Search NASA⌕ Search

SEARCH · Search NASA

Results for “Scanning electron microscopy”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

In search of the elusive IrB{sub 2}: Can mechanochemistry help?

The previously unknown hexagonal ReB{sub 2}-type IrB{sub 2} diboride and orthorhombic IrB monoboride phases were produced by mechanochemical syntheses. High energy ball milling of elemental Ir and B powder for 30 h, followed by annealing of the powder at 1050 °C for 48 h, resulted in the formation of the desired phases. Both traditional laboratory and high resolution synchrotron X-ray diffraction (XRD) analyses were used for phase identification of the synthesized powder. In addition to XRD, scanning electron microscopy and transmission electron microscopy were employed to further characterize the microstructure of the phases produced. - Graphical abstract: ReB{sub 2}-type IrB{sub 2} and a new IrB have been successfully synthesized for the first time using mechanochemical method. Crystal structures of IrB{sub 2} and IrB were studied by synchrotron X-ray diffraction. Microstructures of the new phases were characterized by SEM and TEM. - Highlights: • ReB{sub 2}-type IrB{sub 2} and a new IrB have been synthesized by mechanochemical method. • Crystal structures of IrB{sub 2} and IrB were studied by synchrotron XRD. • Microstructures of the new phases were characterized by SEM and TEM.

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

Characteristics of SnO{sub 2} nanofiber/TiO{sub 2} nanoparticle composite for dye-sensitized solar cells

SnO{sub 2} nanofibers and their composites based photoanodes were fabricated and investigated in the application of dye-sensitized solar cells. The photoanode made of SnO{sub 2}/TiO{sub 2} composites yielded an over 2-fold improvement in overall conversion efficiency. The microstructure of SnO{sub 2} nanofibers was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). A compact morphology of composites was observed using scanning electron microscopy (SEM). A long charge diffusion length (62.42 μm) in the composites was derived from time constant in transient photovoltage and photocurrent analysis. These experimental results demonstrate that one-dimensional nanostructured SnO{sub 2}/TiO{sub 2} composites have a great potential for application in solar cells.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of Nd Addition on the Microstructure and Mechanical Properties of Extruded Mg-6Gd-2.5Y-0.5Zr Alloy

The microstructure, age-hardening behavior, mechanical properties and texture of extruded Mg-6Gd-2.5Y-0.5Zr alloys with various additions of Nd have been investigated through optical microscopy, x-ray diffraction, scanning electron microscopy, transmission electron microscopy, electron back-scattered diffraction, hardness and tensile tests. The results indicate that the number of second-phase particles in the as-extruded alloys increases (especially with the addition of 1.5 wt.% Nd), and the amount of the strengthening β′ phase in the peak-aged sample initially increases, and then decreases when the content of Nd increases above 1.0 wt.%. The precipitation of second-phase particles in the extrusion process weakens the age strengthening. The peak-aged Mg-6Gd-2.5Y-1Nd-0.5Zr alloy shows a maximum yield strength of 259 MPa and an ultimate tensile strength of 350 MPa, which can be attributed to the finely dispersed strengthening β′ phase. All as-extruded alloys exhibit that (0001) planes are aligned perpendicular to the extrusion direction, and the maximum intensity of the texture increases gradually with Nd addition.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Physical properties of RF magnetron sputtered GaN/n-Si thin film: impacts of RF power

GaN thin film was successfully produced on n-Si(100) substrate by RF magnetron sputter under different RF power. Experimental measurement techniques such as UV/Vis spectroscopy, field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and Micro-Raman Spectroscopy were used to research effects of Radio Frequency power on physical properties of produced thin film. It has been found that produced thin film was polycrystalline structure with (100) and (110) planes of hexagonal GaN from X-ray diffraction measurement result. It also proved that increasing RF power gives rise to deterioration in crystal quality of GaN thin film. Reason of this deterioration was discussed. It has been achieved that increasing RF power has resulted in decreasing optical band gap energy of GaN thin film. Reasons for these changes in optical band gap energy were explained. It was seen that some thin films were grown as layer-plus-island mode (Stranski–Krastanov growth mode) and others were grown as layer-by-layer growth mode (Frank van der Merwe mode) from AFM analysis. It has been found that increasing RF power has resulted in improvement of surface morphology of thin film from field emission scanning electron microscopy analysis. However, reaching RF power to 125 W leads to start to deteriorate of surface of GaN thin film. The reasons for this have been discussed. E{sub 1}(TO) transverse optical phonon mode of hexagonal GaN with different intensity was detected from Micro-Raman Spectroscopy measurement. The reasons for this difference have been discussed. It was concluded that RF power has played a significant role in growing high quality GaN thin film. Morphological, structural, and optical properties of GaN thin film were enhanced by controlling RF power, making them a potential candidate for LED, solar cell, diode application.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Modified Magnetic and Electrical Properties of Perovskite-Spinel Multiferroic Composites

Multiferroic composite samples (1 − x) Bi{sub 0.9}Pr{sub 0.1}FeO{sub 3}–xNi{sub 0.5}Co{sub 0.5}Fe{sub 2}O{sub 4} for x = 0, 0.1, 0.2, 0.3, and 1.0 were synthesized by sol-gel auto-combustion method. Detailed investigations were made on the structural, magnetic, and electrical properties of these composites. The X-ray diffraction (XRD) patterns confirm the co-existence of perovskite BPFO and spinel ferrite NCFO without any impurity phase. The average particle size of BPFO and NCFO nanoparticles is nearly equal to 110 nm and 35 nm respectively which are confirmed by XRD and transmission electron microscopy (TEM) analysis. Structural and surface morphology are studied by scanning electron microscopy (SEM). The dielectric properties of the composites are also studied at room temperature. The saturation and remnant magnetization are found to increase with increase in NCFO weight percentage in the composites. The saturation magnetization (Ms) values are 3.38 emu/g, 8.65 emu/g, and 13.87 emu/g and coercivity (Hc) values are 936.52 Oe, 1058.12 Oe, and 1046.77 Oe for BPFO-NCFO 1, 2, and 3 composite samples respectively. The incorporation of BPFO and NCFO enhances the multiferroic properties in the present composite materials which are quite promising for applications point of view.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Mechanism of electrochemical lithiation of a metal-organic framework without redox-active nodes

Metal-organic frameworks (MOFs) have many potential uses for separations, storage, and catalysis, but their use as intercalation hosts for batteries has been scarce. In this article, we examine the mechanism of Li insertion in a MOF to provide guidance to future design efforts in this area. As a model system, we choose UiO-66, a MOF with the formula (Zr{sub 6}O{sub 4}(OH){sub 4}){sub 4}(1,4-benzenedicarboxylate){sub 6}, as an electrode material for lithium-ion batteries; this MOF is of special interest because the zirconium is not redox active. We report both quantum mechanical characterization of the mechanism and experimental studies in which the material is synthesized as nanoparticles to reduce diffusion lengths for lithium ions and increase the contact area with a conductive carbon phase. The calculated changes in the IR spectra of UiO-66 and lithiated UiO-66 are consistent with the experimental FTIR results. We found experimentally that this MOF can maintain a specific discharge capacity of at least 118 mAh/g for 30 lithiation and delithiation cycles at a rate of C/5, exhibiting good cyclability. Density functional electronic structure calculations show that the charge transfer during lithiation is mainly from Li to node oxygens and carboxylate oxygens, that is, it involves anions rather than cations or aromatic rings, and they provide a mechanistic understanding of the potential for increased Li capacity because the theoretical capacity of UiO-66 with Li at the oxygens in the metal oxide nodes and the carboxylate linkers is more than 400 mAh/g. The lithiation process greatly decreases the bandgap of UiO-66, which is expected to increase its electronic conductivity. The electrode material was also characterized by X-ray diffraction and scanning electron microscopy, which were consistent in confirming that smaller particle sizes were obtained in lower-temperature syntheses.

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

Diamond synthesis at atmospheric pressure by microwave capillary plasma chemical vapor deposition

Polycrystalline diamond has been synthesized on silicon substrates at atmospheric pressure, using a microwave capillary plasma chemical vapor deposition technique. The CH{sub 4}/Ar plasma was generated inside of quartz capillary tubes using 2.45 GHz microwave excitation without adding H{sub 2} into the deposition gas chemistry. Electronically excited species of CN, C{sub 2}, Ar, N{sub 2}, CH, H{sub β}, and H{sub α} were observed in the emission spectra. Raman measurements of deposited material indicate the formation of well-crystallized diamond, as evidenced by the sharp T{sub 2g} phonon at 1333 cm{sup −1} peak relative to the Raman features of graphitic carbon. Field emission scanning electron microscopy images reveal that, depending on the growth conditions, the carbon microstructures of grown films exhibit “coral” and “cauliflower-like” morphologies or well-facetted diamond crystals with grain sizes ranging from 100 nm to 10 μm.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Novel comparison of microscopy and diffraction techniques on the structure of iron oxide nanoparticle monolayers transferred by Langmuir-Schaefer method

Iron oxide nanoparticles undergo self-assembly into well-ordered monolayer films of macroscopic size at the air-water interface. This self-assembly process is the result of the van der Waals forces between the constituent particles. For roughly spherical particles, this monolayer is a 2D hexagonal close packed lattice. With Grazing Incidence X-Ray Diffraction (GID), one can obtain global statistical information about the film’s spacing and correlation length. Herein, we demonstrate that comparable structural information can be obtained by a novel Fourier transform analysis method applied to Scanning Electron Microscopy (SEM) images taken of the film after it has been transferred to a silicon substrate. This consists of using numerical methods to isolate the lattice structure of the monolayer in the SEM image to which a 2D discrete Fourier Transform is applied and the result integrated. This results in Bragg peak information akin to that obtained from GID, whose structure shows the same hexagonal close packed lattice with similar spacing and of greater peak contrast. Furthermore, this analysis technique may prove to be a suitable alternative or compliment to GID for many applications.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effective properties of a fly ash geopolymer: Synergistic application of X-ray synchrotron tomography, nanoindentation, and homogenization models

Microstructural and micromechanical investigation of a fly ash-based geopolymer using: (i) synchrotron X-ray tomography (XRT) to determine the volume fraction and tortuosity of pores that are influential in fluid transport, (ii) mercury intrusion porosimetry (MIP) to capture the volume fraction of smaller pores, (iii) scanning electron microscopy (SEM) combined with multi-label thresholding to identify and characterize the solid phases in the microstructure, and (iv) nanoindentation to determine the component phase elastic properties using statistical deconvolution, is reported in this paper. The phase volume fractions and elastic properties are used in multi-step mean field homogenization (Mori–Tanaka and double inclusion) models to determine the homogenized macroscale elastic modulus of the composite. The homogenized elastic moduli are in good agreement with the flexural elastic modulus determined on macroscale paste beams. The combined use of microstructural and micromechanical characterization tools at multiple scales provides valuable information towards the material design of fly ash geopolymers.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure Analysis of Bismuth Absorbers for Transition-Edge Sensor X-ray Microcalorimeters

Given its large X-ray stopping power and low specific heat capacity, bismuth (Bi) is a promising absorber material for X-ray microcalorimeters and has been used with transition-edge sensors (TESs) in the past. However, distinct X-ray spectral features have been observed in TESs with Bi absorbers deposited with different techniques. Evaporated Bi absorbers are widely reported to have non-Gaussian low-energy tails, while electroplated ones do not show this feature. In this study, we fabricated Bi absorbers with these two methods and performed microstructure analysis using scanning electron microscopy and X-ray diffraction microscopy. The two types of material showed the same crystallographic structure, but the grain size of the electroplated Bi was about 40 times larger than that of the evaporated Bi. This distinction in grain size is likely to be the cause of their different spectral responses.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

In Situ TEM Investigation of ZnO Nanowires during Sodiation and Lithiation Cycling

The development of sodium-ion batteries has drawn lots of attention recently due to the low-cost and eco-friendly sodium source. However, a fundamental understanding of the sodiation behavior for commonly used electrode materials is still limited. Here, combining in situ transmission electron microscopy, aberration-corrected scanning transmission electron microscopy, and ex situ battery cycling tests, the lithiation and sodiation behavior of ZnO nanowires is investigated. The findings show a direct correlation between the mechanical behavior of the lithiated/sodiated ZnO nanowires and their electrochemical cyclability. The mechanical brittleness of LiZn and the formation of nanocracks lead to the poor cyclability of Li-ion batteries with a ZnO anode. However, the sodiated ZnO nanowires show profuse dislocation plasticity. The observed high-density dislocations offer the sodiated ZnO anode more ductility and subsequently better cyclability than its Li-ion counterpart. The results reveal the importance of understanding the correlation between mechanical properties of battery electrodes and their cycling abilities.

Asayesh-Ardakani, Hasti↗
DOE OSTI2020

(Oxy)hydroxides Formed on Aluminum Fuel Materials After Irradiation and Long-Term Wet Storage - 20354

The aluminum cladding of research-reactor fuel experiences general corrosion when in contact with water during in-reactor service and post-discharge wet storage, resulting in the formation of adherent aluminum (oxy)hydroxide films. These (oxy)hydroxides contain chemically-bound water that poses challenges for extended dry storage due to the risk of thermal or radiolytic decomposition releasing free water and/or hydrogen and oxygen gases. This study describes characterization of the (oxy)hydroxides present on several aluminum materials used in reactor operation and subsequently stored wet in the L-Basin storage facility at the Savannah River Site (SRS) for an extended period. Characterization data providing insight into the loading, composition, and morphology of (oxy)hydroxides to be expected on service-exposed aluminum cladding provides valuable benchmarks for designing adequate drying and dry-storage approaches. This work is part of a broader investigation to address knowledge gaps and technical data needs for dry storage of aluminum-clad spent nuclear fuel (ASNF), which included in-lab growth of (oxy)hydroxide films on aluminum alloy substrates to investigate formation behavior, investigation of drying methods to remove existing (oxy)hydroxides from ASNF cladding, and measurement of radiolytic yield of hydrogen from (oxy)hydroxide powders and films. In this study, (oxy)hydroxide films were characterized for three aluminum-alloy materials used in reactors and subsequently stored wet for up to approximately 40 years in L-Basin at SRS: one cropping from a Missouri University Research Reactor (MURR) fuel element (Al-6061 alloy), one cropping from a Universal Sleeve Housing (USH) (Al-6063 alloy), and one Mark-16B fuel assembly (either Al-6061 or Al- 6063). The USH and Mark-16B were used in SRS production reactors. Characterization of the as-received (oxy)hydroxides included scanning electron microscopy (SEM) in both plan-view and cross-section to characterize the (oxy)hydroxide layer's morphology, thickness, and structure. X-ray diffraction (XRD) was used to identify the chemical composition and distinguish between the various aluminum (oxy)hydroxides known to form under reactor and storage conditions. XRD analysis revealed both bayerite (Al(OH)3) and boehmite (AlOOH) on the surface of the MURR and USH samples, as well as bayerite, boehmite, and gibbsite (another Al(OH)3 polymorph) on the surface of the Mark-16B sample. The aluminum trihydroxides, bayerite and gibbsite, are typically associated with corrosion in low-temperature (<80 deg. C) water, while boehmite is expected to form at higher water temperature (>80 deg. C). The presence of bayerite on the USH, which is believed to have operated close to 90 deg. C, suggests that boehmite formed during in-reactor exposure was not protective against further hydroxide growth in low-temperature wet storage. Cross-section scanning electron microscopy (SEM) showed total (oxy)hydroxide layer thicknesses of ∼5- 10 μm for the MURR and ∼5-15 μm for the Mark-16B. The thickness of the USH's (oxy)hydroxide layer was indiscernible by the current mounting and imaging method, despite plan-view SEM and XRD confirming the presence of an (oxy)hydroxide layer. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Gelatin/Gelatinized Sago Starch Biomembranes as a Drug Delivery System Using Rubber Latex as Plasticizer

Preparation and properties of gelatin and gelatin/gelatinized sago starch biomembranes as a drug delivery system are presented. Deproteinized natural rubber latex (DNRL) was chosen to blend as a plasticizer in biomembranes due to its elasticity. The opaque biomembranes were formed, and the effect of DNRL amounts (10–50 part per hundred of gelatin; phg) on mechanical properties of biomembranes was investigated. It was discovered that increasing the amounts of DNRL could decrease the brittleness of biomembranes. However, these DNRL blended biomembranes still swelled, dissolved in water, and eroded within 2 h. The 50 phg DNRL was further chosen for biomembrane preparations. Then, the 5–30 phg gelatinized sago starch which was prepared in-house was added. These gelatin/gelatinized sago starch biomembranes were homogenous and opaque. They portrayed good water uptake properties, and the highest values occurred in 20–30 min, then these biomembranes eroded slowly. Increasing the amounts of sago starch in biomembranes raised the water uptake rates but reduced the erosion properties. Biomembranes with and without starch blends showed the same tensile strengths. Their elongations at break increased when the amounts of starch were raised but still were lower than that of gelatin/DNRL biomembranes. The morphology, scanning electron microscopy, atomic force electron microscopy, Fourier transform infrared spectroscopy, differential scanning calorimeter, and X-ray diffractometer confirmed the compatibility of ingredients in biomembranes. Lidocaine and its hydrochloride salt were successfully incorporated in these biomembranes with good properties. The drug release and permeation of biomembrane showed good drug controlled release and were able to permeate through the pig skin.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Indium-bump-free antimonide superlattice membrane detectors on silicon substrates

We present an approach to realize antimonide superlattices on silicon substrates without using conventional Indium-bump hybridization. In this approach, PIN superlattices are grown on top of a 60 nm Al0.6Ga0.4Sb sacrificial layer on a GaSb host substrate. Following the growth, the individual pixels are transferred using our epitaxial-lift off technique, which consists of a wet-etch to undercut the pixels followed by a dry-stamp process to transfer the pixels to a silicon substrate prepared with a gold layer. Structural and optical characterization of the transferred pixels was done using an optical microscope, scanning electron microscopy, and photoluminescence. The interface between the transferred pixels and the new substrate was abrupt, and no significant degradation in the optical quality was observed. An Indium-bump-free membrane detector was then fabricated using this approach. Spectral response measurements provided a 100% cut-off wavelength of 4.3 μm at 77 K. The performance of the membrane detector was compared to a control detector on the as-grown substrate. The membrane detector was limited by surface leakage current. The proposed approach could pave the way for wafer-level integration of photonic detectors on silicon substrates, which could dramatically reduce the cost of these detectors.

Zamiri, M. (ORCID:000000020042735X)↗
DOE OSTI2018

Investigation of Interfacial Layer for Friction Stir Scribe Welded Aluminum to Steel Joints

Friction stir scribe (FSS) welding as a recent derivative of friction stir welding has successfully fabricated a linear joint between automotive Al and steel sheets. However, there is a lack of understanding on its bonding mechanism. In this paper, the microstructures and phases at the bonding interface of FSS welded Al to ultra-high strength steel joints were studied using scanning electron microscopy and transmission electron microscopy. Based on the microstructural analysis, it is found that both mechanical and chemical bonding occurred simultaneously, and the energy-dispersive X-ray spectroscopy revealed that a thin intermetallic compound (IMC) layer was formed at the interface. Owing to the varied material flow and heat generation, the IMC layer thickness gradually decreased from the advancing side to the retreating side, and two IMCs (i.e. Fe2Al5 and Fe4Al13) were confirmed in different weld regions using diffraction pattern (or 1D fast Fourier transform pattern). Also, a Fe/Al solid solution was noticed in the IMC layer, and several Al fringes were found in the Fe-rich side in the scribe stir zone.

friction stir scribe welding, interfacial layer, i↗
DOE OSTI2020

Laser-interference pulse number dependence of surface chemistry and sub-surface microstructure of AA2024-T3 alloy

The laser-based treatment of a metal surface is an intrinsically non-chemical technique that can alter both the topology and chemistry of surfaces. A laser-based treatment for coating and joining applications can offer alternative surface preparations to the chemically-based surface preparation techniques, which are subject to severe environmental protection and hazardous-waste management considerations. In this study, the surface chemistry and sub-surface microstructural changes are investigated for a novel surface processing method using laser interferometry produced by two beams of a pulsed Nd:YAG laser. The two-beam laser-interference allowed the structuring of the surface at length scales much less than that of the laser beam spot. Surface chemistry changes in the oxide layer of AA 2024-T3 aluminum alloy rolled sheet due to laser processing were investigated using x-ray photoelectron spectroscopy (XPS). Near surface microstructural changes have been investigated with scanning electron microscopy and energy dispersive x-ray spectroscopy (SEM/EDS), and scanning transmission electron microscopy (STEM) as a function of number of interfering laser shots. SEM microstructure pictures of the top surface shows the minimization of surface defects, as all of the sharp features from a rolled sheet surface were smoothed by laser-structuring. STEM images indicate that the laser-interference processing reduced the formation of CuMn-rich precipitates over a 500–800 nm depth from the top surface. XPS data indicated that the Al oxide layer is modified compared to that of the baseline specimen and that the oxide thickness increases with the number of shots per spot. Finally, the additional thicker oxide on Al alloys is expected to increase the corrosion resistance of the coated Al 2024.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Evolution of Tantalum Content During Vacuum Induction Melting and Electroslag Remelting of a Novel Martensitic Steel

The need for materials with superior thermal and mechanical properties while mitigating cost increases interest in new complex alloy compositions which brings challenges to manufacturing processes. In this investigation, vacuum induction melting (VIM) and electroslag remelting (ESR) of a novel tantalum (Ta)-containing martensitic steel was performed using standard industry practices at a laboratory scale. A 25 pct loss of Ta was measured from the VIM electrode to the ESR ingot using X-ray fluorescence. Several tools were used for broad characterization of the ingots, including LECO for chemistry analysis, scanning electron microscopy, and electron probe microanalysis for observation of the precipitate and inclusion phases post-VIM and post-ESR as well as computational modeling of the ESR process for the calculation of macrosegregation and inclusion travel. It was found that a significant amount of Ta{sub 2}O{sub 5} inclusions formed during VIM and were transferred to the slag during ESR. While ESR was particularly successful at decreasing the number density of inclusions by 95 pct, additional efforts are needed with regard to vacuum leak rate and purity of stock material when melting novel advanced steels.

36 MATERIALS SCIENCE↗