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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 1,441 records · Page 80
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Dose-rate controlled energy dispersive x-ray spectroscopic mapping of the metallic components in a biohybrid nanosystem

In this work, we showcase that through precise control of the electron dose rate, state-of-the-art large solid angle energy dispersive X-ray spectroscopy (EDS) mapping in aberration-corrected scanning transmission electron microscope (STEM) is capable of faithful and unambiguous chemical characterization of the Pt and Pd distribution in a peptide-mediated nanosystem. This low-dose-rate recording scheme adds another dimension of flexibility to the design of elemental mapping experiments, and holds significant potential for extending its application to a wide variety of beam sensitive hybrid nanostructures.

composition mapping↗
DOE OSTI2015

Structural and superconducting features of Tl-1223 prepared at ambient pressure

This study provides an account of the bulk preparation of TlBa 2 Ca 2 Cu 3 O 9-δ (Tl-1223) superconductor at ambient pressure, and the Tc features under thermal-annealing conditions. The ‘as-prepared’ Tl-1223 (Tc =106 K) presents a significantly higher T c = 125 K after annealing the polycrystalline material in either flowing Ar+4% H 2 , or N 2 gases. In order to understand the fundamental reasons for a particular Tc, we refined the average bulk structures using powder X-ray diffraction data. Although Ar+4%H2 annealed Tl- 1223 shows an increased ‘c’ lattice parameter, it shrinks by 0.03% (approximately unchanged) upon N2 anneal. Due to such indeterminate conclusions on the average structural changes, local structures were investigated at using aberration-corrected scanning-transmission electron microscopy technique. Similar compositional changes in the atomic arrangements of both annealed-samples of Tl-1223 were detected in which the plane containing Ca atomic layer gives a non-uniform contrast, due to substitution of some heavier Tl. In this report, extensive bulk properties are summarized through temperature-dependent resistivity, and shielding and Meissner fractions of magnetic susceptibility results; the bulk and local structures are investigated to correlate to properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Probing the electronic structure and optical response of a graphene quantum disk supported on monolayer graphene

In this paper, we show that a graphene quantum disk (GQD) can be generated on monolayer graphene via structural modification using the electron beam. The electronic structure and local optical responses of the GQD, supported on monolayer graphene, were probed with electron energy-loss spectrum imaging on an aberration-corrected scanning transmission electron microscope. We observe that for small GQD, {approx}1.3 nm in diameter, the electronic structure and optical response are governed by the dominating edge states, and are distinctly different from either monolayer graphene or double-layer graphene. Highly localized plasmon modes are generated at the GQD due to the confinement from the edge of the GQD in all directions. The highly localized optical response from GQDs could find use in designing nanoscale optoelectronic and plasmonic devices based on monolayer graphene.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Subsurface Synthesis and Characterization of Ag Nanoparticles Embedded in MgO

Metal nanoparticles exhibit localized surface plasmon resonance (LSPR) which is very sensitive to the size and shape of the nanoparticle and the dielectric medium surrounding it. LSPR causes field enhancement near the surface of the nanoparticle making them interesting candidates for plasmonic applications. In particular, partially exposed metallic nanoparticles distributed in a dielectric matrix form hotspots which are prime locations for LSPR spectroscopy and sensing. This study involves synthesizing partially buried Ag nanoparticles in MgO and investigating the characteristics of this material system. Ag nanoparticles of different shapes and size distributions were synthesized below the surface of MgO by implanting 200 keV Ag+ ions followed by annealing at 10000C for 10 and 30 hours. A detailed optical and structural characterization was carried out to understand the evolution of Ag nanoparticle microstructure and size distribution inside the MgO matrix. Micro x-ray diffraction (MicroXRD) was employed to investigate the structural properties and estimate the crystallite size. The nanoparticles evolved from a spherical to faceted morphology with annealing time, assuming an octahedral shape truncated at the (001) planes as seen from aberration corrected transmission electron microscopy (TEM) images. The nanoparticles embedded in MgO were shown to be pure metallic Ag using atom probe tomography (APT). The nanoparticles were partially exposed to the surface employing plasma etch techniques to remove the overlaying MgO. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to study the surface morphology and obtain a height distribution for the partially exposed nanoparticles.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2019

PIV/BOS synthetic image generation in variable density environments for error analysis and experiment design

In this work, we present an image generation methodology based on ray tracing that can be used to render realistic images of Particle Image Velocimetry (PIV) and Background Oriented Schlieren (BOS) experiments in the presence of density/refractive index gradients. This methodology enables the simulation of aero-thermodynamics experiments for experiment design, error, and uncertainty analysis. Images are generated by emanating light rays from the particles or dot pattern, and propagating them through the density gradient field and the optical elements, up to the camera sensor. The rendered images are realistic, and can replicate the features of a given experimental setup, like optical aberrations and perspective effects, which can be deliberately introduced for error analysis. We demonstrate this methodology by simulating a BOS experiment with a known density field obtained from direct numerical simulations (DNS) of homogeneous buoyancy driven turbulence, and comparing the light ray displacements from ray tracing to results from BOS theory. The light ray displacements show good agreement with the reference data. This methodology provides a framework for further development of simulation tools for use in experiment design and development of image analysis tools for PIV and BOS applications. Finally, an implementation of the proposed methodology in a Python-CUDA program is made available as an open source software for researchers.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Hierarchical domain structures associated with oxygen octahedra tilting patterns in lead-free (Bi 1/2 Na 1/2 )TiO 3

Hierarchical domain structures associated with oxygen octahedra tilting patterns were observed in lead-free (Bi 1/2 Na 1/2 )TiO 3 ceramics using aberration-corrected high-resolution transmission electron microscopy (HRTEM). Three types of domains are induced by distinct mechanisms: the 'orientation-domain' is induced at micrometer scale formed by different tilting orientations of the oxygen octahedra, the 'meso-chemical-domain' occurs at a few tens of nanometer scale by chemical composition variation on the A-site in the ABO 3 perovskite structure, and the 'nano-cluster-region' runs across several unit-cells with apparent A-site cation segregation with oxygen vacancies clustering around Na cations. Based on HRTEM amplitude contrast imaging (ACI), the correlation between the oxygen octahedral tilting pattern and compositional non-stoichiometry was established. The role of the hierarchical domain structure associated with the tilting patterns of the oxygen octahedra on the ferroelectric behavior of (Bi 1/2 Na 1/2 )TiO 3 is also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2011

LARGE PECULIAR MOTION OF THE SOLAR SYSTEM FROM THE DIPOLE ANISOTROPY IN SKY BRIGHTNESS DUE TO DISTANT RADIO SOURCES

According to the cosmological principle, the universe should appear isotropic, without any preferred directions, to an observer whom we may consider to be fixed in the comoving coordinate system of the expanding universe. Such an observer is stationary with respect to the average distribution of the matter in the universe and the sky brightness at any frequency should appear uniform in all directions to such an observer. However, a peculiar motion of such an observer, due to a combined effect of Doppler boosting and aberration, will introduce a dipole anisotropy in the observed sky brightness; in reverse an observed dipole anisotropy in the sky brightness could be used to infer the peculiar velocity of the observer with respect to the average universe. We determine the peculiar velocity of the solar system relative to the frame of distant radio sources, by studying the anisotropy in the sky brightness from discrete radio sources, i.e., an integrated emission from discrete sources per unit solid angle. Our results give a direction of the velocity vector in agreement with the cosmic microwave background radiation (CMBR) value, but the magnitude ({approx}1600 {+-} 400 km s{sup -1}) is {approx}4 times the CMBR value (369 {+-} 1 km s{sup -1}) at a statistically significant ({approx}3{sigma}) level. A genuine difference between the two dipoles would imply an anisotropic universe, with the anisotropy changing with the epoch. This would violate the cosmological principle where the isotropy of the universe is assumed for all epochs, and on which the whole modern cosmology is based upon.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

WHAT IS THE DIFFERENCE? BLAZHKO AND NON-BLAZHKO RRab STARS AND THE SPECIAL CASE OF V123 IN M3

In an extended photometric campaign of RR Lyrae variables of the globular cluster M3, an aberrant-light-curve, non-Blazhko RRab star, V123, was detected. Based on its brightness, colors and radial-velocity curve, V123 is a bona fide member of M3. The light curve of V123 exhibits neither a bump preceding the light minimum, nor a hump on the rising branch, and has a longer than normal rise time, with a convex shape. A similar shape characterizes the mean light curves of some large-modulation-amplitude Blazhko stars, but none of the regular RRab variables with similar pulsation periods. This peculiar object thus mimics Blazhko variables without showing any evidence of periodic amplitude and/or phase modulation. We cannot find any fully convincing answer to the peculiar behavior of V123, however, the phenomenon raises again the possibility that rotation and aspect angle might play a role in the explanation of the Blazhko phenomenon, and that some source of inhomogeneity (magnetic field, chemical inhomogeneity) deforms the radial pulsation of Blazhko stars during the modulation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Controlled growth of ultrathin Mo 2 C superconducting crystals on liquid Cu surface

Exhibiting thickness-dependent change in the critical temperature (T c ) for the onset of superconductivity, Mo 2 C is an important new member in the family of two-dimensional atomic crystals. Controllable growth in terms of morphology and thickness is necessary to elucidate its intrinsic properties at the 2D limit. Here we demonstrate the chemical vapor deposition of ultrathin Mo 2 C crystals on liquid Cu surface where the morphology of the crystals can be controlled by tuning the carbon supersaturation. A unique staggered carbon vacancy ordering is discovered in Mo 2 C crystals having particular geometries. Thickness engineering of the crystal can be achieved by controlling the thickness of the Cu catalyst layer, which affords a facile route to grow ultrathin 2D samples. Ultrathin Mo 2 C crystals so obtained, have been characterized using aberration corrected scanning transmission electron microscopy annular dark field imaging, where the co-existence of both AA and AB stacking modes is observed. The high crystallinity of the Mo 2 C crystals synthesized in this work is attested by its characteristic sharp superconducting transition.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Large-area synthesis of high-quality monolayer 1T’-WTe 2 flakes

Large-area growth of monolayer films of the transition metal dichalcogenides is of the utmost importance in this rapidly advancing research area. The mechanical exfoliation method offers high quality monolayer material but it is a problematic approach when applied to materials that are not air stable. One important example is 1T’-WTe 2 , which in multilayer form is reported to possess a large non saturating magnetoresistance, pressure induced superconductivity, and a weak antilocalization effect, but electrical data for the monolayer is yet to be reported due to its rapid degradation in air. Here we report a reliable and reproducible large-area growth process for obtaining many monolayer 1T’-WTe 2 flakes. We confirmed the composition and structure of monolayer 1T’-WTe 2 flakes using x-ray photoelectron spectroscopy, energy-dispersive x-ray spectroscopy, atomic force microscopy, Raman spectroscopy and aberration corrected transmission electron microscopy. We studied the time dependent degradation of monolayer 1T’-WTe 2 under ambient conditions, and we used first-principles calculations to identify reaction with oxygen as the degradation mechanism. Finally we investigated the electrical properties of monolayer 1T’-WTe 2 and found metallic conduction at low temperature along with a weak antilocalization effect that is evidence for strong spin–orbit coupling.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Beam-driven dynamics of aluminium dopants in graphene

Abstract Substituting heteroatoms into graphene can tune its properties for applications ranging from catalysis to spintronics. The further recent discovery that covalent impurities in graphene can be manipulated at atomic precision using a focused electron beam may open avenues towards sub-nanometer device architectures. However, the preparation of clean samples with a high density of dopants is still very challenging. Here, we report vacancy-mediated substitution of aluminium into laser-cleaned graphene, and without removal from our ultra-high vacuum apparatus, study their dynamics under 60 keV electron irradiation using aberration-corrected scanning transmission electron microscopy and spectroscopy. Three- and four-coordinated Al sites are identified, showing excellent agreement with ab initio predictions including binding energies and electron energy loss spectrum simulations. We show that the direct exchange of carbon and aluminium atoms predicted earlier occurs under electron irradiation, although unexpectedly it is less probable than the same process for silicon. We also observe a previously unknown nitrogen–aluminium exchange that occurs at Al–N double-dopant sites at graphene divacancies created by our plasma treatment.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Ion microscopy with evolutionary-algorithm-based autofocusing

Abstract Ion microscopy is an established technique for laser focus diagnostics and the accurate, intensity-resolved measurement of laser ionization processes. In the present feasibility study, we discuss a new ion microscope design, which improves its resolution across a large range of magnifications and simplifies its operation. Instead of the common two einzel lens configuration, which is usually optimized for a fixed magnification, we propose a generic design consisting of an array of equally spaced ring electrodes, whose individually adjustable voltages are controlled by an evolutionary algorithm. In this way, we can realize aberration minimized magnifications between 25 and 100. Moreover, the algorithm can adjust the voltage settings under changing experimental conditions and facilitates autofocusing for user-defined magnification.

Haniel, Franz E.↗
DOE OSTI2019

MiR-144 overexpression as a promising therapeutic strategy to overcome glioblastoma cell invasiveness and resistance to chemotherapy

Abstract Glioblastoma (GB) is the most aggressive and common form of primary brain tumor, characterized by fast proliferation, high invasion, and resistance to current standard treatment. The average survival rate post-diagnosis is only of 14.6 months, despite the aggressive standard post-surgery treatment approaches of radiotherapy concomitant with chemotherapy with temozolomide. Altered cell metabolism has been identified as an emerging cancer hallmark, including in GB, thus offering a new target for cancer therapies. On the other hand, abnormal expression levels of miRNAs, key regulators of multiple molecular pathways, have been correlated with pathological manifestations of cancer, such as chemoresistance, proliferation, and resistance to apoptosis. In this work, we hypothesized that gene therapy based on modulation of a miRNA with aberrant expression in GB and predicted to target crucial metabolic enzymes might impair tumor cell metabolism. We found that the increase of miR-144 levels, shown to be downregulated in U87 and DBTRG human GB cell lines, as well as in GB tumor samples, promoted the downregulation of mRNA of enzymes involved in bioenergetic pathways, with consequent alterations in cell metabolism, impairment of migratory capacity, and sensitization of DBTRG cells to a chemotherapeutic drug, the dichloroacetate (DCA). Taken together, our findings provide evidence that the miR-144 plus DCA combined therapy holds promise to overcome GB-acquired chemoresistance, therefore deserving to be explored toward its potential application as a complementary therapeutic approach to the current treatment options for this type of brain tumor.

Cardoso, Ana M. S.↗
DOE OSTI2024

Molecular-Resolution Electron Imaging of Defects and Dynamics at the Ice-Water Interface

Water crystallization into hexagonal ice (type I h ) is one of the most critical processes relevant to the Earth’s environment and human activities. However, despite recent breakthroughs in imaging non-equilibrium condensed ice structures, the ice-water interface has never been imaged at a molecular resolution. This is primarily due to the low stability of the hydrogen bonds in ice under high-resolution microscopy conditions and a lack of methods to prepare compatible samples. Here, this presentation describes the first molecular-resolution imaging of ice crystallized from liquid water and the ice-water interface using high-resolution transmission electron microscopy (HRTEM). By encapsulating deionized (DI) water between two amorphous carbon (a-C) TEM grids and subsequently freezing it with liquid N 2 on a cryo sample stage, we generated two types of ice: non-equilibrium, condensed ice from the atmosphere and encapsulated ice from the DI water (Fig. 1A). Condensed ice usually shows irregular, spherulitic shapes (Fig. 1B). Selected area electron diffraction (SAED) shows that they are a mixture of cubic and hexagonal crystals (Fig. 1C). On the contrary, encapsulated ice forms thin films that contain large-area single-crystalline regions of hexagonal ice oriented along the [0001] zone axis (Fig. 1D). Differential electron energy-loss spectroscopy (EELS) confirmed the high purity of the encapsulated ice free from organic contaminations that are common in other encapsulation methods for HRTEM such as graphene liquid cells. These single-crystalline areas are robust under the electron beam up to ~100 e/Å 2 s. Aberration-corrected HRTEM imaging in these areas achieved a line resolution of ~1.3 Å (Fig. 1E and F). This platform allows us to study near-equilibrium ice structures and dynamics at an unprecedented spatial resolution (Fig. 2). For example, we discovered subdomain-rich regions near the defective crystal edges despite the structure appearing single-crystalline according to diffraction criteria. These subdomains connect via low-angle grain boundaries with flat energy landscapes as a function of tilt angles (according to simulations), showing the high tolerance of ice to defect structures. When we tuned the sample temperature and electron flux rate, we observed radiolysis-controlled bubble generation and dissolution in ice single crystals near a steady state of bubble dynamics. Furthermore, rich beam-induced melting and recrystallization dynamics were observed at the ice-water interface with lattice resolution. These data represent the first observation of the ice-water phase transformation at the sub-nanometer level. In summary, the methods developed in this work enabled molecular-resolution observations of ice and the ice-water interface and shed light on the microstructures and phase transformation pathways. Finer control on the temperature, electron irradiation profile, and imaging detector could eventually lead to real-time observation of ice nucleation in water and address long-standing questions in the nucleation pathways.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Single Electron Self-coherence and Its Wave/Particle Duality in the Electron Microscope

Intensities in high-resolution phase-contrast images from electron microscopes build up discretely in time by detecting single electrons. A wave description of pulse-like coherent-inelastic interaction of an electron with matter implies a time-dependent coexistence of coherent partial waves. Their superposition forms a wave package by phase decoherence of 0.5 - 1 radian with Heisenbergs energy uncertainty ΔE H = $\hbar$/2 Δt -1 matching the energy loss ΔE of a coherent-inelastic interaction and sets the interaction time Δt. In these circumstances, the product of Planck's constant and the speed of light hc is given by the product of the expression for temporal coherence λ 2 /Δλ and the energy loss ΔE. Experimentally, the self-coherence length was measured by detecting the energy-dependent localization of scattered, plane matter waves in surface proximity exploiting the Goos–Hänchen shift. Chromatic-aberration Cc-corrected electron microscopy on boron nitride (BN) proves that the coherent crystal illumination and phase contrast are lost if the self-coherence length shrinks below the size of the crystal unit cell at ΔE > 200 eV. Finally, in perspective, the interaction time of any matter wave compares with the lifetime of a virtual particle of any elemental interaction, suggesting the present concept of coherent-inelastic interactions of matter waves might be generalizable.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Enabling the Acquisition of Electron Beam-Induced Current (EBIC) Images in Conventional SEM and STEM Instruments

Electron beam-induced current (EBIC) imaging is a well-established scanning electron microscope (SEM) technique used to analyze the behavior of microelectronic devices including solar cells. Recently, the application of EBIC imaging in an aberration-corrected scanning transmission electron microscope (STEM) has been demonstrated and offers great potential for the in situ study of electronic materials, correlating charge transport properties to atomic structural and elemental information. Here, this work presents two ways to implement EBIC imaging in conventional SEM and STEM systems: one relying on the instrument's inherent scanning and imaging electronics and the other involving third-party systems usually available in electron microscopes. The implementation of lock-in EBIC in systems equipped with a fast beam blanker is also described. In addition, this work shows and discusses the different mechanisms at play in EBIC imaging and their dependence on beam energy, sample impedance, and electrical measurement configuration, providing researchers with the basic information needed to apply the technique to their research.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗