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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

The effects of glass doping, temperature and time on the morphology, composition, and iron redox of spinel crystals

Precipitation of large crystals/agglomerates of spinel and their accumulation in the pour spout riser of a Joule-heated ceramic melter during idling can plug the melter and prevent pouring of molten glass into canisters. Thus, there is a need to understand the effects of spinel-forming components, temperature, and time on the growth of crystals in connection with an accumulation rate. In our study, crystals of spinel [Fe, Ni, Mn, Zn, Sn][Fe, Cr]₂O₄ were precipitated from simulated high-level waste borosilicate glasses containing different concentrations of Ni, Fe, and Cr by heat treating at 850 and 900°C for different times. These crystals were extracted from the glasses and analyzed with scanning electron microscopy and image analysis for size and shape, with inductively coupled plasma-atomic emission spectroscopy and atom probe tomography for concentration of spinel-forming components, and with wet colorimetry and Mössbauer spectroscopy for Fe²⁺/Fe total ratio. High concentrations of Ni, Fe, and Cr in glasses resulted in the precipitation of crystals larger than 100 µm in just two days. Crystals were a solid solution of NiFe₂O₄, NiCr₂O₄, and -Fe₂O₃ (identified only in the high-Ni-Fe glass) and also contained small concentrations of less than 1 at% of Li, Mg, Mn, and Al.

chemical analysis↗
DOE OSTI2019

Toward G protein-coupled receptor structure-based drug design using X-ray lasers

Rational structure-based drug design (SBDD) relies on the availability of a large number of co-crystal structures to map the ligand-binding pocket of the target protein and use this information for lead-compound optimization via an iterative process. While SBDD has proven successful for many drug-discovery projects, its application to G protein-coupled receptors (GPCRs) has been limited owing to extreme difficulties with their crystallization. Here, a method is presented for the rapid determination of multiple co-crystal structures for a target GPCR in complex with various ligands, taking advantage of the serial femtosecond crystallography approach, which obviates the need for large crystals and requires only submilligram quantities of purified protein. The method was applied to the human β 2 -adrenergic receptor, resulting in eight room-temperature co-crystal structures with six different ligands, including previously unreported structures with carvedilol and propranolol. The generality of the proposed method was tested with three other receptors. This approach has the potential to enable SBDD for GPCRs and other difficult-to-crystallize membrane proteins.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Divalent europium doped and un-doped calcium iodide scintillators: Scintillator characterization and single crystal growth

Initially, the alkaline-earth scintillator, CaI 2 :Eu 2+ , was discovered around 1964 by Hofstadter, Odell, and Schmidt. Serious practical problems quickly arose, however, that were associated with the growth of large monolithic single crystals of this material due to its lamellar, mica-like structure. As a result of its theoretically higher light yield, CaI 2 :Eu 2+ has the potential to exceed the excellent scintillation performance of SrI 2 :Eu 2+ . In fact, theoretical predictions for the light yield of CaI2:Eu 2+ scintillators suggested that an energy resolution approaching 2% at 662 keV could be achievable. Like the early SrI 2 :Eu 2+ scintillator, the performance of CaI 2 :Eu 2+ scintillators has traditionally suffered due, at least in part, to outdated materials synthesis, component stoichiometry/purity, and single-crystal-growth techniques. Based on our recent work on SrI 2 :Eu 2+ scintillators in single-crystal form, we have developed new techniques that are applied here to CaI 2 :Eu 2+ and pure CaI 2 with the goal of growing large un-cracked crystals and, potentially, realizing the theoretically predicted performance of the CaI 2 :Eu 2+ form of this material. Calcium iodide does not adhere to modern glassy carbon Bridgman crucibles - so there should be no differential thermal-contraction-induced crystal/crucible stresses on cooling that would result in crystal cracking of the lamellar structure of CaI 2 . Here we apply glassy carbon crucible Bridgman growth, high-purity growth-charge compounds, our molten salt processing/filtration technique, and extended vacuum-melt-pumping methods to the growth of both CaI 2 :Eu 2+ and un-doped CaI 2 . Moreover, large scintillating single crystals were obtained, and detailed characterization studies of the scintillation properties of CaI 2 :Eu 2+ and pure CaI 2 single crystals are presented that include studies of the effects of plastic deformation of the crystals on the scintillator performance.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Correlations of crystallographic defects and anisotropy with magnetotransport properties in Fe x TaS 2 single crystals ( 0.23 ≤ x ≤ 0.35 )

Very large magnetoresistance discovered in single crystals of the ferromagnetic Fe-intercalated transition metal dichalcogenide, Fe 0.28 TaS 2 was attributed to the deviation of the Fe concentration from commensurate values (x = 1/4 or 1/3), which caused magnetic moment misalignments. Here we report a study of Fe x TaS 2 crystals with 0:23 ≤ x ≤ 0:35, demonstrating that crystallographic defects lead to spin disorder, which correlates with magneto-transport properties such as switching magnetic fi eld HS, magnetoresistance MR, and even zero-field resistivity ρ0 and temperature coefficient A in ρ(T) = ρ 0 + AT 2 : The ordering temperature T C and Weiss temperature θ W are maximized at the superstructure composition x = 1/4, while H s , MR, ρ 0 , and A are minimum. Conversely, at a composition intermediate between the superstructure compositions x = 1/4 and 1/3, the corresponding magneto-transport properties reach local maxima.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1993

Chemical Vapor Deposition Of Silicon Carbide

Large single-crystal SiC boules from which wafers of large area cut now being produced commerically. Availability of wafers opens door for development of SiC semiconductor devices. Recently developed chemical vapor deposition (CVD) process produces thin single-crystal SiC films on SiC wafers. Essential step in sequence of steps used to fabricate semiconductor devices. Further development required for specific devices. Some potential high-temperature applications include sensors and control electronics for advanced turbine engines and automobile engines, power electronics for electromechanical actuators for advanced aircraft and for space power systems, and equipment used in drilling of deep wells. High-frequency applications include communication systems, high-speed computers, and microwave power transistors. High-radiation applications include sensors and controls for nuclear reactors.

Powell, J. Anthony↗
DOE OSTI2014

Phosphate single mode large mode area all-solid photonic crystal fiber with multi-watt output power

An index-depressed active core, single-mode phosphate all-solid large-mode-area photonic crystal fiber (PCF) is theoretically investigated using full-vectorial finite difference approach and experimentally realized. The PCF has a maximum output power of 5.4 W and 31% slope efficiency. Single-mode operation is realized through PCFs with core diameters of 30, 35, and 40 μm, respectively. The beam quality is not degraded even at maximum output power. Our simulations and experiments reveal that the laser performance is significantly affected by the center-to-center distance between the two nearest rods Λ, the rod diameter d, and their ratio d/Λ, implying that much attention should be given in employing optimal parameters to achieve excellent laser performance.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1983

Seeded crystal growth of pseudobinary systems with large liquidus-solidus separation

The design and execution of seeded melt growth involving concentrated alloys is strongly dependent on the crystal-melt interface temperature and its change during seeding and growth. Thermodynamic instabilities during the seeding process can be controlled by the choice of the seed and melt composition and by the axial temperature gradient of the growth apparatus. These basic factors controlling seeded melt growth of concentrated alloys are of major importance for planning space experiments.

Bourret, E. D.↗
NASA NTRS1981

Role of substrate quality on IC performance and yields

The development of silicon and gallium arsenide crystal growth for the production of large diameter substrates are discussed. Large area substrates of significantly improved compositional purity, dopant distribution and structural perfection on a microscopic as well as macroscopic scale are important requirements. The exploratory use of magnetic fields to suppress convection effects in Czochralski crystal growth is addressed. The growth of large crystals in space appears impractical at present however the efforts to improve substrate quality could benefit from the experiences gained in smaller scale growth experiments conducted in the zero gravity environment of space.

Thomas, R. N.↗
DOE OSTI2011

Quasicompactons in inverted nonlinear photonic crystals

We study large-amplitude one-dimensional solitary waves in photonic crystals featuring competition between linear and nonlinear lattices, with minima of the linear potential coinciding with maxima of the nonlinear pseudopotential, and vice versa (inverted nonlinear photonic crystals, INPCs), in the case of the saturable self-focusing nonlinearity. Such crystals were recently fabricated using a mixture of SU-8 and Rhodamine-B optical materials. By means of numerical methods and analytical approximations, we find that large-amplitude solitons are broad sharply localized stable pulses (quasicompactons, QCs). With the increase of the total power, P, the QC's centroid performs multiple switchings between minima and maxima of the linear potential. Unlike cubic INPCs, the large-amplitude solitons are mobile in the medium with the saturable nonlinearity. The threshold value of the kick necessary to set the soliton in motion is found as a function of P. Collisions between moving QCs are considered too.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Feedback regulation of crystal growth by buffering monomer concentration

Abstract Crystallization is a ubiquitous means of self-assembly that can organize matter over length scales orders of magnitude larger than those of the monomer units. Yet crystallization is notoriously difficult to control because it is exquisitely sensitive to monomer concentration, which changes as monomers are depleted during growth. Living cells control crystallization using chemical reaction networks that offset depletion by synthesizing or activating monomers to regulate monomer concentration, stabilizing growth conditions even as depletion rates change, and thus reliably yielding desired products. Using DNA nanotubes as a model system, here we show that coupling a generic reversible bimolecular monomer buffering reaction to a crystallization process leads to reliable growth of large, uniformly sized crystals even when crystal growth rates change over time. Buffering could be applied broadly as a simple means to regulate and sustain batch crystallization and could facilitate the self-assembly of complex, hierarchical synthetic structures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Understanding the atomic and electronic origin of mechanical property in thaumasite and ettringite mineral crystals

Ettringite and thaumasite are 2 of the relevant secondary products in portland cement minerals. They are rare crystals with high water content. Two density functional theory based ab initio packages VASP and the OLCAO were used for exploring the geometry structure, electronic, and mechanical properties of ettringite and thaumasite. The calculations focus on the comparison of their structures and properties to gain insights that can reveal the minute difference in properties due to differences in their structure, composition and water content. Detailed analysis of interatomic bonding shows the similarities and subtle difference between them even though thaumasite has the Si tetrahedron as the backbone unit in contrast to ettringite with Al-columns and no Si atoms. Moreover, thaumasite has strong C–O bonds that are absent in ettringite, and ettringite has far more water molecules with a substantial contribution from the hydrogen bonding. It is shown that the role played by relatively strong S–O bonds in both crystals has a large impact on the hydration in these crystals. On the basis of calculated total bond order density, it is concluded that thaumasite is slightly more cohesive than ettringite consistent with the calculated mechanical properties. The detailed comparative results for these 2 important minerals we obtained in this paper, many of them for the first time, will pave the way to understanding the structure and electronic structure origin of other more complex cement crystals.

36 MATERIALS SCIENCE↗
NASA NTRS1976

Stellar crystal X-ray spectroscopy on OSO-8

The large-area graphite crystal X-ray spectrometer on the OSO-8 satellite is described, and its response to stellar line and continuum radiation is discussed. A high resolution X-ray spectrum of Sco X-1 obtained from a preliminary analysis of quick look data shows a strong, smooth continuum with an absence of emission or absorption features over the energy range 2.2 to 8 keV. Upper limits are set on narrow line emission from highly ionized states of S, Ca, and Fe.

Kestenbaum, H. L.↗
NASA NTRS1976

The graphite crystal X-ray spectrometer on OSO-8

The large-area graphite crystal X-ray spectrometer aboard the OSO-8 satellite is described. The instrument can be used to measure continuum profiles over the energy band from 2 to 8 keV with a resolution of several tens of electron volts and to detect narrow line emission from strong X-ray sources with a limiting sensitivity (3 sigmas) of the order of 10-eV, equivalent width for a three-day observing period.

Kestenbaum, H. L.↗
NASA NTRS2013

The Effect of Thermal Cycling on Crystal-Liquid Separation During Lunar Magma Ocean Differentiation

Differentiation of magma oceans likely involves a mixture of fractional and equilibrium crystallization [1]. The existence of: 1) large volumes of anorthosite in the lunar highlands and 2) the incompatible- rich (KREEP) reservoir suggests that fractional crystallization may have dominated during differentiation of the Moon. For this to have occurred, crystal fractionation must have been remarkably efficient. Several authors [e.g. 2, 3] have hypothesized that equilibrium crystallization would have dominated early in differentiation of magma oceans because of crystal entrainment during turbulent convection. However, recent numerical modeling [4] suggests that crystal settling could have occurred throughout the entire solidification history of the lunar magma ocean if crystals were large and crystal fraction was low. These results indicate that the crystal size distribution could have played an important role in differentiation of the lunar magma ocean. Here, I suggest that thermal cycling from tidal heating during lunar magma ocean crystallization caused crystals to coarsen, leading to efficient crystal-liquid separation.

Mills, Ryan D.↗
DOE OSTI2016

Mini Compton Camera Based on an Array of Virtual Frisch-Grid CdZnTe Detectors

In this study, we constructed a mini Compton camera based on an array of CdZnTe detectors and assessed its spectral and imaging properties. The entire array consisted of 6×6 Frisch-grid CdZnTe detectors, each with a size of 6×6 ×15 mm 3 . Since it is easier and more practical to grow small CdZnTe crystals rather than large monolithic ones, constructing a mosaic array of parallelepiped crystals can be an effective way to build a more efficient, large-volume detector. With the fully operational CdZnTe array, we measured the energy spectra for 133 Ba -, 137 Cs -, 60 Co-radiation sources; we also located these sources using a Compton imaging approach. Although the Compton camera was small enough to hand-carry, its intrinsic efficiency was several orders higher than those generated in previous researches using spatially separated arrays, because our camera measured the interactions inside the CZT detector array, wherein the detector elements were positioned very close to each other. Lastly, the performance of our camera was compared with that based on a pixelated detector.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Van der Waals epitaxial growth of two-dimensional single-crystalline GaSe domains on graphene

Two-dimensional (2D) van der Waals (vdW) heterostructures are a family of artificially-structured materials that promise tunable optoelectronic properties for devices with enhanced functionalities. Compared to stamping, direct epitaxy of vdW heterostructures is ideal for clean interlayer interfaces and scalable device fabrication. Here, we explore the synthesis and preferred orientations of 2D GaSe atomic layers on graphene (Gr) by vdW epitaxy. Guided by the wrinkles on graphene, GaSe nuclei form that share a predominant lattice orientation. Due to vdW epitaxial growth many nuclei grow as perfectly aligned crystals and coalesce to form large (tens of microns), single-crystal flakes. Through theoretical investigations of interlayer energetics, and measurements of preferred orientations by atomic-resolution STEM and electron diffraction, a 10.9 interlayer rotation of the GaSe lattice with respect to the underlying graphene is found to be the most energetically preferred vdW heterostructure with the largest binding energy and the longest-range ordering. These GaSe/Gr vdW heterostructures exhibit an enhanced Raman E 2 1g band of monolayer GaSe along with highly-quenched photoluminescence due to strong charge transfer. Despite the very large lattice mismatch of GaSe/Gr through vdW epitaxy, the predominant orientation control and convergent formation of large single-crystal flakes demonstrated here is promising for the scalable synthesis of large-area vdW heterostructures for the development of new optical and optoelectronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

FMX – the Frontier Microfocusing Macromolecular Crystallography Beamline at the National Synchrotron Light Source II

Two new macromolecular crystallography (MX) beamlines at the National Synchrotron Light Source II, FMX and AMX, opened for general user operation in February 2017 [Schneider et al. (2013). J. Phys. Conf. Ser. 425 , 012003; Fuchs et al. (2014). J. Phys. Conf. Ser. 493 , 012021; Fuchs et al. (2016). AIP Conf. Proc. SRI2015 , 1741 , 030006]. FMX, the micro-focusing Frontier MX beamline in sector 17-ID-2 at NSLS-II, covers a 5–30 keV photon energy range and delivers a flux of 4.0 × 10 12 photons s −1 at 1 Å into a 1 µm × 1.5 µm to 10 µm × 10 µm (V × H) variable focus, expected to reach 5 × 10 12 photons s −1 at final storage-ring current. This flux density surpasses most MX beamlines by nearly two orders of magnitude. The high brightness and microbeam capability of FMX are focused on solving difficult crystallographic challenges. The beamline's flexible design supports a wide range of structure determination methods – serial crystallography on micrometre-sized crystals, raster optimization of diffraction from inhomogeneous crystals, high-resolution data collection from large-unit-cell crystals, room-temperature data collection for crystals that are difficult to freeze and for studying conformational dynamics, and fully automated data collection for sample-screening and ligand-binding studies. FMX's high dose rate reduces data collection times for applications like serial crystallography to minutes rather than hours. With associated sample lifetimes as short as a few milliseconds, new rapid sample-delivery methods have been implemented, such as an ultra-high-speed high-precision piezo scanner goniometer [Gao et al. (2018). J. Synchrotron Rad. 25 , 1362–1370], new microcrystal-optimized micromesh well sample holders [Guo et al. (2018). IUCrJ , 5 , 238–246] and highly viscous media injectors [Weierstall et al. (2014). Nat. Commun. 5 , 3309]. The new beamline pushes the frontier of synchrotron crystallography and enables users to determine structures from difficult-to-crystallize targets like membrane proteins, using previously intractable crystals of a few micrometres in size, and to obtain quality structures from irregular larger crystals.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1993

Systematic chemical variations in large 3AB iron meteorites: Clues to core crystallization

Analysis of numerous individual iron meteorites have shown that fractional crystallization of iron cores result in variations in chemical concentration of the solid core which span several orders of magnitude. The magnitude and direction of the resulting spatial gradients in the core can provide clues to the physical nature of the core crystallization process. We have analyzed suites of samples from three large 3AB irons (Cape York, 58t; Chupaderos, 24t; Morito, 10t) in order to estimate local chemical gradients. Initial results for the concentrations of Ge, Pd, Pt (Massey group), Ir, Au, As, Co, Os, and Rh (Dalhouse group), and P (Arizona group) show significant ranges among the Cape York and Chupaderos samples and marginally significant ranges among the Morito samples. Measurements of Au, Ir, Co, Ni, Cu, Ga, As, W, Re (from UCLA) and Ni and Co (Arizona group) are in progress. We find a spatial Ir gradient in Chupaderos with a magnitude similar to the one reported for Agpalilik (Cape York iron) by Esbensen et al.

Haack, H.↗