyroelectric power/energy meters.
Formation kinetics of nanocrystalline FeBSi alloy by crystallization of the metallic glass
Authors: Tong H. Y. , Ding B. Z. , Jiang H. G. , Lu K. , Wang J. T. , Hu Z. Q.
Published: July 2002

In order to clarify the formation mechanism of extremely fine-grained microstructures by crystallization of the FeBSi metallic glass, the nucleation and crystal-growth rates have been determined. The results indicate that the parabolic growth rate increases with annealing temperature, showing a maximum nucleation rate at an intermediate temperature range. Obviously it is possible to obtain nanocrystalline structures by controlling crystallization of the metallic glass on annealing at temperatures near the maximum nucleation rate.
A novelty optical filter with multilayer coating of ZnO-CdTe
Authors: Chen Pin Ao
Published: July 2002

A ZnO-CdTe thin film multilayer structure was shown to attenuate the transmitted light as function of incident light intensity. Sample transmittance measurements suggest that it is the charge separation of the photogenerated electron-hole pairs that contributed to the enhancement of light scattering.
Misfit dislocations and antiphase domain boundaries in GaAs/Si interface
Authors: Komninou Ph. , Stoemenos J. , Dimitrakopulos G. P. , Karakostas Th.
Published: July 2002

The interaction of the antiphase boundaries that are formed at the early stage of growth with the interfacial misfit dislocations is studied by transmission electron microscopy using contrast criteria. Experimental analysis has shown that the shifting of the misfit dislocation families, by half of their periodicity, is due to their intersection with antiphase boundaries emanating from demisteps on the Si substrate. The observed discontinuity of dislocation lines is attributed to dynamical contrast conditions. The antiphase boundaries do not interrupt the continuity of the network of dislocations. The dichromatic theory of interfacial defects is applied in order to illustrate the geometrical features of the pattern. The disymmetrization mechanism of the pattern obeys the principle of symmetry compensation. A symmetry analysis of the GaAs/Si interface justifies the agreement of the observations with the structural model.
Analysis of the variation in the field-dependent behavior of thermally oxidized tantalum oxide films
Authors: Choi W. K. , Ling C. H.
Published: July 2002

The field-dependent behavior of the conductivity (σ) of thermally oxidized tantalum oxide films has been analyzed based on a model we developed previously [W. K. Choi, J. J. Delima, and A. E. Owen, Phys. Status Solidi B 137, 345 (1986)]. Comparison with published data shows that the agreement in the log(σ) versus the square root of the applied field is very good. The relative dielectric constants obtained from the simulations compared very favorably with the published results. The donor density for the tantalum oxide films were estimated to be between 1.7×1014 and 2×1017 cm−3 depending on the films preparation conditions.
The optical nonlinearity and structure for a PbO, TiO2, SiO2, and K2O quaternary glass system
Authors: Zhu Xinhua , Meng Zhongyan
Published: July 2002

The nonlinear refractive index n2 of a PbO, TiO2, SiO2, and K2O quaternary glass system measured by the laser beam longitudinal scanning (Z-SCAN) method was found to be 7.72×10−19 m2/W and it was strongly correlated with the presence of more polarizable ions rather than the nonbridging oxygen content. The structural units of the present glass system has been studied by infrared (IR), Raman spectra, and x-ray photoelectron spectroscopy (XPS) techniques. The results indicate that the IR absorption band at 1020 cm−1 and the Raman peak at 1100 cm−1 attributed to the stretching vibration of the Si—O—Si bond shift to a lower wave number with an increase of the relative content of K2O. The XPS O1s spectra are decomposed into two main components, which reveal that oxygen atoms of the glass network occur in both bridging and nonbridging oxygen with binding energies of 531.77±0.30 eV and 530.17±0.40 eV, respectively. Si4+ ions are in the form of SiO4 to form the glass network, Ti4+ ions are dual 4- and 6-coordinated with oxygen ions, K+ ions act as network modifiers, and Pb2+ as network modifiers at a low content of PbO, but are network formers at high content. A structural model has been proposed.
A mechanism for obtaining a single magnetization state in permalloy films
Authors: Flynn David I. , Shi Xu
Published: July 2002

Magnetoresistive permalloy films are characterized by having two possible output states that correspond to different directions of magnetization. This article describes the use of a pulsed easy axis field to obtain a single predictable state that does not depend upon the past history of the external applied field. The magnetization reversal occurs at one field value only which is opposite in direction to the pulsed easy axis field direction and is accurately predicted by the Stoner–Wohlfarth model.
AlAs/AlGaAs X-valley quantum-well normal-incidence infrared detectors on Si substrates
Authors: Zhang Y. , Baruch N. , Wang W. I.
Published: July 2002

AlAs/AlGaAs X-valley multiquantum-well detectors grown on Si substrate are reported. Normal-incidence infrared-absorption measurements were performed on [113]- and [115]-oriented samples grown on Si substrate at a wavelength range of 5–20 μm. An absorption peak was observed in the [113]-oriented quantum wells with an infrared-absorption coefficient of α=1400 cm−1 (quantum efficiency η=13%); similar results were attained with the [115] sample. The experimental results indicate the potential of these novel structures as normal-incidence infrared photodetectors. The results point to the possibility of integrating photodetectors and signal processing circuits on the same Si substrate.
Early stages of growth of YBa2Cu3O7−δ high T
c superconducting films on (001) Y-ZrO2 substrates
Authors: Alarco J. A. , Brorsson G. , Olin H. , Olsson E.
Published: July 2002

The early stages of growth of high quality YBa2Cu3O7−δ (YBCO) films grown on (001) Y-ZrO2 (YSZ) substrates by pulsed laser deposition have been studied using a combination of atomic force microscopy and transmission electron microscopy. A one unit cell thick YBCO layer and relatively large CuO particles formed in the initial stages. Additional YBCO grew on top of the first layer in the form of one or a few unit cell high c-axis oriented islands about 30 nm in diameter. The rounded islands subsequently coalesced into faceted domains. Elongated Y2BaCuO5 particles nucleated after the first layer of YBCO. A highly textured BaZrO3 layer formed between the YSZ and the YBCO with a cube-on-cube dominant orientation relationship with respect to the YBCO film.
The enhancement of optical third harmonic susceptibility in a parabolic quantum well by triple resonance
Authors: Huang Yimin , Lien Chenhsin
Published: July 2002

The third harmonic susceptibility for the finite parabolic quantum well (PQW) is studied theoretically. An important feature of the finite PQW is that the subband eigenenergies En form an equally spaced energy-level ladder. Since the eigenenergy spacing ℏω0 can be designed to resonate with the pumping source, the third harmonic susceptibility can be greatly enhanced through the triple resonance. A third harmonic susceptibility as high as 2000 (nm/V)2 could be achieved for the finite parabolic quantum well structure. This is a more than six orders of magnitude enhancement as compared to that of the bulk GaAs.
Magnetic multilayers: A detailed analysis of continuum versus discrete treatments
Authors: Altbir Dora , Kiwi Miguel
Published: July 2002

A critical comparison is made between discrete and continuum treatments put forward to determine the magnetic ordering of exchange coupled superlattices. In particular, our interest is focused on the spatial patterns adopted by the coupling between ferromagnetic layers across the nonmagnetic spacers. We find that for values of the spacer electron Fermi wavevector kF≳π/a, where a is the lattice parameter, the continuum model breaks down. This gives rise to interesting interference effects, which emerge in the discrete three–dimensional treatment, but which are missed in a continuum pseudo one–dimensional approximation. The experimental evidence is discussed, and an analytic derivation of the critical kF value is also given.
Spatial light modulator using polymer-dispersed liquid crystal: Dependence of resolution on reading light intensity
Authors: Takizawa Kuniharu , Kikuchi Hiroshi , Fujikake Hideo , Kodama Kenichi , Kishi Kiyoshi
Published: July 2002

A spatial light modulator consisting of a polymer-dispersed liquid crystal (PDLC) film, a dielectric mirror, and a Bi12SiO20 photoconductor is useful for projection-type displays, optical image processing, and optical computing. However, a portion of the reading light scattered by the PDLC film passes through the dielectric mirror and illuminates the photoconductor, thus causing deterioration of display-image quality. This article reports on the results of a detailed study on the influence of reading light on the resolution and amplification factor, which is the ratio of reading light intensity to the maximum intensity of writing light. Angular distributions of light scattered by a PDLC cell were measured and the results were used to calculate the intensity of scattered light absorbed by the photoconductor. We then analyzed the optical input/output characteristics of the spatial light modulator with regard to the optical feedback effect caused by the reading light in order to discover the parameter for evaluating image quality. The relation between amplification and resolution is derived from this parameter. We have also considered a light absorption layer for preventing the deterioration of image quality and obtained the relation between the amplification factor and the transmittance of the light absorption layer for high definition images of high brightness. Finally, these theoretical results were confirmed by an experiment using a spatial light modulator with no dielectric mirror.
Drift and diffusion in low-dimensional p-n junctions
Authors: Sadra K. , Streetman B. G.
Published: July 2002

We present a theoretical drift-and-diffusion study of the current-voltage characteristics of low-dimensional p-n junctions. Under low-level injection, low-dimensional p-n junctions exhibit current-voltage characteristics similar to those of three-dimensional diodes. Under high-level injection, the dependence of minority-carrier diffusion coefficients on the low-dimensional density of states may lead to the appearance of features in the small-signal properties. Such features become more pronounced as the temperature is lowered.
NiGe-based ohmic contacts to n-type GaAs. I. Effects of In addition
Authors: Oku Takeo , Wakimoto Hiroki , Otsuki Akira , Murakami Masanori
Published: July 2002

Contact resistances of NiGe ohmic contacts, which had been previously developed in our laboratory, were reduced significantly by adding a small amount of In to the NiGe contacts without deteriorating the thermal stability, the surface smoothness, and the shallow diffusion depth. The optimum layer thicknesses to prepare the low resistance ohmic contacts were determined to be 60 nm for Ni, 100 nm for Ge, and 3 nm for In, and the contact resistances (Rc) less than 0.3 Ω mm were obtained after annealing at temperatures in the range between 600 and 700 °C. Microstructural analysis at the GaAs/metal interface of the contact with low Rc showed formation of ‘‘regrown’’ GaAs and InxGa1−xAs layers between the GaAs substrate and high melting point NiGe compounds. Based on the present electrical measurements and microstructural analysis, a model for the current transport of the NiGe-based ohmic contacts was proposed, which explained well the dependencies of the contact resistances on the microstructure at the GaAs/metal interface.
A new magnetoplasma amplification effect in the optical frequency range
Authors: Iida Takashi , Mizushima Yoshihiko
Published: July 2002

In the Voigt configuration of electromagnetic wave propagation, for components perpendicular to the magnetic field, the secular equation describing the wave instability is theoretically analyzed. The operating frequency is in the infrared or submillimeter range. Within the magnetic field the electron-cyclotron motion is proposed to be able to interact with an optical wave, giving rise to amplification. There are two kinds of amplification. One appears when the plasma frequency (ωp) is larger than the cyclotron frequency (ωc), and the other when ωp<ωc. In a 1 T magnetic field, the gain is about 15 dB per wavelength for InSb at the near 17 μm infrared wavelength region. The gain is similar to that of a semiconductor laser. It is a unidirectional traveling wave amplifier with tunable frequency. It operates at room temperature.
Defect-enhanced interdiffusion at the InGaAs/InAlAs interface due to Si ion implantation
Authors: Yamamura Shin’ichi , Saito Riichiro , Yugo Shigemi , Kimura Tadamasa , Murata Michio , Kamiya Takeshi
Published: July 2002

Interdiffusion at the InGaAs/InAlAs interfaces which are implanted with Si ions has been studied. Quantum well (QW) structures are grown on InP(Fe) substrates by metalorganic vapor phase epitaxy. Each sample has three InGaAs wells of 2.6, 5.9, and 17.6 nm in thickness and is separated by 24-nm-thick InAlAs barrier layers with each other. The samples are implanted with Si ions at uniform Si densities ranging from 1.8×1017 to 3.9×1019 cm−3 over the QWs, and then annealed under various annealing conditions. The photoluminescence (PL) peak energy from each well is monitored to study the intermixing at the interface. Blue shifts in the PL peak energy are found to occur almost in the early stage of thermal annealing (within 15 s) above the critical Si dose of 2–3×1018 cm−3. The saturated value of the energy shift is determined mostly by the Si density but hardly dependent on the annealing temperature and time. It is concluded that defects formed by Si ion implantation enhance the thermal interdiffusion of Ga and Al atoms at the InGaAs/InAlAs interface, which finishes when implantation-induced defects are annealed out.
Effect of crystal structure on the electrical resistivity of copper-germanium thin-film alloys
Authors: Aboelfotoh M. O. , Tawancy H. M.
Published: July 2002

Resistivity measurements have been performed on Cu-Ge thin-film alloys with Ge concentration ranging from 0 to 40 at. % in the temperature range 4.2–300 K. It is found that the dependence of resistivity on Ge concentration is not monotonic. This behavior is correlated to changes observed in the crystal structure of the alloys as the Ge concentration is increased. The resistivity is found to remain remarkably low (typically less than 10 μΩ cm at room temperature) over a range of Ge concentration that extends from 25 to 35 at. %, even though above 25 at. % Ge, the alloys consist of the low resistivity ε1-phase of Cu3Ge and of a Ge-rich solid solution.
The stopping power of 1–3 MeV hydrogen and helium in polyimide
Authors: Wallace W. E. , Rothman J. B. , Composto R. J.
Published: July 2002

The stopping power for hydrogen (1H)and helium (4He) in thermally imidized pyromellitic dianhydride-oxydianaline polyimide was measured using the thin-film backscattering method. As the incident energy increased from 1 to 3 MeV, the hydrogen stopping power decreased from 4.2 to 1.8 eV/(1015 atoms/cm2), whereas the helium stopping power decreased from 33.6 to 18.6 eV/(1015 atoms/cm2). These results were in excellent agreement with values predicted by either Bragg’s rule or the cores-and-bonds model. This work demonstrates the advantages of using spun-cast thin (<3 μm) polymer films supported on silicon wafers for stopping power measurements. Prior measurements of the stopping power relied on transmitting the ion beam through relatively thick (∼10 μm) free-standing films where the uncertainty in the film thickness often introduced significant systematic errors. With polymer films supported on silicon, ellipsometry can be used to accurately determine film thickness.
Effects of argon ion bombardment on the microstructures and electrical conductivities of hydrogenated amorphous carbon films prepared by plasma-enhanced chemical vapor deposition
Authors: Chou L. H. , Hsieh W. T.
Published: July 2002

Hydrogenated amorphous carbon films were prepared from plasma-enhanced chemical vapor deposition. Films thermally annealed at 300 °C for 2 h as well as those as-deposited films exhibited insulating characteristics. The as-deposited films were found to possess mainly polymerlike structures. A hydrogen etching effect was observed in these films after argon-plasma bombardment. The implanted argon ions transferred momentum to atoms in films which led to both a reduction in the polymer content and also an increase in the graphite and diamond contents in both as-deposited and annealed hydrogenated amorphous carbon films. This change in the microstructures resulted in an increase in the electrical conductivity up to six orders of magnitude at room temperature. In addition, films which exhibited thermally activated conductivity characteristics were found and an activation energy of around 0.3 eV was measured.