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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

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

A Quantitative Assessment of Site Formation at the Dmanisi Archaeological Site, Republic of Georgia

Description: The focus of this thesis was to gather and analyze micromorphological and petrographic data on soils at the archaeological site of Dmanisi in order to better understand the extent to which the deposition and alteration of the sediments has affected the preservation of artifacts and faunal remains. A major goal of this research was to test hypothesis related to why bone material is discovered in some strata and not in others. This research focuses on the application of micromorphology (supplemented with other methods) to the soils through the use of petrographic analysis of thin sections and scanning electron microscopy. These techniques complement previous field analyses by providing a quantitative assessment of individual strata through point counting and chemical mapping. The results of this research support the hypothesis that the sediments are predominantly mafic ashes, while showing that there is very little soil development in the strata. This suggests quick episodic burial in a relatively dry climate, confirming the hypothesis for a short time sequence in the strata. Additionally, differential weathering probably did not play a significant role in the differential abundance of bone remains among the strata at Dmanisi.
Date: August 2013
Creator: Crislip, Peter S.
Partner: UNT Libraries

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

Heavy-Ion Irradiation of Thulium(III) Oxide Targets Prepared by Polymer-Assisted Deposition

Description: Thulium(III) oxide (Tm{sub 2}O{sub 3}) targets prepared by the polymer-assisted deposition (PAD) method were irradiated by heavy-ion beams to test the method's feasibility for nuclear science applications. Targets were prepared on silicon nitride backings (thickness of 1000 nm, 344 {micro}g/cm{sup 2}) and were irradiated with an {sup 40}Ar beam at laboratory frame energy of {approx}210 MeV (50 particle nA). The root mean squared (RMS) roughness prior to irradiation is 1.1 nm for a {approx}250 nm ({approx}220 {micro}g/cm{sup 2}) Tm{sub 2}O{sub 3} target, and an RMS roughness of 2.0 nm after irradiation was measured by atomic force microscopy (AFM). Scanning electron microscopy of the irradiated target reveals no significant differences in surface homogeneity when compared to imaging prior to irradiation. Target flaking was not observed from monitoring Rutherford scattered particles as a function of time.
Date: September 15, 2008
Creator: Garcia, Mitch A.; Ali, Mazhar N.; Chang, Noel N.; Parsons-Moss, Tashi; Ashby, Paul D.; Gates, Jacklyn M. et al.
Partner: UNT Libraries Government Documents Department

Glass particles produced by laser ablation for ICP-MSmeasurements

Description: Pulsed laser ablation (266nm) was used to generate glass particles from two sets of standard reference materials using femtosecond (150fs) and nanosecond (4ns) laser pulses with identical fluences of 50 J cm{sup -2}. Scanning electron microscopy (SEM) images of the collected particles revealed that there are more and larger agglomerations of particles produced by nanosecond laser ablation. In contrast to the earlier findings for metal alloy samples, no correlation between the concentration of major elements and the median particle size was found. When the current data on glass were compared with the metal alloy data, there were clear differences in terms of particle size, crater depth, heat affected zone, and ICP-MS response. For example, glass particles were larger than metal alloy particles, the craters in glass were less deep than craters in metal alloys, and damage to the sample was less pronounced in glass compared to metal alloys samples. The femtosecond laser generated more intense ICP-MS signals compared to nanosecond laser ablation for both types of samples, although glass sample behavior was more similar between ns and fs-laser ablation than for metals alloys.
Date: June 1, 2007
Creator: Gonzalez, J.; Liu, C.; Wen, S.; Mao, X. & Russo, R.E.
Partner: UNT Libraries Government Documents Department

Lithographic measurement of EUV flare in the 0.3-NA Micro ExposureTool optic at the Advanced Light Source

Description: The level of flare present in a 0.3-NA EUV optic (the MET optic) at the Advanced Light Source at Lawrence Berkeley National Laboratory is measured using a lithographic method. Photoresist behavior at high exposure doses makes analysis difficult. Flare measurement analysis under scanning electron microscopy (SEM) and optical microscopy is compared, and optical microscopy is found to be a more reliable technique. In addition, the measured results are compared with predictions based on surface roughness measurement of the MET optical elements. When the fields in the exposure matrix are spaced far enough apart to avoid influence from surrounding fields and the data is corrected for imperfect mask contrast and aerial image proximity effects, the results match predicted values quite well. The amount of flare present in this optic ranges from 4.7% for 2 {micro}m features to 6.8% for 500 nm features.
Date: January 1, 2005
Creator: Cain, Jason P.; Naulleau, Patrick & Spanos, Costas J.
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

Reversible wetting of NaCl nanoparticles at relative humidities below deliquescence observed by environmental non-contact AFM

Description: The behavior of NaCl nanoparticles as a function of relative humidity (RH) was characterized by depositing particles on a prepared hydrophobic surface and measuring their height via non-contact environmental atomic force microscopy (AFM). Non-contact AFM allows greater sensitivity to changes in the size of particles than does contact AFM or scanning electron microscopy, and greater sensitivity to changes in shape than do mass-based techniques. Crystalline cubic NaCl nanoparticles with sides of 35 to 150 nm were found to reversibly take up water with increasing RH, and to form a liquid-like surface layer of thickness 2 to 4 nm at humidities well below the deliquescence point of 75.0% at 20°C. Measurable uptake begins at 70% RH. The maximum thickness of the layer increases with increasing RH for a given particle size and, for a given RH, increases with increasing particle size over the range studied. The liquid-like behavior of the layer is indicated by a reversible “rounding” at the tops of the particles, where the ratio of particle height to radius of curvature increases from zero (flat top) at 68% RH to 0.7 at 74% RH. These observations suggest that a reorganization of mass occurs on the solid NaCl nanoparticle, and hence that the behavior of NaCl aerosol nanoparticles at RH between 70 and 75% RH is more complex than an abrupt first-order phase transition. Theoretical treatments of the phase transition should therefore account for both the presence of a liquid-like layer prior to deliquescence, and the RH-dependent thickness of the layer.
Date: December 14, 2009
Creator: Bruzewicz, D.A.; Lewis, E.; Ocko, B. M.; McGraw, R. L. & Schwartz, S. E.
Partner: UNT Libraries Government Documents Department

Ductile grinding of Ba(Sr)TiO{sub 3} detector substrates

Description: Several precision machining techniques have been applied to barium strontium titanate wafers as deterministic replacements for lapping, polishing and reticulation. Surface finishes approaching polish quality have been achieved in less time than normally required, leading to potentially lower manufacturing costs for uncooled FPA`s.
Date: August 1, 1994
Creator: Kahl, W.K.
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

Plastic-casting intrinsic-surface unique identifier (tag)

Description: This report describes the development of an authenticated intrinsic-surf ace tagging method for unique- identification of controlled items. Although developed for control of items limited by an arms control treaty, this method has other potential applications to keep track of critical or high-value items. Each tag (unique-identifier) consists of the intrinsic, microscopic surface topography of a small designated area on a controlled item. It is implemented by making a baseline plastic casting of the designated tag area and usually placing a cover (for example, a bar-code label) over this area to protect the surface from environmental alteration. The plastic casting is returned to a laboratory and prepared for high-resolution scanning electron microscope imaging. Several images are digitized and stored for use as a standard for authentication of castings taken during future inspections. Authentication is determined by numerically comparing digital images. Commercially available hardware and software are used for this tag. Tag parameters are optimized, so unique casting images are obtained from original surfaces, and images obtained from attempted duplicate surfaces are detected. This optimization uses the modulation transfer function, a first principle of image analysis, to determine the parameters. Surface duplication experiments confirmed the optimization.
Date: April 1, 1995
Creator: Palm, R.G. & De Volpi, A.
Partner: UNT Libraries Government Documents Department

Nanometer-Scale Compositional Structure in III-V Semiconductor Heterostructures Characterized by Scanning Tunneling Microscopy

Description: Nanometer-scale compositional structure in InAsxP1.InNYAsxPl.x-Y/InP, grown by gas-source molecular-beam epitaxy and in InAsl-xPJkAsl$b#InAs heterostructures heterostructures grown by metal-organic chemical vapor deposition has been characterized using cross-sectional scanning tunneling microscopy. InAsxP1-x alloy layers are found to contain As-rich and P-rich clusters with boundaries formed preferentially within (T 11) and (111) crystal planes. Similar compositional structure is observed within InNYAsxP1-x-Y alloy layers. Imaging of InAsl-xp@Asl#bY superlattices reveals nanometer-scale clustering within both the hAsI-.p and InAsl$bY alloy layers, with preferential alignment of compositional features in the direction. Instances are observed of compositional structure correlated across a heterojunction interface, with regions whose composition corresponds to a smaller unstrained lattice, constant relative to the surrounding alloy material appearing to propagate across the interface.
Date: November 10, 1998
Creator: Allerman, A.A.; Bi, W.G.; Biefeld, R.M.; Tu, C.W.; Yu, E.T. & Zuo, S.L.
Partner: UNT Libraries Government Documents Department

Use of strain-annealing to evolve the grain boundary character distribution in polycrystalline copper

Description: We have used a two-step (low and high temperature) strain-annealing process to evolve the grain boundary character distribution (GBCD) in fully recrystallized oxygen-free electronic (OFE) Cu bar that was forged and rolled. Orientation imaging microscopy has been used to characterize the GBCD after each step in the processing. The fraction of special grain boundaries was {similar_to}70% in the starting recrystallized material. Three different processing conditions were employed: high, moderate, and low temperature. The high-temperature process resulted in a reduction in the fraction of special GBs while both the lower temperature processes resulted in an increase in special fraction up to 85%. Further, the lower temperature processes resulted in average deviation angles from exact misorientation, for special boundaries, that were significantly smaller than observed from the high temperature process. Results indicate the importance of the low temperature part of the two-step strain-annealing process in preparing the microstructure for the higher temperature anneal and commensurate increase in the special fraction.
Date: November 6, 1996
Creator: King, W.E. & Schwartz, A.J.
Partner: UNT Libraries Government Documents Department

Environmental scanning electron microscope (ESEM). Final report

Description: The Environmental Scanning Electron Microscope (ESEM) was acquired by a grant from the Department of Energy University Research Instrumentation Program and matching funds from Lehigh University and industry. The equipment is installed as part of the electron microscopy laboratories and is being utilized on a regular basis. Over 20 graduate and undergraduate students from the Department of Materials Science and Engineering as well as other department in the University have included this instrument in their research. In addition, the ESEM has been used in several courses including MAT 427 -- Advanced Scanning Electron Microscopy, a graduate course offered every other year. Examples are given of how the ESEM has been included in the research programs.
Date: November 1, 1998
Creator: Marder, A.; Barmak, K. & Williams, D.
Partner: UNT Libraries Government Documents Department

Surface structure and analysis with scanning probe microscopy and electron tunneling spectroscopy. Final report

Description: This report summarizes the results accomplished during the funding period of this grant (June 1, 1995 to May 31, 1998). The projects are (1) room-temperature atomic force microscopy (AFM) studies of NbSe{sub 3} doped with various elements and (2) low-temperature scanning tunneling microscopy (STM) studies of NbSe{sub 3}. In addition, AFM was used to study the surface morphology and defects of GaAs films grown on Ge and Ge/Si substracts.
Date: May 1, 1998
Creator: Hsu, Julia
Partner: UNT Libraries Government Documents Department

Advanced lithography for nanofabrication

Description: A novel method for generating lateral features by patterning the naturally forming surface hydride layer on Si is described. Because of the relatively strong chemical bonding between silicon and hydrogen, the hydride layer acts as a robust passivation layer with essentially zero surface mobility at ordinary temperatures. A focused electron beam from a scanning electron microscope was used for patterning. Upon losing the hydrogen passivation the silicon surface sites become highly reactive. Ideally, the lifetime of such a pattern in a clean environment should be infinite. Deliberate exposure of the entire wafer to a suitable gas phase precursor results in selective area film growth on the depassivated pattern. Linewidths and feature sizes of silicon dioxide on silicon below 100nm were achieved upon exposure to air. The silicon dioxide is robust and allows effective pattern transfer by anisotropic wet-chemical etching. In this paper, the mechanism of hydrogen desorption and subsequent pattern formation, and the factors that govern the ultimate pattern resolution will be discussed.
Date: June 1, 1997
Creator: Hui, F. & Eres, G.
Partner: UNT Libraries Government Documents Department

Ultrafast scanning tunneling microscopy using a photoexcited low-temperature-grown gallium arsenide tips

Description: The invention of the scanning tunneling microscope (STM) revolutionized the field of surface science, enabling the first images of surface structure on an atomic length scale. In the quest for both atomic spatial and temporal resolution several groups have integrated an ultrafast optoelectronic switch which gates the current from the tip, achieving picosecond time resolution. In this paper, the authors describe a novel STM tip consisting of a cleaved GaAs substrate with a 1-{micro}m thick epilayer of low-temperature-grown GaAs (LT-GaAs) deposited on the face. Since the LT-GaAs has a carrier lifetime of 1 ps, photoexcitation of the tip with an ultrafast, above-bandgap pulse both provides carriers for the tunneling current and photoconductively gates (with ps resolution) the current from the tip. They use this tip to detect picosecond transients on a coplanar stripline and demonstrate a temporal resolution of 1.2 ps in tunneling mode.
Date: February 1, 1998
Creator: Donati, G.P.; Some, D.; Rodriguez, G. & Taylor, A.J.
Partner: UNT Libraries Government Documents Department

Support Services for Ceramic Fiber-Ceramic Matrix Composites

Description: To increase national energy self-sufficiency for the near future, power systems will be required to fire low-grade fuels more efficiently than is currently possible. The typical coal-fired steam cycle used at present is limited to a maximum steam temperature of 540 C and a conversion efficiency of 35%. Higher working-fluid temperatures are required to boost efficiency, exposing subsystems to very damaging conditions. Issues of special concern to materials developers are corrosion and warping of hot-gas particulate filters and corrosion and erosion of high-temperature heat exchangers. The University of North Dakota Energy and Environmental Research Center (EERC) is working with the National Energy Technology Laboratory in conjunction with NCC Engineering, Inc., to provide technical assistance and coal by-products to the Fossil Energy Materials Advanced Research and Technology Development Materials Program investigating materials failure in fossil energy systems. The main activities of the EERC are to assemble coal slag and hot-gas filter ash samples for use by materials researchers, to assist in providing opportunities for realistic tests of advanced materials in pilot-scale fossil energy systems, and to provide analytical support in determining corrosion mechanisms of the exposed materials. In this final report for the project year of September 2000 through August 2001, the facilities at the EERC that can be used by researchers for realistic testing of materials are described. Researchers can include sample coupons in each of these facilities at no cost since they are being operated under separate funding. In addition, two pilot-scale coal combustion tests are described in which material sample coupons were included from researchers involved in the development of fossil energy materials. The results of scanning electron microscopy (SEM) energy dispersive x-ray analyses of the corrosion products and interactions between the surface scales of the coupons and the products of coal combustion found on the coupons exposed ...
Date: August 16, 2001
Creator: Hurley, JP
Partner: UNT Libraries Government Documents Department

Multivariate statistical analysis of low-voltage EDS spectrum images

Description: Whereas energy-dispersive X-ray spectrometry (EDS) has been used for compositional analysis in the scanning electron microscope for 30 years, the benefits of using low operating voltages for such analyses have been explored only during the last few years. This paper couples low-voltage EDS with two other emerging areas of characterization: spectrum imaging and multivariate statistical analysis. The specimen analyzed for this study was a finished Intel Pentium processor, with the polyimide protective coating stripped off to expose the final active layers.
Date: March 1, 1998
Creator: Anderson, I.M.
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