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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

An interchangeable scanning Hall probe/scanning SQUID microscope

We have constructed a scanning probe microscope for magnetic imaging, which can function as a scanning Hall probe microscope (SHPM) and as a scanning SQUID microscope (SSM). The scanning scheme, applicable to SHPM and SSM, consists of a mechanical positioning (sub) micron-XY stage and a flexible direct contact to the sample without a feedback control system for the Z-axis. With the interchangeable capability of operating two distinct scanning modes, our microscope can incorporate the advantageous functionalities of the SHPM and SSM with large scan range up to millimeter, high spatial resolution (⩽4 μm), and high field sensitivity in a wide range of temperature (4.2 K-300 K) and magnetic field (10{sup −7} T-1 T). To demonstrate the capabilities of the system, we present magnetic images scanned with SHPM and SSM, including a RbFeB magnet and a nickel grid pattern at room temperature, surface magnetic domain structures of a La{sub 2/3}Ca{sub 1/3}MnO{sub 3} thin film at 77 K, and superconducting vortices in a striped niobium film at 4.2 K.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Time resolved imaging of magnetization dynamics in hard disk writer yokes excited by bipolar current pulses

A partially built hard disk writer structure with a NiFe/CoFe/Ru/NiFe/CoFe synthetic antiferromagnetic (SAF) yoke was studied by time and vector resolved scanning Kerr microscopy. All three time dependent components of the magnetization were recorded simultaneously as a bipolar current pulse with 1 MHz repetition rate was delivered to the coil. The component of magnetization parallel to the symmetry axis of the yoke was compared at the pole and above a coil winding in the centre of the yoke. The two responses are in phase as the pulse rises, but the pole piece lags the yoke as the pulse falls. The Kerr signal is smaller within the yoke than within the confluence region during pulse cycling. This suggests funneling of flux into the confluence region. Dynamic images acquired at different time delays showed that the relaxation is faster in the centre of the yoke than in the confluence region, perhaps due to the different magnetic anisotropy in these regions. Although the SAF yoke is designed to support a single domain to aid flux conduction, no obvious flux beaming was observed, suggesting the presence of a more complicated domain structure. The SAF yoke writer hence provides relatively poor flux conduction but good control of rise time compared to single layer and multi-layered yokes studied previously.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

The ChiS-Family DNA-Binding Domain Contains a Cryptic Helix-Turn-Helix Variant

Sequence-specific DNA-binding domains (DBDs) are conserved in all domains of life. These proteins carry out a variety of cellular functions, and there are a number of distinct structural domains already described that allow for sequence-specific DNA binding, including the ubiquitous helix-turn-helix (HTH) domain. In the facultative pathogen Vibrio cholerae, the chitin sensor ChiS is a transcriptional regulator that is critical for the survival of this organism in its marine reservoir. We recently showed that ChiS contains a cryptic DBD in its C terminus. This domain is not homologous to any known DBD, but it is a conserved domain present in other bacterial proteins. Here, we present the crystal structure of the ChiS DBD at a resolution of 1.28 Å. We find that the ChiS DBD contains an HTH domain that is structurally similar to those found in other DNA-binding proteins, like the LacI repressor. However, one striking difference observed in the ChiS DBD is that the canonical tight turn of the HTH is replaced with an insertion containing a β-sheet, a variant which we term the helix-sheet-helix. Through systematic mutagenesis of all positively charged residues within the ChiS DBD, we show that residues within and proximal to the ChiS helix-sheet-helix are critical for DNA binding. Finally, through phylogenetic analyses we show that the ChiS DBD is found in diverse proteobacterial proteins that exhibit distinct domain architectures. Together, these results suggest that the structure described here represents the prototypical member of the ChiS-family of DBDs.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Effect of the Sintering Temperature on the Formation of Ferroelectric Properties of a Lead Zirconate–Titanate Ceramic

Effect of the sintering temperature on the formation of the microstructure, the domain structure, and the ferroelectric properties of a lead zirconate–titanate Pb(Ti{sub x}Zr{sub 1–} {sub x})O{sub 3} piezoelectric ceramics has been studied. It is shown that the ferroelectric phase forms at a sintering temperature of 860°C. At higher sintering temperatures, the main effect on the properties is due to a unit cell deformation and free charge carriers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Magnetic vortex in epitaxially-grown Co{sub 2}(Fe,Mn)Si alloy

We report magnetic vortex formation in epitaxially grown Co{sub 2}Fe{sub 0.4}Mn{sub 0.6}Si (CFMS) Heusler alloy discs that was confirmed using photoemission electron microscopy and the magneto-optical Kerr effect. The phase diagram of magnetic domain structures as functions of the disc thickness (t) and diameter (D) indicates that the magnetic vortex is stable in wide ranges of t and D even for the epitaxial CFMS. The annihilation field of vortex core depended not only on the disc aspect ratio but also on t. Numerical simulation suggests that this t dependence results from extrinsic pinning of a vortex core due to the epitaxial growth.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Structural, Mechanistic, and Antigenic Characterization of the Human Astrovirus Capsid

Human astroviruses (HAstVs) are nonenveloped, positive-sense, single-stranded RNA viruses that are a leading cause of viral gastroenteritis. HAstV particles display T=3 icosahedral symmetry formed by 180 copies of the capsid protein (CP), which undergoes proteolytic maturation to generate infectious HAstV particles. Little is known about the molecular features that govern HAstV particle assembly, maturation, infectivity, and immunogenicity. Here we report the crystal structures of the two main structural domains of the HAstV CP: the core domain at 2.60-Å resolution and the spike domain at 0.95-Å resolution. Fitting of these structures into the previously determined 25-Å-resolution electron cryomicroscopy density maps of HAstV allowed us to characterize the molecular features on the surfaces of immature and mature T=3 HAstV particles. The highly electropositive inner surface of HAstV supports a model in which interaction of the HAstV CP core with viral RNA is a driving force in T=3 HAstV particle formation. Additionally, mapping of conserved residues onto the HAstV CP core and spike domains in the context of the immature and mature HAstV particles revealed dramatic changes to the exposure of conserved residues during virus maturation. Indeed, we show that antibodies raised against mature HAstV have reactivity to both the HAstV CP core and spike domains, revealing for the first time that the CP core domain is antigenic. Together, these data provide new molecular insights into HAstV that have practical applications for the development of vaccines and antiviral therapies. Astroviruses are a leading cause of viral diarrhea in young children, immunocompromised individuals, and the elderly. Despite the prevalence of astroviruses, little is known at the molecular level about how the astrovirus particle assembles and is converted into an infectious, mature virus. In this paper, we describe the high-resolution structures of the two main astrovirus capsid proteins. Fitting these structures into previously determined low-resolution maps of astrovirus allowed us to characterize the molecular surfaces of immature and mature astroviruses. Our studies provide the first evidence that astroviruses undergo viral RNA-dependent assembly. We also provide new insight into the molecular mechanisms that lead to astrovirus maturation and infectivity. Finally, we show that both capsid proteins contribute to the adaptive immune response against astrovirus. Together, these studies will help to guide the development of vaccines and antiviral drugs targeting astrovirus.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Positive magnetoresistance in ferromagnetic Nd-doped In{sub 2}O{sub 3} thin films grown by pulse laser deposition

We report the magnetic and magnetotransport properties of (In{sub 0.985}Nd{sub 0.015}){sub 2}O{sub 2.89} thin films grown by pulse laser deposition. The clear magnetization hysteresis loops with the complementary magnetic domain structure reveal the intrinsic room temperature ferromagnetism in the as-prepared films. The strong sp-f exchange interaction as a result of the rare earth doping is discussed as the origin of the magnetotransport behaviours. A positive magnetoresistance (∼29.2%) was observed at 5 K and ascribed to the strong ferromagnetic sp-f exchange interaction in (In{sub 0.985}Nd{sub 0.015}){sub 2}O{sub 2.89} thin films due to a large Zeeman splitting in an external magnetic field of 50 KOe.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Chemically Synthesized FeCo Powder for Advanced Applications

Very weak stray magnetic fields, H ∼ 10{sup − 4} Oe, of an assembly of FeCo particles of mesoscopic dimensions, d = 10–50 μm, are investigated using a sensitive scanning giant magneto-impedance magnetometer. Direct magnetic force microscopy measurement of individual FeCo particles reveals a complicated domain structure. It is proved, however, that the mean square value of the stray magnetic field of a dilute assembly of FeCo particles randomly distributed on the plane is a statistically well-defined quantity. It depends on the average particle diameter, average distance between the particles, and average particle magnetization per unit volume. It is shown that the average particle magnetization can be determined using a measured mean square value of the stray magnetic field and geometrical parameters of the assembly obtained from optical measurement.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Growth and characterization of nonpolar, heavily Mn-substituted ZnO films

Eight percent of Mn was successfully diluted into nonpolar ZnO films deposited by pulsed laser deposition on single crystal (100) SrTiO{sub 3} substrates. X-ray diffraction patterns and energy-dispersive X-ray spectroscopy confirmed high crystallinity of the films and excluded unintentional magnetic doping. A unique surface domain structure was observed by scanning electron microscope and atomic force microscope, which might play a vital role to strain release induced by lattice mismatch between nonpolar (11–20) ZnO film and (100) SrTiO{sub 3} substrate. In addition, the films showed strong ferromagnetism with a large coercivity H{sub C} ∼ 180 Oe at room temperature. The large magnetic moment is ascribed to carrier-mediated exchange interaction between the Mn ions, where the majority of the carriers are oxygen vacancies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Magneto-optical visualization by Bi:YIG thin films prepared at low temperatures

A device for the imaging of magnetic fields and domain structures based on the Faraday effect has been developed using garnet thin films prepared by the metal-organic decomposition method as indicators. The sensitivity was improved by using high concentration bismuth substituted yttrium iron garnet thin films with in-plane magnetic anisotropy. Low temperature synthesis of the films (Bi{sub x}Y{sub 3−x}Fe{sub 5}O{sub 12}; x = 2) on glass substrates of thickness about 0.8 μm is described and the Faraday rotation angle is measured to be about −11°/μm.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Optical properties of C-doped bulk GaN wafers grown by halide vapor phase epitaxy

Freestanding bulk C-doped GaN wafers grown by halide vapor phase epitaxy are studied by optical spectroscopy and electron microscopy. Significant changes of the near band gap (NBG) emission as well as an enhancement of yellow luminescence have been found with increasing C doping from 5 × 10{sup 16} cm{sup −3} to 6 × 10{sup 17} cm{sup −3}. Cathodoluminescence mapping reveals hexagonal domain structures (pits) with high oxygen concentrations formed during the growth. NBG emission within the pits even at high C concentration is dominated by a rather broad line at ∼3.47 eV typical for n-type GaN. In the area without pits, quenching of the donor bound exciton (DBE) spectrum at moderate C doping levels of 1–2 × 10{sup 17} cm{sup −3} is observed along with the appearance of two acceptor bound exciton lines typical for Mg-doped GaN. The DBE ionization due to local electric fields in compensated GaN may explain the transformation of the NBG emission.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Effect of annealing on exchange stiffness of ultrathin CoFeB film with perpendicular magnetic anisotropy

The effect of annealing on the exchange stiffness of ultrathin CoFeB films with perpendicular magnetic anisotropy was investigated through the observation of magnetic domain structures by magneto-optic Kerr-effect microscopy. A significant reduction of the exchange stiffness after an annealing process was observed, which is in striking contrast to a previous report that studied thick CoFeB films with in-plane magnetic anisotropy. Our results suggest that interdiffusion of non-magnetic atoms from the adjacent layer into CoFeB layer reduces the exchange stiffness, which explains the difference between the annealing effect on ultrathin and the thick CoFeB films. Thus, it is critical to prevent annealing-induced interdiffusion in order to suppress undesired sub-volume switching that degrades thermal stability of a free-layer in spin-transfer torque magnetic random access memory.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Spin-triplet electron transport in hybrid superconductor heterostructures with a composite ferromagnetic interlayer

Hybrid YBa{sub 2}Cu{sub 3}O{sub 7−x}/SrRuO{sub 3}/La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/Au-Nb superconductor mesastructures with a composite manganite-ruthenate ferromagnetic interlayer are studied using electrophysical, magnetic, and microwave methods. The supercurrent in the mesastructure is observed when the interlayer thickness is much larger than the coherence length of ferromagnetic materials. The peak on the dependence of the critical current density on the interlayer material thickness corresponds to the coherence length, which is in qualitative agreement with theoretical predictions for a system with spit-triplet superconducting correlations. The magnetic-field dependence of the critical current is determined by penetration of magnetic flux quanta and by the magnetic domain structure, as well as by the field dependence of disorientation of the magnetization vectors of the layers in the composite magnetic interlayer. It is found that the supercurrent exists in magnetic fields two orders of magnitude stronger than the field corresponding to entry of a magnetic flux quantum into the mesastructure. The current-phase relation (CPR) of the supercurrent of mesastructures is investigated upon a change in the magnetic field from zero to 30 Oe; the ratio of the second CPR harmonic to the first, determined from the dependence of the Shapiro steps on the microwave radiation amplitude, does not exceed 50%.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

High energy storage density performance of Ba, Sr-modified lead lanthanum zirconate titanate stannate antiferroelectric ceramics

Graphical abstract: Polarization hysteresis (P–E) loops of the (Pb{sub 0.85}Ba{sub 0.08}Sr{sub 0.03}La{sub 0.03}) (Zr{sub 0.74}Sn{sub 0.22}Ti{sub 0.04}) samples: (a) measured at different applied electric-field and (b) measured at different temperatures is shown. It is typical antiferroelectrics whose remnant polarization is zero. As the remnant polarization of AFE is small and the ceramics are accompanied by the formation of the anti-parallel domain structure, energy stored in PLZST can be effectively released. Thus we calculated the energy density from the P–E loop and obtained the power density was up to 1.2 J/cm{sup 3} at 55 °C, and at 45 °C the energy density was ∼1.24 J/cm{sup 3}. As usual, for bulk ceramics, the switching between the AFE and FE states occurs at lower field. This value is much higher than that reported previously for the PLZT bulk ceramic (0.4 J/cm{sup 3}). - Highlights: • Ba{sup 2+}, Sr{sup 2+} co-doping caused the T{sub c} of PLZST moved to the lower temperature (T{sub c} ≈ 40 °C). • The ΔE was so smaller, E{sub AF} ≈ 90 kV/cm and E{sub FA} ≈ 85 kV/cm. • Ba, Sr co-doped PLZST ceramic exhibited slanted P–E loops with a large breakdown field (100 kV/cm). • A high energy density was up to 1.2 J/cm{sup 3}. - Abstract: (Pb{sub 0.85}Ba{sub 0.08}Sr{sub 0.03}La{sub 0.03})(Zr{sub 0.74}Sn{sub 0.22}Ti{sub 0.04}) (Ba, Sr co-doped PLZST) co-doping antiferroelectric (AFE) ceramics with orthorhombic perovskite structure were prepared by the traditional solid state reaction process. It was observed that the doping of barium and strontium caused the Curie temperature of PLZST move to the lower temperature (T{sub c} ≈ 40 °C). Ba, Sr co-doped PLZST AFE ceramics exhibited excellent electrical properties, the AFE to ferroelectric (FE) transition occurred at field E{sub AF} ≈ 90 kV/cm, and the transition from FE to AFE occurred at E{sub FA} ≈ 85 kV/cm. The maximum relative permittivity was about 4800, occurring at a field near the AFE to FE transition point, with a dielectric loss of 0.006. The samples exhibited small ΔE and slanted hysteresis loops with a large breakdown field of 100 kV/cm due to Ba, Sr co-doping ceramics, and a high energy density of 1.2 J/cm{sup 3}.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Surface potential at a ferroelectric grain due to asymmetric screening of depolarization fields

Nonlinear screening of electric depolarization fields, generated by a stripe domain structure in a ferroelectric grain of a polycrystalline material, is studied within a semiconductor model of ferroelectrics. It is shown that the maximum strength of local depolarization fields is rather determined by the electronic band gap than by the spontaneous polarization magnitude. Furthermore, field screening due to electronic band bending and due to presence of intrinsic defects leads to asymmetric space charge regions near the grain boundary, which produce an effective dipole layer at the surface of the grain. This results in the formation of a potential difference between the grain surface and its interior of the order of 1 V, which can be of either sign depending on defect transition levels and concentrations. Exemplary acceptor doping of BaTiO{sub 3} is shown to allow tuning of the said surface potential in the region between 0.1 and 1.3 V.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Magnetic surface domain imaging of uncapped epitaxial FeRh(001) thin films across the temperature-induced metamagnetic transition

The surface magnetic domain structure of uncapped epitaxial FeRh/MgO(001) thin films was imaged by in-situ scanning electron microscopy with polarization analysis (SEMPA) at various temperatures between 122 and 450 K. This temperature range covers the temperature-driven antiferromagnetic-to-ferromagnetic phase transition in the body of the films that was observed in-situ by means of the more depth-sensitive magneto-optical Kerr effect. The SEMPA images confirm that the interfacial ferromagnetism coexisting with the antiferromagnetic phase inside the film is an intrinsic property of the FeRh(001) surface. Furthermore, the SEMPA data display a reduction of the in-plane magnetization occuring well above the phase transition temperature which, thus, is not related to the volume expansion at the phase transition. This observation is interpreted as a spin reorientation of the surface magnetization for which we propose a possible mechanism based on temperature-dependent tetragonal distortion due to different thermal expansion coefficients of MgO and FeRh.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The exo-β- N -acetylmuramidase NamZ from Bacillus subtilis is the founding member of a family of exo-lytic peptidoglycan hexosaminidases

Endo-β-N-acetylmuramidases, commonly known as lysozymes, are well-characterized antimicrobial enzymes that catalyze an endo-lytic cleavage of peptidoglycan; i.e., they hydrolyze the β-1,4-glycosidic bonds connecting N-acetylmuramic acid (MurNAc) and N-acetylglucosamine (GlcNAc). In contrast, little is known about exo-β-N-acetylmuramidases, which catalyze an exo-lytic cleavage of β-1,4-MurNAc entities from the non-reducing ends of peptidoglycan chains. Such an enzyme was identified earlier in the bacterium Bacillus subtilis, but the corresponding gene has remained unknown so far. We now report that ybbC of B. subtilis, renamed namZ, encodes the reported exo-β-N-acetylmuramidase. A ΔnamZ mutant accumulated specific cell wall fragments and showed growth defects under starvation conditions, indicating a role of NamZ in cell wall turnover and recycling. Recombinant NamZ protein specifically hydrolyzed the artificial substrate para-nitrophenyl β-MurNAc and the peptidoglycan-derived disaccharide MurNAc-β-1,4-GlcNAc. Together with the exo-β-N-acetylglucosaminidase NagZ and the exo-muramoyl-L-alanine amidase AmiE, NamZ degraded intact peptidoglycan by sequential hydrolysis from the non-reducing ends. A structure model of NamZ, built on the basis of two crystal structures of putative orthologs from Bacteroides fragilis, revealed a two-domain structure including a Rossmann-fold-like domain that constitutes a unique glycosidase fold. Thus, NamZ, a member of the DUF1343 protein family of unknown function, is now classified as the founding member of a new family of glycosidases (CAZy GH171). NamZ-like peptidoglycan hexosaminidases are mainly present in the phylum Bacteroidetes and less frequently found in individual genomes within Firmicutes (Bacilli, Clostridia), Actinobacteria, and γ-proteobacteria.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Phonon dynamics and Urbach energy studies of MgZnO alloys

The Mg{sub x}Zn{sub 1−x}O alloy system is emerging as an environmentally friendly choice in ultraviolet lighting and sensor technologies. Knowledge of defects which impact their optical and material properties is a key issue for utilization of these alloys in various technologies. The impact of phase segregation, structural imperfections, and alloy inhomogeneities on the phonon dynamics and electronic states of Mg{sub x}Zn{sub 1−x}O thin films were studied via selective resonant Raman scattering (SRRS) and Urbach analyses, respectively. A series of samples with Mg composition from 0–68% were grown using a sputtering technique, and the optical gaps were found to span a wide UV range of 3.2–5.8 eV. The extent of the inherent phase segregation was determined via SRRS using two UV-laser lines to achieve resonance with the differing optical gaps of the embedded cubic and wurtzite structural domains. The occurrence of Raman scattering from cubic structures is discussed in terms of relaxation of the selection rules due to symmetry breaking by atomic substitutions. The Raman linewidth and Urbach energy behavior indicate the phase segregation region occurs in the range of 47–66% Mg. Below the phase segregation, the longitudinal optical phonons are found to follow the model of one-mode behavior. The phonon decay model of Balkanski et al. indicates that the major contributor to Raman linewidth arises from the temperature-independent term attributed to structural defects and alloy inhomogeneity, while the contribution from anharmonic decay is relatively small. Moreover, a good correlation between Urbach energy and Raman linewidth was found, implying that the underlying crystal dynamics affecting the phonons also affect the electronic states. Furthermore, for alloys with low Mg composition structural defects are dominant in determining the alloy properties, while at higher compositions alloy inhomogeneity cannot be neglected.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗