bluuebunny/crossref_metadata_2025 huggingface dataset:
Good quality Al/SiNx:H/InP metal-insulator-semiconductor devices obtained with electron cyclotron resonance plasma method
Authors: Garcia S. , Mártil I. , Gonzalez Diaz G. , Castan E. , Dueñas S. , Fernandez M.
Published: July 2002

We have obtained Al/SiNx:H/InP metal-insulator-semiconductor devices depositing SiNx:H thin films by the electron cyclotron resonance plasma method at 200 °C. The electrical properties of the structures were analyzed according to capacitance–voltage and deep level transient spectroscopy measurements. We deduce an inverse correlation between the insulator composition—the N/Si ratio—and the density of interface traps: those films with the maximum N/Si ratio (1.49) produce devices with the minimum trap density—2×1012 cm−2 eV−1 at 0.42 eV. above the midgap. We explain the influence of film composition on the interface trap density in terms of a substitution of phosphorous vacancies at the InP surface, Vp, by N atoms coming from the insulator, NVp. The values obtained in our research for the interface trap distribution were similar to other published results for devices that use chemical and/or physical passivation processes of the InP surface prior to the deposition of the insulator.
The origin of the integral barrier height in inhomogeneous Au/Co/GaAs67P33-Schottky contacts: A ballistic electron emission microscopy study
Authors: Olbrich Alexander , Vancea Johann , Kreupl Franz , Hoffmann Horst
Published: July 2002

In this work we investigated the relationship between the integral Schottky barrier height (SBH) obtained from conventional current–voltage (I–V) measurement and the distribution of the local SBH measured by ballistic electron emission microscopy (BEEM) on a nanometer scale length. For this purpose, we investigated inhomogeneous Au/Co/GaAs67P33-Schottky contacts. The samples were prepared by the deposition of a discontinuous Co film on the semiconductor followed by the deposition of a continuous Au film. This provided regions with local presence of one or the other metal (Au or Co) at the metal-semiconductor interface, resulting in mesoscopically extended SBH inhomogeneities. The local SBH distribution as well as the integral SBH depended on the preparation parameter of the Co layer, i.e., on the combination of the substrate temperature (300 or 500 K) and the nominal Co thickness (0, 0.25, 0.5, 0.8, 1.0 nm). For the different preparation parameters, statistical distributions of the local SBH were measured by BEEM. Treating these SBH distributions in terms of a parallel conduction model for the electron transport across the MS interface, we calculated for each preparation parameter an integral SBH and compared it with the measured integral SBH obtained from conventional I–V measurement. The calculated and measured integral SBH’s were in very good agreement, demonstrating clearly the strong influence of the low SBH regions on the electron transport across the interface and therefore on the integral SBH. The SBH values for homogeneous Au/GaAs67P33- and Co/GaAs67P33-Schottky contacts, i.e., with only one sort of metal at the interface, were determined to be ΦSBAu=1180±10 meV and ΦSBCo=1030±10 meV. As with regard to the inhomogeneous Schottky contacts the fraction of area of the MS interface covered by Co increased, the local SBH distributions as well as the integral SBH’s decreased gradually from the value of ΦSBAu to ΦSBCo.
Plasma immersion ion implantation of the interior surface of a large cylindrical bore using an auxiliary electrode
Authors: Zeng X. C. , Kwok T. K. , Liu A. G. , Chu P. K. , Tang B. Y.
Published: July 2002

A model utilizing cold, unmagnetized, and collisionless fluid ions as well as Boltzmann electrons is used to comprehensively investigate the sheath expansion into a translationally invariant large bore in the presence of an auxiliary electrode during plasma immersion ion implantation (PIII) of a cylindrical bore sample. The governing equation of ion continuity, ion motion, and Poisson’s equation are solved by using a numerical finite difference method for different cylindrical bore radii, auxiliary electrode radii, and voltage rise times. The ion density and ion impact energy at the cylindrical inner surface, as well as the ion energy distribution, maximum ion impact energy, and average ion impact energy for the various cases are obtained. Our results show a dramatic improvement in the impact energy when an auxiliary electrode is used and the recommended normalized auxiliary electrode radius is in the range of 0.1–0.3.
Interdiffusion and phase formation in Cu(Sn) alloy films
Authors: Clevenger L. A. , Arcot B. , Ziegler W. , Colgan E. G. , Hong Q. Z. , d’Heurle F. M. , Cabral C. , Gallo T. A. , Harper J. M. E.
Published: July 2002

The interdiffusion of Cu and Sn, and the formation and dissolution of Cu–Sn precipitates have been examined for Cu alloy films. Cu(Sn) films were deposited by electron beam evaporation either as Sn/Cu bilayers or Cu/Sn/Cu trilayers, with overall Sn concentrations from 0.1 to 5 at. %. In situ resistance, calorimetry, electron, and x-ray diffraction measurements indicate that η–Cu6Sn5 forms during film deposition. Upon heating, ε–Cu3Sn forms at 170 °C, then this phase dissolves into the Cu matrix at approximately 350 °C. Finally, ζ–Cu10Sn3 forms and precipitates after thermal cycling to 500 °C. The final resistivity of Cu/Sn/Cu films with more than 2 at. % Sn exceeds 3.5 μΩ cm. However, resistivities from 1.9 to 2.5 μΩ cm after annealing were reached in Cu/Sn/Cu films with less than 2 at. % Sn. Auger and Rutherford backscattering analysis of Cu/Sn bilayers (1 mm thick) showed that the homogenization of Sn in Cu requires annealing in excess of 350 °C for 30 min; after annealing, the Sn concentration at the surface is approximately 20 at. %. The interdiffusion of Sn and Cu is inhibited by contamination at the Sn/Cu interface caused by air exposure.
Mechanism of the negative nonlinear absorption effect in a five-level system of the Er3+ ion
Authors: Maeda Yoshinobu
Published: July 2002

The dependence of the negative nonlinear absorption effect on the modulation degree and frequency, the sample temperature, and the erbium concentration was investigated in erbium yttrium aluminum garnet crystals. With a decreasing modulation degree, a reverse-phased wave form was obtained in the transmitted wave form at modulation frequency lower than 1 MHz. However, the transmitted laser wave form was asymmetrical at higher than 5 MHz and the time-dependent characteristics agreed with the lifetime of the S3/24 level in Er3+. At temperatures lower than 77 K, the negative nonlinear absorption effect weakened because the number of phonons decreased due to low temperature. It is considered that the Er3+ concentration dependence for modulation frequency depends on the lifetime of the S3/24 level. It has been confirmed that a mechanism of negative nonlinear absorption can be explained by calculating the rate equations based on an analytical model for a five-level system of the Er3+ ion. Experimental results agreed well with the calculated values. It is suggested that the effect was due to stimulated emission from the S3/24 level to the I3/24 level.
Channel effective mass and interfacial effects in Si and SiGe metal-oxide-semiconductor field effect transistor: A charge control model study
Authors: Zhang Yifei , Singh Jasprit
Published: July 2002

We present results of a numerical formalism developed to address the band structure and charge control problem in n- and p-type silicon and silicon-germanium metal-oxide-semiconductor field effect transistors. We focus on the following issues: (i) the dependence of the in-plane carrier effective mass on sheet charge density and germanium content; (ii) the fraction of charge near the interface and the evaluation of the interface roughness matrix element. Results are compared to existing models. For n-type structure, the effective mass approximation and deformation potential theory is used to describe the electron states. However, for p-type structure, a six-band k⋅p Kohn–Luttinger formulation is used to describe the hole states due to the strong coupling of heavy-hole, light-hole, and split-off bands. This allows us to examine the influence of the coupling of the heavy-hole, light-hole, and the split-off bands.
Effects of interface phonon scattering in three-interface heterostructures
Authors: Kisin Mikhail V. , Stroscio Michael A. , Belenky Gregory , Gorfinkel Vera B. , Luryi Serge
Published: July 2002

A detailed study of the electron–optical–phonon interaction in an asymmetric one-well/one-barrier heterostructure is given. Dispersion relations and phonon potential distributions for interface phonon modes are derived in the framework of the macroscopic dielectric continuum model. It is found that for intrawell relaxation processes the sum of the scattering rates by all interface polar-optical phonon modes is approximately independent of the width of the barrier layer. Consequently, a simplified Hamiltonian for electron–phonon interaction in a single quantum well can be used for scattering rate calculation in multiple heterointerface structures. The combined scattering rates by interface and confined phonon modes are compared with the results obtained in an idealized model using the bulklike phonon spectrum. The practical invalidity of the latter approximation is shown for electron kinetic energies comparable with the typical energy of optical phonons in the heterostructure.
Structure and properties of rapid thermal chemical vapor deposited polycrystalline silicon–germanium films on SiO2 using Si2H6, GeH4, and B2H6 gases
Authors: Li V. Z-Q , Mirabedini M. R. , Hornung B. E. , Heinisch H. H. , Xu M. , Batchelor D. , Maher D. M. , Wortman J. J. , Kuehn R. T.
Published: July 2002

Deposition of undoped and in situ boron-doped polycrystalline silicon-germanium (poly-Si1−xGex) films on oxide has been investigated at temperatures below 625 °C and a pressure of 4 Torr in a rapid thermal chemical vapor deposition system. The influences of reactant gases such as Si2H6, SiH4, GeH4, and B2H6 on the nucleation behavior, and structural properties of poly-Si1−xGex films formed on oxide were studied. The experimental results showed that in situ boron-doped or undoped poly-Si1−xGex films can be directly deposited on oxide without an initial Si predeposition layer to provide the necessary nucleation sites on the surface when using Si2H6 as the Si source gas. However, when SiH4 was used as the Si source gas, only in situ boron-doped films can be deposited nonselectively on the oxide without the initial Si predeposition layer, and to deposit undoped poly-Si1−xGex films, Si predeposition is needed, otherwise Si1−xGex islands are formed on the oxide. X-ray diffraction analysis showed that poly-Si1−xGex films deposited using Si2H6, GeH4, and B2H6 gas mixture have three singular peaks corresponding to {311}, {220}, and {111} planes, thus indicating the Si1−xGex alloy is formed. In addition, we found that B2H6 gas has a minor effect on the Ge incorporation into the films but reduces the overall deposition rate.
A comparison between a two-material and three-material magnetic current limiter
Authors: Young S. , Dawson F. P. , Iwahara M. , Yamada S.
Published: July 2002

This paper investigates the inductance versus current characteristics of a two-material and a three-material magnetic current limiter. The two-material device consists of a NdFeB permanent magnet, a high saturation flux density magnetic material, and a high saturation flux density magnetic pole piece placed on both sides of the magnet. The three-material device consists of a NdFeB permanent magnet, a high saturation flux density magnetic material, and a low saturation flux density material. Finite-element results for the three-material device agree with the results obtained using design equations. In contrast, the results obtained for the two-material device show that the transition current is overestimated and that the ratio of the maximum safe current and transition current, as well as the unsaturated inductance is underestimated. Extending the magnet beyond the adjoining surfaces improves the sharpness of the transition characteristics when the ratio of the core length to the core width is large.
Reversible and irreversible components of tensor magnetization and magnetostriction
Authors: Liorzou F. , Yu Y. , Atherton D. L.
Published: July 2002

Tensor magnetostriction and magnetization hysteresis loops for a 25 mm ferrite magnet cube were measured. These describe the magnetization properties and reflect the anisotropy of the system. The sample investigated allowed the magnetization to be interpreted in terms of a magnetization vector rotation process and described by the Stoner–Wohlfarth model. The reversible and irreversible components were extracted for both the magnetostriction and magnetization tensors. Up to now, very few direct measurements of these reversible changes in strain have been reported. The different magnitudes of reversible magnetization and magnetostriction are analyzed and explained qualitatively by a representation involving both magnetization and magnetostriction processes. The magnetostrictive effect is taken into account quite simply by considering a demagnetized sphere distorted into an ellipsoid of revolution when saturated. The ellipsoid will rotate as the magnetization vector according to the Stoner–Wohlfarth model. Two cases are illustrated depending on the easy axes location. These explain the experimental results obtained with the ferrite sample.
Fundamental study for rosary-shaped magnetic actuators
Authors: Saotome H. , Sakaguchi K.
Published: July 2002

Rosary-shaped magnetic actuators are proposed. The actuators consist of multiple permanent magnet cubes connected in a queue or in a circle. By applying the magnetic field to the magnet cubes, the actuators are supposed to move in liquid and convey medicine in a human body. For the first stage, this article shows the fundamental analysis and experimental results of controlling one-magnet motions. We studied motions of a magnet of two poles, put in water, where the magnet was equipped with a float. The floating magnet was column shaped with a 10 mm diam and 6 mm height. We have succeeded in independently fixing the position and angle of the magnet by controlling the currents flowing in two separate coils.
A neutron diffraction structural study of R2Fe17−xAlx(C) (R=Tb, Ho) alloys
Authors: Yelon W. B. , Luo H. , Chen M. , Chang W. C. , Tsai S. H.
Published: July 2002

The title compounds were confirmed to have the Th2Zn17 type rhombohedral structure (space group R3̄m) except for Ho2Fe16Al and Ho2Fe15Al2 which have the Th2Ni17 type hexagonal structure (space group P63/mmc) while Ho2Fe13Al3 is a mixture of the two phases with the hexagonal phase dominant. A larger unit cell favors the formation of an ordered rhombohedral phase rather than a disordered hexagonal phase. Both the substitution of Fe by Al and the insertion of C can expand the cell and lead to the formation of an ordered rhombohedral phase. The site preferences of Al are somewhat different with and without C. In both series, C is mainly found at the 9e interstitial site.
Contrasting magnetic and structural properties of two La manganites with the same doping levels
Authors: McGuire T. R. , Duncombe P. R. , Gong G. Q. , Gupta A. , Li X. W. , Pickart S. J. , Crow M. L.
Published: July 2002

Powder and sintered samples of La0.9MnO3 (LMO) and La0.62Y0.07Ca0.31MnO3 (LYCMO) are used in this study. The two initial calcined in air powders have almost identical ferromagnetic properties with Tc≈250 K, and saturation magnetization of σ≈90 emu/gm corresponding to Mn4+(0.3)/Mn3+(0.7). Heating the calcined powders in argon to high temperatures lowers Tc to ≈120 K; however, subsequent oxygen annealing brings back the high Tc form. The LYCMO remains ferromagnetic with σ≈90 emu/gm in both heat treatments but only has a colossal magnetoresistance (MR) for Tc≈120 K. In contrast the LMO with Tc≈120 K has σ reduced to one-half its ferromagnetic value and the MR is almost zero. Neutron diffraction shows only the ferromagnetic structure below Tc for LYCMO but the low magnetization of LMO is best interpreted as a mixed ferro–antiferromagnetic structure rather than a canted one.
Magnetic properties of Pb2Sr2PrCu3O8 studied by ac susceptibility
Authors: Wu S. Y. , Chang Y. C. , Lee K. C. , Li W.-H.
Published: July 2002

The magnetic responses of vacuum annealed polycrystalline Pb2Sr2PrCu3O8 to a magnetic field have been studied by ac magnetic susceptibility measurements, where both the in-phase component χ′ and the out-of-phase component χ″ were measured. Diamagnetic responses in χ′(T) below 60 K were clearly seen, showing the occurrence of superconductivity, but it is filamentary. This filamentary superconductivity was also evident in the χ″(T). Under an applied dc field, both the χ′(T) and χ″(T) behave as what are expected for a superconducting system. At lower temperatures, a well-defined peak associated with the Pr spin ordering is also clearly revealed at 5 K. Correspondingly, an anomaly is also seen in the specific heat data.
Non-Heisenberg couplings and ferromagnetic instability in a random antiferromagnetic spin-1 chain
Authors: Bhatt R. N. , Yang Kun
Published: July 2002

A random antiferromagnetic spin-1 chain with both Heisenberg and biquadratic nearest neighbor couplings is found to exhibit a novel ferromagnetic-like instability at low energies, if there is competition between the Heisenberg and biquadratic couplings, even though each individual nearest neighbor coupling is such as to produce a singlet ground state for the isolated pair. This instability leads to the generation of ferromagnetic couplings, and thus to the formation of weakly coupled large moments at low temperatures. A perturbative calculation (up to 4th order) is performed to investigate whether such a situation is physically realizable in spin-1 systems.
Tilted antiferromagnetic ordering of Mn in Nd0.62Ca0.38MnO3
Authors: Wu S. Y. , Li W.-H. , Lee K. C. , Lynn J. W. , Liu R. S. , Wu J. B. , Huang C. Y.
Published: July 2002

The magnetic ordering of the Mn spins in polycrystalline Nd0.62Ca0.38MnO3 has been investigated by means of neutron diffraction and ac magnetic susceptibility measurements. Three peaks around 230, 90, and 40 K were observed in the temperature dependence of the in-phase component of the ac susceptibility, χ′(T). Neutron diffraction measurements show that the peak at 90 K is associated with the ordering of the Mn spins, and that at 40 K is due to the reorientation of the Mn spins. Both ferromagnetic and antiferromagnetic coupling between the Mn spins were observed. The spins order at TN≈130 K, with a spin structure consisting of ferromagnetically coupled, tilted antiferromagnetic sheets. No evidence was found from the neutron diffraction data to indicate that the peak around 230 K in χ′(T) is of magnetic origin, which suggests that it is associated with charge ordering.
Emission studies of Ba-hexaferrite plume produced by a KrF excimer laser
Authors: Papakonstantinou P. , O’Neill M. C. , Atkinson R. , Al-Wazzan R. , Morrow T. , Salter I. W.
Published: July 2002

Optical emission measurements and intensified charge coupled detector images of a plasma generated by the interaction of a KrF excimer laser with a Ba-ferrite target have been used to study the laser ablation deposition of Ba ferrite thin films. Time integrated spectra were collected as a function of distance above the target surface and as a function of oxygen pressure. Temporal profiles showed that close to the target the plume is insensitive to ambient oxygen pressure and at greater distances a much more pronounced influence is observed. Time resolved images of the overall optical plasma emission clearly demonstrated how the presence of oxygen confines the plasma and enhances its emission.
Surface spin waves in metamagnets with nonuniaxial single-ion anisotropy
Authors: Anselmo D. H. A. L. , Albuquerque E. L. , Cottam M. G.
Published: July 2002

A microscopic theory is employed to investigate the spin wave spectra in metamagnetic materials that consist of ferromagnetically ordered layers, with the intralayer ferromagnetic exchange interactions being much stronger than the weak antiferromagnetic interaction between adjacent layers.
Growth and characterization of epitaxial thin films of conductive ferromagnetic oxide SrRuO3
Authors: Eom C. B. , Rao R. A. , Gan Q. , Kacedon D. B.
Published: July 2002

We have grown epitaxial thin films of the conductive ferromagnetic oxide SrRuO3 on vicinal (001) SrTiO3 substrates with different miscut angles and miscut direction. Scanning tunneling microscopy and x-ray diffraction studies indicate that when the miscut angle of the substrate is small (α⩽1°), the films grow by a combination of two-dimensional nucleation and step flow leading to a two domain in-plane texture. As the miscut angle of the substrate is increased, complete step flow growth occurs resulting in single domain thin films if the miscut direction is close to the [010] direction. When the miscut direction of the substrate is changed towards the in-plane [110] direction, two directional step flow growth occurs leading to two domain texture with both domains being present in equal volume fraction. Such differences in the growth mechanism and domain structure of the films lead to significant differences in their magnetization and magnetotransport behavior.
Magnetic anisotropies of Ni–Pt and Co–Pt alloys
Authors: Razee S. S. A. , Staunton J. B. , Pinski F. J. , Ginatempo B. , Bruno E.
Published: July 2002

We present the magnetocrystalline anisotropy of disordered Ni1−xPtx and disordered fcc Co1−xPtx alloys using the spin-polarized relativistic Korringa–Kohn–Rostoker coherent-potential approximation in which the spin-orbit coupling and magnetism are treated on an equal footing. In both the pure fcc ferromagnetic elements (Ni as well as Co), the magnetic easy axis is along the [111] direction of the crystal. Addition of Pt to Ni changes the magnetic easy axis to the [001] direction, in agreement with the experimental observations, although the magnitudes of the calculated magnetocrystalline anisotropy energies for different compositions are somewhat different from the corresponding experimental values. In contrast, addition of Pt to Co does not alter the magnetic easy axis, only the magnitude of the magnetocrystalline anisotropy energy is affected. The origin of this contrasting behavior may lie in the larger size of the magnetic moment of Co (as compared to Ni).
Magnetoresistance effects of La0.7M0.3MnO3−δ far below the Curie temperature (M=Ca, Pb)
Authors: Dörr K. , Müller K.-H. , Vlakhov E. S. , Chakalov R. A. , Chakalova R. I. , Nenkov K. A. , Handstein A. , Holzapfel B. , Schultz L.
Published: July 2002

Single-crystalline and nontextured polycrystalline thin films of La0.7Pb0.3MnO3−δ (LPMO) and La0.7Ca0.3MnO3−δ (LCMO) have been prepared by pulsed laser deposition and by magnetron sputtering, respectively. The oxygen deficiency δ of the samples was controlled by heat treatments under defined oxygen pressure. For δ≈0, the polycrystalline as well as the single-crystalline films are ferromagnetic metals with Curie temperatures Tc of 220–270 K. At low temperatures T≪Tc, the polycrystalline LCMO films show a negative magnetoresistance ratio (MR) at T=20, 77, and 180 K of −30%, −20%, and −8%, respectively, for a field of 1.5 kOe. At 20 K, around 200 Oe, the field sensitivity is as high as −0.5% (Oe)−1. A possible mechanism for this phenomenon is the spin-polarized tunneling through grain boundaries. For the single-crystalline films, the change of δ from 0 to about 0.1 has a similar effect as changing the doping level x from 0.3 to 0.1, namely, a transition from a ferromagnetic metal to a ferromagnetic insulator. By variation of δ, the low-temperature resistivity of these samples can be controlled within many orders of magnitude. The negative MR of oxygen-deficient single-crystalline LPMO and LCMO films was found to be as large as −20% at T=0.2Tc.
Magnetic, electrical, and structural studies on the metal-insulator transition in CuIr2S4−xSex (0⩽x⩽4)
Authors: Somasundaram P. , Kim D. , Honig J. M. , Pekarek T. M. , Gu T. , Goldman A. I.
Published: July 2002

Magnetic transitions and structural transformations have been investigated in CuIr2S4−xSex (0⩽x⩽4). It is found from magnetic, resistivity, and thermopower studies that the transition temperature decreases as the Se concentration is increased. The change in magnetization occurs over a 10–15 K range at lower Se concentration, while it broadens to 30 K for an Se concentration of x=0.5. Low-temperature studies proved that beyond the composition corresponding to x=0.5 the cubic structure is stabilized. The metal-insulator transition beyond the x=0.5 composition arises from the electronic rather than from the lattice contribution.
Application of the ratio Δλ/ΔM to giant magnetostrictive materials in the 〈110〉 easy regime
Authors: Busbridge S. C. , Piercy A. R.
Published: July 2002

The parameter Δλ/ΔM is a useful tool for investigating the magnetization process in magnetostrictive materials. This work extends the use of this parameter from that previously explored in the 〈100〉 and 〈111〉 easy regimes to the 〈110〉 easy regime. Theoretical values of Δλ/ΔM are presented for all possible domain wall motions that produce an increase in magnetization. In the 〈110〉 easy regime, Δλ/ΔM has contributions from both λ100 and λ111, but for practical purposes it is only necessary to consider the latter for the C15 phase giant magnetostrictive materials, because λ111≫λ100. Under such conditions there are 61 different wall motions but only four (nonzero) values for Δλ/ΔM. We have obtained the theoretically generated magnetostrain versus magnetization curve, derived from a model of distinct domain wall motions with successively higher values of Δλ/ΔM. It is shown that this curve is a good fit to the experimental magnetostrain versus magnetization curve obtained for Tb0.1Ho0.9Fe1.9, measured at intervals over the temperature range 213–373 K. Since it is known that equivalent theoretical curves in the 〈100〉 and 〈111〉 easy regimes model the magnetization process well, and that TbxHo1−xFe1.9 (0<x<0.2) undergoes a spin reorientation from 〈111〉 to 〈110〉 at approximately 260 K, and then to 〈100〉 as the temperature is reduced further, we conclude that Δλ/ΔM may be used in the 〈110〉 easy regime. However, the large number of wall motions makes it more difficult to identify any particular motion.
Spin-dependent extended x-ray absorption fine structure in magnetic oxides
Authors: Ahlers D. , Attenkofer K. , Schütz G.
Published: July 2002

The spin-dependent extended x-ray absorption fine-structure (EXAFS), i.e., the magnetic counterpart to the conventional EXAFS when using circularly polarized light in a ferro(i)magnet, was measured at the L2,3 edges of Eu in Eu3Fe5O12 and EuO and at the K edge of CrO2. Complementary near-edge x-ray magnetic circular dichroism measurements at the O K edge were made to directly access the oxygen magnetization. It is shown that there is an influence of the nearly nonmagnetic oxygen atoms on the magnetic EXAFS depending on the local symmetry of the crystal as well as on the relative direction of the magnetic moments of neighboring atoms. The observed influences at distances corresponding to the oxygen neighbors in EuO are interpreted as the harmonic focusing effect, i.e., over-next magnetic neighbors behind the oxygen are responsible for the observed contributions.
Mie scattering effects from monodispersed ZnS nanospheres
Authors: Scholz S. M. , Vacassy R. , Dutta J. , Hofmann H. , Akinc M.
Published: July 2002

Transmission spectra of monodispersed particles exhibit pronounced resonance features from which particle properties can be deduced. ZnS powders were used as model materials since they can be synthesized by homogeneous precipitation with a narrow size distribution. The optical extinction spectra can be simulated using Mie scattering theory, and can be used as an in situ diagnostic tool for following the growth of particles during precipitation reactions. Using results of particle diameter measurements by other methods, information on the refractive index of the particles can be retrieved, indicating a highly porous internal structure of the spheres. Distinct features in the experimental and simulated spectra have been interpreted as to arise from circumference and diameter resonance effects in the particles. The simultaneous observation of these two effects allows one to estimate size and solid volume fraction from simple transmission spectra by application of an effective-medium model for the simulation parameters. The potential of application of Mie resonance effects for selective light screening or as pigments are discussed.
Dynamic composite elastic medium theory. Part II. Three-dimensional media
Authors: Kaelin Bruno , Johnson Lane R.
Published: July 2002

Non-self-consistent and self-consistent methods of estimating velocity and attenuation of P waves and S waves at all frequencies for heterogeneous media with three-dimensional inclusions are formulated using the scattering functions of the individual inclusions. The methods are the generalization of methods for one-dimensional media presented in the first paper of this series. The specific case of spherical inclusions is calculated with the exact scattering function and compared with several low frequency approximations. The self-consistent estimates are consistent with Berryman’s low frequency approximation. We present spectra and wave forms of materials with solid and liquid inclusions in a solid matrix. The results show that the exact scattering functions are required to adequately describe wave propagation at all frequencies. The analysis of liquid inclusions demonstrates that viscous damping may become important only if scattering attenuation due to spherical pores is small.
Effect of parallel-perpendicular kinetic energy coupling under effective mass approximation at heterostructure boundaries in a quantum wire
Authors: Lee Byoungho , Kim Kyoung-Youm
Published: July 2002

At heterostructure boundaries under effective mass approximation, parallel momentum conservation results in coupling between the perpendicular and parallel kinetic energies. We discuss the effect of this on the perpendicular kinetic energy quantization inside a heterostructure quantum wire and as its application, we deal with its effect on electron wave coupled devices.
A method for in situ characterization of tip shape in ac-mode atomic force microscopy using electrostatic interaction
Authors: Olsson L. , Lin N. , Yakimov V. , Erlandsson R.
Published: July 2002

We present a method for in situ characterization of the tip shape in atomic force microscopes that can operate in noncontact ac mode. By sweeping the voltage between tip and sample while recording the sample position as it is regulated to give a constant force gradient, we obtain curves giving information about the tip geometry. The measurements were performed in ultrahigh vacuum using electrochemically etched tungsten tips against a surface of doped silicon. Our results show that the sphere model gives a good description of the interaction, and that the radii we obtain are consistent with data from scanning electron microscopy. The method can also be used to estimate the value of the Hamaker constant and the contact potential between tip and sample.
Effect of composition and annealing on structural defects in high-dose arsenic-implanted Si1−xGex alloys
Authors: Gaiduk P. I. , Tishkov V. S. , Shiryaev S. Yu. , Larsen A. Nylandsted
Published: July 2002

The evolution of structural defects in high-dose arsenic-implanted (peak concentration 9×1020–2.7×1021 cm−3), epitaxially grown, relaxed Si1−xGex (0.15⩽x⩽0.50) during rapid-thermal annealing (RTA) has been investigated as a function of composition x and RTA using transmission-electron microscopy. The formation of monoclinic GeAs precipitates is confirmed and examined at high RTA temperature. A new type of three-dimensional defect (which we call a “hair-like” defect) is found in the alloys of x=0.15–0.25. Such defects have not been observed in pure silicon and their presence in SiGe alloys is suggested to result from interactions between dislocations and GeAs precipitates. The effects of heating rate, annealing ambient, and implantation dose on both the formation of GeAs precipitates and the removal of dislocations are investigated. A possible influence of point defects on precipitate formation is discussed.
Dynamic behavior of dislocations in InAs: In comparison with III–V compounds and other semiconductors
Authors: Yonenaga I.
Published: July 2002

The dynamic behavior of α and β dislocations in both undoped and impurity-doped InAs crystals is investigated as a function of stress and temperature by means of the etch pit technique. Suppression of the generation of dislocations from a surface scratch is found in S doped InAs, which is interpreted in terms of dislocation locking due to impurity clusters and/or impurity-defect complexes as has been observed in other III–V compounds. α dislocations move faster than β dislocations in the undoped and impurity-doped InAs. S donors reduce the velocities of both α and β dislocations. On the other hand, Zn acceptors enhance the velocity of α dislocations and reduce the velocity of β dislocations. Such features are related to an electronic state of the dislocations in the elementary process of the motion. The measured velocities are expressed using a simple empirical equation as a function of stress and temperature in the same manner as for other semiconductors. The linear dependence of the activation energies for dislocation motion on the band gap energy shows a clear distinction dependent on the group of semiconductors, i.e., the elemental and IV–IV compound, III–V compound, and II–VI compound.
First-principles study of structural stability and electronic properties of Sb/GaSb(111) semimetal–semiconductor superlattice
Authors: Zhou Yu-mei , Wang E. G.
Published: July 2002

The structural stability and electronic properties of a (Sb2)2/(GaSb)2(111) semimetal–semiconductor superlattice are investigated by a first-principles all-electron linearized augmented plane-wave method within the local spin density functional approximation. When bulk values are used the two interfacial distances D1 and D2 are energetically unfavorable. The fully optimized structure shows that the bond lengths of Sb–Ga and Sb–Sb at interfaces are 1.3% and 2.8% longer than their bulk values, respectively. Further electronic band calculations of the stable (Sb2)2/(GaSb)2(111) superlattice show that the system has semimetallic behavior. A p-like interface band is observed below the Fermi level.
The formation of ohmic and Schottky enhanced contacts to III–V compound semiconductors via the exchange mechanism: A combined thermodynamic and kinetic model
Authors: Swenson D. , Jan C.-H. , Chang Y. A.
Published: July 2002

A methodology is presented for altering the electrical properties of contacts to III–V compound semiconductors through the use of controlled interfacial chemical reactions. The process by which this is accomplished has been termed the exchange mechanism. Under this mechanism, a metallization consisting of a transition metal and a group III element (denoted TIII′) is reacted with the semiconductor (denoted IIIV) in such a way that the group III elements of the metallization and substrate, III′ and III, are exchanged without the formation of any new phases. This leads to the creation of a ternary semiconductor alloy S, or IIIXS′III1−XSV, at the contact interface, where XS denotes the mole fraction of III′V in the semiconductor alloy phase S. The electrical properties of the contact subsequent to the exchange reaction then correspond to those of a metal/IIIXS′III1−XSV interface. Moreover, by employing ternary metallizations of varying composition M, or TIIIXM′III1−XM (where XM represents the mole fraction of TIII′ within the ternary metallic phase M), the resulting interfacial composition of the semiconductor and hence the electrical properties of the contact may be varied in a systematic fashion. Rather stringent thermodynamic and kinetic criteria must be met in order for the exchange reaction mechanism to be operative. These factors are described using a quantitative model. The limitations of applicability of the model are also discussed.
Anomalous evolution of torque curves with the applied magnetic field in amorphous ribbons due to surface roughness
Authors: Tejedor M. , Garcı́a J. A. , Carrizo J. , Elbaile L. , Mira J. , Rivas J.
Published: July 2002

The behavior of torque curves of amorphous ribbons, in which their amplitude decreases with the applied magnetic field has been obtained in some samples of Vitrovac 6150. An explanation is given for this behavior based on the analysis of the superposition of orthogonal uniaxial magnetic anisotropies caused by the oriented surface roughness of the amorphous ribbons. Based on this explanation, important information on the magnetic anisotropies of amorphous magnetic ribbons is obtained and the values of the involved anisotropy constants are calculated.
Positron beam studies of argon irradiated CdS thin films
Authors: Amarendra G. , Narayanan K. L. , Rao G. Venugopal , Viswanathan B. , Nair K. G. M. , Vijayakumar K. P.
Published: July 2002

Depth profiling studies of defects in CdS thin films using a low energy positron beam are reported. CdS films of 1 μm thickness on a glass substrate have been grown using the chemical bath deposition method and irradiated with 140 keV Ar ions to doses of 5×1014 and 5×1016 cm−2, respectively. The Doppler broadening line shape S parameter in as-grown and irradiated films has been monitored as a function of positron beam energy Ep. S vs Ep curves have been analyzed, using a positron diffusion model in terms of annihilations at surface, epithermal and bulk states. The S parameter at the surface (Ss) is found to be significantly higher than that in the bulk. This is understood as due to positron trapping at a large concentration of Cd vacancies in the surface region, which act as acceptors. The observed reduction of Ss with increasing Ar ion dose seems to indicate the formation of antisite defects in the surface region, brought about by irradiation. At sample depths corresponding to the peak damage layers, the observed behavior of the S parameter indicates that no large vacancy clusters are formed. Isochronal annealing studies have been carried out to investigate the thermal stability of defects in irradiated and as-grown samples.
Luminescence properties of thin film Ta2Zn3O8 and Mn doped Ta2Zn3O8
Authors: Rack Philip D. , Potter Michael D. , Kurinec Santosh , Park Wounjhang , Penczek John , Wagner Brent K. , Summers Christopher J.
Published: July 2002

Blue luminescence from Ta2Zn3O8 and green luminescence from Mn doped Ta2Zn3O8 has been observed under low voltage cathodoluminescent excitation. In this article, the luminescence mechanisms of Ta2Zn3O8 and Mn doped Ta2Zn3O8 are discussed in detail. The results suggest that the intrinsic blue luminescence of Ta2Zn3O8 results from a metal-to-ligand transition, whereas the green luminescence of Mn doped Ta2Zn3O8 results from the Mn 4T1–6A1 transition. The suppression of the blue intrinsic luminescence in Mn doped Ta2Zn3O8 suggests that efficient energy transfer from the host material to the Mn occurs. This energy transfer phenomenon is also discussed by comparing the photoluminescence excitation spectra of both thin film materials. Finally, the relative efficiency versus voltage and current density is demonstrated and discussed pertaining to field emission device operation.
Electroreflectance measurements of electric fields in ordered GaInP2
Authors: Perkins J. D. , Zhang Y. , Geisz J. F. , McMahon W. E. , Olson J. M. , Mascarenhas A.
Published: July 2002

Ordered Ga0.52In0.48P alloys (GaInP2 for simplicity) grown on miscut [001] GaAs resemble monolayer superlattices with alternating Ga- and In-rich layers along either the [1̄11] or [11̄1] directions. Recent calculations suggest that, in fully ordered GaInP2, an intrinsic ordering-induced electric field of order 1600 kV/cm should exist. In partially ordered samples, as can actually be grown, the expected field is reduced to 400 kV/cm. For such a strong internal electric field, clear Franz–Keldysh Oscillations (FKOs) would be expected in an electroreflectance measurement. We report electroreflectance measurements of ordered GaInP2 layers measured at T=100 K. For all samples measured, no FKOs are observed in the absence of an additional external dc bias voltage. At the lowest bias voltages for which FKOs are seen, the internal electric field in the GaInP2 layer, determined from the FKOs, is ∼60 kV/cm along the [001] direction corresponding to ∼100 kV/cm along the ordering direction. Hence, we conclude that, at least in the organometallic vapor phase epitaxy grown samples studied here, any net macroscopic internal electric field in the GaInP2 layer is less than ∼100 kV/cm along the ordering direction.
Effects of oxygen content on properties of silicon oxide films prepared at room temperature by sputtering-type electron cyclotron resonance plasma
Authors: Furukawa Katsuhiko , Liu Yichun , Nakashima Hiroshi , Gao Dawei , Kashiwazaki Yasuhiro , Uchino Kiichiro , Muraoka Katsunori , Tsuzuki Hirohisa
Published: July 2002

We present the study of the effects of gas-phase oxygen fraction on properties of silicon oxide films prepared in a sputtering-type electron cyclotron resonance plasma discharge. Dielectric breakdown characteristics of the films are considerably improved by an increase in oxygen flow rate, FO2, with a constant Ar gas flow rate of 16 sccm. Films prepared at FO2 of more than 6 sccm have good dielectric breakdown fields of 9–11 MV/cm, which are comparable with those of high quality thermally grown SiO2. Moreover, the increase of FO2 improved structural properties of the films. Detailed measurements of their composition and microstructure were carried out using ellipsometry, chemical etch rate measurement in a mixture of HF, H2O, and HNO3 (P etch), x-ray photoelectron spectroscopy (XPS), and infrared (IR) spectroscopy techniques. Ellipsometry and XPS measurements indicated that films prepared at FO2 of more than 3 sccm are stoichiometric. Dependence of the IR spectra and P etch rate on FO2 of more than 3 sccm indicated that distribution of Si–O–Si bond angle and Si–O bond strain in the films decreases with an increase of FO2. Based on the behavior of the Si–O–Si bond angle and refractive index of the films, we discuss the improvements in structural properties in terms of growth kinetics.
Controlling magnetic and transport properties of granular alloys through Joule heating
Authors: da Silva F. C. S. , Ferrari E. F. , Knobel M.
Published: July 2002

Melt-spun Cu–Co ribbons are annealed by linearly varying current Joule heating. During the annealing, the electrical resistance is measured in order to follow the structural transformations within the samples. The resistance versus current curves show a characteristic behavior for all samples studied. This fact is used to specify optimum conditions to obtain the best nanostructure which displays the maximum giant magnetoresistance ratio.
Localization of excitons by potential fluctuations and its effect on the Stokes shift in InGaP/InP quantum confined heterostructures
Authors: Aı̈t-Ouali A. , Chennouf A. , Yip R. Y.-F. , Brebner J. L. , Leonelli R. , Masut R. A.
Published: July 2002

We present investigations of the temperature evolution of the photoluminescence (PL) and optical absorption spectra of a series of tensile-strained InGaP/InP multiple quantum wells (MQW) samples. As in previous work on compressive-strained InAsP/InP MQW, the results support the assignment of the low temperature PL transitions to recombination from excitonic band-tail states. The energy of such transition is redshifted with respect to the free exciton recombination energy. This results in a large apparent energy difference between PL and optical absorption peaks which is, at 6 K, about 5 meV in the coherently strained samples and less than 1 meV in the partially relaxed ones. The analysis of the low temperature PL line shape which we present enables the determination of the excitonic band-gap energy for all the samples. The difference between the energy of the optical absorption transition and the excitonic band-gap energy thus determined gives a measure of the Stokes shift arising from thermalization effects alone. The values of the Stokes shift thus obtained are in better agreement with the sharpness of the optical absorption transitions which indicate samples of high crystalline quality.
Observation of bolometric optical response in superconducting microwave meander lines
Authors: Cho Shinho , Choi Deok , Fetterman Harold R.
Published: July 2002

The change in the resonant frequency of YBa2Cu3O7−x meander lines under thermal and optical perturbations was used to determine whether pair breaking effects are induced either by bolometric or nonbolometric responses. The frequency-domain measurements were performed by monitoring the change of both the microwave resonance mode frequency and frequency width. The variation of the resonant frequency induced by two external perturbations shows a quadratic dependence on each perturbation in the range of 0.28Xc–0.56Xc. A perturbation to the fourth dependence is observed above 0.63Xc, where Xc is either the critical temperature or the critical optical pulse energy at which resonance can no longer be distinguished. The results suggest that the photoresponse of the superconducting meander line is bolometric due to laser heating.
Magnetic force microscopy of avalanche dynamics in magnetic media
Authors: Walsh Brian , Austvold Shane , Proksch Roger
Published: July 2002

The slow dynamics of the micromagnetic structure in a CoPtCr thin film were imaged in an applied field with a magnetic force microscope (MFM). Images taken over time scales ranging from minutes to weeks revealed slow micromagnetic avalanches along the direction of the applied field. The avalanche sizes followed a power law distribution in a manner consistent with Bak, Tang, and Weisenfeld’s concept [Phys. Rev. Lett. 59, 381 (1987); Phys. Rev. A 38, 364 (1988)] of “self-organized criticality.” The avalanches appeared to be the result of both random (thermal) excitations and micromagnetic perturbations from the tip of the MFM. We extended the sandpile model of Bak, Tang, and Weisenfeld to include a periodically rastering drop site (analogous to raster scanning a MFM tip over a sample). Although the sequence of avalanche events in the sandpile model depended on the manner in which the grains were dropped, the underlying distribution of avalanche sizes remained the same for both random and periodic grain-dropping methods. This suggests that the distribution of the magnetic avalanches reflects an underlying structure, independent of how the switching is initiated.
Relationship between deep-level centers and stoichiometry in semi-insulating gallium arsenide
Authors: Lin Lanying , Chen NuoFu , Zhong Xingru , He Hongjia , Li Chengji
Published: July 2002

Experimental results have shown the fact that the deep-level centers in semi-insulating GaAs decrease with the improvement in stoichiometry. The electrical resistivity doubles when the concentration of EL2 centers decreases to a half. The microgravity-growth experiments also show that improved crystal stoichiometry results in a decrease of deep-level centers.