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Analytical Electron Microscopy Characterization of Uranium-Contaminated Soils from the Fernald Site, FY1993 Report

Description: A combination of optical microscopy, scanning electron microscopy with backscattered electron detection (SEM/BSE), and analytical electron microscopy (AEM) is being used to determine the nature of uranium in soils from the Fernald Environmental Management Project. The information gained from these studies is being used to develop and test remediation technologies. Investigations using SEM have shown that uranium is contained within particles that are typically 1 to 100 micrometers in diameter. Further analysis with AEM has shown that these uranium-rich regions are made up of discrete uranium-bearing phases. The distribution of these uranium phases was found to be inhomogeneous at the microscopic level.
Date: October 1994
Creator: Buck, E. C.; Cunnane, J. C.; Brown, N. R. & Dietz, N. L.
Partner: UNT Libraries Government Documents Department

Study of dislocations in copper by weak beam, stereo, and in situ straining TEM

Description: Conventional transmission electron microscopy (TEM) has been an invaluable tool for verifjhg and developing dislocation theories since the first direct observations of dislocations were made using a TEM in the 1950s. Several useful techniques and technological advancements have been made since, helping fbrther the advancement of dislocation knowledge. The present paper concerns two studies of dislocations in copper made by coupling several of these techniques, specifically weak beam, in situ straining, and stereo TEM. Stereo-TEM coupled with in situ straining TEM was used for tracking 3D dislocation motion and interactions in low dislocation density copper foils. A mechanism by which dislocations in a pileup bypass a dislocation node is observed and discussed. Weak beam TEM is used in conjunction with stereo-TEM to analyze the dislocation content of a dense dislocation wall (DDW).
Date: January 1, 2002
Creator: McCabe, R. J. (Rodney J.); Misra, A. (Amit) & Mitchell, T. E. (Terence E.)
Partner: UNT Libraries Government Documents Department

Photoelectric Emission Measurements for CVD Grown Polycrystalline Diamond Films

Description: We examined CVD grown polycrystalline diamond films having different methane concentrations to detect defects and study the possible correlation between the methane concentration used during the growth process and the defect density. SEM and Raman results show that the amorphous and sp2 carbon content of the films increases with methane concentration. Furthermore, photoelectric emission from diamond is confirmed to be a two-photon process, hence the electrons are emitted from normally unoccupied states. We found that the photoelectric yield, for our samples, decreases with the increase in methane concentration. This trend can be accounted for in two different ways: either the types of defects observed in this experiment decrease in density as the methane concentration increases; or, the defect density stays the same or increases, but the increase in methane concentration leads to an increase in the electron affinity, which reduces the overall photoelectric yield.
Date: August 1999
Creator: Hassan, Tarek
Partner: UNT Libraries

Ultrastructure of Azotobacter vinelandii

Description: Article discussing research on vegetative cells and cysts for Azotobacter vinelandii 12837 prepared for electron microscopy by several methods assumed to preserve structural details destroyed by techniques previously reported in literature.
Date: August 8, 1970
Creator: Vela, G. Roland, 1927-; Cagle, Gerald D. & Holmgren, P. R.
Partner: UNT College of Arts and Sciences

Polishing Methods for Metallic and Ceramic Transmission Electron Microscopy Specimens, Rev. 1

Description: "In recent years, the increasing sophistication of transmission electron microscope (TEM) studies of materials has necessitated more exacting methods of specimen preparation. The present report describes improved equipment and techniques for electropolishing and chemically polishing a wide variety of specimens. Many of the specimens used in developing or improving the techniques to be described were irradiated with heavy ions such as nickel or vanadium to study radiation damage. The high cost of these specimens increased the need for reproducible methods of initial preparation postirradiation processing, and final thinning for TEM examination. A technique was also developed to salvage specimens that had previously been thinned but were unusable for various reasons. Jet polishing is, in general, the method of choice for surface polishing, sectioning, and thinning. The older beaker electropolishing method is included in this report because it is inexpensive and simple, and gives some insight into how the more recent methods were developed"--NTIS abstract.
Date: March 1986
Creator: Kestel, B. J.
Partner: UNT Libraries Government Documents Department

Polishing Methods for Metallic and Ceramic Transmission Electron Microscopy Specimens

Description: "In recent years, the increasing sophistication of transmission electron microscope (TEM) studies of materials has necessitated more exacting methods of specimen preparation. The present report describes improved equipment and techniques for electropolishing and chemically polishing a wide variety of specimens. Many of the specimens used in developing or improving the techniques to be described were irradiated with heavy ions such as nickel or vanadium to study radiation damage. The high cost of these specimens increased the need for reproducible methods of initial preparation, postirradiaton processing, and final thinning for TEM examination. A technique was also developed to salvage specimens that had previously been thinned but were unusable for various reasons. Jet polishing is, in general, the method of choice for surface polishing, sectioning, and thinning. The older beaker electropolishing method is included in this report because it is inexpensive and simple, and gives some insight into how the more recent methods were developed. 29 figures, 8 tables. (ERA citation 07:004650)."--NTIS abstract.
Date: July 1981
Creator: Kestel, B. J.
Partner: UNT Libraries Government Documents Department

Interface Characterization Techniques for 304L Stainless Steel Resistance Upset Welds

Description: In an effort to better characterize and classify austenitic stainless steel resistance upset welds, standard methods have been examined and alternative methods investigated. Optical microscopy yields subjective classification due to deformation obscured bond lines and individual perception. The use of specimen preparations that better reveal grain boundaries aids in substantiating optical information. Electron microscopy techniques produce quantitative information in relation to microstructural constituents. Orientation Imaging Microscopy (OIM) is a relatively new technique for obtaining objective, quantitative information pertaining to weld integrity, i.e., percent grain boundary growth across the interface.
Date: July 26, 1998
Creator: Abeln, T.G.; Kackenko, E.J.; Necker, C.T. & Field, R.D.
Partner: UNT Libraries Government Documents Department

Alpha-null defocus: An optimum defocus condition with relevance for focal-series reconstruction

Description: Two optimum defocus conditions are used in high-resolution transmission electron microscopy. Scherzer defocus produces an image of the specimen ''projected potential'' to the resolution of the microscope, and Lichte defocus minimizes dispersion. A third optimum defocus is best for focal-series reconstruction; alpha-null defocus maximizes transfer of high-frequency diffracted beam amplitudes into the microscope image. Beam transfer is confined by incident-beam convergence to a Gaussian ''packet'' of defocus values centered on the alpha-null defocus. For a diffracted beam hkl, with a spatial frequency of u, the envelope for incident beam convergence has null damping effect when defocus is set to -Cs. (wavelength.u)**2. On either side of this alpha-null defocus value, the damping effect of incident-beam convergence reduces diffracted-beam transfer. The position of alpha-null defocus for any spatial frequency depends only on the value of Cs, but defocus-packet width around the alpha-null defocus depends only on the convergence semi-angle. Under NCEM OAM (one-Angstrom microscope) conditions, a [110] diamond image with the correct 0.89A spacing appears when the Si (004) alpha-null defocus is selected. The alpha-null defocus should be included as the (furthest underfocus) limit for all high-resolution focal series reconstruction.
Date: February 14, 2001
Creator: O'Keefe, Michael A.
Partner: UNT Libraries Government Documents Department

Sub-Angstrom transmission electron microscopy at 300keV

Description: We have demonstrated sub-Angstrom TEM to a resolution of 0.78 Angstrom with the one-Angstrom microscope (OAM) project at the National Center for Electron Microscopy. The OAM combines a modified CM300FEG-UT with computer software able to generate sub-Angstrom images from experimental image series. We achieved sub-Angstrom resolution with the OAM by paying close attention to detail. We placed the TEM in a favorable environment. We reduced its three-fold astigmatism A2 from 2.46mm to 300 Angstrom (corresponding to transfer of 0.68 Angstrom spacings at a pi/4 phase limit). We improved its information limit by minimizing high-voltage and lens current ripple. Energy spread of 0.93eV FWHH gave a focus spread of 20 Angstrom and an information limit of 0.78 Angstrom, allowing successful resolution of the 0.89 Angstrom (400) atom spacings in [110] diamond. As a further test, we reduced the electron gun extraction voltage to 3kV to improve our information limit to 0.75 Angstrom, and then imaged 0 .7 Angstrom (444) atom spacings in [112] silicon as distinct pairs of 'white atoms' near an alpha-null defocus of -3783 Angstrom.
Date: February 14, 2001
Creator: O'Keefe, Michael A.; Nelson, E. Christian; Turner, John H. & Thust, Andreas
Partner: UNT Libraries Government Documents Department

Sixth International Conference on X-ray Microscopy

Description: More than 180 participants from around the world crowded the Clark Kerr Campus of the University of California, Berkeley, from August 1-6, 1999 for the Sixth International Conference on X-Ray Microscopy (XRM99). Held every three years since 1983, the XRM conferences have become the primary international forum for the presentation and discussion of advances in high-spatial-resolution x-ray imaging and applications (including the use of x-ray spectroscopic and analytical techniques) in biological and medical sciences, environmental and soil sciences, and materials and surface sciences.
Date: August 23, 1999
Creator: Robinson, Arthur L.
Partner: UNT Libraries Government Documents Department

Effects of Impurities on Alumina-Niobium InterfacialMicrostructures

Description: Optical microscopy, scanning electron microscopy, and transmission electron microscopy were employed to examine the interfacial microstructural effects of impurities in alumina substrates used to fabricate alumina-niobium interfaces via liquid-film-assisted joining. Three types of alumina were used: undoped high-purity single-crystal sapphire; a high-purity, high-strength polycrystalline alumina; and a lower-purity, lower-strength polycrystalline alumina. Interfaces formed between niobium and both the sapphire and high-purity polycrystalline alumina were free of detectable levels of impurities. In the lower-purity alumina, niobium silicides were observed at the alumina-niobium interface and on alumina grain boundaries near the interface. These silicides formed in small-grained regions of the alumina and were found to grow from the interface into the alumina along grain boundaries. Smaller silicide precipitates found on grain boundaries are believed to form upon cooling from the bonding temperature.
Date: June 20, 2005
Creator: McKeown, Joseph T.; Sugar, Joshua D.; Gronsky, Ronald & Glaeser,Andreas M.
Partner: UNT Libraries Government Documents Department

Characterization of Glass-Like Fragments from the 3714 Building

Description: This report describes characterization of a sample obtained from the 3714 building in the 300 Area. Characterization of this unknown material was required for the demonolition activities in the 300 Area. The object of the study was to dertermine the nature of the material, composition, possible structure, evidence for hazards components. The green material is a sodium alumino-silicate glass. This conclusion is based on the composition provided by SEM-EDS, and the images that suggest a glass-like morphology. Further analysis with Ramin and/or infrared could be used to determine the presence of any organics.
Date: February 23, 2010
Creator: Buck, Edgar C.
Partner: UNT Libraries Government Documents Department

Classification of Multiple Types of Organic Carbon Composition in Atmospheric Particles by Scanning Transmission X-Ray Microscopy Analysis

Description: A scanning transmission X-ray microscope at the Lawrence Berkeley National Laboratory is used to measure organic functional group abundance and morphology of atmospheric aerosols. We present a summary of spectra, sizes, and shapes observed in 595 particles that were collected and analyzed between 2000 and 2006. These particles ranged between 0.1 and 12 mm and represent aerosols found in a large range of geographical areas, altitudes, and times. They include samples from seven different field campaigns: PELTI, ACE-ASIA, DYCOMS II, Princeton, MILAGRO (urban), MILAGRO (C-130), and INTEX-B. At least 14 different classes of organic particles show different types of spectroscopic signatures. Different particle types are found within the same region while the same particle types are also found in different geographical domains. Particles chemically resembling black carbon, humic-like aerosols, pine ultisol, and secondary or processed aerosol have been identified from functional group abundance and comparison of spectra with those published in the literature.
Date: May 16, 2007
Creator: Kilcoyne, Arthur L; Takahama, S.; Gilardoni, S.; Russell, L.M. & Kilcoyne, A.L.D.
Partner: UNT Libraries Government Documents Department

Atomic resolution 3D electron diffraction microscopy

Description: Electron lens aberration is the major barrier limiting the resolution of electron microscopy. Here we describe a novel form of electron microscopy to overcome electron lens aberration. By combining coherent electron diffraction with the oversampling phasing method, we show that the 3D structure of a 2 x 2 x 2 unit cell nano-crystal (framework of LTA [Al12Si12O48]8) can be ab initio determined at the resolution of 1 Angstrom from a series of simulated noisy diffraction pattern projections with rotation angles ranging from -70 degrees to +70 degrees in 5 degrees increments along a single rotation axis. This form of microscopy (which we call 3D electron diffraction microscopy) does not require any reference waves, and can image the 3D structure of nanocrystals, as well as non-crystalline biological and materials science samples, with the resolution limited only by the quality of sample diffraction.
Date: March 1, 2002
Creator: Miao, Jianwei; Ohsuna, Tetsu; Terasaki, Osamu & O'Keefe, Michael A.
Partner: UNT Libraries Government Documents Department

Isolation and Characterization of Novel Microbacteriophage Barbara

Description: Poster presentation for the 2010 University Scholars Day at the University of North Texas discussing research on the isolation of a new strain of mycobacteriophage from soil collection using a Mycobacterium smegmatis host strain and an enrichment protocol.
Date: April 15, 2010
Creator: Mitchell, Angel; Simon, Stephanie E.; Benjamin, Robert C. & Hughes, Lee E.
Partner: UNT Honors College

Atomic Scale coexistence of Periodic and quasiperiodic order in a2-fold A1-Ni-Co decagonal quasicrystal surface

Description: Decagonal quasicrystals are made of pairs of atomic planes with pentagonal symmetry periodically stacked along a 10-fold axis. We have investigated the atomic structure of the 2-fold surface of a decagonal Al-Ni-Co quasicrystal using scanning tunneling microscopy (STM). The surface consists of terraces separated by steps of heights 1.9, 4.7, 7.8, and 12.6{angstrom} containing rows of atoms parallel to the 10-fold direction with an internal periodicity of 4{angstrom}. The rows are arranged aperiodically, with separations that follow a Fibonacci sequence and inflation symmetry. The results indicate that the surfaces are preferentially Al-terminated and in general agreement with bulk models.
Date: November 14, 2005
Creator: Park, Jeong Young; Ogletree, D. Frank; Salmeron, Miquel; Ribeiro,R.A.; Canfield, P.C.; Jenks, C.J. et al.
Partner: UNT Libraries Government Documents Department

Optical Spectroscopy Study of Transparent Non-Carious Human Dentin and Dentin-Enamel Junction

Description: Improving our knowledge of the morphology, composition and properties of the dentin, enamel, and the dentin-enamel junction (DEJ) is vital for the development of improved restorative materials and clinical placement techniques. Most studies of dental tissues have used light microscopy for characterization. In our investigation, the spectroscopic properties of normal and non-carious transparent human root dentin, and the dentin-enamel junction were investigated using emission imaging microscopy, and micro-spectroscopy. Experimental results reveal new information on the structural and biochemical characteristics of these dental tissues.
Date: December 14, 1999
Creator: Marshall, G.W.; Marshall, S.J.; Gallagher, R.R. & Demos, S.
Partner: UNT Libraries Government Documents Department

Point-by-point compositional analysis for atom probe tomography

Description: This article demonstrates a new alternate approach to data processing for analyses that traditionally employed grid-based counting methods, as demonstrated using an atom-probe analysis of a Ni-based super-alloy.
Date: March 5, 2014
Creator: Stephenson, Leigh T.; Ceguerra, Anna V.; Li, Tong; Rojhirunsakool, Tanaporn; Nag, Soumya; Banerjee, Rajarshi et al.
Partner: UNT College of Engineering