bluuebunny/crossref_metadata_2025 huggingface dataset:
MBE Growth of GaAs on Porous Silicon
Authors: Lin T. L. , Sadwick L. , Wang K. L. , Rhee S. S. , Kao Y. C , Hull R. , Nieh C.W. , Jamieson D. N. , Liu J. K. , Nicolet M-A.
Published: March 2011

GaAs layers have been grown on porous silicon (PS) substrates by molecular beam epitaxyNo surface morphology deterioration was observed onGaAs-on-PS layers in spite of the roughness of PS. A 10% Rutherford backscattering spectroscopy (RBS) channeling minimum yield for GaAs-on-PS layers as compared to 16% for GaAs-on-Si layers grown under the same condition indicates a possible improvement of crystallinity when GaAs is grown on PS. Transmission electron microscopy (TEM) reveals that the dominant defects in the GaAs-on-PS layers are microtwins and stacking faults, which originate from the GaAs/PS interface. GaAs is found to penetrate into the PS layers.
Improved MOCVD Growth of GaAs on Si
Authors: Lum R.M. , Klingert J.K. , Davidson B.A. , Lamont M.G.
Published: March 2011

In the direct growth of GaAs on Si by MOCVD the overall quality of the heteroepitaxial film is controlled to a large extent by the growth parameters of the initial GaAs buffer layer. We have investigated the structural properties of this layer using Rutherford Backscattering Spectrometry (RBS) and X-ray double crystal diffractometry. The crystallinity of the buffer layer was observed to improve with increasing layer thickness in the range 10–100nm, and then to rapidly degrade for thicker layers. High temperature (750°C) annealing of the buffer layers resulted in considerable reordering of all but the thicker (>200 nm) layers. Alteration of the usual GaAs/Si growth sequence to include an in-situ anneal of the buffer layer after growth interruption yielded GaAs films with improved structural, optical and electrical properties.
The Two-Step Growth Mechanism of MOCVD GaAs/Si
Authors: Ishida Koichi
Published: March 2011

The growth mechanism and lattice defects are studied for GaAs/Si grown by the two-step MOCVD growth procedure using transmission electron microscopy (TEM). The large misfit stress between GaAs and Si is relieved by misfit dislocations at the GaAs/Si interface, which are introduced during epitaxial regrowth of the thin (<200A) polycrystalline buffer layer grown at 400∼450°C. The regrown buffer layer is relaxed to a nearly stress free state, and therefore a thick GaAs layer can subsequently be grown at the higher growth temperature (∼750°C). The tensile stress in GaAs at room temperature is shown to be a direct consequence of the misfit stress relaxation at the higher growth temperature. TEM revealed high density (<106cm−2) of the threading dislocations in the GaAs layer, contrary to the results of molten KOH etching.
Materials Aspects of GaAs on Si
Authors: Fischer Russ
Published: March 2011

SUMMARY ABSTRACT

Despite the 4.2% lattice mismatch, several laboratories have demonstrated that the quality of GaAs grown on Si is high enough for practical device applications [1–5]. At the GaAs/Si interface, a dislocation density of roughly 1012cm−2 is required to accommodate the mismatch. Therefore various techniques of dislocation filtering are necessary to provide material with acceptable dislocation counts. Among these techniques are the use of tilted substrates, strained layer superlattices, and intermediate layers.
Raman Scattering Spectrum Along a Bevel Etched GaAs on Si, Tem Study and GaAs P-I-N Photodetector on Si
Authors: Lo Y.H. , Charasse M.-N. , Lee H. , Vakhshoori D. , Huang Y. , Yu Peter , Liliental-Weber Z. , Werner M. , Wang S.
Published: March 2011

Raman scattering is measured along a bevel etched GaAs epitaxial film grown on Si by molecular beam epitaxial (MBE). From the correlation length profile of Raman scatteringmost dislocation lines are confined in the 2000Å regions close to the interface. The strain profile calculated from the Raman peak shift shows that about 0.6% compressive strain exists near the interface because of lattice mismatch. However, as one moves away from the interface, the compressive strain is gradually counterbalanced by thermal expansion. Transmission electron microscope (TEM) studies of the local dislocation image and properties show that an ultra clean Si surface is essential for dislocation confinement. From high resolution TEM, we find that the distance between dislocations at the interface is nonuniform, varying from 50Å to 125Å with an average distance at 81Å. Finally, a GaAs p-i-n photodetector on Si substrate is fabricated. Even though a normal photoresponse curve is obtained, the high dark current (50nA) and relatively low responsivity (0.01A/W) show that the material quality needs to be further improved to make a minority carrier vertical transition device.
Epitaxial GaAs on Si: Progress and Potential Applications
Authors: Shaw Don W.
Published: March 2011

Recent successes, such as the demonstration of a 1K SRAM, have established epitaxial GaAs on Si substrates as a promising technology rather than a device designer's dream. For the first time we can seriously consider combining the individual electronic and optical properties of GaAs and Si within a single epitaxial structure. Applications for GaAs on Si range from those that simply utilize the Si as a low-cost, large-areapassive substrate with superior strength and thermal conductivity to the long-sought multifunction integrated circuits where Si and III–V components are integrated within a single monolithic chip. This paper will attempt to provide a realistic appraisal of the potential applications of epitaxial GaAs on Si with emphasis on the special demands imposed by each application and barriers that must be circumvented.
Structural Characterization of Thin, Low Temperature Films of GaAs on Si Substrates
Authors: Rosner S. J. , Koch S. M. , Harris J. S.
Published: March 2011

The technology of heteroepitaxially growing compound semiconductors, particularly GaAs, on Si has attracted an increasing volume of attention in the past 3–5 years. In the past two years there have been few major advances in the growth recipes, which all include a high temperature Si preheat, a two-step growth temperature profile, and the use of misoriented substrates. The need for mechanistic understanding of the effect of these parameters is crucial to advancing the state of the art beyond this current practice. This work focusses on the effect of the misorientation in inducing asymmetry in early stages of the molecular beam epitaxy of GaAs on Si substrates. The strain in the films is found to have greatly different rates of relaxation in the plane of the film when measured in the two orthogonal <220> directions. This asymmetry persists to greater than 30 nm film thickness at 400°C. The nucleation morphology was also examined as a function of substrate misorientation. At low substrate tilts, nucleation density was sparse and there was not substantial ordering of the nuclei. As the tilt was increased, a distinct habit emerged where collections of nuclei were quite coherent along the steps for several 100 nm, with dimensions of the order of 10's of nm perpendicular to the steps. The density of steps with nuclei was also substantially less than that predicted by the widely accepted “array of double-height steps” used to explain the curious lack of anti-phase disorder in these films.
MBE Growth of GaAs on Si (100)
Authors: Ahearn J. S. , Uppal P.
Published: March 2011

Molecular beam epitaxy (MBE) growth of GaAs on Si was investigated for three Si substrate orientations: exact (100), 4° off (100) towards (011), and 4° off towards (010). Cross-sectional transmission electron microscopy (X-TEM) analysis indicated a high dislocation density at the GaAs-Si interface that decreased away from the interface. Changing the orientation significantly affected the dislocation arrangement in the films.

In the exact (100) case, dislocations from different glide systems formed pyramids, and dislocation annihilation resulted in linear defects propagating to the bottom of pits on the GaAs surface. On Si substrates oriented 4° off of (100), dislocation pyramids were not observed which we attribute to the different stresses acting on different glide systems. Planar TEM sections indicated that the dislocation densities at th surfaces of the 2-μm-thick films were 8 × 108 /cm2 for exact (100), 3.4 × 108/cm2 for 4° off (100) towards (010), and 1.6 × 108/cm2 for 4° off towards (011) orientations. When etching was used to evaluate anti-phase domain (APD) density, the exact (100) and off (100) orientations toward (010) showed APD's in some areas; off (100) toward (011) orientations were apparently APD-free. Results of photoluminescence (PL) spectroscopy of each of the wafers showed marked differences in peak intensities for the different orientations. Secondary ion mass spectrometry (SIMS) showed that roughly 1/4 of a monolayer of Si was incorporated in the GaAs, mostly concentrated in the first 250 nm near the GaAs-Si interface.
Characterization of APBs in GaAs Grown on Si and Ge
Authors: Carter C.B. , Cho N.-H. , Mckernan S. , Wagner D.K.
Published: March 2011

Antiphase boundaries are observed in epilayers of GaAs grown by organometallic vapor phase epitaxy on Ge substrates and are then invariably found to show a tendency to facet. Stacking-fault-like fringes caused by the translation of adjacent grains give the information on the relative displacement of the two grains at these interfaces and show that this translation does not have a fixed magnitude for a particular interface but varies with the orientation of the interface. Preferred orientations of the antiphase boundaries and the rigid-body translations have been studied using transmission electron microscopy. Interactions between antiphase boundaries and interfaces have been examined here in heterolayer structures consisting of alternating layers of GaAs and AlxGal−xAs grown on an (001) Ge substrate. The possibility of using atomic-resolution imaging to investigate the atomic structure of APBs is illustrated and the images are compared with those predicted by image simulation.
{224} Plane X-Ray Diffraction Study of GaAs on Si Wafers Using a Conventional Double Crystal Diffractometer
Authors: Lee J.W. , Bowen D.K. , Salerno J.P.
Published: March 2011

In an effort to evaluate the near surface crystal quality of GaAs on Si wafers, {224} plane diffraction were investigated using a conventional double crystal x-ray diffractometer without any high intensity radiation source. The x-ray incident angle to wafer surface varied from 3.6 to 9.6 degrees for different {224} planes due to the substrate tilt angle of 3 degrees. The GaAs to Si rocking curve intensity ratio increased significantly as the incident angle decreased. For the diffraction with 3.6 degree incident angle, only the GaAs peak was detected from the 3.5 um thick GaAs on Si wafer and the GaAs peak became narrower. These indicates that this conventional x-ray diffraction technique is applicable for the near surface quality evaluation of GaAs on Si wafers.
Prospects for GaAs-on-Si LSI Circuits
Authors: Shichijo H. , Tran L.T. , Matyi R.J. , Lee J.W.
Published: March 2011

This paper will review some of the recent progress in GaAs-on-Si devices and circuits, and discuss the issues involved in realizing large scale ICs in GaAs-on-Si wafers. With a recent success in fabricating 1 Kbit static RAMs in GaAs-on-Si wafers, it has become apparent that this material is indeed acceptable for LSI complexity circuits. GaAs MESFETs fabricated using a standard process show an excellent threshold voltage uniformity which is comparable to that for bulk GaAs devices. GaAs bipolar devices on GaAs-on-Si have realized a gain of 25 which is the highest reported for bipolar devices in GaAs-on-Si material. Bipolar ring oscillators and 256-bit ROMs consisting of more than 100 gates have also been realized. In spite of these successes, however, there are numerous issues that need to be solved before this material becomes practical.
Deep Electron Traps In Mbe Gaas On Si
Authors: Nauka K. , Reid G.A. , Rosner S.J. , Koch S.M. , Harris J.S.
Published: March 2011

Deep electron traps were investigated in MBE GaAs grown directly on Si substrates with orientations a few degrees off the <100> axis. Capacitance Deep Level Transient Spectroscopy (CDLTS) revealed the presence of eleven electron traps in the GaAs epilayer. Their activation energies ranged from 0.21 eV to 0.83 eV below the conduction band. Most of these traps were previously observed in homoepitaxial GaAs films grown under As-rich conditions (VPE, MBE), or in electron irradiated bulk GaAs. Trap concentrations tracked Si dopant density and MBE growth conditions. Observed deep levels are not introduced by metals or other contaminants present at the GaAs-Si interfaces. Rather, they are caused by defect complexes. These complexes involve native point defects, whose formation is favoured by As-rich environments, by lattice mismatch, and by different thermal expansion coefficients. Si dopant atoms may also participate in the formation of these defects. A similar deep level generation mechanism is proposed for the electron traps in homoepitaxial MBE GaAs layers.
Low-Temperature Photoluminescence of Mocvd GaAs Grown Directly on Si
Authors: Wilson B.A. , Bonner Carl E. , Harris T. D. , Lamont M. G. , Miller R. C. , Sputz S. K. , Vernon S. M. , Haven V. E. , Lum R. M. , Klingert J. K.
Published: March 2011

We present a systematic study of the low-temperature photoluminescence from undoped GaAs layers grown directly on Si substrates by MOCVD. GaAs layers from 100Å to 4 μm in thickness were deposited on Si substrates prepared with a variety of doping levels and orientations. The emission from thicker samples is dominated by pairs of lines in the band-edge region. Photoluminescence excitation measurements show that this multiplicity results from two regions in the material with different levels of strain. The stress-induced splitting of the valence band is also studied using excitation spectroscopy. In thinner samples we observe strong emission in the midgap range due to stoichiometric defects. The nature of the defects near the interface depends strongly on the character of the substrate.
Optoelectronic Properties of Pseudomorphic SixGel1−x,/Ge Heterostructures on (001) Ge
Authors: People R.
Published: March 2011

The optical and electronic properties of pseudomorphic SixGel1−x/Ge heterostructures are reviewed in brief. Potential applications of conduction and valence band alignments for modulation doped field effect transistors are outlined. Optical transition energies are calculated for ultra-thin, alternating four monolayer, Si/Ge heterostructures on (001) Ge.
Atomic-Scale Simulation of Silicon Atomic Beam Deposition
Authors: Dodson Brian W.
Published: March 2011

The mechanisms which control low energy (10–100 eV) beam deposition of silicon onto a relaxed (111) silicon substrate have been studied using a molecular dynamics technique. A many-body empirical potential was used to describe the covalent Si-Si bonding. 10 eV silicon beams with near-perpendicular incidence were simulated to study capture mechanisms and the local lattice excitation resulting from impact. Grazing angles of incidence (3°–30°) were studied for beam energies of 20–100 eV. For incidence angles less than an energy- and orientation-dependent critical value, the phenomenon of ‘surface channeling’ is predicted, in which the incoming particle is steered parallel to, and roughly 2 Å above, the surface of the substrate through inelastic substrate interactions. The phenomena seen in low-energy beam deposition offer new avenues of control over growth of modulated semiconductor structures.
Fabrication of Si-Gate CMOS Devices In A Heteroepitaxial Si/Caf2/Si Structure
Authors: Onoda Hiroshi , Sasaki Masayoshi , Katoh Teruo , Hirashita Norio
Published: March 2011

The results of recent developments on device fabrication in a heteroepitaxial Si/CaF2/Si structure have been presented and discussed. A high quality heteroepitaxial Si/CaF2/Si structure has been obtained by successive molecular beam epitaxy of CaF2 and Si. The epitaxial Si film on CaF2/Si structure has an ion channeling minimum yield of 7 %. It was found, however, that Ca and F segregated at the surface of epitaxial Si films. A possibility of reducing the segregation effect by the use of solid phase epitaxy of Si has been proposed.

Si-gate CMOS devices have been successfully fabricated in a Si/CaF2/Si structure with alt improved CMOS proress. The maximum effective mobiliiies are about 570 cm2/V.sec and 240 cm2/V.sec for n-channel and p-channel transistors, respectively. Propagation delays below 360 ps have been obtained for CMOS inverter chains with Leff = 2 μm. These results indicate that the Si/CaF2/Si structure has potential for the fabrication of high-speed silicon-on-insulator devices.
Lattice-Matched Gaas/Ca0.45Sr0.55F2/Ge(100) Heterostrucuures Grown By Molecular Beam Epitaxy
Authors: Tu C. W. , Beggy J. C. , Baiocchi F. A. , Abys S. M. , Pearton S. J. , Hsieh S. J. , Kopf R. F. , Caruso R. , Jordan A. S.
Published: March 2011

Epitaxial, lattice-matched GaAs/Ca0.45Sr0.55/F2 heterostructures were grown on Ge(100) substrates by molecular beam epitaxy. The films were analyzed by Rutherford backscattering and secondary ion mass spectroscopy to determine crystallinity and Ge outdiffusion. The Xmin (channeling over random yield) of a 1.5 μm-thick GaAs film grown on the fluoride is 0.075, indicating reasonably good epitaxy. After rapid thermal annealing, the crystallinity of higher-Xmin films improves, and Ge diffuses only 200 A into the fluoride, indicating that a thin fluoride layer is an effective barrier to Ge outdiffusion.
Temperature Dependence Of The Electrical Properties Of Epitaxial Caf2 Layers On Si(111) Summary Abstract
Authors: Fathauer R.W. , Schowalter L.J.
Published: March 2011

CaF2 is an insulator with a number of attractive properties for epitaxial growth on Si1 Epitaxial CaF2 layers have been grown on Si(111) by Molecular Beam Epitaxy and are found to have smooth surfaces and a high degree of crystalline perfection.1 For applications such as a gate insulator in metal-insulator-semiconductor field-effect transistors or in silicon-on-insulator technology, the electrical properties of these layers are also critical.
Liquid Phase Epitaxy of Si1−xGex(O<×≲1) On Partially Masked Si-Substrates
Authors: Trah H.-P. , Alonso M.I. , Konuma M. , Bauser E. , Cerva H. , Strunk H.P.
Published: March 2011

Single-crystal Si1−x Gex(O<×≲1) layers are grown by seeded growth on partially SiO2-masked Si-substrates, using a one-step liquid phase epitaxy (LPE) process. The seed regions are stripe- and hole-shaped windows in the oxide, having linear dimensions between 1.5 and 100 μm. The windows extend in different orientation on (111) and (100) orientated substrates. Lateral overgrowth over the oxide-masked areas is achieved up to 70 μm in <110>-directions. X-ray diffraction and Raman scattering show that the epitaxial islands are homogeneous and of excellent crystal quality. In the regions of lateral overgrowth the dislocation density is reduced considerably as shown by defect-etching and cross section transmission electron microscopy.
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

The 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

Primitive (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

Transmission 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

CoSi2 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

The 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

Reflection 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

The 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

InxGa11-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

The 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

The 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

The 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

Certain 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

Many 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

Nd-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

Magnetic 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

Initial 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

A 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

Using 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

A 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

This 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

The 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

The 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

Barium 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

Polycrystalline 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.
The Formation of Y-Ba-Cu-O Phases During Solid State Reaction
Authors: Chin T. S. , Huang T. W. , Lin W. T , Wu N. C. , Chou Y. H. , Wu T. C. , Wu P. T. , Yen H. H.
Published: March 2011

The formation of Y-Ba-Cu-O phases, including the high Tc superconducting YBa2Cu3O7−x (Y123) phase, during solid state reaction of the mixture of Y2O3: BacO3: CuO, in molar ratio of 0.2:0.6:1 to conform the formula of the perovskite (Y0.4 Ba0.6)CuO3 composition was studied by means of DTA, DTG and X-ray difractometry(XRD). For continuous heating at 10 C/min, it was found that the Y123 phase exists at 790–995 C, and gradually disappears at higher temperatures. The insulating Y2BaCuO5 (Y211) phase exists at 985 to 1190 C, the maximum experiment temperature. While the semiconducting YBa3Cu2O7-y, (Y132) phase coexists with the Y123 phase. For isothermal heating, it was found that the most appropriate temperature and time for the formation of the Y123 phase is 900 C and 16 hours. Semiquantitative data on the amount of phases presented, including the above mentioned phases and other binary Ba-Y-O or Ba-Cu-O phases, during heating are also given. High temperature superconductor with a Tc of around 93 K can be synthesized reproducibly by the processes based on this study.
Effect of Thermal Processing on the Microstructures and Superconducting Properties of YBa2Cu3Oy
Authors: Gotoh K. , Enomoto H. , Iida K. , Takano Y. , Mori N. , Ozaki H.
Published: March 2011

The effect of thermal processing in the sample preparation of YBa2Cu3Oy has been investigated systematically on microstructures and electrical properties. The grain size was found to grow preferably during the cooling process rather than during the sintering process. The high Tc superconducting phase appears around 500 C in this thermal processing. The annealing experiment shows that the grains still grow at low temperature such as 300 °C.
Processing - Property Relations in YBa2Cu3O6+x Superconductor
Authors: Safari S. A. , Wachtman J. B. , Parkhe V. , Caracciolo R. , Jeter D. , Rao A. S. , Sundar H. G. K. , Jisrawi N. , McLean W. L.
Published: March 2011

Processing of YBa2Cu3O6+x superconducting samples by employing different precursor powder preparation techniques such as ball milling, attrition milling and also narrow particle size distribution powder preparation through coprecipitation by spraying will be discussed. CuO coated with oxalates shows the lowest resistance above T up to room temperature. The extent of corrosion by water has been studied by employing magnetic susceptibility, XPS and X-ray diffraction. Superconducting samples are affected to a considerable extent when treated in water at 60° C and the severity of the attack increases with time.
Laser Induced Deposition of YBa2Cu3O7−x Thin Films
Authors: Kwok H. S. , Mattocks P. , Shaw D. T. , Shi L. , Wang X. W. , Witanachchi S. , Ying Q. Y. , Zheng J. P. , Bush P.
Published: March 2011

We describe here the deposition of the YBCO superconducting thin films by the laser evaporation technique. The characterization of this process, and possible optimization with regards to wavelength and pulse duration of the laser will be discussed.
Effect of Oxygen Annealing on Low-Resistivity Contactsfor High-Tc Superconductors
Authors: Ekin J. W. , Panson A. J. , Blankenship B. A.
Published: March 2011

A method for making low resistivity contacts to high-Tc superconductors has been developed, consisting of depositing noble metal contact pads (silver or gold) on a clean superconductor surface at low temperatures (<150°C). After annealing the silver contact pads in oxygen at intermediate temperatures (<500°C) for one hour, contact resistivities less than 2 × 10'° Ω-cm2 at 76 K are obtained, about six orders of magnitude less than for indium-solder contacts. Before annealing, the contact resistivities are still very low, in the 10-6 to 10-5 Ω-cm range at 76 K, which would be useful when contacts with low fabrication temperatures are required. The voltage-current characteristics of the contacts are strongly nonlinear after annealing, having a superconducting transition character. This is ascribed to the critical current of the superconducting material being exceeded at the contact interface. External connections to the contact pads have been made using both solder and thermosonic wire-bonding techniques.
Fabrication and Superconducting Properties of High Tc Oxide Wire
Authors: Sadakata N. , Ikeno Y. , Nakagawa M. , Gotoh K. , Kohno O.
Published: March 2011

Since the discovery of high Tc superconducting oxide such as Ln-Ba-Cu-O system which shows superconductivity above liquid nitrogen temperature, intensive study has been carried out to investigate its intrinsic properties[l-4]. Superconducting wire which operates in liquid nitrogen is one of the emerging products among application, however, there are many factors to be investigated for practical use. Critical current density, Jc, is one of the most important characteristics of superconductor, although, only few report describing Jc measurement ever published[5]. In this paper, fabrication procedure of silver sheathed Y-Ba-Cu-O wire by powder metallurgical technique and its superconducting properties have been reported. Other factors which may influence superconductivity such as microstructure of the oxide, configuration of wires, etc. are also discussed.