Search

Details the fabrication of a three bit single flux quantum (SFQ) shift register based on high-temperature bicrystal Josephson junction. Components of SFQ circuit; Design of the Josephson junctions; Results of an experimental testing of the shift register at 50 Kelvin for binary data sequence.

Ga1-xMnxN thin films with a Mn content as high as x=0.18 have been grown using ion-assisted deposition and a combination of Rutherford backscattering spectroscopy and nuclear reaction analysis was used to determine their composition. The structure of the films was determined from x-ray diffraction, transmission electron microscopy, and extended x-ray absorption fine structure (EXAFS). The films are comprised of nanocrystals of random stacked GaMnN and there is no evidence of Mn-rich secondary phases or clusters. EXAFS measurements at the Mn and Ga edge are almost identical to those at the Ga edge from Mn-free nanocrystalline GaN films, showing that the Mn occupies the Ga lattice sites, and simulated radial distribution functions of possible Mn-rich impurity phases bear no resemblance to the experimental data. The results indicate that these are the most heavily Mn-doped single phase GaN films studied to date. [ABSTRACT FROM AUTHOR]

In this work we present a study of the optoelectronic properties of nanocrystalline GaN (nc-GaN) and amorphous GaON (a-GaON) grown by ion-assisted deposition. The two classes of film show very distinct photoconductive responses; the nc-GaN has a fast small response while the a-GaON films have a much larger response which is persistent. To describe the observed intensity, wavelength, and temperature dependence of the photoconductivity in each class of film, we build a model which takes into account the role of a large density of localized states in the gap. The photoconductivity measurements are supplemented by thermally stimulated conductivity, measurement of the absorption coefficient, and determination of the Fermi level. Using the model to aid our interpretation of this data set, we are able to characterize the density of states in the gap for the two materials. [ABSTRACT FROM AUTHOR]

We report Raman measurements on thin films of strongly disordered GaN and GaN:O prepared by ion-assisted deposition. The incident photon energies used in the experiments ranged from 1.95 to 3.8 eV, spanning the interband edge. Under subgap excitation the signal resembles the crystalline GaN vibrational density-of-modes, with significant broadening as expected for disordered material. There is a strong resonant behavior at the interband edge of the same mode for which a strong resonance is found in crystalline GaN, with a width suggesting that the entire vibrational branch contributes to the signal. Even nanocrystalline material is found to display Raman spectra characteristic of very short-range (<1 n) translational symmetry, in agreement with x-ray diffraction evidence for the random stacking nature of the 3 nm diameter crystallites. The presence of oxygen at even 25 at.% has only a subtle effect on Raman spectra at the network vibrational frequencies below 800 cm-1, but its presence is signaled by the appearance of an oxygen mode at 1000 cm-1. An N2 line at 2360 cm-1 correlates with a nitrogen excess introduced during growth. [ABSTRACT FROM AUTHOR]

Epitaxial growth of (100)-oriented rare-earth nitrides (RENs) SmN, GdN, and DyN on (100)LaAlO3 (LAO) substrates is demonstrated using molecular beam epitaxy. RHEED and ϕ-scans confirm that the cubic RENs grow 45° rotated with respect to the pseudocubic (100)-surface of LAO, which leads to lattice mismatches between −5.8% and −8.7% for the selected RENs. Those lattice mismatches, despite being significant, are smaller than in previously reported epitaxial (100)RENs, with the exception of growth on (100)YSZ (yttria stabilized zirconia), which however causes the formation of an interface oxide layer. The SmN RHEED pattern shows intense streaks, indicating a high quality, flat surface, and the rocking curves are among the narrowest reported for (100)RENs. In contrast to growth on Si, the epitaxial RENs readily form over a wide range of substrate temperatures, without the need of special substrate treatment or intermediate layers. This robust, high quality growth paired with their clear magnetic switching behavior makes epitaxial RENs grown on LAO ideal candidates for future spintronic devices. [ABSTRACT FROM AUTHOR]

SmN is a ferromagnetic semiconductor with the unusual property of an orbital-dominant magnetic moment that is largely canceled by an antiparallel spin contribution, resulting in a near-zero net moment. However, the ferromagnetic ground state is not fully understood, with existing density functional theory calculations providing values of the 4f magnetic moments at odds with experimental data. To clarify the situation, we employ an effective 4f Hamiltonian incorporating spin-orbit coupling, exchange, the crystal field, and J mixing to calculate the ground state 4f moments. Our results are in excellent agreement with experimental data, revealing moderate quenching of both spin and orbital moments to magnitudes of ~2 µB in bulk SmN, enhanced to an average of ~3 µB in SmN layers within a SmN/GdN superlattice. [ABSTRACT FROM AUTHOR]

We investigate the previously observed superconductivity in ferromagnetic SmN in the context of the breakdown of order between two magnetic phases. Nitrogen vacancy doped SmN 1 - δ is a semiconductor which lies in the intermediary between ferromagnetic SmN and anti-ferromagnetic Sm. Optical data reported here corroborate the prediction that electrical transport is mediated by Sm 4f defect states, and electrical transport measurements characterise the metal-insulator transition over the doping range. Our measurements show that the superconducting state in nitrogen vacancy doped SmN 1 - δ is the most robust near the breakdown of magnetic order, and indicate the location of a quantum critical point. Furthermore we provide additional evidence that the superconducting state is formed from majority spin electrons and thus of unconventional S = 1 type. [ABSTRACT FROM AUTHOR]

We demonstrate a nonvolatile cryogenic magnetic memory element needed to support emerging superconducting- and quantum-computing technologies. The central element is a switchable tri-layer thin film magnetic dot comprising two semiconducting ferromagnetic GdxSm1−xN layers separated by an exchange-blocking Al layer. The materials are explored for their tunable magnetic responses, the potential to engineer compensating magnetic moments in the anti-parallel tri-layers. The stability of the parallel and anti-parallel states and the reproducibility over repeated cycles are also demonstrated. We show that the tri-layer stacks can be formed into dots as small as 4 μm diameter, without affecting their magnetic behavior. [ABSTRACT FROM AUTHOR]

We report magnetoresistance measurements on epitaxial films of the intrinsic ferromagnetic semiconductor GdN electron doped with ∼ 10 20 cm − 3 to ∼ 10 21 cm − 3 . The magnetoresistance across the temperature range of 10–300 K is dominated by a reduction of spin-disorder scattering in the presence of a magnetic field, imposing a resistance reduction of 27% in a field of 8 T. We show that the magnetoresistance closely follows the magnetic disorder as signaled by the departure of the magnetization from its fully saturated value M s of 7 μ B / G d 3 + . [ABSTRACT FROM AUTHOR]

Hepatitis associated antigen may be detected quickly and reliably by the latex agglutination test, using antiserum from guinea pigs immunized with the antigen. The latex test has a sensitivity comparable to the counter current immunoelectrophoresis technique. [ABSTRACT FROM PUBLISHER]

The American Academy of Pediatrics' recent technical report entitled 'Mercury in the Environment: Implications for Pediatricians' was widely reported on by the news media. After the media reports, the New Jersey Poison Information and Education System experienced a notable increase in the volume of calls on this topic. We surveyed local, county, and state health officers who would likely be contacted by citizens with the question: 'How should a fever mercury thermometer be disposed of?' Our initial contacts with health officers corroborated our caller's account: a lack of uniformity of response. This led us to question if there was any consensus in advice being offered to the public at large. [Abstract for this article also available on page 945 of printed version. Full article available at www.pediatrics.org] [ABSTRACT FROM AUTHOR]

A unique bulk-origin perpendicular magnetic anisotropy (PMA) is reported in thin films of the cubic ferromagnetic semiconductor GdxSm1−xN. PMA behavior is clearly signaled by in-vs-out-of-plane magnetic hysteresis showing out-of-plane remanence of ∼ 80 % of the saturation magnetization in films with up to 30% Gd. Anomalous Hall effect data show further that the conduction-band spin imbalance shows complete 100% remanence to retain half-metallic conduction even as the out-of-plane applied field is reduced to zero, in stark contrast to the 80% magnetization remanence. The unusual occurrence of PMA in this cubic material is discussed as stabilized by a mix of two in-plane crystal orientations in the epitaxial (111)-oriented films. [ABSTRACT FROM AUTHOR]

We measured the static error rate of a high-T[sub c] superconductor dc superconducting quantum interference device (SQUID), which, in the form as a storage loop for single flux quanta, is a basic element of rapid single flux quantum circuits. Using high-T[sub c] multilayer bicrystal technology, we fabricated a stacked dc SQUID pair, one SQUID serving as the storage loop, the other one as the readout device. The escape rate of a stored flux quantum was measured as a function of the bias current at a temperature of 28 K. The measured error rates were in good agreement with a model calculation based on thermally activated barrier crossing. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The strong spin-orbit interaction in the rare-earth elements ensures that even within a ferromagnetic state there is a substantial orbital contribution to the ferromagnetic moment, in contrast to more familiar transition metal systems in which the orbital moment is usually quenched. The orbital-dominant magnetization that is then possible within rare-earth systems facilitates the fabrication of entirely new magnetic heterostructures, and here we report a study of a particularly striking example comprising interfaces between GdN and SmN. Our investigation reveals a twisted magnetization arising from the large spin-only magnetic moment in GdN and the nearly zero, but orbital-dominant, moment of SmN. The unusual twisted phase is driven by (i) the similar ferromagnetic Gd-Gd, Sm-Sm, and Gd-Sm exchange interactions, (ii) a SmN Zeeman interaction 200 times weaker than that of GdN, and (iii) the orbital-dominant SmN magnetic moment. The element specificity of x-ray magnetic circular dichroism is used in separate modes probing both bulk and surface regions, revealing the depth profile of the twisting magnetization. [ABSTRACT FROM AUTHOR]

Far infrared measurements of the absorption into the IR-active TO(Γ) mode are reported for a selection of the rare-earth mononitrides. The frequencies harden as anticipated by ≈15% as the lattice constant shrinks by ≈6% from SmN to LuN, though they are typically ∼25% softer than the LSDA+U prediction published a decade ago. The data are in much closer agreement with our computation based on more recent software for two in the series: GdN and LuN. The resonances show surprisingly heavy damping, diminishing from the lighter to heavier rare earth elements. [ABSTRACT FROM AUTHOR]

We report electrical transport and optical spectroscopy measurements on LuN thin films variously doped with nitrogen vacancies along with the computed band structures of stoichiometric and nitrogen vacancy doped LuN. LuN has been the subject of several recent computational studies; however, the most recent experimental studies regarding its electronic properties are already over four decades old. Here, we bridge the void between computation and experiment with a combined study of LuN focusing on its electronic properties. We find that LuN is a semiconductor with an optical bandgap of ∼1.7 eV. Its conductivity can be controlled by nitrogen vacancy doping, which results in defect states at the conduction band minimum and valence band maximum. These results not only provide information on LuN but also help underpin understanding of the electronic properties of the entire rare-earth nitride series. [ABSTRACT FROM AUTHOR]

We report the results from structural, electrical and magnetic measurements on Gd-implanted ion beam deposited zinc oxide (ZnO) films. 40 keV Gd ions were implanted into 150 nm thick ZnO films with fluence 2.8 × 10 cm. RBS spectra reveal the implanted atoms are located in the near-surface region in as-implanted and up to 923 K annealed films, diffusing deeper into the films after 1073 K annealing. SEM images show that the average grain size increases from 10 to 30 nm upon annealing. High-resolution and energy-filtered transmission electron microscopy of a ZnO:Gd sample annealed at 923 K reveal the presence of Gd-rich regions in the film, but no evidence of pure Gd precipitates. Annealing increases the resistivity, and the carrier concentration decreases by as much as six orders of magnitude after annealing at up to 1073 K. All annealed films display a mix of paramagnetic, superparamagnetic and ferromagnetic behaviour extending to temperatures above 300 K that we attribute to the spatially inhomogeneous Gd distribution. The paramagnetic behaviour can be attributed to isolated Gd moments, while the ordered magnetic phases appear to arise from Gd-rich regions within the ZnO. X-ray absorption near edge spectroscopy provides evidence that there exist oxygen vacancies. [ABSTRACT FROM AUTHOR]

Background and objective: Prompted by continuing concerns about the safety of over-the-counter (OTC) cough and cold medications, we examined the frequency and severity of pediatric adverse drug reactions (ADRs) to OTC cough and cold products reported to a major poison control center. The goal was to focus on cases that are usually managed out of hospitals and may not be recognized by the traditional adverse events surveillance and reporting programs. Methods: We conducted a retrospective review of electronic records on ADRs reported to the New Jersey Poison Information and Education System (NJPIES) through the National Poison Data System. Analyses included ADRs involving a single OTC cough and cold product. The number and proportion of reported ADRs to OTC cough and cold medicines were examined and compared by severity level between children <2 years of age, and children from 2 through 11 years of age. Results: A total of 91 pediatric ADRs to OTC cough and cold products were reported to the NJPIES from 2000 through 2007. Of these, 61 cases (67%) were of minor severity. A larger proportion of the children 2–11 years of age (21·2%), compared with children <2 years of age (8·0%), experienced a reaction of moderate to major severity. Conclusions: While we found fewer ADR cases of moderate to major severity in younger children, our results call for a further review of the safety of OTC cough and cold medicines in children 2 years of age and older. [ABSTRACT FROM AUTHOR]

GdN and SmN are two of the lanthanide nitrides, most of which are intrinsic ferromagnetic semiconductors. Superlattices comprising the pair offer a unique opportunity to investigate heterojunctions that feature simultaneous conductivity and magnetic interface influences. Here we report an investigation of these influences, using magnetisation and X-ray magnetic circular dichroism for magnetic effects, and magnetoresistance and Hall effect studies of their electrical conductance. Magnetic data show clear signatures of a conflicting Zeeman vs. interfacial exchange and the magnetic disruption that results, while resistivity and Hall measurements show conduction in both GdN and SmN. [ABSTRACT FROM AUTHOR]

We report on the effect of the nitrogen to rare earth (N2/RE) flux ratio on the structural, transport, and magnetic properties of samarium nitride (SmN) and dysprosium nitride (DyN) thin films. Both materials display a reduced lattice constant when the N2/RE flux ratio decreases, i.e., with increased nitrogen vacancies (VN) concentration. The films show several orders of magnitude increase in the electrical resistivity with increased N2/RE flux ratio. Finally, magnetic measurements on DyN films display a deviation from the free ion moment at low temperature, which is eased in more conductive films. This was interpreted as a further reduction in the quenching of the orbital angular momentum caused by the increased VN concentration. The Curie temperature was also found to increase with VN. [ABSTRACT FROM AUTHOR]

Most members of the ferromagnetic rare-earth nitride series display doping control over electron transport, with nitrogen vacancies being the most common donor. This paper reports the control and characterization of vacancies in one of the fourteen in the series, DyN. Electrical transport and optical spectra in films with controlled concentrations of vacancies show a pair of in-gap impurity levels ∼ 0.4 eV below the conduction band minimum and a third impurity level that lies nearly coincident with the conduction band minimum. Electron transport is found to be activated for concentrations ≤ 1019 cm−3, with signatures of extended state conduction at the Fermi level for higher concentrations. [ABSTRACT FROM AUTHOR]

We present the structural and photoluminescence properties of 30 keV gadolinium implanted and subsequently annealed zinc oxide (ZnO) single crystals. Rutherford backscattering and channeling results reveal a low surface region defect density which was reduced further upon annealing. For low implantation fluence, around 85% of the Gd atoms are estimated to be in sites aligned with the ZnO lattice, while for higher fluences the Gd is largely disordered and likely forms precipitates. The Raman spectra of the implanted samples show defect-induced modes, which match the one-phonon density of states for the most heavily implanted samples. Annealing eliminates these features implying the removal of Gd-associated lattice disorder. Low temperature photoluminescence spectra revealed a red-shift in the defect emission, from green to orange/yellow, indicating the suppression of a deep level, which is thought to be due to oxygen vacancies. It is suggested that the orange/yellow emission is unmasked when the green emission is quenched by the presence of the implanted Gd atoms. [ABSTRACT FROM AUTHOR]

Epitaxial gadolinium nitride films with well-oriented crystallites of up to 30 nm have been grown on yttria-stabilized ziconia substrates using a plasma-assisted pulsed laser deposition technique. We observe that the epitaxial GdN growth proceeds on top of a gadolinium oxide buffer layer that forms via reaction between deposited Gd and mobile oxygen from the substrate. Hall effect measurements show the films are electron doped to degeneracy, with carrier concentrations of 4×1020 cm-3. Magnetic measurements establish a TC of 70 K with a coercive field that can be tuned from 200 Oe to as low as 10 Oe. [ABSTRACT FROM AUTHOR]

The intrinsic ferromagnetic semiconductor GdN offers a unique opportunity to separate the anomalous and ordinary contributions to the Hall effect, and to investigate the strength of the anomalous Hall effect (AHE) as a function of carrier concentration and relaxation time. The data show an AHE that is inversely proportional to the carrier concentration n in a single spin channel. There is no dependence at all on the relaxation time τ, rather than the usual τ¹ or τ² dependencies predicted by conventional mechanisms. However, the n and τ dependencies are identical to those of the ordinary Hall effect, which suggests a semiclassical wave-packet description of an intrinsic AHE contribution that ultimately provides a quantitative agreement with the data. [ABSTRACT FROM AUTHOR]

The rare-earth nitrides have recently regained attention due to findings that most members of the series are intrinsic ferromagnetic semiconductors, a class of materials that is crucial for the development of spintronics devices. Here we present a study of NdN thin films, with films grown via molecular beam epitaxy. Optical transmission measurements revealed a band gap of about 0.9 eV, while resistivity measurements confirmed semiconducting behavior with a negative temperature coefficient of resistance, though semimetallic behavior could not be ruled out. The room temperature resistivity of 0.6mΩcm indicates strong doping by nitrogen vacancies. Magnetization measurements show a ferromagnetic moment of 1.0±0.2μB below the Curie temperature TC of 43±1 K, strongly suppressed from the Hund's rules value of 3.27μB per ion. The ferromagnetic moment is strongly quenched and the TC is enhanced compared to previously studied bulk NdN, and crystal field calculations reveal that the quenched moment is likely due to lattice strain. X-ray magnetic circular dichroism measurements show that the magnetic moment is orbital dominant, placing NdN in the same category as SmN, an intrinsic ferromagnetic semiconductor with an orbital-dominant ferromagnetic moment. [ABSTRACT FROM AUTHOR]

We report the growth by molecular beam epitaxy of highly resistive GdN, using intentional doping with magnesium. Mg-doped GdN layers with resistivities of 10³ Ω cm and carrier concentrations of 1016cm-3 are obtained for films with Mg concentrations up to 5 x 1019 atoms/cm³. X-ray diffraction rocking curves indicate that Mg-doped GdN films have crystalline quality very similar to undoped GdN films, showing that the Mg doping did not affect the structural properties of the films. A decrease of the Curie temperature with decreasing the electron density is observed, supporting a recently suggested magnetic polaron scenario [F. Natali, B. J. Ruck, H. J. Trodahl, D. L. Binh, S. Vezian, B. Damilano, Y. Cordier, F. Semond, and C. Meyer, Phys. Rev. B 87, 035202 (2013)]. [ABSTRACT FROM AUTHOR]

The increasing availability and use of synchrotron radiation has opened up new horizons in materials research. These sources offer very high brightness photon probes in an unparalleled wavelength range from the UV to the hard X-ray region. Although the medium to hard energy extended X-ray absorption fine structure (EXAFS) has been widely used in materials characterisation, the near edge absorption spectrum (XANES), especially in the soft X-ray region below 2 kV, has been exploited to only a limited degree. This relates to both the difficulties and limited availability of soft X-ray monochromators and the complexity of the spectra relative to the EXAFS region. We have used XANES in studies of semiconductor oxide and nitride materials, the speciation of sulfur in industrial smelting anodes and the development of oxide based electrode materials for Li ion batteries. Although of limited quantitative applicability, the chemical detail available in these spectra is considerably superior to that in the X-ray photoelectron (XPS) spectrum and demonstrates the considerable power of the method. [Copyright &y& Elsevier]