bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of the glycine-metal nitrate combustion method for preparing barium ferrite (abstract)
Authors: Wade Manson L. , Agresti David G. , Hai Jenny O. , Griffin Robin , Hong Yang-Ki
Published: July 2002

A combustion-synthesis method1 has been adapted2 for the preparation of barium ferrite. In this method, stoichiometric amounts of metal-nitrate solutions are mixed and glycine (aminoacetic acid) is added at specific glycine/metal-nitrate ratios. The resulting solution is then heated until autoignition (combustion). The combustion products for several G/N ratios have been analyzed by XRD, Mössbauer spectroscopy, and EDS; they consist of hematite and/or maghemite with traces of residual barium nitrate that vary according to the G/N ratio. Packing experiments reveal a dramatic variation in density of the powdered combustion products ranging from 0.08 to 0.87 g/cm3 for G/N=0.4 to 0.7 molar, respectively. SEM micrographs show what appear to be sintered ceramic flakes of undetermined particle shape. Barium ferrite is obtained with subsequent heat treatment. Along with TEM, SSA, and VSM analysis of the combustion products and the converted barium ferrite, a DTA determination of minimum phase-change temperature from γ-Fe2O3, Ba(NO3)2, and α-Fe2O3 to barium ferrite for specific G/N ratios will be given. Using these data, we will discuss optimum conditions for the preparation of pure barium ferrite with this combustion method, according to the physical and magnetic properties desired for the final product.
Ferromagnetic resonance and transverse susceptibility measurements on particulate recording media (abstract)
Authors: Orth Th. , Pelzl J. , Chantrell R. W. , Veitch R. , Jakusch H.
Published: July 2002

The FMR absorption of different particulate recording tapes was investigated at microwave frequencies in the X band and Q band using temperatures from 70 to 400 K. The FMR spectra as a function of the external magnetic field were recorded for four different orientations of the static and high frequency magnetic fields with respect to the tape. Particular interest of the experimental and theoretical study was devoted to the interaction fields between the particles, texture effects within the tape sample and the effective anisotropy fields. Tape samples with different particle materials, varying packing densities and orientation ratios were prepared. The shape and line position of the FMR spectra obtained are strongly dependent on the pigment material and the tape parameters mentioned above. The experimental data are compared with theoretical calculations, based on a phenomenological model and a computer simulation. This comparison gives information on the orientational distribution of the particles, which is the most important source for inhomogeneous line broadening, the mean interaction, and anisotropy fields which govern the line position, the effective magnetization of the tape, and the relaxation time. The influence of the crystalline anisotropy can be investigated via temperature dependent measurements. The results are proved by additional transverse susceptibility measurements.
Texture dependence of power losses in nonoriented SiFe electrical steels
Authors: Bertotti G. , Ban G. , Abbruzzese G.
Published: July 2002

Epstein-frame loss measurements were performed on 3.2% Si-Fe nonoriented strips cut along and transverse to the rolling direction, in the frequency range 10–100 Hz and at various peak inductions between 0.3 and 1.6 T. The behavior of hysteresis loss Ph and excess loss Pe vs peak induction B and frequency f was worked out and analyzed. The B dependence exhibits a rich structure, as a consequence of the coupling between magnetic domains and the grain structure. The f dependence follows the law Pe∝f3/2, in agreement with previous experiments. These results are interpreted in the frame of a generalized Preisach model recently proposed. It is shown that the excess loss dependence on B is in direct relation with that of the permeability B/H along the virgin magnetization curve. The results of numerical calculations of model predictions are presented and discussed in comparison with experimental data.
Effect of annealing on the magnetics of NiFeMo thin films (abstract)
Authors: Narayan P. B. , Silkensen R. D. , Dey S.
Published: July 2002

NiFeMox thin films, where 0<x<0.1, are considered for usage in high frequency magnetic sensors. Since the device manufacturing process requires that the thin film be exposed to temperatures above 200 °C, its thermal stability is an important criterion for device reliability.1 NiFeMox thin films, with a thickness of 75 nm and 0<x<0.1, were sputter-deposited on single crystal silicon wafers and their magnetic properties were measured after annealing for 2 h at various temperatures up to 350 °C. At lower Mo content, the anisotropy field Hk decreased with annealing temperature,2 whereas at higher Mo content, Hk showed an initial decrease and then an increase above 300 °C. With increasing temperature, the angle of dispersion θk showed a monotonous increase at lower Mo content. At higher Mo content, θk decreased at higher temperatures. At all Mo contents, the magnetostriction increased at higher temperatures. All as-deposited films had a residual tensile stress of about 200 MPa. At temperatures between 250 and 300 °C, the in situ tensile stress sharply increased. Above 300 °C, the stress started decreasing due to grain growth, the amount of decrease being dependent on the Mo content. The films were found to have much higher residual tensile stress (around 2000 MPa) after annealing, depending on the Mo content. The stress was calculated by measuring the wafer curvature with a laser. The microstructure was studied with transmission electron microscopy (TEM). ESCA indicated preferential oxidation of surface iron in NiFeMo during annealing. Changes in magnetics of NiFeMo were correlated to and explained by microstructural and compositional changes.
Volume dependence of Anderson hybridization in cubic CeCd and CeAg
Authors: Monachesi P. , Andreani L. C. , Continenza A. , McMahan A. K.
Published: July 2002

We have undertaken a first-principles theoretical study of the Anderson hybridization in cubic CeCd and CeAg as a function of volume reduction. We present results for the hybridization width Δ(ε) in both the J=5/2 multiplet and in the Γ8, Γ7 crystal field states of the f1 Ce configuration. We also calculate the hybridization contribution to the magnetic transition temperature. This is found to increase with pressure but is smaller than the experimental values, indicating that the Coulomb exchange contribution to the magnetic coupling is not negligible in these compounds.
Magnetic properties of an isolated missing link in the anisotropic two-dimensional Heisenberg antiferromagnet
Authors: Haas Stephan
Published: July 2002

We consider an isolated missing link in an anisotropic Heisenberg antiferromagnet of spin S and coupling constants Jz≥Jxy on a square lattice. The interplay between longitudinal terms, involving Sz , and transverse terms, representing the quantum fluctuations, of the Hamiltonian is investigated. Within the linearized spin-wave approximation (LSWA), we find that the local magnetic moment is slightly enhanced at the sites adjacent to the impurity link. It is also shown that quantum fluctuations on neighboring sites are drastically reduced in the vicinity of the impurity. Using perturbation theory we argue that the longitudinal zero-temperature susceptibility (χ∥) vanishes up to O(hz4). The static transversal susceptibility [χ⊥ (T=0)] is obtained within the LSWA, and is shown to be enhanced due to the defect.
Studies of magnetization currents in YBa2Cu3O7−x superconductors
Authors: Liu Jianxiong , Chen In-Gann , Weinstein Roy , Xu Jianchun
Published: July 2002

The trapped magnetic field of melt-textured Y-Ba-Cu-O samples has been studied. The measured field distributions can be well reproduced by a simple two-current model consisting of a constant surface current and a constant volume current. If the sample is maximally magnetized (saturated case), the remnant sample magnetic moment can be calculated from the two-current model, and the results agree with vibrating sample magnetometer measurements to typically 10%. Jc of the sample can then be obtained. The application of the two-current model to the analysis of the nonsaturated case is also reported, for both field-cooled and zero-field-cooled samples. The experimental data show the general features predicted by the Bean model, which, however, has to be modified to account for the data quantitatively.
Critical processing parameters for bulk and wire high temperature superconductors for applications (invited) (abstract)
Authors: Chu C. W.
Published: July 2002

To make true large applications of high temperature superconductors (HTS’s), one requires not just a large critical current density (Jc) and high transition temperature (Tc), but also large total current (Ic is the JcA, where A is the cross sectional area) and large total current length (Icl where l is the length) of an HTS which can be further shaped into a usable form, e.g., disk, bar, cylinder, or wire. The large anisotropy, short coherence length, and large penetration depth of HTS’s pose serious challenges to efforts to enhance the Jc, Ic, or Icl of HTS’s. Melt-texturing technique by slow cooling through the peritectic temperature has proven to be effective in removing large-angle grain boundaries detrimental to Jc in HTS samples of small size; but many problems remain. The short coherence length reduces the pinning potential for magnetic fluxoids and also renders ineffective the nonsuperconducting dispersion in the HTS matrix to enhance pinning through the conventional metallurgical method. Defects of atomic scale acting as pinning centers to raise Jc have been obtained through irradiation by high energy particles and in situ chemical decomposition. However, in most of these studies Jc was determined only by magnetic measurements, not by transport techniques. We have therefore carried out a systematic study on the melt-texturing of HTS’s in both bulk and wire forms. We have identified major processing parameters in reducing the microcracks, increasing the dimensions of the bulk HTS, controlling the grain alignment, improving the chemical homogeneity, enhancing the processing rate, and controlling the epitaxial growth of HTS’s in an Ag sheath. Effects of irradiation by various types of particles of different energies on Jc determined both by magnetic and transport techniques have also been examined. These results will be presented and discussed, following a brief review on the current status of bulk and wire processing of HTS’s.
Antiferromagnetic domains in UPdSn
Authors: Nakotte H. , Brück E. , de Boer F. R. , Svoboda P. , Tuan N. C. , Havela L. , Sechovský V. , Robinson R. A.
Published: July 2002

The magnetization of a single crystal of the hexagonal antiferromagnet UPdSn has been studied in fields up to 5 T in order to examine the energetics associated with antiferromagnetic domains. The magnetic unit cell is orthorhombic, so there are three possible domain orientations within the parent lattice. The low-temperature magnetization reflects both spin-flop transition and domain-depopulation effects. Although the interpretation of our results is complicated by the coexistence of these two phenomena, we can conclude that the domain occupancies are history dependent below the spin-reorientation transition which lies at 25 K, but history independent between this transition and TN=40 K. Comparing magnetization results with those from previous neutron-diffraction studies, we propose a magnetic phase diagram for UPdSn.
Computer simulation of magnetization states in a magnetic thin film consisting of magnetostatically coupled grains with randomly oriented cubic anisotropy
Authors: Murata Osamu , Saito Kaz , Nakatani Yoshinobu , Hayashi Nobuo
Published: July 2002

Computer simulations are performed to model the magnetically soft but isotropic behavior of an Fe-Si-Al alloy film. Solving the Landau–Lifshitz–Gilbert equation under the periodic boundary condition, magnetization states are simulated in a single layer film represented by a two-dimensional array of closely packed hexagonal prisms. Each prism represents a single crystal grain which is assumed to have randomly oriented cubic anisotropy and similar magnetic parameters as those of an Fe-Si-Al alloy film. It is also assumed that the magnetization is always uniform inside each grain and the exchange coupling among grains is zero. It is observed that the film without an external field shows a demagnetized state with considerably dispersed domain configuration where the characteristic wall and vortex structures are formed. It is also observed that the film is switched by applying an external field of which intensity depends on the cubic anisotropy constant of the grains. Analyzing the sum of exerting torque to the magnetization of grains, it is derived that the torque by cubic anisotropy is completely balanced with that by demagnetizing field.
Dimensional crossover and anisotropy effects in the magnetization of Fe(110)/Ag(111) superlattices
Authors: Macció M. , Pini M. G. , Politi P. , Rettori A.
Published: July 2002

Recent experimental data, showing a dimensional crossover of the T-dependent magnetization in MBE-grown Fe(110)/Ag(111) superlattices with different Ag spacer thickness, are theoretically reanalyzed, using a Heisenberg model of localized spins with intraplane and interplane exchange interactions and including easy-plane and easy-axis surface anisotropies. The latter ones are shown to play an important role in the stabilization of the long range order, more evident for large thickness of the Ag spacer. The spin-wave dispersion curves and the magnetization are calculated in the framework of a Green’s function method and the correct asymptotic forms for the temperature dependence of the spin deviation in the quasi-2D regime (T ln T) and in the 3D one (T3/2) are obtained.
Investigations of surface and bulk spin wave modes in as-prepared and annealed FeNi multilayers by spin wave resonance
Authors: Kordecki R. , Meckenstock R. , Pelzl J. , Nikitov S.
Published: July 2002

Magnetic multilayers consisting of alternating layers of polycrystalline Fe and Ni were investigated by spin wave resonance experiments at room temperature. Nonpropagating surface spin wave modes, as well as standing volume modes, could be observed in the perpendicular field configuration. The appearance of the surface modes is connected with the surface anisotropy at the bottom and the top layers of the structure. The experimental SWR spectra have been compared with the results of calculations. Values of the surface anisotropy, the effective spin wave stiffness constant, and the effective magnetization of the multilayered structure were deduced from the measured spectra for as-prepared and annealed samples. The results are compared with those obtained by torque measurements.
Kerr domain contrast and hysteresis as a tool for determination of the coupling strength of double soft magnetic films
Authors: Niedoba H. , Heyderman L. J. , Hubert A.
Published: July 2002

A method to determine the coupling strength of double soft magnetic films has been developed. It involves double films with anisotropy induced along different directions in the two magnetic films and is based on a measurement of the magnetization deviation from the induced easy axes either from Kerr domain contrast, or from hysteresis curves.
Band structure of multilayer structures and the strength and sign of the magnetic interlayer coupling (abstract)
Authors: Fairbairn W. M.
Published: July 2002

The interactions between magnetic layers in multilayer structures are affected strongly by the topography of the Fermi surface because of its influence on the electron-mediated RKKY coupling between pairs of spin-bearing atoms. Layered metallic structures have real-space unit cells that are considerably larger than those of their constituent metals so that their band structures and Fermi surfaces are more complex, with the occurrence of superzones as in magnetically ordered rare earths, for example. Interzonal electronic transitions can be as significant in their contributions to the coupling as the more commonly discussed intrazonal transitions.1 A simple but realistic parametrization of the electron energy in the multilayer structure, with varying thicknesses of the nonmagnetic spacer layer, is used to analyze the interaction between the magnetic layers.2 The overall width of the constituent bilayers characterizes the superzone geometry of the Fermi surface and the detail of the layering within the bilayers determines the local properties of the Bloch wave functions. Both of these affect the strength and the oscillatory period of the coupling.
Nuclear magnetic resonance of molecular beam epitaxially grown Co-Cu superlattices that exhibit large magnetoresistance
Authors: Lord J. S. , Kubo H. , Riedi P. C. , Walker M. J.
Published: July 2002

The 59Co NMR has been measured for superlattices of Co(15 Å)/Cu (7 or 18 Å) grown with either a Au or Cu buffer layer between the substrate and the superlattice. As was reported earlier the Co (15 Å)/Cu (7 Å) (Au) superlattice has the largest magnetoresistance (ΔR/R∼26%) known for a MBE grown Co/Cu multilayer. The NMR measurements show that the Au-based superlattices have very flat interfaces and (111) orientation, two features which were supposed to preclude a large value of ΔR/R, and that the average strain in the Co layers is greater for a Au than a Cu buffer layer.
Effects of the application of magnetic field during rapid solidification on structure and magnetic properties of Mn55Al45 magnetic materials
Authors: Hasegawa Masashi , Harada Nobumichi , Asai Shigeo
Published: July 2002

A twin-rolls process for the rapid solidification of metals in a static magnetic field up to 14 kOe has been developed using original composite twin-rolls which are portions of a magnetic circuit. The effects of a magnetic field applied during rapid solidification on the structure and magnetic properties of Mn55Al45 magnetic materials, particularly of the τ single phase materials, have been investigated. The x-ray diffraction technique, optical microscopy, and the hysteresis loop measurement were employed to clarify the effects. It was found that the applied magnetic field decreased the solidification speed and subsequently stabilized the ferromagnetic metastable τ phase in an appropriate rotation rate. In addition, the application of magnetic field led to the increase of the coercivity of the τ single phase materials. This effect is considered to be attributable to the difference in the degree of order of the τ phase in the absence and presence of a magnetic field during rapid solidification.
The temperature dependence of the variation in the complex permeability of yttrium iron garnet (YIG) with applied magnetic field
Authors: Bush Gary G.
Published: July 2002

In previous work the variation with applied magnetic field of the real and imaginary parts of the permeability of high purity yttrium iron garnet in the form of a polycrystalline sintered ferrite has been measured and phenomenologically modeled. These measurements were done at room temperature. The present work explores these effects over a temperature range of −60 to 180 F.
The complex permeability of a high purity yttrium iron garnet (YIG) sputtered thin film
Authors: Bush Gary G.
Published: July 2002

In previous articles various ion implantations were used to explore the magnetic characteristics of high purity single crystal Y3Fe5O12 (YIG) on GGG. The work presented here is an investigation of the rf characteristics of a high purity YIG film that is not a single crystal and is laid down as a thin film on a flexible substrate. The measured properties are quite different from the sintered form. The film has relatively low losses in the very high and ultrahigh frequencies.
The magnetic and structural properties of pulsed laser deposited epitaxial Mn1−xZnxFe2O4 ferrite films (abstract)
Authors: Williams C. M. , Chrisey D. B. , Lubitz P. , Grabowski K. S.
Published: July 2002

Since modern high frequency device technology is shifting towards planar miniaturization, ferrite films will play an important role in facilitating the design and fabrication nonreciprocal monolithic integrated devices such as isolators and circulators. The authors have examined magnetic and structural properties for a series of pulsed laser deposited (PDL) single crystal MnZn-ferrite films. The films were epitaxially grown on (001) MgO at substrate temperatures of 300 °C, 400 °C, 600 °C, and 800 °C in an oxygen partial pressure of 30 mTorr. The film microstructure, crystal structure, and composition were characterized by SEM, x-ray diffraction and atomic absorption spectroscopy, respectively. The magnetocrystalline anisotropy constant K1, uniaxial anisotropy constant Ku, saturation magnetization Ms, and coercive force Hc were examined by torque and vibrating sample magnetometry. Ferrimagnetic resonance measurements were made on the films to obtain the linewidth ΔH. A comparison of the magnetic, structural, and chemical properties shows that K1 and Ms scale with the Fe2+ ion concentration and that Ku, Ms, and ΔH are very sensitive to the microstructure. The values of K1, Ms, and ΔH obtained for films deposited at 800 °C were compared with those of bulk MnZn-ferrite and found to exceed the bulk values (Table I), thus making PLD ferrite films very attractive for nonreciprocal device applications.
Observation of intrinsic electrical conduction in barium ferrite (abstract)
Authors: Wittenauer M. A. , Sato H. , Nyenhuis J. A. , Friedlaender F. J.
Published: July 2002

Basal plane electrical resistivity measurements on single crystals of barium ferrite (BaM) are reported as a function of temperature. The room temperature resistivity increases by an order of magnitude over the ‘‘as grown’’ value after thermal cycling to 1200 °C. In addition, a sharp change in slope above room temperature is observed in a plot of log(ρ) vs 1/T. These results are consistent with a model in which the carrier concentration undergoes an extrinsic to intrinsic transformation upon heating. The activation energy in the intrinsic regime is 1.1 eV, the largest value reported for BaM. An extrapolation from the high temperature data suggests that the room temperature intrinsic resistivity of single crystalline BaM is greater than 1014 Ω cm.
Effect of magnetostriction on bias fields in self-biased MR heads
Authors: Dee Richard H. , King Darwin D.
Published: July 2002

The effect of magnetostriction on the bias conditions in self-biased magnetoresistive (MR) heads is reported. In self-biased MR heads where the bias field is derived from the sense current, the optimum bias point is where the head delivers the maximum output per unit input current. The optimum point depends on the element and head geometry, demagnetizing effects, and the permeability of the MR film. During head construction and operation the MR film is subjected to various sources of stress which can directly affect the permeability of the film and thus the position of this optimum bias point. Many self-biased MR heads were fabricated using MR elements made from thin (<1000 Å) oriented NiFe films with the magnetostriction coefficient close to but varied around zero. The results show quite a marked effect and a correlation between as-deposited measurements and completed device performance. When the magnetostriction is negative the bias current has to be driven to higher values to achieve the defined optimum. This is attributed to an increase in the net value of Hk (permeability decrease) by compressive stresses. The converse is found to be true for positive magnetostriction films.
A renormalization group study of the 2D antiferromagnetic Heisenberg model
Authors: Lin H. Q. , Campbell D. K. , Pan C. Y.
Published: July 2002

We study the problem of the existence of long-range staggered magnetic order in the antiferromagnetic Heisenberg model on the square lattice by a renormalization group analysis. We first map the Heisenberg model onto an approximate effective model, described by the Hamiltonian: H = ∑Lj=1S(j)S(j + 1) + ∑Lj=1( − 1)j‖J(j)‖S(0)S(j), where S(0) represents a single spin located in the center of the ring. We show that the Ji tend to non-zero values as one increases the block size by successive renormalizations, thus establishing the existence of long-range staggered magnetic order in the effective model. We discuss the implications of this result for the original Heisenberg model.
The role of vacancies in the magnetic and magneto-optic properties of Tb-doped EuO and EuS films
Authors: Gambino R. J. , Ruf R. R. , Fumagalli P.
Published: July 2002

Rocksalt structure solid solutions were prepared by coevaporating Eu2O3 and Tb metal. The films have the general formula Eu1−xTbxO1−y⧠y where y, the oxygen vacancy fraction, is given by y=(3x−1)/2. We have also prepared Tb-doped EuS solid solutions where y≂x so we can compare the effects of anion vacancies in both the oxide and sulfide systems. The coercivity, Hc, increases rapidly with Tb doping at about x=0.15 in the sulfide system and x=0.45 in the oxide system. The Hc of both systems falls on a universal curve, however, when plotted vs vacancies/RE (⧠/RE) with the rapid increase occurring at ⧠/RE=0.15. This value is close to 1/6 (0.166) which in octahedral coordination corresponds to one anion vacancy/RE. This suggests that the near neighbor vacancy is producing a strong crystal field at the Tb site which causes strong single ion anisotropy and thus a high coercivity. The MO spectra of the oxides show a strong dependence on x. At x=0.25, peaks are observed at 1.5 eV (−3°), 2.2 eV (5.5°), and 2.7 eV (−2°). At x=0.33, the spectra change completely. A narrow peak with a rotation θK=−20° appears at 2.5 eV, dominating the spectrum. The reflectivity, R, goes through a sharp minimum at the same energy (R<1%), possibly causing the enhancement in θK.
Characterization of diamondlike films by x-ray emission spectroscopy with high-energy resolution
Authors: Shamin S. N. , Pivin J. C. , Kurmaev E. Z.
Published: July 2002

X-ray emission spectroscopy with high-energy resolution was used for characterizing differences in the valence band of carbon films deposited by ion implantation in various conditions of bombardment and with various substrates, with respect to crystalline diamond and other diamondlike coatings. The obtained results were compared with calculations of the partial density of 2p states in defected diamond, and the nature of point defects in the implanted films could be identified. In addition, x-ray emission spectra of substrate atoms indicated a chemical interaction at some interfaces.
Improvement in the properties of a-SiGe:H films: Roles of deposition rate and hydrogen dilution
Authors: Middya A. R. , De S. C. , Ray Swati
Published: July 2002

Device quality a-SiGe:H thin films have been deposited by radio-frequency plasma-assisted decomposition of silane and germane diluted with and without hydrogen. Improvement in structural and electronic properties have been achieved employing low deposition rate and high hydrogen dilution. It has been observed that low deposition rate can reduce the preferential attachment of H to silicon throughout the alloy region while the beneficial effect of hydrogen dilution is more effective in a low band gap region (Eg≤1.40 eV). The photoconductivities of the good quality a-SiGe:H alloy films under white light illumination (50 mW/cm2) are 1.34×10−4 S cm−1 and 1.9×10−5 S cm−1 at the optical gaps of 1.51 and 1.35 eV, respectively. The changes in midgap defect density and tail states have been correlated with the photoconductivities of the samples deposited under different conditions. An attempt has been made to explain the results from the growth kinetics of the films.
Two-dimensional electron transport in selectively doped n-AlGaAs/InGaAs/GaAs pseudomorphic structures
Authors: Bhattacharyya Keya , Orwa J. O. , Goodnick S. M.
Published: July 2002

The transport properties of the two-dimensional electron gas in selectively doped AlyGa1−yAs/InxGa1−xAs/GaAs pseudomorphic structures grown by molecular beam epitaxy are studied. The mobility in the temperature range from 1.7 to 300 K is reported based on the Hall effect and high-field magnetoconductance measurements. The relative strengths of various scattering mechanisms are assessed through a numerical iterative solution of the Boltzmann equation and compared with the experimental Hall mobility versus temperature data. Comparison shows that at low temperature, alloy scattering determines the low-field mobility with a suitable choice of alloy scattering potential. At room temperature, polar-optical phonon scattering is the dominant mechanism. However, alloy scattering also contributes in reducing the room-temperature mobility by approximately 20% compared to polar optical scattering alone.
Quantitative analysis of arsenic losses during the formation of Au(Zn)/p-GaAs ohmic contacts
Authors: Piotrowska A. , Kamińska E. , Kwiatkowski S. , Turos A.
Published: July 2002

The formation of Au(Zn)/p-GaAs ohmic contacts by furnace annealing either in open or closed configurations with a dielectric cap has been investigated. Evaluation of the extent to which the GaAs substrate decomposes under these conditions was of primary concern. This was studied by measuring the amount of As losses, using the Cr-collector method, and correlating this with the amount of Ga diffused into the Au(Zn) metallization. The thermally induced decomposition of GaAs in contact with Au(Zn) metallization strongly depends on both the application of the capping layer, and on the thickness of the metallization. The loss of As is reduced to 6×1014 atom/cm2 using thin 10 nm Au/10 nm Zn/30 nm Au metallization annealed with a insulating capping layer deposited by sputtering. Electrical measurements indicate that under these conditions good ohmic contacts are obtained. Thus, the contact reaction sufficient to produce good ohmic contacts can be limited to about one monoatomic layer of GaAs.
Piezoresistive graphite/polyimide thin films for micromachining applications
Authors: Frazier A. Bruno , Allen Mark G.
Published: July 2002

In this work, graphite/polyimide composite thin films are introduced and characterized for micromachining applications. The material consists of submicron-sized graphite particles suspended in a benzophenone tetracarboxylic dianhydride–oxydianiline/metaphenylene diamine polyimide matrix. The resultant material represents a low cost, plasma-definable polyimide material which has been found to have a large piezoresistive coefficient over a range of graphite loadings. Selected film properties: Young’s modulus, residual stress, and piezoresistivity are investigated for a graphite loading range of 15%–25% by weight using a slightly modified in situ load/deflection technique. Results of mechanical property characterization show that the residual stress is independent of graphite loading and the Young’s modulus increases with increasing graphite loading. The maximum piezoresistive coefficient (gage factor) is 16.8 and occurs at a graphite loading of 18%.
Depth profiles of ion-implanted fluorine in tin-oxide films prepared by atmospheric-pressure chemical vapor deposition
Authors: Tan Chunyu , Xia Yueyuan , Chen Youpeng , Li Shuying , Liu Jitian , Liu Xiangdong , Xu Bingzhang , Li Jinhua , Cao Wenjiang
Published: July 2002

Depth profiles of fluorine in 19F+-implanted tin-oxide films have been accurately measured using 19F(p,αγ)16O resonance nuclear reactions at ER=872.1 keV and ER=340.46 keV. A proper deconvolution calculation method was used to extract the true range distribution of implanted fluorine from the experimental excitation yield curves. The range distribution parameters, RP and ΔRp, were thereby obtained and were compared with those obtained by Monte Carlo simulations. The experimental Rp values agree with the Monte Carlo simulation values very well, while the experimental ΔRp values are larger than those obtained theoretically. This phenomenon may be attributed to the enhanced diffusion during the ion implantation.
Atomic transport in thermal spike induced ion mixing
Authors: Chae K. H. , Song J. H. , Jung S. M. , Jang H. G. , Woo J. J. , Jeong K. , Whang C. N. , Oh Y. J. , Jung H. J.
Published: July 2002

A simple relationship between the ratio of atomic transport induced by ion mixing and the activation energies for the impurity diffusion of constituents in a bilayer is presented to describe quantitatively the symmetric and asymmetric atomic transport in the thermal spike induced ion mixing. The model predicts fairly satisfactorily the trend of experimental observations in the bilayer systems which have near zero heats of mixing and relatively high spike activation energies. For instance, the Pd/Co bilayer system shows nearly symmetric atomic transport, since its constituents have similar activation energies for the impurity diffusion.
Phase selection in interfacial reaction of Ni/amorphous Si multilayers
Authors: Wang W. H. , Bai H. Y. , Zhang Y. , Wang W. K.
Published: July 2002

The interfacial reaction in Ni and amorphous Si (a-Si) multilayers (Ni/a-Si) has been studied. Transmission electron microscope observation was used to monitor the progress of the solid-state reaction. It was found that amorphous Ni-silicide phase [a-(Ni,Si)] is the first phase formed in the Ni and a-Si interfacial reaction. A relatively large composition range for the amorphous phase exists in these Ni/a-Si multilayers. In the as-deposited Ni/a-Si multilayers with shorter modulation period, the uniform a-(Ni,Si) phase forms at least in the composition range of 25–62 at. % Ni. These results are consistent with predictions from the calculated Gibbs free-energy diagram. The δ-Ni2Si phase is the preferred phase in the crystallization process of a-(Ni,Si) even for the equiatomic Ni/a-Si multilayers. The mechanism that controls phase selection in the Ni/a-Si interfacial reaction is discussed using nucleation theory. A nucleation control model for phase selection is proposed.
Interfacial defects in silicides on Si(100): ‘‘Coreless defects,’’ 1/12〈111〉 dislocations, and twinning mechanisms
Authors: Eaglesham D. J. , Tung R. T. , Sullivan J. P. , Schrey F.
Published: July 2002

‘‘Coreless defects’’ are one of the long-standing surprises of silicide epitaxy on Si. For symmetry reasons a NiSi2 or CoSi2 film cannot grow over a step on Si(100), but must incorporate a dislocation; apparently, however, very thin films avoided this dislocation by introducing a trench through the silicide, the coreless defect. Here we use high-resolution microscopy, electron diffraction and dark-field imaging to show that these defects are in fact microtwins ≊4 atomic planes thick. The twins are highly unusual in that they follow curved lines, apparently dictated by steps at the interface. A mechanism for the formation of these curved twin defects by repeated formation of a 1/12〈111〉 interfacial partial at steps is postulated.
Dependence of the optical properties of p-CdTe and p-Cd0.96Zn0.04Te on the bromine concentration in a bromine-methanol etching solution
Authors: Kim M. D. , Kang T. W. , Kim G. H. , Han M. S. , Cho H. D. , Kim J. M. , Jeoung Y. T. , Kim T. W.
Published: July 2002

Photoluminescence measurements were carried out to investigate the dependence of the optical properties of p-CdTe and p-Cd0.96Zn0.04Te on various relative concentrations of bromine in a mixture of methanol and bromine. As the bromine concentration increased, the intensity of the luminescence increased; additionally, an exciton bound to a neutral acceptor (A°X) peak at 1.588 eV in p-CdTe was resolved into an exciton bound to neutral donor (D°X) peak at 1.592 eV and an A°X peak. The mixed bands of the 1.574 and 1.546 eV peaks were well resolved by using an etching bromine concentration of 2%; in particular, the intensities of the D°X and 1.574 eV peaks increased as much as five and seven times, respectively. The intensity of the peak at 1.48 eV related to defects also increased. The intensity of A°X at 1.609 eV in p-Cd0.96Zn0.04Te changed slightly with the bromine concentration. The intensities of the luminescence peaks due to the recombination of the electrons in conduction band with acceptors and to the defect relation did not vary. These results indicated that the number of Cd vacancies could be reduced due to the addition of Zn.
Solid phase epitaxy of Bi2Sr2CaCu2Ox superconducting thin films
Authors: Chen J. , Lu H. A. , DiMeo F. , Wessels B. W. , Schulz D. L. , Marks T. J. , Schindler J. L. , Kannewurf C. R.
Published: July 2002

Epitaxial superconducting Bi2Sr2CaCu2Ox (BSCCO) thin films have been formed by solid phase epitaxy from amorphous films deposited by metallorganic chemical vapor deposition. (100) MgO and LaAlO3 single crystals were used as the substrates. After high-temperature annealing in flowing oxygen, the films consist predominantly of the BSCCO (2212) phase and are epitaxial to the LaAlO3 with the c axis perpendicular to the substrate surface. The epitaxial structure of the films is confirmed by x-ray diffraction measurements including θ/2θ and in-plane Φ scans as well as by cross-sectional high-resolution transmission electron microscopy. Four-probe resistivity measurements show that the critical temperature of the film on LaAlO3 is 78 K. The critical current density of the epitaxial layer was one order of magnitude greater than that of textured films on MgO.
Simulation of electron-beam transport in low-pressure gas conditioning cells
Authors: Hubbard Richard F. , Slinker Steven P. , Fernsler Richard F. , Joyce Glenn , Lampe Martin
Published: July 2002

The resistive hose instability can disrupt propagation of self-pinched beams in dense gas. To reduce growth of the instability, beams can be conditioned prior to propagation. The objectives of beam conditioning are to center the beam in order to reduce initial transverse perturbations which seed the hose instability, and to ‘‘tailor’’ the beam emittance in order to detune the head-to-tail coherence of the instability. Emittance tailoring can be performed by transporting the beam through a ‘‘passive ion-focused regime’’ (IFR) cell, a low-pressure gas cell that induces a head-to-tail taper of the beam radius. The radius taper is then converted to an emittance taper by passing the beam through a thick exit foil which scatters the beam. Beam centering can be accomplished by transporting the beam through either: (i) a passive IFR cell that is narrow enough to provide wall guiding, or (ii) a laser-ionized ‘‘active’’ IFR cell, or (iii) a wire cell in which the centering is provided by a current-carrying wire. Axisymmetric particle simulation studies of IFR tailoring cells, alone and in tandem with each of these types of centering cells, and also the effect of supplementary focusing lenses and conducting foils are reported. The parameter choices that are conducive to effective beam conditioning are discussed. The emphasis is on conditioning configurations and beam parameters that have actually been tested in experiments with the Advanced Test Accelerator and SuperIBEX accelerator.
Hot carrier photovoltaic effect induced by 10.6 μm laser radiation in Ge and PAsGa junctions
Authors: Encinas-Sanz F. , Guerra Pérez J. M. , Ferrari E. Domínguez
Published: July 2002

The observation of CO2 (10.6 μm wavelength) laser-induced photoeffects in Ge and PAsGa junctions is reported. A moderately nonlinear low laser excitation intensity regime and a strongly nonlinear high laser excitation intensity behavior are observer in Ge junctions as was previously reported in Si junctions. Two strongly nonlinear behaviors are observed in PAsGa junctions. A opposite sign prepulse is also observed as in Si junctions. The observation of the same photoeffects in three different materials is proof of the universal character of the studied phenomenon. A interpretation on the basis of a hot carrier plasma model is discussed.
The effects of oxygen on the electronic and optical properties of AlInAs layers lattice-matched to InP substrates grown by atmospheric-pressure metal-organic chemical vapor deposition
Authors: Kamada Mikio , Ishikawa Hideto , Miwa Shiro , Stillman Gregory E.
Published: July 2002

AlInAs layers lattice-matched to InP substrates were grown by atmospheric-pressure metal-organic chemical vapor deposition. The residual oxygen concentration determined by secondary ion mass spectrometry ranged from 3×1016 to 3×1019 cm−3, and was high when the growth temperature was low or the V/III ratio was low. The oxygen concentration and the residual carrier concentration showed the same dependence on the V/III ratio in the high V/III ratio region. This suggests that oxygen is the origin of the residual carrier concentration. Strong correlations between the oxygen concentration and the photoluminescence intensity and reverse current through Schottky diodes suggest that oxygen creates generation-recombination centers in AlInAs layers.
Epitaxial growth of naphthalocyanine thin films vacuum deposited on alkali halides
Authors: Yanagi Hisao , Kouzeki Takashi , Ashida Michio
Published: July 2002

Epitaxial thin films of naphthalocyanines (Nc’s) were prepared on the (001) surface of alkali halide (AX) by a vacuum-deposition technique. Two types of molecular stacking and orientation were found depending on the molecular structure. Metal-free Nc(H2Nc) and divalent zinc Nc(ZnNc) took the face-to-face, eclipsed stacking, P orientation, in which their molecular planes came into a parallel contact to the substrate surface. Trivalent chloroaluminum Nc(AlNcCl) and fluorogallium Nc(GaNcF), and tetravalent vanadyl Nc(VONc) took the eclipsed, slipped stacking, I orientation, holding their molecular planes slightly inclined to the substrate surface. In the latter orientation an unexpected face-to-face stacking caused a stacking defect structure. The tetragonal lattice of the Nc crystals demonstrated five types of commensurate matchings to the ionic lattice of AX, depending on the lattice parameters of the Nc and AX crystals. On NaCl unidirectional AX(001)(4×4)R+45°-Nc was a predominant orientation, and on KCl and KBr bidirectional AX(001)(√10 ×√10)R±26.5°-Nc was mainly found.
Subband effect on miniband transport in laterally confined superlattices
Authors: Lei X. L. , Wang X. F.
Published: July 2002

Linear and nonlinear miniband electron transport through a laterally confined superlattice is investigated systematically using the balance-equation theory. Up to 21 transverse subbands with intrasubband and intersubband impurity and phonon scatterings are included. Nonlinear drift velocity and electron temperature as functions of the electric field are calculated at lattice temperatures ranging from 45 to 300 K for several sets of superlattices having different degrees of transverse confinements. With increasing the lateral cross-section diameters, linear mobility, peak drift velocity, threshold electric field, and all the other transport properties discussed exhibit significant oscillations at lattice temperatures as high as 300 K. Drastic changes in transport properties occur in GaAs-based systems when polar optic phonon scatterings set in or are prohibited due to subband structure.
Quantum conduction through double-bend electron waveguide structures
Authors: Kawamura T. , Leburton J. P.
Published: July 2002

Quantum transport properties through a variety of electron waveguide structures that have a double-bend geometry are investigated using the recursive Greens function technique. The conductance is calculated as a function of the chemical potential using the two-probe, multichannel Landauer–Büttiker formula. The results for the right-angle double-bend structure are in agreement with previous calculations based on mode-matching techniques. For multiple double-bend structures in series, the existence of an energy gap between the first and second subband threshold energies where the conductance is suppressed is shown. The effects of disorder and thermal broadening on the conductance are also investigated.
Growth of YBa2Cu3Oy single crystals from a mixture of YBa2Cu3Oy and Ag2O
Authors: Huang Y. , Lin Y. F. , Wang M. J. , Wu M. K. , Ma K. J.
Published: July 2002

Single crystals of the superconductor YBa2Cu3Oy have been grown from a mixture of solid phase YBa2Cu3Oy and liquid phase silver. Crystals with a thickness of up to 1 mm along the c axis can be obtained when the mixture is soaked at 1005 °C for more than 8 h. Silver melt enhances the peritectic partial melting of the YBa2Cu3Oy solid phase, and induces the solution and reprecipitation process during sintering at 1005 °C. Stacked plate-like YBa2Cu3Oy grains grow through a coalescence process. Crystals are heavily twinned after 20 h of O2 annealing at 500 °C. They exhibit a sharp superconducting transition with an onset temperature of 93 K in zero field.
Proton- and ammonium-exchanged optical waveguides in KTiOPO4
Authors: Roelofs M. G. , Ferretti A. , Bierlein J. D.
Published: July 2002

The potassium of KTiOPO4 has been exchanged for protons or ammonium ions to form optical waveguides. Proton exchange is relatively fast, does not give depth profiles expected for diffusive processes, and distinct potassium-depleted phases are formed. The kinetics for ammonium exchange are relatively slow and diffusion limited, similar to those for Rb and Tl exchange processes. Increases in surface refractive index of up to 0.053 for proton exchange and 0.046 for ammonium exchange have been observed, with higher values for mixed NH4/H and Rb/H exchanges.
Fission-fragment excited xenon/rare gas mixtures. I. Laser parameters of the 1.73 μm xenon transition
Authors: Hebner G. A. , Hays G. N.
Published: July 2002

Laser parameters for the 1.73 μm (5d[3/2]1−6p[5/2]2) xenon transition in fission-fragment excited Ar/Xe, He/Ar/Xe, Ne/Ar/Xe, and He/Ne/Ar/Xe gas mixtures are presented. Using a cw F center laser, time resolved small signal gain was probed as a function of total pressure, xenon concentration, pump power, He/Ne/Ar buffer ratio and impurity concentration. Small signal gains of up to 2%/cm were observed for pump rates of 30 W/cm3. Addition of helium and/or neon to the argon buffer increased the width of the time resolved laser gain pulse and reduced the absorption observed under some experimental conditions. Experimentally determined gain scaling laws for several gas mixtures are presented. The measured small signal gain was coupled with the results of laser cavity measurements to calculate the saturation intensity for several gas mixtures. The addition of helium or neon increases the saturation intensity for several gas mixtures. Laser cavity measurements as well as the gain × saturation intensity product indicate that the 1.73 μm power efficiency is approximately 2% for several gas mixtures.
Molecular beam epitaxy interface contamination by suboxide transport
Authors: Wood Colin E. C. , Wilson Richard A.
Published: July 2002

Evidence is presented to suggest that unintentional concentrations of silicon, germanium, and aluminum at gallium arsenide film substrate interfaces are transported as suboxides. A thermodynamic treatment is used to conclude that arsenic oxide, desorbed from substrates, provides the oxygen for suboxide formation in the vicinity of effusion cells. Silicon and germanium suboxides can then be reduced by gallium on substrate surfaces. Reduction of aluminum suboxide is thermodynamically unfavorable, thus oxygen is incorporated with aluminum. An approximate value of 68.4 entropy units is derived for the process As4 ■ 2As2.