bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of Interface States on Mbe CoSi2/Si Schottky Contacts by Forward Bias Capacitance Measurement
Authors: Chen H. Y. , Kao Y. C. , Mii Y. J. , Wang K. L. 
Published: March 2011

ABSTRACTThe properties of the interface states of MBE grown CoSi2/n-Si(111) intimate contacts has been investigated using forward bias capacitance measurement. The barrier height øbn for this structure is 0.66±0.01 V. It has been found that there is an interface state band located in 0.44–0.50 eV bfow the conduction band edge of Si. The density of states D it is about 4×1012 cm−2 eV−1, lower than those made by other methods. This intrface state band is in equilibrium with Si and the charge exchange occurs mainly with the electrons in the conduction band of Si. The electron capture cross section oa is about 3×10−15 cm2 . In addition, some discrete interface states were found at 0.53 eV, 0.51 eV and 0.47 eV below the conduction band edge of Si, respectively for several samples. The density of states D it ranges (1.5–3.5)×1010 cm−2 . They are probably caused by localized point defects formed during CoSi2 growth.
Steps on (001) Si Surfaces
Authors: Aspnes D. E. , Ihm J. 
Published: March 2011

ABSTRACTPrimitive (001) surfaces contain only biatomic (ao/2) steps and thereby provide a topological way of suppressing antiphase domain formation in polar materials heteroepitaxially grown on nonpolar (001) substrates. We show that thermodynamic equilibrium is a necessary and sufficient condition to form primitive (001) Si surfaces due to a π-bonded step reconstruction that lowers the relative enthalpy of reconstructed [110] biatomic steps by 0.04 eV per step atom, and to correlation, which freezes out the step configurational entropy thereby suppressing the formation of all other types of steps. Implications for general vicinal (001) Si surfaces are discussed.
Epitaxial Growth Of Nickel and Cobalt Germanides On Germanium
Authors: Hsieh Y.F. , Chen L.J. , Marshall E.D. , Lau S.S. 
Published: March 2011

ABSTRACTTransmission and scanning electron microscopy, Rutherford backscattering-channeling and Read camera glancing angle x-ray diffraction techniques have been applied to study the epitaxial growth of nickel and cobalt germanides on germanium.NiGe, Co5Ge7 and CoGe2 were found to grow epitaxially on both (001) and (111)Ge. More extensive epitaxy on (111)Ge is correlated with better lattice matches at the germanide/Ge interfaces than those on (001)Ge for these epitaxial germanides.
Epitaxial CoSi2/Porous-Si Strained Layer Structres Grown by Mbe
Authors: Kao Y. C. , Jamieson D. , Bai G. , Nieh C. W. , Lin T. L. , Wu B. J. , Chen H. Y. , Wang K. L. 
Published: March 2011

ABSTRACTCoSi2 epitaxial layers with thickness ranging from 24 nm to 170 nm have been grown onto porous Si substrates by molecular beam epitaxy. The X-ray rocking curves and transmission electron microscopy (TEM) are used to examine the strain relaxation and interface quality. Backscattering with channeling is used to characterize the crystallinity of the epilayers. The results show that it is necessary to grow a thin buffer Si layer in order to improve the interfacial sharpness and crystallinity of the epilayers; near perfect crystallinity is then obtained as the thickness of the CoSi2 films exceed 50 nm. TEM results reveal that both CoSi2/Si and CoSi2/porous-Si interfaces are flat and layer thickness is uniform. It is found by TEM that the dislocation density of CoSi2 grown on porous Si is much lower than that on single-crystal Si. For thin CoSi2 grown on porous Si, the TEM and strain measurement results imply that part of the film is pseudomorphic where no dislocations are observed. Average strains of CoSi2 films grown on porous Si substrates with thicknesses greater than 30 nm show a lower strains comparing to that on crystalline Si. This suggests that by using porous Si as substrates the stress energy in the epilayer can be accommodated by the Si buffer layer that bridged over the trenches of porous Si.
On the Critical Layer Thickness of Strained-Layer Heteroepitaxial CoSi2 Films on 〈111〉Si
Authors: Jamieson David N. , Bai G. , Kao Y. C. , Nieh C. W. , Nicolet M-A. , Wang K. L. 
Published: March 2011

ABSTRACTThe technique of Double Crystal X-Ray Diffractometry (DXD) and ion beam channeling are applied to investigate, as a function of thickness, the average perpendicular strain and crystal quality of CoSi2 layers grown by MBE on 〈111〉Si. The results show that thin layers (from 20 to 30 nm) are partially relaxed but with a strain greater than that expected for a free CoSi2 lattice. For layers thicker than 30nm the magnitude of the CoSi2 strain incrgases to 1.7%, somewhat less than the maximum magnitude strain expected for coherent growth (2.1%). For layers thicker than 50 nm, the perpendicular strain relaxes very slowly, with the strain at 225 nm only 5% less than that at 50nm. It was concluded that a coherent epitaxial layer does not form initially and the relaxation of the strained layers is not consistent with a planar growth mechanism of the CoSi2 epilayers. Therefore the concept of a critical thickness, below which the epilayers are strained and above which the epilayers are relaxed, cannot be applied to our CoSi2/Si system.
Control of GaAs Domain Formation Via Monolayer and Multilayer Steps on Misoriented Si(100)
Authors: Pukite P.R. , Cohen P.I. 
Published: March 2011

ABSTRACTReflection high energy electron diffraction (RHEED) measurements indicate that the adsorption of As on misoriented Si(100) surfaces drives a multilayer step transition. We find that the formation of multilayer steps is a strong function of substrate temperature and As pressure. Monolayer steps are metastable at low substrate temperature or As pressure. The subsequent nucleation and growth of GaAs by molecular beam epitaxy (MBE) is controlled by the initial Si step distribution. Single domain GaAs grown on the monolayer stepped substrate has Ga terminated steps. Conversely, single domain GaAs grown on the multilayer stepped substrate has As terminated steps.
Heteroepitaxy of GaAs on Si by MOCVD
Authors: Soga Tetsuo , Imori Toru , Umeno Masayoshi 
Published: March 2011

ABSTRACTThe stress and strain of GaAs on Si grown by using strained superlattice intermediate layers and a two-step growth method are characterized by the photoluminescence, X-ray diffraction and the curvature radius. The strain of GaAs grown using strained superlattice intermediate layers is smaller than that grown by the two-step growth method.
Defect Reduction in GaAs Epilayers on Si Substrates Using Strained Layer Superlattices
Authors: El-Masry N. , Hamaguchi N. , Tarn J.C.L. , Karam N. , Humphreys T.P. , Moore D. , Bedair S.M. , Lee J. W. , Salerno J. 
Published: March 2011

ABSTRACTInxGa11-xAs-GaAsl-yPy strained layer superlattice buffer layers have been used to reduce threading dislocations in GaAs grown on Si substrates. However, for an initially high density of dislocations, the strained layer superlattice is not an effective filtering system. Consequently, the emergence of dislocations from the SLS propagate upwards into the GaAs epilayer. However, by employing thermal annealing or rapid thermal annealing, the number of dislocation impinging on the SLS can be significantly reduced. Indeed, this treatment greatly enhances the efficiency and usefulness of the SLS in reducing the number of threading dislocations.
Spin Reorientations in (ErxY1-x)2Fe14B and (ErxPr1-x)2Fe14B Systems
Authors: Boltich E. B. , Pedziwiatr A. T. , Wallace W. E. 
Published: March 2011

ABSTRACTThe bulk magnetic properties of (ErxY1-x)2Fe14B and (ErxPr1-x)2Fe14B systems were studied over the temperature range 4.2-1100 K. Lattice parameters, saturation magnetizations, Curie temperatures and spin reorientation temperatures were determined. Theoretical description of the detailed magnetic behavior is presented, based on a crystal field model. The (ErxY1-x)2Fe14B compounds were all found to exhibit plane-to-axis spin reorientations similar to that observed for Er2Fe14B, with the transition temperature decreasing with increasing Y content. In contrast, the spin reorientations in the (ErxPr1-x)2Fe14B systems appear to be of the cone-to-axis type. Since higher order crystal field terms appear to be significant only in the cases of Nd3+ and Ho3+, the results are discussed in terms of a crystal field Hamiltonian involving only 2nd order terms. Using known values of the exchange field, Fe anisotropy and the ratios of the crystal field coefficients, the multi-ion cr 6.tal field problem was formulated in terms of a single adjustable parameter (B02(f). It is shown that 2nd order crystal field terms are capable, not only of explaining the conical anisotropy of the (ErxPr1-x)2Fe14B systems, but also the decrease in the Er moment upon passing through the spin reorientation (as has been observed for Er2Fe14B). The magnetic structure of Er1.5Pr0.5Fe14B is also predicted.
NdFeB Magnets with Improved Temperature Characteristics
Authors: Ma B. M. 
Published: March 2011

ABSTRACTThe temperature dependence of magnetic properties for NdFeCoB alloys were investigated. It is well known that dysprosium substitution for neodymium increases the intrinsic coercivity. Aluminum also improves the intrinsic coercivity, Hci, at room temperature but impairs the Curie temperature and the intrinsic coercivity at elevated temperatures. The rate of increase of the Hci with increasing dysprosium in the NdFeCoB system is less than when dysprosium is added to the NdFeB system. A combination of aluminum and dysprosium is more effective than aluminum alone in raising Hci. Molybdenum addition into the NdDyFeCoB alloy was found to reduce the temperature coefficients of Br and Hci. Temperature coefficients of Br and Hci obtained on a Nd10Dy5Fe67Co10Mo1Al1B6 alloy are -0.07 %/°C and -0.4 %/°C respectively.
Elevated Temperature Properties of Sintered Magnets of (Nd,Dy)-Fe-B Modified with Cobalt and Aluminum
Authors: Xiao Y. , Mildrum H. F. , Strnat K. J. , Ray A. E. 
Published: March 2011

ABSTRACTThe effect of small aluminum additions on the temperature dependence of remanence and intrinsic coercivity in Co- and Dy-containing Nd-Fe-B was studied. Sintered magnets were prepared and demagnetization curves measured at temperatures between −50 to +200°C. Curie temperatures and irreversible flux losses in open circuit were determined. Al increases the coercivity while decreasing remanence, energy product and Curie temperature. Other unfavorable side effects are the increase in temperature coefficients of Br and, especially, MHc. Substitution of Al is not beneficial for magnets used at elevated temperature.
Studies of Substituted R2 T14 B and R2 Co17 Systems (T = Fe or Co)
Authors: Wallace W. E. , Pedziwiatr A. T. , Boltich E. B. , Smith H. Kevin , Jiang S. Y. , Sankar S. G. , Oswald E. 
Published: March 2011

ABSTRACTCertain R2Co17 and R2 T14 B systems (R = a rare earth, T = Fe or Co) are of significance for use in the fabrication of high energy magnets. Improvements in these systems as high energy magnet materials are effected by partially replacing Co or T by appropriate d transition metals. A description is given of the magnetic behavior of a number of systems based on R2 Co17 and R2T14 B. Also, an account is given of recent work dealing with the systems RCo4 B and PrCo4-xFex B. The latter materials have large magnetizations and high Curie temperatures. However, they are not useful permanent magnet materials because they exhibit planar anisotropy.Results of some Auger spectroscopy studies of R2 Fe14 B systems (R = Pr,Nd or Er) are presented. This work shows the intergranular region to be rich in B, O and R. This region is undoubtedly non-magnetic, a feature which is most probably of significance in regard to the observed coercivity of R2 Fe14 B magnets.
Impact of The High-Energy Product Materials on Magnetic Circuit Design
Authors: Leupold Herbert A. , Potenziani Ernest , Clarke John P. , Basarab Douglas J. 
Published: March 2011

ABSTRACTMany devices that employ magnetic fields are encumbered by massive solenoids with their equally bulky power supplies or by inefficient permanent-magnet structures designed for use with obsolescent magnet materials. This paper describes how the high-energy product materials are employed in several structures to afford mass and bulk reductions of an order of magnitude or more. Also discussed are novel designs that are not attainable with the older materials such as the alnicos. Substitution of solenoids with permanent magnets also eliminates considerable energy consumption and the attendant problems arising from generation of heat. In many cases, all this is accomplished within leakage-free systems. Among the designs described are: nuclear magnetic resonance imagers; cylindrical solenoidal field structures for klystrons and nonperiodic field TWT's; cylindrical field structures with arbitrary axial gradients for advanced gyrating beam sources; annular field sources for high harmonic gyrotrons; helical transverse field sources for circularly polarized radiation sources; miniature periodic permanent-magnet configurations; and clad permanent-magnet circuits for biasing fields in millimeter-wave filters. Where alternate designs exist, they are compared with regard to performance, bulk, and economy. All of the structures are in various stages of design and construction, and, for completed structures, comparisons are made between theoretical projections and actual performance.
Radiation Effects in Rare-Earth Permanent Magnets
Authors: Cost J. R. , Brown R. D. , Giorgi A. L. , Stanley J. T. 
Published: March 2011

ABSTRACTNd-Fe-B and Sm-Co permanent magnets have been irradiated with fission neutrons and gamma rays. Irradiated samples were periodically removed for room temperature measurements of the open-circuit remanence. Hysteresis loops were measured before and after irradiation. For neutron irradiation, two Nd-Fe-B magnets showed a rapid loss of remanence, while a third magnet from another manufacturer decayed more slowly, suggesting that the radiation hardness of Nd-Fe-B magnets may depend on microstructural details. Irradiation in the Omega West Reactor at Los Alamos with fast neutrons caused the fast-decay samples to have an Wtial loss of remanence of 1% for irradiation at 350 K to a fluence of 1015 n/cm2. Both SmCo5 and Sm2Co17 magnets showed excellent resistance to radiatifg-induied loss of remanence for neutron irradiation to a fluence of 2.6×1018 n/cm2. Results for gamma radiation showed no loss of remanence for a dose of about 49 Mrad using a 60Co source. Possible mechanisms for radiation-induced loss of magnetic properties are discussed.
Cost and Performance of Low Field Magnetic Resonance Imaging
Authors: Crooks Lawrence E. , Yao Ching , Arakawa Mitsuaki , Hale James D. , Carlson Joseph W. , Licato Paul , Hoenninger John , Watts Jeffrey , Kaufman Leon 
Published: March 2011

ABSTRACTMagnetic Resonance Imaging technology has advanced on many fronts. Two important areas are the improvement of signal-to-noise levels and the understanding of imaging pulse sequence optimization. Based on these advances, low cost imagers using very low field permanent magnets are providing images of diagnostic quality.
Initial Magnetization Behavior of Rapidly Quenched Neodymium-Iron-Boron Magnets
Authors: Pinkerton F. E. 
Published: March 2011

ABSTRACTInitial magnetization and demagnetization data are reported for three forms of rapidly solidified Nd-Fe-B permanent magnet materials: melt-spun ribbons, hot pressed magnets, and die upset magnets. In all three materials the results are consistent with domain wall pinning at grain boundary phases as the coercivity mechanism. Optimally quenched ribbons are comprised of randomly oriented single domain Nd2Fe14B grains, and both initial magnetization and demagnetization are controlled by strong domain wall pinning at grain boundaries. Maximum coercivity is accompanied by a low initial permeability. Coercivity is reduced in overquenched ribbons by partial retention of a magnetically soft amorphous or very finely crystalline microstructure. Coercivity decreases in underquenched ribbons because wall pinning weakens as the grain size increases above optimum. Correlation of magnetization and demagnetization behaviors suggests that maximum coercivity in ribbons is largely determined by the resistance to domain wall formation in grains smaller than the single domain particle limit. Grain size is much less important in the aligned die upset magnets. Domain walls are initially free to move until they become strongly pinned at grain edges, and complete magnetization requires an applied field greater than the coercive field. Hot pressed magnets show a mixture of ribbon and die upset behavior.
In-Situ Production of Superconducting YBa2Cu3O7-y Thin Films by High Pressure Reactive Evaporation with Rapid Thermal Annealing
Authors: Lathrop D. K. , Russek S. E. , Buhrman R. A. 
Published: March 2011

ABSTRACTA high pressure reactive evaporation process has been established that can produce highly oriented YBa2Cu3O7-y high Tc films without the necessity of an extended post-deposition oven anneal cycle. The process is based on the electron beam co-evaporation of the metals Y, Ba and Cu onto heated (600–750 C) substrates in an oxygen partial pressure of 10-3 Torr. In general the films are superconducting when examined directly after termination of the growth process. However a brief rapid thermal anneal step in oxygen, which can be done either in-situ in the growth chamber or elsewhere, is often effective in further improving the superconducting transition. Highly oriented film growth has been obtained on both strontium titanate and yttria-stabilized cubic zirconia substrates. The best films that have been produced thus far with this technique on the cubic zirconia substrates have Tc (zero resistance) = 83 K, transition width ΔTc = 2 K, and room temperature resistivity (ρRT) = 0.5 mQ-cm. Similar results, with somewhat higher values of Tc, have been obtained on SrTiO3. On both substrates the critical current density at 4.2 K is in excess of 106 A/cm2.
Radiation Damage in Thin Films of High Tc Superconductors
Authors: Clark G. J. , Legoues F. K. , Marwick A. D. , Laibowitz R. B. , Koch R. H. 
Published: March 2011

ABSTRACTUsing O and As ions, we have investigated the effects of ion irradiation on the superconducting, electrical and microstructural properties of thin films of Y1Ba2Cu3Ox. Superconducting transitions were found to degrade in polycrystalline films by a decoupling of the superconducting grains while epitaxial films degrade due to bulk damage. Damage in the films was a result of elastic rather than electronic processes. Evidence is presented for 1D normal conductivity in the films.
Single-Crystal Structural Study of La2Cu0.95Li0.05O4.
Authors: Delgado J. M. , Speck J. S. , McMullan R. K. , Diaz de Delgado G. , Wuensch B. J. 
Published: March 2011

ABSTRACTA large crystal of flux-grown La2CuO4, examined through single-crystal neutron diffraction, was found to have an orthorhombic superstructure derived from the K2NiF4 structure type with a=5.359(1), b=5.363(1), c=13.127(2) Å. The pattern of systematically absent intensities indicated space group Pccn but meaningful refinement of thermal vibration parameters could not be obtained in this symmetry. Systematic examination of all possible orthorhombic subgroups of Fmmm yielded satisfactory refinement to R(F2)=2.57% only in space group Bmab. Incorporation in the crystal of Li derived from the flux results in an orthorhombic distortion smaller than found for pure La2CuO4. Refinement of the Cu site occupancy provided Cu0.95Li0.050(3), in excellent accord with a bulk chemical analysis. Reflections which violate the systematic absences of Bmab are attributed to a smaller volume fraction of domains in orientation twinned by 90° rotation about c. This interpretation is supported by transmission electron microscopy which revealed intergrown lamellae. Dark field imaging with a forbidden reflection illuminated only the twin lamellae.
Preparation of High TC YBa2Cu3O7−x Powders from Nitrate and Oxalate Precursors
Authors: Kayser M. H. , Borglum B. , Antony G. , Shyu S. G. , Buchanan R. C. 
Published: March 2011

ABSTRACTThis study presents two methods for preparing the High Tc superconducting YBa2Cu3O7−x compound. Aqueous nitrate solutions consisting of Yttrium, Barium and Copper were mixed, dried, blended and the resulting homogeneous mixture calcined at 700–900°C for 2–4h to develop the superconducting (1,2,3) phase. As an alternative, oxalates of Yttrium, Copper and Barium were coprecipitated from the mixed metal nitrate solution using (Et3NH)2C2O4. The resulting pale blue coprecipitate was dried and calcined in air at 700–900°C/2–4h. Both methods provided high homogeneity precursors for the High Tc YBa2Cu3O7−x superconductor. Resistance measurements, SEM, x-ray and VSM were used to characterize the microstructures and properties.
Anisotropic Normal State Transport Properties of Oxide Superconductors Predicted from Lapw Band Structures
Authors: Allen Philip B. , Pickett Warren E. , Krakauer Henry 
Published: March 2011

ABSTRACTThe resistivity, Hall, and thermopower tensors are calculated for the normal state of oxide superconductors on the assumption of band quasiparticle behavior. The shape of the resistivity ραβin the metallic a-b plane is consistent with ordinary impurity and electron-phonon scattering, but the magnitude is larger than predicted. The Hall tensor is predicted to be hole-like for orbits in the a-b plane but electron-like for a-c or b-c orbits, while the thermopower is predicted to be electron-like in the a-b plane and hole-like along the c-axis. Single crystal experiments have confirmed some of these predictions for the Hall tensor.
Ba2YCu3O7-σ; Effect of Oxygen Stoichiometry
Authors: Cava R. J. , Batlogg B. , Ramirez A. P. , Werder D. , Chen C. H. , Rietman E. A. , Zahurak S. M. 
Published: March 2011

ABSTRACTThe effect of changes of oxygen stoichiometry on the properties of Ba2YC3O7-σ is discussed. Crystallographic, susceptability, resistivity, and specific heat data from 1 set of samples prepared by Zr gettered annealing are described and discussed.
Ba2YCu3O6.9 Powder Preparation by Sol-Gel Emulsion Techniques
Authors: Cima M. J. , Chiu R. , Rhine W. E. 
Published: March 2011

ABSTRACTBarium yttrium cuprate powders were prepared by a sol-gel emulsion process in which an aqueous nitrate solution containing Ba, Y, and Cu in the correct stoichiometry was emulsified in heptane. The resulting micrometer-sized droplets were gelled by adding a high-molecular-weight primary amine that extracts nitric acid from the aqueous phase and raises the pH of the droplets. Thermal gravimetric analysis revealed that the correct overall stoichiometry was obtained at temperatures lower than 400 °C during calcination, but X-ray diffraction showed that calcination at temperatures greater than 800° may be required to produce the correct phase. One possible advantage of this technique is the control of powder morphology on a micrometer scale so that powders can be prepared for advanced ceramics processing methods. Also, segregation of components, if any, will be restricted to distances less than one micrometer.
Synthesis and Characterization of Ba2Cu3PrO7−x
Authors: Amador J. , Cascales C. , Rasines I. 
Published: March 2011

ABSTRACTPolycrystalline black coloured Ba2Cu3PrO7−x is prepared from a mixture of analytical grade BaO2, CuO, Cu metal, and Pr 2O3 (2 : 2 : 1 : 0.5), which are ground, pelletized, and heated in evacuated quartz ampoules at 1273 K for 4 days, and then slowly cooled.X-ray powder diffraction data show that Ba2Cu3PrO7−x is orthorhombic, a = 3.823(2), b = 3.877(2), c= 11.793(5) Å, space group Pmmm (no. 47), Z = 1. The structure of Ba2Cu3PrO7−x is refined from 37 reflections by using a least-squares method up to Rc = 0.044 and Rw = 0.041. Structural data and main interatomic distances are given.