bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency dependence of the hysteresis loops in amorphous magnetoelastic wires controlled by longitudinal stress and torsional strain (abstract)
Authors: Wun-Fogle Marilyn , Savage H. T.
Published: July 2002

We have imposed static longitudinal stresses (LS) and torsional strain (TS) on 100-mm-long amorphous wires (diameter=125 μm) of composition Fe77.5Si7.5B15. The quasistatic magnetization takes place by a bifurcation process (the moment ‘‘jumps’’ as a function of field) that is a function of LS and TS. We find that the sample reaches apparent (not complete) saturation at the demagnetizing field and demagnetizes at a field dependent on LS for a fixed TS created by a uniform twist of 85° over the 100-mm-long sample. In the parameter range from 9 to 25 MPa the demagnetizing bifurcation (shown in Fig. 1) moves to higher fields as LS is decreased. The apparent coercivity is a function of LS and TS. For magnetization curves taken at frequencies from 10 to 300 Hz, the hysteresis loop changes because of anomolous eddy current losses in the sample. This effect is so large that the loops at 10 Hz are visibly different from the quasistatic loops. We have measured the area of the hysteresis loops as a function of LS at 100 Hz and 300 Hz. For values of LS from 8 to 66 MPa with a TS of 85°, the area of the hysteresis loop increases linearly with LS. These observations are important for torque transducers. A theory describing the losses and bifurcation process will be presented.
Dynamic thermal profiling in magneto-optic recording thin films
Authors: Schultz Mark D. , Freedman Joshua M. , Weng Robert S. , Kryder Mark K.
Published: July 2002

The thermal behavior of magneto-optic thin films is critical to their performance. The determination of thermal profiles which result in magneto-optic thin films when they are being written has up to now been limited to theoretical calculations occasionally matched against the thresholds for writing domains into the films. Such ‘‘switching temperature’’ experimental data is of limited use due to the dependence of magnetic domain shape, size, and placement on much more than just a simple isotherm location. Through the use of a high-speed (10-ns time resolution) observation system developed for examining dynamic magnetic processes in magneto-optic materials, the thermal profiles created in these films were observed as the profiles developed during the application of laser heating pulses. Images of the profiles caused by both static and scanning laser pulses are shown. Comparison of static pulse data with theoretical computations indicates that the thermal conductivity of these magneto-optic films is approximately an order of magnitude below the bulk value.
The magnetization of superconducting La1.85Sr0.15Cu1−xVxO4−∂
Authors: Wallace J. B. , Payzant E. A. , King H. W. , Stroink G. , Dahn D. C.
Published: July 2002

Oxides of the type La1.85Sr0.15Cu1−xVxO4−∂ were prepared with vanadium contents, x, ranging from 0 to 0.10 in increments of 0.01. Vanadium entered into solid solution in the tetragonal K-phase structure at concentrations up to x=0.05. Further additions of vanadium resulted in the formation of SrV5O11 and an orthorhombic distortion of the K-phase structure. An increase in the irreversibility of the magnetization at 4.2 K, at a vanadium concentration of x=0.01, was attributed to increased flux pinning due to solid solution hardening. Reduced magnetic irreversibilities and critical temperatures were observed at higher vanadium concentrations, and attributed to a loss of strontium from the K phase due to the formation of SrV5O11.
Meissner, shielding, and flux loss behavior in single-crystal YBa2Cu3O6+x
Authors: Bennett L. H. , Swartzendruber L. J. , Kaiser D. L.
Published: July 2002

Meissner effect measurements were performed on a nearly cubic single crystal of YBCO, which exhibited a predominant (110) twin habit, by cooling the crystal from above Tc to 10 K in an applied field H of 10 Oe. A significant difference was observed for H applied parallel and perpendicular to the c axis, but little difference could be seen for H perpendicular and parallel to the twin boundaries. After cooling from above Tc in 10 Oe to 10 K, the field was reduced to zero. The magnetization changed sign, increasing by ∼15 G, which is the value expected for complete flux expulsion by a crystal of this geometry. Magnetization measurements were then made as the temperature was raised back to 100 K. Again, there is a significant difference for the results with H parallel and perpendicular to the c axis, especially above 60 K, with only a small (but possibly meaningful) difference for perpendicular and parallel to the twin boundaries.
Magnetic properties of La2Cu1−xMxO4 with M=Zn and Ni (abstract)
Authors: Ting S. T. , Weaver J. , Wise P. , Crow J. E.
Published: July 2002

The temperature and concentration dependence of the magnetic susceptibililty of La2Cu1−xMxO4 with M=Zn and Ni and 0≤x<0.10 has been measured for 1.8≤T≤400 K. The 3D antiferromagnetic order in La2CuO4 is highly sensitive to doping, introducing additional holes by increasing x in La2−xSrxCuO4 from 0 to 0.02 suppresses the TN from 240 to 0 K. The Néel temperature of La2Cu1−xZnxO4 with x=0.0, 0.01, 0.02, 0.04, 0.06, 0.08, 0.10 has been determined by using the temperature derivative of the magnetic susceptibility measured on random polycrystalline and aligned polycrystalline samples. TN is depressed rapid with Zn doping with an initial depression rate dTN/dxZn≊20 K. Similar studies of Ni-doped La2CuO4 will be presented and discussed.
Isolated ferromagnetic bonds in the two-dimensional spin-1/2 Heisenberg antiferromagnet (abstract)
Authors: Lee Kong-Ju-Bock , Schlottmann P.
Published: July 2002

Several mechanisms for high-temperature superconductivity invoke the strong antiferromagnetic correlations within the CuO planes. In particular, properties of the high-Tc compounds are believed to be related to defects in the planes, e.g., static vacancies, ferromagnetic bonds, and mobile holes. We consider the effects of isolated ferromagnetic links on an otherwise antiferromagnetic square lattice. The addition of holes in La2CuO4 (by doping with Sr) introduces a local ferromagnetic exchange coupling between Cu spins. We describe the Heisenberg antiferromagnet within the linearized spin-wave theory; the problem of a single ferromagnetic bond embedded in an otherwise antiferromagnetic square lattice can then be solved exactly. The procedure is similar to the one employed in Ref. 1 for a vacancy. The longitudinal terms, involving Sz, tend to enhance the ordered staggered magnetic moment, competing in this way with the transverse terms, involving Sx and Sy, which represent the quantum fluctuations and suppress the sublattice magnetization. The interplay between these two interactions is discussed as a function of the ferromagnetic coupling strength.
Computation of superconductor critical current densities and magnetization curves
Authors: Hodgdon M. L.
Published: July 2002

Using a constitutive law for superconductor hysteresis and the ideas of the critical state model, a system of equations is developed for the critical current density Jc, the equilibrium magnetization Me, the upper and lower portions MU and ML of the major hysteresis loop, and their derivatives with respect to the applied field. The constitutive law consists of the differential equation dB/dH=α(H)s(Ḣ)[f(H)−B]+g(H) for Ḣ≠0, and a rule governing the abrupt changes observed at the turning points of H. For the case presented here in which f, g, and α have analytic forms, the constitutive law yields an easily differentiable expression for the major loop. Hysteresis curves computed from this constitutive law are shown to be in good agreement with experiments. Exponential approximations are given for the critical current densities computed by this method for a polycrystalline sample of YBa2Cu3Ox between 5 and 40 K.
Microwave absorption measurements of high temperature superconductors using a coplanar waveguide
Authors: Krafft C. S. , Beckner C. F.
Published: July 2002

A wideband microwave absorption spectrometer with a coplanar waveguide transmission line was used to characterize the magnetic field dependence of microwave absorption in high temperature superconductors. This technique is useful for the nondestructive evaluation of high temperature superconductor bulk and thin film samples prior to their application in microwave devices and sensors. Results are presented for various types and forms of samples including bulk YBCO, laser-ablated thin film YBCO, and Ag-doped YBCO wire.
Brown paradox of micromagnetic theory (abstract)
Authors: Pinto Marc A.
Published: July 2002

The Brown paradox1 concerns an order of magnitude discrepancy between micromagnetic theory and experiments: the theoretical nucleation field for an elongated iron specimen is −500 Oe whereas the measured value for high-quality iron whiskers is about 0.1 Oe. It is a fairly widespread view that the paradox may be resolved by the inclusions of imperfections but no quantitative solution has yet been produced. In this work a new attack on the paradox is presented based on a detailed examination of the thermodynamical basis of the theory.
Magnetic and structural phase transitions in UAu2Si2
Authors: Rebelsky L. , McElfresh M. W. , Torikachvili M. S. , Powell B. M. , Maple M. B.
Published: July 2002

We report magnetic susceptibility, neutron, and x-ray diffraction measurements on polycrystalline UAu2Si2. Magnetic susceptibility data show the existence of two phases below 50 K. Since no superlattice neutron peaks were observed within the sensitivity of the apparatus we conclude that the system is not a canted ferromagnet, as was suggested earlier. On the basis of the temperature dependence of the neutron and x-ray intensity we discuss a possibility that UAu2Si2 undergoes two structural phase transitions, at 48 and at 18 K and that these transitions are correlated with the magnetic state of the material.
Magneto-optic disks for high-density recording with a shorter wavelength laser (abstract)
Authors: Takahashi M. , Nakamura J. , Kirino F. , Miyamura Y. , Ohta N. , Suzuki R.
Published: July 2002

In order to increase the recording density of the optic disks, it is necessary to shorten the wavelength of the laser beams. Recently, Pt/Co multilayered films have been investigated for the optic recording media using the laser with the wavelength shorter than 600 nm because of the high Kerr rotation. It is, however, difficult to write the magnetic domains with the diameter less than 0.5 μm stably due to the small coercivity and the uniaxial anisotropy field. On the other hand, it is easy to write the domains with the diameter of 0.3 μm on the conventional media of TbFeCo. To use this advantage, the exchange-coupled double-layered film of (Pt/Co)/(TbFeCo) has been developed. The disk structure is Al-alloy/nitride/(Pt/Co)/TbFeCo/nitride/substrate. The multilayered film of Pt/Co has been optimized to write smaller domains and have a higher Kerr rotation for high output signal. Consequently, the thickness is 20 Å/5 Å, respectively. It has been confirmed that the 0.3 μm φ domains can be written clearly and the figure of merit √Rθk is twice as large as that of the conventional TbFeCo at the short wavelength region of 400–500 nm. Finally, the read/write characteristics have been tested with the SHG laser of 532 nm.
Control of exchange coupling for overwritable MO media by sputtering conditions (abstract)
Authors: Hayashi Kazuhiko , Shimizu Shoji , Okada Osamu
Published: July 2002

The sputtering condition effect on interface wall energy σw in overwritable MO media has been investigated. The media consist of a polycarbonate substrate, a SiN underlayer, a TbFe or TbFeCo memory layer, a NdFeCo exchange coupling control layer, a GdTbFeCo complementary layer, and a SiN protective layer. Underlayer SiN sputter etching effect on σw and Ar gas pressure effect on σw for memory layer deposition were examined. The sputter etching rate was fixed to 13 Å/min. By measuring saturation magnetization and switching field for the complementary layer in the M-H loop, σw between the memory layer and the complementary layer was calculated according to the exchange-coupled double-layer theory.1 With increasing sputtering etching time, σw changes from 0.6 to 1.7 erg/cm2 at about 5-min sputter etching. Correspondingly, not only does memory layer coercive force Hc change from 6.5 to 1.8 kOe, but also coercive squareness S* is improved. FE-SEM observation reveals that the structureless uniform memory layer is formed when the SiN underlayer surface is treated by sputter etching. With decreasing Ar gas pressure, S* is improved and film becomes structureless. Based on these facts, the authors conclude that sputtering condition control to form magnetic films without fine microstructures is effective for reducing interface wall energy σw. A 45-dB overwrite C/N ratio has been obtained at 11.3 m/s linear velocity and 7.4-MHz carrier frequency by controlling these sputtering conditions, as well as by adjusting film compositions and thickness.
Temperature variation in the resistivity of palladium
Authors: Vuillemin J. J. , Khellaf A.
Published: July 2002

The resistivity in palladium is thought to have a significant spin-fluctuation component at low temperatures which varies as T2. Measurement of the intrinsic value of this component of the resistivity requires a high-quality specimen. The resistivity in high-purity, single-crystal Pd is reported for the temperature range 15–300 K. Electron-phonon scattering adequately accounts for the total resistivity at intermediate and higher temperatures. The resistivity due to other mechanisms is estimated at lower temperatures and compared with calculations of the spin-fluctuation resistivity. The results suggest that the low-temperature T2 component of the resistivity is attenuated relatively suddenly as the temperature increases beyond about 25 K.
Analysis of periodic magneto-optic multilayers
Authors: Ledbetter C. H. , Parker M. R.
Published: July 2002

Recent published work has indicated Kerr rotation enhancement in periodic magneto-optic (MO) multilayers as compared to values obtained for single magnetic films. This paper describes both computational and analytical investigations of MO multilayers. Computational studies indicate only marginal gains in shot-noise-limited signal-to-noise ratio in periodic magnetic film-dielectric spacer systems over the corresponding values for fully optimized single magnetic films.
Magneto-optic properties of uranium-based compounds
Authors: Kirby Roger D. , Shen J. X. , Woollam J. A. , Sellmyer D. J.
Published: July 2002

Uranium-based compounds often show interesting magnetic properties and large polar Kerr rotations. Because of this, the wavelength and temperature dependencies of the polar Kerr rotation in several uranium-based compounds, including UMn2Ge2, UFe2, and UGa2, have been investigated. The Mn moments order ferromagnetically in UMn2Ge2 below 380 K, and while the U moments do not order ferromagnetically until the temperature is below 150 K. The measurements presented here show that the size of the Kerr rotation increases from 0.05° at room temperature to 0.15° when the U moments are ordered. The wavelength dependence of the Kerr rotation between 500 and 1000 nm is rather weak. UGa2 orders ferromagnetically at 130 K, and a Kerr rotation of 0.2° at 85 K and 632.8 nm can be measured, with the rotation increasing to 0.4° at 1000 nm. UFe2 orders ferromagnetically at 180 K, and the Kerr rotation (85 K, 632.8 nm) is 0.17°. These magnetic and optical properties are discussed in terms of the electronic states of uranium.
Micromagnetics of passivated and unpassivated iron particles
Authors: Schabes Manfred E.
Published: July 2002

Initial results of a micromagnetic study on elongated iron particles are presented. A numerical micromagnetic model is utilized to compute the magnetization configurations and switching fields for both the homogeneous metal particle and the inhomogeneous passivated particle from first principles. The volume of the passivated particle is divided into a metallic core and a passivated shell with significantly reduced magnetic-moment density. The calculations show that the topology of the magnetization configurations is similar to those of homogeneous γ-Fe2O3 particles. The switching field is higher for the passivated particles as compared to the homogeneous particle depending on the exchange interaction in the passivation layer. The enhancement of the switching field is explained in terms of reduced torques and reduced demagnetization at the passivated particle ends.
Field response of surface spins on Co-adsorbed γ-Fe2O3 (abstract)
Authors: Parker F. T. , Berkowitz A. E.
Published: July 2002

The Mössbauer spectrum of a small particle (250 Å diameter), partially reduced γ-Fe2O3 sample coated sequentially with 57Fe and Co was obtained in a 1.8-kOe field transverse to the γ-ray propagation direction at room temperature. The adsorbed 57Fe, less than a monolayer thick, provided half the Mössbauer signal. The data were fit with a distribution in hyperfine fields. The relative areas of the Mössbauer lines of each subspectrum are in the ratio 3:2p:1:1:2p:3, with p the common polarization; large p implies small HK.1 For several possibilities of B-site to A-site population ratios and variations in core isomer shifts, the resultant spectrum least-squares fit values of p were found to be about 1.4. Theoretical calculations1 of composite Mössbauer line intensities based on a model2 of a rigid random-spin shell and a core with its p determined by the anisotropy field obtained1 from magnetization vs applied field measurements yield a composite p≊1.2. Since this value is substantially smaller than experimentally observed, the outer shell spins are not rigidly pinned even in this weak applied field. A simple theoretical free-energy minimization calculation of a linear chain of ferrimagnetically coupled atoms in an external field applied along the hard axis shows that a high anisotropy ‘‘shell’’ will cause a parabolic dependence of sublattice spin angle vs position along the chain, with the maximum deviation from collinearity of a few degrees.
Hole dynamics in the copper oxide planes (invited) (abstract)
Authors: Trugman S. A.
Published: July 2002

The physics of a hole doped into the Mott insulating state of the CuO2 planes is studied in a large variational space. The hole quasiparticle that forms is quite different from a free electron by virtue of the cloud of spin flips (with respect to the background antiferromagnet) that it carries with it. The momentum dependence of the quasiparticle energy is unusual: ε(k) is lowest at nonzero momentum, and has an anisotropic dispersion. At finite doping, the quasiparticles are assumed to fill the rigid band described by the single-hole ε(k), forming a weakly interacting Fermi gas. Normal state properties of the high-temperature superconducting oxides, such as La2−xSrxCuO4, are calculated in the relaxation time approximation. Good agreement with experiment is obtained for the magnetic susceptibility, Hall coefficient, thermopower, specific heat, and plasma frequency as a function of both doping x and temperature.1
An investigation of the Pd-In-Ge nonspiking Ohmic contact to n-GaAs using transmission line measurement, Kelvin, and Cox and Strack structures
Authors: Wang L. C. , Wang X. Z. , Hsu S. N. , Lau S. S. , Lin P. S. D. , Sands T. , Schwarz S. A. , Plumton D. L. , Kuech T. F.
Published: July 2002

The Pd-In-Ge nonspiking Ohmic contact to n-GaAs has been investigated using the transmission line, the Kelvin, and the Cox and Strack structures. It has been found that a layered structure of Pd/In/Pd/n-GaAs with 10–20 Å of Ge imbedded in the Pd layer adjacent to the GaAs can lead to a hybrid contact. When the Ohmic formation temperature is above 550 °C, a layer of InxGa1−xAs doped with Ge is formed between the GaAs structure and the metallization. When the Ohmic formation temperature is below 550 °C, a regrown layer of GaAs also doped with Ge is formed at the metallization/GaAs interface. The contact resistivity of 2–3×10−7 Ω cm2 for this contact structure is nearly independent of the contact area from 900 to 0.2 μm2. Low-temperature Ohmic characteristics and thermal stability are also examined.
Determination of oxygen content and carbonate impurity in YBa2Cu3O7−x by diffuse reflectance infrared spectroscopy
Authors: Merzbacher C. I. , Bonner B. P.
Published: July 2002

Samples of YBa2Cu3O7−x with x ranging from ∼0 to 0.65 have been analyzed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in the midinfrared region (400–6000 cm−1). Spectral line shapes vary gradually as a function of oxygen stoichiometry, and the reflectance at 400 and 1000 cm−1 decreases linearly with decreasing oxygen content. Spectra of samples that were incompletely synthesized or exposed to a 4% CO2 atmosphere at 650 °C clearly indicated the presence of carbonate. DRIFTS is therefore a quick, nondestructive method for determining oxygen content in YBa2Cu3O7−x powders, and for detecting carbonate species due to synthesis error or reaction with CO2-bearing atmosphere.
The characteristics of a conducting polymer gel by use of a radical initiator
Authors: Morita Shigenori , Kawai Tsuyoshi , Yoshino Katsumi
Published: July 2002

Soluble poly (3-alkylthiophene) can be transformed into a conducting polymer gel by using a radical initiator. The volume of the sample in chloroform shrinks drastically upon introduction of ethanol, and also by doping. The shrinkage ratio depends on the preparation conditions of the sample. The spectrum of the gel also changes reversibly as the volume varies.
Investigation of the interfacial defects in a nanocrystalline Ni-P alloy by positron annihilation spectroscopy
Authors: Sui M. L. , Xiong L. Y. , Deng W. , Lu K. , Patu S. , He Y. Z.
Published: July 2002

A nanocrystalline Ni-P alloy prepared by the crystallization method has been studied by using positron lifetime spectroscopy. The lifetime results and the corresponding interfacial defects in the sample are discussed in comparison with those of the nanocrystalline iron materials prepared by compacting ultrafine powders.
New degrees of freedom in resonant tunneling heterostructure devices
Authors: Coon D. D. , Sorar E. , Bandara K. M. S. V. , Urban N.
Published: July 2002

Lateral degrees of freedom in resonant tunneling heterostructure devices are investigated in a model which omits the usual assumption that the electric field and current density are laterally uniform. Relaxation of spatially nonuniform configurations of field and current into the usual uniform configurations is examined. For certain device parameters and operating conditions, stable nonuniform configurations are found in addition to the conventional uniform configurations. An eigenvalue criterion for stability is established. The possibility of nonuniform configurations with spatially localized oscillation is also discussed.
Microstructure changes after annealing of undoped and Cr-doped liquid-encapsulated Czochralski-grown GaAs
Authors: Visser E. P. , Weyher J. L. , Giling L. J.
Published: July 2002

Microinhomogeneities in semi-insulating, liquid-encapsulated Czochralski (LEC) GaAs crystals were investigated by selective photoetching and spatially resolved photoluminescence at 1.8 K. The interaction of point defects with dislocations was studied by annealing the samples in a metalorganic chemical vapor deposition reactor under AsH3 pressure. The changes in microstructure, induced by the anneal process, were investigated for both undoped and Cr-doped crystals. A weakening of the photoetching contrast after annealing was observed for both types of crystals, with no essential difference between undoped and Cr-doped ones. The overall near-band-gap photoluminescence (PL) intensities were found to have increased after annealing. This increase amounted to about one order of magnitude for the Cr-doped crystals, and two orders of magnitude for the undoped ones. In addition, for the undoped samples the contrast in PL intensity between dislocated areas and the undisturbed crystal matrix was increased by the anneal process. Analysis of the local PL spectra taken at different regions on these samples showed a strong enhancement of acceptor-bound exciton (A0,X) transitions relative to donor-bound exciton (D0,X) transitions, especially at dislocated areas. Furthermore, a new emission for LEC GaAs at 1.5116±0.0003 eV was also found to be strongly enhanced at these regions. The PL results are explained by the disappearance of deep, nonradiative, excess As-related PL killer centers during annealing. The disappearance is proposed to proceed via diffusion of interstitial As atoms and the formation of As precipitates, for which dislocations act as nucleation centers. Additional deep level photoluminescence spectra of the 0.65 and 0.80-eV emission bands are shown to be in accordance with the proposed model.
Epitaxial growth of CoSi2 on (111)Si inside miniature-size oxide openings by rapid thermal annealing
Authors: Hsu H. F. , Chen L. J. , Chu J. J.
Published: July 2002

Epitaxial growth of CoSi2 on (111)Si inside two-dimensional and linear oxide openings by rapid thermal annealing has been investigated by transmission electron microscopy. Both annealing temperature and time were found to be critical in obtaining 100% epitaxy. The size of oxide openings and annealing temperature were found to exert strong influences on the morphology of epitaxial CoSi2 on silicon. The faceting of CoSi2 was found to occur at a lower temperature inside oxide openings of smaller size. The change in morphology of epitaxial CoSi2 with the size of oxide openings in the present study indicated that interfacial energy and/or stress, in addition to the surface energy, are important in determining the morphology of epitaxial CoSi2 on (111)Si.
Advantages of two-step annealing for 1-MeV arsenic-ion-implanted layers in silicon
Authors: Inada T. , Iwasaki H. , Koyama Y.
Published: July 2002

The effects of two-step annealing, rapid thermal annealing (RTA) followed by furnace annealing (FA), on the crystalline and electrical properties of buried n-type layers formed in (100) Si by As implantation at an incident energy of 1 MeV have been investigated. The crystalline properties have been examined by Rutherford backscattering measurements and by transmission electron microscopic observations. The electrical properties have been studied by differential Hall measurements. A comparison between the annealing process of two-step annealing and that of RTA or FA alone is made. The experimental results obtained from this work clearly show that buried n+ layers without residual defects can be formed by the use of RTA at 1050 °C followed by FA at 1000 °C, and that they are difficult to be formed by one-step annealing of FA or of RTA.
Point defect concentrations in InGaAsP quaternary alloys
Authors: Ichimura Masaya , Wada Takao
Published: July 2002

Point defect concentrations in InGaAsP grown from liquid phases were calculated. Vacancies and antisites were taken to be dominant defects. The calculated antisite concentrations decrease with increasing band gap, while the vacancy concentrations are weakly dependent on composition. Although development of dislocations is known to be easier in InGaAsP lattice matched to GaAs than in those lattice matched to InP, the difference in the vacancy concentration between them is small when their growth temperatures are assumed to be the same. However, a high growth temperature usually adopted for InGaAsP on GaAs will result in larger vacancy concentrations.
Photocapacitance and photoconductance of Bi-doped ZnO
Authors: Simpson J. C. , Cordaro J. F.
Published: July 2002

The density of occupied interface states as a function of energy in nonohmic polycrystalline Bi-doped ZnO was obtained using photocapacitance measurements. Peaks in the interface states’ densities were observed at depths of 2.46 and 2.79±0.08 eV from the bottom of the conduction band. The combination of these two states was found in photoconductance measurements on Bi-doped samples of ZnO and not found in undoped samples; thus, these states were assumed to be related to interface states that arise from doping with Bi.
Low-power pulsed-laser annealing of implanted GaAs
Authors: Vitali G. , Rossi M. , Karpuzov D. , Budinov H. , Kalitzova M.
Published: July 2002

Low-power annealing by a pulsed laser is used to recover the structure of low-dose implanted (100) GaAs crystals. Reflection high-energy electron diffraction with variable glancing incidence is employed to detect the structural changes at different depths in the specimens. The depth dependence of the damage is studied in more detail by Rutherford backscattering analysis. The annealing results depend on the irradiation conditions. A laser energy window below the melting threshold is found within which the structure can be restored to about as high degree of crystallinity as the virgin one, without any visible surface damage. A simple theoretical estimate shows that the temperature rise of the material is far below the melting threshold. This rise is too short in time to cause substantial dopant diffusion; however, it can enhance well the point-defect mobility.
High-field electron-transport properties in an In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As double heterostructure
Authors: Shigekawa Naoteru , Furuta Tomofumi , Arai Kunihiro
Published: July 2002

Effects of the parameters characterizing the electron-transport properties in an In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As double heterostructure are theoretically investigated using the Monte Carlo approach. The calculated results are compared with the previously measured electron velocity versus electric-field relationship for the investigated structure. It is found that the effects of the Γ-valley nonparabolicity factor and the intervalley energy separations in In0.53Ga0.47As are the most remarkable within the investigated parameters.
Infrared and ellipsometric studies of amorphous hydrogenated carbon films
Authors: Sunil D. , Vankar V. D. , Chopra K. L.
Published: July 2002

Amorphous hydrogenated carbon films have been deposited on a powered electrode by decomposition of acetylene in an rf discharge. Infrared and spectroscopic ellipsometry have been used to study the bonding characteristics and optical properties of these films. The films possess a mixture of bonding configurations which are very sensitive to discharge conditions. Large changes in refractive index and extinction coefficients have been observed. These changes are associated with ion-induced structural modifications and hydrogen incorporation during the deposition process.
The effect of auxiliary light on the performance of the NaCl:OH− color center laser
Authors: Carrig Timothy J. , Pollock Clifford R.
Published: July 2002

Spectroscopic and laser performance data show that the choice of auxiliary light used to optimize the performance of the NaCl F+2:O2− color center laser has little impact on the tuning range or output power of the system. When F-band auxiliary light is used to process the laser crystal a transient absorption due to F−2 centers occurs, but this feature disappears during laser operation. No such transients appear when other auxiliary light sources are used.
Photoluminescence and electrical studies of Si-doped AlxGa1−xAs grown on various substrate orientations by metalorganic chemical vapor deposition
Authors: Tang X. , Visser E. P. , van Lin P. M. A. , Giling L. J.
Published: July 2002

The photoluminescence and electrical behavior of Si-doped AlxGa1−xAs has been investigated on various GaAs substrate orientations viz. (100)2°(110), (111)Ga, and (110). The growth has been performed by metalorganic chemical vapor deposition with a systematic variation of the silane input mole fraction, the V/III ratio and the aluminum fraction. It is found that the (110) layers show an abnormal electrical behavior especially in carrier concentration and mobility. On these layers also two new PL peaks have been found. By correlating all possible pair defects with the peaks as a function of the experimental conditions, these two peaks could be assigned to originate from a VAs-AsGa complex and a VAs-SiAs or VAs-SiGa complex. The abnormal electrical results for (110) can be explained by the presence of these complexes.
Reactive metal overlayer formation on high-temperature superconductors at 20 K
Authors: Kimachi Y. , Hidaka Y. , Ohno T. R. , Kroll G. H. , Weaver J. H.
Published: July 2002

Photoemission results demonstrate that atom deposition of Ti, Cr, and Cu at 20 K on the high-temperature superconductors (HTSs) dramatically reduces interfacial reaction relative to 300 K growth but does not completely eliminate it. Thin Ti-O or Cr-O layers are formed during atom deposition of ∼2 Å of Ti or Cr on YBa2Cu3O7 or Bi2Sr2Ca1Cu2O8 because oxygen is withdrawn from the Bi-O and/or Cu-O layers. Interfacial reactions are diffusion limited at 20 K, and metal overlayers nucleate on the reacted layers. These metal layers are more uniform than those grown at 300 K because clustering is suppressed. There is no additional disruption for Cr/HTS interfaces when warmed to 300 K, but increased disruption is evident for Ti/HTS interfaces. The differences reflect the stabilities of Cr and Ti in contact with their own interfacial oxide. Cu atom deposition on Bi2Sr2Ca1Cu208(100) at 20 K also leads to much less disruption than observed for deposition at 300 K.
In situ formation of Y-Ba-Cu-O epitaxial films by 40.68-MHz rf magnetron sputtering
Authors: Tsai R. Y. , Chu J. J. , Tseng M. R. , Wang L. P. , Teng W. C. , Wu P. T.
Published: July 2002

The in situ epitaxial growth of the Y-Ba-Cu-O films on MgO (001) was carried out by 40.68- MHz rf magnetron sputtering with an on-axis single target. It appeared that the rf discharge strongly affected film composition, crystallinity, superconductivity, and reproducibility. Highly orientated superconducting films with the c-axis perpendicular to the substrate surfaces and having zero resistance transition temperature of 78.2 K were obtained without a post-annealing.
Magnetic trapping properties of high-T
c superconductors
Authors: Xu Yunhui
Published: July 2002

The field and the time dependencies of trapped magnetic field, Btr(He) and Btr(t), at 77 K in solid and hollow cylinders of YBa2Cu3O7−y have been investigated. The plateaus in plots Btr(He) are observed for all the investigated cylinders. In a short hollow cylinder we observed a negative trapped field. It is very unusual and never observed before. Various time dependencies of Btr(t) are obtained: following a logarithmic law or remaining constant. Again in the case of hollow cylinder, an unexpected time dependence of Btr(t) is demonstrated. Instead of a decay, the trapped field increases with time after the applied field is switched off. However, these ‘‘anomalous’’ phenomena can be explained most naturally by the weak link granular superconductivity.
Physical behavior of ruthenium in silicon
Authors: Zhou Jie , Wu Ji-an , Lu Li-wu , Han Zhi-yuong
Published: July 2002

We report the physical behavior of Ru atom in silicon in this paper. Two energy levels E(0.58) and H(0.34) were observed. The pure substitutional Ru in silicon was responsible for the H(0.34), and the E(0.58) was introduced by a complex of a Ru atom and a vacancy (or vacancies). By use of scattered wave-Xα (SW-Xα) cluster method the theoretical calculation of electronic states for substitutional Ru atom in silicon has been performed. The results obtained were compared with those of experimental measurements.
Inversion induced in silicon by corona-charged PVDF, P(VDF/TriFE), and P(VDF/ClTriFE)
Authors: Andry P. , Filion A. Y. , Blain S. , Rambo A. , Caron L. G.
Published: July 2002

Polyvinylidene fluoride, as well as two of its copolymers made with trifluoroethylene and cholorotrifluoroethylene, respectively, is cast onto p-type silicon substrates and positively corona charged. This produces a strong induced inversion at the oxide-passivated silicon surface. Field-effect transistor structures are used to monitor the strength and stability of the inversion, which is seen to decay in a period of time dependent on the polymer and on the fabrication conditions. When a thicker (200–500 Å) thermally grown SiO2 barrier layer is included between the silicon and polymer film, the devices are much more stable, remaining in inversion for many weeks. The physical and dielectric properties of the solution-cast polymer films are studied in order to gain a better understanding of the initial charge distributions and of the charge-transport properties associated with inversion layer decay in the thin oxide (12 Å) structures. Instability in these devices appears to be more appropriately described by a space-charge-limited current model than by a Schottky emission model.
Theory of optical anisotropy in quantum-wire arrays on vicinal substrates
Authors: Citrin D. S. , Chang Yia-Chung
Published: July 2002

The effective bond-orbital model is used to calculate the conduction- and valence-subband structures and optical matrix elements of recently grown epitaxially buried GaAs/AlGaAs/AlAs quantum-wire arrays. Band mixing, band anisotropy, and lateral intermixing of Ga and Al during growth strongly affect the energy levels and features in the optical data. Strong anisotropy in the optical properties is predicted for the case of perfect lateral interfaces while for cases with significant lateral intermixing, the optical properties show weak anisotropy. Our results are compared with the observed photoluminescence excitation spectra.
Sequential resonant and nonresonant tunneling in GaAs/AlGaAs multiple quantum wells
Authors: Helgesen P. , Finstad T. G. , Johannessen K.
Published: July 2002

Sequential resonant and nonresonant tunneling have been investigated in doped GaAs/AlGaAs multiple quantum wells. Negative differential resistance attributable to high field domains expanding through the structure are observed. It is argued that the conductance mechanism is changing with increasing bias, from resonant ground-state tunneling in the low bias regime to nonresonant ground and ground to first exited state in the oscillating differential resistance regime. At higher bias the evolution from nonresonant to resonant tunneling is studied. Calculated tunneling currents are in good agreement with the measured currents both for on and off resonance.
Molecular-beam-epitaxial growth of III-VI layered semiconductor GaSe on amorphous SiO2
Authors: Kambe N.
Published: July 2002

Crystalline thin films of III-VI layered semiconductor GaSe have been grown on amorphous SiO2 substrates using molecular-beam-epitaxy techniques. This attests possible formation of a crystalline/noncrystalline heterostructure when inactive GaSe surfaces are involved. Reflection-high-energy-electron-diffraction and (00ℓ ) x-ray diffraction results show in-plane and stacking ordering, respectively. Although the coexistence of multiple crystalline domains in plane is suggested, the photoluminescence spectra are comparable to those of a GaSe bulk single crystal. Excitonic emission with the full-width at the half magnitude of 5 nm (19 meV) is observed at 591 nm (2.10 eV) at 77 K.
Raman scattering in AlxGa1−xAsySb1−y quaternary alloys
Authors: Jaw D. H. , Cao D. S. , Stringfellow G. B.
Published: July 2002

The Raman scattering of AlGaAsSb quaternary alloy semiconductors has been investigated for the first time. The AlGaAsSb quaternary alloys, including the AlGaSb ternary alloys, were grown by organometallic vapor phase epitaxy. The dependence of the long-wavelength longitudinal-optical phonon frequencies on the composition are reported. The first-order Raman spectra show a two-mode behavior for the AlGaSb ternary alloys and a three-mode behavior for the AlGaAsSb quaternary alloys. For AlGaAsSb, two peaks located below 300 cm−1 are assigned as the GaAs- and GaSb-like LO modes. Two peaks observed above 300 cm−1 are assigned as the ‘‘AlAs plus AlSb’’ LO and TO modes. A broad peak observed below 200 cm−1 is assigned as a disorder-activated acoustic phonon mode.
Novel hysteresis effects in Nb/AlOx/Al/AlOx/Nb tunnel junctions
Authors: Blamire M. G. , Kirk E. C. G. , Somekh R. E. , Evetts J. E.
Published: July 2002

Measurements on current-biased Nb/AlOx/Al/AlOx/Nb double tunnel junction devices with very thin central Al layers show a novel double hysteretic structure in the subgap region. Similar junction structures have previously exhibited very large nonequilibrium effects; the effects reported here appear close to and above the equilibrium critical temperature of Al. A model is presented in which the hysteresis is shown to arise from a transition from finite to zero voltage across one barrier on increasing current, due to the nucleation of an inhomogeneous state in the ultrathin central Al layer in which normal and superconducting states coexist. This reverse switching effect is shown to arise from the self-shunting effect of low-gap regions. Predictions of this model are shown to agree with the experimental data.
Growth kinetics of amorphous interlayers by solid-state diffusion in ultrahigh vacuum deposited polycrystalline Nb and Ta thin films on (111)Si
Authors: Cheng J. Y. , Chen L. J.
Published: July 2002

The growth kinetics of amorphous interlayer (a-interlayer) formed by solid-state diffusion in ultrahigh vacuum deposited polycrystalline Nb and Ta thin films on (111)Si have been investigated by cross-sectional transmission electron microscopy. The growth of a-interlayers in Nb/Si and Ta/Si systems was found to exhibit similar behaviors. The growth was found to follow a linear growth law initially in sample annealed at 450–500  °C and 550–625  °C for Nb/Si and Ta/Si, respectively. The growth then slows down and deviates from a linear growth law as a critical thickness of a-interlayer was reached. The activation energy for the linear growth of a-interlayer was found to be 0.8±0.3 and 0.9±0.3 eV for Nb/Si and Ta/Si, respectively. The correlations among difference in atomic size between metal and Si atoms, growth rate and activation energy of the linear growth, critical and maximum a-interlayer thickness, the largest heat of formation energy for crystalline silicides, the calculated free energy difference in forming amorphous phase as well as atomic mobility in Ti/Si, Zr/Si, Hf/Si, Ta/Si, and Nb/Si systems are discussed.
Canonical aberration theory for calculating higher-order chromatic aberrations
Authors: Ximen Jiye
Published: July 2002

Canonical aberration theory has been developed in previous papers by the author. In the present study, the canonical aberration theory has been used to deal with first- and third-order chromatic aberrations (including position and momentum aberrations at an arbitrary observation plane) for rotationally symmetrical optical systems. All first- and third-order chromatic aberrations have been expressed in canonical matrix representations, which are general in nature and appropriate for computer calculations.
Critical concentration for ferromagnetism in binary Fe alloys
Authors: Sostarich M.
Published: July 2002

A survey of data on the critical concentration xc for the onset of ferromagnetism in binary FexM1−x alloys, with M being a nonmagnetic component, is given. The xc values range from about 0.05 to over 0.7, with the bulk of the data for amorphous alloys centered at about 0.4. For random binary alloys a model which takes into account the effects of local environment, percolation, and frustration yields critical concentrations quite similar to those encountered in many amorphous systems.
Functional dependence of the imaginary part of the initial permeability of the YIG family of ferrites
Authors: Bush Gary G.
Published: July 2002

This paper reports the experimental results of an investigation of the relationship between the composition of certain yttrium iron garnets (YIG) and the resulting initial permeability. A complimentary study of the compositional dependence of the real part of the permeability has been reported in the literature. A simple theory reported in a previous paper to explain the dependence of permeability on an applied quasistatic magnetic field predicts a dependence on the magnetization. With the previous work and the data to be reported here, the dependence of the complex permeability on magnetization has been confirmed for substitutions of calcium, vanadium, and indium. These substitutions were chosen to reduce the magnetization while maintaining the linewidth. A substitution of indium alone increases the magnetization above that of prototype YIG and agrees with the phenomenological theory for the imaginary part of permeability, but not for the real part.
Measurement theory of the cavity characteristic equation method and experimental research on microwave permeability for ferrites
Authors: Zhu Sheng-chuan , Chen Hai-ying , Wen Fan-ping , Qin Yuan , Liu Jin
Published: July 2002

The characteristic equation for a TE102 or TE104 rectangular cavity loaded by a ferrite slab in the middle has been derived on the basis of electromagnetic theory. This characteristic equation is used in a new measurement technique with improved precision, theoretical inference, and sample loading. A lot of experimental research and computational analysis have been done for the characteristic equation method. Microwave magnetic spectrum researches have been carried out for a series of polycrystalline microwave ferrites.
A contribution to the theory of beam-induced current characterization of dislocations
Authors: Pasemann L.
Published: July 2002

A new procedure of calculating the electron-beam-induced current contrast of a crystal defect is presented which yields an exact solution for the contrast of a surface-perpendicular dislocation both in a Schottky diode and in a planar p-n diode. The calculations are based on the bulk recombination model describing a dislocation as a cylindrical inhomogeneity (with radius rd) where the total lifetime (τ′) is lower than that outside the cylinder. Evaluations of the exact solution for the dependence of the contrast on the electron range show that (i) the input parameters of the model, rd and τ′, can be consistently determined from the characteristic of the contrast versus the electron range, and (ii) the traditionally used first-order recombination strength is not a generally valid measure of the recombination activity of a surface-perpendicular dislocation.
Observation of surface modification and nucleation during deposition of diamond on silicon by scanning tunneling microscopy
Authors: Turner K. F. , Stoner B. R. , Bergman L. , Glass J. T. , Nemanich R. J.
Published: July 2002

The surface topography of silicon substrates after the initial stages of diamond growth, by microwave plasma enhanced chemical vapor deposition, has been observed by scanning tunneling microscopy. The initial surfaces were polished with diamond paste before deposition to enhance nucleation, and the scratches were examined. After one half hour growth, the surface showed additional topography over all regions, and widely spaced faceted structures were detected which were attributed to diamond nuclei. The surface between nuclei showed increased roughness with increased deposition time. The faceted nuclei were found along the scratches. The nuclei showed facets which were smooth to within 5 Å. Fingerlike ridge structures were found extending from and in-between some of the nuclei. These structures indicate a mechanism of the lateral diamond growth. The electronic properties of the surface were probed by local I-V measurements, and characteristics attributable to SiC were observed.