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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Effect of heat treatment on the physical properties of bimetallic doped catalyst, Cu-Ni/TiO{sub 2}

Post heat treatment is critical for the doped semiconductor oxide in order to improve its photocatalytic performance. Thus work had been carried out to understand the effect of different calcination temperature (400, 450 and 500°C) on the physical properties of nanosized Cu-Ni/TiO{sub 2}Cu-Ni doped TiO{sub 2} nanoparticles prepared using a combined method of sol-gel and hydrothermal. The treated samples were characterized using Raman spectroscopy, Brunauer–Emmett–teller (BET) measurement, high resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FESEM), and diffuse reflectance UV-Vis spectroscopy (DR-UV-Vis). Raman analysis showed that all samples displayed anatase (101) phase of TiO{sub 2}, which is in good agreement with the TEM results. BET data showed that all prepared Cu-Ni/TiO{sub 2} with different calcination temperature are mesoporous. SEM images displayed spherical particles with typical size of about 15 to 20 nm. UV-Vis spectra illustrated that the absorbance edge of all prepared Cu-Ni/TiO{sub 2} have extended to the visible region with bandgap energies (2-2.1 eV) less than the pure anatase TiO{sub 2} (3.2 eV). Calcination temperature of 450°C is considered to be the optimum as it converts the synthesized Cu-Ni/TiO{sub 2} sample to have smaller average particle size with higher surface area that lead to more absorbance in the visible region and lower bandgap energy.

36 MATERIALS SCIENCE↗
NASA NTRS1988

Microstructure and growth model for rice-hull-derived SiC whiskers

The microstructure of silicon carbide whiskers grown from rice hulls has been studied using methods of high-resolution analytical electron microscopy. Small, partially crystalline inclusions (about 10 nm) containing calcium, manganese, and oxygen are concentrated in whisker core regions, while peripheral regions are generally inclusion free. The distinct microphase distribution is evidence of a two-stage growth process in which the core region grows first, followed by normal growth toward whisker sides. Partial dislocations extend radially from the core region to the surface and tend to be paired in V-shaped configurations. Whisker surfaces exhibit microroughness due to a tendency to develop small facets on close-packed planes. The microstructural data obtained from TEM observations are used as a basis for discussion of the mechanisms involved in whisker growth, and a model of the growth process is proposed. The model includes a two-dimensional growth mechanism involving vapor, liquid, and solid phases, although it is significantly different from the classical vapor-liquid-solid (VLS) process of whisker growth.

Nutt, Steven R.↗
NASA NTRS1989

Epitaxial growth of InSb (111) on sapphire (0001)

Indium antimonide has been epitaxially grown directly on sapphire. Reflection high-energy electron diffraction, TEM, and SEM data are presented to show that the indium antimonide layer is epitaxial, has an abrupt interface with the sapphire, and grows in the 111-line direction. Mobility data show room-temperature mobilities as high as 10,000 sq cm/V s from some regions on the wafer.

Jamison, K. D.↗
DOE OSTI2022

Facile polymerization in a bicellar template to produce polymer nano-rings

We report a well-defined discoidal bicelle composed of three lipids, specifically zwitterionic long-chain 1,2-dipalmitoyl phosphocholine (DPPC) and short-chain 1,2-dihexanoyl phosphocholine (DHPC) doped with anionic 1,2-dipalmitoyl phosphoglycerol (DPPG) provides a generalized template for the synthesis of hydrophobic polymer nano-rings. The lipid molar ratio of DPPC/DHPC/DPPG is 0.71/0.25/0.04. The detailed investigation and discussion were based on styrene but tested on three other vinyl monomers. The structure of nano-rings is identified through the detailed analysis of small angle X-ray/neutron scattering (SAXS and SANS) data and transmission electron micrographs (TEM), supported by the differential scanning calorimetric (DSC) data before and after polymerization. The investigation covers samples with a styrene-to-lipid ratio ranged varied from 1:50 to 1:10.The styrene monomers are initially located at both the discoidal planar (long-chain lipid rich) and rim (short-chain lipid rich) regions. During polymerization, they migrate to the more fluid rim region-section. The formation mechanism involves the interplay of hydrophobic interaction, mismatched miscibility of polystyrene between the ordered and disordered phases, and crystallinity of the long lipid acyl chains. This facile synthesis is proven applicable for several hydrophobic monomers. The well-defined nano-rings greatly enhance the interfacial area and have the potential to be the building blocks for functional materials, if monomers are incorporated with desirable functions, for future applications. Crosslinked polymer nano-rings are produced in well-defined discoidal bicelles. The enhanced immiscibility in the planar region drives the hydrophobic polymers to the fluidic rim. The platform can be generalized for synthesis of other hydrophobic polymer nano-rings.

36 MATERIALS SCIENCE↗
NASA NTRS1992

X-ray scattering measurements from thin foil X-ray mirrors

Thin foil X-ray mirrors are to be used as the reflecting elements in the telescopes of the X-ray satellites Spectrum-X-Gamma (SRG) and ASTRO-D. High resolution X-ray scattering measurements from the Au coated and dip-lacquered Al foils are presented. These were obtained from SRG mirrors positioned in a test quadrant of the telescope structure and from ASTRO-D foils held in a simple fixture. The X-ray data is compared with laser data and other surface structure data such as STM, atomic force microscopy (AFM), TEM, and electron micrography. The data obtained at Cu K-alpha(1), (8.05 keV) from all the mirrors produced on Al foils shows a scatter which limits the obtainable half-power width to above 1.5 arcmin. Mirrors based on electroformed Ni foils, however, show local regions with a factor of 4 better performance, and they are being developed for future applications.

Christensen, F. E.↗
DOE OSTI2016

Synthesis of nano-forsterite powder by making use of natural silica sand

Nano-forsterite powder with natural silica sand and magnesium powder as the raw materials have been succesfully synthesized. The silica sand was purified followed by a coprecipitation process to obtain colloidal silica. The magnesium powder was dissolved in a chloric acid solution to obtain MgCl{sub 2} solution. The nanoforsterite powder was synthesised using a sol-gel method which included the mixing the colloidal silica and the MgCl{sub 2} solution with various aging and filtering processes. The samples were dried at 100 °C using a hot plate and then the dried powders were calcinated at 900 °C for 2 hours. The samples were characetised for their elements and phase compositions using X-ray Flourescence (XRF) and X-ray Diffraction (XRD) methods, respectively. The diffraction data were qualitatively analyzed using Match!2 software and quantitatively using Rietica software. The crystallite size was verified using Transmission Electron Microscopy (TEM). Results of XRD data analysis showed that the forsterite content reached up to 90.5% wt. The TEM average crystallite size was approximately 53(6) nm.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Predicting neutron damage using TEM with in situ ion irradiation and computer modeling

We have constructed a computer model of irradiation defect production closely coordinated with TEM and in situ ion irradiation of Molybdenum at 80 degrees C over a range of dose, dose rate and foil thickness. We have reexamined our previous ion irradiation data to assign appropriate error and uncertainty based on more recent work. The spatially dependent cascade cluster dynamics model is updated with recent Molecular Dynamics results for cascades in Mo. After a careful assignment of both ion and neutron irradiation dose values in dpa, TEM data are compared for both ion and neutron irradiated Mo from the same source material. Using the computer model of defect formation and evolution based on the in situ ion irradiation of thin foils, the defect microstructure, consisting of densities and sizes of dislocation loops, is predicted for neutron irradiation of bulk material at 80 degrees C and compared with experiment. Reasonable agreement between model prediction and experimental data demonstrates a promising direction in understanding and predicting neutron damage using a closely coordinated program of in situ ion irradiation experiment and computer simulation.

42 ENGINEERING↗
DOE OSTI2023

Multi-Scale Characterization of Porosity and Cracks in Silicon Carbide Cladding after Transient Reactor Test Facility Irradiation

Silicon carbide (SiC) ceramic matrix composite (CMC) cladding is currently being pursued as one of the leading candidates for accident-tolerant fuel (ATF) cladding for light water reactor applications. The morphology of fabrication defects, including the size and shape of voids, is one of the key challenges that impacts cladding performance and guarantees reactor safety. Therefore, quantification of defects’ size, location, distribution, and leak paths is critical to determining SiC CMC in-core performance. This research aims to provide quantitative insight into the defect’s distribution under multi-scale characterization at different length scales before and after different Transient Reactor Test Facility (TREAT) irradiation tests. A non-destructive multi-scale evaluation of irradiated SiC will help to assess critical microstructural defects from production and/or experimental testing to better understand and predict overall cladding performance. X-ray computed tomography (XCT), a non-destructive, data-rich characterization technique, is combined with lower length scale electronic microscopic characterization, which provides microscale morphology and structural characterization. This paper discusses a fully automatic workflow to detect and analyze SiC-SiC defects using image processing techniques on 3D X-ray images. Following the XCT data analysis, advanced characterizations from focused ion beam (FIB) and transmission electron microscopy (TEM) were conducted to verify the findings from the XCT data, especially quantitative results from local nano-scale TEM 3D tomography data, which were utilized to complement the 3D XCT results. In this work, three SiC samples (two irradiated and one unirradiated) provided by General Atomics are investigated. The irradiated samples were irradiated in a way that was expected to induce cracking, and indeed, the automated workflow developed in this work was able to successfully identify and characterize the defects formation in the irradiated samples while detecting no observed cracking in the unirradiated sample. These results demonstrate the value of automated XCT tools to better understand the damage and damage propagation in SiC-SiC structures for nuclear applications.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
NASA NTRS1990

Technical Evaluation Motor no. 5 (TEM-5)

Technical Evaluation Motor No. 5 (TEM-5) was static test fired at the Thiokol Corporation Static Test Bay T-97. TEM-5 was a full scale, full duration static test fire of a high performance motor (HPM) configuration solid rocket motor (SRM). The primary purpose of TEM static tests is to recover SRM case and nozzle hardware for use in the redesigned solid rocket motor (RSRM) flight program. Inspection and instrumentation data indicate that the TEM-5 static test firing was successful. The ambient temperature during the test was 41 F and the propellant mean bulk temperature (PMBT) was 72 F. Ballistics performance values were within the specified requirements. The overall performance of the TEM-5 components and test equipment was nominal. Dissembly inspection revealed that joint putty was in contact with the inner groove of the inner primary seal of the ignitor adapter-to-forward dome (inner) joint gasket; this condition had not occurred on any previous static test motor or flight RSRM. While no qualification issues were addressed on TEM-5, two significant component changes were evaluated. Those changes were a new vented assembly process for the case-to-nozzle joint and the installation of two redesigned field joint protection systems. Performance of the vented case-to-nozzle joint assembly was successful, and the assembly/performance differences between the two field joint protection system (FJPS) configurations were compared.

Cook, M.↗
DOE OSTI2015

Aberration‐Corrected Transmission Electron Microscopy and In Situ XAFS Structural Characterization of Pt/γ‐Al 2 O 3 Nanoparticles

Abstract Aberration‐corrected (AC) STEM, AC TEM and in situ X‐ray absorption fine structure spectroscopy (XAFS) were used to characterize the Pt clusters present on a 0.35 wt % Pt on γ‐alumina support after reduction in hydrogen at 700 °C. STEM high‐angle annular dark field imaging shows that cluster formation takes place at temperatures up to approximately 350 °C, and this is followed by gradual growth in cluster size for heat treatments in hydrogen up to 700 °C. The STEM data show that after 700 °C reduction the Pt clusters are present in a narrow size distribution centered at 0.88 nm, and using a method involving a redistribution of the Pt atoms using a high electron dosage in the STEM, it is shown that the clusters are present in two‐dimensional morphology. This conclusion is verified using intensity line scans. The in situ extended X‐ray absorption fine structure data are in good agreement with these observations. High‐resolution AC–TEM, which uses a broad coherent electron beam, and can thus offer advantages relative to STEM for structure determination of fine clusters, supported by image simulations of through‐focus series, were used to analyze the structures of Pt particles. The structures determined by using AC–TEM are consistent with STEM and EXAFS data in having a flat two‐dimensional morphology. Comparison of AC–STEM and AC TEM data for the same 700 °C reduced sample suggests that parallel‐beam TEM mode of imaging may be advantageous because of the less pronounced beam‐induced structural rearrangements that occur when imaging with a fine STEM probe.

Sinkler, Wharton↗
DOE OSTI2015

Scanning EM of non-heavy metal stained biosamples: Large-field of view, high contrast and highly efficient immunolabeling

Scanning electron microscopy (SEM) is increasing its application in life sciences for electron density measurements of ultrathin sections. These are traditionally analyzed with transmission electron microscopy (TEM); by most labs, SEM analysis still is associated with surface imaging only. Here we report several advantages of SEM for thin sections over TEM, both for structural inspection, as well as analyzing immuno-targeted labels such as quantum dots (QDs) and gold, where we find that QD-labeling is ten times more efficient than gold-labeling. Furthermore, we find that omitting post-staining with uranyl and lead leads to QDs readily detectable over the ultrastructure, but under these conditions ultrastructural contrast was even almost invisible in TEM examination. Importantly, imaging in SEM with STEM detection leads to both outstanding QDs and ultrastructural contrast. STEM imaging is superior over back-scattered electron imaging of these non-contrasted samples, whereas secondary electron detection cannot be used at all. We conclude that examination of ultrathin sections by SEM, which may be immunolabeled with QDs, will allow rapid and straightforward analysis of large fields with more efficient labeling than can be achieved with immunogold. The large fields of view routinely achieved with SEM, but not with TEM, allows straightforward raw data sharing using virtual microscopy, also known as nanotomy when this concerns EM data in the life sciences. - Highlights: • High resolution and large fields of view via nanotomy or virtual microscopy. • Highly relevant for EM‐datasets where information density is high. • Sample preparation with low contrast good for STEM, not TEM. • Quantum dots now stand out in STEM‐based detection. • 10 Times more efficient labeling with quantum dots compared to gold.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

DEVELOPING THE NATIONAL GEOTHERMAL DATA SYSTEM ADOPTION OF CKAN FOR DOMESTIC & INTERNATIONAL DATA DEPLOYMENT

The National Geothermal Data System (NGDS) De- sign and Testing Team is developing NGDS software currently referred to as the “NGDS Node-In-A-Box”. The software targets organizations or individuals who wish to host at least one of the following: • an online repository containing resources for the NGDS; • an online site for creating metadata to register re- sources with the NGDS • NDGS-conformant Web APIs that enable access to NGDS data (e.g., WMS, WFS, WCS); • NDGS-conformant Web APIs that support dis- covery of NGDS resources via catalog service (e.g. CSW) • a web site that supports discovery and under- standing of NGDS resources A number of different frameworks for development of this online application were reviewed. The NGDS Design and Testing Team determined to use CKAN (http://ckan.org/), because it provides the closest match between out of the box functionality and NGDS node-in-a-box requirements. To achieve the NGDS vision and goals, this software development project has been inititated to provide NGDS data consumers with a highly functional inter- face to access the system, and to ease the burden on data providers who wish to publish data in the sys- tem. It is important to note that this software package constitutes a reference implementation. The NGDS software is based on open standards, which means other server software can make resources available, and other client applications can utilize NGDS data. A number of international organizations have ex- pressed interest in the NGDS approach to data access. The CKAN node implementation can provide a sim- ple path for deploying this technology in other set- tings.

15 GEOTHERMAL ENERGY↗
NASA NTRS1989

Technical Evaluation Motor 3 (TEM-3)

A primary objective of the technical evaluation motor program is to recover the case, igniter and nozzle hardware for use on the redesigned solid rocket motor flight program. Two qualification objectives were addressed and met on TEM-3. The Nylok thread locking device of the 1U100269-03 leak check port plug and the 1U52295-04 safe and arm utilizing Krytox grease on the barrier-booster shaft O-rings were both certified. All inspection and instrumentation data indicate that the TEM-3 static test firing conducted 23 May 1989 was successful. The test was conducted at ambient conditions with the exception of the field joints (set point of 121 F, with a minimum of 87 F at the sensors), igniter joint (set point at 122 F with a minimum of 87 F at sensors) and case-to-nozzle joint (set point at 114 F with a minimum of 87 F at sensors). Ballistics performance values were within specification requirements. Nozzle performance was nominal with typical erosion. The nozzle and the case joint temperatures were maintained at the heaters controlling set points while electrical power was supplied. The water and the CO2 quench systems prevented damage to the metal hardware. All other test equipment performed as planned, contributing to a successful motor firing. All indications are that the test was a success, and all expected hardware will be refurbished for the RSRM program.

Garecht, Diane↗
DOE OSTI2015

Frontiers of in situ electron microscopy

In situ transmission electron microscopy (TEM) has become an increasingly important tool for materials characterization. It provides key information on the structural dynamics of a material during transformations and the correlation between structure and properties of materials. With the recent advances in instrumentation, including aberration corrected optics, sample environment control, the sample stage, and fast and sensitive data acquisition, in situ TEM characterization has become more and more powerful. In this article, a brief review of the current status and future opportunities of in situ TEM is included. It also provides an introduction to the six articles covered by in this issue of MRS Bulletin explore the frontiers of in situ electron microscopy, including liquid and gas environmental TEM, dynamic four-dimensional TEM, nanomechanics, ferroelectric domain switching studied by in situ TEM, and state-of-the-art atomic imaging of light elements (i.e., carbon atoms) and individual defects.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Developments in TEM Nanotomography of Calcium Silicate Hydrate

This investigation was designed to explore the possibility of using transmission electron microscope ( TEM ) tomography on cement‐based systems gain a greater understanding of their nanostructure and pore network. The preliminary results show a clearly a well‐defined pore network at the nanoscale, with pore size approximately 1.7–2.4 nm in diameter and spaced around 5–8 nm apart. A comparison of small angle X‐ray scattering data with 2‐D TEM images analyzed with the Fourier slice theorem documents an excellent structural correlation.

Taylor, Rae↗
DOE OSTI2024

Tutorial on In Situ and Operando (Scanning) Transmission Electron Microscopy for Analysis of Nanoscale Structure–Property Relationships

In situ and operando (scanning) transmission electron microscopy [(S)TEM] is a powerful characterization technique that uses imaging, diffraction, and spectroscopy to gain nano-to-atomic scale insights into the structure–property relationships in materials. This technique is both customizable and complex because many factors impact the ability to collect structural, compositional, and bonding information from a sample during environmental exposure or under application of an external stimulus. In the past two decades, in situ and operando (S)TEM methods have diversified and grown to encompass additional capabilities, higher degrees of precision, dynamic tracking abilities, enhanced reproducibility, and improved analytical tools. Much of this growth has been shared through the community and within commercialized products that enable rapid adoption and training in this approach. This tutorial aims to serve as a guide for students, collaborators, and nonspecialists to learn the important factors that impact the success of in situ and operando (S)TEM experiments and assess the value of the results obtained. As this is not a step-by-step guide, readers are encouraged to seek out the many comprehensive resources available for gaining a deeper understanding of in situ and operando (S)TEM methods, property measurements, data acquisition, reproducibility, and data analytics.

(S)TEM↗
DOE OSTI2018

Comparative SEM and TEM analyses of apatite phases prepared by a multi-sample loading device

Highlights: • A multi-sample loading device which ultrasonically disperses samples was developed. • Comparative EM analyses on various apatite phases were efficiently carried out. • SEM-EDS data revealed distinctive values of O/P and Ca/P intensity ratios. • TEM-SAED data presented characteristic structural features of apatite phases. • Lattice parameters of bone and fossil apatite were affected by CO{sub 3} content. - Abstract: Comparative chemical and structural characterization of various apatite phases from both synthetic and natural sources were carried out by utilizing a multi-sample loading device developed for scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. The device is capable of spraying nanoparticles via ultrasonication, and four separate samples were loaded on a single TEM grid by a masking tool to characterize different apatite phases in consistent instrumental and analytical conditions. SEM energy dispersive spectroscopy (EDS) analysis of the apatite samples revealed distinctive values of O/P and Ca/P intensity ratios except for the fossil apatite due to its high proportion of externally originating phases. Selected area electron diffraction (SAED) pattern analysis presented the characteristic lattice parameters of the apatite phases, especially the bone and fossil apatite which had CO{sub 3}in their chemistry. Analyzing distinctive chemical and structural features among varied apatite phases can be efficiently carried out through electron microscopy with multiple samples on a single TEM grid, and such methods can be employed for characterizing a wider range of materials.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Comprehensive ecosystem model-experiment synthesis using multiple datasets at two temperate forest free-air CO2 enrichment experiments: model performance and compensating biases

Free Air CO2 Enrichment (FACE) experiments provide a remarkable wealth of data to test the sensitivities of terrestrial ecosystem models (TEMs). In this study, a broad set of 11 TEMs were compared to 22 years of data from two contrasting FACE experiments in temperate forests of the south eastern US the evergreen Duke Forest and the deciduous Oak Ridge forest. We evaluated the models' ability to reproduce observed net primary productivity (NPP), transpiration and Leaf Area index (LAI) in ambient CO2 treatments. Encouragingly, many models simulated annual NPP and transpiration within observed uncertainty. Daily transpiration model errors were often related to errors in leaf area phenology and peak LAI. Our analysis demonstrates that the simulation of LAI often drives the simulation of transpiration and hence there is a need to adopt the most appropriate of hypothesis driven methods to simulate and predict LAI. Of the three competing hypotheses determining peak LAI (1) optimisation to maximise carbon export, (2) increasing SLA with canopy depth and (3) the pipe model the pipe model produced LAI closest to the observations. Modelled phenology was either prescribed or based on broader empirical calibrations to climate. In some cases, simulation accuracy was achieved through compensating biases in component variables. For example, NPP accuracy was sometimes achieved with counter-balancing biases in nitrogen use efficiency and nitrogen uptake. Combined analysis of parallel measurements aides the identification of offsetting biases; without which over-confidence in model abilities to predict ecosystem function may emerge, potentially leading to erroneous predictions of change under future climates.

Walker, Anthony P↗