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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

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

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

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

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

Actinic imaging of native and programmed defects on a full-field mask

Description: We describe the imaging and characterization of native defects on a full field extreme ultraviolet (EUV) mask, using several reticle and wafer inspection modes. Mask defect images recorded with the SEMA TECH Berkeley Actinic Inspection Tool (AIT), an EUV-wavelength (13.4 nm) actinic microscope, are compared with mask and printed-wafer images collected with scanning electron microscopy (SEM) and deep ultraviolet (DUV) inspection tools. We observed that defects that appear to be opaque in the SEM can be highly transparent to EUV light, and inversely, defects that are mostly transparent to the SEM can be highly opaque to EUV. The nature and composition of these defects, whether they appear on the top surface, within the multilayer coating, or on the substrate as buried bumps or pits, influences both their significance when printed, and their detectability with the available techniques. Actinic inspection quantitatively predicts the characteristics of printed defect images in ways that may not be possible with non-EUV techniques. As a quantitative example, we investigate the main structural characteristics of a buried pit defect based on EUV through-focus imaging.
Date: March 12, 2010
Creator: Mochi, I.; Goldberg, K. A.; Fontaine, B. La; Tchikoulaeva, A. & Holfeld, C.
Partner: UNT Libraries Government Documents Department

Detailed Description of Electronic Microscope Stage Manipulator

Description: A stage manipulator is described which scans the slide automatically. Means are provided for presetting the horizontal and vertical limits of motion, horizontal rate, and vertical step size, The following components of the manipulator are described: electronic control system, horizontal programmer, and vertical programmer. (D.L.C.)
Date: July 1, 1963
Creator: Rogers, E. J.
Partner: UNT Libraries Government Documents Department

Direct sublattice imaging of interface dislocation structures in CdTe/GaAs(001)

Description: This paper presents directly interpretable atomic resolution images of dislocation structures at interfaces in CdTe/GaAs(001) systems. This is achieved using the technique of Z-contrast imaging in a 300 kV scanning transmission electron microscope in conjunction with maximum entropy image analysis. In addition to being used to further the understanding of the relation between growth conditions and exhibited properties, the data presented provides direct information on the atomic arrangements at dislocation cores.
Date: January 1995
Creator: McGibbon, A.J.; Pennycook, S.J.; Angelo, J.E. & Mills, M.J.
Partner: UNT Libraries Government Documents Department

Atomic structures of inversion domain boundaries and dislocations in sintered AlN

Description: AlN is an attractive material because of its mechanical, thermal and electronic properties. However, these properties are often adversely altered by extended defects such as inversion domain boundaries (IDBs), and through impurities associated with the defects, especially oxygen. Thus to improve the properties of the material it is important to understand the structures of the defects. A number of studies have been carried out to characterize these defects using fringe contrast, weak-beam, convergent-beam electron diffraction and conventional high-resolution phase contrast imaging. These techniques all require the use of model structures for data interpretation. In this paper, the authors report a direct determination of the structures of IDBs and dislocation cores in AlN by high resolution Z-contrast imaging using a 300 kV VG HB603U scanning transmission electron microscope, with a probe size of 1.3 A.
Date: February 1, 1998
Creator: Yan, Y.; Chisholm, M.F. & Pennycook, S.J.
Partner: UNT Libraries Government Documents Department

Quantitative Sub-Angstrom Imaging Through ADF STEM

Description: ORNL/CP-100163 Annular dark-field (ADF) imaging in a scanning transmission electron microscope (STEM) at atomic resolution provides an incoherent image that can be described as the convolution between the intensity of the illuminating STEM probe and an object function consisting of localised sources at the atomic-column positions. It has been shown that the resolution limit of the microscope limits the accuracy to which the object function can be reconstructed [1]. Here we demonstrate how a number of images recorded at various degrees of underfocus can be reconstructed to give sub- angstrom information, and discuss how quantitative physical measurements may be deduced from these images. The conventionally used optimum probe intensity profile for the VG Microscopes HB603U STEM (300 kV, C{sub 5}=l mm), shown in Fig. la, requires an objective aperture radius of 9 mrad and 40 nm of underfocus. However, using a larger aperture and a greater degree of underfocus can give a probe with a much narrower central maximum (Fig 1b), but at the expense of creating side-lobes with increased intensity. Since this probe contains sharper features than the conventionally optimum probe, information at much higher spatial frequencies can be recorded. Figure 2 shows information transfer down to a resolution of 0.78 A. Although the images recorded using such a probe are not as intuitively interpretable as those recorded using the optimum probe, the lack of a phase problem in incoherent imaging means that the probe maybe immediately deconvolved from the image intensity data, and phase retrieval techniques are not required [1]. The geometry of ADF imaging makes this method robust to chromatic defocus spread, unlike focal-series reconstruction methods in conventional, coherent transmission electron microscopy.
Date: August 31, 1998
Creator: Nellist, P.D. & Pennycook, S.J.
Partner: UNT Libraries Government Documents Department

Direct Observations of Defect Structures in Optoelectronic Materials by Z-Contrast STEM

Description: Optoelectronic semiconductor materials have wide and important technological applications. For example, wide gap nitride semiconductors have attracted significant attention recently due to their promising performance as short-wavelength light emitting diodes (LEDs) and blue lasers, while HgCdTe II-VI semiconductors are the most promising candidates for applications as infrared detectors, or large array x-ray or r-ray detectors. In this paper, two examples are given to show that high-resolution Z-contrast imaging is an effective technique to determine the atomic structures of defects in these complex semiconductor materials.
Date: August 31, 1998
Creator: Beaumont, B.; Browning, N.D.; Chen, Y.P.; Faurie, J.-P.; Gibart, P.; Nellist, P.D. et al.
Partner: UNT Libraries Government Documents Department

Structural properties of free-standing 50 mm diameter GaN waferswith (101_0) orientation grown on LiAlO2

Description: (10{und 1}0) GaN wafers grown on (100) face of {gamma}-LiAlO{sub 2} were studied using transmission electron microscopy. Despite good lattice matching in this heteroepitaxial system, high densities of planar structural defects in the form of stacking faults on the basal plane and networks of boundaries located on prism planes inclined to the layer/substrate interface were present in these GaN layers. In addition, significant numbers of threading dislocations were observed. High-resolution electron microscopy indicates that stacking faults present on the basal plane in these layers are of low-energy intrinsic I1type. This is consistent with diffraction contrast experiments.
Date: September 27, 2005
Creator: Jasinski, Jacek; Liliental-Weber, Zuzanna; Maruska, Herbert-Paul; Chai, Bruce H.; Hill, David W.; Chou, Mitch M.C. et al.
Partner: UNT Libraries Government Documents Department

Three-Dimensional Aberration-Corrected Scanning Transmission Electron Microscopy for Biology

Description: Recent instrumental developments have enabled greatly improved resolution of scanning transmission electron microscopes (STEM) through aberration correction. An additional and previously unanticipated advantage of aberration correction is the greatly improved depth sensitivity that has led to the reconstruction of a three-dimensional (3D) image from a focal series. In this chapter the potential of aberration-corrected 3D STEM to provide major improvements in the imaging capabilities for biological samples will be discussed. This chapter contains a brief overview ofthe various high-resolution 3D imaging techniques, a historical perspective of the development of STEM, first estimates of the dose-limited axial and lateral resolution on biological samples and initial experiments on stained thin sections.
Date: January 1, 2007
Creator: De Jonge, Niels; Sougrat, Rachid; Pennycook, Stephen J; Peckys, Diana B & Lupini, Andrew R
Partner: UNT Libraries Government Documents Department

Structure of low-density nanoporous dielectrics revealed by low-vacuum electron microscopy and small-angle x-ray scattering

Description: We use low-vacuum scanning electron microscopy to image directly the ligament and pore size and shape distributions of representative aerogels over a wide range of length scales ({approx} 10{sup 0}-10{sup 5} nm). The images are used for unambiguous, real-space interpretation of small-angle scattering data for these complex nanoporous systems.
Date: June 5, 2006
Creator: Kucheyev, S O; Toth, M; Baumann, T F; Hamza, A V; Ilavsky, J; Knowles, W R et al.
Partner: UNT Libraries Government Documents Department

Transmission Electron Microscopy Study of Nonpolar a-Plane GaNGrown by Pendeo-Epitaxy on (112_0) 4H-SiC

Description: Pendeo-epitaxy has been applied to nonpolar a-plane GaN layers in order to observe if such process will lead to defect reduction in comparison with direct growth on this plane. Uncoalesced and coalesced a-plane GaN layers with thicknesses 2{micro}m and 12{micro}m, respectively have been studied by conventional and high resolution electron microscopy. The following structural defects have been observed in pendeo-epitaxial layers: (1) basal stacking faults, (2) threading dislocations and (3) prismatic stacking faults. Drastic decrease of threading dislocation density and stacking faults have been observed in 'wing' areas with respect to 'seed' areas. Cross-section images reveal cracks and voids at the areas where two coalesced wings meet each other. High resolution electron microscopy shows that the majority of stacking faults are low-energy planar defects of the types I{sub 1}, I{sub 2} and I{sub 3}. The I{sub 3} type basal stacking fault, predicted theoretically, has been observed experimentally for the first time.
Date: March 10, 2005
Creator: Zakharov, D.N.; Liliental-Weber, Z.; Wagner, B.; Reitmeier, Z.J.; Preble, E.A. & Davis, R.F.
Partner: UNT Libraries Government Documents Department

Z-contrast imaging and grain boundaries in semiconductors

Description: Interest in grain boundaries in semiconductors is linked to the application of polycrystalline semiconductors as photovoltaic and interconnect materials. In real devices such as solar cells and MOS structures as well as future devices such as flat-panel displays, the intergranular regions of the polycrystalline solid have a significant effect on the flow of electronic current. These grain boundary barriers exist because the chemical potential of the boundary atoms are shifted from the bulk value by the change in local symmetry. The chemical potential is also changed by impurities, other structural defects, and other phases in the boundary. The lack of knowledge on the atomic structure of grain boundaries is, at present, the greatest barrier to advancements in the understanding of the electrical properties of these defects. The advances of the last few years have provided the tools with which to probe these interfaces at the true atomic scale. One such tool is the high-resolution scanning transmission electron microscope installed at Oak Ridge National Laboratory (VG Microscopes HB603) that can form a 1.27 {Angstrom} electron probe. Images are formed by scanning the probe across a thin sample and using an annular detector to collect electrons scattered to high angles. Because the annular detector collects electrons scattered over a wide range of angles, phase correlation and dynamical diffraction effects are averaged by this annular integration. Thus, an image with incoherent characteristics is produced and retained to relatively large specimen thickness. The key advantage of incoherent imaging is that when the microscope is focused to produce maximum image contrast, the bright image features directly correspond to the positions of the atomic columns.
Date: March 1, 1996
Creator: Chisholm, M.F. & Pennycook, S.J.
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