Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Transmission 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 37 records · Page 2

Transmission electron microscopy characterization of microstructural features of Al-Li-Cu alloys

A transmission electron microscopy (TEM) examination of aluminum-lithium-copper alloys was conducted. The principal purpose is to characterize the nature, size, and distribution of stringer particles which result from the powder metallurgy (P/M) processing of these alloys. Microstructural features associated with the stringer particles are reported that help explain the stress corrosion susceptibility of the powder metallurgy-processed Al-Li-Cu alloys. In addition, matrix precipitation events are documented for a variety of heat treatments and process variations. Hot rolling is observed to significant alter the nature of matrix precipitation, and the observations are correlated with concomitant mechanical property variations.

Avalos-Borja, M.↗

Transmission electron microscopy characterization of microstructural features in aluminum-lithium-copper alloys

A transmission electron microscopy (TEM) examination of aluminum-lithium-copper alloys was conducted. The principal purpose is to characterize the nature, size, and distribution of stringer particles which result from the powder metallurgy (P/M) processing of these alloys. Microstructural features associated with the stringer particles are reported that help explain the stress corrosion susceptibility of the powder metallurgy-processed Al-Li-Cu alloys. In addition, matrix precipitaton events are documented for a variety of heat treatments and process variations. Hot rolling is observed to significantly alter the nature of matrix precipitation, and the observations are correlated with concomitant mechanical property variations.

Avalos-Borja, M.↗

Evidence from transmission electron microscopy for an oxynitride layer in oxidized Si3N4

Microstructural and energy dispersive spectrometry evidence is produced, from transmission electron microscopy, to show that a silicon oxynitride inner layer is produced by the oxidation of silicon nitride in dry oxygen at 1350 C as proposed by Tressler et al. (1989). However, details of the microstructures at the oxide/nitride interface do not agree entirely with the rest of the Tressler model for the oxidation of Si3N4.

Ogbuji, Linus U. J. T.↗

Transmission Electron Microscopy of Cometary Residues from Micron-Sized Craters in the Stardust Al-Foils

We report Transmission Electron Microscopy (TEM) investigations of micro-craters that originated from hypervelocity impacts of comet 81P/Wild 2 dust particles on the aluminium foil of the Stardust collector. The craters were selected by Scanning Electron Microscopy (SEM) and then prepared by Focused Ion Beam (FIB) milling techniques in order to provide electron transparent cross-sections for TEM studies. The crater residues contain both amorphous and crystalline materials in varying proportions and compositions. The amorphous component is interpreted as resulting from shock melting during the impact and the crystalline phases as relict minerals. The latter show evidence for shock metamorphism. Based on the residue morphology and the compositional variation, the impacting particles are inferred to have been dominated by mixtures of submicron olivine, pyroxene and Fe-sulfide grains, in agreement with prior results of relatively coarse-grained mineral assemblages in the aerogel collector.

Leroux, Hugues↗

Soot Nanostructure: Using Fringe Analysis Software on High Resolution Transmission Electron Microscopy of Carbon Soot

Using high resolution transmission electron images of carbon nanotubes and carbon particles, we are able to use image analysis program to determine several carbon fringe properties, including length, separation, curvature and orientation. Results are shown in the form of histograms for each of those quantities. The combination of those measurements can give a better indication of the graphic structure within nanotubes and particles of carbon and can distinguish carbons based upon fringe properties. Carbon with longer, straighter and closer spaced fringes are considered graphite, while amorphous carbon contain shorter, less structured fringes.

King, James D.↗

In situ transmission electron microscopy study on the epitaxial growth of CoSi2 on Si(111) at temperatures below 150 C

This paper reports an in situ transmission electron microscopy study on the epitaxial growth of CoSi2 on Si(111) from a 10-nm-thick amorphous mixture of Co and Si in the ratio 1:2, which was formed by codeposition of Co and Si near room temperature. Nuclei of CoSi2 are observed in the as-deposited film. These nuclei are epitaxial and extend through the whole film thickness. Upon annealing, these columnar epitaxial CoSi2 grains grow laterally at temperatures as low as 50 C. The kinetics of this lateral epitaxial growth was studied at temperatures between 50 and 150 C. The activation energy of the growth process is 0.8 + or - 0.1 eV.

Nieh, C. W.↗

Molecular beam epitaxial growth and transmission electron microscopy studies of thin GaAs/InAs(100) multiple quantum well structures

GaAs/InAs(100) multiple interface structures involving 7.4 percent lattice mismatch have been fabricated via molecular beam epitaxy and examined via transmission electron microscopy. It is found that high-quality, dislocation-free interfaces involving such high lattice mismatch can indeed be experimentally realized for very thin layers provided proper care is given to achieve a balance between the growth kinetics and the thermodynamics leading to the equilibrium ground state of the strained layer. The compressive strain is homogeneously accommodated and a tetragonal distortion is induced in the InAs layer with a perpendicular lattice constant in close agreement with that expected on the basis of the continuum theory and elastic constants of bulk InAs.

Grunthaner, F. J.↗

High resolution transmission electron microscopy of two stony meteorites - Murchison and Kenna

Matrix material from the Murchison C2(M) carbonaceous chondrite and less than micrometer-size pyroxene inclusions in an olivine from the Kenna ureilite have been characterized using high resolution transmission electron microscopy. A diversity of textures and mineral associations, including serpentine-type and brucite-type mixed-layering, occur in the Murchison matrix. Such mixed layer structures are new types of layer silicate. Their presence in the matrix may prove to be genetically significant. The Kenna inclusions, formed at the olivine grain margins, are of two types: (1) a disordered orthopyroxene-clinopyroxene which may have inverted from protopyroxene and (2) a pigeonite with narrow anti-phase domains (80 A to 250 A) and boundaries parallel to (100).

Mackinnon, I. D. R.↗

Carbon Nanostructure Examined by Lattice Fringe Analysis of High Resolution Transmission Electron Microscopy Images

The dimensions of graphitic layer planes directly affect the reactivity of soot towards oxidation and growth. Quantification of graphitic structure could be used to develop and test correlations between the soot nanostructure and its reactivity. Based upon transmission electron microscopy images, this paper provides a demonstration of the robustness of a fringe image analysis code for determining the level of graphitic structure within nanoscale carbon, i.e. soot. Results, in the form of histograms of graphitic layer plane lengths, are compared to their determination through Raman analysis.

VanderWal, Randy L.↗

Carbon Nanostructure Examined by Lattice Fringe Analysis of High Resolution Transmission Electron Microscopy Images

The dimensions of graphitic layer planes directly affect the reactivity of soot towards oxidation and growth. Quantification of graphitic structure could be used to develop and test correlations between the soot nanostructure and its reactivity. Based upon transmission electron microscopy images, this paper provides a demonstration of the robustness of a fringe image analysis code for determining the level of graphitic structure within nanoscale carbon, i.e., soot. Results, in the form of histograms of graphitic layer plane lengths, are compared to their determination through Raman analysis.

VanderWal, Randy L.↗

(abstract) Transmission Electron Microscopy of Al(sub x)Ga(sub 1-x)N/SiC Multilayer Structures

The potential of wide-band-gap III-V nitrides as solar-blind ultraviolet sensors and light emitters has prompted an increasing amount of work recently, including the fabrication of the first UV sensors from as-deposited single crystal GaN. We have used high resolution transmission electron microscopy (TEM) to study the microstructure of two novel developments of wide-band-gap III-V nitrides: the growth of ultra-short period GaN/AlN super lattices (digital alloys); and the incorporation of SiC layers into Al(sub x)Ga(sub 1-x)N structures. By varying the relative periods in a GaN/AlN superlattice, it should be possible to tailor the band gap of the composite to lie between the elemental values of 365 nm for GaN and 200 nm for AlN. The group IV semiconductor, SiC, has a close lattice match (< 3%) to Al(sub x)Ga(sub 1-x)N for growth on the basal plane. Demonstration of epitaxial growth for Al(sub x)Ga(sub 1-x)N/SiC multilayers could enable an extension of direct band-gap material towards the visible.

microscopy GaN AlN semiconductor SiC↗

Transmission electron microscopy study of the formation of epitaxial CoSi2/Si (111) by a room-temperature codeposition technique

Co and Si have been codeposited on Si (111) substrates near room temperature in a stoichiometric 1:2 ratio in a molecular beam epitaxy system. Annealing of these deposits yields high-quality single-crystal CoSi2 layers. Transmission electron microscopy has been used to examine as-deposited layers and layers annealed at 300, 500, and 600 C. Single-crystal epitaxial grains of CoSi2 embedded in a matrix of amorphous Co/Si are observed in as-deposited samples, while the layer is predominantly single-crystal, inhomogeneously strained CoSi2 at 300 C. At 600 C, a homogeneously strained single-crystal layer with a high density of pinholes is observed. In contrast to other solid phase epitaxy techniques used to grow CoSi2 on Si (111), no intermediate silicide phases are observed prior to the formation of CoSi2.

D'Anterroches, Cecile↗

(abstract) Transmission Electron Microscopy of Al(sub x)Ga(sub 1-x)N/SiC Multilayer Structures Grown on Sapphire Substrates

The potential of wide-band-gap III-V nitrides as ultraviolet sensors and light emitters has prompted an increasing amount of work recently, including the fabrication of the first UV sensors from as-deposited single crystal GaN. We have used high resolution transmission electron microscopy (TEM) to study the microstructure of two novel developments of wide-band-gap III-V nitrides: the growth of ultra-short period GaN/AlN superlattices; and the incorporation of SiC layers into Al(sub x)Ga(sub 1-x)N structures. By varying the relative periods in a GaN/AlN superlattice, the band gap of the composite can be tailored to lie between the elemental values of 365 nm for GaN and 200 nm for AlN. The group IV semiconductor, SiC, has a wide band-gap and has a close lattice match (less than 3 %) to Al(sub x)Ga(sub 1-x)N for growth on the basal plane. Demonstration of epitaxial growth for Al(sub x)Ga(sub 1-x)N/SiC multilayers would introduce a wide band-gap analog to the already existing family of III-V and Si(sub 1-x)Ge(sub x) heteroepitaxial growth systems. Although good quality growth of GaN on SiC substrates has been demonstrated, Al(sub x)Ga(sub 1-x)N/SiC multilayer structures have never been grown and the interfacial structure is unknown.

GaN AlN GaN/AlN↗

Transmission Electron Microscopy of Iron Metal in Almahata Sitta Ureilite

Almahata Sitta (AS) is a polymict breccia mainly composed of variable ureilite lithologies with small amounts of chondritic lithologies [1]. Fe metal is a common accessory phase in ureilites, but our earlier study on Fe metals in one of AS fragments (#44) revealed a unique mineralogy never seen in other ureilites [2,3]. In this abstract we report detailed transmission electron microscopy (TEM) on these metal grains to better understand the thermal history of ureilites. We prepared FIB sections of AS#44 by JEOL JIB-4000 from the PTS that was well characterized by SEM-EBSD in our earlier study [2]. The sections were then observed by STEM (JEOL JEM- 2100F). One of the FIB sections shows a submicron-sized symplectic intergrown texture composed of Fe metal (kamacite), Fe carbide (cohenite), Fe phosphide (schreibersite), and Fe sulfide (troilite). Each phase has an identical SAED pattern in spite of its complex texture, suggesting co-crystallization of all phases. This is probably caused by shock re-melting of pre-existing metal + graphite to form a eutectic-looking texture. The other FIB section is mostly composed of homogeneous Fe metal (93 wt% Fe, 5 wt% Ni, and 2 wt% Si), but BF-STEM images exhibited the presence of elongated lathy grains (approx. 2 microns long) embedded in the interstitial matrix. The SAED patterns from these lath grains could be indexed by alpha-Fe (bcc) while interstitial areas are gamma-Fe (fcc). The elongated alpha-Fe grains show tweed-like structures suggesting martensite transformation. Such a texture can be formed by rapid cooling from high temperature where gamma-Fe was stable. Subsequently alpha-Fe crystallized, but gamma-Fe remained in the interstitial matrix due to quenching from high temperature. This scenario is consistent with very rapid cooling history of ureilites suggested by silicate mineralogy.

Mikouchi, T.↗

Transmission Electron Microscopy (TEM) Sample Preparation of Si(1-x)Gex in c-Plane Sapphire Substrate

The National Aeronautics and Space Administration-invented X-ray diffraction (XRD) methods, including the total defect density measurement method and the spatial wafer mapping method, have confirmed super hetero epitaxy growth for rhombohedral single crystalline silicon germanium (Si1-xGex) on a c-plane sapphire substrate. However, the XRD method cannot observe the surface morphology or roughness because of the method s limited resolution. Therefore the authors used transmission electron microscopy (TEM) with samples prepared in two ways, the focused ion beam (FIB) method and the tripod method to study the structure between Si1-xGex and sapphire substrate and Si1?xGex itself. The sample preparation for TEM should be as fast as possible so that the sample should contain few or no artifacts induced by the preparation. The standard sample preparation method of mechanical polishing often requires a relatively long ion milling time (several hours), which increases the probability of inducing defects into the sample. The TEM sampling of the Si1-xGex on sapphire is also difficult because of the sapphire s high hardness and mechanical instability. The FIB method and the tripod method eliminate both problems when performing a cross-section TEM sampling of Si1-xGex on c-plane sapphire, which shows the surface morphology, the interface between film and substrate, and the crystal structure of the film. This paper explains the FIB sampling method and the tripod sampling method, and why sampling Si1-xGex, on a sapphire substrate with TEM, is necessary.

Kim, Hyun Jung↗

A New Coordinated NanoSIMS, Transmission Electron Microscopy and Atom Probe Tomography Approach For the Characterization of Primitive Astromaterials

Presolar grains are remnants of evolved stellar systems preserved within primitive extraterrestrial materials. They are important for studying physical and chemical processing, and formation mechanisms occurring within the interstellar medium, Solar Nebula and their parent stellar environments [1]. Our recent work has shown coordinated nano-scale Secondary Ion Mass Spectrometry (NanoSIMS) and Atom Probe Tomography (APT) can show isotopic and chemical signatures at major to trace levels, morphological signatures, and regional contextual relationships [2,3]. Previous studies have shown Transmission Electron Microscopy (TEM) of Focus Ion Beam (FIB) TEM lamella, can provide localized contextual relationships, crystallographic information and chemical information [1]. Coordinating NanoSIMS, TEM, and APT could gain access to almost all contextual, structural and geochemical signatures within each presolar grain. However, this has proved challenging owing to the preparation requirements for TEM and APT. For example, studying specimen prepared as APT needles in TEM removes the local context, the higher degree of surface exposure can alter the chemistry of beam sensitive materials, and the shank angle of the needle can impact the quality of TEM diffraction images. We designed a new FIB method which takes a 100 nm thick FIB-TEM lamella and sandwiches it between two indium slices (5 μm x ~300 nm x 3 μm). The indium is melted onto the lamella surface using the electron beam (Fig 1). This process adds bulk to the lamella, making it more amenable to APT needle formation (Fig 2). Consequently, samples can be prepared per the optimal requirements for each technique improving data quality, acquisition stability, and access to the signatures and relationships summarised earlier. This technique can be used for measuring multiple phases across a TEM lamella and targeting an individual phase. For example, a presolar grain identified in NanoSIMS could be targeted, studied in TEM and then indium sandwiched with its precise location in the TEM lamella marked using a Pt button for preparation of an APT needle and atomic scale acquisition. [1] A. M. Davis (2014) Meteorites and cosmochemical processes, 1. [2] Nevill N. et al. (2023) LPSC, 54, #1707. [3] Nevill N. et al. (2023) LPSC, 54, #1714.

NanoSIMS↗