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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Single-particle detection of enhanced polarizability in Au-decorated semiconducting nanorods via scanning dielectric microscopy

Hybrid nanostructures that combine semiconducting and metallic components offer great potential for photothermal therapy, optoelectronics, and sensing, by integrating tunable optical properties with enhanced light absorption and charge transport. Boosting the integrated performance of these hybrid systems demands techniques capable of probing local variations of the physical properties inaccessible to bulk analysis. Here, we report the single-particle dielectric characterization of hybrid, semiconducting bismuth sulfide (Bi 2 S 3 ) nanorods (NR) decorated with metallic Au nanoparticles (NP), employing scanning dielectric microscopy, which uses electrostatic force microscopy in combination with finite-element numerical simulations. We reveal a pronounced enhancement in the local dielectric response of Bi2S3 upon Au decoration, attributed to interfacial polarization and electron transfer from Au to the Bi 2 S 3 matrix, thus suggesting a enhanced metallic-like polarizability at the single-particle level. Numerical simulations show that the response is dominated by the vertical component of the permittivity and that the decorating metallic Au NP produce only moderate shielding of the semiconductor Bi 2 S 3 NR core, indicating that the large increase in the dielectric response originates primarily from intrinsic modifications within the NR. Overall, these findings provide direct insight into structure–property relationships at the single-particle level, supporting the rational design of advanced hybrid nanostructures with tailored electronic functionalities.

36 MATERIALS SCIENCE↗
NASA NTRS1980

On the particle-size distribution function of cometary dust

The characterization of the particle size distribution in cometary tails is considered. The particle-size related distribution function of the acceleration exerted on the cometary particle by solar radiation pressure used by Finson and Probstein (1968) is introduced, and distribution functions observed for the comets Arend-Roland 1957 III, Bennett 1970 II and Seki-Lines 1962 III are illustrated. It is pointed out that although the distribution functions have features in common, the rate of decrease of the distribution towards zero acceleration (large particles) is not well determined. An approximation for the size distribution in this range obtained from a photometric study of anomalous cometary tails is presented, and used to formulate an a priori distribution law which can be used to approximate all types of expected distributions by varying three key parameters.

Sekanina, Z.↗
NASA NTRS2011

Global CALIPSO Observations of Aerosol Changes Near Clouds

Several recent studies have found that clouds are surrounded by a transition zone of rapidly changing aerosol optical properties and particle size. Characterizing this transition zone is important for better understanding aerosol-cloud interactions and aerosol radiative effects, and also for improving satellite retrievals of aerosol properties. This letter presents a statistical analysis of a monthlong global data set of Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar observations over oceans. The results show that the transition zone is ubiquitous over all oceans and extends up to 15 km away from clouds. They also show that near-cloud enhancements in backscatter and particle size are strongest at low altitudes, slightly below the top of the nearest clouds. Also, the enhancements are similar near illuminated and shadowy cloud sides, which confirms that the asymmetry of Moderate Resolution Imaging Spectroradiometer reflectances found in an earlier study comes from 3-D radiative processes and not from differences in aerosol properties. Finally, the effects of CALIPSO aerosol detection and cloud identification uncertainties are discussed. The findings underline the importance of accounting for the transition zone to avoid potential biases in studies of satellite aerosol products, aerosol-cloud interactions, and aerosol direct radiative effects.

Varnai, Tamas↗
NASA NTRS2009

Metal Decorated Multi-Walled Carbon Nanotube/Polyimide Composites with High Dielectric Constants and Low Loss Factors

The measurement of observable electromagnetic phenomena in materials and their derived intrinsic electrical material properties are of prime importance in the discovery and development of material systems for electronic and aerospace applications. Nanocomposite materials comprised of metal decorated multi-walled carbon nanotubes (MWCNTs) were prepared by a facile method and characterized. Metal particles such as silver(Ag), platinum(Pt) and palladium(Pd) with diameters ranging from less than 5 to over 50 nanometers were distributed randomly on the MWCNTs. The present study is focused on silver decorated MWCNTs dispersed in a polyimide matrix. The Ag-containing MWCNTs were melt mixed into Ultem(TradeMark) and the mixture extruded as ribbons. The extruded ribbons exhibited a moderate to high degree of MWCNT alignment as determined by HRSEM. These ribbons were then fabricated into test specimens while maintaining MWCNT alignment and subsequently characterized for electrical and electromagnetic properties at 8-12 GHz. The results of the electromagnetic characterization showed that certain sample configurations exhibited a decoupling of the permittivity (epsilon ) and loss factor (epsilon") indicating that these properties could be tailored within certain limits. The decoupling and independent control of these fundamental electrical material parameters offers a new class of materials with potential applications in electronics, microwave engineering and optics.

Elliott, Holly A.↗
DOE OSTI2019

Production of Particle Reference and Quality Control Materials

Maintaining the superior performance of new analytical instrumentation and pushing the boundaries of ever-smaller particle analysis by methods such as secondary ion mass spectrometry (SIMS) has become limited by the availability of certified particle standards for calibration, quality control, and validation. To meet this growing demand for a reliable and universal approach to the generation of uranium particle reference material, the Pacific Northwest National Laboratory (PNNL) and Savannah River National Laboratory (SRNL) are collaborating on a joint venture that establishes a number of chemical pathways to the fabrication, purification, and stabilization of uranium particle material to within a fixed particle size range, and well-characterized isotopics. PNNL particle standards are designed and tailored to meet the criteria essential to the calibration and benchmarking of instruments used in both the non-destructive and destructive assay of particulate material, typically collected from environmental swipe sampling. Previous testing and optimization of this colloidal approach to particulate material has centred on tight size distributions, singular composition and density, uniform morphology, and tailored isotopic abundances. Extensive validation of this material has since been performed, both at the National Institute of Standards and Technology (NIST) and the International Atomic Energy Agency (IAEA), demonstrating its suitability for quality control needs of large geometry (LG)-SIMS analysis. Building on this momentum, the production of low-enriched uranium particle reference material, with specially tailored isotopics, has moved from development to full operation. Herein, various aspects of the production cycle will be discussed, including detailed accounts of the technical methodologies being employed, as well as insights into the sample characterization and acceptance testing requirements.

Nuclear Safeguards, Particle Standards, IAEA↗
DOE OSTI2021

Exact Landau Level Description of Geometry and Interaction in a Flatband

Flatbands appear in many condensed matter systems, including the two-dimensional electron gas in a high magnetic field, correlated materials, and moiré heterostructures. They are characterized by intrinsic geometric properties such as the Berry curvature and Fubini-Study metric. The influence of the band geometry on electron-electron interaction is difficult to understand analytically because the geometry is in general nonuniform in momentum space. In this work, we study the topological flatband of Chern number C = 1 with a momentum-dependent but positive definite Berry curvature that fluctuates in sync with Fubini-Study metric. We derive an exact correspondence between such ideal flatbands and Landau levels and show that the band geometry fluctuation gives rise to a new type of interaction in the corresponding Landau levels that depends on the center of mass of two particles. We characterize such interactions by generalizing the usual Haldane pseudopotentials. This mapping gives exact zero-energy ground states for short-ranged repulsive generalized pseudopotentials in flatbands, in analogy to fractional quantum Hall systems. Driving the center-of-mass interactions beyond the repulsive regime leads to a dramatic reconstruction of the ground states towards gapless phases. The generalized pseudopotential could be a useful basis for future numerical studies.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Production and characterization of thin, self-supporting Si foils for use as targets in radioactive beam experiments

Development of thin, self-supporting silicon foils (both natural and isotopically-enriched) for use as targets in reaction studies with radioactive beams is detailed. Foils with a thickness of ~220 μg/cm 2 were produced using vapor deposition and were floated onto aluminum frames with 10–15 mm diameter holes. During their production, the foil thickness was measured using a quartz crystal monitor. Subsequently, the foil thickness was characterized by particle energy loss measurements and Rutherford backscattering (RBS). These measurements demonstrated that the thickness could be determined to within a 0.5% uncertainty. The elemental purity of the foils was assessed using RBS and X-ray photoelectron spectroscopy. Lastly, this analysis demonstrated that the foils have 87%–90% silicon abundance.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2008

The New Horizons Mission to Pluto and Flyby of Jupiter

New Horizons (NH) is NASA's mission to provide the first in situ reconnaissance of Pluto and its moons Charon, Nix, and Hydra. The NH spacecraft will reach Pluto in July 2015 and will then, if approved for an extended mission phase, continue on to a flyby encounter with one or more Kuiper belt objects (KBOs). NH was launched on 19 January 2006 and received a gravity assist during a flyby encounter with Jupiter (with closest approach at -32 RJ on 28 February 2007) that reduced its flight time to Pluto by 3 years. During the Jupiter flyby, NH collected a trove of multi-wavelength imaging and fields-and-particles measurements. Among the many science results at Jupiter were a detection of planet-wide mesoscale waves, eruptions of atmospheric ammonia clouds, unprecedented views of Io's volcanic plumes and Jupiter's tenuous ring system, a first close-up of the Little Red Spot (LRS), first sightings of polar lightning, and a trip down the tail of the magnetosphere. In 2015, NH will conduct a seven-month investigation of the Pluto system culminating in a closest approach some 12,500 km from Pluto's surface. Planning is presently underway for the Pluto encounter with special emphasis on longidentified science goals of studying the terrain, geology, and composition of the surfaces of Pluto and Charon, examining the composition and structure of Pluto's atmosphere, searching for an atmosphere on Charon, and characterizing Pluto's ionosphere and solar wind interaction. Detailed inspections will also be performed of the newly discovered satellites Nix and Hydra. Additionally, NH will characterize energetic particles in Pluto's environment, refine the bulk properties of Pluto and Charon, and search for additional satellites and rings.

Stern, Alan↗
DOE OSTI2019

Formation of Polycyclic Aromatic Hydrocarbon Oxidation Products in alpha-Pinene Secondary Organic Aerosol Particles Formed through Ozonolysis

Accurate long-range atmospheric transport (LRAT) modeling of polycyclic aromatic hydrocarbons (PAHs) and PAH oxidation products (PAH-OPs) in secondary organic aerosol (SOA) particles relies on the known chemical composition of the particles. Four PAHs, phenanthrene (PHE), dibenzothiophene (DBT), pyrene (PYR), and benz(a)anthracene (BaA), were studied individ-ually to identify and quantify PAH-OPs produced and incorporated into SOA particles formed by ozonolysis of a-pinene in the presence of PAH vapor. SOA particles were characterized using real-time in situ instrumentation, and collected on quartz ?ber ?lters for o?ine analysis of PAHs and PAH-OPs. PAH-OPs were measured in all PAH experiments at equal or greater concentrations than the individual PAHs they were produced from. The total mass of PAH and PAH-OPs, relative to the total SOA mass, varied for di?erent experiments on individual parent PAHs: PHE and 6 quanti?ed PHE-OPs (3.0%), DBT and dibenzothiophene sulfone (4.9%), PYR and 3 quanti?ed PYR-OPs (3.1%), and BaA and benz(a)anthracene-7,12-dione (0.26%). Further exposure of PAH-SOA to ozone generally increased the concentration ratio of PAH-OPs to PAH, suggesting longer atmospheric lifetimes for PAH-OPs, relative to PAHs. These data indicate that PAH-OPs are formed during SOA particle formation and growth.

Kramer, Amber L.↗
DOE OSTI2022

MULTI-TECHNIQUE CHARACTERIZATION OF SUPERCONDUCTING MATERIALS FOR PARTICLE ACCELERATOR APPLICATIONS

We investigated the performance limitations of superconducting radio-frequency (SRF) cavities and materials using multiple experimental techniques. In particular, this study focuses on understanding the surface properties of nitrogen-doped Nb cavities and super?conducting thin films with higher Tc such as Nb3Sn. The main goal of this work is to use different techniques to better understand each aspect of the complex loss mechanism in superconductors to further improve the already highly efficient SRF cavities. Nitrogen doping applied to a Nb SRF cavity significantly improves the quality factor Q0 compared to a conventional Nb cavity, at an expense of reduced maximum accelerating gradient. The early quench mechanism was analyzed by using temperature maps before and during the quenching. The temperature maps revealed insignificant heating before the quench, and we concluded that nitrogen doping reduces critical magnetic fields in local regions, leading to premature quenching. To understand the origin of the increasing Q0 with the rf field, the density of states (DOS) of cold spots from nitrogen-doped and standard cavities were measured and analyzed using scanning tunneling microscopy. The results suggested that nitrogen doping reduces the spatial inhomogeneity of superconducting properties and shrinks the metallic suboxide layers, which tunes the DOS in such a way as to produce the field-induced reduction in the surface resistance. To characterize SRF thin films, an experimental setup for measuring a coplanar waveguide (CPW) resonator was developed and tested. A surface impedance measurement of the Nb film showed good agreement with the BCS calculation. The preliminary results from measurements of Nb3Sn and NbTiN films are also presented here. The nonlinear Meissner effect was investigated in Nb3Sn film CPW resonators by mea?suring the resonant frequency as a function of a parallel magnetic field. Contrary to a conventional quadratic dependence of the penetration depth ?(B) on the applied magnetic field B, as expected in s-wave superconductors, nearly a linear increase of ?(B) with B was observed. It was concluded that this behavior of ?(B) is due to weakly linked grain bound?aries on the polycrystalline Nb3Sn films, which can mimic the NLME expected in a clean d-wave superconductor.

Makita, Junki↗
DOE OSTI2022

Quantifying the Impact of Charge Rate and Number of Cycles on Structural Degeneration of Li-Ion Battery Electrodes

A quantitative link between crack evolution in lithium-ion positive electrodes and the degrading performance on cells is not yet well established nor is any single technique capable of doing so widely available. Here, we demonstrate a widely accessible high-throughput approach to quantifying crack evolution within electrodes. The approach applies super-resolution scanning electron microscopy (SEM) imaging of cross-sectioned NMC532 electrodes, followed by segmentation and quantification of crack features. Crack properties such as crack intensity, crack width and length are quantified as a function of charge rate (1C, 6C, and 9C) and cycle number (25, 225, and 600 cycles). Hundreds of particles are characterized for statistical confidence in the quantitative crack measurements. The data on crack evolution is compared to electrochemical data from full cells and half cells with the NMC532 positive electrodes. We show that while crack evolution strongly correlates with capacity fade in the first 25 cycles, it does not correlate well for the following hundreds of cycles indicating that cracking may not be the dominant cause of capacity fade throughout the cycle-life of cells.

25 ENERGY STORAGE↗
DOE OSTI2018

Electron drift properties in high pressure gaseous xenon

Gaseous time projection chambers (TPC) are a very attractive detector technology for particle tracking. Characterization of both drift velocity and diffusion is of great importance to correctly assess their tracking capabilities. NEXT-White is a High Pressure Xenon gas TPC with electroluminescent amplification, a 1:2 scale model of the future NEXT-100 detector, which will be dedicated to neutrinoless double beta decay searches. NEXT-White has been operating at Canfranc Underground Laboratory (LSC) since December 2016. The drift parameters have been measured using 83m Kr for a range of reduced drift fields at two different pressure regimes, namely 7.2 bar and 9.1 bar. The results have been compared with Magboltz simulations. In conclusion, agreement at the 5% level or better has been found for drift velocity, longitudinal diffusion and transverse diffusion.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Structural Color Production in Melanin-Based Disordered Colloidal Nanoparticle Assemblies in Spherical Confinement

Melanin is a ubiquitous natural pigment that exhibits broadband absorption and high refractive index. Despite its widespread use in structural color production, how the absorbing material, melanin, affects the generated color is unknown. Using a combined molecular dynamics and finite-difference time-domain computational approach, here we investigates structural color generation in one-component melanin nanoparticle-based supraparticles (called supraballs) as well as binary mixtures of melanin and silica (nonabsorbing) nanoparticle-based supraballs. Experimentally produced one-component melanin and one-component silica supraballs, with thoroughly characterized primary particle characteristics using neutron scattering, produce reflectance profiles similar to the computational analogs, confirming that the computational approach correctly simulates both absorption and multiple scattering from the self-assembled nanoparticles. These combined approaches demonstrate that melanin's broadband absorption increases the primary reflectance peak wavelength, increases saturation, and decreases lightness factor. Additionally, the dispersity of nanoparticle size more strongly influences the optical properties of supraballs than packing fraction, as evidenced by the production of a larger range of colors when size dispersity is varied versus packing fraction. For binary melanin and silica supraballs, the chemistry-based stratification allows for more diverse color generation and finer saturation tuning than does the degree of mixing/demixing between the two chemistries.

broadband absorption↗
DOE OSTI2019

Unveiling the Photo- and Thermal-Stability of Cesium Lead Halide Perovskite Nanocrystals

Lead halide perovskites possess unique characteristics that are well-suited for optoelectronic and energy capture devices, however, concerns about their long-term stability remain. Limited stability is often linked to the methylammonium cation, and all-inorganic CsPbX 3 (X = Cl, Br, I) perovskite nanocrystals have been reported with improved stability. In this work, the photostability and thermal stability properties of CsPbX 3 (X = Cl, Br, I) nanocrystals were investigated via electron microscopy, x-ray diffraction, thermogravimetric analysis coupled with FTIR (TGA-FTIR), ensemble and single particle spectral characterization. CsPbBr 3 was found to be stable under 1-sun illumination for 16 h in ambient conditions, although single crystal luminescence analysis after illumination via a solar simulator indicates that the luminescence states are changing over time. CsPbBr 3 was also stable to heating to 250°C. Large CsPbI 3 crystals (34 ± 5 nm) were shown to be the least stable composition under the same conditions as both XRD reflections and Raman bands diminish under irradiation; and with heating the (black) phase reverts to the non-luminescent $δ$ phase. Smaller CsPbI 3 nanocrystals (14 ± 2 nm) purified by a different washing strategy exhibited improved photostability with no evidence of crystal growth but were still thermally unstable. Both CsPbCl 3 and CsPbBr 3 show crystal growth under irradiation or heat, likely with a preferential orientation based on XRD patterns. TGA-FTIR revealed nanocrystal mass loss was only from liberation and subsequent degradation of surface ligands. Encapsulation or other protective strategies should be employed for long-term stability of these materials under conditions of high irradiance or temperature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Characterization of Calibrated Gelatin Sponge Particles in a Rabbit Renal Embolization Model

Purpose: To evaluate the level of artery occlusion, degradation periods, tissue response and vessel recanalization of calibrated gelatin sponge particles after segmental renal artery embolization. Materials and Methods: Superselective embolization of 14 adult rabbits was performed with calibrated gelatin sponge particles (150–350 μm). Two rabbits were killed immediately after the procedure (day 0). One pair of rabbits was killed on each of the following days: 1, 3, 7, 14, 28 and 56. One rabbit from each pair underwent CT angiography before embolization and killing. The pathologic changes of the embolized renal parenchyma and embolic characteristics of calibrated gelatin sponge particles were evaluated histologically and angiographically. Results: Calibrated gelatin sponge particles were distally located in interlobular artery with a dense packing on day 0. The level of occlusion paralleled the size of the particles. Partial degradation of the particles was observed on day 3, and complete degradation was observed on day 14. Vessel recanalization was observed through both CTA and histological analysis starting on day 3. Vascular inflammation responding to gelatin sponge particles was mild and subsided with the degradation of the particles. On day 28 and day 56, attenuation of embolized vessels occurred due to marked intimal proliferation, and vascular occlusion developed. Conclusions: Gelatin sponge particles of 150–350 μm produced dense and distal embolization, and were resorbed before day 14 with a mild tissue reaction. Vessel recanalization occurred secondary to the resorption of gelatin sponge particles, but permanent vascular occlusion developed due to marked intimal hyperplasia after day 28.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Green Emitting Cerium Doped CaS Whiskers Grown by Solid State Diffusion Method

Undoped and cerium doped Calcium sulfide (CaS) phosphors were synthesized using solid state diffusion method. The X-ray diffraction pattern revealed that both undoped and doped CaS crystallites have cubic structure with average crystallite size varying from 20 to 30 nm. Scanning electron micrographs indicated that Ce doped CaS phosphors were composed of whiskers with different dimensions and orientations. The optical properties of undoped and Ce doped particles were characterized using Photoluminescence (PL) and UV-Vis absorption spectroscopy. The PL emission spectrum of cerium doped CaS phosphors for an excitation wavelength 465 nm showed a main peak at 500 nm and a shoulder peak at 556 nm due to 5d → 4f transition in Ce{sup 3+} ions. The variation of PL intensity with cerium concentration was investigated and the maximum PL intensity was obtained for a doping concentration of 3 wt.%. The optical band gap of the samples was estimated from the diffuse reflectance spectrum and was found to increase with increase in cerium concentration. The enhanced optical properties of these phosphors can be exploited in various optoelectronic devices including displays and bioimaging techniques.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Diffusive shock re-acceleration

Here, we have performed two-dimensional hybrid simulations of non-relativistic collisionless shocks in the presence of pre-existing energetic particles (‘seeds’); such a study applies, for instance, to the re-acceleration of galactic cosmic rays (CRs) in supernova remnant (SNR) shocks and solar wind energetic particles in heliospheric shocks. Energetic particles can be effectively reflected and accelerated regardless of shock inclination via a process that we call diffusive shock re-acceleration. We determine that re-accelerated seeds can drive the streaming instability in the shock upstream and produce effective magnetic field amplification. This can later trigger the injection of thermal protons even at oblique shocks that ordinarily cannot inject thermal particles. We characterize the current in reflected seeds, finding that it tends to a universal value $J\simeq en_{\text{CR}}v_{\text{sh}}$ , where $en_{\text{CR}}$ is the seed charge density and $v_{\text{sh}}$ is the shock velocity. When applying our results to SNRs, we find that the re-acceleration of galactic CRs can excite the Bell instability to nonlinear levels in less than ${\sim}10~\text{yr}$ , thereby providing a minimum level of magnetic field amplification for any SNR shock. Finally, we discuss the relevance of diffusive shock re-acceleration also for other environments, such as heliospheric shocks, galactic superbubbles and clusters of galaxies.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Single-Polymer–Particle Growth Kinetics with Molecular Catalyst Speciation and Single-Turnover Imaging

The dynamics of the local environments surrounding molecular polymerization catalysts plausibly impact turnover kinetics, but the impact of and nature of such dynamics have previously been obscured by ensemble averaging. With Grubbs’ second generation ruthenium metathesis catalyst and a precipitation polymerization system, studies at the single-particle and -turnover level establish that (1) an inverse correlation exists between rate and duration of single-polymer–particle growth of aggregates, consistent with a local environment density model for the time-variable kinetics; (2) cross-linking additives produced a small, but detectible, reduction in overall monomer incorporation; (3) total ruthenium quantity within the polymer particles (as characterized by energy dispersive X-ray spectroscopy) is differentiable from the quantity that is catalytically active (as characterized by in situ fluorescence microscopy), providing catalyst speciation information; and (4) time-resolved enyne metathesis reactions can be imaged, corresponding to single turnovers at individual molecular catalysts during polymer growth under synthetically relevant conditions. Here, these findings identify and characterize reactivity distributions likely arising from the dynamics of local environments. As such, these data provide reactivity information that is unavailable through traditional ensemble analytical methods that obscure this type of information through averaging.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗